JP3794229B2 - OPTICAL PICKUP DEVICE, RECORDING / REPRODUCING DEVICE EQUIPPED WITH THE OPTICAL PICKUP DEVICE, INFORMATION RECORDING / REPRODUCING METHOD, AND OBJECTIVE LENS FOR OPTICAL PICKUP DEVICE - Google Patents

Description

【０１４２】
【数２】

【０１４３】
これら２つの表現方法は、単位が異なるが、回折輪帯のピッチを表わす意味では同等である。即ち、主波長λ（単位ｍｍ）に対し、位相差関数の係数Ｂに、λ／２πを掛ければ光路差関数の係数ｂに換算でき、また逆に光路差関数の係数ｂに、２π／λを掛ければ位相差関数の係数Ｂに換算できる。
【０１４４】
今、説明を簡単にする為、１次回折光を用いる回折レンズについて述べることにすると、光路差関数なら、関数値が主波長λの整数倍を超える毎に輪帯が刻まれ、位相差関数なら、関数値が２πの整数倍を超える毎に輪帯が刻まれることになる。
【０１４５】
例えば、屈折パワーのない円筒状の両平面の物体側面に回折輪帯を刻んだレンズを想定し、主波長を０．５μ＝０．０００５ｍｍ、光路差関数の２次係数（２乗項）を−０．０５（位相差関数の２次係数に換算すると−６２８．３）、他の次数の係数を全て零とすると、第１輪帯の半径はｈ＝０．１ｍｍであり、第２輪帯の半径はｈ＝０．１４１ｍｍということになる。また、この回折レンズの焦点距離ｆについては、光路差関数の２次係数ｂ２＝−０．０５に対して、ｆ＝−１／（２・ｂ２）＝１０ｍｍとなることが知られている。
【０１４６】
今、上記の定義を基にした場合、位相差関数若しくは光路差関数の２次係数を零でない値とすることにより、光軸に近い、いわゆる近軸領域での色収差を補正することができる。また、位相差関数若しくは光路差関数の２次以外の係数、例えば、４次係数、６次係数、８次係数、１０次係数等を零でない値とすることにより、２波長間での球面収差を制御することができる。尚、ここで、制御するということは、２波長間で、球面収差の差を極めて小さくすることもできるし、光学的仕様に必要な差を設けることも可能であるということを意味する。
【０１４７】
上記の具体的な適用としては、波長の違う２光源からのコリメート光（平行光）を同時に対物レンズに入射させ、光ディスク上に結像させるときは、まず、位相差関数若しくは光路差関数の２次係数を使って近軸の軸上色収差を補正するとともに、位相差関数若しくは光路差関数の４次以降の係数を使って球面収差の２波長間での差を許容内になるよう小さくするのがよい。
【０１４８】
また、別の例として、波長の違う２光源からの光を一つの対物レンズを使い、一方の波長の光に対しては、ｔ１の厚み（透明基板の厚み）のディスクに対して収差が補正されるようにし、もう一方の波長の光に対しては、ｔ２の厚みのディスクに対して収差が補正されるようにする仕様の場合について考えてみる。この場合、主に位相差関数若しくは光路差関数の４次以降の係数を使うことにより、球面収差の２波長間での差を設け、それぞれの厚みに対しては、それぞれの波長で球面収差が補正されるようにすることができる。また、いずれの場合にも屈折面は球面であるよりも非球面であるほうが、２波長間での収差補正をし易い。
【０１４９】
上記の非球面屈折面は、異なる波長に対してはそれぞれ屈折力が異なり、集光点が異なるので、それぞれの集光点をそれぞれ基板厚の異なる光ディスクに対応させることができる。この場合、短い方の光源波長は７００ｎｍ以下であり、長い方の光源波長は６００ｎｍ以上であり、その波長差が８０ｎｍ以上であることが好ましい。また、その波長差が４００ｎｍ以下であることがより好ましく、更に好ましくは、その波長差が１００ｎｍ以上２００ｎｍ以下である、そして、回折面は、異なる２波長光に対し、ほぼその中間の波長で回折効率が最大であることが望ましいが、どちらか一方の波長で最大の回折効率を有するものであってもよい。
【０１５０】
上記球面収差の補正と同一の作用を利用することにより、光学面上に回折輪帯レンズを設け、異なる２波長の光源の各々に対して、ある１つの同次数の回折光により軸上色収差を補正することができる。すなわち、異なる２波長の光源の光に対する軸上色収差を±λ／（２ＮＡ^２）の範囲に補正することができる。ただし、λは２波長のうち長いほうの波長、ＮＡは長いほうの波長に対応する像側開口数とする。
【０１５１】
また、上記異なる２波長の光源の波長差が８０ｎｍ以上であり、対物レンズの硝材のアッベ数をνｄとしたとき、
νｄ ＞ ５０ ・・・（１）
を満足することが望ましい。上記条件（１）は、異なる２波長の光源に対して軸上色収差を補正した場合に、２次スペクトルを小さくするための条件である。
【０１５２】
次に、薄肉単玉レンズの一方の面に回折面が設けられている場合に、単玉レンズ全体を、回折レリーフを外したベースとなる屈折レンズと回折面との合成と考えてこの合成レンズの色収差について検討する。ある波長λx と波長λy （λx ＜λy ）とでの色消し条件は次式となる。
【０１５３】
ｆR ・νR ＋ｆD ・νD ＝０
ただし、ｆR 、ｆD ：それぞれ屈折レンズ、回折面の焦点距離
νR 、νD ：それぞれ屈折レンズ、回折面のアッベ数で、次式で定まる。
νR ＝（ｎ0−１）／（ｎx −ｎy ）
νD ＝λ0／（λx −λy ）
【０１５４】
ただし、ｎ0：基準波長での屈折率、λ0：基準波長
【０１５５】
このとき、ある波長λz に対する色収差δｆは次式となる。
δｆ＝ｆ（θR −θD ）／（νR −νD ） ・・・（２）
ただし、θR 、θD ：それぞれ屈折レンズ、回折面の部分分散比で次式で定まる。
【０１５６】
θR ＝（ｎx −ｎz ）／（ｎx −ｎy ）
【０１５７】
θD ＝（λx −λz ）／（λx −λy ）
ただし、ｎz ：波長λz での屈折率
【０１５８】
例として、λ0＝λx ＝６３５ｎｍ、λy ＝７８０ｎｍ、λz ＝６５０ｎｍとし、ベースとなる屈折レンズの硝材をホーヤ社ＢＳＣ７（νｄ＝６４．２）としてみると、
νR＝１３４．５， νD＝−４．３８， θR＝０．１２８， θD＝０．１０３となり、δｆ＝０．１８×１０^−３ｆとなる。
【０１５９】
また、ベースとなる屈折レンズの硝材をホーヤ社Ｅ−ＦＤ１（νｄ＝２９．５）に変えてみると、
νR＝７０．５， θR＝０．１３６ となり、 δｆ＝０．４４×１０^−３ｆとなる。
【０１６０】
このように式（２）においては、右辺分母（νR −νD ）は｜νD｜が｜νR｜より十分小さいため、屈折レンズの硝材を変えることによる色収差δｆの変化にとっては、屈折レンズのアッベ数νRの変化が支配的である。一方、θR とθD とは波長によってのみ定まり、右辺分子（θR −θD ）は、その変化の寄与が右辺分母（νR −νD ）に比べて小さい。
【０１６１】
上記により、回折面を有するレンズにおいては、２次スペクトルδｆを小さく抑えるには、屈折レンズの材料としてアッベ数νRの大きい材料を選ぶことが有効であることがわかる。条件式（１）は光源の波長変化などに対応できるよう、２次スペクトルを抑えるのに有効な限界を示す。
【０１６２】
また、回折面を使用せずに、２種類の材料の屈折レンズを貼合わせて色消しを行う場合は、それぞれの材料について、θR ＝ａ＋ｂ・νR ＋△θR （ａ，ｂは定数）と表したとき、△θR は小さく、異常分散性が無いならば２次スペクトルδｆは２つの屈折レンズのアッベ数νR にはよらない。したがって、式（１）は回折光学系に特有の条件であることがわかる。
【０１６３】
本実施の形態の回折レンズを簡易に製造するためには、対物レンズをプラスチック材料で構成することが望ましい。条件式（１）を満たすプラスチック材料としては、アクリル系、ポリオレフィン系が用いられるが、耐湿性、耐熱性などから、ポリオレフィン系が好ましい。
【０１６４】
次に、本発明の第２の実施の形態の対物レンズおよびこれを備えた光ピックアップ装置の構成を具体的に説明する。
【０１６５】
図４８に、本実施の形態の光ピックアップ装置の概略構成図を示す。光ピックアップ装置により情報記録および／または再生する光情報記録媒体である光ディスク２０は、透明基板の厚さｔ１の第１光ディスク（例えばＤＶＤ）及び第２光ディスク（例えば青色レーザ使用次世代高密度光ディスク）と、ｔ１とは異なる透明基板の厚さｔ２を有する第３光ディスク（例えばＣＤ）の３種であるとして説明する。ここでは、透明基板の厚さｔ１＝０．６ｍｍ、ｔ２＝１．２ｍｍである。
【０１６６】
図示の光ピックアップ装置は、光源として第１光源である第１半導体レーザ１１（波長λ_１＝６１０ｎｍ〜６７０ｎｍ）と、第２光源である青色レーザ１２（波長λ_２＝４００ｎｍ〜４４０ｎｍ）と、第３光源である第２半導体レーザ１３（波長λ_３＝７４０ｎｍ〜８７０ｎｍ）とを有しているとともに、光学系の一部として対物レンズ１を有している。第１光源、第２光源及び第３光源は、情報を記録および／または再生する光ディスクに応じて選択使用される。
【０１６７】
第１半導体レーザ１１、青色レーザ１２あるいは第２半導体レーザ１３から出射された発散光束は、ビームスプリッタ１９および絞り３を介し、光ディスク２０の透明基板２１を透過して、対物レンズ１によってそれぞれの情報記録面２２上に集光され、スポットを形成する。
【０１６８】
各レーザからの入射光は、情報記録面２２上の情報ピットによって変調された反射光となり、ビームスプリッタ１８、トーリックレンズ２９を介して共通の光検出器３０に入射し、その出力信号を用いて、光ディスク２０に記録された情報の読み取り信号、合焦検出信号やトラック検出信号が得られる。
【０１６９】
また、光路内に設けられている絞り３は、この例においては固定の開口数（ＮＡ０．６５）を有する絞りであり、余分な機構を必要とせず、低コスト化を実現できるものである。なお、第３光ディスクの記録および／または再生時には不要光（ＮＡ０．４５以上）を除去できるように、絞り３の開口数を可変としてもよい。
【０１７０】
対物レンズ１の光学面に実使用開口の外側の一部の光束を遮蔽するように輪帯状のフィルターを一体に形成することで、実使用開口の外側のフレア光を安価な構成で容易に除去することも可能である。
【０１７１】
本実施の形態のように有限共役型の光学系を用いる場合には、集光性能を維持するため、光源と集光光学系との関係を一定に保つ必要があり、合焦やトラッキングのための移動は、光源１１、１２、１３と対物レンズ１とを１つのユニットとして行うことが望ましい。
【０１７２】
次に、本発明の第３の実施の形態の対物レンズおよびこれを含む光ピックアップ装置の構成を具体的に説明する。
【０１７３】
図４９に、本実施の形態の光ピックアップ装置の概略構成図を示す。図４９の光ピックアップ装置はレーザー、光検出器およびホログラムをユニット化したレーザ／検出器集積ユニット４０を用いた例であり、図４８と同じ構成要素は同じ符号で示す。この光ピックアップ装置においては、第１半導体レーザ１１、青色レーザ１２、第１の光検出手段３１、第２の光検出手段３２、ホログラムビームスプリッタ２３がレーザ／検出器集積ユニット４０としてユニット化されている。
【０１７４】
第１光ディスクを再生する場合、第１半導体レーザ１１から出射された光束は、ホログラムビームスプリッタ２３を透過し、絞り３によって絞られ、対物レンズ１により第１光ディスク２０の透明基板２１を介して情報記録面２２に集光される。そして、情報記録面２２で情報ピットにより変調されて反射した光束は、再び対物レンズ１、絞り３を介してホログラムビームスプリッタ２３のディスク側の面で回折され、第１半導体レーザ１１に対応した第１の光検出器３１上へ入射する。そして、第１の光検出器３１の出力信号を用いて、第１光ディスク２０に記録された情報の読み取り信号、合焦検出信号やトラック検出信号が得られる。
【０１７５】
第２光ディスクを再生する場合、青色レーザ１２から出射された光束は、ホログラムビームスプリッタ２３のレーザ側の面で回折され、上記の第１半導体レーザ１１からの光束と同じ光路を取る。すなわち、このホログラムビームスプリッタ２３の半導体レーザ側の面は、光合成手段としての機能を果たす。さらに絞り３、対物レンズ１を介して第２光ディスク２０の透明基板２１を介して情報記録面２２に集光される。そして、情報記録面２２で情報ピットにより変調されて反射した光束は、再び対物レンズ１、絞り３を介して、ホログラムビームスプリッタ２３のディスク側の面で回折されて青色レーザ１２対応した第２の光検出器３２上へ入射する。そして、第２の光検出器３２の出力信号を用いて、第２光ディスク２０に記録された情報の読み取り信号、合焦検出信号やトラック検出信号が得られる。
【０１７６】
さらに、第３光ディスクを再生する場合、第２半導体レーザ１３、第３の光検出手段３３、およびホログラムビームスプリッタ２４がユニット化されたレーザ／検出器集積ユニット４１が使用される。第２半導体レーザ１３から出射された光束は、ホログラムビームスプリッタ２４を透過し、出射光の合成手段であるビームスプリッタ１９で反射し、絞り３によって絞られ、対物レンズ１により光ディスク２０の透明基板２１を介して情報記録面２２に集光される。そして、情報記録面２２で情報ピットにより変調されて反射した光束は、再び対物レンズ１、絞り３、ビームスプリッタ１９を介してホログラムビームスプリッタ２４で回折されて第３の光検出器３３上へ入射する。そして、第３の光検出機３３の出力信号を用いて、第３光ディスク２０に記録された情報の読み取り信号、合焦検出信号やトラック検出信号が得られる。
【０１７７】
第２および第３の実施の形態の光ピックアップ装置においては、対物レンズ１の非球面屈折面に光軸４と同心の輪帯状回折面が構成されている。一般に非球面屈折面だけで対物レンズを構成すると、ある波長λａに対して球面収差を補正した場合、λａよりも短い波長λｂに対しては球面収差がアンダーとなる。一方回折面を使用すると、ある波長λａに対して球面収差を補正した場合、λａよりも短い波長λｂに対しては球面収差がオーバーとなる。従って、屈折面による非球面光学設計と、回折面の位相差関数の係数を適当に選んで、屈折パワーと回折パワーとを組み合わせることにより、異なる波長間での球面収差を補正することが可能となる。また、非球面屈折面では、波長が異なると屈折力も変化し集光位置も異なる。よって、非球面屈折面を適当に設計することで、異なる波長に対しても各透明基板２１の情報記録面２２に集光させることができる。
【０１７８】
また、第２および第３の実施の形態の対物レンズ１では、非球面屈折面と輪帯状回折面の位相差関数とを適当に設計することで、第１半導体レーザ１１、青色レーザ１２あるいは第２半導体レーザ１３から出射した各光束に対して、光ディスク２０の透明基板２１厚さの違いにより発生する球面収差を補正している。さらに、輪帯状回折面において、輪帯の位置を表す位相差関数が、冪級数の４乗以降の項の係数を用いると球面収差の色収差を補正することが可能となる。なお、第３光ディスク（ＣＤ）については実使用上の開口はＮＡ０．４５であり、第３光ディスクではＮＡ０．４５以内で球面収差を補正し、ＮＡ０．４５より外側の領域の球面収差をフレアとしている。これらの補正により各光ディスク２０に対して、情報記録面２２上の集光スポットの収差が回折限界（０．０７λｒｍｓ）とほぼ同程度あるいはそれ以下になっている。
【０１７９】
上記のような第２および第３の実施の形態の光ピックアップ装置は、例えばＣＤ、ＣＤ−Ｒ、ＣＤ−ＲＷ、ＣＤ−Ｖｉｄｅｏ、ＣＤ−ＲＯＭ、ＤＶＤ、ＤＶＤ−ＲＯＭ、ＤＶＤ−ＲＡＭ、ＤＶＤ−Ｒ、ＤＶＤ−ＲＷ、ＭＤ等の、任意の異なる２つまたはそれ以上の複数の光情報記録媒体に対して、コンパチブルなプレーヤ、またはドライブ等、あるいはそれらを組み込んだＡＶ機器、パソコン、その他の情報端末等、の音声および／または画像の記録、および／または、音声および／または画像の再生装置に搭載することができる。
【０１８０】
次に、本発明の第４の実施の形態の対物レンズおよびこれを含む光ピックアップ装置の構成を具体的に説明する。
【０１８１】
図６７は本実施の形態の光ピックアップ装置１０の概略構成図である。図６７においては、第２および第３の実施の形態と共通の部材については同じ符号を用いることがある。図６７において光ピックアップ装置１０は、光情報記録媒体である複数の光ディスク２０を記録／再生するものである。以下、この複数の光ディスク２０は、透明基板の厚さｔ１の第１光ディスク（ＤＶＤ）および第２光ディスク（青色レーザ使用次世代高密度光ディスク）と、ｔ１とは異なる透明基板の厚さｔ２を有する第３光ディスク（ＣＤ）として説明する。ここでは、透明基板の厚さｔ１＝０．６ｍｍ、ｔ２＝１．２ｍｍである。
【０１８２】
光ピックアップ装置１０は、光源として第１光源である第１半導体レーザ１１（波長λ_１＝６１０ｎｍ〜６７０ｎｍ）と第２光源である青色レーザ１２（波長λ_２＝４００ｎｍ〜４４０ｎｍ）及び第３光源である第２半導体レーザ１３（波長λ_３＝７４０ｎｍ〜８７０ｎｍ）とを有している。これら第１光源、第２光源及び第３光源は、記録／再生する光ディスクに応じて排他的に使用される。
【０１８３】
集光光学系５は、第１半導体レーザ１１、青色レーザ１２あるいは第２半導体レーザ１３から出射された光束を、光ディスク２０の透明基板２１を介して、それぞれの情報記録面２２上に集光させ、スポットを形成する手段である。本実施の形態では、集光光学系５として、光源から出射された光束を平行光（略平行でよい）に変換するコリメータレンズ２と、コリメータレンズ２によって平行光とされた光束を集光させる対物レンズ１とを有している。
【０１８４】
対物レンズ１の両面には、光軸４と同心の輪帯状回折面が構成されている。一般に非球面屈折面だけで集光光学系５を構成すると、ある波長λａに対して球面収差を補正した場合、λａよりも短い波長λｂに対しては球面収差がアンダーとなる。一方、回折面を使用すると、ある波長λａに対して球面収差を補正した場合、λａよりも短い波長λｂに対しては球面収差がオーバーとなる。従って、屈折面による非球面光学設計と、回折面の位相関数の係数を適当に選んで、屈折パワーと回折パワーとを組み合わせることにより、異なる波長間での球面収差を補正することが可能となる。また非球面屈折面では、波長が異なると屈折力も変化し集光位置も異なる。よって、非球面屈折面を適当に設計することで、異なる波長に対しても各透明基板の情報記録面２２に集光させることができる。
【０１８５】
上記の輪帯状回折面では、第１半導体レーザ１１、青色レーザ１２あるいは第２半導体レーザ１３から出射した各光束に対して１次回折光を利用して収差補正を行っている。同次数の回折光を対応させると、異なる次数の回折光を対応させる場合に比べて光量損出が少なく、さらに、高次の回折光を対応させるよりも、１次回折光を用いると光量損出が少ない。したがって、本実施の形態の対物レンズ１は、ＤＶＤ−ＲＡＭなどの高密度な情報を記録する光ディスクに情報を記録する光ピックアップ装置において有効となる。また、回折面は、異なる３つの波長光に対し、その中間の波長で回折効率が最大であることが望ましいが、両端の波長で最大の回折効率を有するものであってもよい。
【０１８６】
また、非球面屈折面と輪帯状回折面の位相差関数とを適当に設計することで、第１半導体レーザ１１、青色レーザ１２あるいは第２半導体レーザ１３から出射した各光束に対して、光ディスク２０の透明基板２１厚さの違いにより発生する球面収差を補正している。さらに、対物レンズ１に形成された輪帯の位置を表す位相差関数において、冪級数の４乗以降の項の係数を用いると球面収差の色収差を補正することが可能となる。なお、第３光ディスク（ＣＤ）については実使用上の開口はＮＡ０．４５であり、ＮＡ０．４５以内で球面収差を補正し、ＮＡ０．４５より外側の領域の球面収差をフレアとしている。ＮＡ０．４５以内の領域を通過する光束が情報記録面で光スポットを形成し、ＮＡ０．４５の外側を通るフレア光は、悪影響を与えないように情報記録面で光スポットから間隔を隔てたところを通る。これらの補正により各光ディスク２０に対して、情報記録面２２上の集光スポットの収差が回折限界（０．０７λｒｍｓ）とほぼ同程度あるいはそれ以下になっている。
【０１８７】
本実施の形態では、光路内に設けられた絞り３は固定の開口数（ＮＡ０．６５）を有しており、余分な機構を必要とせず、低コスト化を実現できるものである。なお、第３光ディスクの記録／再生時には不要光（ＮＡ０．４５以上）を除去できるように、絞り３の開口数を可変としてもよい。また、ビームスプリッタ６、７は、各レーザ光の光軸を合わせるためのものである。光検出器（図示せず）は、周知のように、各光源ごとにそれぞれ設けても良く、１つの光検出器で３つの光源１１、１２、１３に対応する反射光を受光するようにしても良い。
【０１８８】
次に、本発明の第５の実施の形態の対物レンズについて説明する。
【０１８９】
本実施の形態では、対物レンズの輪帯状回折面において、輪帯の位置を表す位相差関数が冪級数の２乗の項の係数を用いる点のみにおいて、上述した第４の実施の形態の対物レンズと異なっており、これによって軸上色収差をも補正することが可能となっている。また、本実施の形態の対物レンズによると、第４の実施の形態と同様に各光ディスク２０に対して、情報記録面２２上の集光スポットの収差が回折限界（０．０７λｒｍｓ）とほぼ同程度あるいはそれ以下となっている。
【０１９０】
次に、本発明の第６の実施の形態の光ピックアップ装置について説明する。
【０１９１】
本実施の形態の光ピックアップ装置では、第１光ディスク（例えばＤＶＤ）と第２光ディスク（例えば、青色レーザ使用次世代高密度光ディスク）に対しては、光源から射出された光束をカップリングレンズによって平行光とし、第３光ディスク（例えばＣＤ）に対しては、光源から射出された光束をカップリングレンズによって発散光とし、それぞれ対物レンズによって集光させる。第１および第２光ディスクの透明基板２１の厚さは０．６ｍｍであり、第３光ディスクの透明基板２１の厚さは１．２ｍｍである。
【０１９２】
本実施の形態では、第１光ディスクと第２光ディスクとの両方の球面収差を回折面の効果により回折限界以内に補正し、また、第３光ディスクに対しては第１および第２光ディスクよりディスク厚が大きいことによって生じる球面収差を主として対物レンズに発散光束が入射することによって生じる球面収差によって打ち消し、第３光ディスクの記録／再生に必要な所定の開口数ＮＡ、例えばＮＡ０．５或いはＮＡ０．４５以下における球面収差を回折限界以内に補正するようにしている。
【０１９３】
従って、λ_１、λ_２、λ_３（λ_１＜λ_２＜λ_３）の各波長に対応する光情報記録媒体に対して、記録／再生を行うのに必要な所定の開口数をＮＡ１、ＮＡ２、ＮＡ３とするとき、それぞれの波長に対して、ＮＡ１の範囲で波面収差のＲＭＳを０．０７λ_１以下、ＮＡ２の範囲で０．０７λ_２以下、ＮＡ３の範囲で０．０７λ_２以
下に補正することができる。
【０１９４】
また、第３光ディスクに対しては、所定の開口数ＮＡよりも大きい開口数ＮＡの光束によってビームスポット径が小さくなり過ぎることは好ましくない。そのため、第４の実施の形態と同様に必要な開口数よりも大きな開口数では球面収差をフレアとすることが好ましい。
【０１９５】
上記のような異なる波長光の３光源を有する第４〜第６の実施の形態の光ピックアップ装置は、例えばＣＤ、ＣＤ−Ｒ、ＣＤ−ＲＷ、ＣＤ−Ｖｉｄｅｏ、ＣＤ−ＲＯＭ、ＤＶＤ、ＤＶＤ−ＲＯＭ、ＤＶＤ−ＲＡＭ、ＤＶＤ−Ｒ、ＤＶＤ−ＲＷ、ＭＤ等の、任意の異なる２つ以上の複数の光情報記録媒体に対して、コンパチブルなプレーヤ、またはドライブ等、あるいはそれらを組み込んだＡＶ機器、パソコン、その他の情報端末等、の音声および／または画像の記録、および／または、音声および／または画像の再生装置に搭載することができる。
【０１９６】
【実施例】
以下、本発明の対物レンズについての実施例について説明する。
〈実施例１〜８〉
【０１９７】
実施例１〜８の対物レンズは、第１の実施の形態に係る対物レンズの具体例であり、次の〔数３〕で表される非球面形状を屈折面に有している。
【０１９８】
【数３】

【０１９９】
ただし、Ｚは光軸方向の軸、ｈは光軸と垂直方向の軸（光軸からの高さ：光の進行方向を正とする）、Ｒ0は近軸曲率半径、κは円錐係数、Ａは非球面係数、２ｉは非球面のべき数である。また、実施例１〜３、６〜８では回折面が単位をラジアンとした位相差関数ΦBとして〔数１〕で表され、同様に実施例４，５では回折面が単位をｍｍとした光路差関数Φbとして〔数２〕で表わされる。
【０２００】
【数１】

【０２０１】
【数２】

【０２０２】
（実施例１）
【０２０３】
図１に、実施例１の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図を示す。また、図２に、実施例１の回折光学レンズについてのλ＝６３５ｎｍに対する開口数０．６０までの球面収差図を示す。また、図３および図４に、実施例１の回折光学レンズについての波長λ＝７８０ｎｍに対する開口数０．４５および０．６０までの球面収差図をそれぞれ示す。なお、図１の回折光学レンズは、レンズ全面にブレーズド型の同心円状の輪帯回折部を有しているが、図面において回折部のレリーフ形状は省略されている。また、以降の多くの図面においても、回折部のレリーフ形状は省略されている。
【０２０４】
実施例１の回折光学レンズによると、図２に示すように、波長λ＝６３５ｎｍに対してはＮＡ０．６０までの全開口がほぼ無収差である。また、図３に示すように、波長λ＝７８０ｎｍに対しては、実使用範囲であるＮＡ０．４５までがほぼ無収差である。その外側のＮＡ０．４５〜０．６０の部分については、図４に示すように球面収差は大きくアンダーとされ、フレアとなっている。これによって、波長λ＝７８０ｎｍについて、適正なスポット径を得ることが可能となっている。
【０２０５】
図５、図６に、実施例１の回折光学レンズについてのλ＝６３５ｎｍおよび波長λ＝７８０ｎｍに対する波面収差図をそれぞれ示す。これらの図から分かるように、実施例１の回折光学レンズによると、いずれの波長に対しても、光軸上ではほぼ無収差となり、像高０．０３ｍｍにおいても、実用上無収差に近いレベルとなっている。
【０２０６】
以下、実施例１のレンズデータを示す。〔表１〕中、Ｒは曲率半径、ｄは面間隔、ｎは主波長での屈折率、νはアッベ数を示す。
【０２０７】
実施例１
【０２０８】
光源波長λ1＝６３５ｎｍのとき
焦点距離ｆ1＝３.３４ 開口数ＮＡ1＝０.６０ 無限仕様
【０２０９】
光源波長λ2＝７８０ｎｍのとき
焦点距離ｆ2＝３.３６ 開口数ＮＡ2＝０.４５ 無限仕様
【０２１０】
本実施例は、λ１の光束において＋１次回折光を他の次数の回折光に比して多く発生させ、λ２の光束においても、＋１次回折光を他の次数の回折光に比して多く発生させる。λ１に対する＋１次回折光の回折効率を１００％とすれば、λ２に対する回折効率は８４％となる。また、λ２に対する＋１次回折光の回折効率を１００％とすれば、λ１に対する回折効率は８９％となる。
【０２１１】
【表１】

【０２１２】
非球面係数
非球面１
κ ＝−０.１７０２１
Ａ4 ＝−０.００３２３１５
Ａ6 ＝−０.０００５８１６０
Ａ8 ＝−４.６３１６×１０^−５
Ａ10＝−３.７９８５８×１０^−５
Ａ12＝−６.０３０８×１０^−６
非球面２
κ ＝−１１.６５３
Ａ4 ＝０.０３８４５６
Ａ6 ＝−０.０２０８００
Ａ8 ＝０.００７８６４８
Ａ10＝ −０.００１９４３１
Ａ12＝ ０.０００２４３４３
【０２１３】
回折面係数
Ｂ2 ＝−９６.７６６
Ｂ4 ＝ −２.９９５０
Ｂ6 ＝ ２.１３０６
Ｂ8 ＝ −０.１２６１４
Ｂ10＝ −０.０９５２８５
【０２１４】
（実施例２、実施例３）
【０２１５】
次に、実施例２、実施例３について説明する。図７および図８に、実施例２の対物レンズである回折光学レンズのλ＝４０５ｎｍおよび６３５ｎｍに対する光路図をそれぞれ示す。また、図９および図１０に、実施例２の回折光学レンズについてのλ＝４０５ｎｍおよび６３５ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。また、図１１および図１２に、実施例２の回折光学レンズについての波長λ＝４０５ｎｍおよび６３５ｎｍに対する波面収差図をそれぞれ示す。
【０２１６】
また、図１３および図１４に、実施例３の対物レンズである回折光学レンズのλ＝４０５ｎｍおよび６３５ｎｍに対する光路図をそれぞれ示す。また、図１５および図１６に、実施例３の回折光学レンズについてのλ＝４０５ｎｍおよび６３５ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。また、図１７および図１８に、実施例３の回折光学レンズについての波長λ＝４０５ｎｍおよび６３５ｎｍに対する波面収差図をそれぞれ示す。
【０２１７】
実施例２、３においては、波長λ＝４０５ｎｍおよび波長λ＝６３５ｎｍに対し、基板厚は共に０．６ｍｍ、ＮＡは０．６０であり、波面収差は光軸上はほぼ無収差、像高０．０３ｍｍにおいても、実用上無収差に近いレベルとなっている。
【０２１８】
以下、実施例２、３のレンズデータを示す。
【０２１９】
実施例２
【０２２０】
光源波長λ1＝４０５ｎｍのとき
焦点距離ｆ1＝３.２３ 開口数ＮＡ1＝０.６０ 無限仕様
【０２２１】
光源波長λ2＝６３５ｎｍのとき
焦点距離ｆ2＝３.３４ 開口数ＮＡ2＝０.６０ 無限仕様
【０２２２】
本実施例は、λ１の光束において＋１次回折光を他の次数の回折光に比して多く発生させ、λ２の光束においても、＋１次回折光を他の次数の回折光に比して多く発生させる。
【０２２３】
【表２】

【０２２４】
非球面係数
非球面１
κ ＝−０.１５０７９
Ａ4 ＝−０.００２１２３０
Ａ6 ＝−０.０００７６５２８
Ａ8 ＝−８.８４９５７×１０^−５
Ａ10＝−３.４９８０３×１０^−５
Ａ12＝−２.３８９１６×１０^−６
非球面２
κ ＝−３.８２８８
Ａ4 ＝ ０.０３６９６２
Ａ6 ＝−０.０２０８５８
Ａ8 ＝ ０.００７９７３２
Ａ10＝−０.００１８７１３
Ａ12＝ ０.０００２２５０４
【０２２５】
回折面係数
Ｂ2 ＝ ０.０
Ｂ4 ＝−６.７１６９
Ｂ6 ＝ ２.０７９１
Ｂ8 ＝−０.３１９７０
Ｂ10＝ ０.０００１６７０８
【０２２６】
実施例３
【０２２７】
光源波長λ1＝４０５ｎｍのとき
焦点距離ｆ1＝３.３１ 開口数ＮＡ1＝０.６０ 無限仕様
【０２２８】
光源波長λ2＝６３５ｎｍのとき
焦点距離ｆ2＝３.３４ 開口数ＮＡ2＝０.６０ 無限仕様
【０２２９】
本実施例は、λ１の光束において＋１次回折光を他の次数の回折光に比して多く発生させ、λ２の光束においても、＋１次回折光を他の次数の回折光に比して多く発生させる。
【０２３０】
【表３】

【０２３１】
非球面係数
非球面１
κ ＝−０.１９０２９
Ａ4 ＝ ０.０００３０５３８
Ａ6 ＝−０.００１０６１９
Ａ8 ＝−７.５７４７×１０^−５
Ａ10＝−６.７５９９×１０^−５
Ａ12＝−３.３７８８×１０^−６
非球面２
κ ＝ ６.４４３０
Ａ4 ＝ ０.０３７０４５
Ａ6 ＝−０.０２１４７４
Ａ8 ＝ ０.００７８１７５
Ａ10＝−０.００１６０６４
Ａ12＝ ０.０００１４３３２
【０２３２】
回折面係数
Ｂ2 ＝−９６.７６６
Ｂ4 ＝ −２.９９５０
Ｂ6 ＝ −０.２５５６０
Ｂ8 ＝ −０.０８７８９
Ｂ10＝ ０.０１４５６２
【０２３３】
（実施例４、実施例５）
【０２３４】
次に、色収差補正を行った実施例４、実施例５について説明する。図１９に、実施例４の対物レンズである回折光学レンズの光路図をそれぞれ示す。また、図２０に、実施例４の回折光学レンズについてのλ＝６３５ｎｍ、６５０ｎｍおよび７８０ｎｍに対する開口数０．５０までの球面収差図をそれぞれ示す。また、図２１に、実施例５の対物レンズである回折光学レンズの光路図をそれぞれ示す。また、図２２に、実施例５の回折光学レンズについてのλ＝６３５ｎｍ、６５０ｎｍおよび７８０ｎｍに対する開口数０．５０までの球面収差図をそれぞれ示す。
【０２３５】
図２０および図２２から分かるように、実施例４、５の回折光学レンズによると、波長λ＝６３５ｎｍ、波長λ＝７８０ｎｍに対しては、ほぼ完全に色によるずれは補正され、波長λ＝６５０ｎｍに対しても、実用上全く問題はない程度に補正されている。
【０２３６】
以下、実施例４、５のレンズデータを示す。
【０２３７】
実施例４
【０２３８】
光源波長λ1＝６３５ｎｍのとき
焦点距離ｆ1＝３.４０ 開口数ＮＡ1＝０.５０ 無限仕様
【０２３９】
光源波長λ2＝７８０ｎｍのとき
焦点距離ｆ2＝３.４１ 開口数ＮＡ2＝０.５０ 無限仕様
【０２４０】
本実施例は、λ１の光束において＋１次回折光を他の次数の回折光に比して多く発生させ、λ２の光束においても、＋１次回折光を他の次数の回折光に比して多く発生させる。
【０２４１】
【表４】

【０２４２】
非球面係数
非球面１
κ ＝−０.５３２４５
Ａ4 ＝ ０.２４０３３×１０^−２
Ａ6 ＝−０.９１４７２×１０^−３
Ａ8 ＝ ０.１５５９０×１０^−４
Ａ10＝−０.１１１３１×１０^−３
非球面２
κ ＝ ７.３９８８
Ａ4 ＝ ０.９０４０８×１０^−２
Ａ6 ＝−０.１８７０４×１０^−２
Ａ8 ＝−０.４７３６８×１０^−３
Ａ10＝ ０.１６８９１×１０^−３
【０２４３】
回折面係数
ｂ2 ＝−０.３６７６４×１０^−２
ｂ4 ＝−０.９１７２７×１０^−４
ｂ6 ＝−０.３４９０３×１０^−４
ｂ8 ＝ ０.７７４８５×１０^−５
ｂ10＝−０.１５７５０×１０^−５
【０２４４】
実施例５
【０２４５】
光源波長λ1＝６３５ｎｍのとき
焦点距離ｆ1＝３.４０ 開口数ＮＡ1＝０.５０ 無限仕様
【０２４６】
光源波長λ2＝７８０ｎｍのとき
焦点距離ｆ2＝３.４０ 開口数ＮＡ2＝０.５０ 無限仕様
【０２４７】
本実施例は、λ１の光束において＋１次回折光を他の次数の回折光に比して多く発生させ、λ２の光束においても、＋１次回折光を他の次数の回折光に比して多く発生させる。
【０２４８】
【表５】

【０２４９】
非球面係数
非球面１
κ ＝−０.１７００６
Ａ4 ＝−０.３０５６３×１０^−２
Ａ6 ＝−０.４５１９９×１０^−３
Ａ8 ＝ ０.５８８１１×１０^−５
Ａ10＝−０.１３００２×１０^−４
非球面２
κ ＝−４０.７８２
Ａ4 ＝ ０.７３４４７×１０^−２
Ａ6 ＝ ０.８５１７７×１０^−３
Ａ8 ＝ −０.８２７９５×１０^−３
Ａ10＝ ０.２３０２９×１０^−３
【０２５０】
回折面係数
ｂ2 ＝−０.７４４６１×１０^−２
ｂ4 ＝ ０.１１１９３×１０^−２
ｂ6 ＝−０.８５２５７×１０^−３
ｂ8 ＝ ０.５０５１７×１０^−３
ｂ10＝−０.１１２４２×１０^−３
【０２５１】
（実施例６〜８）
【０２５２】
次に、実施例６〜８について説明する。図２３、図３０および図３７に、実施例６〜８の対物レンズである回折光学レンズのλ＝６５０ｎｍに対する光路図をそれぞれ示す。また、図２４、図３１および図３８に、実施例６〜８の回折光学レンズのλ＝７８０ｎｍ（ＮＡ＝０．５）に対する光路図をそれぞれ示す。また、図２５、図３２および図３９に、実施例６〜８の回折光学レンズについてのλ＝６５０±１０ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。また、図２６、図３３および図４０に、実施例６〜８の回折光学レンズについてのλ＝７８０±１０ｎｍに対する開口数０．５０までの球面収差図をそれぞれ示す。また、図２７、図３４および図４１に、実施例６〜８の回折光学レンズについてのλ＝７８０ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。
【０２５３】
また、図２８、図３５および図４２に、実施例６〜８の回折光学レンズについてのλ＝６５０ｎｍに対する波面収差ｒｍｓ図をそれぞれ示す。また、図２９、図３６および図４３に、実施例６〜８の回折光学レンズについてのλ＝７８０ｎｍに対する波面収差ｒｍｓ図をそれぞれ示す。また、図４４、図４５および図４６に、実施例６〜８の回折光学レンズについての回折輪帯数と光軸からの高さとの関係を示すグラフをそれぞれ示す。ここで、回折輪帯数は、位相差関数を２πで割った値として定義される。
【０２５４】
実施例６〜８では、球面収差図に示されたとおり、波長λ＝６５０ｎｍに対してはＮＡ０．６０までの全開口がほぼ無収差となっている。また、波長λ＝７８０ｎｍに対しては、実使用範囲であるＮＡ０．５０までがほぼ無収差となっているが、その外側のＮＡ０．５０〜０．６０の部分については球面収差が大きく、フレアとなっている。これによって、波長λ＝７８０ｎｍについて、適正なスポット径を得ることが可能となっている。
【０２５５】
以下、実施例６〜８のレンズデータを示す。〔表６〕〜〔表８〕、更に〔表１５〕〜〔表１８〕中、ＳＴＯは絞り、ＩＭＡは像面を表しており、絞りを含めた形で表現している。また、ＯＢＪは、物点（光源）を表しており、以下の各表においても同じである。
【０２５６】
実施例６
【０２５７】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３.３３ 像側開口数ＮＡ＝０.６０ 無限仕様
【０２５８】
光源波長λ＝７８０ｎｍのとき
焦点距離ｆ＝３.３７ 像側開口数ＮＡ＝０.５０（ＮＡ＝０.６０） 無限仕様
ｗ（７８０ｎｍの光束の結像面での１３．５％強度のビーム径）＝１．２０μｍ
【０２５９】
本実施例は、図４４に見るように、λ１の光束においても、λ２の光束においても、光軸からの高さが有効径のおよそ半分以下の中心部では、−１次回折光を他の次数の回折光に比して多く発生させ、光軸からの高さが有効径のおよそ半分以上の周辺部では、＋１次回折光を他の次数の回折光に比して多く発生させる。ただし、本実施例において、輪帯ピッチを整数倍して、±１次回折光ではなく、高次の同次回折光を発生させるようにしてもよい。
【０２６０】
また、本実施例において、図２７に示されるように、第２の光情報記録媒体では、ＮＡ１＝０．６のとき、球面収差は＋２９μｍであり、ＮＡ２＝０．５のとき、球面収差は＋１μｍである。
また、本実施例において、開口数（ＮＡ）０．４における回折部のピッチは１４μｍである。
【０２６１】
【表６】

【０２６２】
非球面係数
非球面１
κ＝ −１．０７９５２
Ａ4 ＝ ０.５１９１９７２５×１０^−２
Ａ6 ＝ ０.１０９８８８６１×１０^−２
Ａ8 ＝−０.４４３８６５１９×１０^−３
Ａ10＝ ５．４０５３１３７×１０^−５
非球面２
κ＝ −３．４５２９２９
Ａ4 ＝ ０.１５５９１２９２×１０^−１
Ａ6 ＝−０.４４５２８７３８×１０^−２
Ａ8 ＝ ０.６５４２３４０４×１０^−３
Ａ10＝−４．７６７９９９２×１０^−５
【０２６３】
回折面係数
Ｂ2 ＝２９．４４３１０４
Ｂ4 ＝−１４．４０３６８３
Ｂ6 ＝３．９４２５９５１
Ｂ8 ＝−２．１４７１９５５
Ｂ10＝０．３１８５９２４８
【０２６４】
実施例７
【０２６５】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３.３３ 像側開口数ＮＡ＝０.６０ 無限仕様
【０２６６】
光源波長λ＝７８０ｎｍのとき
焦点距離ｆ＝３.３７ 像側開口数ＮＡ＝０.５０（ＮＡ＝０.６０） 有限仕様
【０２６７】
本実施例は、図４５に見るように、λ１の光束においても、λ２の光束においても、全面的に、＋１次回折光を他の次数の回折光に比して多く発生させる。ただし、本実施例において、輪帯ピッチを整数倍して、＋１次回折光ではなく、高次の同次回折光を発生させるようにしてもよい。
【０２６８】
【表７】

【０２６９】
非球面係数
非球面１
κ＝ −１．８０１３２９
Ａ4 ＝ ０.１６１５４２２×１０^−１
Ａ6 ＝−０.４９３７９６９×１０^−３
Ａ8 ＝ ０.１１０３８３２２×１０^−３
Ａ10＝−２．１８２３３０６×１０^−５
非球面２
κ＝ −８．８７１６４７
Ａ4 ＝ ０.１４９２５１１×１０^−１
Ａ6 ＝−０.４４４７４４５×１０^−２
Ａ8 ＝ ０.６００６７１４３×１０^−３
Ａ10＝−３．４６８４２０６×１０^−５
【０２７０】
回折面係数
Ｂ2 ＝−１７．１５０２３７
Ｂ4 ＝−４．１２２７０４５
Ｂ6 ＝１．１９０２２４９
Ｂ8 ＝−０．２６２０２２２２
Ｂ10＝０．０１８８４５３１５
【０２７１】
実施例８
【０２７２】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３.３３ 像側開口数ＮＡ＝０.６０ 無限仕様
【０２７３】
光源波長λ＝７８０ｎｍのとき
焦点距離ｆ＝３.３５ 像側開口数ＮＡ＝０.５０（ＮＡ＝０.６０） 無限仕様
ｗ（７８０ｎｍの光束の結像面での１３．５％強度のビーム径）＝１．２７μｍ
【０２７４】
本実施例は、図４６に見るように、λ１の光束においても、λ２の光束においても、ごく周辺部のみ−１次回折光を他の次数の回折光に比して多く発生させ、他は＋１次回折光を他の次数の回折光に比して多く発生させる。ただし、本実施例において、輪帯ピッチを整数倍して、±１次回折光ではなく、高次の同次回折光を発生させるようにしてもよい。
【０２７５】
また、本実施例において、図４１に示されるように、第２の光情報記録媒体では、ＮＡ１＝０．６のとき、球面収差は＋６８μｍであり、ＮＡ２＝０．５のとき、球面収差は＋９μｍである。
【０２７６】
また、本実施例において、開口数（ＮＡ）０．４におけるピッチは６１μｍである。
【０２７７】
【表８】

【０２７８】
非球面係数
非球面１
κ＝ −１．２５３２
Ａ4 ＝ ０.１００７×１０^−１
Ａ6 ＝−０.８５８４９×１０^−３
Ａ8 ＝−１．５７７３×１０^−５
Ａ10＝ ３．２８５５×１０^−５
非球面２
κ＝ −９．１５１３６２
Ａ4 ＝ ０.１３３３２７×１０^−１
Ａ6 ＝−０.３７８６８２×１０^−２
Ａ8 ＝ ０.３００１×１０^−３
Ａ10＝ ４．０２２２１×１０^６
【０２７９】
回折面係数
Ｂ2 ＝３．４２５１×１０^−２１
Ｂ4 ＝０．０７６３９７７
Ｂ6 ＝−５．５３８６
Ｂ8 ＝０．０５９３８
Ｂ10＝０．２２２４
ここで、実施例６〜８に基づいて、レンズに入射する半導体レーザの波長の変動要因について考察する。半導体レーザの波長の個体ばらつきは、±２から３ｎｍ程度、多モード発振の幅が±２ｎｍ程度、書き込み時のモードホップが２ｎｍ程度と考えられる。これらの要因による半導体レーザの波長変動に伴う、レンズの球面収差の変動を考慮した場合について説明する。
【０２８０】
つまり、異なる２波長の光源に対し、光ディスクの透明基板の厚みがそれぞれで異なる場合、実施例６に関するデータから理解されるように、異なる２波長の光源からの無限光（平行光束）に対して無収差に補正したレンズでは、１つの光源での波長１０ｎｍ程度の変化に対し、球面収差変動が比較的大きい。実施例６では、６５０ｎｍの波長においては波面収差が０．００１λｒｍｓであるが、６４０ｎｍおよび６６０ｎｍの波長においては、波面収差が０．０３５λｒｍｓ程度に劣化する。もちろん、レーザの波長がよく管理された光学系に対しては、実施例６も十分実用に供することができる。これに対し、実施例７のレンズのように、どちらか一方の光源からの無限光に対してほぼ無収差で、もう一方の波長の光源からの有限光（非平行光束）に対してほぼ無収差に補正したレンズでは、１つの光源の波長１０ｎｍ程度の変化に対し、球面収差変動を極めて小さく抑えることが可能となる。
【０２８１】
次に、本実施の形態の回折光学系（回折光学レンズを有する光学系）の性能の温度変化について考察する。まず、半導体レーザの波長は、温度が３０℃上昇すると６ｎｍ程度伸びる傾向がある。これに対し、回折光学系がプラスチックレンズで構成されている場合、３０℃温度が上昇すると、屈折率が０．００３ないし０．００４程度減少する傾向がある。実施例６のような、２つの波長のどちらの無限光に対しても無収差に補正したレンズでは、半導体レーザの波長の温度変化による要因とプラスチックレンズの屈折率の温度変化による要因とが補償効果を起こし、温度変化に極めて強い光学系を作り出すことができる。また、実施例６において、素材がガラスである場合も、温度変化に対し許容幅のある光学系にすることは可能である。また、実施例７においても、実施例６には及ばないものの、３０℃の温度変化で、波面収差の劣化は０．０３５λｒｍｓ程度であり、実用上充分な温度補償ができている。
【０２８２】
上述の温度変化の補償効果について更に説明する。波長の異なる２つの光源により、透明基板の厚さが異なる２種類の光情報記録媒体の記録及び／または再生する場合において、回折パターンを有する対物レンズを用いることにより、それぞれの光ディスクの情報記録面に必要とされる開口数ないしそれ以上の開口数においても波面収差のｒｍｓ値がそれぞれの波長の０．０７以下とすることができるので、専用の対物レンズと同等の結像特性を得ることができる。低価格でコンパクトな光ピックアップ装置とするために、光源には半導体レーザが用いられ、対物レンズにはプラスチックレンズが用いられることが多い。
【０２８３】
レンズ用のプラスチック材料には種々のものがあるが、屈折率の温度変化や線膨張係数がガラスに比べて大きい。特に、屈折率の温度変化がレンズの諸特性に影響を及ぼす。２５℃近傍の屈折率の温度変化としては、光ピックアップの光学素子として用いられるプラスチック材料では、−０．０００２／℃ないし−０．００００５／℃である。さらに、低複屈折材料は−０．０００１／℃のものが多い。また、レンズ用の熱硬化性プラスチックはさらに温度変化に対して屈折率の変化が大きく、上記範囲を外れるものもある。
【０２８４】
半導体レーザに関しても、現在の技術で製作されるものについては、発振波長に温度依存性があり、２５℃近傍の発振波長の温度変化は、０．０５ｎｍ／℃ないし０．５ｎｍ／℃である。
【０２８５】
光情報記録媒体の情報を再生または光情報記録媒体に情報を記録するための光束の波面収差が温度により変化しｒｍｓ値が波長の０．０７以上となると光ピックアップ装置としての特性を維持することが困難であり、特に、より高密度の光情報媒体において波面収差の温度変化について留意する必要がある。プラスチックレンズの温度変化による波面収差の変化では焦点ズレと球面収差の変化の双方が起こっているが、前者は光ピックアップ装置において焦点制御を行うので、後者が重要である。ここで、プラスチック材料は温度変化ΔＴ（℃）があったときの屈折率の変化量をΔｎとしたときに、
−０．０００２／℃＜Δｎ／ΔＴ＜−０．００００５／℃
の関係を満たし、半導体レーザは、温度変化ΔＴがあったときの発振波長の変化量をΔλ１としたときに、
０．０５ｎｍ／℃＜Δλ１／ΔＴ＜０．５ｎｍ／℃
の関係を満たすと、プラスチックレンズの屈折率の温度変化による波面収差の変動と、半導体レーザ光源の波長の温度変化とによる波面収差の変動とが打ち消しあう方向に作用し、補償効果を得ることができる。
【０２８６】
また、環境温度変化が△Ｔ（℃）あったときに、波面収差の３次の球面収差成分の変化量を△ＷＳＡ３（λｒｍｓ）とすると、これは対物レンズを通過する光束の対物レンズの光情報媒体側の開口数（ＮＡ）の４乗に比例し、プラスチックレンズの焦点距離ｆ（ｍｍ）に比例し、波面収差を波長単位で評価しているので光源の波長λ（ｍｍ）に反比例する。したがって、次式が成立する。
△ＷＳＡ３＝ｋ・（ＮＡ）^４・ｆ・△Ｔ／λ （ａ１）
ここで、ｋは対物レンズの種類に依存する量である。
ちなみに、プラスチック製の両面非球面対物レンズで、焦点距離３．３６ｍｍ、光情報媒体側の開口数が０．６で入射光束が平行光の場合に最適化されているものが、MOC/GRIN'97 Techical Digest C5 p40-p43、"The Temperature characteristics of a new optical system with quasi-finite conjugate plastic objective for high density optical disk use"に記載されているが、この文献の中のグラフから、３０℃の温度変化でＷＳＡ３が０．０４５λｒｍｓだけ変化しており、ＤＶＤ用途であることから、波長は、λ＝６５０ｎｍと考えられる。以上のデータを式（ａ１）に代入すると、ｋ＝２．２×１０^−６が得られる。また、温度変化による波長変化の影響に関しては記載がないが、発振波長の温度変化が小さい場合、回折を使用しない対物レンズについては、温度による屈折率変化の影響のほうが大きい。
【０２８７】
ＤＶＤについて記録及び／または再生する光ピックアッブ装置に関しては、ｋが上記値以下であることが必要となる。透明基板の厚さが異なる２種類の光情報記録媒体の記録及び／または再生する場合に、回折パターンを有する対物レンズにおいて、温度変化による波長変化の影響も無視することはできなくなる。特にｋに関し、焦点距離、プラスチック材料の屈折率の温度変化、透明基板の厚さの差、二つの光源の発振波長の差等によりｋの値は異なるが、実施例６においては、半導体レーザの波長の温度変化による要因とプラスチックレンズの屈折率の温度変化による要因とが補償効果を起こし、対物レンズがプラスチックレンズであっても温度変化による波面収差の変化は少なくシミュレーションによると、
ｋ＝２．２×１０^−６／℃、ｋ＝０．４×１０^−６／℃
となる。
【０２８８】
ｋとしては、０．３＜ｋ＜２．２の範囲を取ることができる。したがって、式（ａ１）より、
ｋ＝ΔＷＳＡ３・λ／｛ｆ・（ＮＡ１）^４・ΔＴ（ＮＡ）｝ （ａ２）
であるから、
０．３×１０^−６／℃＜ΔＷＳＡ３・λ／｛ｆ・（ＮＡ１）^４・ΔＴ｝＜
２．２×１０^−６／℃ （ａ３）
となる。式（ａ３）において、ｋの値が上限を越えると、温度変化により光ピックアップ装置としての特牲を維持することが困難となり易く、また、下限を越えると、温度変化に対しての変動は少ないが、波長たけが変化した場合において光ピックアップ装置としての特性を維持することが困難となり易い。
【０２８９】
また、実施例８においては、実施例６と比較して、一方の波長、即ち、７８０ｎｍの波長の性能を許容範囲内でやや悪くすることにより、もう一方の波長、即ち、６５０ｎｍの波長近傍±１０ｎｍでの球面収差変動を小さくすることができる。実施例６においては、波長６４０ｎｍ若しくは６６０ｎｍでの波面収差は０．０３５λｒｍｓ程度であるが、実施例８においては、波長６４０ｎｍ若しくは６６０ｎｍでの波面収差は０．０２０λｒｍｓ程度に向上させることができる。この二つの要因はトレードオフの関係があるが、バランスを保つことが重要であり、０．０７λｒｍｓを超えると、レンズ性能が悪化し、光ディスク用光学系として用いることは困難となってくる。
【０２９０】
次に、実施例６に基づいて、波長変化に対する、マージナル光線の球面収差の変化量と軸上色収差の変化量との関係について説明する。実施例６のように透明基板の厚さが薄い方の情報記録媒体には短い方の波長の光束を使用し、透明基板の厚さが厚い方の情報記録媒体には長い方の波長の光束を使用する一つの光ピックアップ装置で、それら光束に使用される対物レンズでは、回折面の作用によって、或る波長に対して波長が長くなった場合に球面収差をアンダー側に変位させることで、透明基板厚の差によって生じる球面収差を補正することができる。
【０２９１】
この対物レンズにおいて、少なくとも一方の光源の使用波長の微小な変化に対する、マージナル光線の球面収差の変化量と軸上色収差の変化量とを、それぞれ△ＳＡ、△ＣＡとすれば、
−１＜△ＳＡ／△ＣＡ＜−０．２
を満たすことが望ましい。この式は使用波長が変化した時の、マージナル光線の球面収差の変化量と軸上色収差の変化量との比を示し、この条件式の下限を上回ることで、回折輪帯の間隔を大きくでき、回折効率の高い回折面が製造し易く、条件式の上限を下回ることで、回折面が負で大きな屈折力を持つことを抑制でき、また軸上色収差の波長変化が過大にならず、モードポップ等の波長変化に対して焦点位置の変動を抑えることができる。なお、波長の微小な変化とは、１０ｎｍ以下程度の変化を意味する。実施例６では図２５に見るように、波長６５０ｎｍにおいて△ＳＡ／△ＣＡの値は−０．７である。
【０２９２】
ここで、回折パワーとレンズ形状との関係について説明する。図４７に、回折パワーとレンズ形状との関係を模式的に示す。図４７（ａ）は回折パワーがすべての部分で正のレンズ形状を示す図であり、図４７（ｂ）は回折パワーがすべての部分で負のレンズ形状を示す図である。実施例６のレンズは、図４７（ｃ）に示すように、回折パワーが光軸付近では負のパワーであり、途中で正のパワーに切り替わるように設計されている。これにより、回折輪帯のピッチが細かくなりすぎないようにすることができる。また、実施例８のように、レンズの周辺部付近で回折パワーが、正のパワーから負のパワーに切り替わるように設計することにより、２波長間で、良好な収差を得ることもできる。図４７（ｄ）のように、例えば、回折パワーが光軸付近では正のパワーであり、途中で負のパワーに切り替わるようにできる。
【０２９３】
図４７（ｃ）では、回折面はブレーズ化された複数の回折輪帯を有し、光軸に近い側の回折輪帯ではその段差部が光軸から離れた側に位置し、光軸から離れた側の回折輪帯ではその段差部が光軸に近い側に位置している。また、図４７（ｄ）では、回折面はブレーズ化された複数の回折輪帯を有し、光軸に近い側の回折輪帯ではその段差部が光軸に近い側に位置し、光軸から離れた側の回折輪帯ではその段差部が光軸から離れた側に位置している。
【０２９４】
〈実施例９、１０〉
【０２９５】
実施例９、１０の対物レンズは、上述した〔数３〕で表される非球面形状を屈折面に有しており、実施例９は２光源対応の有限共役型、実施例１０は、第２の実施の形態に係る対物レンズの具体例であり、３光源対応の有限共役型である。また、実施例９、１０では回折面が単位をラジアンとした位相差関数ΦBとして上述の〔数１〕で表される。
【０２９６】
図５０および図５１に、実施例９の対物レンズのλ＝６５０ｎｍおよびλ＝７８０ｎｍにおける光路図を示す。また、図５２に、実施例９の対物レンズについてのλ＝６５０ｎｍに対する開口数０．６０までの球面収差図を示す。また、図５３および図５４に、実施例９の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５および０．６０までの球面収差図をそれぞれ示す。また、図５５、図５６に、実施例９の対物レンズについてのλ＝６５０ｎｍおよび波長λ＝７８０ｎｍに対する波面収差図をそれぞれ示す。
【０２９７】
図５７〜図５９に、実施例１０の対物レンズのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍにおける光路図を示す。また、図６０、図６１に、実施例１０の対物レンズについてのλ＝６５０ｎｍおよびλ＝４００ｎｍに対する開口数０．６５までの球面収差図を示す。また、図６２および図６３に、実施例１０の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５および０．６５までの球面収差図をそれぞれ示す。また、図６４〜図６６に、実施例１０の対物レンズについてのλ＝６５０ｎｍ、λ＝４００ｎｍおよび波長λ＝７８０ｎｍに対する波面収差図をそれぞれ示す。
【０２９８】
実施例９、１０の対物レンズによると、何れの実施例でも、７８０ｎｍ波長光に対しては、実使用上のＮＡ０．４５を超える光束では大きな球面収差を生じ、フレアとして情報の記録および／または再生には寄与しない。
【０２９９】
以下、実施例９、１０のレンズデータを示す。〔表９〕、〔表１０〕中、ｒはレンズの曲率半径、ｄは面間隔、ｎは各波長での屈折率、νはアッベ数を示す。また、参考として、ｄ線（λ＝５８７．６ｎｍ）での屈折率と、νｄ（アッベ数）を記す。また、面No.の数字は、絞りを含めて表示しており、また、本実施例では、便宜上、光ディスクの透明基板に相当する部分の前後２か所に空気間隔を分けて表現している。
【０３００】
実施例９
f＝3.33 像側 NA 0.60 倍率 -0.194 (波長λ＝650nmのとき)
f＝3.35 像側 NA 0.45(NA 0.60) 倍率 -0.195 (波長λ＝780nmのとき)
【０３０１】
【表９】

【０３０２】
非球面１
κ ＝-0.1295292
A4 ＝-0.0045445253
A6 ＝-0.0011967305
A8 ＝-0.00011777995
A10＝-5.3843777×10^−５
A12＝-9.0807729×10^−６
回折面１
B2 ＝ 0
B4 ＝-7.6489594
B6 ＝ 0.9933123
B8 ＝-0.28305522
B10＝ 0.011289605
【０３０３】
非球面２
κ ＝-5.161871
A4 ＝ 0.019003845
A6 ＝-0.010002187
A8 ＝ 0.004087239
A10＝-0.00085994626
A12＝ 7.5491556×10^−５
【０３０４】
実施例１０
f＝3.31 像側 NA 0.65 倍率 -0.203 (波長λ＝650nmのとき)
f＝3.14 像側 NA 0.65 倍率 -0.190 (波長λ＝400nmのとき)
f＝3.34 像側 NA 0.45(NA 0.65) 倍率 -0.205 (波長λ＝780nmのとき)
【０３０５】
【表１０】

【０３０６】
非球面１
κ ＝-0.08796008
A4 ＝-0.010351744
A6 ＝ 0.0015514472
A8 ＝-0.00043894535
A10＝ 5.481801×10^−５
A12＝-4.2588508×10^−６
回折面１
B2 ＝ 0
B4 ＝-61.351934
B6 ＝ 5.9668445
B8 ＝ -1.2923244
B10＝ 0.041773541
【０３０７】
非球面２
κ ＝-302.6352
A4 ＝ 0.002
A6 ＝ -0.0014
A8 ＝ 0.0042
A10＝ -0.0022
A12＝ 0.0004
回折面２
B2 ＝ 0
B4 ＝ 341.19136
B6 ＝-124.16233
B8 ＝ 49.877242
B10＝ -5.9599182
【０３０８】
なお、上記実施例１０の対物レンズの具体例は、第３の実施の形態にも同様に適用できる。
【０３０９】
〈実施例１１〜１４〉
【０３１０】
実施例１１〜１４の対物レンズは、上述した〔数３〕で表される非球面形状を屈折面に有しており、また、実施例１１〜１３では回折面が単位をラジアンとした位相差関数ΦBとして上述の〔数１〕で表され。実施例１４では回折面が単位をｍｍとした光路差関数Φbとして上述の〔数２〕で表わされる。
【０３１１】
これら実施例１１〜１４の対物レンズ特性を得るに当たって、第１光ディスク（ＤＶＤ）用の光源波長を６５０ｎｍ、第２光ディスク（青色レーザ使用次世代高密度光ディスク）用の光源波長を４００ｎｍとし、第１および第２光ディスクの透明基板厚さｔ１は共にｔ１＝０．６ｍｍである。また、ｔ１とは異なる透明基板の厚さｔ２＝１．２ｍｍを有する第３光ディスク（ＣＤ）用の光源波長は７８０ｎｍとした。また、光源波長４００ｎｍ、６５０ｎｍ、７８０ｎｍに対応する開口数ＮＡとして、０．６５、０．６５、０．５をそれぞれ想定している。
【０３１２】
（実施例１１）
【０３１３】
実施例１１は、第４の実施の形態に係わる対物レンズの具体例であり、対物レンズには平行光が入射するように構成されている。この実施例では、回折面の位相差関数の係数に２乗項が含まれず（Ｂ2＝０）、２乗項以外の項の係数だけを使用している。
【０３１４】
図６８〜図７０に、実施例１１の対物レンズのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍにおける光路図を示す。また、図７１および図７２に、実施例１１の対物レンズについてのλ＝６５０ｎｍおよびλ＝４００ｎｍに対する開口数０．６５までの球面収差図を示す。また、図７３および図７４に、実施例１１の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５および０．６５までの球面収差図をそれぞれ示す。また、図７５〜図７７に、実施例１１の対物レンズについてのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍに対する波面収差図をそれぞれ示す。
【０３１５】
以下、実施例１１のレンズデータを示す。〔表１１〕中、ｒはレンズの曲率半径、ｄは面間隔、ｎは各波長での屈折率を示す。また、面No.の数字は、絞りを含めて表示している。
【０３１６】
実施例１１
f＝3.33 像側 NA 0.65 (波長λ＝650nmのとき)
f＝3.15 像側 NA 0.65 (波長λ＝400nmのとき)
f＝3.37 像側 NA 0.45(NA 0.65) (波長λ＝780nmのとき)
【０３１７】
【表１１】

【０３１８】
非球面１
κ ＝-0.1847301
A4 ＝-0.0090859227
A6 ＝ 0.0016821871
A8 ＝-0.00071180761
A10＝ 0.00012406905
A12＝-1.4004589×10^−５
回折面１
B2 ＝ 0
B4 ＝-69.824562
B6 ＝ 0.35641549
B8 ＝ 0.6877372
B10＝ -0.18333885
【０３１９】
非球面２
κ ＝-186.4056
A4 ＝ 0.002
A6 ＝ -0.0014
A8 ＝ 0.0042
A10＝ -0.0022
A12＝ 0.0004
回折面２
B2 ＝ 0
B4 ＝ 745.72117
B6 ＝-334.75078
B8 ＝ 81.232224
B10＝ -5.3410176
【０３２０】
実施例１１（および後述する実施例１２）のような対物レンズと３つの光源とを有する光ピックアップ装置において、非球面係数及び位相差関数の係数を適当に設計することで、透明基板厚さの違いにより発生する球面収差及び波長の違いにより発生する球面収差の色収差を各ディスクともに補正することが可能である。また、図７４から明らかなように、第３光ディスクでは実使用上の開口数ＮＡ０．４５の外側をフレアとしている。
【０３２１】
（実施例１２）
【０３２２】
また、実施例１２の対物レンズは、有限距離からの発散光が入射するように構成されている。この実施例では、回折面の位相差関数の係数に２乗項が含まれず（Ｂ2＝０）、２乗項以外の項の係数だけを使用している。
【０３２３】
図７８〜図８０に、実施例１２の対物レンズのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍにおける光路図を示す。また、図８１および図８２に、実施例１２の対物レンズについてのλ＝６５０ｎｍおよびλ＝４００ｎｍに対する開口数０．６５までの球面収差図を示す。また、図８３および図８４に、実施例１２の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５および０．６５までの球面収差図をそれぞれ示す。また、図８５〜図８７に、実施例１２の対物レンズについてのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍに対する波面収差図をそれぞれ示す。
【０３２４】
以下、実施例１２のレンズデータを示す。
【０３２５】
実施例１２
f＝3.31 像側 NA 0.65 倍率 -0.203 (波長λ＝650nmのとき)
f＝3.14 像側 NA 0.65 倍率 -0.190 (波長λ＝400nmのとき)
f＝3.34 像側 NA 0.45(NA 0.65) 倍率 -0.205 (波長λ＝780nmのとき)
【０３２６】
【表１２】

【０３２７】
非球面１
κ ＝-0.08796008
A4 ＝-0.010351744
A6 ＝ 0.0015514472
A8 ＝-0.00043894535
A10＝ 5.481801×10^−５
A12＝-4.2588508×10^−６
回折面１
B2 ＝ 0
B4 ＝-61.351934
B6 ＝ 5.9668445
B8 ＝ -1.2923244
B10＝ 0.041773541
【０３２８】
非球面２
κ ＝-302.6352
A4 ＝ 0.002
A6 ＝ -0.0014
A8 ＝ 0.0042
A10＝ -0.0022
A12＝ 0.0004
回折面２
B2 ＝ 0
B4 ＝ 341.19136
B6 ＝-124.16233
B8 ＝ 49.877242
B10＝ -5.9599182
【０３２９】
実施例１２のような対物レンズと３つの光源とを有する光ピックアップ装置において、透明基板厚さの違いにより発生する球面収差及び波長の違いにより発生する球面収差の色収差について各ディスクともに補正することが可能である。また、図８４から明らかなように、第３光ディスクでは実使用上の開口数ＮＡ０．４５の外側をフレアとしている。
【０３３０】
（実施例１３）
【０３３１】
また、実施例１３の対物レンズは、第４の実施の形態に係わる対物レンズの他の具体例であり、無限距離からの平行光が入射するように構成されている。この実施例では、回折面の位相差関数の係数として２乗項および２乗項以外の項が使用されている。
【０３３２】
図８８〜図９０に、実施例１３の対物レンズのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍにおける光路図を示す。また、図９１および図９２に、実施例１３の対物レンズについてのλ＝６５０ｎｍおよびλ＝４００ｎｍに対する開口数０．６０までの球面収差図を示す。また、図９３および図９４に、実施例１３の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５および０．６０までの球面収差図をそれぞれ示す。また、図９５〜図９７に、実施例１３の対物レンズについてのλ＝６５０ｎｍ、λ＝４００ｎｍおよびλ＝７８０ｎｍに対する波面収差図をそれぞれ示す。
【０３３３】
以下、実施例１３のレンズデータを示す。
【０３３４】
実施例１３
f＝3.31 像側 NA 0.60 (波長λ＝650nmのとき)
f＝3.14 像側 NA 0.60 (波長λ＝400nmのとき)
f＝3.34 像側 NA 0.45(NA 0.60) (波長λ＝780nmのとき)
【０３３５】
【表１３】

【０３３６】
非球面１
κ ＝-0.3363369
A4 ＝-0.0025421455
A6 ＝-0.0010660122
A8 ＝ 4.7189743×10^−５
A10＝ 1.5406396×10^−６
A12＝-7.0004876×10^−６
回折面１
B2 ＝-177.66083
B4 ＝ -46.296284
B6 ＝ -6.8014831
B8 ＝ 1.6606499
B10＝ -0.39075825
【０３３７】
非球面２
κ ＝43.44262
A4 ＝ 0.002
A6 ＝-0.0014
A8 ＝ 0.0042
A10＝-0.0022
A12＝ 0.0004
回折面２
B2 ＝ 241.52445
B4 ＝ 402.41974
B6 ＝-191.87213
B8 ＝ 64.779696
B10＝ -8.6741764
【０３３８】
本実施例では、回折面の位相差関数の係数として２乗項および２乗項以外の項が使用されているために、透明基板厚さの違いにより発生する球面収差及び波長の違いにより発生する球面収差の色収差と軸上色収差について各ディスクともに補正することが可能となっている。また、図９４から明らかなように、第３光ディスクでは実使用上の開口数ＮＡ０．４５の外側をフレアとしている。
【０３３９】
（実施例１４）
【０３４０】
実施例１４の対物レンズは、第６の実施の形態に係わる対物レンズの具体例であり、無限距離から波長４００ｎｍと６５０ｎｍの平行光が入射し、有限距離から波長７８０ｎｍの発散光が入射するように構成されている。この実施例では、回折面の光路差関数の係数として２乗項および２乗項以外の項が使用されている。
【０３４１】
図９８に、実施例１４の対物レンズのλ＝４００ｎｍにおける光路図を示す。また、図９９および図１０１に、実施例１４の対物レンズについてのλ＝４００ｎｍ±１０ｎｍ、λ＝６５０ｎｍ±１０ｎｍおよびλ＝７８０ｎｍ±１０ｎｍに対する開口数０．６５までの球面収差図を示す。
【０３４２】
以下、実施例１４のレンズデータを示す。
【０３４３】
実施例１４
f＝ 像側 NA 0.65 (波長λ＝650nmのとき)
f＝ 像側 NA 0.65 (波長λ＝400nmのとき)
f＝ 像側 NA 0.45(NA 0.65) (波長λ＝780nmのとき)
【０３４４】
【表１４】

【０３４５】
非球面１
κ ＝-2.0080
A4 ＝ 0.18168×10^−１
A6 ＝-0.91791×10^−３
A8 ＝ 0.16455×10^−３
A10＝-0.11115×10^−４
回折面
b2 ＝-0.51589×10^−３
b4 ＝-0.24502×10^−３
b6 ＝ 0.49557×10^−４
b8 ＝-0.14497×10^−４
【０３４６】
非球面２
κ ＝ 3.1831
A4 ＝ 0.14442×10^−１
A6 ＝ -0.17506×10^−２
A8 ＝ 0.21593×10^−４
A10＝ 0.12534×10^−４
【０３４７】
なお、本発明は上記実施例に限定されるものではない。回折を対物レンズの両面に形成したが、光ピックアップ装置の光学系内の光学素子のある一面に設けてもよい。また輪帯状回折面をレンズ面全体に形成したが、部分的に回折面を形成しても良い。さらに、青色レーザ使用次世代高密度光ディスクとして、光源波長４００ｎｍ、透明基板の厚さ０．６ｍｍと仮定して光学設計を進めたが、これ以外の仕様である光ディスクに関しても本発明は適用が可能である。
【０３４８】
次に、本発明の第７の実施の形態について説明する。
【０３４９】
図１１７は、本実施の形態の対物レンズ及びこれを含む光ピックアップ装置の概略構成である。図１１７のように、第１の半導体レーザ１１１と第２の半導体レーザ１１２が光源としてユニット化されている。コリメータ１３と対物レンズ１６との間にビームスプリッタ１２０が配置され、コリメータ１３でほぼ平行にされた光がビームスプリッタ１２０を通過し対物レンズ１６へ向かう。また、情報記録面２２から反射した光束が光路変更手段としてのビームスプリッタ１２０で光検出器３０に向かうように光路を変える。対物レンズ１６はその外周にフランジ部１６ａを有し、このフランジ部１６ａにより対物レンズ１６を光ピックアップ装置に容易に取り付けることができる。また、フランジ部１６ａは対物レンズ１６の光軸に対し略垂直方向に延びた面を有するから、更に精度の高い取付が容易にできる。
【０３５０】
第１の光ディスクを再生する場合、第１半導体レーザ１１１から出射された光束は、コリメータ１３を透過し平行光束となる。さらにビームスプリッタ１２０を経て絞り１７によって絞られ、対物レンズ１６により第１の光ディスク２０の透明基板２１を介して情報記録面２２に集光される。そして、情報記録面２２で情報ピットにより変調されて反射した光束は、再び対物レンズ１６、絞り１７を介して、ビームスプリッタ１２０で反射され、シリンドリカルレンズ１８０により非点収差が与えられ、凹レンズ５０を経て、光検出器３０上ヘ入射し、光検出器３０から出力される信号を用いて、第１の光ディスク２０に記録された情報の読み取り信号が得られる。
【０３５１】
また、光検出器３０上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第１の半導体レーザ１１１からの光束を第１の光ディスク２０の情報記録面２２上に結像するように対物レンズ１６を移動させるとともに、第１の半導体レ―ザ１１１からの光束を所定のトラックに結像するように対物レンズ１６を移動させる。
【０３５２】
次に、第２の光ディスクを再生する場合、第２の半導体レーザ１１２から出射された光束は、コリメータ１３を透過し平行光束となる。さらにビームスプリッタ１２０を経て絞り１７によって絞られ、対物レンズ１６により第２の光ディスク２０の透明基板２１を介して情報記録面２２に集光される。そして、情報記録面２２で情報ピットにより変調されて反射した光束は、再び対物レンズ１６、絞り１７を介して、ビームスプリッタ１２０で反射され、シリンドリカルレンズ１８０により非点収差が与えられ、凹レンズ５０を経て、光検出器３０上ヘ入射し、光検出器３０から出力される信号を用いて、第２の光ディスク２０に記録された情報の読み取り信号が得られる。また、光検出器３０上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５か第１の半導体レーザ１１２からの光束を第２光ディスク２０の情報記録面２２上に結像するように対物レンズ１６を移動させるとともに、第２の半導体レーサ１１２からの光束を所定のトラックに結像するように対物レンズ１６を移動させる。
【０３５３】
対物レンズ（回折レンズ）１６は、第１の光ディスク、第２の光ディスクの記録及び／または再生に必要な開口数のうち大きい方の開口数（最大開口数）まで、それぞれの半導体レーザからの入射光に対して、それぞれの波長（λ）に対して０．０７λｒｍｓ以下であるように設計されている。このため、それぞれの光束の結像面上の波面収差は、０．０７λｒｍｓ以下となっている。従って、結像面上及び検出器３０上でどちらの光ディスクの記録及び／または再生時にフレアがなく、合焦誤差検出やトラック誤差検出の特性が良好となる。
【０３５４】
なお、第１の光ディスクをＤＶＤ（光源波長６５０ｎｍ）、第２の光ディスクをＣＤ（光源波長７８０ｎｍ）とするケースや、第１の光ディスクを次世代高密度光ディスク（光源波長４００ｎｍ）、第２の光ディスクをＤＶＤ（光源波長６５０ｎｍ）のケースが想定されるが、特に、それぞれの光ディスクの必要開口数に大きな差がある場合には、上記のような場合には、必要なスポット径に比較してスポットが小さすぎる場合もある。このときは本明細書の他の箇所で説明している開口制限手段を導入し、所望のスポット径とすればよい。
【０３５５】
以下、第７の実施の形態に係わる対物レンズの具体例として、球面収差補正レンズの実施例１５、１６，１７，１８を説明する。各実施例で波面収差が、最大開口数に対し０．０７λｒｍｓ以下に補正されている。なお、以下において像側とは光情報記録媒体側の意味である。
【０３５６】
〈実施例１５〉
【０３５７】
図１１８に、実施例１５の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図を示す。また、図１１９に、実施例１５の回折光学レンズについての波長（λ）＝６４０，６５０，６６０ｎｍに対する開口数０．６０までの球面収差図を示す。また、図１２０は光情報記録媒体の透明基板が図１１８より厚い場合の実施例１５の回折光学レンズの光路図を示す。図１２１に、図１２０の場合の回折光学レンズについての波長λ＝７７０，７８０，７９０ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。
【０３５８】
実施例１５の回折光学レンズによると、図１１９に示すように、波長λ＝６５０ｎｍに対してはＮＡ０．６０までの全開口がほぼ無収差である。また、図１２０、図１２１に示すように、透明基板が厚い場合で、波長λ＝７８０ｎｍに対しては、ＮＡ０．６０までがほぼ無収差である。なお、λ＝７８０ｎｍのときの所定開口数は０．４５である。
【０３５９】
以上のように、実施例１５では、実施例１，６，８と比べて、光情報記録媒体の透明基板が厚く波長が７８０ｎｍの場合の球面収差を透明基板がこれよりも薄く波長が６５０ｎｍの場合と同じ開口数（ＮＡ０．６０）まで補正できる。
【０３６０】
以下、実施例１５のレンズデータを示す。
【０３６１】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３．３３ 像側開口数 ＮＡ＝０．６０ 無限仕様（平行光束入射）
【０３６２】
光源波長λ＝７８０ｎｍのとき
焦点距離ｆ＝３．３８ 像側開口数 ＮＡ＝０．６０ 無限仕様
【０３６３】
【表１５】

【０３６４】
非球面係数
非球面１
κ ＝−１．０３５８
Ａ_４＝４．８６３２×１０^−３
Ａ_６＝５．３８３２×１０^−４
Ａ_８＝−１．５７７３×１０^−４
Ａ_１０＝３．８６８３×１０^−７
【０３６５】
非球面２
κ ＝−９．２５６３５２
Ａ_４＝１．５８８７×１０^−２
Ａ_６＝−５．９７４２２×１０^−３
Ａ_８＝１．１１６１３×１０^−３
Ａ_１０＝−９．３９６８２×１０^−５
【０３６６】
回折面係数（基準波長６５０ｎｍ）
ｂ_２＝６．０００×１０^−３
ｂ_４＝−１．３１７×１０^−３
ｂ_６＝１．５２７４×１０^−４
ｂ_８＝−６．５７５７×１０^−５
ｂ_１０＝６．２２１×１０^−６
【０３６７】
〈実施例１６〉
【０３６８】
図１２２に、実施例１６の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図を示す。また、図１２３に、実施例１６の回折光学レンズについての波長（λ）＝６４０，６５０，６６０ｎｍに対する開口数０．６０までの球面収差図を示す。また、図１２４は光情報記録媒体の透明基板が図１２２より厚い場合の実施例１６の回折光学レンズの光路図を示す。図１２５に、図１２４の場合の回折光学レンズについての波長λ＝７７０，７８０，７９０ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。
【０３６９】
実施例１６の回折光学レンズによると、図１２３に示すように、波長λ＝６５０ｎｍに対してはＮＡ０．６０までの全開口がほぼ無収差である。また、図１２４、図１２５に示すように、透明基板が厚い場合で、波長λ＝７８０ｎｍに対しては、ＮＡ０．６０までがほぼ無収差である。なお、λ＝７８０ｎｍのときの所定開口数は０．４５である。
【０３７０】
以上のように、実施例１６では、実施例１，６，８と比べて、光情報記録媒体の透明基板が厚く波長が７８０ｎｍの場合の球面収差を透明基板がこれよりも薄く波長が６５０ｎｍの場合と同じ開口数（ＮＡ０．６０）まで補正できる。なお、実施例１５，１６では、透明基板の厚さの差による球面収差をＮＡ０．６まで補正するために、回折による球面収差の補正作用が強いことが必要であるが、このため輪帯ピッチが狭くなるが、回折の近軸パワーを負にしてピッチの減少を緩和している。
【０３７１】
以下、実施例１６のレンズデータを示す。
【０３７２】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３．３３ 像側開口数 ＮＡ＝０．６０ 無限仕様
【０３７３】
光源波長λ＝７８０ｎｍのとき
焦点距離ｆ＝３．３６ 像側開口数 ＮＡ＝０．６０ 無限仕様
【０３７４】
【表１６】

【０３７５】
非球面係数
非球面１
κ＝−１．１３３１
Ａ_４＝４．５３７５×１０^−３
Ａ_６＝１．２９６４×１０^−３
Ａ_８＝−３．６１６４×１０^−４
Ａ_１０＝２．０７６５×１０^−５
【０３７６】
非球面２
κ＝−４．３５６２９８
Ａ_４＝１．５７４２７×１０^−２
Ａ_６＝−４．９１１９８×１０^−３
Ａ_８＝７．７２６０５×１０^−４
Ａ_１０＝−５．７５４５６×１０^−５
【０３７７】
回折面係数（基準波長６５０ｎｍ）
ｂ_２＝２．１６６５×１０^−３
ｂ_４＝−２．０２７２×１０^−３
ｂ_６＝５．５１７８×１０^−４
ｂ_８＝−１．８３９１×１０^−４
ｂ_１０＝１．８１４８×１０^−５
【０３７８】
〈実施例１７〉
【０３７９】
図１２６に、実施例１７の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図を示す。また、図１２７に、実施例１７の回折光学レンズについての波長（λ）＝６４０，６５０，６６０ｎｍに対する開口数０．６０までの球面収差図を示す。また、図１２８は光情報記録媒体の透明基板が図１２６より厚い場合の実施例１７の回折光学レンズの光路図を示す。図１２９に、図１２８の場合の回折光学レンズについての波長λ＝７７０，７８０，７９０ｎｍに対する開口数０．６０までの球面収差図をそれぞれ示す。
【０３８０】
実施例１７の回折光学レンズによると、図１２７に示すように、波長λ＝６５０ｎｍに対してはＮＡ０．６０までの全開口がほぼ無収差である。また、図１２８、図１２９に示すように、透明基板が厚い場合で、波長λ＝７８０ｎｍに対しては、ＮＡ０．６０までがほぼ無収差である。なお、λ＝７８０ｎｍのときの所定開口数は０．４５である。また、実施例１５〜１７は軸上色収差が異なり、また、輪帯ピッチも変わっている。
【０３８１】
以上のように、実施例１７では、実施例１，６，８と比べて、光情報記録媒体の透明基板が厚く波長が７８０ｎｍの場合の球面収差を透明基板がこれよりも薄く波長が６５０ｎｍの場合と同じ開口数（ＮＡ０．６０）まで補正できる。
【０３８２】
以下、実施例１７のレンズデータを示す。
【０３８３】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３．３３ 像側開口数 ＮＡ＝０．６０ 無限仕様
【０３８４】
光源波長λ＝７８０ｎｍのとき
焦点距離ｆ＝３．３４ 像側開口数 ＮＡ＝０．６０ 無限仕様
【０３８５】
【表１７】

【０３８６】
非球面係数
非球面１
κ＝−１．０７５１
Ａ_４＝５．０７３２×１０^−３
Ａ_６＝４．３７２２×１０^−４
Ａ_８＝−１．４７７４×１０^−４
Ａ_１０＝９．６６９４×１０^−７
【０３８７】
非球面２
κ＝−１０．４１４１１
Ａ_４＝１．５９４６３×１０^−２
Ａ_６＝−６．０２９６３×１０^−３
Ａ_８＝１．１１２６８×１０^−３
Ａ_１０＝−９．３１５１×１０^−５
【０３８８】
回折面係数（基準波長６５０ｎｍ）
ｂ_２＝−２．０００×１０^−３
ｂ_４＝−１．４４６２×１０^−３
ｂ_６＝１．１３３１×１０^−４
ｂ_８＝−６．６２１１×１０^−５
ｂ_１０＝６．８２２０×１０^−６
【０３８９】
〈実施例１８〉
【０３９０】
図１３０に、実施例１８の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図を示す。また、図１３１に、実施例１８の回折光学レンズについての波長（λ）＝３９０，４００，４１０ｎｍに対する開口数０．７０までの球面収差図を示す。また、図１３２は光情報記録媒体の透明基板が図１３０より厚い場合の実施例１８の回折光学レンズの光路図を示す。図１３３に、図１３２の場合の回折光学レンズについての波長λ＝６４０，６５０，６６０ｎｍに対する開口数０．７０までの球面収差図をそれぞれ示す。
【０３９１】
実施例１８の回折光学レンズによると、図１３１に示すように、波長λ＝４００ｎｍに対してはＮＡ０．７０までの全開口がほぼ無収差である。また、図１３２、図１３３に示すように、透明基板が厚い場合で、波長λ＝６５０ｎｍに対しては、ＮＡ０．７０までがほぼ無収差である。
【０３９２】
以上のように、実施例１７では、実施例１，６，８と比べて、光情報記録媒体の透明基板が厚く波長が６５０ｎｍの場合の球面収差を透明基板がこれよりも薄く波長が４００ｎｍの場合と同じ開口数（ＮＡ０．７０）まで補正できる。
【０３９３】
以下、実施例１８のレンズデータを示す。
【０３９４】
光源波長λ＝４００ｎｍのとき
焦点距離ｆ＝３．３３ 像側開口数 ＮＡ＝０．７０ 無限仕様
【０３９５】
光源波長λ＝６５０ｎｍのとき
焦点距離ｆ＝３．４３ 像側開口数 ＮＡ＝０．７０ 無限仕様
【０３９６】
【表１８】

【０３９７】
非球面係数
非球面１
κ＝０．０
Ａ_４＝−７．９６１６×１０^−４
Ａ_６＝−５．７２６５×１０^−４
Ａ_８＝８．３２０９×１０^−５
Ａ_１０＝−４．１５９９×１０^−５
【０３９８】
非球面２
κ＝０．０
Ａ_４＝３．１１１３１×１０^−２
Ａ_６＝−１．１８５４８×１０^−２
Ａ_８＝１．６３９３７×１０^−３
Ａ_１０＝−６．６０５１４×１０^−５
【０３９９】
回折面係数（基準波長４００ｎｍ）
ｂ_２＝−１．４０４６×１０^−３
ｂ_４＝−８．６９５９×１０^−４
ｂ_６＝２．３４８８×１０^−４
ｂ_８＝−５．２４５５×１０^−５
ｂ_１０＝３．６３８５×１０^−６
【０４００】
次に、上述の実施例１〜３，１４〜１８の各回折光学レンズの複数の輪帯のピッチについて説明する。複数の輪帯は光軸を中心としたほぼ同心円状に形成されており、レンズの像側の最大開口数に対応する輪帯のピッチＰｆ（ｍｍ）、最大開口数の１／２の開口数に対応する輪帯のピッチＰｈ（ｍｍ）、及び（（Ｐｈ／Ｐｆ）−２）の各値を表１９に示す。
【０４０１】
【表１９】

【０４０２】
０．４≦｜（Ｐｈ／Ｐｆ）−２｜≦２５ （ｂ１）
【０４０３】
本発明者らの更なる検討によれば、上述の式（ｂ１）が成立すると、即ち、この式の下限以上であると、高次の球面収差を補正する回折の作用が弱まることがなく、従って、透明基板の厚さが異なることによって生じる２波長間の球面収差の差を回折の作用で補正でき、また、上限以下であると、回折輪帯のピッチが過小となる箇所が生じ難くなり、回折効率の高いレンズを製造することが可能となることが判明した。
【０４０４】
また、上記関係式は、次の式（ｂ２）が好ましく、式（ｂ３）が更に好ましい。
【０４０５】
０．８≦｜（Ｐｈ／Ｐｆ）−２｜≦６．０ （ｂ２）
【０４０６】
１．２≦｜（Ｐｈ／Ｐｆ）−２｜≦２．０ （ｂ３）
【０４０７】
次に、本発明の第８の実施の形態について説明する。
【０４０８】
波長６５０ｎｍの光源を使ってのＤＶＤの記録再生に必要な対物レンズの光情報記録媒体側の必要開口数ＮＡ１は０．６程度であり、波長７８０ｎｍの光源を使ってのＣＤの再生に必要な対物レンズの光情報記録媒体側の必要開口数ＮＡ２は０．４５程度（記録のときは０．５程度）である。したがって、上述の収差補正のための回折パターンは、開口数ＮＡ１までは必須ではない。
【０４０９】
さらに、光軸近傍は焦点深度が深く、球面収差量も少ないので、回折パターンは必須ではない。
【０４１０】
必要最低限の部分に回折パターンを形成し、残りの部分を屈折面とすることで、金型加工時のツールの損傷、成形時の離型性の向上、ＣＤ側で必要以上に集光スポットが絞られることに起因するディスクの厚みに誤差があるときや、ディスクが傾いたときの性能劣化を防ぐことができる。
【０４１１】
このためには、対物レンズの回折パターンは光軸に対して回転対称であり、前記第１の光源からの光束の前記対物レンズの回折パターンの最も光軸から離れた円周からの＋１次回折光は、光情報記録媒体の開口数がＮＡＨ１の光束に変換され、前記第１の光源からの光束の前記対物レンズの回折パターンの最も光軸側の円周からの＋１次回折光は、光情報記録媒体側の開口数がＮＡＬ１の光束に変換されるとき、下記の条件を満足すれば良い。
ＮＡＨ１ ＜ ＮＡ１
０ ≦ ＮＡＬ１ ≦ ＮＡ２
【０４１２】
第１の光情報記録媒体がＤＶＤで、第１の光源の波長λ１が６５０ｎｍ、第２の光情報記録媒体がＣＤで第２の光源の波長λ２か７８０ｎｍの場合、
ＮＡＨ１は０．４３から０．５５
ＮＡＬ１は０．１０から０．４０
であることが好ましい。
【０４１３】
回折パターンを有する部分についての対物レンズの光学設計は、第１の光源から対物レンズに入射する光束の＋１次回折光がほぼ無収差の集光スポットとなるように行われる。一方、回折パターンのない部分についての対物レンズの光学設計は、第１の光源から対物レンズに入射する光束がほぼ無収差の集光スポットとなるように行われる。
【０４１４】
両者の集光位置は、ほぼ一致する必要がある。さらに、それぞれの光束の位相も揃っていることが重要である。なお、位相に関しては、ｋを小さな整数としたとき、２ｋπずれていても、設計波長での集光特性は殆ど変わらないが、｜ｋ｜の絶対値が大きくなると、波長変動に弱くなってしまう。｜ｋ｜は１〜１０であることが好ましい。
【０４１５】
このとき、第２の光源からの光束のうち、対物レンズの回折パターンの最も光軸から離れた円周からの＋１次回折光は光情報記録媒体側の開口数がＮＡＨ２の光束に変換され、同時に回折パターンの最も光軸側の円周からの＋１次回折光は、光情報記録媒体側の開口数がＮＡＬ２の光束に変換され、
【０４１６】
第２光情報記録媒体の記録再生が可能となるようなスポットを、第２の光源からの光束のうち、対物レンズを通ったときの開口数がＮＡＨ２以下の光束を利用して光情報記録媒体の情報記録面上に形成するように、回折パターンを有する部分からの光束と、回折パターンのない部分からの光束との集光位置と位相差が最適となるように、対物レンズを通った光束の球面収差の設定がなされている。
【０４１７】
実際には、前記第１の光源からの光束のうち、対物レンズを通ったときの開口数がＮＡ１以下の光束が第１光情報記録媒体の透明基板を介した最良像点における波面収差が０．０７λｒｍｓ以下であり、かつ、前記第２の光源からの光束のうち、対物レンズを通ったときの開口数がＮＡＨ２以下の光束が第２光情報記録媒体の透明基板を介した最良像点における波面収差が０．０７λｒｍｓ以下であることが望ましい。
【０４１８】
なお、特に、第１の光源からの光束のうち、対物レンズを通ったときの開口数がＮＡ１以下の光束が、第１光情報記録媒体の透明基板を介した最良像点における波面収差の球面収差成分は０．０５λｒｍｓ以下であることが望ましい。
【０４１９】
第１の光源と対物レンズの間および第２の光源と対物レンズの間に少なくとも一つのコリメータを含み、第１の光源から対物レンズに入射する光束および第２の光源から対物レンズに入射する光束が、それぞれ平行光であるような光ピックアップ装置とすることで、ピックアップの調整が容易となる。
【０４２０】
また、第１の光源からの光束と第２の光源からの光束に対してコリメータを共通にすることで、光ピックアップ装置のコストダウンを図ることができる。
【０４２１】
なお、第１の光源と第２の光源が別のパッケージである場合、コリメータに対してそれぞれの光源の位置を対物レンズに入射する光束がそれぞれ平行光となるように設定すれば良い。
【０４２２】
また、第１の光源と第２の光源とが同じパッケージである場合、それぞれの光源の位置の光軸方向の差を適切に設定して、対物レンズへの入射光がそれぞれ平行光となるようにしても良いし、その調整ができない場合、コリメータの色収差が最適化されたものを用いて対物レンズへの入射光がそれぞれ平行光になるようにしても良い。
【０４２３】
さらに、対物レンズに入射する光束が、収束光束であっても発散光束であっても良く、特に第１の光源から対物レンズに入射する光束よりも第２の光源から対物レンズに入射する光束をより発散度の強いものとすることによって、発散度の差によるアンダーの球面収差が発生し、回折パターンで補正する球面収差量を減らすことができる。
【０４２４】
図１１４は、開口数ＮＡＨ２、ＮＡＬ２が同じであり、近軸色収差を補正しない場合とした場合（ΔｆＢ＝０）に、第２光源からの光束について、第２光情報記録媒体（ＣＤ）の透明基板を通過した光束の球面収差を表す模式図である。
【０４２５】
ＮＡＨ２以下の第２光情報記録媒体の再生に寄与する光束の収束位置は、回折パターンによって補正されていない場合、Ｂ点にあるが、回折パターンによって補正され、ΔｆＢをほぼ０にされてＡ点に収束する。しかし、ＮＡＨ２より外側では回折パターンによって補正されず、その収差は屈折面のみによる収差曲線Ｓを示すことになる。
【０４２６】
図から明らかなように、光束の収束点とＮＡＨ２における球面収差の跳びは、近軸色収差の補正量ΔｆＢだけ大きくなり、ＮＡＨ２からＮＡ１までのフレア成分が収束する位置は、ＮＡＨ２以下の第２光情報記録媒体の再生に寄与する光束の収束位置と大きく離れるため、光検出器上においてフレア成分の影響が小さくなる。
【０４２７】
また、λ１とλ２で近軸色収差を補正することで、λ１近傍とλ２近傍においても、近軸色収差は小さくなり、光情報記録媒体への情報記録時に、レーザのパワー変動で発振波長が変化しても、焦点ずれが起きにくくなり、高速記録が可能となる。
【０４２８】
前述のようにＮＡＨ２からＮＡ１までのフレア成分の収束位置とＮＡＨ２以下の光束の収束位置とを離れたものとするためには、前記の回折パターンの外側に、第２の回折パターンを配設し、第１光源からの光束に対しては第２の回折パターンの＋１次回折光が前記の収束位置に集光され、第２光源からの光束は第２の回折パターンでは回折されずに透過するように第２の回折パターンを設計することによって、図１１５に示す収差補正状況にすることができる。
【０４２９】
すなわち、同図（ａ）は第１光源からの光束の収差補正状況を示し、ＮＡＨ１以上においても以下においても、比較的大きく設定された屈折面による収差は、＋１次回折光の補正効果により、無収差で収束位置に集光されている。しかし、同図（ｂ）のように、第２光源からの光束は、ＮＡＨ２より外側の回折パターン部分を通過する光束では、回折作用を受けない０次光となるので、その収差補正状況は回折パターンによる補正を受けない収差がそのまま表れるため、ＮＡＨ２における球面収差の跳びが大きくなり、フレア成分の収束位置と情報の再生に寄与する光束の収束位置が大きく離れるため、光検出器上においてフレア成分の影響が小さくなる。
【０４３０】
また、この第２の回折パターンでは、第１の光源からの光束は回折されず、第２の光源からの光束は、主に−１次回折光となるように第２の回折パターンを設計しても良い。これにより、図１１３で見るように、ＮＡＨ２からＮＡ１までの光束の、回折による球面収差をよりオーバーにすることによって、第２の光源について、対物レンズを通ったときの開口数がＮＡＨ２以下の光束の第２光情報記録媒体の透明基板を通ったときの球面収差は良好に補正され、一方、ＮＡＨ２より外側の光束のオーバーの球面収差を大きくすることが出来る。その結果、図１１６（ｂ）に見るように、ＮＡＨ２における球面収差の跳びが大きくなり、フレア成分の収束位置と情報の再生に寄与する光束の収束位置が大きく離れるため、光検出器上においてフレア成分の影響が小さくなる。
【０４３１】
同様に、光源から対物レンズまでの光路中に第１光源からの光束は透過し、第２光源の光束のうち、前記第１の回折パターンの光軸とは反対側の領域を通過する光束を透過させない開口制限手段を設け、光検出器上へ到達するフレア成分を減ずることで、その影響を小さくすることができる。
【０４３２】
この開口制限手段は、第１の光源からの出射光束と、第２光源からの出射光束とを光合波手段により合波した後の光路中に、第１光源からの光束は透過し、第２光源の光束のうち、前記第１の回折パターンの光軸とは反対側の領域を通過する光束を反射または吸収する輪帯フィルターを配設すれば良い。
【０４３３】
このようなフィルターには、例えば多層膜を利用したダイクロイックフィルターを利用することができる。勿論、対物レンズのいずれかの面に、上述のフィルター効果を持たせることもできる。
【０４３４】
また、この開口制限手段は、第１光源からの光束は透過し、第２光源の光束のうち、前記回折パターンの光軸とは反対側の領域を通過する光束を回折させる輪帯フィルターであっても良い。
【０４３５】
以下、図面を参照して本発明の第８の実施の形態にかかるる第１〜第７の光ピックアップ装置を具体的に説明する。
【０４３６】
図１０２に示す第１の光ピックアップ装置は、第１の光ディスクの再生用の第１光源である半導体レーザ１１１と、第２の光ディスク再生用の半導体レーザ１１２とを有している。
【０４３７】
まず第１の光ディスクを再生する場合、第１半導体レーザ１１１からビームを出射し、出射された光束は、両半導体レーザ１１１、１１２からの出射光の合成手段であるビームスプリッタ１９０を透過し、偏光ビームスプリッタ１２０、コリメータ１３０、１／４波長版１４を透過して円偏光の平行光束となる。この光束は絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４３８】
そして情報記録面２２０で情報ビットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０、１／４波長板１４０、コリメータ１３０を透過して、偏光ビームスプリッタ１２０に入射し、ここで反射してシリンドリカルレンズ１８により非点収差が与えられ、光検出器３００上へ入射し、その出力信号を用いて、第１の光ディスク２００に記録された情報の読み取り信号が得られる。
【０４３９】
また、光検出器３００上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第１の半導体レーザ１１１からの光束を第１の光ディスク２００の記録面２２０上に結像するように対物レンズ１６０を移動させると共に、半導体レーザ１１１からの光束を所定のトラックに結像するように対物レンズ１６０を移動させる。
【０４４０】
第２の光ディスクを再生する場合、第２半導体レーザ１１２からビームを出射し、出射された光束は、光合成手段であるビームスプリッタ１９０で反射され、上記第１半導体１１１からの光束と同様、偏光ビームスプリッタ１２０、コリメータ１３０、１／４波長板１４０、絞り１７０、対物レンズ１６０を介して第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４４１】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０、１／４波長板１４０、コリメータ１３０、偏光ビームスプリッタ１２０、シリンドリカルレンズ１８０を介して、光検出器３００上へ入射し、その出力信号を用いて、第２の光ディスク２００に記録された情報の読み取り信号が得られる。
【０４４２】
また、第１の光ディスクの場合と同様、光検出器３００上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４４３】
図１０３の第２の光ピックアップ装置は、記録再生用の光学系に適した構成であるが、再生の場合について説明する。なお、以下の実施例において、図１０２の光ピックアップ装置と同一部材は同一符号で示す。
【０４４４】
第１の光ディスクを再生する場合、第１半導体レーザ１１１からビームを出射し、出射された光束は、偏光ビームスプリッタ１２１で反射され、コリメータ１３１、１／４波長板１４１を透過して円偏光の平行光となる。さらに、光合成手段であるビームスプリッタ１９０を透過し、絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４４５】
そして情報記録面２２０で情報ビットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、さらにビームスプリッタ１９０、１／４波長板１４１、コリメータ１３１を透過して、偏光ビームスプリッタ１２１に入射し、ここを透過して非点収差が与えられ、光検出器３０１上へ入射し、その出力信号を用いて、第１の光ディスク２００に情報記録された情報の読み取り信号が得られる。
【０４４６】
また、光検出器３０１上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第１の半導体レーザ１１１からの光束を第２の光ディスク２００の記録面２２０上に結像するように対物レンズ１６０を移動させると共に、半導体レーザ１１１からの光束を所定のトラックに結像するように対物レンズ１６０を移動させる。
【０４４７】
第２の光ディスクを再生する場合、第２半導体レーザ１１２からビームを出射し、出射された光束は、偏光ビームスプリッタ１２２で反射され、コリメータ１３２、１／４波長板１４２を透過して円偏光の平行光となる。さらに、光合成手段であるビームスプリッタ１９０で反射され、絞り１７０、対物レンズ１６０により第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４４８】
そして情報記録面２２０で情報ビットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介してビームスプリッタ１９０で反射され、１／４波長板１４２、コリメータ１３２を透過して、偏光ビームスプリッタ１２２に入射し、ここを透過して非点収差が与えられ、光検出器３０２上へ入射し、その出力信号を用いて、第２の光ディスク２００に情報記録された情報の読み取り信号が得られる。
【０４４９】
また、光検出器３０２上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第２の半導体レーザ１１２からの光束を第１の光ディスク２００の記録面２２０上に結像するように対物レンズ１６０を移動させると共に、半導体レーザ１１２からの光束を所定のトラックに結像するように対物レンズ１６０を移動させることは同様である。
【０４５０】
図１０４の第３の光ピックアップ装置は、記録再生用の光学系に適した構成であるが、再生の場合について説明する。
【０４５１】
第１の光ディスクを再生する場合、第１半導体レーザ１１１からビームを出射し、発散光束の発散度を小さくするカップリングリングレンズ６０、光合成手段であるビームスプリッタ１９０、ビームスプリッタ１２０を透過し、さらにコリメータ１３０、１／４波長板１４０を透過して円偏光の平行光となる。さらに、絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４５２】
そして情報記録面２２０で情報ビットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、１／４波長板１４０、コリメータ１３０を透過して、ビームスプリッタ１２０に入射し、ここで反射され、シリンドリカルレンズ１８０で非点収差が与えられ、凹レンズ５０を介して光検出器３０１上へ入射し、その出力信号を用いて、第１の光ディスク２００に情報記録された情報の読み取り信号が得られる。
【０４５３】
また、光検出器３０１上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第１の半導体レーザ１１１からの光束を第１光ディスク２００の記録面２２０上に結像するように対物レンズ１６０を移動させると共に、半導体レーザ１１１からの光束を所定のトラックに結像するように対物レンズ１６０を移動させる。
【０４５４】
第２の光ディスクを再生するための第２半導体レーザ１１２は、レーザ／検出器集積ユニット４００に光検出器３０２およびホログラム２３０とユニット化されている。「ユニット」あるいは「ユニット化」とは、ユニット化されている部材や手段が一体となって光ピックアップ装置に組込ができるようになっていることを意味し、装置の組立て時には１部品として組付けることができる上タイトされている。
【０４５５】
第２半導体レーザ１１２から出射された光束は、ホログラム２３０を透過し、光合成手段であるビームスプリッタ１９０で反射され、ビームスプリッタ１２０、コリメータ１３０、１／４波長板１４０を透過し平行光束となる。さらに絞り１７０、対物レンズ１６０を介して第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４５６】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介し、１／４波長板１４０、コリメータ１３０、ビームスプリッタ１２０を透過し、ビームスプリッタ１９０で反射され、ホログラム２３０で回折されて光検出器３０２上へ入射し、その出力信号を用いて、第２光ディスク２００に記録された情報の読み取り信号が得られる。
【０４５７】
また、光検出器３０２上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４５８】
図１０５の第４の光ピックアップ装置においては、第１の光ディスクを再生する場合、第１半導体レーザ１１１は、レーザ／検出器集積ユニット４１０に光検出器３０１およびホログラム２３１とユニット化され、第１半導体レーザ１１１から出射された光束は、ホログラム２３１を透過し、光合成手段であるビームスプリッタ１９０、コリメータ１３０を透過し平行光束となる。さらに絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４５９】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、コリメータ１３０、ビームスプリッタ１９０を透過し、ホログラム２３１で回折されて光検出器３０１上へ入射し、その出力信号を用いて、第１光ディスク２００に記録された情報の読み取り信号が得られる。
【０４６０】
また、光検出器３０２上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４６１】
第２の光ディスクを再生する場合、第２半導体レーザ１１２は、レーザ／検出器集積ユニット４２に光検出器３０２およびホログラム２３２とユニット化され、第２半導体レーザ１１２から出射された光束は、ホログラム２３２を透過し、光合成手段であるビームスプリッタ１９０で反射され、コリメータ１３０を透過して平行光束となる。さらに絞り１７０、対物レンズ１６０を介して第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４６２】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、コリメータ１３０を透過し、ビームスプリッタ１９０で反射され、ホログラム２３２で回折されて光検出器３０２上へ入射し、その出力信号を用いて、第２光ディスク２００に記録された情報の読み取り信号が得られる。
【０４６３】
また、光検出器３０２上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、この検出に基づいて２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４６４】
図１０６の第５の光ピックアップ装置においては、第１半導体レーザ１１１、第２半導体レーザ１１２、光検出手段３０、ホログラム２３０がレーザ／検出器集積ユニット４３０としてユニット化されている。
【０４６５】
第１の光ディスクを再生する場合、第１半導体レーザ１１１から出射された光束は、ホログラム２３０、コリメータ１３０を透過し平行光束となる。さらに絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４６６】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、コリメータ１３０を透過し、ホログラム２３０で回折されて光検出器３００上へ入射し、その出力信号を用いて、第１光ディスク２００に記録された情報の読み取り信号が得られる。
【０４６７】
また、光検出器３００上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４６８】
第２の光ディスクを再生する場合、第２半導体レーザ１１２から出射された光束は、ホログラム２３０、コリメータ１３０を透過してほぼ平行光束となる。さらに絞り１７０、対物レンズ１６０を介して第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４６９】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、コリメータ１３０を透過し、ホログラム２３０で回折されて光検出器３００上へ入射し、その出力信号を用いて、第２の光ディスク２００に記録された情報の読み取り信号が得られる。
【０４７０】
また、光検出器３００上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、この検出に基づいて２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４７１】
図１０７の第６の光ピックアップ装置においては、第１半導体レーザ１１１、第２半導体レーザ１１２、第１の光検出手段３０１、第２の光検出手段３０２、ホログラム２３０がレーザ／検出器集積ユニット４３０としてユニット化されている。
【０４７２】
第１の光ディスクを再生する場合、第１半導体レーザ１１１から出射された光束は、ホログラム２３０のディスク側の面、コリメータ１３０を透過し平行光束となる。さらに絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４７３】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、コリメータ１３０を透過し、ホログラム２３０のディスク側の面で回折され、第１の光源に対応した光検出器３０１上へ入射し、その出力信号を用いて、第１の光ディスク２００に記録された情報の読み取り信号が得られる。
【０４７４】
また、光検出器３０１上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４７５】
第２の光ディスクを再生する場合、第２半導体レーザ１１２から出射された光束は、ホログラム２３０の半導体レーザ側の面で回折され、、コリメータ１３０を透過してほぼ平行光束となる。このホログラムの半導体レーザ側の面は、光合成手段としての機能を果たす。さらに絞り１７０、対物レンズ１６０を介して第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４７６】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、コリメータ１３０を透過し、ホログラム２３０のディスク側の面で回折されて第２の光源対応した光検出器３０２上へ入射し、その出力信号を用いて、第２の光ディスク２００に記録された情報の読み取り信号が得られる。
【０４７７】
また、光検出器３０２上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、この検出に基づいて２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４７８】
図１０８の第７の光ピックアップ装置は、記録再生用の光学系に適した構成であるが、再生の場合について説明する。
【０４７９】
第１の光ディスクを再生する場合、第１半導体レーザ１１１からビームを出射し、発散光束の発散度を小さくするカップリングリングレンズ６０、光合成手段であるビームスプリッタ１９０、ビームスプリッタ１２０を透過し、さらにコリメータ１３０、１／４波長板１４０を透過して円偏光の平行光となる。さらに、絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４８０】
そして情報記録面２２０で情報ビットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介して、１／４波長板１４０、コリメータ１３０を透過して、ビームスプリッタ１２０に入射し、ここで反射され、シリンドリカルレンズ１８０で非点収差が与えられ、凹レンズ５０を介して光検出器３０１上へ入射し、その出力信号を用いて、第１の光ディスク２００に情報記録された情報の読み取り信号が得られる。
【０４８１】
また、光検出器３０１上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第１の半導体レーザ１１１からの光束を第１光ディスク２００の記録面２２０上に結像するように対物レンズ１６０を移動させると共に、半導体レーザ１１１からの光束を所定のトラックに結像するように対物レンズ１６０を移動させる。
【０４８２】
第２の光ディスクを再生するための第２半導体レーザ１１２は、レーザ／検出器集積ユニット４００に光検出器３０２およびホログラム２３０とユニット化されている。
【０４８３】
第２半導体レーザ１１２から出射された光束は、ホログラム２３０を透過し、光合成手段であるビームスプリッタ１９０で反射され、ビームスプリッタ１２０、コリメータ１３０、１／４波長板１４０を透過し平行光束となる。さらに絞り１７０、対物レンズ１６０を介して第２の光ディスク２００の透明基板２１０を介して情報記録面２２０に集光される。
【０４８４】
そして、情報記録面２２０で情報ピットにより変調されて反射した光束は、再び対物レンズ１６０、絞り１７０を介し、１／４波長板１４０、コリメータ１３０、ビームスプリッタ１２０を透過し、ビームスプリッタ１９０で反射され、ホログラム２３０で回折されて光検出器３０２上へ入射し、その出力信号を用いて、第２光ディスク２００に記録された情報の読み取り信号が得られる。
【０４８５】
また、光検出器３０２上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行い、２次元アクチュエータ１５０により、合焦、トラッキングのために対物レンズ１６０を移動させる。
【０４８６】
透明基板の厚さｔ１が第１の光ディスクとほぼ同じで、波長λ１の第１の光源で記録再生するために必要な前記対物レンズの光情報記録媒体側の必要開口数ＮＡも第１の光ディスクと同程度の第３のＳｕｐｅｒ ＲＥＮＳ方式のディスクを記録再生する場合について説明する。
【０４８７】
Ｓｕｐｅｒ ＲＥＮＳ方式のディスクは、現在精力的に検討が進められているもので、その構成の１例を図１０９に示す。その記録再生は近接場光学に基づき、再生信号としては反射光を利用する方式と透過光を利用する方式があり、本実施例の構成は透過光を利用して再生信号を得る方式を示す。
【０４８８】
Ｓｕｐｅｒ ＲＥＮＳ方式の第３のディスクを記録再生する場合には、第１半導体レーザ１１１からビームを出射し、発散光束の発散度を小さくするカップリングレンズ６０、光合成手段であるビームスプリッタ１９０、ビームスプリッタ１２０を透過し、さらにコリメータ１３０、１／４波長板１４０を透過し平行光束となる。さらに絞り１７０によって絞られ、対物レンズ１６０により第１の光ディスク２００の透明基板２１０、第１の保護膜２４０を介して非線形光学膜２５０に集光される。非線形光学膜２５０には、微小な開口が形成され、第２の保護膜２６０を介して情報記録層上の情報記録面２２０にエネルギーが伝達される。そして、情報記録面２２０で情報ピットにより変調されて透過した光は、第３の保護膜２７０を透過し、対物レンズとは反対側の集光レンズ９０で集められ、光検出器３０５に到達し、その出力信号により、第３の光ディスク２００に情報記録された情報の読み取り信号が得られる。
【０４８９】
一方、非線形光学膜２５０から反射された光束は、再び対物レンズ１６０、絞り１７０を介して、１／４波長板１４０、コリメータ１３０を透過して、ビームスプリッタ１２０に入射し、ここで反射され、シリンドリカルレンズ１８０で非点収差が与えられ、凹レンズ５０を介して光検出器３０１上へに入射する。光検出器３０１上でのスポットの形状変化、位置変化による光量変化を検出して、合焦検出やトラック検出を行う。この検出に基づいて２次元アクチュエータ１５０が第１の半導体レーザ１１１からの光束を第１の光ディスク２００の非線形光学膜２５０上に結像する用に対物レンズ１６０を移動させると共に、半導体レーザ１１１からの光束を所定のトラックに結像するように対物レンズ１６０を移動させる。
【０４９０】
前述の光ピックアップ装置の対物レンズとして、第１の光源から無収差の平行光束が入射し、ＤＶＤの透明基板を通して無収差のスポットを形成するように設計された専用対物レンズを使って、対物レンズに第２の光源から無収差の平行光が入射し、ＣＤの透明基板を通ってスポットを形成した場合、
▲１▼対物レンズの屈折率の波長依存性
▲２▼光情報記録媒体の透明基板厚みの差
▲３▼透明基板屈折率の波長依存性
により球面収差が発生するが、▲２▼によるものがほとんどであることは既に述べた。
【０４９１】
この▲２▼の要因による球面収差は、ＣＤの記録再生に必要な開口数ＮＡ２において、ほぼ｜ｔ２−ｔ１｜および（ＮＡ２）^４に比例する。図１１０は、対物レンズに波長λ１＝６５０ｎｍの平行光束が入射したときにＤＶＤの透明基板を通して無収差となるように設計された専用レンズについて、透明基板がＣＤの厚さで、波長λ２＝７８０ｎｍの光源を使用したときの、対物レンズから出射する光束の開口数を０．４５としたときの結像倍率Ｍ２と波面収差との関係を示したものである。結像倍率Ｍ２が０の場合は、ＤＶＤと同様、対物レンズに平行光束が入射する。
【０４９２】
図示のように、Ｍ２＝０のときは、約０．１３λｒｍｓの球面収差が発生し、回折限界性能のマレシャルの限界０．０７λｒｍｓより大きい。従って、何らかの手段によりＤＶＤ、ＣＤ双方とも波面収差がマレシャルの限界以下となるように球面収差を設定する必要が生じる。
【０４９３】
この対物レンズにおいて、結像倍率を負にして行くと、対物レンズで負の球面収差が発生し、Ｍ≒−０．０６のとき極小値となり、マレシャル限界内の値になる。このように、結像倍率によって、補正しなければならない球面収差量は異なり、図示の例においては、Ｍ≒−０．０６のときはあえて他の手段によって球面収差を補正する必要はない。また、ＣＤ−Ｒの情報記録に必要なＮＡが０．５のときは、さらに補正する球面収差は大きくなる。
【０４９４】
次に、上述の各光ピックアップ装置において、好ましいコリメート調整手段について説明する。説明を簡単にするために、コリメータと対物レンズからなる集光光学系を使用した光ピックアップ装置について考察する。コリメータと光源の距離は、コリメータの光軸上の焦点位置に光源を配置することで所望の平行光がコリメータより出射する。コリメータのバックフォーカス、半導体レーザの取り付け位置と発光点との間隔、コリメータや半導体レーザをマウントする光ピックアップ装置のハウジングの製造バラツキが小さく押さえられているため、半導体レーザとコリメータの間隔を調整しなくても、実用上間題ない精度の平行光が得られる。
【０４９５】
ところで、波長の異なる２つの光源により、透明基板の厚さが異なる２種類の光情報記録媒体の記録及び／または再生する場合において、回折パターンを有する対物レンズを用い、さらにそれぞれの光源に対して０でない同じ次数の回折光を利用する場合において、レーザの発振波長の変動により球面収差の変動が既存の両面非球面対物レンズと比較して大きい。特に、実施例６のような対物レンズでは、６５０ｎｍの波長においては波面収差が０．００１λｍｓであるが波長が±１０ｎｍ変化すると０．０３５λｒｍｓ程度に劣化する。このとき発生するのは球面収差である。半導体レーザには発振波長の個体差があり、光ピックアップ装置に個体差の大きい半導体レーザを適用すると、回折パターンを有する対物レンズの球面収差の規格が厳しくなるといった問題が生じる。
【０４９６】
光ピックアップ装置に用いられる対物レンズでは、入射光束が平行光から発散光になると負の３次球面収差が増加し、平行光束から収束光になると正の３次球面収差が増加するのであるが、対物レンズヘの入射光束の発散度を変えることで、３次の球面収差をコントロールすることができる。実施例６のような対物レンズにおいては、半導体レーザの発振波長の個体差で発生する球面収差の主成分は３次の球面収差であることから、対物レンズヘの入射光束の発散度を変えることにより、集光光学系全体の３次の球面収差を設計値通りにすることができる。
【０４９７】
なお、集光光学系にコリメータ等のカップリングレンズがあれば、これを光軸方向に動かすことで、対物レンズの３次の球面収差をコントロールすることができる。また、コリメータ等のカップリングレンズがある場合は、半導体レーザを光軸方向に動かすことで同様に目的が達成される。もちろん、コリメータ等のカップリングレンズがある場合も、半導体レーザを光軸方向に動かしてもよい。
【０４９８】
〈実施例１９〉
【０４９９】
以下、第８の実施の形態に係わる対物レンズの具体例として、球面収差補正レンズの実施例１９を図１１１及び表２０，表２１に示す。
【０５００】
表２０中、ｒｉは屈折面の曲率半径、ｄｉ、ｄｉ’は面間隔、ｎｉ、ｎｉ’は主波長での屈折率を示す。また、面形状式を次の〔数４〕に示す。
【０５０１】
【数４】

【０５０２】
但し、Ｘは光軸方向の軸、ｈは光軸と垂直方向の軸、光の進行方向を正とし、ｒは近軸曲率半径、κは円錐形数、Ａｊは非球面係数、Ｐｊ（Ｐｉ≧３）は非球面べき数である。
【０５０３】
また、回折面は光路差関数として数１に示す通りである。単位はｍｍとして表している。
【０５０４】
【表２０】

【０５０５】
ｄｉ，ｎｉは、第１光情報記録媒体（ｔ１＝０．６ｍｍ）のときの値
ｄｉ’，ｎｉ’は、第２光情報記録媒体（ｔ２＝１．２ｍｍ）のときの値
【０５０６】
【表２１】

【０５０７】
上記実施例のレンズ断面図を図１１１に、その球面収差を図１１２に示す。図１１１において、第２面Ｓ２の光軸を含む部分Ｓ２ｄは回折パターンを有し、その外側の部分Ｓ２ｒは非球面屈折面である。図１１２（ａ）は波長６３５ｎｍ、第１光情報記録媒体（ｔ１＝０．６ｍｍ）での球面収差図で十分に収差補正されている。同図（ｂ）は波長７８０ｎｍ、第２光情報記録媒体（ｔ２＝１．２ｍｍ）での球面収差図であり、第１分割面Ｓ２ｄを通る光束は回折の効果により球面収差が補正されており、第２分割面Ｓ２ｒを通る光束はフレア光となり絞りと同様の効果になっている。
【０５０８】
上記実施例のレンズは、ＮＡＨ２＝０．５とし、ＮＡＬ２＝０の対物レンズである。このレンズの回折パターン部分は、光軸を中心とした輪帯上のパターンとなり、そのステップ数は１３程度となる。また、回折パターン部の最も光軸から離れた円周部分と屈折面との境界は、約２１μｍの段差を持っている。
【０５０９】
ＮＡＨ２＝０．４５とした場合においては、回折パターンのステップ数は９程度で、上記段差量は１３μｍ程度である。段差量、回折パターンのステップ数は、ほぼＮＡＨ２の４乗に比例する。
【０５１０】
この例のようにＮＡＬ２＝０の場合には、補正する球面収差に比例して回折パターンのステップ数が増加してしまう。
【０５１１】
本発明の対物レンズにおいては、回折パターンの光軸方向の深さは２μｍ以下でも良好な効果を得ることができるが、やはり回折パターンのステップ数が多いと、金型加工、成形が難しくなるので、できるだけステップ数が少ないことが望ましい。
【０５１２】
これは、▲１▼ＣＤの結像倍率をＤＶＤの結像倍率よりやや小さくし、補正すべき球面収差量をあらかじめ小さくする。好ましくは、mCD(CDの記録・再生時の倍率)-mDVD(DVDの記録・再生時の倍率)が、-1/15〜0であることが好ましい、▲２▼深度の深い開口数の小さい部分には回折パターンを設けない、等によって達成できる。
【０５１３】
例えば、ＤＶＤの結像倍率を０、ＣＤの結像倍率を−０．０３とすれば補正すべき球面収差は半分になるので、ＣＤ−Ｒ対応のため、ＮＡＨ２を０．５としても、ステップ数は７程度で、段差量も１１μｍ程度となる。
【０５１４】
段差量が小さい場合、段差Ｓ２ｓの形状は回折パターン部Ｓ２ｄから屈折面部Ｓ２ｒへ滑らかに移行するものであっても良い。
【０５１５】
また、ＤＶＤの結像倍率、ＣＤの結像倍率とも０の場合においては、例えばＮＡＬ２＝０．３６とすれば、開口数がＮＡＬ２以下の光束の波面収差の残留球面収差成分ＷＳＡ（ＮＡＬ２）は約０．０５３λｒｍｓである。これに最適な回折パターンを付けることで、ＤＶＤの波面収差をほぼ０にに保ちながらＮＡＨ２までの波面収差のＲＭＳ値を小さくすることができる。
【０５１６】
開口数がＮＡＨ２以下の光束の波面収差の残留球面収差成分ＷＳＡ（ＮＡＨ２）は、以下の式で近似できる。
【０５１７】
ＷＳＡ（ＮＡＨ２）＝（ＮＡＬ２／ＮＡＨ２）2×ＷＳＡ（ＮＡＬ２）
よって、ＮＡＨ２＝０．４５のとき、上記値は０．０３４λｒｍｓ、ＮＡＨ２＝０．５のとき０．０２７λｒｍｓとなり、マレシャルの限界値より十分小さい。
【０５１８】
このとき、ＮＡＬ２以下ではオーバーの球面収差が発生しているため、ＮＡＬ２からＮＡＨ２までの球面収差を０とするのではなく、ＮＡＬ２以下の光束のベストフォーカスにほぼ一致するようにすれば良い。このベストフォーカス位置は近軸焦点よりオーバーな位置であるため、回折パターンで補正する球面収差量は小さくてすむ。また、ＮＡＬ２以下の光束に対しては、回折パターンは不要である。この二つの効果で、ＮＡＨ２＝０．５のとき、回折パターンのステップ数は約６、ＮＡＨ２＝０．４５のときは回折パターンのステップ数は４ですむ。
【０５１９】
勿論、ＣＤの結像倍率をＤＶＤの結像倍率より小さくすることで、回折パターンをさらに少なくでき、最低２ステップあれば、ＤＶＤとＣＤの互換再生が可能となる。
【０５２０】
ところで、透明基板厚が０．１ｍｍの高密度光情報記録媒体が提案されている。この記録再生には青色半導体レーザを使用し、２枚玉の対物レンズを用い、ＮＡ１として０．８５が必要とされている。一方において、ＣＤ−ＲＷは透明基板厚が１．２ｍｍで波長７８０なのの光源を用い、ＮＡ２は０．５５とされている。この互換光学系では、ＤＶＤ、ＣＤ−Ｒ（ＮＡＨ２＝０．５）の場合と比較して、ＮＡ２が大きく、ｔ１−ｔ２も大きいため、球面収差の補正量も２．７倍大きい。そのため、回折パターンのステップ数も３５程度になる。
【０５２１】
さらに、近軸の色収差を補正するには、回折パターンのステップ数が増加する。またＮＡ１まで近軸色収差を含めて補正するとなると、数百のステップ数になる。このような場合、回折パターンを複数の光学面に施すことも可能である。
【０５２２】
また、必要に応じて、ＮＡＬ２からＮＡＨ２までのある部分を屈折面としても良い。
【０５２３】
さらに、ｔ１＞ｔ２である場合には、発生する球面収差の符号が逆になるので、−１次光を利用することになる。
【０５２４】
同様に、ＤＶＤとＣＤの場合も、対物レンズのＣＤの結像倍率がＤＶＤの結像倍率よりかなり小さくなり、アンダーの球面収差が残る場合も、同様に−１次光を利用することになる。
【０５２５】
なお、現在重要関心事であるＤＶＤとＣＤについて、記録または波長の異なる２つのレーザを使って単一の対物レンズで実施する例について示した。既に説明したとおり、第１の光源の波長をλ１とし、第２の光源の波長をλ２（λ２＞λ１）とした場合、ｔ１＜ｔ２である場合は＋１次回折光を利用し、ｔ１＞ｔ２である場合は−１次回折光を利用した第１の回折パターンを導入するのであるが、ＤＶＤ（第１の光源を利用）とＣＤ（第２の光源を利用）の場合は前者である。
【０５２６】
ところで、青色半導体レーザ、ＳＨＧレーザ等、近年様々な波長の光源が実用化され、今後とも多くの新しい光情報記録媒体が登場すると思われる。この場合、光情報記録媒体の記録密度から必要となるスポットサイズが決まるが、記録または記録再生に必要なＮＡは、使用する光源の波長によって変化する。このため、光情報記録媒体の透明基板の厚さ、必要ＮＡが２つの光情報記録媒体にたいして、以下の４つに分類される。
（１） ｔ１＜ｔ２， ＮＡ１＞ＮＡ２
（２） ｔ１＜ｔ２， ＮＡ１＜ＮＡ２
（３） ｔ１＞ｔ２， ＮＡ１＞ＮＡ２
（４） ｔ１＞ｔ２， ＮＡ１＜ＮＡ２
【０５２７】
以上の説明においては、特に（１）のケースについて使用する第１の回折パターンのそれぞれの光源に対する回折次数、第１の回折パターンの範囲（ＮＡＨ１，ＮＡＬ１，ＮＡＨ２，ＮＡＬ２）、回折パターン部と透過部が同一位置に集光する必要のある光源の種類とＮＡ範囲、各光源に対しての球面収差を設定するＮＡの範囲、各光源に対して波面収差が０．０７λｒｍｓ以下である必要性があるＮＡの範囲、第２の回折パターンのそれぞれの光源に対する回折次数と第１の回折パターンと同一位置に集光させる必要性、開口制限を導入する場合の、どちらの光源からの光束を制限するかの条件等について詳述したが、（２）（３）（４）の場合については、（１）の詳述から容易に遂行しえるので、詳細な説明は省略した。
【０５２８】
また、レンズの製作時には、回折パターンを刻んだ金型により、プラスチック材料やガラス材料を一体成形することも可能であり、ガラスないしプラスチックの母材に紫外線硬化樹脂等により、本発明の回折パターンを含む光学面を形成しても良い。さらに、コーティングや、直接加工により製作しても良い。
【０５２９】
上述のように、本発明の効果を持つ光学面は、対物レンズとは別の光学素子に設け、該光学素子を対物レンズの光源側ないしは光情報記録媒体側に配設しても良い。勿論、コリメータや光合成手段の第一の光源からの光束と第２の光源からの光束とが共に通過する光学面に配設しても良い。しかし、トラッキング等で対物レンズが動く際に、回折パターンの光軸と対物レンズの光軸とが相対的に移動するため、トラッキングの量が制限される。
【０５３０】
また、説明の都合上、回折パターンは光学軸に対して同心円状としたが、これに制限されるものではない。
【０５３１】
以上の実施例１〜１９に具体的に示した対物レンズは、いずれも単レンズからなる例を挙げたが、対物レンズが複数のレンズから構成されたものでもよく、その少なくとも１つの面に本発明の回折面を有する場合も本発明に含まれるものである。
【０５３２】
本発明において、互いに異なる２つの波長のそれぞれの光に対して、その特定次数の回折光の回折効率が他の次数のそれぞれの回折光の回折効率よりも１０％以上高い効率であることが好ましく、３０％以上高い効率であることが更に好ましく、また、その特定次数の回折光の回折効率が５０％以上であることが好ましく、更に好ましくは７０％以上であることが、光量損失が少なく、実用上も好ましい。
【０５３３】
また、本発明の回折面は、以上の実施の形態およびレンズの具体的な実施例にも示されたように、その回折面があることによって、互いに異なる少なくとも２つの波長の選択的に発生された特定次数の回折光がそれぞれ焦点を結ぶに際して、その回折面が無い場合すなわちその回折面のレリーフを包絡した面をシュミレーション等により想定した場合に比較して球面収差が改善されることが望ましい。
【０５３４】
また、更に、本発明において、互いに異なる少なくとも２つの波長のそれぞれの光（波長λ）に対して、それぞれ選択的に発生する特定次数の回折光は、その結像面上での波面収差が０．０７λｒｍｓ以下であることが、実用上で有効な所望のスポットを得るうえで好ましい。なお、上述した実施の態様は本発明の技術的思想及び範囲から逸脱しないで当業者により変更が可能である。
【０５３５】
以上のように、本発明によると、回折面を有する少なくとも１つの光学素子を用いた簡単な構成で互いに異なる少なくとも２つの波長の光に対して球面収差および軸上色収差の補正が可能になる光学系、光ピックアップ装置、記録再生装置、レンズ、光学素子、光ディスク用回折光学系、音声および／または画像の記録および／または再生装置、および対物レンズを得ることができる。また、少なくとも光学系の小型軽量化および低コスト化を図ることができる。また、光学素子が互いに異なる少なくとも２つの波長の光に対して同じ次数の回折光の回折効率を最大とする回折面を有する場合には、回折面が異なる次数の回折光の回折効率を最大とする場合と比較して光量の損失を少なくすることができる。
【０５３６】
また、特に、屈折面上に回折レンズを設けることにより、波長の異なる２つの光源を持つ記録再生用光学系に用い、それぞれの光源波長に対して光量の損失が少なく、ほぼ回折限界まで収差の補正された回折光学系を得ることができる。
【０５３７】
また、特に、上記のように、互いに波長の異なる３光源に対して、１つの対物レンズによって、異なる光ディスクに情報を記録および／または情報の再生を可能とするだけでなく、コリメーター等のカップリングレンズを使用していないため、光ピックアップ装置を薄型化することができ、しかもコストが高いといった問題を解消することができる。
【０５３８】
また、特に、異なる波長の３光源を有する光ピックアップ装置において、非球面係数及び位相差関数の係数を適当に設計することで、透明基板厚さの違いにより発生する球面収差及び波長の違いにより発生する球面収差の色収差、さらには軸上色収差を補正した光ピックアップ装置及び対物レンズを提供することができる。
【０５３９】
また、特に、対物レンズに複数の分割面を設けて、第１分割面に回折面を配設することによって、厚さの異なる透明基板を有する光情報記録媒体に対し、単一の集光光学系によって、波長の異なる光束によって記録再生するのできる光情報記録媒体の記録再生用球面収差補正対物レンズ及び光ピックアップ装置を提供できる。
【０５４０】
更に、光ピックアップ装置用対物レンズは、同心円状に分割された複数の輪帯からなり、各輪帯は、波長の異なる複数の光源、及び／または、記録面の厚みの異なる透明基板に対してほぼ回折限界に収差補正され、光検出器に入射するフレア光を減じ、製作の容易なものにできる。
【０５４１】
【発明の効果】
以上のように、本発明によると、回折面を有する少なくとも１つの光学素子を用いた簡単な構成で互いに異なる少なくとも２つの波長の光に対して球面収差および軸上色収差の補正が可能で、温度変化に対して安定したピックアップ装置、記録再生装置、記録再生方法、および対物レンズを得ることができる。また、少なくとも光学系の小型軽量化および低コスト化を図ることができる。また、光学素子が互いに異なる少なくとも２つの波長の光に対して同じ次数の回折光の回折効率を最大とする回折面を有する場合には、回折面が異なる次数の回折光の回折効率を最大とする場合と比較して光量の損失を少なくすることができる。
【図面の簡単な説明】
【図１】本発明の実施例１の回折光学レンズの光路図である。
【図２】本発明の実施例１の回折光学レンズによる波長λ＝６３５ｎｍに対する球面収差図である。
【図３】本発明の実施例１の回折光学レンズによる波長λ＝７８０ｎｍに対するＮＡ０．４５までの球面収差図である。
【図４】本発明の実施例１の回折光学レンズによる波長λ＝７８０ｎｍに対するＮＡ０．６０までの球面収差図である。
【図５】本発明の実施例１の回折光学レンズによる波長λ＝６３５ｎｍに対する波面収差図である。
【図６】本発明の実施例１の回折光学レンズによる波長λ＝７８０ｎｍに対する波面収差図である。
【図７】本発明の実施例２の回折光学レンズによる波長λ＝４０５ｎｍに対する光路図である。
【図８】本発明の実施例２の回折光学レンズによる波長λ＝６３５ｎｍに対する光路図である。
【図９】本発明の実施例２の回折光学レンズによる波長λ＝４０５ｎｍに対する球面収差図である。
【図１０】本発明の実施例２の回折光学レンズによる波長λ＝６３５ｎｍに対する球面収差図である。
【図１１】本発明の実施例２の回折光学レンズによる波長λ＝４０５ｎｍに対する波面収差図である。
【図１２】本発明の実施例２の回折光学レンズによる波長λ＝６３５ｎｍに対する波面収差図である。
【図１３】本発明の実施例３の回折光学レンズによる波長λ＝４０５ｎｍに対する光路図である。
【図１４】本発明の実施例３の回折光学レンズによる波長λ＝６３５ｎｍに対する光路図である。
【図１５】本発明の実施例３の回折光学レンズによる波長λ＝４０５ｎｍに対する球面収差図である。
【図１６】本発明の実施例３の回折光学レンズによる波長λ＝６３５ｎｍに対する球面収差図である。
【図１７】本発明の実施例３の回折光学レンズによる波長λ＝４０５ｎｍに対する波面収差図である。
【図１８】本発明の実施例３の回折光学レンズによる波長λ＝６３５ｎｍに対する波面収差図である。
【図１９】本発明の実施例４の回折光学レンズによる光路図である。
【図２０】本発明の実施例４の回折光学レンズによる波長λ＝６３５ｎｍ、６５０ｎｍ、、７８０ｎｍに対する球面収差図である。
【図２１】本発明の実施例５の回折光学レンズによる光路図である。
【図２２】本発明の実施例５の回折光学レンズによる波長λ＝６３５ｎｍ、６５０ｎｍ、、７８０ｎｍに対する球面収差図である。
【図２３】本発明の実施例６の回折光学レンズによる波長λ＝６５０ｎｍに対する光路図である。
【図２４】本発明の実施例６の回折光学レンズによる波長λ＝７８０ｎｍ（ＮＡ＝０．５）に対する光路図である。
【図２５】本発明の実施例６の回折光学レンズによる波長λ＝６５０±１０ｎｍに対する開口数０．６０までの球面収差図である。
【図２６】本発明の実施例６の回折光学レンズによる波長λ＝７８０±１０ｎｍに対する開口数０．５０までの球面収差図である。
【図２７】本発明の実施例６の回折光学レンズによる波長λ＝７８０ｎｍに対する開口数０．６０までの球面収差図である。
【図２８】本発明の実施例６の回折光学レンズによる波長λ＝６５０ｎｍに対する波面収差ｒｍｓ図である。
【図２９】本発明の実施例６の回折光学レンズによる波長λ＝７８０ｎｍに対する波面収差ｒｍｓ図である。
【図３０】本発明の実施例７の回折光学レンズによる波長λ＝６５０ｎｍに対する光路図である。
【図３１】本発明の実施例７の回折光学レンズによる波長λ＝７８０ｎｍ（ＮＡ＝０．５）に対する光路図である。
【図３２】本発明の実施例７の回折光学レンズによる波長λ＝６５０±１０ｎｍに対する開口数０．６０までの球面収差図である。
【図３３】本発明の実施例７の回折光学レンズによる波長λ＝７８０±１０ｎｍに対する開口数０．５０までの球面収差図である。
【図３４】本発明の実施例７の回折光学レンズによる波長λ＝７８０ｎｍに対する開口数０．６０までの球面収差図である。
【図３５】本発明の実施例７の回折光学レンズによる波長λ＝６５０ｎｍに対する波面収差ｒｍｓ図である。
【図３６】本発明の実施例７の回折光学レンズによる波長λ＝７８０ｎｍに対する波面収差ｒｍｓ図である。
【図３７】本発明の実施例８の回折光学レンズによる波長λ＝６５０ｎｍに対する光路図である。
【図３８】本発明の実施例８の回折光学レンズによる波長λ＝７８０ｎｍ（ＮＡ＝０．５）に対する光路図である。
【図３９】本発明の実施例８の回折光学レンズによる波長λ＝６５０±１０ｎｍに対する開口数０．６０までの球面収差図である。
【図４０】本発明の実施例８の回折光学レンズによる波長λ＝７８０±１０ｎｍに対する開口数０．５０までの球面収差図である。
【図４１】本発明の実施例８の回折光学レンズによる波長λ＝７８０ｎｍに対する開口数０．６０までの球面収差図である。
【図４２】本発明の実施例８の回折光学レンズによる波長λ＝６５０ｎｍに対する波面収差ｒｍｓ図である。
【図４３】本発明の実施例８の回折光学レンズによる波長λ＝７８０ｎｍに対する波面収差ｒｍｓ図である。
【図４４】本発明の実施例６の回折光学レンズについての回折輪帯数と光軸からの高さとの関係を示すグラフである。
【図４５】本発明の実施例７の回折光学レンズについての回折輪帯数と光軸からの高さとの関係を示すグラフである。
【図４６】本発明の実施例８の回折光学レンズについての回折輪帯数と光軸からの高さとの関係を示すグラフである。
【図４７】本発明の実施例にかかる回折光学レンズについて、回折レンズパワーとレンズ形状との関係を模式的に示す図である。
【図４８】本発明の第２の実施の形態にかかる光ピックアップ装置の構成を示す光路図である。
【図４９】本発明の第３の実施の形態にかかる光ピックアップ装置の構成を示す光路図である。
【図５０】本発明の実施例９の対物レンズの波長λ＝６５０ｎｍに対する光路図である。
【図５１】本発明の実施例９の対物レンズの波長λ＝７８０ｎｍに対する光路図である。
【図５２】本発明の実施例９の対物レンズについての波長λ＝６５０ｎｍに対する球面収差図である。
【図５３】本発明の実施例９の対物レンズについての波長λ＝７８０ｎｍに対するＮＡ０．４５までの球面収差図である。
【図５４】本発明の実施例９の対物レンズについての波長λ＝７８０ｎｍに対するＮＡ０．６０までの球面収差図である。
【図５５】本発明の実施例９の対物レンズについての波長λ＝６５０ｎｍに対する波面収差図である。
【図５６】本発明の実施例９の対物レンズについての波長λ＝７８０ｎｍに対する波面収差図である。
【図５７】本発明の実施例１０の対物レンズについての波長λ＝６５０ｎｍに対する光路図である。
【図５８】本発明の実施例１０の対物レンズについての波長λ＝４００ｎｍに対する光路図である。
【図５９】本発明の実施例１０の対物レンズについての波長λ＝７８０ｎｍに対する光路図である。
【図６０】本発明の実施例１０の対物レンズについての波長λ＝６５０ｎｍに対する球面収差図である。
【図６１】本発明の実施例１０の対物レンズについての波長λ＝４００ｎｍに対する球面収差図である。
【図６２】本発明の実施例１０の対物レンズについての波長λ＝７８０ｎｍに対するＮＡ０．４５までの球面収差図である。
【図６３】本発明の実施例１０の対物レンズについての波長λ＝７８０ｎｍに対するＮＡ０．６５までの球面収差図である。
【図６４】本発明の実施例１０の対物レンズについての波長λ＝６５０ｎｍに対する波面収差図である。
【図６５】本発明の実施例１０の対物レンズについての波長λ＝４００ｎｍに対する波面収差図である。
【図６６】本発明の実施例１０の対物レンズについての波長λ＝７８０ｎｍに対する波面収差図である。
【図６７】本発明の第４の実施の形態にかかる光ピックアップ装置の構成を示す図である。
【図６８】本発明の実施例１１の対物レンズについての波長λ＝６５０ｎｍに対する光路図である。
【図６９】本発明の実施例１１の対物レンズについての波長λ＝４００ｎｍに対する光路図である。
【図７０】本発明の実施例１１の対物レンズについての波長λ＝７８０ｎｍに対する光路図である。
【図７１】本発明の実施例１１の対物レンズについての波長λ＝６５０ｎｍに対する球面収差図である。
【図７２】本発明の実施例１１の対物レンズについての波長λ＝４００ｎｍに対する球面収差図である。
【図７３】本発明の実施例１１の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５までの球面収差図である。
【図７４】本発明の実施例１１の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．６５までの球面収差図である。
【図７５】本発明の実施例１１の対物レンズについての波長λ＝６５０ｎｍに対する波面収差図である。
【図７６】本発明の実施例１１の対物レンズについての波長λ＝４００ｎｍに対する波面収差図である。
【図７７】本発明の実施例１１の対物レンズについての波長λ＝７８０ｎｍに対する波面収差図である。
【図７８】本発明の実施例１２の対物レンズについての波長λ＝６５０ｎｍに対する光路図である。
【図７９】本発明の実施例１２の対物レンズについての波長λ＝４００ｎｍに対する光路図である。
【図８０】本発明の実施例１２の対物レンズについての波長λ＝７８０ｎｍに対する光路図である。
【図８１】本発明の実施例１２の対物レンズについての波長λ＝６５０ｎｍに対する球面収差図である。
【図８２】本発明の実施例１２の対物レンズについての波長λ＝４００ｎｍに対する球面収差図である。
【図８３】本発明の実施例１２の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５までの球面収差図である。
【図８４】本発明の実施例１２の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．６５までの球面収差図である。
【図８５】本発明の実施例１２の対物レンズについての波長λ＝６５０ｎｍに対する波面収差図である。
【図８６】本発明の実施例１２の対物レンズについての波長λ＝４００ｎｍに対する波面収差図である。
【図８７】本発明の実施例１２の対物レンズについての波長λ＝７８０ｎｍに対する波面収差図である。
【図８８】本発明の実施例１３の対物レンズについての波長λ＝６５０ｎｍに対する光路図である。
【図８９】本発明の実施例１３の対物レンズについての波長λ＝４００ｎｍに対する光路図である。
【図９０】本発明の実施例１３の対物レンズについての波長λ＝７８０ｎｍに対する光路図である。
【図９１】本発明の実施例１３の対物レンズについての波長λ＝６５０ｎｍに対する球面収差図である。
【図９２】本発明の実施例１３の対物レンズについての波長λ＝４００ｎｍに対する球面収差図である。
【図９３】本発明の実施例１３の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．４５までの球面収差図である。
【図９４】本発明の実施例１３の対物レンズについての波長λ＝７８０ｎｍに対する開口数０．６５までの球面収差図である。
【図９５】本発明の実施例１３の対物レンズについての波長λ＝６５０ｎｍに対する波面収差図である。
【図９６】本発明の実施例１３の対物レンズについての波長λ＝４００ｎｍに対する波面収差図である。
【図９７】本発明の実施例１３の対物レンズについての波長λ＝７８０ｎｍに対する波面収差図である。
【図９８】本発明の実施例１３の対物レンズについての波長λ＝４００ｎｍに対する光路図である。
【図９９】本発明の実施例１３の対物レンズについての波長λ＝４００ｎｍ±１０ｎｍに対する球面収差図を示す。
【図１００】本発明の実施例１３の対物レンズについての波長λ＝６５０ｎｍ±１０ｎｍに対する球面収差図を示す。
【図１０１】本発明の実施例１３の対物レンズについての波長λ＝７８０ｎｍ±１０ｎｍに対する球面収差図を示す。
【図１０２】本発明の第８の実施の形態にかかる光ピックアップ装置の第１の構成を示す光路図である。
【図１０３】本発明の第８の実施の形態にかかる光ピックアップ装置の第２の構成を示す光路図である。
【図１０４】本発明の第８の実施の形態にかかる光ピックアップ装置の第３の構成を示す光路図である。
【図１０５】本発明の第８の実施の形態にかかる光ピックアップ装置の第４の構成を示す光路図である。
【図１０６】本発明の第８の実施の形態にかかる光ピックアップ装置の第５の構成を示す光路図である。
【図１０７】本発明の第８の実施の形態にかかる光ピックアップ装置の第６の構成を示す光路図である。
【図１０８】本発明の第８の実施の形態にかかる光ピックアップ装置の第７の構成を示す光路図である。
【図１０９】Ｓｕｐｅｒ ＲＥＮＳ方式の光ディスクの構成を示す模式図である。
【図１１０】本発明の第８の実施の形態にかかる実施例１５の対物レンズの、結像倍率ｍ２と波面収差との関係を示すグラフである。
【図１１１】本発明の第８の実施の形態にかかる実施例１５の断面図である。
【図１１２】上記実施例１５の球面収差図である。
【図１１３】回折パターンの作用の説明図である。
【図１１４】本発明の第８の実施の形態にかかる対物レンズの球面収差への色収差の影響を示す模式図である。
【図１１５】本発明の第８の実施の形態にかかる対物レンズの球面収差への＋１次回折の影響を示す模式図である。
【図１１６】本発明の第８の実施の形態にかかる対物レンズの球面収差への−１次回折の影響を示す模式図である。
【図１１７】本発明の第７の実施の形態にかかる光ピックアップ装置の構成を示す光路図である。
【図１１８】本発明の第７の実施の形態にかかる実施例１５の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図である。
【図１１９】図１１８の回折光学レンズについての波長（λ）＝６４０，６５０，６６０ｎｍに対する開口数０．６０までの球面収差図である。
【図１２０】実施例１５において光情報記録媒体の透明基板が図１１８より厚い場合の回折光学レンズの光路図である。
【図１２１】図１２０の回折光学レンズについての波長λ＝７７０，７８０，７９０ｎｍに対する開口数０．６０までの球面収差図である。
【図１２２】本発明の第７の実施の形態にかかる実施例１６の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図である。
【図１２３】図１２２の回折光学レンズについての波長（λ）＝６４０，６５０，６６０ｎｍに対する開口数０．６０までの球面収差図である。
【図１２４】実施例１６において光情報記録媒体の透明基板が図１２２より厚い場合の回折光学レンズの光路図である。
【図１２５】図１２４の回折光学レンズについての波長λ＝７７０，７８０，７９０ｎｍに対する開口数０．６０までの球面収差図である。
【図１２６】本発明の第７の実施の形態にかかる実施例１７の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図である。
【図１２７】図１２６の回折光学レンズについての波長（λ）＝６４０，６５０，６６０ｎｍに対する開口数０．６０までの球面収差図である。
【図１２８】実施例１７において光情報記録媒体の透明基板が図１２６より厚い場合の回折光学レンズの光路図である。
【図１２９】図１２８の回折光学レンズについての波長λ＝７７０，７８０，７９０ｎｍに対する開口数０．６０までの球面収差図である。
【図１３０】本発明の第７の実施の形態にかかる実施例１８の対物レンズである回折光学レンズ（回折面を有する対物レンズ）の光路図である。
【図１３１】図１３０の回折光学レンズについての波長（λ）＝３９０，４００，４１０ｎｍに対する開口数０．７０までの球面収差図である。
【図１３２】実施例１８において光情報記録媒体の透明基板が図１３０より厚い場合の回折光学レンズの光路図である。
【図１３３】図１３２の回折光学レンズについての波長λ＝６４０，６５０，６６０ｎｍに対する開口数０．７０までの球面収差図である。
【図１３４】本発明における回折輪帯のピッチと、段差の深さを説明するための図である。
【符号の説明】
１ 対物レンズ
２ コリメータレンズ
３ 絞り
４ 光軸
５ 集光光学系
６，７ ビームスプリッタ
１０ 光ピックアップ装置
１１ 第１半導体レーザ
１２ 青色レーザ
１３ 第２半導体レーザ
１６ 対物レンズ
１６ａ フランジ部
２０ 光ディスク
２１ 透明基板
２２ 情報記録面
１１１，１１２ 半導体レーザ
１２０，１２１，１２２ 偏光ビームスプリッタ
１３０，１３１，１３２ コリメータ
１４０，１４１，１４２ １／４波長板
１５０ ２次元アクチュエータ
１６０ 対物レンズ
１７０ 絞り
１８０ シリンドリカルレンズ
１９０ ビームスプリッタ
２００ 光ディスク
２１０ 透明基板
２２０ 情報記録面
２３０，２３１，２３２ ホログラム
２４０ 第１の保護膜
２５０ 非線形光学膜
２６０ 第２の保護膜
２７０ 第３の保護膜
３００，３０１，３０２，３０５ 光検出器
４００，４１０，４２０，４３０ レーザ／検出器集積ユニット
５０ 凹レンズ
６０ カップリングリングレンズ
９０ 集光レンズ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device, a recording / reproducing device including the optical pickup device, a method for recording / reproducing information, and an objective lens used in the optical pickup device.
[0002]
[Prior art]
In recent years, with the practical use of short-wavelength red lasers, DVDs, which are high-density optical information recording media (also referred to as optical discs) that have the same size and large capacity as CDs (compact discs), have been commercialized. . In the DVD recording / reproducing apparatus, the numerical aperture NA on the optical disk side of the objective lens when a 650 nm semiconductor laser is used is set to 0.6 to 0.65. DVD has a track pitch of 0.74 μm and a shortest bit length of 0.4 μm, and has a density less than half that of a CD track pitch of 1.6 μm and a shortest pit length of 0.83 μm. Further, in the DVD, the transparent substrate thickness is 0.6 mm, which is half of the CD transparent substrate thickness, in order to suppress coma aberration generated when the optical disk is tilted with respect to the optical axis.
[0003]
In addition to the above-mentioned CD and DVD, optical discs of various standards such as different light source wavelengths and transparent substrate thicknesses, such as CD-R, RW (recordable compact disc), VD (video disc), MD (mini disc). ), MO (magneto-optical disk), etc. are also commercialized and popularized. Further, as the wavelength of semiconductor lasers has been shortened, a short wavelength blue laser having an oscillation wavelength of about 400 nm is being put to practical use. Since the wavelength is shortened, the capacity of the optical information recording medium can be further increased even if the same numerical aperture as that of the DVD is used.
[0004]
In addition, the thickness and recording of the transparent substrate on the recording surface, such as a CD-R that can be recorded and reproduced, and a DVD that has a higher recording density, are approximately the same size as a CD that is a conventional optical information recording medium as described above. Development of a plurality of optical information recording media having different wavelengths of reproduction laser light has progressed, and it has been demanded that these optical information recording media can be recorded and reproduced with the same optical pickup. For this reason, various types of optical pickups have been proposed in which a plurality of laser light sources corresponding to the used wavelengths are provided and the laser beam is converged with a necessary numerical aperture on the recording surface with the same objective lens (for example, Japanese Patent Laid-Open No. 8-55363). No., No. 10-92010, etc.).
[0005]
Among these, in JP-A-9-54973, 635 nm is transmitted light (0th order diffracted light), 785 nm is an optical system using a hologram optical element using -1st order diffracted light, and 635 nm is + 1st order diffracted light, 785 nm is An optical system using a hologram optical element using transmitted light (0th order diffracted light) is disclosed. Japanese Patent Application Laid-Open No. 10-283668 discloses an optical system that transmits 100% through a hologram type ring lens at 650 nm and first-order diffracts at a hologram type ring lens at 780 nm.
[0006]
However, in these hologram elements and hologram type ring lenses, when the diffraction efficiency of the 0th order light is almost 100% at one wavelength, the diffraction of the + 1st order diffracted light or the −1st order diffracted light at the other wavelength is unavoidable. There is a limit to the efficiency, and a desired high diffraction efficiency cannot be obtained, and there is a problem that a loss of light amount occurs and the light amount utilization efficiency deteriorates. When a loss of light intensity occurs, a higher power laser is required, particularly when recording information.
[0007]
Further, in the hologram element and the hologram type ring lens, the diffraction efficiency of the 0th order light is almost 100% at one wavelength, and the 0th order light is not transmitted as much as possible at the other wavelength. When the diffraction efficiency is increased, the depth of the hologram is increased to 3.8 to 5.18 μm. For this reason, in particular, when the function of the hologram optical element or the hologram type ring lens is integrated with the objective lens, there is a problem that it is very difficult to process and mold the mold.
[0008]
[Problems to be solved by the invention]
The inventors of the present invention previously consisted of a plurality of concentric annular zones, and each annular zone is substantially diffracted with respect to a plurality of light sources having different wavelengths and / or transparent substrates having different recording surface thicknesses. An objective lens that can constitute an optical pickup whose aberration has been corrected to the limit and whose structure has been simplified has been proposed (Japanese Patent Application No. 9-286554). This objective lens has a function of automatically obtaining a necessary aperture according to the wavelength used and / or the thickness of the transparent substrate. However, when a laser / detector integrated unit in which a laser light source and a photodetector are integrated is used, there is a problem in that accurate detection may not be possible due to flare light incident on the photodetector. This is particularly remarkable in a laser / detector integrated unit in which a light beam is deflected using a hologram and guided to a photodetector. In addition, when recording on a DVD-type recordable disc (DVD-RAM, DVD-R, DVD-RW, DVD + RW, etc.) or a CD-type recordable disc (CD-R, CD-RW, etc.), Compared to an optical system using a dedicated lens, a part of the light is flare, so the efficiency of using the light amount is poor, and it is necessary to increase the power of the laser light source.
[0009]
An object of the present invention is to provide an optical pickup device and a recording / reproducing device that enable recording and / or reproduction of different types of optical information recording media using light of at least two wavelengths different from each other with one optical pickup device. It is to provide an optical element and a recording / reproducing method.
[0010]
Furthermore, even when light of at least two wavelengths different from each other is used and applied to different types of optical information recording media, different optical information recording media can be used without causing large spherical aberration or chromatic aberration. It is an object to enable recording and / or reproduction of information with a single pickup device. Moreover, it is an object to provide an optical pickup device having a simple configuration. In particular, when different types of optical information recording media having transparent substrates with different thicknesses are used, the problem of spherical aberration becomes more serious, but even in such a case, large spherical aberration and chromatic aberration are generated. It is another object of the present invention to record and / or reproduce information on different optical information recording media with a single optical pickup device.
[0011]
Furthermore, even in a pickup device using an integrated unit of a plurality of lasers and a plurality of detectors, flare light that adversely affects detection is not irradiated on the photodetector, and the light from the photodetector is not irradiated. The object is to perform detection well and to improve the S-characteristic in detection. Furthermore, it is an object of the present invention to provide an optical pickup device, a recording / reproducing apparatus, an optical element, and a recording / reproducing method that have little loss of light amount and are excellent in light quantity utilization efficiency.
[0012]
Compatible for recording and / or reproducing information using one objective lens without generating large spherical aberration or chromatic aberration for both DVD and CD with different working wavelength and transparent substrate thickness Various optical systems have been proposed. However, what is put into practical use is that the divergent light beam from the light source is reduced by a coupling lens, the divergence is reduced to a parallel light beam, or a weak convergent light beam, and the objective lens and the transparent substrate of the optical information recording medium are connected. Thus, the light beam is converged on the information recording surface, and two lenses, a coupling lens and an objective lens, are required. Therefore, there is a problem that it is difficult to reduce the size and thickness of the optical pickup device and the cost is increased.
[0013]
On the other hand, as described above, various optical discs other than CD and DVD have become widespread, and an optical system that is compatible with these optical discs and that has a simple configuration and an optical pickup device including the same are required. It is said that. It is also an object of the present invention to provide such an optical system, a lens, a diffractive optical system for an optical disc, a reproducing device, and an objective lens for an optical pickup device.
[0014]
[Means for Solving the Problems]
To achieve the above object, an optical pickup device according to claim 1 is a first transparent substrate in an optical pickup device for reproducing information from an optical information recording medium or recording information on an optical information recording medium. A first light source that emits a first light beam having a first wavelength for reproducing information from a first optical information recording medium having a recording medium or recording information on the first optical information recording medium For reproducing information from a second optical information recording medium having a second transparent substrate having a thickness different from that of the first transparent substrate, or for recording information on the second optical information recording medium A second light source that emits a second light beam having a second wavelength different from the first wavelength; a condensing optical system having an objective lens, an optical axis, and a diffraction portion; and the first optical information recording. Information recording surface of the medium or the second optical information recording medium A light detector for receiving the light beam reflected from the information recording surface, and the condensing optical system allows the first light beam to pass through at least a part of the diffraction part, thereby Diffracted light of at least one order in which the amount of light of n-order diffracted light (where n is an integer other than 0) of one light beam is larger than the amount of light of any other order of diffracted light of the first light beam is generated. In order to reproduce information from the first optical information recording medium or to record information on the first optical information recording medium, the nth-order diffracted light of the first light flux is used as the first optical information recording medium. The light can be condensed on the information recording surface of the first optical information recording medium via the transparent substrate, and the condensing optical system allows the second light beam to pass through at least a part of the diffraction part. By doing so, the second-order diffracted light of the second light beam (where n is other than 0) In order to reproduce information from the second optical information recording medium by generating at least one order of diffracted light having a light quantity of (integer) greater than the light quantity of any other order of diffracted light of the second light flux Alternatively, in order to record information on the second optical information recording medium, the n-th order diffracted light of the second light flux is transmitted through the second transparent substrate to the second optical information recording medium. In addition to being able to concentrate on the information recording surface,Less thanThe following conditional expression is satisfied.
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Where ΔT (° C): temperature change
Δn:When there was a temperature change ΔTChange in refractive index of the objective lens
Δλ1 (nm) : Amount of change in wavelength of the first luminous flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux
[0015]
  ClaimsFor 19 optical pickup devicesThe objective lens is an objective lens used in an optical pickup device for reproducing information from an optical information recording medium or recording information on the optical information recording medium, and has an optical axis and a diffraction part. A first light beam having a first wavelength for reproducing information from a first optical information recording medium having a first transparent substrate or recording information on the first optical information recording medium is diffracted. By passing at least a part of the part, the light quantity of the nth-order diffracted light (where n is an integer other than 0) of the first light flux is any light quantity of any other order of the first light flux. In order to generate at least one order of diffracted light that is greater than and reproduce information from the first optical information recording medium or to record information on the first optical information recording medium. The n-th order diffracted light of one luminous flux is A second transparent substrate having a thickness different from that of the first transparent substrate, the second transparent substrate being capable of condensing on the information recording surface of the first optical information recording medium via the transparent substrate. A second light beam having a second wavelength different from the first wavelength for reproducing information from the optical information recording medium or recording information on the second optical information recording medium is at least in the diffractive portion. By passing through a part, the light quantity of the n-th order diffracted light (where n is an integer other than 0) of the second light flux is greater than the light quantity of any other order of the second light flux. In order to generate diffracted light of at least one order and reproduce information from the second optical information recording medium, or to record information on the second optical information recording medium, the second light flux The nth-order diffracted light of the second through the second transparent substrate It is possible to condense on the information recording surface of the optical information recording medium, and satisfies the following conditional expression.
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Where ΔT (° C): temperature change
Δn:When there was a temperature change ΔTChange in refractive index of the objective lens
Δλ1 (nm) : Amount of change in wavelength of the first luminous flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux
[0016]
  Claims37The recording / reproducing apparatus is an apparatus for reproducing information from an optical information recording medium or recording information on an optical information recording medium, comprising an optical pickup device, and the optical pickup device includes a first transparent device. A first light source that reproduces information from a first optical information recording medium having a substrate or emits a first light beam having a first wavelength for recording information on the first optical information recording medium And reproducing information from a second optical information recording medium having a second transparent substrate having a thickness different from that of the first transparent substrate, or recording information on the second optical information recording medium. A second light source that emits a second light beam having a second wavelength different from the first wavelength, a condensing optical system having an objective lens, an optical axis, and a diffractive portion, and the first optical information The information recording surface of the recording medium or the information of the second optical information recording medium A light detector for receiving the light beam reflected from the recording surface, and the condensing optical system allows the first light beam to pass through at least a part of the diffractive portion, thereby Generating at least one order of diffracted light in which the amount of light of n-order diffracted light (where n is an integer other than 0) is greater than the amount of light of any other order of diffracted light of the first light beam, In order to reproduce information from the first optical information recording medium or to record information on the first optical information recording medium, the nth-order diffracted light of the first light flux is used as the first optical information recording medium. The light can be condensed on the information recording surface of the first optical information recording medium via a transparent substrate, and the condensing optical system allows the second light flux to pass through at least a part of the diffraction section. N-order diffracted light of the second light flux (where n is other than 0) In order to reproduce information from the second optical information recording medium by generating at least one order of diffracted light that is greater than the amount of light of any other order of diffracted light in the second light flux Alternatively, in order to record information on the second optical information recording medium, the n-th order diffracted light of the second light flux is transmitted through the second transparent substrate to the second optical information recording medium. In addition to being able to concentrate on the information recording surface,Less thanThe following conditional expression is satisfied.
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Where ΔT (° C): temperature change
Δn:When there was a temperature change ΔTChange in refractive index of the objective lens
Δλ1 (nm) : Amount of change in wavelength of the first luminous flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux
[0017]
  Claims38The information recording / reproducing method is a recording / reproducing method for reproducing or recording information on at least two types of optical information recording media by an optical pickup device, the optical pickup device comprising: a first light source; 2, a condensing optical system having an objective lens that satisfies the following conditional expression, an optical axis, and a diffractive portion, and a photodetector, and the first light flux from the first light source or the first A step of emitting a second light flux different from the wavelength of the first light flux from two light sources, and passing the first light flux or the second light flux through at least a part of the diffractive portion. Generating at least one order diffracted light of the light beam or at least one order diffracted light of the second light beam (here, nth order diffracted light of at least one order diffracted light of the first light beam) (Where n is 0 or greater ) Is larger than the light quantity of any other order of diffracted light of the first light flux, the light quantity of n-order diffracted light of at least one order of diffracted light of the second light flux. Is larger than the amount of diffracted light of any other order of the second light beam) and the condensing optical system causes the n-th order diffracted light of the first light beam to pass through the first transparent substrate. The second optical information recording medium is provided on the information recording surface of the first optical information recording medium or through the second transparent substrate having a thickness different from that of the first transparent substrate. Condensing the optical pickup device on the information recording surface to record information on or reproduce information from the first optical information recording medium or the second optical information recording medium; and The first n-order diffracted light collected by the photodetector is collected. Detecting a first reflected light from the information recording surface of the optical information recording medium or a second reflected light from the information recording surface of the second optical information recording medium of the condensed n-th order diffracted light; ,includingAnd satisfies the following conditional expressionIt is characterized by that.
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Where ΔT (° C): temperature change
Δn:When there was a temperature change ΔTChange in refractive index of the objective lens
Δλ1 (nm) : Amount of change in wavelength of the first luminous flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux
[0018]
Note that the n-th order diffracted light amount is larger than any other order diffracted light amount, and the diffraction efficiency of the n-th order diffracted light with respect to light of a predetermined wavelength is that of each other order other than the n-th order. That is, it is higher than the diffraction efficiency of diffracted light. The n-th order n includes up to the sign, and in the first light flux that has passed through the diffractive portion of the present invention, more + 1st-order diffracted light is generated than other orders of diffracted light. Is intended to generate more + 1st order diffracted light than other orders of diffracted light in the second light flux that has passed through the diffracting section, and in the second light flux that has passed through the diffracting section, It does not include the generation of -1st order diffracted light more than other orders of diffracted light.
[0019]
The optical pickup apparatus of the present invention enables recording and / or reproduction of different types of optical information recording media using light of at least two wavelengths different from each other with a single pickup apparatus. That is, the optical pickup device of the present invention is used for recording / reproduction of different information recording media such as a first optical information recording medium and a second optical information recording medium. The first light beam of the first light source of the optical pickup device of the present invention is used for reproducing information from the first optical information recording medium or recording information on the first optical information recording medium. The second light flux of the second light source is used to reproduce information from the second optical information recording medium or to record information on the second optical information recording medium. In general, the optical information recording medium has a transparent substrate on the information recording surface.
[0020]
In other words, the function of the present invention is expressed by the condensing optical system using the first light information as the nth-order diffracted light of the first light beam generated in the diffractive part by the first light beam reaching the diffractive part. In order to reproduce information recorded on the recording medium or to record information on the first information recording medium, the first information recording surface of the first optical information recording medium is passed through the first transparent substrate. The condensing optical system can collect the information recorded on the second optical information recording medium by the n-th order diffracted light of the second light beam generated in the diffractive part by the second light beam reaching the diffractive part. In order to reproduce or record information on the second information recording medium, the light can be condensed on the second information recording surface of the second optical information recording medium via the second transparent substrate. The detector can receive the light beam reflected from the first information recording surface or the second information recording surface. It will be.
[0021]
A more preferred embodiment is shown below. The condensing optical system has a predetermined aperture in the first light flux on the image side of the objective lens, on the first information recording surface of the first optical information recording medium, the nth-order diffracted light in the first light flux that has passed through the diffraction section. The number can be collected in a state of 0.07λrms or less, that is, in a state where the light beam in the aperture is at the diffraction limit performance or less at the best image point in practical use. The nth-order diffracted light in the second light flux that has passed through the part is 0.07λ rms or less within the predetermined numerical aperture of the second light flux on the image information side of the objective lens on the second information recording surface of the second optical information recording medium. In other words, the light beam in the aperture in practical use can be condensed in a state where the diffraction limit performance or less is obtained at the best image point.
[0022]
Further, even when a wavelength shift of about ± 10 nm or less based on a temperature change or a current change occurs in the first light source or the second light source, a predetermined value on the image side of the objective lens on each information recording surface. It is preferable that the n-th order diffracted light is collected in a state of 0.07λrms or less within the numerical aperture. In particular, even if the first light beam or the second light beam has a wavelength of 600 nm or less (for example, 350 nm to 480 nm) and a wavelength shift of about ± 10 nm or less occurs, the image of the objective lens It is particularly preferable that the nth-order diffracted light is collected in a state of 0.07λrms or less within the predetermined numerical aperture on the side.
[0023]
In addition, it is preferable that the n-order diffracted light is the first-order diffracted light or the −1st-order diffracted light because the loss of the light amount is reduced as compared with the case where higher-order diffracted light is used.
[0024]
Further, the diffraction efficiency of the n-th order diffracted light of the first light flux in the diffractive portion is A%, and the diffraction efficiency of the diffracted light of another certain order (preferably the order having the highest diffraction efficiency among orders other than n) is When B%, it is preferable that A−B ≧ 10, the diffraction efficiency of the nth-order diffracted light of the second light flux in the diffractive portion is A ′%, and the diffraction efficiency of other diffracted light of a certain order is B ′. %, It is preferable that A′−B ′ ≧ 10. Further, AB ≧ 30 and A′−B ′ ≧ 30 are more preferable, AB ≧ 50 and A′−B ′ ≧ 50 are more preferable, and AB ≧ 70, A ′. More preferably, −B ′ ≧ 70.
[0025]
Further, when both the first light flux and the second light flux are used for recording information on the optical information recording medium, the diffraction efficiency of the nth-order diffracted light in the diffractive portion is determined by the wavelength of the first light flux and the wavelength of the second light flux. It is preferable to maximize the wavelength between the two.
[0026]
When only the first light beam or the second light beam is used for recording information on the optical information recording medium and the other light beam is used only for reproduction, the diffraction efficiency of the n-th order diffracted light in the diffractive portion is It is preferable to minimize the wavelength between the wavelength of the first light flux and the wavelength of the second light flux. More preferably, the diffraction efficiency of the n-th order diffracted light in the diffractive portion is maximized in the information recording method of the wavelength of the first light beam or the wavelength of the second light beam.
[0027]
The optical element provided with the diffractive portion is not particularly limited, and examples thereof include a lens having a refracting surface, a flat element, and the like provided in the condensing optical system.
[0028]
When a lens having a refracting surface is used as the optical element for providing the diffractive portion, specific examples of the optical element include an objective lens, a collimator lens, and a coupling lens. A diffractive portion can be provided on the refractive surface of these lenses. Moreover, you may add the flat plate-shaped or lens-shaped optical element only for providing a diffraction part to a condensing optical system.
[0029]
When the diffractive portion is provided on the refracting surface of the objective lens, it is preferable that the outer diameter of the objective lens (the outer diameter including the flange when the flange is provided) is 0.4 mm to 2 mm larger than the aperture diameter.
[0030]
The diffractive portion may be provided on the optical surface on the light source side of the optical element, may be provided on the image side (optical information recording medium side), or may be provided on both surfaces. The diffractive portion may be provided on the convex surface or the concave surface.
[0031]
Providing a diffractive portion in the objective lens is more preferable because it leads to a reduction in the number of parts and an assembly error during the manufacture of the optical pickup device can be reduced. In this case, the objective lens is preferably a single ball, but may be a double ball. A plastic lens is preferable, but a glass lens may also be used. Moreover, you may provide the resin layer in which the diffraction part was formed in the glass lens surface. Moreover, it is preferable that the objective lens provided with the diffraction part has a flange part having a surface extending in a direction perpendicular to the optical axis on the outer periphery. As a result, high-precision mounting to the pickup device can be easily performed, and stable performance can be obtained even when the environmental temperature changes. Moreover, it is preferable that the refracting surface of the objective lens is an aspheric surface, and the diffractive portion is provided on the aspheric surface. Of course, the diffraction part may be provided on one side of the objective lens or on both sides.
[0032]
The optical element provided with the diffractive part is preferably made of a material having an Abbe number νd of 50 or more and 100 or less. Further, it may be plastic or glass. In the case of a plastic lens, the refractive index of the material is preferably 1.4 to 1.75, more preferably 1.48 to 1.6, and 1.5 to 1.56. More preferably.
[0033]
Further, when the diffractive portion is provided in a lens (preferably a plastic lens), it is preferable to satisfy the following conditional expression in order to obtain an optical pickup device and an optical element that are stable with respect to temperature changes.
-0.0002 / ℃ <Δn / ΔT <-0.00005 / ℃
ΔT: Temperature change
Δn: change in refractive index of the lens
[0034]
Furthermore, it is preferable to satisfy the following conditional expression.
0.05nm / ℃ <Δλ1 / ΔT <0.5nm / ℃
Δλ1 (nm): Amount of change in wavelength of the first light source when there is a temperature change ΔT
[0035]
The diffraction part may be an amplitude type diffraction part, but is preferably a phase type diffraction part from the viewpoint of light utilization efficiency. The diffraction pattern of the diffraction part is preferably rotationally symmetric with respect to the optical axis. In addition, the diffractive portion has a plurality of annular zones when viewed from the direction of the optical axis, and the plurality of annular zones are formed on substantially concentric circles centered on the optical axis or a point near the optical axis. preferable. A circle is preferable, but an ellipse may be used. In particular, a blazed annular diffractive surface having a step is preferable. Further, it may be an annular diffraction surface formed in a step shape. Further, it may be an annular diffraction surface formed stepwise as an annular zone that discretely shifts in a direction in which the lens thickness increases as the distance from the optical axis increases. The diffractive portion is preferably ring-shaped, but may be a one-dimensional diffraction grating.
[0036]
When the diffractive portion is a concentric ring zone, the pitch of the diffraction zone is defined using a phase difference function or an optical path difference function. In this case, it is preferable that the phase difference function represented by the power series indicating each position of the plurality of annular zones has a coefficient other than 0 in at least one term other than the square term. With this configuration, it is possible to correct spherical aberration of chromatic aberration caused by light of different wavelengths.
[0037]
In addition, it is preferable that the phase difference function represented by the power series indicating each position of the plurality of annular zones of the diffractive portion has a coefficient other than 0 in the square term, because it is possible to correct paraxial chromatic aberration. However, when emphasizing not to make the pitch of the diffraction ring zone too small, the phase difference function represented by the power series indicating each position of the plurality of ring zones of the diffraction unit may not include the square term. Good.
[0038]
In addition, it is preferable that the number of steps of the diffraction ring zone of a diffraction part is 2 or more and 45 or less. More preferably, it is 40 or less. More preferably, it is 15 or less. In order to count the number of steps, the number of steps in the annular zone may be counted.
[0039]
Moreover, it is preferable that the depth in the optical axis direction of the step of the diffraction zone of the diffractive portion is 2 μm or less. With this configuration, the optical element can be easily manufactured, and the n-order diffracted light can be easily converted into the first-order or −1st-order diffracted light.
[0040]
Moreover, when providing a diffraction part in the light source side surface of an optical element, it is preferable that the depth of a level | step difference becomes deep as it leaves | separates from an optical axis.
[0041]
In the present invention, the action of the diffractive surface for deflecting the light beam is referred to as a positive action when the light beam is deflected further toward the optical axis, and is referred to as a negative action when it is deflected away from the optical axis.
[0042]
Further, the pitch of the zonal diffraction surface may be provided in inverse proportion to the height from the optical axis. Further, the way in which the pitch is provided is not inversely proportional to the height from the optical axis, that is, a pitch having a higher-order term in the optical path difference function may be provided.
[0043]
In particular, when a pitch having a higher-order term of the optical path difference function is provided, that is, when no pitch is provided in inverse proportion to the height from the optical axis, the optical path difference function may have an inflection point. Although it is good, it is preferable not to have an inflection point.
[0044]
Further, the diffractive action added by the diffractive part may be positive on the entire surface of the diffractive part or negative on the entire surface of the diffractive part. Further, the sign of the diffracting action added by the diffractive portion may be switched at least once in the direction perpendicular to the optical axis and away from the optical axis. For example, there is a type that changes from negative to positive in the direction away from the optical axis perpendicular to the optical axis as shown in FIG. In other words, the multiple zones of the diffractive part are blazed, and in the diffractive ring zone closer to the optical axis, the step is located on the side away from the optical axis and away from the optical axis. In the diffractive ring zone on the side, it can be said that the step portion is located on the side close to the optical axis. Further, as shown in FIG. 47 (d), a type that changes from positive to negative in the direction away from the optical axis perpendicular to the optical axis may be used. In other words, the zonal zone of the diffractive part is blazed, and in the diffractive ring zone on the side close to the optical axis, the step is located on the side close to the optical axis. In the diffraction ring zone on the side away from the axis, it can be said that the step portion is located on the side away from the optical axis.
[0045]
In FIG. 134, the pitch of the diffraction ring zone means the distance p between the ring zone step perpendicular to the optical axis and the step of the zone, and the step depth means the length of the step in the optical axis direction. Say d.
[0046]
As the pitch becomes finer, the degree of convergence and divergence of that part becomes stronger, and as the pitch becomes larger, the degree of convergence and divergence of that part becomes weaker.
[0047]
In an optical element having a diffractive part, the diffractive part may be provided on the entire surface through which the light beam passes. In other words, it can be said that all the light beams having the maximum numerical aperture or less on the image side of the objective lens may pass through the diffraction section. Further, a diffractive portion may be provided on the entire optical surface of the optical element, and 70% or more (preferably 80% or more, more preferably 90% or more) of one optical surface of the optical element is diffracted. It is good also as a part.
[0048]
Further, the diffraction part may be provided only on a part of the surface through which the light beam of the optical element passes, and the other part may be a refracting surface or a transmitting surface. In other words, among the light fluxes corresponding to the maximum numerical aperture on the image side of the objective lens, the light flux in a part of the area perpendicular to the optical axis passes through the diffraction part and the light flux in the other part of the area. It can be said that does not pass through the diffractive part but passes through the refracting surface or the transmitting surface. When the diffractive part is provided only on a part of the surface through which the light beam passes, the diffractive part may be provided only in the vicinity of the optical axis including the optical axis, or the diffractive part is provided in an annular shape without providing the diffractive part in the vicinity of the optical axis. May be. For example, 10% or more and less than 90% of one optical surface of the optical element may be used as the diffraction part. Alternatively, the diffraction part may be 10% or more and less than 50%.
[0049]
When the diffractive portion is provided only on a part of the surface through which the light beam of the optical element passes, it is preferable that NA1> NAH1, NAH1 ≧ NA2, NA2 ≧ NAL1 ≧ 0 when NA1> NA2. When NA2> NA1, it is preferable that NA2> NAH2, NAH2 ≧ NA1, NA1 ≧ NAL2 ≧ 0. NA1 and NA2 are predetermined numerical apertures on the image side of the objective lens when using the first light flux and the second light flux, respectively. NAH1 and NAH2 are the numerical apertures on the image side of the objective lens of the first light flux and the second light flux that have passed through the outermost part of the diffraction section. NAL1 and NAL2 are the numerical apertures on the image side of the objective lens of the first light flux and the second light flux that have passed through the innermost side of the diffraction section.
[0050]
Further, in the case where the diffractive portion is provided only on a part of the surface through which the light beam of the optical element passes, when NA1> NA2, the light beam that has passed through the diffractive portion at NA1 or less and the refraction other than the diffractive portion when NA1> NA2. It is preferable that the condensing positions of the light passing through the surface are substantially equal. In the case of NA2> NA1, it is preferable that the condensing position of the light beam that has passed through the diffractive portion with NA2 or less and the light beam that has passed through the refracting surface other than the diffractive portion in the second light beam is substantially equal.
[0051]
Moreover, the aspect in which a diffraction part has the 1st diffraction pattern and the 2nd diffraction pattern, and the 2nd diffraction pattern is separated from the optical axis rather than the 1st diffraction pattern may be sufficient. Moreover, you may combine a diffraction part and the refractive surface without a diffraction part on the same surface.
[0052]
In addition, in the case of having two types of diffraction patterns, a large amount of nth-order diffracted light is generated in the first light flux that has passed through the first diffraction pattern of the diffractive portion, compared to diffracted light of other orders, and The n-th order diffracted light is generated more than the other orders of diffracted light even in the second light beam that can be condensed on one information recording surface and passed through the first diffraction pattern of the diffraction section. In the first light beam that can be condensed on the second information recording surface and has passed through the second diffraction pattern of the diffractive portion, the n-th order diffracted light is compared with other orders of diffracted light. In the second light flux that is generated frequently and can be condensed on the first information recording surface and has passed through the second diffraction pattern of the diffractive portion, the 0th-order light that is transmitted light has other orders. It may be generated more than diffracted light. In this case, the nth order is preferably the first order.
[0053]
As another aspect, in the first light flux that has passed through the first diffraction pattern of the diffractive portion, a large amount of nth-order diffracted light is generated as compared with diffracted light of other orders, and the first information Even in the second light beam that can be condensed on the recording surface and has passed through the first diffraction pattern of the diffractive portion, a large amount of n-th order diffracted light is generated as compared with other orders of diffracted light, In the first light beam that can be condensed on the second information recording surface and passed through the second diffraction pattern of the diffractive portion, more n-th order diffracted light is generated compared to other orders of diffracted light. In the second light beam that can be condensed on the first information recording surface and has passed through the second diffraction pattern of the diffractive portion, negative order diffracted light that is not nth order has other orders. It occurs more than diffracted light. In this case, the nth order is preferably the first order, and the negative order is preferably the −1st order.
[0054]
In the case of an optical pickup device or an optical element used in a plurality of optical information recording media having different thicknesses of the transparent substrate, it is particularly preferable that the pitch of the annular zone of the diffraction part satisfies the following conditional expression.
0.4 ≦ | (Ph / Pf) −2 | ≦ 25
[0055]
More preferably, 0.8 ≦ | (Ph / Pf) −2 | ≦ 6, and further preferably 1.2 ≦ | (Ph / Pf) −2 | ≦.
[0056]
The pitch of the annular zone of the diffraction part corresponding to the maximum numerical aperture on the image side of the objective lens is Pf, and the pitch of the annular zone of the diffraction part corresponding to 1/2 of the maximum numerical aperture is Ph. The maximum numerical aperture is the maximum numerical aperture among the predetermined numerical apertures of several types of optical information recording media in which information is read / recorded in the optical pickup device. The predetermined numerical aperture is a numerical aperture that enables reading / recording of information on an optical information recording medium with a light beam having a predetermined wavelength in the optical pickup device, and is determined by a standard of an optical information recording medium. It may be a numerical aperture. Further, the pitch of the annular zone of the diffractive portion corresponding to the maximum numerical aperture on the image side of the objective lens is the pitch of the annular zone located at the outermost peripheral portion of the light beam passing therethrough at the maximum numerical aperture. means. In addition, the pitch of the annular zone of the diffractive portion corresponding to ½ of the maximum numerical aperture is positioned at the outermost peripheral portion of the light beam passing through the diffractive portion when the numerical aperture is ½ of the maximum numerical aperture. It means the pitch of the ring zone.
[0057]
It should be noted that one of the light beams of the two light sources may be an optical pickup device in which no aberration is obtained up to the actual use aperture and aberration is flare in the outer portion.
[0058]
In other words, it can be expressed as follows. When the first light flux is used, the first light flux within a predetermined numerical aperture on the image side of the objective lens is in a state of 0.07λrms or less on the first information recording surface of the first optical information recording medium. When the first light flux is used, the first light flux that has passed outside the predetermined numerical aperture on the image side of the objective lens is in a state larger than 0.07 λrms on the first information recording surface. The second light beam that has passed through the predetermined numerical aperture using the second light beam and the second light beam that has passed outside the predetermined numerical aperture are both recorded in the second information recording medium of the second optical information recording medium. The light is collected on the surface in a state of 0.07λrms or less. In this case, NA1 <NA2, and the light flux between NA1 and NA2 is flare when recording / reproducing the first optical information recording medium.
[0059]
Alternatively, when the second light flux is used, the second light flux within a predetermined numerical aperture on the image side of the objective lens is 0.07 λrms or less on the second information recording surface of the second optical information recording medium. When the second light flux is used, the second light flux that has passed outside the predetermined numerical aperture on the image side of the objective lens is larger than 0.07λrms on the second information recording surface. The first light beam that has passed through the predetermined numerical aperture using the first light beam and the first light beam that has passed outside the predetermined numerical aperture are both the first light beam of the first optical information recording medium. The light is condensed on the information recording surface in a state of 0.07λrms or less. In this case, NA1> NA2, and when the second optical information recording medium is recorded / reproduced, the light flux between NA2 and NA1 is flare.
[0060]
These modes can be arbitrarily set depending on the design of the diffraction part. For example, while providing a diffractive part on the entire surface of the optical element, the design of the diffractive part may cause flare to occur at a predetermined numerical aperture or more, or a diffractive part may be provided on a part of the surface of the optical element. A refracting surface may be used, and flare may be generated by the refracting surface or the diffraction part.
[0061]
In the aspect of generating the flare, aperture limiting means that shields or diffracts the first light beam outside the predetermined numerical aperture on the image side of the objective lens when the first light beam is used, and transmits the second light beam. However, it is preferable that the second light beam outside the predetermined numerical aperture on the image side of the objective lens when the second light beam is used is shielded or diffracted and there is no aperture limiting means for transmitting the first light beam. . That is, it is preferable to provide only a normal diaphragm without providing a dichroic filter or a hologram filter. As long as the diffractive portion is designed to satisfy the above functions, only a normal diaphragm needs to be provided, which is preferable because the mechanism is simple.
[0062]
However, flare may be generated using a filter such as a hologram filter. When a filter such as a hologram filter is provided, a separate filter may be provided in the condensing optical system, or a filter may be provided on the objective lens.
[0063]
Further, a flare may be provided in the under or a flare may be provided in the over with respect to the position where the minimum spot is formed when the light beam having a smaller predetermined numerical aperture is condensed. . Preferably, it should be provided over.
[0064]
Further, when flare is generated as described above, flare may be generated continuously or discontinuously in the spherical aberration diagram.
[0065]
Further, as another aspect, there is an aspect of an optical pickup device that does not generate flare. The following are listed.
[0066]
In other words, it can be expressed as follows. When the first light flux is used, the first light flux within a predetermined numerical aperture on the image side of the objective lens is in a state of 0.07λrms or less on the first information recording surface of the first optical information recording medium. When the first light beam is condensed and passed through the outside of the predetermined numerical aperture on the image side of the objective lens, the first light beam is in a state of 0.07 λrms or less on the first information recording surface. The second light that is condensed or shielded and does not reach the first information recording surface and has passed through a predetermined numerical aperture on the image side of the objective lens when using the second light flux. Both the light beam and the second light beam that has passed outside the predetermined numerical aperture are collected on the second information recording surface of the second optical information recording medium in a state of 0.07 λrms or less. In this case, NA1 <NA2 and when the first optical information recording medium is recorded / reproduced, the light flux between NA1 and NA2 is also condensed or shielded.
[0067]
Alternatively, when the second light flux is used, the second light flux within a predetermined numerical aperture on the image side of the objective lens is 0.07 λrms or less on the second information recording surface of the second optical information recording medium. When the second light beam is collected in this state, the second light beam that has passed outside the predetermined numerical aperture on the image side of the objective lens is 0.07λrms or less on the second information recording surface. Condensed in the state or shielded so as not to reach the second information recording surface and passed through a predetermined numerical aperture on the image side of the objective lens when using the first light flux. Both the first luminous flux and the first luminous flux that has passed outside the predetermined numerical aperture are collected on the first information recording surface of the first optical information recording medium in a state of 0.07λrms or less. In this case, NA1> NA2 and when the second optical information recording medium is recorded / reproduced, the light flux between NA2 and NA1 is also condensed or shielded.
[0068]
These modes can be arbitrarily set depending on the design of the diffraction part.
[0069]
In an aspect in which the flare is not generated and the light beam between NA1 and NA2 or between NA2 and NA1 is shielded, a second numerical aperture outside the predetermined numerical aperture on the image side of the objective lens when the first light beam is used. An aperture limiting unit that shields or diffracts one light beam and transmits the second light beam, or shields a second light beam outside a predetermined numerical aperture on the image side of the objective lens when the second light beam is used. Alternatively, it is preferable to provide aperture limiting means that diffracts and transmits the first light flux. Alternatively, it is preferable to provide an aperture limiting means that provides a predetermined numerical aperture for each light beam.
[0070]
That is, in one of the first light flux and the second light flux, the light flux is preferably shielded by an annular filter such as a dichroic filter or a hologram filter that is an aperture limiting unit at a predetermined numerical aperture or more. When a filter such as a dichroic filter or a hologram filter is provided, a separate filter may be provided in the condensing optical system, or a filter may be provided on the objective lens.
[0071]
However, even when flare is not generated, it is possible to provide only a normal aperture without providing a dichroic filter or hologram filter so that all light beams within the maximum numerical aperture are condensed on the information recording surface. Good. In other words, within the maximum numerical aperture on the image side of the objective lens, both the first light beam and the second light beam are condensed on the information recording surface in a state of 0.07λrms or less. Also good.
[0072]
Even when NA1 = NA2, it is preferable not to generate flare in the above-described manner.
[0073]
Note that different information recording media such as the first optical information recording medium and the second optical information recording medium mean information recording media having different wavelengths of light used for recording / reproducing. The thickness and refractive index of the transparent substrate may be the same or different. Further, the predetermined numerical aperture values may be the same or different. Of course, the recording density of information may be the same or different. Paraxial chromatic aberration and spherical aberration caused by the difference in wavelength of light used for recording / reproduction of different information recording media are corrected by the diffraction section of the present invention. It is most preferable to correct both the spherical aberration and the paraxial chromatic aberration, and the mode in which only the spherical aberration is corrected and the paraxial chromatic aberration is not corrected is the next preferred mode, but the mode in which only the paraxial chromatic aberration is corrected and the spherical aberration is not corrected. It may be.
[0074]
Furthermore, even when different information recording media have different transparent substrate thicknesses and spherical aberration occurs based on the thickness of the transparent substrate, the spherical aberration is corrected by the diffraction unit of the present invention. . In the first optical information recording medium and the second optical information recording medium, when the thicknesses of the transparent substrates are different, the generated spherical aberration becomes larger, so that the effect of the present invention is more remarkable and preferable.
[0075]
The difference between the wavelength of the first light beam and the wavelength of the second light beam is preferably 80 nm or more and 400 nm or less. More preferably, it is 100 nm or more and 200 nm or less. More preferably, it is 120 nm or more and 200 nm or less. In addition, as the first light source and the second light source, for example, two types of light sources that emit light having a wavelength of 760 to 820 nm, 630 to 670 nm, 350 nm to 480 nm, and the like are preferably used in combination. be able to. Of course, three light sources or four light sources may be used. In the case of having a third light source that emits the third light beam and a fourth light source that emits the fourth light beam, the n-th order diffracted light is also detected in the third light beam and the fourth light beam that have passed through the diffraction section. It is preferable to generate a larger amount than the diffracted light of the order.
[0076]
In addition, when the wavelength of the second light beam is longer than the wavelength of the first light beam, it is preferable that the axial chromatic aberration in the second light beam and the first light beam satisfy the following conditional expression: .
-Λ2 / {2 × (NA2)²} ≦ Z ≦ λ2 / {2 × (NA2)²}
λ2: wavelength of the second light beam
NA2: a predetermined numerical aperture on the image side of the objective lens with respect to the second light flux
[0077]
In addition, when optical information recording media having different transparent substrate thicknesses are used, and t2> t1 and λ2> λ1, it is preferable that the following conditional expression is satisfied.
0.2 × 10^-6/ ℃ <ΔWSA3 ・ λ1 / {f ・ (NA1)⁴・ ΔT} <2.2 × 10^-6/ ℃
NA1: Necessary numerical aperture of the objective lens on the image side when reproducing or recording an optical information recording medium using the first light flux
λ1: Wavelength of the first beam
f: Focal length of the objective lens for the first beam
ΔT: Environmental temperature change
ΔWSA3 (λ1rms): The amount of change in the third-order spherical aberration component of the wavefront aberration of the light beam collected on the optical information recording surface when the optical information recording medium is reproduced or recorded using the first light beam.
[0078]
In addition, when the first light beam is used, the first light beam, which is a non-parallel light beam such as divergent light or convergent light, is incident on the objective lens, and when the second light beam is used, divergent light, convergent light, or the like is used. A second light beam that is a non-parallel light beam may be incident on the objective lens.
[0079]
Alternatively, when the first light beam is used, the first light beam that is a parallel light beam is incident on the objective lens, and when the second light beam is used, the second light beam that is a non-parallel light beam such as divergent light or convergent light is used. The light beam may be incident on the objective lens. Alternatively, when the first light beam is used, the first light beam, which is a non-parallel light beam such as divergent light or convergent light, is incident on the objective lens, and when the second light beam is used, the second light beam is a parallel light beam. You may make it make a light beam inject into an objective lens.
[0080]
When a non-parallel light beam is used in either the first light beam, the second light beam, or both, the magnification m1 with respect to the objective lens in the case of using the first light beam and the second light beam are used. In this case, the absolute value of the difference from the magnification m2 with respect to the objective lens is preferably 0 to 1/15. More preferably, it is 0 to 1/18. When λ2> λ1, t2> t1, m1 is preferably larger. In particular, the above range is preferable when the second light beam is used for a CD and the first light beam is used for a DVD. Note that the wavelength of the first light source is λ1, the wavelength of the second light source is λ2, the thickness of the first transparent substrate is t1, and the thickness of the second transparent substrate is t2.
[0081]
Alternatively, in the case of using the first light beam and the case of using the second light beam, a parallel light beam may be incident on the objective lens. In this case, the diffractive portion may have a form as shown in FIGS. 47B and 47C, but the form shown in FIGS. 47A and 47D is preferable.
[0082]
Further, the optical pickup device is provided with a divergence changing means (hereinafter also referred to as “divergence correction means”) for correcting the divergence of the light beam incident on the objective lens, and the objective lens is used for the first light beam and the second light beam. You may make it change the divergence degree of the light beam which injects into a lens.
[0083]
When diverging light is incident on the objective lens, the objective lens is preferably a glass lens.
[0084]
In the case where reproduction / recording can be performed only on either the first information recording medium or the second information recording medium and only reproduction is performed on the other, the first light flux can be obtained in the optical pickup device. It is preferable that the imaging magnification of the entire optical pickup device with respect to is different from the imaging magnification of the entire optical pickup device with respect to the second light flux. In this case, the imaging magnification of the objective lens for the first light flux and the imaging magnification of the objective lens for the second light flux may be the same or different.
[0085]
Further, when λ1 <λ2 and t1 <t2 and reproduction / recording can be performed only on the first information recording medium and reproduction is performed only on the second information recording medium, the first light flux It is preferable that the imaging magnification of the entire optical pickup device with respect to is smaller than the imaging magnification of the entire optical pickup device with respect to the second light flux. Further, when the above is satisfied and 0.61 <NA1 <0.66, in the condensing optical system, a coupling lens that changes the magnification is provided between the first light source and the collimator lens, In the optical optical system, it is preferable to provide a first collimator lens for the light beam and a second collimator lens for the light beam. It is preferable that the imaging magnification of the objective lens for the first light flux and the imaging magnification of the objective lens for the second light flux are both 0. The wavelength of the first light source is λ1, the wavelength of the second light source is λ2, the thickness of the first transparent substrate is t1, and the thickness of the second transparent substrate is t2. The predetermined numerical aperture on the image side of the objective lens necessary for recording or reproduction of the first optical information recording medium is NA1.
[0086]
Further, when λ1 <λ2 and t1 <t2 and reproduction / recording can be performed only on the second information recording medium and reproduction is performed only on the first information recording medium, the first light flux It is preferable that the imaging magnification of the entire optical pickup device with respect to is larger than the imaging magnification of the entire optical pickup device with respect to the second light flux. It is preferable that the imaging magnification of the objective lens for the first light flux and the imaging magnification of the objective lens for the second light flux are both 0.
[0087]
In the case where reproduction / recording can be performed with respect to both the first information recording medium and the second information recording medium, or when only reproduction is performed with respect to both, the optical pickup device uses the first information recording medium and the second information recording medium. It is preferable that the imaging magnification of the entire optical pickup device with respect to the light beam is substantially equal to the imaging magnification of the entire optical pickup device with respect to the second light beam. In this case, the imaging magnification of the objective lens for the first light flux and the imaging magnification of the objective lens for the second light flux may be the same or different.
[0088]
The photodetector may be common to the first light flux and the second light flux. Alternatively, a second photodetector may be provided, the photodetector may be for the first light flux, and the second photodetector may be for the second light flux.
[0089]
Moreover, the photodetector and the first light source or the second light source may be unitized. Alternatively, the photodetector, the first light source, and the second light source may be unitized. Alternatively, the photodetector, the second photodetector, the first light source, and the second light beam may all be integrated into a unit. Furthermore, only the first light source and the second light source may be unitized.
[0090]
In particular, when the first light source and the second light source are unitized and are arranged on the same plane, if NA1> NA2, the first light source is placed on the optical axis of the objective lens. If NA1 <NA2, it is preferable to provide the second light source on the optical axis of the objective lens. The predetermined numerical aperture on the image side of the objective lens necessary for recording or reproduction of the first optical information recording medium is NA1, and the image side of the objective lens necessary for recording or reproduction of the second optical information recording medium is NA1. The predetermined numerical aperture is NA2.
[0091]
When the working distance when recording / reproducing the first optical information recording medium is WD1, and when the working distance when recording / reproducing the second optical information recording medium is WD2, | It is preferable that WD1-WD2 | ≦ 0.29 mm. In this case, it is more preferable that the magnification when recording / reproducing the first optical information recording medium is equal to the magnification when recording / reproducing the second optical information recording medium. Further, the magnification is more preferably 0. Further, when t1 <t2 and λ1 <λ2, it is preferable that WD1 ≧ WD2. These conditions regarding working distance are particularly preferable when the first optical information recording medium is a DVD and the second optical information recording medium is a CD. When the working distance is satisfied, the diffractive portion may have a form as shown in FIGS. 47A and 47D, but the form shown in FIGS. 47B and 47C is preferable.
[0092]
An optical element such as a condensing optical system or an objective lens forms a spot on the information recording surface of an optical information recording medium so that the light beam is condensed and information can be recorded / reproduced. is there. In particular, when NA1> NA2 and λ1 <λ2, and with respect to the second light flux, the light flux outside NA2 is caused to flare on the second information recording surface of the second optical information recording medium. (When the wavefront aberration on the imaging surface is larger than 0.07λ2 rms), the spot preferably satisfies the following conditions.
0.66 × λ2 / NA2 ≦ w ≦ 1.15 × λ2 / NA2
w> 0.83 × λ2 / NA1
λ1: wavelength of the first light beam
λ2: wavelength of the second light beam
NA1: Predetermined numerical aperture for the first luminous flux
NA2: a predetermined numerical aperture for the second light flux
w: 13.5% intensity beam diameter on the image plane of the second light flux
[0093]
When the spot is not a perfect circle, the beam diameter in the direction in which the beam diameter is most narrowed is preferably the beam diameter (w).
[0094]
Furthermore, it is preferable to satisfy the following conditions.
0.74 × λ2 / NA2 ≦ w ≦ 0.98 × λ2 / NA2
[0095]
In addition, the spot shape has a spot with high light intensity used for recording / reproduction at the center, and a flare with low light intensity is present around the spot so as not to adversely affect detection. It may be a shape in which a spot used for recording / reproduction with high light intensity exists at the center, and a flare exists in a donut shape around the spot.
[0096]
Moreover, it is preferable that the S-shaped characteristic of a spot is favorable. Specifically, the overshoot is preferably 0 to 20%.
[0097]
The wavelength of the first light source is λ1, the wavelength of the second light source is λ2, the thickness of the first transparent substrate is t1, the thickness of the second transparent substrate is t2, and the wavelength is λ1. An image of the objective lens necessary for recording or reproduction of the second optical information recording medium with light having a predetermined numerical aperture NA1 on the image side of the objective lens necessary for recording or reproduction of the first optical information recording medium and a wavelength of λ2. When the predetermined numerical aperture on the side is NA2, a preferable example is the following conditional expression. In this case, the nth order diffracted light is preferably a first order diffracted light. Of course, the preferred embodiment is not limited to the following conditional expression.
λ1 <λ2
t1 <t2
NA1> NA2 (preferably NA1> NA2> 0.5 × NA1)
[0098]
When the above conditional expression is satisfied, the objective lens of the condensing optical system has a diffractive portion, and the second optical flux that has passed through the diffracting portion in order to record / reproduce the second optical information recording medium. 112, when the n-th order diffracted light is condensed on the second information recording surface of the second optical information recording medium, the spherical aberration may have at least one discontinuous portion as shown in FIG. .
[0099]
When it has a discontinuous part, it is preferable that spherical aberration has a discontinuous part in the vicinity of NA2. For example, when the numerical aperture (NA) is 0.45, the spherical aberration has a discontinuous portion, and when the numerical aperture (NA) is 0.5, the spherical aberration has a discontinuous portion.
[0100]
When the spherical aberration has a discontinuous portion, the condensing optical system uses the first information recording medium of the first optical information recording medium for the nth-order diffracted light having a numerical aperture of NA1 or less in the first light flux that has passed through the diffracting portion. On the surface, the light is condensed so that the wavefront aberration at the best image point is 0.07 λrms, and the condensing optical system has an nth-order diffracted light having a numerical aperture equal to or less than the numerical aperture that becomes a discontinuous part in the second light flux that has passed through the diffractive part. Is preferably focused on the second information recording surface of the second optical information recording medium so that the wavefront aberration at the best image point is 0.07 λrms.
[0101]
In addition, when the above conditional expression is satisfied, the objective lens of the condensing optical system has a diffractive part, and the second optical information recording medium passes through the diffractive part in order to perform recording / reproduction of the second optical information recording medium. When the nth-order diffracted light in the light beam is collected on the second information recording surface of the second optical information recording medium, as shown in FIG. 27, the spherical aberration is continuous and does not have a discontinuous portion. It may be.
[0102]
When the spherical aberration is continuous and does not have a discontinuous portion, it is preferable that the NA1 has a spherical aberration of 20 μm or more and the NA2 has a spherical aberration of 10 μm or less. More preferably, NA1 has a spherical aberration of 50 μm or more, and NA2 has a spherical aberration of 2 μm or less.
[0103]
In the above conditions, for example, a specific preferable example in the case where a type of DVD is used as the first optical information recording medium and a type of CD is used as the second optical information recording medium is as follows. However, the present invention is not limited to this. 0.55mm <t1 <0.65mm
1.1mm <t2 <1.3mm
630 nm <λ1 <670 nm
760 nm <λ2 <820 nm
0.55 <NA1 <0.68
0.40 <NA2 <0.55
[0104]
In the case of the above range, when the diffraction part is annular diffraction, it is preferable that the diffraction part corresponding to NA2 or less is 19 or less or 21 or more. Moreover, it is preferable that a diffraction part as a whole is 35 ring zones or more or 33 ring zones or less.
[0105]
Moreover, when satisfy | filling the said range, it is preferable that a spot diameter satisfy | fills the following aspects.
[0106]
The objective lens of the condensing optical system has a diffractive portion, λ1 = 650 nm, t1 = 0.6 mm, NA1 = 0.6, and the objective lens is a parallel light having a uniform intensity distribution. When the light beam is incident and condensed on the first information recording surface via the first transparent substrate, the spot diameter at the best focus is preferably 0.88 to 0.91 μm.
[0107]
Alternatively, λ1 = 650 nm, t1 = 0.6 mm, NA1 = 0.65, and the first light beam, which is parallel light having a uniform intensity distribution, is incident on the objective lens, and the first transparent substrate is formed. When the light is condensed on the first information recording surface, the spot diameter at the best focus is preferably 0.81 to 0.84 μm.
[0108]
Further, when the above range is satisfied and the diffractive portion is provided in the objective lens, it is preferable that the pitch of the diffractive portion is 10 to 70 μm at a numerical aperture (NA) of 0.4. More preferably, it is 20-50 micrometers.
[0109]
Furthermore, the following embodiments can be cited as specific preferred examples of the above conditions, but the present invention is not limited to these. In particular, when recording is also performed on a CD as the second optical information recording medium, NA2 is preferably set to 0.5. Further, when recording is also performed on a DVD as the first optical information recording medium, NA1 is preferably set to 0.65.
t1 = 0.6mm
t2 = 1.2mm
λ1 = 650 nm
λ2 = 780 nm
NA1 = 0.6
NA2 = 0.45
[0110]
Moreover, the following aspects may be sufficient. In the case of the following aspects, it is preferable that the nth order diffracted light is −1st order light.
λ1 <λ2
t1> t2
[0111]
Further, specific examples of an optical information recording medium recording or reproducing apparatus that reproduces information from an optical information recording medium or records information on an optical information recording medium having the optical pickup apparatus of the present invention include a DVD / CD reproducing apparatus, DVD / CD / CD-R recording / playback device, DVD-RAM / DVD / CD-R / CD recording / playback device, DVD / CD / CD-RW recording / playback device, DVD / LD playback device, DVD / Blue Examples include, but are not limited to, an optical information recording medium recording / reproducing apparatus using a laser (350 to 480 nm, especially about 400 nm), an optical information recording medium recording / reproducing apparatus using a CD / blue laser, and the like. is not. These optical information recording medium recording or reproducing devices have a power source, a spindle motor, and the like in addition to the optical pickup device.
[0112]
Further, the objective lens of the present invention has a change amount of the spherical aberration of the marginal ray for a minute change in at least one of the wavelength of the first light source and the wavelength of the second light source. When the change amount is ΔCA, the following conditional expression is preferably satisfied.
−1 <ΔSA / ΔCA <−0.2
[0113]
In this specification, each term is as defined below. First, an optical element refers to each of all optical elements applicable to an optical system for recording information on an information recording medium and / or reproducing information on the information recording medium. Examples include, but are not limited to, a lens, an objective lens, a polarizing beam splitter, a quarter wave plate, and a beam splitter for combining light from two or more light sources. Further, the optical element may be an optical element that is provided with only the diffraction portion of the present invention and has no other role.
[0114]
Also, the optical system in the present invention is a set of one or more of the above optical elements that can record or reproduce, for example, CDs and DVDs, and records information and / or records information on an information recording medium. It may mean not only the entire optical system for making information on the medium reproducible, but also a part of the optical system, and includes at least one optical element as described above.
[0115]
Examples of the information recording medium in the present invention include various CDs such as CD, CD-R, CD-RW, CD-Video, and CD-ROM, DVD, DVD-ROM, DVD-RAM, DVD-R, and DVD-RW. And various discs such as MD, LD, and MO. Generally, a transparent substrate exists on the information recording surface of the information recording medium. Of course, the present invention is not limited to these, and includes an optical information recording medium using a blue laser, which is not commercially available at present.
[0116]
In the present invention, recording and reproduction of information with respect to an information recording medium refers to recording information on the information recording surface of the information recording medium as described above and reproducing information recorded on the information recording surface. . The pickup device / optical system of the present invention may be used for only recording or reproduction, or may be used for both recording and reproduction. Further, it may be used for recording on a certain information recording medium and reproducing on another information recording medium, or may be used for recording or recording on a certain information recording medium. It may be used for performing reproduction and recording and reproduction on another information recording medium. Note that reproduction here includes simply reading information.
[0117]
The pickup device / optical system used for at least one of recording and reproduction of information with respect to the information recording medium is of course applicable to such a pickup apparatus / optical system, or such a pickup apparatus / optical system. It also includes a pickup device / optical system that is intended for use.
[0118]
In the present invention, at least two wavelengths of light different from each other include, for example, two different wavelengths of light having a wavelength of 780 nm used for CD and light having a wavelength of 635 nm or 650 nm used for DVD. It may be light, or may be light of three different wavelengths further including light of a wavelength of, for example, 400 nm for recording and / or reproduction of a large-capacity information recording medium recorded with high density . Of course, it may be light of four or more different wavelengths. Of course, even an optical system that uses light of three or more wavelengths that are actually different or an optical system intended for it, it means light of at least two different wavelengths. Of course, a combination of 400 nm and 780 nm or a combination of 400 nm and 650 nm may be used.
[0119]
In the present invention, light of different wavelengths means light of a plurality of wavelengths having a sufficient wavelength difference, which is used according to the type of information recording medium and the difference in recording density as exemplified above. It does not indicate light of different wavelengths due to a temporary shift within about ± 10 nm caused by temperature change or output change of one light source that outputs light of one wavelength. In addition to the above-described differences in the types and recording densities of information recording media, for example, the differences in the thickness of the transparent substrate of the information recording media and the difference between recording and reproduction Etc.
[0120]
A diffractive surface is a surface that provides relief on the surface of an optical element, for example, the surface of a lens, and has a function of condensing or diverging a light beam by diffraction. If there is a region that does not occur, it refers to a region where diffraction occurs. As the shape of the relief, for example, it is formed as a concentric ring zone centered on the optical axis on the surface of the optical element, and each ring zone has a sawtooth shape when viewed in cross section in a plane including the optical axis. Although known, it includes such shapes.
[0121]
In general, diffracted light of infinite number of orders such as 0th order light, ± 1st order light, ± 2nd order light, etc. is generated from the diffracting surface. In this case, the diffraction efficiency of a specific order is made higher than the diffraction efficiency of other orders, or in some cases, the diffraction efficiency of a specific one order (for example, + 1st order light) is almost 100%. The shape of the relief can be set.
[0122]
The diffraction efficiency is calculated by simulation based on the ratio of the amount of diffracted light of each order to the total diffracted light based on the shape of the diffracting surface (relief shape) and the wavelength of the irradiated light set to a predetermined wavelength. Ask. Examples of the predetermined wavelength include wavelengths of 780 nm and 650 nm.
[0123]
Regarding the diffractive action (hereinafter also referred to as “diffraction power”) added to the diffractive surface of the lens, in particular, an optical element having an optical surface having a refractive action and a diffractive action, in other words, on an optical surface having a refractive action. In the case of an optical element having a diffractive surface, an effect of converging or diverging a light beam is added to the refracting function of the refracting surface as a base by the action of the diffractive surface. At this time, when a converging action is added to a light beam of an actual finite height as well as the paraxial region, in the present invention, it is assumed that a predetermined position of the diffractive surface has a positive diffractive power. It is said that it has a negative diffractive power when the action to be added is added.
[0124]
Diffraction-limited performance means that the wavefront aberration of a light beam is measured, and the root mean square (rms value) of the wavefront aberration of the entire light beam is 0.07 times or less the wavelength that is the allowable value of Marechal. Moreover, the aperture in actual use means the numerical aperture defined by the standard of each optical information recording medium, and is a spot necessary for recording or reproducing information on each optical information recording medium. This corresponds to the numerical aperture of a diffraction-limited objective lens capable of obtaining a diameter.
[0125]
Since the numerical aperture in actual use is defined for the optical information recording medium, the numerical aperture on the optical information recording medium side of the actual light beam passing through the optical system of the pickup device may be larger than the numerical aperture in actual use. .
[0126]
Moreover, it is preferable that the maximum numerical aperture means the largest numerical aperture in practical use. That is, in the case of a pickup device that is used interchangeably with a plurality of optical information recording media, a plurality of numerical apertures in actual use are defined. Further, the predetermined numerical aperture and the required numerical aperture have the same meaning as the numerical aperture in actual use.
[0127]
When recording or reproducing information with respect to the optical information recording medium, when using a light source having a wavelength different from the light source specified by the standard in an actual optical pickup device, the specified wavelength and the specified wavelength are used. The actual use numerical aperture is set so that the ratio between the numerical aperture and the ratio between the actual use wavelength and the actual use numerical aperture is constant. As an example, for a CD, the numerical aperture is 0.45 when a light source with a wavelength of 780 nm is used in the standard, but when a light source with a wavelength of 650 nm is used, the numerical aperture is 0.38.
[0128]
A dedicated objective lens designed so that a non-aberration parallel light beam enters the objective lens as described above from the first light source and converges without aberration through the transparent substrate (thickness t1) of the first optical information recording medium. , The case where non-aberration parallel light enters the objective lens from the second light source and passes through the transparent substrate (thickness t2, where t2> t1) of the second optical information recording medium will be considered.
[0129]
For the incident parallel light, when there is no substrate, the back focus when the wavelength is λ1 is fB1, and the back focus when the wavelength is λ2 (where λ2> λ1) is fB2.
[0130]
At this time, the paraxial chromatic aberration ΔfB is
ΔfB = fB2−fB1 (1)
In the case where the objective lens is a refractive aspherical single lens, ΔfB> 0.
[0131]
In addition, the spherical aberration based on the paraxial focal position when converged through the transparent substrate of the second optical information recording medium at the wavelength λ2 does not become zero due to the following factors.
(1) Spherical aberration due to the wavelength dependence of the refractive index of the objective lens due to the change of wavelength from λ1 to λ2.
(2) Spherical aberration caused by the difference between the transparent substrate thickness t1 of the first optical information recording medium and the transparent substrate thickness t2 of the second optical information recording medium.
(3) Spherical aberration caused by the difference between the transparent substrate refractive index nd1 (λ1) of the first optical information recording medium and the transparent substrate refractive index nd2 (λ2) of the second optical information recording medium.
[0132]
When the objective lens is a refractive aspherical single lens, the spherical aberration due to the factor (1) is over. The spherical aberration due to factor (2) is also over. Further, nd2 <nd1, and the spherical aberration due to the factor (3) is also over.
[0133]
The over spherical aberration caused by factors (1) to (3) is mostly due to factor (2), followed by (1). (3) can be almost ignored.
[0134]
The above premise is, for example, when the first optical information recording medium is DVD, the wavelength λ1 of the first light source is 650 nm, the second optical information recording medium is CD, and the wavelength λ2 of the second light source is 780 nm. Correspondingly, the material of the transparent substrate is the same for DVD (thickness t1 = 0.6 mm) and CD (t2 = 1.2 mm), but the thickness is different.
[0135]
Next, looking at the + 1st order diffracted light having a diffraction pattern rotationally symmetric with respect to the optical axis, as shown in FIG. 113 (a), the + 1st order light has a larger diffraction angle as the wavelength becomes longer, and the optical axis side is further increased. The light is diffracted and bent further to the underside. That is, the + 1st-order diffracted light is a case where a non-aberration parallel light beam from a second light source having a wavelength of λ2 is incident as compared to a case where a non-aberration parallel light beam from the first light source having a wavelength of λ1 is incident. , It has the effect of making paraxial chromatic aberration and spherical aberration under. Using this action, spherical aberration when the second optical information recording medium is passed through the transparent substrate at wavelength λ2 and spherical aberration when the wavelength λ1 is passed through the transparent substrate of the first optical information recording medium The difference can be reduced by introducing a rotationally symmetric diffraction pattern and utilizing the + 1st order diffracted light.
[0136]
When the thickness t1 of the substrate of the first optical information recording medium is larger than the transparent substrate thickness t2 of the second optical information recording medium, the spherical aberration due to the factor {circle around (2)} is under, and FIG. As shown in FIG. 5B, the aberration can be reduced by using −1st order diffracted light having an effect that the paraxial chromatic aberration and spherical aberration that occur are over.
[0137]
In the present invention, when + 1st order diffracted light is used, the refractive index of the objective lens material when the wavelength is λ1 is n (λ1), and the refractive index of the objective lens material when the wavelength is λ2 is n (λ2). The depth of the diffraction pattern is λ1 / {n (λ1) -1} to λ2 / {n (λ2) -1}. Even if a plastic material having a relatively small refractive index is used, it is 2 μm or less. The objective lens integrated with the diffraction pattern is easier to manufacture than the conventional hologram optical element and hologram ring lens described above.
[0138]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[0139]
The optical system of the first embodiment of the present invention is basically a double-sided aspherical single lens, and a diffraction zone (annular diffraction surface) is provided on one aspherical surface. In general, in the case of aspherical refracting surfaces, when spherical aberration is corrected with respect to a certain main wavelength light, the spherical aberration is under (undercorrected) for light with a wavelength shorter than the main wavelength light. On the other hand, in a diffractive lens that is a lens having a diffractive surface, when spherical aberration is corrected with a certain main wavelength light, it is possible to overshoot (overcorrect) the spherical aberration with a shorter wavelength than the main wavelength light. is there. Therefore, by properly selecting the aspherical coefficient of the aspherical lens by refraction and the coefficient of the phase difference function of the diffractive lens and combining the refractive power and the diffractive power, the spherical aberration is improved in both different two-wavelength light. It is possible to correct it.
[0140]
In general, the pitch of the diffraction ring zone is defined by using a phase difference function or an optical path difference function, which will be described in detail in an embodiment described later. Specifically, the phase difference function ΦB is expressed by the following [Equation 1] in units of radians, and the optical path difference function Φb is expressed by [Equation 2] in units of mm.
[0141]
[Expression 1]

[0142]
[Expression 2]

[0143]
Although these two representation methods are different in unit, they are equivalent in terms of representing the pitch of the diffraction zone. That is, if the principal wavelength λ (unit: mm) is multiplied by the phase difference function coefficient B by λ / 2π, it can be converted to the optical path difference function coefficient b, and conversely, the optical path difference function coefficient b is 2π / λ. Can be converted to the coefficient B of the phase difference function.
[0144]
For the sake of simplicity, a diffractive lens using first-order diffracted light will be described. If the optical path difference function is used, an annular zone is engraved every time the function value exceeds an integral multiple of the main wavelength λ. Each time the function value exceeds an integer multiple of 2π, an annular zone is engraved.
[0145]
For example, assuming a lens with a diffracting ring zone formed on both sides of a cylindrical object with no refractive power, the principal wavelength is 0.5 μ = 0.0005 mm, and the second order coefficient (square term) of the optical path difference function is -0.05 (-628.3 when converted to the second order coefficient of the phase difference function), when all other order coefficients are zero, the radius of the first ring zone is h = 0.1 mm, and the second wheel The band radius is h = 0.141 mm. Further, it is known that the focal length f of the diffractive lens is f = −1 / (2 · b2) = 10 mm with respect to the second-order coefficient b2 = −0.05 of the optical path difference function.
[0146]
Now, based on the above definition, the chromatic aberration in the so-called paraxial region close to the optical axis can be corrected by setting the second-order coefficient of the phase difference function or the optical path difference function to a non-zero value. Further, spherical aberration between two wavelengths is obtained by setting non-secondary coefficients of the phase difference function or the optical path difference function, for example, fourth-order coefficients, sixth-order coefficients, eighth-order coefficients, tenth-order coefficients, and the like to non-zero values. Can be controlled. Here, controlling means that the difference in spherical aberration between the two wavelengths can be made extremely small, and the difference necessary for the optical specifications can be provided.
[0147]
As a specific application described above, when collimated light (parallel light) from two light sources having different wavelengths is simultaneously incident on the objective lens and imaged on the optical disk, first, the phase difference function or the optical path difference function of 2 is used. Corrects paraxial axial chromatic aberration using the second order coefficient, and reduces the difference between the two wavelengths of spherical aberration to within the allowable range using the fourth and subsequent coefficients of the phase difference function or optical path difference function. Is good.
[0148]
As another example, a single objective lens is used for light from two light sources having different wavelengths, and the aberration is corrected for a disk having a thickness of t1 (thickness of the transparent substrate) for light of one wavelength. Let us consider a case where the specification is such that the aberration is corrected for a disk having a thickness of t2 with respect to the light of the other wavelength. In this case, the difference between the two wavelengths of the spherical aberration is provided mainly by using the fourth and subsequent coefficients of the phase difference function or the optical path difference function, and for each thickness, the spherical aberration is different at each wavelength. It can be corrected. In either case, it is easier to correct aberrations between two wavelengths when the refractive surface is aspherical than spherical.
[0149]
The above-mentioned aspherical refracting surfaces have different refractive powers for different wavelengths and different condensing points, so that each condensing point can correspond to an optical disc having a different substrate thickness. In this case, the shorter light source wavelength is 700 nm or less, the longer light source wavelength is 600 nm or more, and the wavelength difference is preferably 80 nm or more. Further, the wavelength difference is more preferably 400 nm or less, and further preferably, the wavelength difference is 100 nm or more and 200 nm or less, and the diffractive surface is diffracted at a substantially intermediate wavelength with respect to two different wavelength lights. Although it is desirable that the efficiency is maximum, it may have the maximum diffraction efficiency at either one of the wavelengths.
[0150]
By utilizing the same action as the correction of the spherical aberration, a diffractive ring zone lens is provided on the optical surface, and axial chromatic aberration is caused by one diffracted light of the same order for each of two different wavelength light sources. It can be corrected. That is, the axial chromatic aberration for the light of two different wavelength light sources is ± λ / (2NA²) Can be corrected. Where λ is the longer wavelength of the two wavelengths, and NA is the image-side numerical aperture corresponding to the longer wavelength.
[0151]
Further, when the wavelength difference between the two different wavelength light sources is 80 nm or more and the Abbe number of the glass material of the objective lens is νd,
νd> 50 (1)
It is desirable to satisfy The condition (1) is a condition for reducing the secondary spectrum when axial chromatic aberration is corrected for light sources having two different wavelengths.
[0152]
Next, when a diffractive surface is provided on one surface of a thin single lens, this entire lens is considered as a combination of a refracting lens and a diffractive surface as a base with the diffraction relief removed. The chromatic aberration of the lens is examined. The achromatic condition at a certain wavelength λx and wavelength λy (λx <λy) is as follows.
[0153]
fR · νR + fD · νD = 0
Where fR and fD are the refractive lens and the focal length of the diffractive surface, respectively.
νR and νD: Abbe numbers of the refractive lens and the diffractive surface, respectively, which are determined by the following equations.
.nu.R = (n0-1) / (nx-ny)
νD = λ0 / (λx -λy)
[0154]
Where n0: refractive index at the reference wavelength, λ0: reference wavelength
[0155]
At this time, the chromatic aberration δf for a certain wavelength λz is expressed by the following equation.
δf = f (θR−θD) / (νR−νD) (2)
However, θR and θD are respectively determined by the following equations with partial dispersion ratios of the refractive lens and the diffraction surface.
[0156]
θR = (nx -nz) / (nx -ny)
[0157]
θD = (λx −λz) / (λx −λy)
Where nz: refractive index at wavelength λz
[0158]
As an example, λ0 = λx = 635 nm, λy = 780 nm, λz = 650 nm, and the glass material of the refractive lens serving as the base is assumed to be Hoya BSC7 (νd = 64.2).
νR = 134.5, νD = −4.38, θR = 0.128, θD = 0.103, and δf = 0.18 × 10^-3f.
[0159]
In addition, when changing the glass material of the base refractive lens to Hoya E-FD1 (νd = 29.5),
νR = 70.5, θR = 0.136, and δf = 0.44 × 10^-3f.
[0160]
Thus, in the expression (2), the right-side denominator (νR −νD) is sufficiently smaller than | νD | because | νD | is smaller than | νR |. The change in νR is dominant. On the other hand, θR and θD are determined only by the wavelength, and the contribution of the change in the numerator on the right side (θR −θD) is smaller than that in the denominator on the right side (νR −νD).
[0161]
From the above, it can be seen that, in a lens having a diffractive surface, it is effective to select a material having a large Abbe number ν R as the material of the refractive lens in order to keep the secondary spectrum δf small. Conditional expression (1) indicates an effective limit for suppressing the secondary spectrum so as to cope with a wavelength change of the light source.
[0162]
Further, when achromatic lenses are bonded together by using two types of refractive lenses without using a diffractive surface, θR = a + b · νR + ΔθR (a and b are constants) are shown for each material. Then, ΔθR is small and if there is no anomalous dispersion, the secondary spectrum δf does not depend on the Abbe number νR of the two refractive lenses. Therefore, it can be seen that the expression (1) is a condition specific to the diffractive optical system.
[0163]
In order to easily manufacture the diffractive lens of the present embodiment, it is desirable that the objective lens is made of a plastic material. As the plastic material satisfying the conditional expression (1), an acrylic type or a polyolefin type is used, but a polyolefin type is preferable from the viewpoint of moisture resistance, heat resistance and the like.
[0164]
Next, the objective lens according to the second embodiment of the present invention and the configuration of the optical pickup device including the objective lens will be specifically described.
[0165]
FIG. 48 shows a schematic configuration diagram of the optical pickup device of the present embodiment. An optical disc 20 that is an optical information recording medium for recording and / or reproducing information by an optical pickup device includes a first optical disc (eg, DVD) and a second optical disc (eg, next-generation high-density optical disc using a blue laser) having a transparent substrate thickness t1. And a third optical disk (for example, a CD) having a transparent substrate thickness t2 different from t1 will be described. Here, the thickness t1 = 0.6 mm and t2 = 1.2 mm of the transparent substrate.
[0166]
The illustrated optical pickup device includes a first semiconductor laser 11 (wavelength λ) as a first light source as a light source.₁= 610 nm to 670 nm) and the blue laser 12 (wavelength λ) as the second light source₂= 400 nm to 440 nm) and the second semiconductor laser 13 (wavelength λ) as the third light source₃= 740 nm to 870 nm) and the objective lens 1 as part of the optical system. The first light source, the second light source, and the third light source are selectively used according to the optical disc on which information is recorded and / or reproduced.
[0167]
The divergent light beams emitted from the first semiconductor laser 11, the blue laser 12, or the second semiconductor laser 13 are transmitted through the transparent substrate 21 of the optical disk 20 through the beam splitter 19 and the diaphragm 3, and each information is obtained by the objective lens 1. The light is condensed on the recording surface 22 to form a spot.
[0168]
Incident light from each laser becomes reflected light modulated by information pits on the information recording surface 22, enters the common photodetector 30 via the beam splitter 18 and toric lens 29, and uses the output signal thereof. A read signal, a focus detection signal, and a track detection signal for information recorded on the optical disc 20 are obtained.
[0169]
In addition, the diaphragm 3 provided in the optical path is a diaphragm having a fixed numerical aperture (NA 0.65) in this example, and does not require an extra mechanism and can realize cost reduction. The numerical aperture of the diaphragm 3 may be variable so that unnecessary light (NA 0.45 or more) can be removed during recording and / or reproduction of the third optical disk.
[0170]
By forming an annular filter integrally on the optical surface of the objective lens 1 so as to shield a part of the light beam outside the actual use aperture, flare light outside the actual use aperture can be easily removed with an inexpensive configuration. It is also possible to do.
[0171]
When using a finite conjugate optical system as in this embodiment, the relationship between the light source and the condensing optical system must be kept constant in order to maintain the condensing performance. It is desirable to move the light sources 11, 12, and 13 and the objective lens 1 as one unit.
[0172]
Next, the objective lens according to the third embodiment of the present invention and the configuration of the optical pickup device including the objective lens will be specifically described.
[0173]
FIG. 49 shows a schematic configuration diagram of the optical pickup device of the present embodiment. The optical pickup device of FIG. 49 is an example using a laser / detector integrated unit 40 in which a laser, a photodetector, and a hologram are unitized, and the same components as in FIG. In this optical pickup device, the first semiconductor laser 11, the blue laser 12, the first light detection means 31, the second light detection means 32, and the hologram beam splitter 23 are unitized as a laser / detector integrated unit 40. Yes.
[0174]
When reproducing the first optical disk, the light beam emitted from the first semiconductor laser 11 passes through the hologram beam splitter 23, is narrowed down by the diaphragm 3, and information is transmitted through the transparent substrate 21 of the first optical disk 20 by the objective lens 1. The light is condensed on the recording surface 22. Then, the light beam modulated and reflected by the information pits on the information recording surface 22 is diffracted again on the disk side surface of the hologram beam splitter 23 through the objective lens 1 and the diaphragm 3, and the first light beam corresponding to the first semiconductor laser 11 is diffracted. 1 is incident on the photodetector 31. Then, using the output signal of the first optical detector 31, a read signal of information recorded on the first optical disc 20, a focus detection signal, and a track detection signal are obtained.
[0175]
When reproducing the second optical disk, the light beam emitted from the blue laser 12 is diffracted on the laser side surface of the hologram beam splitter 23 and takes the same optical path as the light beam from the first semiconductor laser 11 described above. That is, the surface of the hologram beam splitter 23 on the semiconductor laser side functions as a light combining unit. Further, the light is condensed on the information recording surface 22 through the transparent substrate 21 of the second optical disk 20 through the diaphragm 3 and the objective lens 1. Then, the light beam modulated and reflected by the information pits on the information recording surface 22 is diffracted again on the disk side surface of the hologram beam splitter 23 via the objective lens 1 and the diaphragm 3, and the second light beam corresponding to the blue laser 12 is obtained. The light is incident on the photodetector 32. Then, using the output signal of the second photodetector 32, a read signal, a focus detection signal, and a track detection signal for information recorded on the second optical disc 20 are obtained.
[0176]
Further, when reproducing the third optical disk, a laser / detector integrated unit 41 in which the second semiconductor laser 13, the third light detection means 33, and the hologram beam splitter 24 are unitized is used. The light beam emitted from the second semiconductor laser 13 passes through the hologram beam splitter 24, is reflected by the beam splitter 19 that is a synthesis means of the emitted light, is narrowed down by the diaphragm 3, and is transparent by the objective lens 1 on the transparent substrate 21 of the optical disk 20. Is condensed on the information recording surface 22. The light beam modulated and reflected by the information pits on the information recording surface 22 is again diffracted by the hologram beam splitter 24 via the objective lens 1, the diaphragm 3 and the beam splitter 19, and is incident on the third photodetector 33. To do. Then, using the output signal of the third photodetector 33, a read signal, a focus detection signal, and a track detection signal for information recorded on the third optical disc 20 are obtained.
[0177]
In the optical pickup devices of the second and third embodiments, an annular diffractive surface concentric with the optical axis 4 is formed on the aspherical refracting surface of the objective lens 1. In general, when an objective lens is composed only of an aspheric refracting surface, when spherical aberration is corrected for a certain wavelength λa, the spherical aberration becomes under for a wavelength λb shorter than λa. On the other hand, when the diffractive surface is used, when the spherical aberration is corrected for a certain wavelength λa, the spherical aberration is over for a wavelength λb shorter than λa. Therefore, it is possible to correct spherical aberration between different wavelengths by combining the refractive power and the diffraction power by appropriately selecting the aspherical optical design by the refractive surface and the phase difference function coefficient of the diffraction surface. Become. On the aspherical refracting surface, when the wavelength is different, the refractive power is changed and the condensing position is also different. Therefore, by appropriately designing the aspherical refracting surface, it is possible to focus on the information recording surface 22 of each transparent substrate 21 even for different wavelengths.
[0178]
In the objective lens 1 of the second and third embodiments, the first semiconductor laser 11, the blue laser 12, or the first laser diode 11 is designed by appropriately designing the phase difference function of the aspherical refracting surface and the annular diffractive surface. (2) The spherical aberration generated due to the difference in the thickness of the transparent substrate 21 of the optical disk 20 is corrected for each light beam emitted from the semiconductor laser 13. Further, in the annular diffractive surface, the chromatic aberration of the spherical aberration can be corrected by using the coefficient of the term after the fourth power of the power series as the phase difference function representing the position of the annular zone. For the third optical disc (CD), the actual opening is NA 0.45. In the third optical disc, spherical aberration is corrected within NA 0.45, and spherical aberration in the area outside NA 0.45 is used as flare. Yes. With these corrections, the aberration of the focused spot on the information recording surface 22 is approximately the same as or less than the diffraction limit (0.07λrms) for each optical disc 20.
[0179]
The optical pickup devices of the second and third embodiments as described above are, for example, CD, CD-R, CD-RW, CD-Video, CD-ROM, DVD, DVD-ROM, DVD-RAM, DVD- Compatible with any two or more different optical information recording media such as R, DVD-RW, MD, etc., players, drives, etc., or AV equipment, personal computers, and other information incorporating them It can be mounted on a voice and / or image recording device such as a terminal and / or a voice and / or image playback device.
[0180]
Next, the objective lens according to the fourth embodiment of the present invention and the configuration of the optical pickup device including the objective lens will be specifically described.
[0181]
FIG. 67 is a schematic configuration diagram of the optical pickup device 10 of the present embodiment. In FIG. 67, the same reference numerals may be used for members common to the second and third embodiments. In FIG. 67, an optical pickup device 10 records / reproduces a plurality of optical disks 20 which are optical information recording media. Hereinafter, the plurality of optical disks 20 have a first optical disk (DVD) and a second optical disk (blue laser next-generation high-density optical disk) having a transparent substrate thickness t1, and a transparent substrate thickness t2 different from t1. The third optical disk (CD) will be described. Here, the thickness t1 = 0.6 mm and t2 = 1.2 mm of the transparent substrate.
[0182]
The optical pickup device 10 includes a first semiconductor laser 11 (wavelength λ) as a first light source as a light source.₁= 610 nm to 670 nm) and the blue laser 12 (wavelength λ) as the second light source₂= 400 nm to 440 nm) and the second semiconductor laser 13 (wavelength λ) as the third light source₃= 740 nm to 870 nm). These first light source, second light source and third light source are used exclusively according to the optical disc to be recorded / reproduced.
[0183]
The condensing optical system 5 condenses the light beam emitted from the first semiconductor laser 11, the blue laser 12, or the second semiconductor laser 13 on each information recording surface 22 via the transparent substrate 21 of the optical disk 20. , Means for forming spots. In the present embodiment, as the condensing optical system 5, the collimator lens 2 that converts the light beam emitted from the light source into parallel light (may be substantially parallel), and the light beam that has been converted into parallel light by the collimator lens 2 is collected. An objective lens 1.
[0184]
An annular diffractive surface concentric with the optical axis 4 is formed on both surfaces of the objective lens 1. In general, when the condensing optical system 5 is configured with only an aspherical refracting surface, when the spherical aberration is corrected for a certain wavelength λa, the spherical aberration becomes under for a wavelength λb shorter than λa. On the other hand, when the diffractive surface is used, when the spherical aberration is corrected for a certain wavelength λa, the spherical aberration is over for a wavelength λb shorter than λa. Therefore, it is possible to correct spherical aberration between different wavelengths by combining the refractive power and the diffraction power by appropriately selecting the aspherical optical design by the refractive surface and the phase function coefficient of the diffraction surface. . On the aspherical refracting surface, when the wavelength is different, the refractive power is changed and the condensing position is also different. Therefore, by appropriately designing the aspherical refracting surface, it is possible to focus on the information recording surface 22 of each transparent substrate even for different wavelengths.
[0185]
In the ring-shaped diffraction surface, aberration correction is performed on each light beam emitted from the first semiconductor laser 11, the blue laser 12, or the second semiconductor laser 13 using first-order diffracted light. Corresponding diffracted light of the same order causes less light loss than when corresponding diffracted light of different orders, and moreover, when using first-order diffracted light, the loss of light is less than corresponding to higher-order diffracted light. Less is. Therefore, the objective lens 1 of the present embodiment is effective in an optical pickup device that records information on an optical disk that records high-density information such as a DVD-RAM. Further, although it is desirable that the diffraction surface has the maximum diffraction efficiency at the intermediate wavelength for light of three different wavelengths, the diffraction surface may have the maximum diffraction efficiency at both wavelengths.
[0186]
Further, by appropriately designing the aspherical refracting surface and the phase difference function of the ring-shaped diffractive surface, the optical disc 20 can be applied to each light beam emitted from the first semiconductor laser 11, the blue laser 12, or the second semiconductor laser 13. The spherical aberration caused by the difference in thickness of the transparent substrate 21 is corrected. Further, in the phase difference function representing the position of the annular zone formed on the objective lens 1, the chromatic aberration of the spherical aberration can be corrected by using the coefficient of the term after the fourth power of the power series. For the third optical disc (CD), the aperture in actual use is NA 0.45, the spherical aberration is corrected within NA 0.45, and the spherical aberration in the region outside NA 0.45 is flare. A light beam passing through an area within NA 0.45 forms a light spot on the information recording surface, and flare light passing outside the NA 0.45 is spaced from the light spot on the information recording surface so as not to adversely affect it. Pass through. With these corrections, the aberration of the focused spot on the information recording surface 22 is approximately the same as or less than the diffraction limit (0.07λrms) for each optical disc 20.
[0187]
In the present embodiment, the diaphragm 3 provided in the optical path has a fixed numerical aperture (NA 0.65), and does not require an extra mechanism, so that the cost can be reduced. The numerical aperture of the diaphragm 3 may be variable so that unnecessary light (NA 0.45 or more) can be removed during recording / reproduction of the third optical disk. The beam splitters 6 and 7 are for aligning the optical axes of the respective laser beams. As is well known, a photodetector (not shown) may be provided for each light source, and a single photodetector may receive reflected light corresponding to the three light sources 11, 12, and 13. Also good.
[0188]
Next, an objective lens according to a fifth embodiment of the present invention will be described.
[0189]
In the present embodiment, the objective of the fourth embodiment described above is only used in that the phase difference function representing the position of the annular zone uses the coefficient of the power-square term in the annular diffraction surface of the objective lens. Unlike a lens, this makes it possible to correct axial chromatic aberration. Further, according to the objective lens of the present embodiment, the aberration of the focused spot on the information recording surface 22 is substantially the same as the diffraction limit (0.07λrms) for each optical disc 20 as in the fourth embodiment. It is about or below.
[0190]
Next, an optical pickup device according to a sixth embodiment of the present invention will be described.
[0191]
In the optical pickup device of the present embodiment, the light beam emitted from the light source is made parallel by the coupling lens with respect to the first optical disk (for example, DVD) and the second optical disk (for example, the next generation high-density optical disk using blue laser). For the third optical disc (for example, CD), the light beam emitted from the light source is diverged by the coupling lens and condensed by the objective lens. The thickness of the transparent substrate 21 of the first and second optical disks is 0.6 mm, and the thickness of the transparent substrate 21 of the third optical disk is 1.2 mm.
[0192]
In the present embodiment, the spherical aberration of both the first optical disc and the second optical disc is corrected within the diffraction limit by the effect of the diffraction surface, and the disc thickness of the third optical disc is larger than that of the first and second optical discs. Is canceled by spherical aberration caused by the divergent light beam incident on the objective lens, and a predetermined numerical aperture NA required for recording / reproduction of the third optical disk, for example, NA 0.5 or NA 0.45 or less. Is corrected within the diffraction limit.
[0193]
Therefore, λ₁, Λ₂, Λ₃(Λ₁<Λ₂<Λ₃) Where NA1, NA2, and NA3 are predetermined numerical apertures required for recording / reproducing with respect to the optical information recording medium corresponding to each wavelength in the range of NA1. Aberration RMS is 0.07λ₁Hereinafter, 0.07λ in the range of NA2.₂Hereinafter, 0.07λ in the range of NA3₂After
It can be corrected below.
[0194]
For the third optical disk, it is not preferable that the beam spot diameter becomes too small due to the light flux having a numerical aperture NA larger than a predetermined numerical aperture NA. Therefore, it is preferable to make the spherical aberration flare at a numerical aperture larger than the required numerical aperture as in the fourth embodiment.
[0195]
The optical pickup devices of the fourth to sixth embodiments having the three light sources with different wavelengths as described above are, for example, CD, CD-R, CD-RW, CD-Video, CD-ROM, DVD, DVD- Compatible player or drive for any two or more different optical information recording media such as ROM, DVD-RAM, DVD-R, DVD-RW, MD, etc., or AV equipment incorporating them It can be mounted on a sound and / or image recording device and / or a sound and / or image reproducing device such as a personal computer or other information terminal.
[0196]
【Example】
Examples of the objective lens according to the present invention will be described below.
<Examples 1-8>
[0197]
The objective lenses of Examples 1 to 8 are specific examples of the objective lens according to the first embodiment, and have an aspheric shape expressed by the following [Equation 3] on the refractive surface.
[0198]
[Equation 3]

[0199]
However, Z is an axis in the optical axis direction, h is an axis perpendicular to the optical axis (height from the optical axis: the light traveling direction is positive), R0 is a paraxial radius of curvature, κ is a conical coefficient, A Is the aspheric coefficient, and 2i is the power of the aspheric surface. In Examples 1 to 3 and 6 to 8, the diffractive surface is expressed by [Equation 1] as a phase difference function ΦB in which the unit is radians. Similarly, in Examples 4 and 5, the diffractive surface has an optical path in which the unit is mm. The difference function Φb is expressed by [Equation 2].
[0200]
[Expression 1]

[0201]
[Expression 2]

[0202]
(Example 1)
[0203]
FIG. 1 shows an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is the objective lens of Example 1. FIG. 2 is a spherical aberration diagram up to numerical aperture 0.60 with respect to λ = 635 nm for the diffractive optical lens of Example 1. FIG. FIGS. 3 and 4 show spherical aberration diagrams up to numerical apertures 0.45 and 0.60 with respect to the wavelength λ = 780 nm for the diffractive optical lens of Example 1, respectively. The diffractive optical lens of FIG. 1 has a blazed concentric annular zone diffraction part on the entire lens surface, but the relief shape of the diffraction part is omitted in the drawing. Also, the relief shape of the diffractive portion is omitted in many subsequent drawings.
[0204]
According to the diffractive optical lens of Example 1, as shown in FIG. 2, the entire aperture up to NA 0.60 is almost no aberration with respect to the wavelength λ = 635 nm. Further, as shown in FIG. 3, for the wavelength λ = 780 nm, there is almost no aberration up to NA0.45 which is the actual use range. As for the portion of NA 0.45 to 0.60 on the outside, the spherical aberration is largely under and flare as shown in FIG. This makes it possible to obtain an appropriate spot diameter for the wavelength λ = 780 nm.
[0205]
5 and 6 show wavefront aberration diagrams with respect to λ = 635 nm and wavelength λ = 780 nm for the diffractive optical lens of Example 1, respectively. As can be seen from these figures, according to the diffractive optical lens of Example 1, for any wavelength, there is almost no aberration on the optical axis, and practically no aberration at an image height of 0.03 mm. It has become.
[0206]
The lens data of Example 1 is shown below. In [Table 1], R is a radius of curvature, d is a surface separation, n is a refractive index at a dominant wavelength, and ν is an Abbe number.
[0207]
Example 1
[0208]
When the light source wavelength is λ1 = 635 nm
Focal length f1 = 3.34 Numerical aperture NA1 = 0.60 Infinite specification
[0209]
When the light source wavelength is λ2 = 780 nm
Focal length f2 = 3.36 Numerical aperture NA2 = 0.45 Infinite specification
[0210]
In the present embodiment, the + 1st order diffracted light is generated more in the λ1 light beam than the other order diffracted light, and the + 1st order diffracted light is generated in the λ2 light beam more than the other order diffracted light. . If the diffraction efficiency of + 1st order diffracted light with respect to λ1 is 100%, the diffraction efficiency with respect to λ2 is 84%. If the diffraction efficiency of the + 1st order diffracted light with respect to λ2 is 100%, the diffraction efficiency with respect to λ1 is 89%.
[0211]
[Table 1]

[0212]
Aspheric coefficient
Aspherical surface 1
κ = −0.17021
A4 = -0.30032315
A6 = -0.050005160
A8 = −4.6316 × 10^-5
A10 = −3.77988 × 10^-5
A12 = −6.0308 × 10^-6
Aspherical surface 2
κ = −11.653
A4 = 0.038456
A6 = -0.020800
A8 = 0.0078648
A10 = −0.00001943
A12 = 0.00024343
[0213]
Diffraction surface coefficient
B2 = -96.766
B4 = -2.9950
B6 = 2.1306
B8 = -0.1614
B10 = −0.095285
[0214]
(Example 2, Example 3)
[0215]
Next, Example 2 and Example 3 will be described. 7 and 8 show optical path diagrams for λ = 405 nm and 635 nm of the diffractive optical lens that is the objective lens of Example 2, respectively. FIGS. 9 and 10 show spherical aberration diagrams of the diffractive optical lens of Example 2 up to numerical aperture 0.60 for λ = 405 nm and 635 nm, respectively. FIGS. 11 and 12 show wavefront aberration diagrams with respect to wavelengths λ = 405 nm and 635 nm, respectively, for the diffractive optical lens of Example 2. FIGS.
[0216]
FIGS. 13 and 14 show optical path diagrams with respect to λ = 405 nm and 635 nm of the diffractive optical lens which is the objective lens of Example 3, respectively. FIGS. 15 and 16 show spherical aberration diagrams up to a numerical aperture of 0.60 with respect to λ = 405 nm and 635 nm for the diffractive optical lens of Example 3, respectively. 17 and 18 show wavefront aberration diagrams with respect to wavelengths λ = 405 nm and 635 nm, respectively, for the diffractive optical lens of Example 3. FIG.
[0217]
In Examples 2 and 3, with respect to the wavelength λ = 405 nm and the wavelength λ = 635 nm, the substrate thickness is both 0.6 mm, the NA is 0.60, the wavefront aberration is almost no aberration on the optical axis, and the image height is 0. Even at 0.03 mm, the level is practically close to no aberration.
[0218]
The lens data of Examples 2 and 3 are shown below.
[0219]
Example 2
[0220]
When the light source wavelength is λ1 = 405 nm
Focal length f1 = 3.23 Numerical aperture NA1 = 0.60 Infinite specification
[0221]
When the light source wavelength is λ2 = 635 nm
Focal length f2 = 3.34 Numerical aperture NA2 = 0.60 Infinite specification
[0222]
In the present embodiment, the + 1st order diffracted light is generated more in the λ1 light beam than the other order diffracted light, and the + 1st order diffracted light is generated in the λ2 light beam more than the other order diffracted light. .
[0223]
[Table 2]

[0224]
Aspheric coefficient
Aspherical surface 1
κ = −0.15079
A4 = -0.000021230
A6 = -0.0067528
A8 = −8.84957 × 10^-5
A10 = −3.48803 × 10^-5
A12 = -2.38916 × 10^-6
Aspherical surface 2
κ = −3.8288
A4 = 0.036962
A6 = -0.020858
A8 = 0.0007732
A10 = −0.00001813
A12 = 0.00022504
[0225]
Diffraction surface coefficient
B2 = 0.0
B4 = -6.7169
B6 = 2.0791
B8 = -0.31970
B10 = 0.0016708
[0226]
Example 3
[0227]
When the light source wavelength is λ1 = 405 nm
Focal length f1 = 3.31 Numerical aperture NA1 = 0.60 Infinite specification
[0228]
When the light source wavelength is λ2 = 635 nm
Focal length f2 = 3.34 Numerical aperture NA2 = 0.60 Infinite specification
[0229]
In the present embodiment, the + 1st order diffracted light is generated more in the λ1 light beam than the other order diffracted light, and the + 1st order diffracted light is generated in the λ2 light beam more than the other order diffracted light. .
[0230]
[Table 3]

[0231]
Aspheric coefficient
Aspherical surface 1
κ = −0.109029
A4 = 0.0030538
A6 = -0.00001019
A8 = −7.5747 × 10^-5
A10 = −6.7599 × 10^-5
A12 = −3.3788 × 10^-6
Aspherical surface 2
κ = 6.4430
A4 = 0.037045
A6 = -0.021474
A8 = 0.0078175
A10 = −0.00001664
A12 = 0.0014332
[0232]
Diffraction surface coefficient
B2 = -96.766
B4 = -2.9950
B6 = -0.25560
B8 = -0.08789
B10 = 0.014562
[0233]
(Example 4, Example 5)
[0234]
Next, Example 4 and Example 5 in which chromatic aberration correction is performed will be described. FIG. 19 shows optical path diagrams of the diffractive optical lens that is the objective lens of Example 4. FIG. 20 shows spherical aberration diagrams up to numerical aperture 0.50 for λ = 635 nm, 650 nm and 780 nm for the diffractive optical lens of Example 4. FIG. 21 shows optical path diagrams of the diffractive optical lens that is the objective lens of Example 5. FIG. 22 shows spherical aberration diagrams up to numerical aperture 0.50 for λ = 635 nm, 650 nm and 780 nm for the diffractive optical lens of Example 5.
[0235]
As can be seen from FIGS. 20 and 22, according to the diffractive optical lenses of Examples 4 and 5, for the wavelength λ = 635 nm and the wavelength λ = 780 nm, the color shift is almost completely corrected, and the wavelength λ = 650 nm. However, it has been corrected to such a degree that there is no practical problem at all.
[0236]
The lens data of Examples 4 and 5 are shown below.
[0237]
Example 4
[0238]
When the light source wavelength is λ1 = 635 nm
Focal length f1 = 3.40 Numerical aperture NA1 = 0.50 Infinite specification
[0239]
When the light source wavelength is λ2 = 780 nm
Focal length f2 = 3.41 Numerical aperture NA2 = 0.50 Infinite specification
[0240]
In the present embodiment, the + 1st order diffracted light is generated more in the λ1 light beam than the other order diffracted light, and the + 1st order diffracted light is generated in the λ2 light beam more than the other order diffracted light. .
[0241]
[Table 4]

[0242]
Aspheric coefficient
Aspherical surface 1
κ = −0.53245
A4 = 0.24033 × 10^-2
A6 = -0.91472 × 10^-3
A8 = 0.1590 × 10^-4
A10 = −0.111131 × 10^-3
Aspherical surface 2
κ = 7.3988
A4 = 0.90408 × 10^-2
A6 = −0.17044 × 10^-2
A8 = -0.47368 × 10^-3
A10 = 0.16891 × 10^-3
[0243]
Diffraction surface coefficient
b2 = −0.36764 × 10^-2
b4 = -0.912727 × 10^-4
b6 = −0.39033 × 10^-4
b8 = 0.77745 × 10^-5
b10 = −0.175050 × 10^-5
[0244]
Example 5
[0245]
When the light source wavelength is λ1 = 635 nm
Focal length f1 = 3.40 Numerical aperture NA1 = 0.50 Infinite specification
[0246]
When the light source wavelength is λ2 = 780 nm
Focal length f2 = 3.40 Numerical aperture NA2 = 0.50 Infinite specification
[0247]
In the present embodiment, the + 1st order diffracted light is generated more in the λ1 light beam than the other order diffracted light, and the + 1st order diffracted light is generated in the λ2 light beam more than the other order diffracted light. .
[0248]
[Table 5]

[0249]
Aspheric coefficient
Aspherical surface 1
κ = −0.17006
A4 = -0.35633 × 10^-2
A6 = -0.45199 × 10^-3
A8 = 0.58811 × 10^-5
A10 = −0.13022 × 10^-4
Aspherical surface 2
κ = −40.782
A4 = 0.73447 × 10^-2
A6 = 0.885177 × 10^-3
A8 = −0.82795 × 10^-3
A10 = 0.203029 × 10^-3
[0250]
Diffraction surface coefficient
b2 = −0.74641 × 10^-2
b4 = 0.1193x10^-2
b6 = −0.885257 × 10^-3
b8 = 0.50517 × 10^-3
b10 = −0.11242 × 10^-3
[0251]
(Examples 6 to 8)
[0252]
Next, Examples 6 to 8 will be described. 23, 30 and 37 show optical path diagrams for λ = 650 nm of the diffractive optical lens which is the objective lens of Examples 6 to 8, respectively. FIGS. 24, 31 and 38 show optical path diagrams for λ = 780 nm (NA = 0.5) of the diffractive optical lenses of Examples 6 to 8, respectively. FIGS. 25, 32, and 39 show spherical aberration diagrams up to numerical aperture 0.60 with respect to λ = 650 ± 10 nm for the diffractive optical lenses of Examples 6 to 8, respectively. FIGS. 26, 33, and 40 show spherical aberration diagrams up to numerical aperture 0.50 with respect to λ = 780 ± 10 nm for the diffractive optical lenses of Examples 6 to 8, respectively. FIGS. 27, 34, and 41 show spherical aberration diagrams up to a numerical aperture of 0.60 with respect to λ = 780 nm for the diffractive optical lenses of Examples 6 to 8, respectively.
[0253]
28, 35 and 42 show wavefront aberration rms diagrams for λ = 650 nm for the diffractive optical lenses of Examples 6 to 8, respectively. 29, 36, and 43 show wavefront aberration rms diagrams with respect to λ = 780 nm for the diffractive optical lenses of Examples 6 to 8, respectively. 44, 45 and 46 are graphs showing the relationship between the number of diffractive ring zones and the height from the optical axis for the diffractive optical lenses of Examples 6 to 8, respectively. Here, the number of diffraction ring zones is defined as a value obtained by dividing the phase difference function by 2π.
[0254]
In Examples 6 to 8, as shown in the spherical aberration diagram, the entire aperture up to NA 0.60 is almost no aberration with respect to the wavelength λ = 650 nm. In addition, for the wavelength λ = 780 nm, there is almost no aberration up to the actual use range of NA 0.50, but the outer portion of NA 0.50 to 0.60 has large spherical aberration and flare. It has become. This makes it possible to obtain an appropriate spot diameter for the wavelength λ = 780 nm.
[0255]
The lens data of Examples 6 to 8 will be shown below. In [Table 6] to [Table 8] and [Table 15] to [Table 18], STO represents an aperture, and IMA represents an image plane, which is expressed in a form including the aperture. OBJ represents an object point (light source), and the same applies to the following tables.
[0256]
Example 6
[0257]
When the light source wavelength is λ = 650 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.60 Infinite specification
[0258]
When the light source wavelength λ = 780 nm
Focal length f = 3.37 Image-side numerical aperture NA = 0.50 (NA = 0.60) Infinite specification
w (beam diameter of 13.5% intensity on the imaging surface of the light beam of 780 nm) = 1.20 μm
[0259]
In the present embodiment, as shown in FIG. 44, in the central portion where the height from the optical axis is about half or less of the effective diameter in both the light flux of λ1 and the light flux of λ2, the −1st order diffracted light is changed to other orders. The + 1st order diffracted light is generated more than the other orders of diffracted light at the peripheral portion where the height from the optical axis is about half or more of the effective diameter. However, in this embodiment, the annular zone pitch may be multiplied by an integer to generate higher-order homogeneous diffraction light instead of ± first-order diffracted light.
[0260]
In this example, as shown in FIG. 27, in the second optical information recording medium, when NA1 = 0.6, the spherical aberration is +29 μm, and when NA2 = 0.5, the spherical aberration is +1 μm.
In the present embodiment, the pitch of the diffractive portions at a numerical aperture (NA) of 0.4 is 14 μm.
[0261]
[Table 6]

[0262]
Aspheric coefficient
Aspherical surface 1
κ = −1.07952
A4 = 0.51919725 × 10^-2
A6 = 0.10888861 × 10^-2
A8 = −0.443686519 × 10^-3
A10 = 5.40553137 × 10^-5
Aspherical surface 2
κ = −3,452929
A4 = 0.15591292 × 10^-1
A6 = −0.4528738 × 10^-2
A8 = 0.6542404 × 10^-3
A10 = −4.7769992 × 10^-5
[0263]
Diffraction surface coefficient
B2 = 29.443104
B4 = -14.403683
B6 = 3.9425951
B8 = -2.471955
B10 = 0.31859248
[0264]
Example 7
[0265]
When the light source wavelength is λ = 650 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.60 Infinite specification
[0266]
When the light source wavelength λ = 780 nm
Focal length f = 3.37 Image-side numerical aperture NA = 0.50 (NA = 0.60) Finite specification
[0267]
As shown in FIG. 45, the present embodiment generates more + 1st order diffracted light than the other orders of diffracted light over the entire surface of both the light flux of λ1 and the light flux of λ2. However, in this embodiment, the annular zone pitch may be multiplied by an integer to generate higher-order same-order diffracted light instead of + 1st-order diffracted light.
[0268]
[Table 7]

[0269]
Aspheric coefficient
Aspherical surface 1
κ = −1.801329
A4 = 0.161522 × 10^-1
A6 = −0.4937969 × 10^-3
A8 = 0.11038322 × 10^-3
A10 = −2.1823306 × 10^-5
Aspherical surface 2
κ = −8.8871647
A4 = 0.1492951 × 10^-1
A6 = −0.4447445 × 10^-2
A8 = 0.60067143 × 10^-3
A10 = −3.4684206 × 10^-5
[0270]
Diffraction surface coefficient
B2 = -17.150237
B4 = -4.1227045
B6 = 1.1902249
B8 = -0.2620202222
B10 = 0.0188845315
[0271]
Example 8
[0272]
When the light source wavelength is λ = 650 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.60 Infinite specification
[0273]
When the light source wavelength λ = 780 nm
Focal length f = 3.35 Image-side numerical aperture NA = 0.50 (NA = 0.60) Infinite specification
w (beam diameter of 13.5% intensity at the imaging surface of the light beam of 780 nm) = 1.27 μm
[0274]
In this embodiment, as shown in FIG. 46, both the light flux of λ1 and the light flux of λ2 generate a larger amount of −1st order diffracted light than the diffracted light of other orders only in the very peripheral portion, and the others are +1. More diffracted light is generated than diffracted light of other orders. However, in this embodiment, the annular zone pitch may be multiplied by an integer to generate higher-order homogeneous diffraction light instead of ± first-order diffracted light.
[0275]
In this example, as shown in FIG. 41, in the second optical information recording medium, when NA1 = 0.6, the spherical aberration is +68 μm, and when NA2 = 0.5, the spherical aberration is +9 μm.
[0276]
In this embodiment, the pitch at a numerical aperture (NA) of 0.4 is 61 μm.
[0277]
[Table 8]

[0278]
Aspheric coefficient
Aspherical surface 1
κ = −1.2532
A4 = 0.0107 × 10^-1
A6 = -0.885849 × 10^-3
A8 = -1.5773 × 10^-5
A10 = 3.2855 × 10^-5
Aspherical surface 2
κ = −9.1151362
A4 = 0.133327 × 10^-1
A6 = -0.378682 × 10^-2
A8 = 0.3001 × 10^-3
A10 = 4.022221 × 10⁶
[0279]
Diffraction surface coefficient
B2 = 3.4251 × 10^-21
B4 = 0.076397
B6 = -5.5386
B8 = 0.05938
B10 = 0.224
Here, based on Examples 6 to 8, a factor of fluctuation in the wavelength of the semiconductor laser incident on the lens will be considered. The individual variation of the wavelength of the semiconductor laser is considered to be about ± 2 to 3 nm, the width of the multimode oscillation is about ± 2 nm, and the mode hop at the time of writing is about 2 nm. The case where the variation of the spherical aberration of the lens accompanying the variation of the wavelength of the semiconductor laser due to these factors is considered will be described.
[0280]
That is, when the thickness of the transparent substrate of the optical disc is different for different two-wavelength light sources, infinite light (parallel light flux) from the different two-wavelength light sources, as can be understood from the data related to Example 6. In a lens corrected to be free of aberrations, the spherical aberration fluctuation is relatively large with respect to a change of about 10 nm in wavelength with one light source. In Example 6, the wavefront aberration is 0.001 λrms at a wavelength of 650 nm, but the wavefront aberration is degraded to about 0.035 λrms at wavelengths of 640 nm and 660 nm. Of course, for an optical system in which the wavelength of the laser is well controlled, Example 6 can be sufficiently put into practical use. On the other hand, like the lens of Example 7, there is almost no aberration for infinite light from one of the light sources, and almost no aberration for finite light (non-parallel light beam) from the light source of the other wavelength. With a lens corrected to aberrations, it is possible to keep the spherical aberration fluctuations extremely small with respect to changes in the wavelength of about 10 nm of one light source.
[0281]
Next, a temperature change in the performance of the diffractive optical system (an optical system having a diffractive optical lens) of the present embodiment will be considered. First, the wavelength of the semiconductor laser tends to increase by about 6 nm when the temperature rises by 30 ° C. On the other hand, when the diffractive optical system is formed of a plastic lens, the refractive index tends to decrease by about 0.003 to 0.004 when the temperature of 30 ° C. rises. In a lens that is corrected without aberration for infinite light of two wavelengths as in the sixth embodiment, the factor due to the temperature change of the wavelength of the semiconductor laser and the factor due to the temperature change of the refractive index of the plastic lens are compensated. It is possible to produce an optical system that is effective and extremely resistant to temperature changes. In Example 6, even when the material is glass, it is possible to make an optical system having an allowable width with respect to temperature change. Also in Example 7, although not as much as Example 6, with a temperature change of 30 ° C., the degradation of wavefront aberration is about 0.035 λrms, and practically sufficient temperature compensation is achieved.
[0282]
The above-described compensation effect for temperature change will be further described. When recording and / or reproducing two types of optical information recording media having different transparent substrate thicknesses by using two light sources having different wavelengths, an information recording surface of each optical disc can be obtained by using an objective lens having a diffraction pattern. Since the rms value of the wavefront aberration can be 0.07 or less of the respective wavelengths even at the numerical aperture required for or higher than that, an imaging characteristic equivalent to that of the dedicated objective lens can be obtained. it can. In order to obtain a low-cost and compact optical pickup device, a semiconductor laser is often used as a light source, and a plastic lens is often used as an objective lens.
[0283]
There are various plastic materials for lenses, but the temperature change of the refractive index and the linear expansion coefficient are larger than those of glass. In particular, a change in refractive index with temperature affects various characteristics of the lens. The temperature change of the refractive index in the vicinity of 25 ° C. is −0.0002 / ° C. to −0.00005 / ° C. for a plastic material used as an optical element of an optical pickup. Further, many low birefringence materials are -0.0001 / ° C. Further, some thermosetting plastics for lenses have a large change in refractive index with respect to temperature change, and some of them are outside the above range.
[0284]
With respect to semiconductor lasers manufactured with the current technology, the oscillation wavelength has temperature dependence, and the temperature change of the oscillation wavelength near 25 ° C. is 0.05 nm / ° C. to 0.5 nm / ° C.
[0285]
Maintaining characteristics as an optical pickup device when the wavefront aberration of a light beam for reproducing information on an optical information recording medium or recording information on an optical information recording medium changes with temperature and the rms value is 0.07 or more of the wavelength. In particular, it is necessary to pay attention to the temperature change of wavefront aberration in a higher-density optical information medium. The change of the wavefront aberration due to the temperature change of the plastic lens causes both the focus shift and the change of the spherical aberration. However, the latter is important because the former performs focus control in the optical pickup device. Here, when the amount of change in refractive index when the plastic material has a temperature change ΔT (° C.) is Δn,
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
In the semiconductor laser, when the change in oscillation wavelength when there is a temperature change ΔT is Δλ1,
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
If the above relationship is satisfied, the wavefront aberration fluctuation due to the temperature change of the refractive index of the plastic lens and the wavefront aberration fluctuation due to the temperature change of the wavelength of the semiconductor laser light source will act in a direction to cancel each other, thereby obtaining a compensation effect. it can.
[0286]
Further, when the change in the third-order spherical aberration component of the wavefront aberration is ΔWSA3 (λrms) when the environmental temperature change is ΔT (° C.), this is the light of the objective lens of the light beam passing through the objective lens. It is proportional to the fourth power of the numerical aperture (NA) on the information medium side, proportional to the focal length f (mm) of the plastic lens, and wavefront aberration is evaluated in units of wavelength, and therefore inversely proportional to the wavelength λ (mm) of the light source. . Therefore, the following equation is established.
△ WSA3 = k · (NA)⁴・ F ・ △ T / λ (a1)
Here, k is an amount depending on the type of the objective lens.
Incidentally, a double-sided aspherical objective lens made of plastic that is optimized when the focal length is 3.36 mm, the numerical aperture on the optical information medium side is 0.6, and the incident light beam is parallel light is MOC / GRIN ' 97 Techical Digest C5 p40-p43, "The Temperature characteristics of a new optical system with quasi-finite conjugate plastic objective for high density optical disk use". Since WSA3 is changed by 0.045λrms due to the change and it is used for DVD, the wavelength is considered to be λ = 650nm. Substituting the above data into equation (a1), k = 2.2 × 10^-6Is obtained. Further, although there is no description about the influence of the wavelength change due to the temperature change, when the temperature change of the oscillation wavelength is small, the influence of the refractive index change due to the temperature is larger for the objective lens not using diffraction.
[0287]
With respect to an optical pickup apparatus that records and / or reproduces a DVD, k needs to be equal to or less than the above value. When recording and / or reproducing two types of optical information recording media having different thicknesses of the transparent substrate, the influence of the wavelength change due to the temperature change cannot be ignored in the objective lens having the diffraction pattern. In particular, regarding k, the value of k varies depending on the focal length, the temperature change of the refractive index of the plastic material, the difference in the thickness of the transparent substrate, the difference in the oscillation wavelength of the two light sources, and the like. The factor due to the temperature change of the wavelength and the factor due to the temperature change of the refractive index of the plastic lens cause a compensation effect, and even if the objective lens is a plastic lens, the change in wavefront aberration due to the temperature change is small, and according to the simulation,
k = 2.2 × 10^-6/ ° C, k = 0.4 × 10^-6/ ℃
It becomes.
[0288]
k can be in a range of 0.3 <k <2.2. Therefore, from equation (a1),
k = ΔWSA3 · λ / {f · (NA1)⁴ΔT (NA)} (a2)
Because
0.3 × 10^-6/ ° C <ΔWSA3 · λ / {f · (NA1)⁴・ ΔT} <
2.2 × 10^-6/ ℃ (a3)
It becomes. In the formula (a3), if the value of k exceeds the upper limit, it is difficult to maintain the characteristics as the optical pickup device due to the temperature change, and if the value exceeds the lower limit, there is little variation with respect to the temperature change. However, it is difficult to maintain the characteristics of the optical pickup device when the wavelength shift changes.
[0289]
Further, in Example 8, compared with Example 6, the performance of one wavelength, that is, a wavelength of 780 nm is slightly deteriorated within an allowable range, so that the other wavelength, that is, the vicinity of the wavelength of 650 nm ± The spherical aberration fluctuation at 10 nm can be reduced. In Example 6, the wavefront aberration at a wavelength of 640 nm or 660 nm is about 0.035 λrms, but in Example 8, the wavefront aberration at a wavelength of 640 nm or 660 nm can be improved to about 0.020 λrms. Although these two factors have a trade-off relationship, it is important to maintain a balance. If the ratio exceeds 0.07λrms, the lens performance deteriorates and it becomes difficult to use the optical system for an optical disc.
[0290]
Next, based on Example 6, the relationship between the amount of change in the spherical aberration of the marginal ray and the amount of change in the longitudinal chromatic aberration with respect to the wavelength change will be described. As in the sixth embodiment, a light beam having a shorter wavelength is used for an information recording medium having a thinner transparent substrate, and a light beam having a longer wavelength is used for an information recording medium having a thicker transparent substrate. In the objective lens used for these light beams in one optical pickup device that uses the diffractive surface, when the wavelength becomes longer with respect to a certain wavelength, the spherical aberration is displaced to the under side, Spherical aberration caused by the difference in the thickness of the transparent substrate can be corrected.
[0291]
In this objective lens, if the change amount of the spherical aberration of the marginal ray and the change amount of the axial chromatic aberration are ΔSA and ΔCA, respectively, with respect to a minute change in the wavelength used by at least one of the light sources,
−1 <△ SA / △ CA <−0.2
It is desirable to satisfy. This formula shows the ratio between the amount of change in spherical aberration of the marginal ray and the amount of change in axial chromatic aberration when the wavelength used changes. By exceeding the lower limit of this conditional expression, the distance between the diffraction zones can be increased. It is easy to manufacture a diffractive surface with high diffraction efficiency, and by lowering the upper limit of the conditional expression, it is possible to suppress the diffractive surface from being negative and have a large refractive power, and the wavelength change of axial chromatic aberration is not excessive, and the mode It is possible to suppress fluctuations in the focal position with respect to wavelength changes such as pop. A minute change in wavelength means a change of about 10 nm or less. In Example 6, as shown in FIG. 25, the value of ΔSA / ΔCA is −0.7 at a wavelength of 650 nm.
[0292]
Here, the relationship between the diffraction power and the lens shape will be described. FIG. 47 schematically shows the relationship between the diffraction power and the lens shape. FIG. 47A is a diagram showing a positive lens shape at all portions where the diffraction power is present, and FIG. 47B is a diagram showing a negative lens shape at all portions where the diffraction power is present. As shown in FIG. 47 (c), the lens of Example 6 is designed such that the diffraction power is a negative power near the optical axis and is switched to a positive power in the middle. Thereby, it is possible to prevent the pitch of the diffraction zone from becoming too fine. Further, as in Example 8, by designing the diffraction power to be switched from the positive power to the negative power near the periphery of the lens, it is possible to obtain a good aberration between the two wavelengths. As shown in FIG. 47 (d), for example, the diffraction power is a positive power near the optical axis, and can be switched to a negative power in the middle.
[0293]
In FIG. 47 (c), the diffractive surface has a plurality of blazed diffractive ring zones, and in the diffractive ring zone close to the optical axis, the step portion is located on the side away from the optical axis. In the diffracting ring zone on the far side, the stepped portion is located on the side close to the optical axis. In FIG. 47 (d), the diffractive surface has a plurality of blazed diffraction ring zones, and in the diffraction ring zone near the optical axis, the step portion is located on the side close to the optical axis. In the diffractive ring zone on the side away from the optical axis, the step is located on the side away from the optical axis.
[0294]
<Examples 9 and 10>
[0295]
The objective lenses of Examples 9 and 10 have the above-described aspherical shape represented by [Equation 3] on the refracting surface. Example 9 is a finite conjugate type corresponding to two light sources. It is a specific example of the objective lens which concerns on 2 embodiment, and is a finite conjugate type corresponding to 3 light sources. In Examples 9 and 10, the diffractive surface is expressed by the above-described [Equation 1] as a phase difference function ΦB having a unit of radians.
[0296]
50 and 51 show optical path diagrams of the objective lens of Example 9 at λ = 650 nm and λ = 780 nm. FIG. 52 is a spherical aberration diagram up to numerical aperture 0.60 for λ = 650 nm with respect to the objective lens of Example 9. FIGS. 53 and 54 show spherical aberration diagrams up to numerical apertures 0.45 and 0.60 with respect to the wavelength λ = 780 nm for the objective lens of Example 9, respectively. FIGS. 55 and 56 show wavefront aberration diagrams with respect to λ = 650 nm and wavelength λ = 780 nm, respectively, for the objective lens of Example 9. FIGS.
[0297]
57 to 59 show optical path diagrams of the objective lens of Example 10 at λ = 650 nm, λ = 400 nm, and λ = 780 nm. 60 and 61 show spherical aberration diagrams up to the numerical aperture 0.65 for λ = 650 nm and λ = 400 nm for the objective lens of Example 10. FIG. 62 and 63 show spherical aberration diagrams up to numerical apertures 0.45 and 0.65 with respect to the wavelength λ = 780 nm for the objective lens of Example 10, respectively. FIGS. 64 to 66 show wavefront aberration diagrams for the objective lens of Example 10 with respect to λ = 650 nm, λ = 400 nm, and wavelength λ = 780 nm, respectively.
[0298]
According to the objective lenses of Examples 9 and 10, in any of the Examples, with respect to light having a wavelength of 780 nm, a large spherical aberration is caused by a light beam exceeding NA 0.45 in actual use, and information recording and / or flare is performed. Does not contribute to regeneration.
[0299]
The lens data of Examples 9 and 10 are shown below. In Table 9 and Table 10, r is the radius of curvature of the lens, d is the surface spacing, n is the refractive index at each wavelength, and ν is the Abbe number. For reference, the refractive index at d line (λ = 587.6 nm) and νd (Abbe number) are shown. In addition, the surface number is displayed including the aperture, and in this embodiment, for convenience, the air interval is divided into two places before and after the portion corresponding to the transparent substrate of the optical disk. .
[0300]
Example 9
f = 3.33 Image side NA 0.60 Magnification -0.194 (Wavelength λ = 650 nm)
f = 3.35 Image side NA 0.45 (NA 0.60) Magnification -0.195 (When wavelength λ = 780 nm)
[0301]
[Table 9]

[0302]
Aspherical surface 1
κ = -0.1295292
A4 = -0.0045445253
A6 = -0.0011967305
A8 = -0.00011777995
A10 = -5.3843777 × 10^-5
A12 = -9.0807729 × 10^-6
Diffraction surface 1
B2 = 0
B4 = -7.6489594
B6 = 0.9933123
B8 = -0.28305522
B10 = 0.011289605
[0303]
Aspherical surface 2
κ = -5.161871
A4 = 0.019003845
A6 = -0.010002187
A8 = 0.004087239
A10 = -0.00085994626
A12 = 7.5491556 × 10^-5
[0304]
Example 10
f = 3.31 Image side NA 0.65 Magnification -0.203 (Wavelength λ = 650 nm)
f = 3.14 Image side NA 0.65 Magnification -0.190 (When wavelength λ = 400 nm)
f = 3.34 Image side NA 0.45 (NA 0.65) Magnification -0.205 (When wavelength λ = 780 nm)
[0305]
[Table 10]

[0306]
Aspherical surface 1
κ = -0.08796008
A4 = -0.010351744
A6 = 0.0015514472
A8 = -0.00043894535
A10 = 5.481801 × 10^-5
A12 = -4.2588508 × 10^-6
Diffraction surface 1
B2 = 0
B4 = -61.351934
B6 = 5.9668445
B8 = -1.2923244
B10 = 0.041773541
[0307]
Aspherical surface 2
κ = -302.6352
A4 = 0.002
A6 = -0.0014
A8 = 0.0042
A10 = -0.0022
A12 = 0.0004
Diffraction surface 2
B2 = 0
B4 = 341.19136
B6 = -124.16233
B8 = 49.877242
B10 = -5.9599182
[0308]
It should be noted that the specific example of the objective lens of Example 10 can be similarly applied to the third embodiment.
[0309]
<Examples 11 to 14>
[0310]
The objective lenses of Examples 11 to 14 have the above-described aspheric shape represented by [Equation 3] on the refracting surface, and in Examples 11 to 13, the diffractive surface has a phase difference in units of radians. It is expressed by the above [Equation 1] as the function ΦB. In Example 14, the diffractive surface is expressed by the above-described [Equation 2] as an optical path difference function Φb in which the unit is mm.
[0311]
In obtaining the objective lens characteristics of Examples 11 to 14, the light source wavelength for the first optical disc (DVD) is 650 nm, the light source wavelength for the second optical disc (blue laser next-generation high-density optical disc) is 400 nm, The transparent substrate thickness t1 of the second optical disk is t1 = 0.6 mm. The light source wavelength for the third optical disc (CD) having a transparent substrate thickness t2 = 1.2 mm different from t1 was 780 nm. In addition, 0.65, 0.65, and 0.5 are assumed as numerical apertures NA corresponding to light source wavelengths of 400 nm, 650 nm, and 780 nm, respectively.
[0312]
(Example 11)
[0313]
Example 11 is a specific example of the objective lens according to the fourth embodiment, and is configured such that parallel light is incident on the objective lens. In this embodiment, the coefficient of the phase difference function of the diffraction surface does not include the square term (B2 = 0), and only the coefficient of the term other than the square term is used.
[0314]
68 to 70 show optical path diagrams of the objective lens of Example 11 at λ = 650 nm, λ = 400 nm, and λ = 780 nm. 71 and 72 show spherical aberration diagrams up to numerical aperture 0.65 for λ = 650 nm and λ = 400 nm for the objective lens of Example 11. FIG. 73 and 74 show spherical aberration diagrams up to numerical apertures 0.45 and 0.65 with respect to the wavelength λ = 780 nm for the objective lens of Example 11, respectively. 75 to 77 show wavefront aberration diagrams with respect to λ = 650 nm, λ = 400 nm, and λ = 780 nm for the objective lens of Example 11, respectively.
[0315]
The lens data of Example 11 is shown below. In Table 11, r is the radius of curvature of the lens, d is the surface separation, and n is the refractive index at each wavelength. The surface number is displayed including the aperture.
[0316]
Example 11
f = 3.33 Image side NA 0.65 (When wavelength λ = 650nm)
f = 3.15 Image side NA 0.65 (When wavelength λ = 400 nm)
f = 3.37 Image side NA 0.45 (NA 0.65) (Wavelength λ = 780nm)
[0317]
[Table 11]

[0318]
Aspherical surface 1
κ = -0.1847301
A4 = -0.0090859227
A6 = 0.0016821871
A8 = -0.00071180761
A10 = 0.00012406905
A12 = -1.4004589 × 10^-5
Diffraction surface 1
B2 = 0
B4 = -69.824562
B6 = 0.35641549
B8 = 0.6877372
B10 = -0.18333885
[0319]
Aspherical surface 2
κ = -186.4056
A4 = 0.002
A6 = -0.0014
A8 = 0.0042
A10 = -0.0022
A12 = 0.0004
Diffraction surface 2
B2 = 0
B4 = 745.72117
B6 = -334.75078
B8 = 81.232224
B10 = -5.3410176
[0320]
In the optical pickup apparatus having the objective lens and the three light sources as in the eleventh embodiment (and the twelfth embodiment described later), the aspherical surface coefficient and the phase difference function coefficient are appropriately designed, so that the thickness of the transparent substrate can be increased. It is possible to correct the spherical aberration caused by the difference and the chromatic aberration of the spherical aberration caused by the difference in wavelength for each disk. As is clear from FIG. 74, the third optical disc has a flare outside the numerical aperture NA0.45 in actual use.
[0321]
Example 12
[0322]
Further, the objective lens of Example 12 is configured so that divergent light from a finite distance is incident thereon. In this embodiment, the coefficient of the phase difference function of the diffraction surface does not include the square term (B2 = 0), and only the coefficient of the term other than the square term is used.
[0323]
78 to 80 show optical path diagrams of the objective lens of Example 12 at λ = 650 nm, λ = 400 nm, and λ = 780 nm. 81 and 82 show spherical aberration diagrams up to the numerical aperture 0.65 for λ = 650 nm and λ = 400 nm for the objective lens of Example 12. FIG. 83 and 84 show spherical aberration diagrams up to numerical apertures 0.45 and 0.65 with respect to the wavelength λ = 780 nm for the objective lens of Example 12, respectively. 85 to 87 show wavefront aberration diagrams with respect to λ = 650 nm, λ = 400 nm, and λ = 780 nm for the objective lens of Example 12, respectively.
[0324]
The lens data of Example 12 is shown below.
[0325]
Example 12
f = 3.31 Image side NA 0.65 Magnification -0.203 (Wavelength λ = 650 nm)
f = 3.14 Image side NA 0.65 Magnification -0.190 (When wavelength λ = 400 nm)
f = 3.34 Image side NA 0.45 (NA 0.65) Magnification -0.205 (When wavelength λ = 780 nm)
[0326]
[Table 12]

[0327]
Aspherical surface 1
κ = -0.08796008
A4 = -0.010351744
A6 = 0.0015514472
A8 = -0.00043894535
A10 = 5.481801 × 10^-5
A12 = -4.2588508 × 10^-6
Diffraction surface 1
B2 = 0
B4 = -61.351934
B6 = 5.9668445
B8 = -1.2923244
B10 = 0.041773541
[0328]
Aspherical surface 2
κ = -302.6352
A4 = 0.002
A6 = -0.0014
A8 = 0.0042
A10 = -0.0022
A12 = 0.0004
Diffraction surface 2
B2 = 0
B4 = 341.19136
B6 = -124.16233
B8 = 49.877242
B10 = -5.9599182
[0329]
In the optical pickup apparatus having the objective lens and the three light sources as in the twelfth embodiment, each disk can correct the spherical aberration caused by the difference in the transparent substrate thickness and the chromatic aberration of the spherical aberration caused by the difference in wavelength. Is possible. As is apparent from FIG. 84, the third optical disc has a flare outside the numerical aperture NA0.45 in actual use.
[0330]
(Example 13)
[0331]
The objective lens of Example 13 is another specific example of the objective lens according to the fourth embodiment, and is configured such that parallel light from an infinite distance enters. In this embodiment, terms other than the square term and the square term are used as the coefficients of the phase difference function of the diffractive surface.
[0332]
88 to 90 show optical path diagrams of the objective lens of Example 13 at λ = 650 nm, λ = 400 nm, and λ = 780 nm. 91 and 92 show spherical aberration diagrams up to numerical aperture 0.60 for λ = 650 nm and λ = 400 nm for the objective lens of Example 13. FIG. 93 and 94 show spherical aberration diagrams up to numerical apertures 0.45 and 0.60 with respect to the wavelength λ = 780 nm for the objective lens of Example 13, respectively. 95 to 97 show wavefront aberration diagrams with respect to λ = 650 nm, λ = 400 nm, and λ = 780 nm for the objective lens of Example 13, respectively.
[0333]
The lens data of Example 13 is shown below.
[0334]
Example 13
f = 3.31 Image side NA 0.60 (when wavelength λ = 650 nm)
f = 3.14 Image side NA 0.60 (When wavelength λ = 400 nm)
f = 3.34 Image side NA 0.45 (NA 0.60) (Wavelength λ = 780nm)
[0335]
[Table 13]

[0336]
Aspherical surface 1
κ = -0.3363369
A4 = -0.0025421455
A6 = -0.0010660122
A8 = 4.7189743 × 10^-5
A10 = 1.5406396 × 10^-6
A12 = -7.0004876 × 10^-6
Diffraction surface 1
B2 = -177.66083
B4 = -46.296284
B6 = -6.8014831
B8 = 1.6606499
B10 = -0.39075825
[0337]
Aspherical surface 2
κ = 43.44262
A4 = 0.002
A6 = -0.0014
A8 = 0.0042
A10 = -0.0022
A12 = 0.0004
Diffraction surface 2
B2 = 241.52445
B4 = 402.41974
B6 = -191.87213
B8 = 64.779696
B10 = -8.6741764
[0338]
In the present embodiment, since a term other than the square term and the square term is used as the coefficient of the phase difference function of the diffractive surface, it occurs due to the difference in spherical aberration and wavelength caused by the difference in the transparent substrate thickness. Spherical aberration chromatic aberration and axial chromatic aberration can be corrected for each disk. As is apparent from FIG. 94, the third optical disk has a flare outside the numerical aperture NA0.45 in actual use.
[0339]
(Example 14)
[0340]
The objective lens of Example 14 is a specific example of the objective lens according to the sixth embodiment. Parallel light having wavelengths of 400 nm and 650 nm is incident from an infinite distance, and divergent light having a wavelength of 780 nm is incident from a finite distance. It is configured. In this embodiment, terms other than the square term and the square term are used as coefficients of the optical path difference function of the diffractive surface.
[0341]
FIG. 98 shows an optical path diagram of the objective lens of Example 14 at λ = 400 nm. 99 and 101 show spherical aberration diagrams up to numerical aperture 0.65 for λ = 400 nm ± 10 nm, λ = 650 nm ± 10 nm and λ = 780 nm ± 10 nm for the objective lens of Example 14. FIG.
[0342]
The lens data of Example 14 is shown below.
[0343]
Example 14
f = image side NA 0.65 (wavelength λ = 650 nm)
f = image side NA 0.65 (wavelength λ = 400 nm)
f = Image side NA 0.45 (NA 0.65) (When wavelength λ = 780 nm)
[0344]
[Table 14]

[0345]
Aspherical surface 1
κ = -2.00080
A4 = 0.18168 × 10^-1
A6 = -0.91791 × 10^-3
A8 = 0.16455 × 10^-3
A10 = -0.11115 × 10^-4
Diffractive surface
b2 = -0.51589 × 10^-3
b4 = -0.24502 × 10^-3
b6 = 0.49557 × 10^-4
b8 = -0.14497 × 10^-4
[0346]
Aspherical surface 2
κ = 3.1831
A4 = 0.14442 × 10^-1
A6 = -0.17506 × 10^-2
A8 = 0.21593 × 10^-4
A10 = 0.12534 × 10^-4
[0347]
In addition, this invention is not limited to the said Example. Although diffraction is formed on both sides of the objective lens, it may be provided on one side of the optical element in the optical system of the optical pickup device. Further, although the annular diffractive surface is formed on the entire lens surface, a diffractive surface may be partially formed. Furthermore, as a next-generation high-density optical disk using a blue laser, the optical design has been advanced on the assumption that the light source wavelength is 400 nm and the thickness of the transparent substrate is 0.6 mm. However, the present invention can also be applied to optical disks having other specifications. It is.
[0348]
Next, a seventh embodiment of the present invention will be described.
[0349]
FIG. 117 is a schematic configuration of an objective lens according to the present embodiment and an optical pickup device including the objective lens. As shown in FIG. 117, the first semiconductor laser 111 and the second semiconductor laser 112 are unitized as a light source. A beam splitter 120 is disposed between the collimator 13 and the objective lens 16, and the light substantially parallelized by the collimator 13 passes through the beam splitter 120 toward the objective lens 16. Further, the optical path is changed so that the light beam reflected from the information recording surface 22 is directed to the photodetector 30 by the beam splitter 120 as the optical path changing means. The objective lens 16 has a flange portion 16a on the outer periphery thereof, and the objective lens 16 can be easily attached to the optical pickup device by the flange portion 16a. Further, since the flange portion 16a has a surface extending in a direction substantially perpendicular to the optical axis of the objective lens 16, attachment with higher accuracy can be facilitated.
[0350]
When reproducing the first optical disk, the light beam emitted from the first semiconductor laser 111 passes through the collimator 13 and becomes a parallel light beam. Further, the light is focused by the diaphragm 17 through the beam splitter 120, and is condensed on the information recording surface 22 by the objective lens 16 through the transparent substrate 21 of the first optical disk 20. Then, the light beam modulated and reflected by the information pits on the information recording surface 22 is reflected again by the beam splitter 120 via the objective lens 16 and the diaphragm 17, and given astigmatism by the cylindrical lens 180. Then, a read signal of information recorded on the first optical disc 20 is obtained using a signal incident on the photodetector 30 and output from the photodetector 30.
[0351]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 30. Based on this detection, the two-dimensional actuator 150 moves the objective lens 16 so that the light beam from the first semiconductor laser 111 forms an image on the information recording surface 22 of the first optical disc 20, and also moves the first semiconductor laser. The objective lens 16 is moved so that the light beam from the 111 is imaged on a predetermined track.
[0352]
Next, when reproducing the second optical disk, the light beam emitted from the second semiconductor laser 112 passes through the collimator 13 and becomes a parallel light beam. Further, the light is focused by the diaphragm 17 through the beam splitter 120, and is condensed on the information recording surface 22 by the objective lens 16 through the transparent substrate 21 of the second optical disk 20. Then, the light beam modulated and reflected by the information pits on the information recording surface 22 is reflected again by the beam splitter 120 through the objective lens 16 and the diaphragm 17, and astigmatism is given by the cylindrical lens 180. After that, a read signal of information recorded on the second optical disc 20 is obtained using a signal incident on the photodetector 30 and output from the photodetector 30. In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 30. Based on this detection, the objective lens 16 is moved so that the light beam from the two-dimensional actuator 15 or the first semiconductor laser 112 is imaged on the information recording surface 22 of the second optical disk 20, and the second semiconductor laser 112 is used. The objective lens 16 is moved so that the light beam from the light beam is imaged on a predetermined track.
[0353]
The objective lens (diffraction lens) 16 is incident from each semiconductor laser up to the larger numerical aperture (maximum numerical aperture) of the numerical apertures necessary for recording and / or reproduction of the first optical disc and the second optical disc. It is designed to be 0.07λrms or less for each wavelength (λ) with respect to light. For this reason, the wavefront aberration on the imaging surface of each light flux is 0.07λrms or less. Accordingly, there is no flare during recording and / or reproduction of either optical disc on the image plane and on the detector 30, and the focus error detection and track error detection characteristics are good.
[0354]
The first optical disk is a DVD (light source wavelength 650 nm), the second optical disk is a CD (light source wavelength 780 nm), the first optical disk is a next-generation high-density optical disk (light source wavelength 400 nm), and the second optical disk. The case of DVD (light source wavelength: 650 nm) is assumed. In particular, when there is a large difference in the required numerical aperture of each optical disk, in the above case, the spot is compared with the required spot diameter. May be too small. At this time, the aperture limiting means described elsewhere in this specification may be introduced to obtain a desired spot diameter.
[0355]
Hereinafter, Examples 15, 16, 17, and 18 of spherical aberration correction lenses will be described as specific examples of the objective lens according to the seventh embodiment. In each embodiment, the wavefront aberration is corrected to 0.07 λrms or less with respect to the maximum numerical aperture. In the following, the image side means the optical information recording medium side.
[0356]
<Example 15>
[0357]
FIG. 118 shows an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is the objective lens of Example 15. FIG. 119 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths (λ) = 640, 650, and 660 nm of the diffractive optical lens of Example 15. FIG. 120 shows an optical path diagram of the diffractive optical lens of Example 15 when the transparent substrate of the optical information recording medium is thicker than FIG. FIG. 121 shows spherical aberration diagrams up to numerical aperture 0.60 for wavelengths λ = 770, 780, and 790 nm for the diffractive optical lens in the case of FIG.
[0358]
According to the diffractive optical lens of Example 15, as shown in FIG. 119, for the wavelength λ = 650 nm, the entire aperture up to NA 0.60 is almost no aberration. In addition, as shown in FIGS. 120 and 121, when the transparent substrate is thick, up to NA 0.60 is almost no aberration for the wavelength λ = 780 nm. The predetermined numerical aperture when λ = 780 nm is 0.45.
[0359]
As described above, in Example 15, compared with Examples 1, 6, and 8, the spherical aberration when the transparent substrate of the optical information recording medium is thick and the wavelength is 780 nm is thinner than this, and the wavelength is 650 nm. Correction can be made up to the same numerical aperture (NA 0.60).
[0360]
The lens data of Example 15 is shown below.
[0361]
When the light source wavelength is λ = 650 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.60 Infinite specification (parallel beam incidence)
[0362]
When the light source wavelength λ = 780 nm
Focal length f = 3.38 Image side numerical aperture NA = 0.60 Infinite specification
[0363]
[Table 15]

[0364]
Aspheric coefficient
Aspherical surface 1
κ = −1.0358
A₄= 4.8632 × 10^-3
A₆= 5.383 × 10^-4
A₈= -1.5773 × 10^-4
A₁₀= 3.8683 × 10^-7
[0365]
Aspherical surface 2
κ = −9.256352
A₄= 1.5887 × 10^-2
A₆= -5.97422 × 10^-3
A₈= 1.11613 × 10^-3
A₁₀= −9.36682 × 10^-5
[0366]
Diffraction surface coefficient (reference wavelength 650nm)
b₂= 6.000 × 10^-3
b₄= -1.317x10^-3
b₆= 1.5274 × 10^-4
b₈= −6.5757 × 10^-5
b₁₀= 6.221 × 10^-6
[0367]
<Example 16>
[0368]
FIG. 122 shows an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is the objective lens of Example 16. FIG. 123 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths (λ) = 640, 650, and 660 nm of the diffractive optical lens of Example 16. FIG. 124 shows an optical path diagram of the diffractive optical lens of Example 16 when the transparent substrate of the optical information recording medium is thicker than FIG. FIG. 125 shows spherical aberration diagrams up to a numerical aperture of 0.60 with respect to wavelengths λ = 770, 780 and 790 nm for the diffractive optical lens in the case of FIG.
[0369]
According to the diffractive optical lens of Example 16, as shown in FIG. 123, the entire aperture up to NA 0.60 is almost no aberration for the wavelength λ = 650 nm. As shown in FIGS. 124 and 125, when the transparent substrate is thick, up to NA 0.60 is almost no aberration for the wavelength λ = 780 nm. The predetermined numerical aperture when λ = 780 nm is 0.45.
[0370]
As described above, in Example 16, compared with Examples 1, 6, and 8, the spherical aberration when the transparent substrate of the optical information recording medium is thick and the wavelength is 780 nm is thinner than this, and the wavelength is 650 nm. Correction can be made up to the same numerical aperture (NA 0.60). In Examples 15 and 16, in order to correct the spherical aberration due to the difference in the thickness of the transparent substrate up to NA 0.6, it is necessary that the action of correcting the spherical aberration due to diffraction is strong. However, the paraxial power of diffraction is made negative to mitigate pitch reduction.
[0371]
The lens data of Example 16 is shown below.
[0372]
When the light source wavelength is λ = 650 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.60 Infinite specification
[0373]
When the light source wavelength λ = 780 nm
Focal length f = 3.36 Image side numerical aperture NA = 0.60 Infinite specification
[0374]
[Table 16]

[0375]
Aspheric coefficient
Aspherical surface 1
κ = −1.1331
A₄= 4.5375 × 10^-3
A₆= 1.2964 × 10^-3
A₈= −3.6164 × 10^-4
A₁₀= 2.0765 × 10^-5
[0376]
Aspherical surface 2
κ = −4.3356298
A₄= 1.574727 × 10^-2
A₆= -4.991198x10^-3
A₈= 7.772605 × 10^-4
A₁₀= -5.75456 × 10^-5
[0377]
Diffraction surface coefficient (reference wavelength 650nm)
b₂= 2.1665 × 10^-3
b₄= −2.0272 × 10^-3
b₆= 5.5178 × 10^-4
b₈= -1.8391 × 10^-4
b₁₀= 1.8148 × 10^-5
[0378]
<Example 17>
[0379]
FIG. 126 shows an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is the objective lens of Example 17. FIG. 127 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths (λ) = 640, 650, and 660 nm of the diffractive optical lens of Example 17. FIG. FIG. 128 shows an optical path diagram of the diffractive optical lens of Example 17 when the transparent substrate of the optical information recording medium is thicker than FIG. FIG. 129 shows spherical aberration diagrams up to numerical aperture 0.60 for wavelengths λ = 770, 780 and 790 nm for the diffractive optical lens in the case of FIG.
[0380]
According to the diffractive optical lens of Example 17, as shown in FIG. 127, the entire aperture up to NA 0.60 is almost no aberration for the wavelength λ = 650 nm. In addition, as shown in FIGS. 128 and 129, when the transparent substrate is thick, up to NA 0.60 is almost no aberration for the wavelength λ = 780 nm. The predetermined numerical aperture when λ = 780 nm is 0.45. In Examples 15 to 17, the axial chromatic aberration is different, and the annular pitch is also changed.
[0381]
As described above, in Example 17, compared to Examples 1, 6, and 8, the spherical aberration when the transparent substrate of the optical information recording medium is thick and the wavelength is 780 nm is thinner than this, and the wavelength is 650 nm. Correction can be made up to the same numerical aperture (NA 0.60).
[0382]
The lens data of Example 17 is shown below.
[0383]
When the light source wavelength is λ = 650 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.60 Infinite specification
[0384]
When the light source wavelength λ = 780 nm
Focal length f = 3.34 Image side numerical aperture NA = 0.60 Infinite specification
[0385]
[Table 17]

[0386]
Aspheric coefficient
Aspherical surface 1
κ = −1.0751
A₄= 5.0732 × 10^-3
A₆= 4.3722 × 10^-4
A₈= -1.4774 × 10^-4
A₁₀= 9.6694 × 10^-7
[0387]
Aspherical surface 2
κ = -10.41411
A₄= 1.59463 × 10^-2
A₆= −6.002963 × 10^-3
A₈= 1.11268 × 10^-3
A₁₀= -9.3151 × 10^-5
[0388]
Diffraction surface coefficient (reference wavelength 650nm)
b₂= -2.000 × 10^-3
b₄= -1.4462x10^-3
b₆= 1.1331 × 10^-4
b₈= −6.6211 × 10^-5
b₁₀= 6.8220 × 10^-6
[0389]
<Example 18>
[0390]
FIG. 130 shows an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is the objective lens of Example 18. FIG. 131 is a spherical aberration diagram up to numerical aperture 0.70 for wavelengths (λ) = 390, 400, 410 nm of the diffractive optical lens of Example 18. FIG. 132 shows an optical path diagram of the diffractive optical lens of Example 18 when the transparent substrate of the optical information recording medium is thicker than FIG. FIG. 133 shows spherical aberration diagrams up to numerical aperture 0.70 for wavelengths λ = 640, 650, and 660 nm for the diffractive optical lens in the case of FIG. 132, respectively.
[0390]
According to the diffractive optical lens of Example 18, as shown in FIG. 131, the entire aperture up to NA 0.70 is almost no aberration for the wavelength λ = 400 nm. Further, as shown in FIGS. 132 and 133, when the transparent substrate is thick, up to NA 0.70 is almost no aberration for the wavelength λ = 650 nm.
[0392]
As described above, in Example 17, the spherical aberration when the transparent substrate of the optical information recording medium is thick and the wavelength is 650 nm is thinner than that of Examples 1, 6, and 8, and the wavelength is 400 nm. Correction can be made up to the same numerical aperture (NA 0.70).
[0393]
The lens data of Example 18 is shown below.
[0394]
When the light source wavelength λ = 400 nm
Focal length f = 3.33 Image-side numerical aperture NA = 0.70 Infinite specification
[0395]
When the light source wavelength is λ = 650 nm
Focal length f = 3.43 Image-side numerical aperture NA = 0.70 Infinite specification
[0396]
[Table 18]

[0397]
Aspheric coefficient
Aspherical surface 1
κ = 0.0
A₄= -7.9616 × 10^-4
A₆= −5.7265 × 10^-4
A₈= 8.3209 × 10^-5
A₁₀= -4.1599x10^-5
[0398]
Aspherical surface 2
κ = 0.0
A₄= 3.11131 × 10^-2
A₆= -1.18548 × 10^-2
A₈= 1.63937 × 10^-3
A₁₀= −6.60514 × 10^-5
[0399]
Diffraction surface coefficient (reference wavelength 400nm)
b₂= -1.4046 × 10^-3
b₄= -8.6959 × 10^-4
b₆= 2.3488 × 10^-4
b₈= −5.2455 × 10^-5
b₁₀= 3.6385 × 10^-6
[0400]
Next, the pitches of the plurality of annular zones of the diffractive optical lenses of Examples 1 to 3 and 14 to 18 will be described. The plurality of annular zones are formed substantially concentrically around the optical axis, the annular zone pitch Pf (mm) corresponding to the maximum numerical aperture on the image side of the lens, and the numerical aperture that is 1/2 of the maximum numerical aperture. Table 19 shows the values of the annular zone pitches Ph (mm) and ((Ph / Pf) -2) corresponding to.
[0401]
[Table 19]

[0402]
0.4 ≦ | (Ph / Pf) −2 | ≦ 25 (b1)
[0403]
According to further studies by the present inventors, when the above formula (b1) is established, that is, when the value is equal to or higher than the lower limit of this formula, the action of diffraction for correcting higher-order spherical aberration is not weakened. Accordingly, the difference in spherical aberration between the two wavelengths caused by the difference in the thickness of the transparent substrate can be corrected by the action of diffraction, and if it is below the upper limit, it becomes difficult to generate a portion where the pitch of the diffraction zone is too small. It has been found that a lens with high diffraction efficiency can be manufactured.
[0404]
Further, the above relational expression is preferably the following expression (b2), more preferably expression (b3).
[0405]
0.8 ≦ | (Ph / Pf) −2 | ≦ 6.0 (b2)
[0406]
1.2 ≦ | (Ph / Pf) −2 | ≦ 2.0 (b3)
[0407]
Next, an eighth embodiment of the present invention will be described.
[0408]
The required numerical aperture NA1 on the optical information recording medium side of the objective lens necessary for DVD recording / reproducing using a light source having a wavelength of 650 nm is about 0.6, and is necessary for reproducing a CD using a light source having a wavelength of 780 nm. The required numerical aperture NA2 on the optical information recording medium side of the objective lens is about 0.45 (about 0.5 for recording). Therefore, the diffraction pattern for correcting the aberration described above is not essential up to the numerical aperture NA1.
[0409]
Further, since the depth of focus is deep near the optical axis and the amount of spherical aberration is small, a diffraction pattern is not essential.
[0410]
By forming a diffraction pattern in the minimum necessary part and making the remaining part a refracting surface, damage to the tool during mold processing, improved releasability during molding, and a more focused spot on the CD side It is possible to prevent performance degradation when there is an error in the disc thickness due to the narrowing of the disc or when the disc is tilted.
[0411]
For this purpose, the diffraction pattern of the objective lens is rotationally symmetric with respect to the optical axis, and the + 1st order diffracted light from the circumference farthest from the optical axis of the diffraction pattern of the objective lens of the light beam from the first light source. The optical information recording medium has a numerical aperture NAH1 converted into a light beam. When the numerical aperture on the medium side is converted into a NAL1 light beam, the following condition should be satisfied.
NAH1 <NA1
0 ≤ NAL1 ≤ NA2
[0412]
When the first optical information recording medium is a DVD, the wavelength λ1 of the first light source is 650 nm, the second optical information recording medium is a CD, and the wavelength λ2 or 780 nm of the second light source,
NAH1 is 0.43 to 0.55
NAL1 is 0.10 to 0.40
It is preferable that
[0413]
The optical design of the objective lens for the portion having the diffraction pattern is performed so that the + 1st order diffracted light of the light beam incident on the objective lens from the first light source becomes a substantially aberration-free focused spot. On the other hand, the optical design of the objective lens for the portion without the diffraction pattern is performed so that the light beam incident on the objective lens from the first light source becomes a substantially aberration-free focused spot.
[0414]
The condensing positions of the two need to be substantially the same. Furthermore, it is important that the phases of the respective light beams are also aligned. Regarding the phase, when k is a small integer, the light collection characteristic at the design wavelength is hardly changed even if it is shifted by 2 kπ, but when the absolute value of | k | becomes large, it becomes weak against wavelength fluctuation. . | K | is preferably 1 to 10.
[0415]
At this time, of the light flux from the second light source, the + 1st order diffracted light from the circumference farthest from the optical axis of the diffraction pattern of the objective lens is converted into a light flux having a numerical aperture of NAH2 on the optical information recording medium side. + 1st order diffracted light from the circumference on the most optical axis side of the diffraction pattern is converted into a light flux with a numerical aperture on the optical information recording medium side of NAL2,
[0416]
An optical information recording medium that uses a light beam having a numerical aperture of NAH2 or less when passing through an objective lens, out of the light beam from the second light source, as a spot that enables recording and reproduction of the second optical information recording medium The light beam that has passed through the objective lens so that the focal position and the phase difference between the light beam from the portion having the diffraction pattern and the light beam from the portion without the diffraction pattern are optimized so as to be formed on the information recording surface of The spherical aberration is set.
[0417]
Actually, among the light beams from the first light source, the light beam having a numerical aperture of NA1 or less when passing through the objective lens has zero wavefront aberration at the best image point through the transparent substrate of the first optical information recording medium. 0.07λrms or less, and among the light fluxes from the second light source, the light flux having a numerical aperture of NAH2 or less when passing through the objective lens is at the best image point through the transparent substrate of the second optical information recording medium. It is desirable that the wavefront aberration is 0.07λrms or less.
[0418]
In particular, among the light beams from the first light source, a light beam having a numerical aperture of NA1 or less when passing through the objective lens is a spherical surface wavefront aberration at the best image point through the transparent substrate of the first optical information recording medium. The aberration component is desirably 0.05 λrms or less.
[0419]
A light beam incident on the objective lens from the first light source and a light beam incident on the objective lens from the first light source, including at least one collimator between the first light source and the objective lens and between the second light source and the objective lens However, the adjustment of the pickup is facilitated by using the optical pickup device that is parallel light.
[0420]
Further, by using a common collimator for the light flux from the first light source and the light flux from the second light source, the cost of the optical pickup device can be reduced.
[0421]
When the first light source and the second light source are separate packages, the position of each light source with respect to the collimator may be set so that the light beams incident on the objective lens become parallel lights.
[0422]
Further, when the first light source and the second light source are the same package, the difference in the optical axis direction of the position of each light source is appropriately set so that the incident light to the objective lens becomes parallel light. Alternatively, if the adjustment cannot be performed, the light incident on the objective lens may be parallel light using a collimator whose chromatic aberration is optimized.
[0423]
Further, the light beam incident on the objective lens may be a convergent light beam or a divergent light beam. In particular, the light beam incident on the objective lens from the second light source is more than the light beam incident on the objective lens from the first light source. By making the divergence higher, under spherical aberration due to the difference in divergence occurs, and the amount of spherical aberration corrected by the diffraction pattern can be reduced.
[0424]
In FIG. 114, when the numerical apertures NAH2 and NAL2 are the same and the paraxial chromatic aberration is not corrected (ΔfB = 0), the second optical information recording medium (CD) is transparent for the light flux from the second light source. It is a schematic diagram showing the spherical aberration of the light beam which passed the board | substrate.
[0425]
The convergence position of the light beam that contributes to the reproduction of the second optical information recording medium of NAH2 or less is at point B when it is not corrected by the diffraction pattern, but is corrected by the diffraction pattern, ΔfB is made almost zero, and point A is reached. Converge to. However, outside the NAH2, it is not corrected by the diffraction pattern, and its aberration shows an aberration curve S due to only the refractive surface.
[0426]
As is apparent from the figure, the spherical aberration jump at the convergence point of the light beam and the NAH2 is increased by the correction amount ΔfB of the paraxial chromatic aberration, and the position at which the flare component from NAH2 to NA1 converges is the second light of NAH2 or less. Since it is far away from the convergence position of the light beam contributing to the reproduction of the information recording medium, the influence of the flare component is reduced on the photodetector.
[0427]
In addition, by correcting the paraxial chromatic aberration with λ1 and λ2, the paraxial chromatic aberration is reduced in the vicinity of λ1 and λ2, and when the information is recorded on the optical information recording medium, the oscillation wavelength changes due to laser power fluctuations. However, defocusing is less likely to occur and high speed recording is possible.
[0428]
As described above, in order to separate the convergence position of the flare component from NAH2 to NA1 and the convergence position of the luminous flux below NAH2, a second diffraction pattern is provided outside the diffraction pattern. For the light beam from the first light source, the + 1st order diffracted light of the second diffraction pattern is condensed at the convergence position, and the light beam from the second light source is transmitted without being diffracted by the second diffraction pattern. In addition, by designing the second diffraction pattern, the aberration correction state shown in FIG. 115 can be achieved.
[0429]
That is, FIG. 9A shows the aberration correction status of the light flux from the first light source. In both NAH1 and above, the aberration caused by the relatively large refractive surface is not affected by the correction effect of the + 1st order diffracted light. It is condensed at the convergence position due to aberration. However, as shown in FIG. 5B, the light beam from the second light source is zero-order light that does not receive the diffractive action when the light beam passes through the diffraction pattern portion outside NAH2, and the aberration correction status is diffracted. Since aberrations that are not corrected by the pattern appear as they are, the jump of spherical aberration in NAH2 increases, and the flare component convergence position and the light flux convergence position that contributes to the reproduction of information are greatly separated. The effect of.
[0430]
Also, in this second diffraction pattern, the second diffraction pattern is designed so that the light beam from the first light source is not diffracted, and the light beam from the second light source is mainly −1st order diffracted light. Also good. As a result, as shown in FIG. 113, by making the spherical aberration due to diffraction of the light beams from NAH2 to NA1 more over, the second light source has a numerical aperture of NAH2 or less when passing through the objective lens. The spherical aberration when passing through the transparent substrate of the second optical information recording medium is corrected well, while the spherical aberration of the light beam outside NAH2 can be increased. As a result, as shown in FIG. 116 (b), the jump of spherical aberration in NAH2 increases, and the convergence position of the flare component and the convergence position of the light beam contributing to the reproduction of information are greatly separated from each other. The effect of the ingredients is reduced.
[0431]
Similarly, the light beam from the first light source is transmitted in the optical path from the light source to the objective lens, and the light beam passing through the region opposite to the optical axis of the first diffraction pattern out of the light beam of the second light source. By providing aperture limiting means that does not transmit light, and reducing the flare component that reaches the photodetector, the effect can be reduced.
[0432]
The aperture limiting means transmits the light beam from the first light source into the optical path after the light beam emitted from the first light source and the light beam emitted from the second light source are combined by the light multiplexing means, and the second light source An annular filter that reflects or absorbs a light beam passing through a region opposite to the optical axis of the first diffraction pattern out of the light beam of the light source may be provided.
[0433]
As such a filter, for example, a dichroic filter using a multilayer film can be used. Of course, any of the surfaces of the objective lens can have the above-described filter effect.
[0434]
The aperture limiting means is an annular filter that diffracts a light beam passing through a region opposite to the optical axis of the diffraction pattern out of the light beam of the second light source through the light beam from the first light source. May be.
[0435]
The first to seventh optical pickup devices according to the eighth embodiment of the present invention will be specifically described below with reference to the drawings.
[0436]
The first optical pickup device shown in FIG. 102 includes a semiconductor laser 111 that is a first light source for reproducing the first optical disk, and a semiconductor laser 112 for reproducing the second optical disk.
[0437]
First, when reproducing the first optical disk, a beam is emitted from the first semiconductor laser 111, and the emitted light beam is transmitted through a beam splitter 190, which is a means for synthesizing the emitted light from both semiconductor lasers 111 and 112, and polarized. It passes through the beam splitter 120, the collimator 130, and the quarter wavelength plate 14 and becomes a circularly polarized parallel light beam. This light beam is focused by a diaphragm 170 and is focused on the information recording surface 220 by the objective lens 160 through the transparent substrate 210 of the first optical disk 200.
[0438]
Then, the light beam modulated and reflected by the information bit on the information recording surface 220 is transmitted again through the objective lens 160, the diaphragm 170, the quarter-wave plate 140, and the collimator 130, and enters the polarization beam splitter 120, where it is reflected. Then, astigmatism is given by the cylindrical lens 18 and incident on the photodetector 300, and a read signal of information recorded on the first optical disc 200 is obtained using the output signal.
[0439]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 300. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 220 of the first optical disk 200, and the light beam from the semiconductor laser 111. The objective lens 160 is moved so as to form an image on a predetermined track.
[0440]
When reproducing the second optical disk, a beam is emitted from the second semiconductor laser 112, and the emitted light beam is reflected by the beam splitter 190, which is a light combining unit, and is polarized as in the case of the light beam from the first semiconductor 111. The light is condensed on the information recording surface 220 via the transparent substrate 210 of the second optical disk 200 via the splitter 120, the collimator 130, the quarter wavelength plate 140, the diaphragm 170, and the objective lens 160.
[0441]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 is detected again through the objective lens 160, the diaphragm 170, the quarter wavelength plate 140, the collimator 130, the polarization beam splitter 120, and the cylindrical lens 180. A signal for reading information recorded on the second optical disc 200 is obtained using the output signal.
[0442]
Further, as in the case of the first optical disc, the spot shape change on the photodetector 300 and the light quantity change due to the position change are detected, and focus detection and track detection are performed. The objective lens 160 is moved for tracking.
[0443]
The second optical pickup device shown in FIG. 103 has a configuration suitable for an optical system for recording / reproduction, but the case of reproduction will be described. In the following embodiments, the same members as those in the optical pickup device in FIG.
[0444]
When reproducing the first optical disk, a beam is emitted from the first semiconductor laser 111, and the emitted light beam is reflected by the polarization beam splitter 121, passes through the collimator 131 and the quarter-wave plate 141, and is circularly polarized. It becomes parallel light. Further, the light passes through a beam splitter 190 that is a light combining unit, is narrowed by a diaphragm 170, and is condensed by the objective lens 160 onto the information recording surface 220 via the transparent substrate 210 of the first optical disk 200.
[0445]
Then, the light beam modulated and reflected by the information bit on the information recording surface 220 passes through the objective lens 160 and the diaphragm 170 again, and further passes through the beam splitter 190, the quarter wavelength plate 141, and the collimator 131, and is then polarized. Astigmatism is given through the light beam 121 and incident on the photodetector 301, and a read signal of information recorded on the first optical disc 200 is obtained using the output signal. .
[0446]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 301. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 220 of the second optical disk 200, and the light beam from the semiconductor laser 111. The objective lens 160 is moved so as to form an image on a predetermined track.
[0447]
When reproducing the second optical disk, a beam is emitted from the second semiconductor laser 112, and the emitted light beam is reflected by the polarization beam splitter 122, passes through the collimator 132 and the quarter wavelength plate 142, and is circularly polarized. It becomes parallel light. Further, the light is reflected by a beam splitter 190 which is a light synthesizing unit, and is condensed by the diaphragm 170 and the objective lens 160 onto the information recording surface 220 via the transparent substrate 210 of the second optical disc 200.
[0448]
Then, the light beam modulated and reflected by the information recording surface 220 by the information bit is reflected again by the beam splitter 190 through the objective lens 160 and the diaphragm 170, passes through the quarter-wave plate 142 and the collimator 132, and is polarized. The light enters the splitter 122, passes through this, is given astigmatism, enters the photodetector 302, and uses the output signal to obtain a read signal of information recorded on the second optical disc 200. It is done.
[0449]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 302. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the second semiconductor laser 112 forms an image on the recording surface 220 of the first optical disk 200, and the light beam from the semiconductor laser 112. Moving the objective lens 160 so as to form an image on a predetermined track is the same.
[0450]
The third optical pickup device shown in FIG. 104 has a configuration suitable for an optical system for recording / reproduction, but the case of reproduction will be described.
[0451]
When reproducing the first optical disk, a beam is emitted from the first semiconductor laser 111 and transmitted through the coupling lens 60 that reduces the divergence of the divergent light beam, the beam splitter 190 that is the light combining means, and the beam splitter 120. The light passes through the collimator 130 and the quarter-wave plate 140 and becomes circularly polarized parallel light. Further, the aperture is narrowed down by a diaphragm 170 and focused on the information recording surface 220 by the objective lens 160 through the transparent substrate 210 of the first optical disk 200.
[0452]
The light beam modulated and reflected by the information bit on the information recording surface 220 passes through the objective lens 160 and the diaphragm 170 again, passes through the quarter-wave plate 140 and the collimator 130, and enters the beam splitter 120. Astigmatism is given by the cylindrical lens 180, is incident on the photodetector 301 via the concave lens 50, and the read signal of information recorded on the first optical disc 200 is output using the output signal. Is obtained.
[0453]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 301. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 220 of the first optical disk 200, and the light beam from the semiconductor laser 111 is changed. The objective lens 160 is moved so that an image is formed on a predetermined track.
[0454]
The second semiconductor laser 112 for reproducing the second optical disk is unitized with the photodetector 302 and the hologram 230 in the laser / detector integrated unit 400. “Unit” or “unitized” means that the unitized members and means can be integrated into an optical pickup device and assembled as one component when the device is assembled. Can be put on tight.
[0455]
The light beam emitted from the second semiconductor laser 112 passes through the hologram 230, is reflected by the beam splitter 190, which is a light combining unit, and passes through the beam splitter 120, the collimator 130, and the quarter wavelength plate 140 to become a parallel light beam. Further, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disk 200 via the diaphragm 170 and the objective lens 160.
[0456]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 is transmitted again through the quarter wavelength plate 140, the collimator 130, and the beam splitter 120 through the objective lens 160 and the diaphragm 170, and reflected by the beam splitter 190. Then, the light is diffracted by the hologram 230 and incident on the photodetector 302, and a read signal of information recorded on the second optical disc 200 is obtained using the output signal.
[0457]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 302 is detected, and focus detection and track detection are performed. The two-dimensional actuator 150 moves the objective lens 160 for focusing and tracking. Move.
[0458]
In the fourth optical pickup device of FIG. 105, when the first optical disk is reproduced, the first semiconductor laser 111 is unitized with the photodetector 301 and the hologram 231 in the laser / detector integrated unit 410, so that the first optical disk is reproduced. The light beam emitted from the semiconductor laser 111 passes through the hologram 231 and passes through the beam splitter 190 and the collimator 130 which are light combining means to become a parallel light beam. Further, the aperture is narrowed down by a diaphragm 170 and focused on the information recording surface 220 by the objective lens 160 through the transparent substrate 210 of the first optical disk 200.
[0459]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 passes through the collimator 130 and the beam splitter 190 through the objective lens 160 and the diaphragm 170 again, and is diffracted by the hologram 231 to be reflected on the photodetector 301. The read signal of the information recorded on the first optical disc 200 is obtained using the output signal.
[0460]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 302 is detected, and focus detection and track detection are performed. The two-dimensional actuator 150 moves the objective lens 160 for focusing and tracking. Move.
[0461]
When reproducing the second optical disk, the second semiconductor laser 112 is unitized with the photodetector 302 and the hologram 232 in the laser / detector integrated unit 42, and the light beam emitted from the second semiconductor laser 112 is converted into the hologram 232. Is reflected by the beam splitter 190, which is a light combining means, and passes through the collimator 130 to become a parallel light beam. Further, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disk 200 via the diaphragm 170 and the objective lens 160.
[0462]
The light beam modulated and reflected by the information pits on the information recording surface 220 passes through the collimator 130 again through the objective lens 160 and the diaphragm 170, is reflected by the beam splitter 190, is diffracted by the hologram 232, and is detected. A signal for reading information recorded on the second optical disc 200 is obtained using the output signal.
[0463]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 302 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 150 performs focusing and tracking. The objective lens 160 is moved.
[0464]
In the fifth optical pickup device of FIG. 106, the first semiconductor laser 111, the second semiconductor laser 112, the light detection means 30, and the hologram 230 are unitized as a laser / detector integrated unit 430.
[0465]
When reproducing the first optical disk, the light beam emitted from the first semiconductor laser 111 passes through the hologram 230 and the collimator 130 and becomes a parallel light beam. Further, the aperture is narrowed down by a diaphragm 170 and focused on the information recording surface 220 by the objective lens 160 through the transparent substrate 210 of the first optical disk 200.
[0466]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 passes through the collimator 130 again through the objective lens 160 and the diaphragm 170, is diffracted by the hologram 230, and enters the photodetector 300, A read signal of information recorded on the first optical disc 200 is obtained using the output signal.
[0467]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 300 is detected, and focus detection and track detection are performed. The two-dimensional actuator 150 moves the objective lens 160 for focusing and tracking. Move.
[0468]
When reproducing the second optical disk, the light beam emitted from the second semiconductor laser 112 passes through the hologram 230 and the collimator 130 and becomes a substantially parallel light beam. Further, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disk 200 via the diaphragm 170 and the objective lens 160.
[0469]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 passes through the collimator 130 again through the objective lens 160 and the diaphragm 170, is diffracted by the hologram 230, and enters the photodetector 300, A read signal of information recorded on the second optical disc 200 is obtained using the output signal.
[0470]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 300 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 150 performs focusing and tracking. The objective lens 160 is moved.
[0471]
In the sixth optical pickup device of FIG. 107, the first semiconductor laser 111, the second semiconductor laser 112, the first light detection means 301, the second light detection means 302, and the hologram 230 are included in the laser / detector integrated unit 430. As a unit.
[0472]
When reproducing the first optical disk, the light beam emitted from the first semiconductor laser 111 passes through the disk-side surface of the hologram 230 and the collimator 130 to become a parallel light beam. Further, the aperture is narrowed down by a diaphragm 170 and focused on the information recording surface 220 by the objective lens 160 through the transparent substrate 210 of the first optical disk 200.
[0473]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 is transmitted again through the collimator 130 through the objective lens 160 and the diaphragm 170, and is diffracted by the surface on the disk side of the hologram 230. The signal 301 is incident on the light detector 301 corresponding to the above, and the read signal of the information recorded on the first optical disc 200 is obtained using the output signal.
[0474]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 301 is detected, focus detection and track detection are performed, and the objective lens 160 is used for focusing and tracking by the two-dimensional actuator 150. Move.
[0475]
When reproducing the second optical disk, the light beam emitted from the second semiconductor laser 112 is diffracted on the surface of the hologram 230 on the semiconductor laser side, passes through the collimator 130, and becomes a substantially parallel light beam. The surface of the hologram on the semiconductor laser side functions as a photosynthesis means. Further, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disk 200 via the diaphragm 170 and the objective lens 160.
[0476]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 is transmitted again through the collimator 130 through the objective lens 160 and the diaphragm 170, and is diffracted by the disk side surface of the hologram 230 to be the second light source. The signal is incident on the corresponding photodetector 302, and a read signal of information recorded on the second optical disc 200 is obtained using the output signal.
[0477]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 302 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 150 performs focusing and tracking. The objective lens 160 is moved.
[0478]
The seventh optical pickup device shown in FIG. 108 has a configuration suitable for an optical system for recording / reproduction, and the case of reproduction will be described.
[0479]
When reproducing the first optical disk, a beam is emitted from the first semiconductor laser 111 and transmitted through the coupling lens 60 that reduces the divergence of the divergent light beam, the beam splitter 190 that is the light combining means, and the beam splitter 120. The light passes through the collimator 130 and the quarter-wave plate 140 and becomes circularly polarized parallel light. Further, the aperture is narrowed down by a diaphragm 170 and focused on the information recording surface 220 by the objective lens 160 through the transparent substrate 210 of the first optical disk 200.
[0480]
The light beam modulated and reflected by the information bit on the information recording surface 220 passes through the objective lens 160 and the diaphragm 170 again, passes through the quarter-wave plate 140 and the collimator 130, and enters the beam splitter 120. Astigmatism is given by the cylindrical lens 180, is incident on the photodetector 301 via the concave lens 50, and the read signal of information recorded on the first optical disc 200 is output using the output signal. Is obtained.
[0481]
In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 301. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so that the light beam from the first semiconductor laser 111 forms an image on the recording surface 220 of the first optical disk 200, and the light beam from the semiconductor laser 111 is changed. The objective lens 160 is moved so that an image is formed on a predetermined track.
[0482]
The second semiconductor laser 112 for reproducing the second optical disk is unitized with the photodetector 302 and the hologram 230 in the laser / detector integrated unit 400.
[0483]
The light beam emitted from the second semiconductor laser 112 passes through the hologram 230, is reflected by the beam splitter 190, which is a light combining unit, and passes through the beam splitter 120, the collimator 130, and the quarter wavelength plate 140 to become a parallel light beam. Further, the light is focused on the information recording surface 220 via the transparent substrate 210 of the second optical disk 200 via the diaphragm 170 and the objective lens 160.
[0484]
Then, the light beam modulated and reflected by the information pits on the information recording surface 220 is transmitted again through the quarter wavelength plate 140, the collimator 130, and the beam splitter 120 through the objective lens 160 and the diaphragm 170, and reflected by the beam splitter 190. Then, the light is diffracted by the hologram 230 and incident on the photodetector 302, and a read signal of information recorded on the second optical disc 200 is obtained using the output signal.
[0485]
Further, a change in the amount of light due to a change in the shape and position of the spot on the photodetector 302 is detected, and focus detection and track detection are performed. The two-dimensional actuator 150 moves the objective lens 160 for focusing and tracking. Move.
[0486]
The thickness t1 of the transparent substrate is substantially the same as that of the first optical disk, and the required numerical aperture NA on the optical information recording medium side of the objective lens necessary for recording / reproducing with the first light source having the wavelength λ1 is also the first optical disk. A case of recording / reproducing a third Super RENS disc of the same level as in FIG.
[0487]
The Super RENS disk is being studied energetically, and an example of its configuration is shown in FIG. The recording / reproducing is based on near-field optics, and there are a method using reflected light and a method using transmitted light as a reproduction signal, and the configuration of this embodiment shows a method for obtaining a reproduced signal using transmitted light.
[0488]
When recording / reproducing a third disk of the Super RENS system, a coupling lens 60 that emits a beam from the first semiconductor laser 111 to reduce the divergence of the divergent light beam, a beam splitter 190 that is a light combining unit, a beam splitter 120 passes through the collimator 130 and the quarter-wave plate 140 and becomes a parallel light beam. Further, the aperture is narrowed down by a diaphragm 170 and is condensed by the objective lens 160 onto the nonlinear optical film 250 through the transparent substrate 210 and the first protective film 240 of the first optical disc 200. A minute opening is formed in the nonlinear optical film 250, and energy is transmitted to the information recording surface 220 on the information recording layer via the second protective film 260. The light modulated and transmitted by the information pits on the information recording surface 220 passes through the third protective film 270, is collected by the condenser lens 90 on the side opposite to the objective lens, and reaches the photodetector 305. The read signal of the information recorded on the third optical disc 200 is obtained from the output signal.
[0489]
On the other hand, the light beam reflected from the nonlinear optical film 250 passes through the objective lens 160 and the diaphragm 170 again, passes through the quarter-wave plate 140 and the collimator 130, enters the beam splitter 120, and is reflected there. Astigmatism is given by the cylindrical lens 180 and is incident on the photodetector 301 through the concave lens 50. Focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector 301. Based on this detection, the two-dimensional actuator 150 moves the objective lens 160 so as to form an image of the light beam from the first semiconductor laser 111 on the nonlinear optical film 250 of the first optical disk 200, and from the semiconductor laser 111. The objective lens 160 is moved so that the light beam is focused on a predetermined track.
[0490]
As the objective lens of the optical pickup device described above, an objective lens is used by using a dedicated objective lens designed so that a non-aberration parallel light beam enters from the first light source and forms a non-aberration spot through the transparent substrate of the DVD. When a non-aberration parallel light is incident from the second light source to form a spot through the transparent substrate of the CD,
(1) Wavelength dependence of refractive index of objective lens
(2) Difference in transparent substrate thickness of optical information recording media
(3) Wavelength dependence of transparent substrate refractive index
As described above, spherical aberration occurs due to the above, but most are due to (2).
[0491]
The spherical aberration due to the factor (2) is substantially equal to | t2-t1 | and (NA2) at the numerical aperture NA2 necessary for CD recording / reproduction.⁴Is proportional to FIG. 110 shows a CD with a transparent substrate having a thickness of CD and a wavelength λ2 = 780 nm for a dedicated lens designed to be free of aberration through a transparent substrate of a DVD when a parallel light beam having a wavelength λ1 = 650 nm is incident on the objective lens. 6 shows the relationship between the imaging magnification M2 and the wavefront aberration when the numerical aperture of the light beam emitted from the objective lens is 0.45 when the above light source is used. When the imaging magnification M2 is 0, a parallel light beam enters the objective lens as in the DVD.
[0492]
As shown in the figure, when M2 = 0, spherical aberration of about 0.13 λrms occurs, which is larger than the Marechal limit of diffraction limited performance, 0.07 λrms. Therefore, it is necessary to set the spherical aberration so that the wavefront aberration is below the Marechal limit for both DVD and CD by some means.
[0493]
In this objective lens, when the imaging magnification is made negative, negative spherical aberration occurs in the objective lens, and becomes a minimum value when M≈−0.06, which is within the marginal limit. Thus, the amount of spherical aberration that must be corrected differs depending on the imaging magnification. In the illustrated example, when M≈−0.06, it is not necessary to correct spherical aberration by other means. Further, when the NA necessary for CD-R information recording is 0.5, the spherical aberration to be corrected further increases.
[0494]
Next, a preferred collimator adjusting unit in each of the above optical pickup devices will be described. In order to simplify the explanation, an optical pickup device using a condensing optical system composed of a collimator and an objective lens will be considered. Regarding the distance between the collimator and the light source, a desired parallel light is emitted from the collimator by arranging the light source at a focal position on the optical axis of the collimator. Because the back focus of the collimator, the distance between the mounting position of the semiconductor laser and the light emitting point, and the manufacturing variation of the housing of the optical pickup device that mounts the collimator and the semiconductor laser are suppressed, the distance between the semiconductor laser and the collimator is not adjusted. However, it is possible to obtain parallel light with an accuracy that is practically acceptable.
[0495]
By the way, in the case of recording and / or reproducing two types of optical information recording media having different transparent substrate thicknesses by using two light sources having different wavelengths, an objective lens having a diffraction pattern is used, and further, When diffracted light of the same order other than 0 is used, the fluctuation of spherical aberration is larger than that of an existing double-sided aspheric objective lens due to the fluctuation of the laser oscillation wavelength. In particular, in the objective lens as in Example 6, the wavefront aberration is 0.001 λms at a wavelength of 650 nm, but the wavelength deteriorates to about 0.035 λrms when the wavelength changes ± 10 nm. At this time, spherical aberration is generated. Semiconductor lasers have individual differences in oscillation wavelength, and when a semiconductor laser having a large individual difference is applied to an optical pickup device, there arises a problem that the standard of spherical aberration of an objective lens having a diffraction pattern becomes strict.
[0496]
In the objective lens used in the optical pickup device, negative third-order spherical aberration increases when the incident light beam changes from parallel light to divergent light, and positive third-order spherical aberration increases when the light beam becomes convergent light from the parallel light beam. The third order spherical aberration can be controlled by changing the divergence of the incident light beam to the objective lens. In the objective lens as in the sixth embodiment, the main component of the spherical aberration caused by the individual difference in the oscillation wavelength of the semiconductor laser is the third-order spherical aberration. Therefore, by changing the divergence of the incident light beam to the objective lens, The third-order spherical aberration of the entire focusing optical system can be made as designed.
[0497]
If there is a coupling lens such as a collimator in the condensing optical system, the third-order spherical aberration of the objective lens can be controlled by moving it in the optical axis direction. Further, when there is a coupling lens such as a collimator, the object can be similarly achieved by moving the semiconductor laser in the optical axis direction. Of course, when there is a coupling lens such as a collimator, the semiconductor laser may be moved in the optical axis direction.
[0498]
<Example 19>
[0499]
As a specific example of the objective lens according to the eighth embodiment, Example 19 of the spherical aberration correction lens is shown in FIG. 111, Table 20, and Table 21.
[0500]
In Table 20, ri represents the radius of curvature of the refractive surface, di and di 'represent the surface spacing, and ni and ni' represent the refractive index at the dominant wavelength. The surface shape formula is shown in the following [Equation 4].
[0501]
[Expression 4]

[0502]
Where X is an axis in the optical axis direction, h is an axis perpendicular to the optical axis, the traveling direction of light is positive, r is a paraxial radius of curvature, κ is a cone number, Aj is an aspheric coefficient, Pj (Pi ≧ 3) is an aspheric power.
[0503]
The diffraction surface is as shown in Equation 1 as an optical path difference function. The unit is expressed as mm.
[0504]
[Table 20]

[0505]
di and ni are values for the first optical information recording medium (t1 = 0.6 mm).
di ′ and ni ′ are values for the second optical information recording medium (t2 = 1.2 mm).
[0506]
[Table 21]

[0507]
A lens sectional view of the above example is shown in FIG. 111, and its spherical aberration is shown in FIG. In FIG. 111, a portion S2d including the optical axis of the second surface S2 has a diffraction pattern, and an outer portion S2r thereof is an aspherical refracting surface. FIG. 112 (a) is a spherical aberration diagram with a wavelength of 635 nm and the first optical information recording medium (t1 = 0.6 mm), and the aberration is sufficiently corrected. FIG. 4B is a spherical aberration diagram at a wavelength of 780 nm and the second optical information recording medium (t2 = 1.2 mm). The light beam passing through the first divided surface S2d is corrected for spherical aberration by the effect of diffraction. The light beam passing through the second divided surface S2r becomes flare light, which has the same effect as the diaphragm.
[0508]
The lens of the above example is an objective lens with NAH2 = 0.5 and NAL2 = 0. The diffraction pattern portion of this lens is a ring-shaped pattern with the optical axis as the center, and the number of steps is about 13. Further, the boundary between the circumferential portion farthest from the optical axis of the diffraction pattern portion and the refracting surface has a step of about 21 μm.
[0509]
When NAH2 = 0.45, the number of steps of the diffraction pattern is about 9, and the step amount is about 13 μm. The step amount and the number of steps of the diffraction pattern are substantially proportional to the fourth power of NAH2.
[0510]
When NAL2 = 0 as in this example, the number of steps of the diffraction pattern increases in proportion to the spherical aberration to be corrected.
[0511]
In the objective lens of the present invention, a good effect can be obtained even if the depth of the diffraction pattern in the optical axis direction is 2 μm or less. However, if the number of steps of the diffraction pattern is too large, it becomes difficult to mold and mold. It is desirable that the number of steps is as small as possible.
[0512]
(1) The image forming magnification of CD is made slightly smaller than the image forming magnification of DVD, and the amount of spherical aberration to be corrected is reduced in advance. Preferably, mCD (magnification during CD recording / playback) -mDVD (magnification during DVD recording / playback) is preferably -1/15 to 0. (2) Deep numerical aperture is small This can be achieved by not providing a diffraction pattern in the part.
[0513]
For example, if the imaging magnification of DVD is 0 and the imaging magnification of CD is -0.03, the spherical aberration to be corrected will be halved. The number is about 7, and the step amount is about 11 μm.
[0514]
When the step amount is small, the shape of the step S2s may smoothly transition from the diffraction pattern portion S2d to the refracting surface portion S2r.
[0515]
Further, in the case where the image forming magnification of DVD and the image forming magnification of CD are both 0, for example, if NAL2 = 0.36, the residual spherical aberration component WSA (NAL2) of the wavefront aberration of the light flux having a numerical aperture of NAL2 or less is obtained. About 0.053λrms. By attaching an optimal diffraction pattern to this, the RMS value of the wavefront aberration up to NAH2 can be reduced while keeping the wavefront aberration of DVD almost zero.
[0516]
The residual spherical aberration component WSA (NAH2) of the wavefront aberration of a light beam having a numerical aperture of NAH2 or less can be approximated by the following equation.
[0517]
WSA (NAH2) = (NAL2 / NAH2) 2 × WSA (NAL2)
Therefore, when NAH2 = 0.45, the above value is 0.034λrms, and when NAH2 = 0.5, 0.027λrms, which is sufficiently smaller than the Marechal limit value.
[0518]
At this time, since the over spherical aberration occurs at NAL2 or less, the spherical aberration from NAL2 to NAH2 is not set to 0, but may be substantially matched with the best focus of the light beam at NAL2 or less. Since this best focus position is over the paraxial focus, the amount of spherical aberration to be corrected by the diffraction pattern can be small. In addition, a diffraction pattern is not necessary for a light beam having a wavelength of NAL2 or less. With these two effects, the number of steps of the diffraction pattern is about 6 when NAH2 = 0.5, and the number of steps of the diffraction pattern is 4 when NAH2 = 0.45.
[0519]
Of course, by making the CD imaging magnification smaller than the DVD imaging magnification, the diffraction pattern can be further reduced. With at least two steps, compatible reproduction of DVD and CD becomes possible.
[0520]
Incidentally, a high-density optical information recording medium having a transparent substrate thickness of 0.1 mm has been proposed. For this recording / reproduction, a blue semiconductor laser is used, a double objective lens is used, and NA1 of 0.85 is required. On the other hand, CD-RW uses a light source having a transparent substrate thickness of 1.2 mm and a wavelength of 780, and NA2 is set to 0.55. In this compatible optical system, since NA2 is large and t1-t2 is large compared to the case of DVD and CD-R (NAH2 = 0.5), the correction amount of spherical aberration is also 2.7 times larger. Therefore, the number of steps of the diffraction pattern is about 35.
[0521]
Furthermore, in order to correct paraxial chromatic aberration, the number of steps of the diffraction pattern increases. Further, when correction is performed including paraxial chromatic aberration up to NA1, the number of steps is several hundreds. In such a case, the diffraction pattern can be applied to a plurality of optical surfaces.
[0522]
Further, if necessary, a certain part from NAL2 to NAH2 may be a refractive surface.
[0523]
Further, when t1> t2, the sign of the generated spherical aberration is reversed, so that −1st order light is used.
[0524]
Similarly, in the case of DVD and CD, if the imaging magnification of CD of the objective lens is considerably smaller than the imaging magnification of DVD and the under spherical aberration remains, −1st order light is similarly used. .
[0525]
In addition, about DVD and CD which are important concerns now, the example implemented with a single objective lens using two lasers with different recording or wavelengths was shown. As already described, when the wavelength of the first light source is λ1 and the wavelength of the second light source is λ2 (λ2> λ1), when t1 <t2, + 1st order diffracted light is used, and t1> t2 In some cases, a first diffraction pattern using -1st order diffracted light is introduced, but in the case of DVD (using a first light source) and CD (using a second light source), the former.
[0526]
By the way, light sources with various wavelengths such as blue semiconductor lasers and SHG lasers have been put into practical use in recent years, and many new optical information recording media will appear in the future. In this case, the required spot size is determined from the recording density of the optical information recording medium, but the NA required for recording or recording / reproducing varies depending on the wavelength of the light source used. For this reason, the thickness of the transparent substrate of the optical information recording medium and the required NA are classified into the following four types for the two optical information recording media.
(1) t1 <t2, NA1> NA2
(2) t1 <t2, NA1 <NA2
(3) t1> t2, NA1> NA2
(4) t1> t2, NA1 <NA2
[0527]
In the above description, the diffraction order of the first diffraction pattern used for the light source of the first diffraction pattern, the first diffraction pattern range (NAH1, NAL1, NAH2, NAL2), the diffraction pattern portion and the transmission are used. The type and NA range of the light source that needs to be condensed at the same position, the NA range for setting the spherical aberration for each light source, and the need for the wavefront aberration to be 0.07λrms or less for each light source Limiting the luminous flux from which light source when introducing a certain NA range, the diffraction order for each light source of the second diffraction pattern and the necessity of condensing at the same position as the first diffraction pattern, and aperture restriction The conditions (2), (3), and (4) have been described in detail, but the detailed description is omitted because the cases (2), (3), and (4) can be easily performed from the details of (1).
[0528]
Also, at the time of manufacturing the lens, it is possible to integrally mold a plastic material or a glass material with a mold engraved with a diffraction pattern. An optical surface may be formed. Further, it may be manufactured by coating or direct processing.
[0529]
As described above, the optical surface having the effect of the present invention may be provided on an optical element different from the objective lens, and the optical element may be provided on the light source side or the optical information recording medium side of the objective lens. Of course, you may arrange | position on the optical surface through which the light beam from the 1st light source of a collimator or a photosynthesis means and the light beam from a 2nd light source pass together. However, when the objective lens moves due to tracking or the like, the optical axis of the diffraction pattern and the optical axis of the objective lens move relatively, so that the amount of tracking is limited.
[0530]
Further, for convenience of explanation, the diffraction pattern is concentric with respect to the optical axis, but is not limited thereto.
[0531]
Although the objective lens specifically shown in the above Examples 1 to 19 has been exemplified by a single lens, the objective lens may be composed of a plurality of lenses. The case having the diffractive surface of the invention is also included in the present invention.
[0532]
In the present invention, it is preferable that the diffraction efficiency of the diffracted light of the specific order is 10% or more higher than the diffraction efficiency of the diffracted light of the other orders with respect to the light of two different wavelengths. The diffraction efficiency of the specific order diffracted light is preferably 50% or more, more preferably 70% or more, and the loss of light amount is small. Practically preferred.
[0533]
Further, as shown in the above embodiments and specific examples of lenses, the diffractive surface of the present invention is selectively generated with at least two wavelengths different from each other due to the presence of the diffractive surface. When the diffracted light beams of a specific order are focused on each other, it is desirable that the spherical aberration be improved as compared with the case where there is no diffractive surface, that is, when a surface enveloping the relief of the diffractive surface is assumed by simulation or the like.
[0534]
Furthermore, in the present invention, the diffracted light of a specific order that is selectively generated with respect to each of light of different at least two wavelengths (wavelength λ) has zero wavefront aberration on the image plane. In order to obtain a practically effective desired spot, it is preferable that it is 0.07λrms or less. The embodiments described above can be modified by those skilled in the art without departing from the technical idea and scope of the present invention.
[0535]
As described above, according to the present invention, it is possible to correct spherical aberration and axial chromatic aberration with respect to at least two different wavelengths of light with a simple configuration using at least one optical element having a diffractive surface. System, optical pickup device, recording / reproducing device, lens, optical element, diffractive optical system for optical disc, sound and / or image recording and / or reproducing device, and objective lens can be obtained. In addition, at least the optical system can be reduced in size and weight and cost. Further, when the optical element has a diffractive surface that maximizes the diffraction efficiency of diffracted light of the same order with respect to light of at least two different wavelengths, the diffraction efficiency of diffracted light of different orders is maximized. The loss of light quantity can be reduced as compared with the case of doing so.
[0536]
In particular, by providing a diffractive lens on the refracting surface, it is used in a recording / reproducing optical system having two light sources having different wavelengths. A corrected diffractive optical system can be obtained.
[0537]
In particular, as described above, for one of the three light sources having different wavelengths, one objective lens can record information and / or reproduce information on different optical discs. Since no ring lens is used, the optical pickup device can be thinned, and the problem of high cost can be solved.
[0538]
In particular, in an optical pickup device having three light sources having different wavelengths, the aspherical coefficient and the phase difference function coefficient are appropriately designed to generate a spherical aberration and a wavelength difference caused by a difference in transparent substrate thickness. It is possible to provide an optical pickup device and an objective lens that correct chromatic aberration of spherical aberration and axial chromatic aberration.
[0539]
Further, in particular, by providing a plurality of dividing surfaces on the objective lens and providing a diffraction surface on the first dividing surface, a single condensing optical system for optical information recording media having transparent substrates with different thicknesses. By the system, it is possible to provide a spherical aberration correction objective lens and an optical pickup device for recording / reproducing of an optical information recording medium which can be recorded / reproduced by light beams having different wavelengths.
[0540]
Further, the objective lens for the optical pickup device includes a plurality of annular zones divided concentrically, and each annular zone is provided for a plurality of light sources having different wavelengths and / or transparent substrates having different recording surface thicknesses. Aberration correction is made almost to the diffraction limit, and flare light incident on the photodetector can be reduced, making it easy to manufacture.
[0541]
【The invention's effect】
As described above, according to the present invention, it is possible to correct spherical aberration and axial chromatic aberration with respect to light of at least two wavelengths different from each other with a simple configuration using at least one optical element having a diffractive surface. A pickup device, a recording / reproducing apparatus, a recording / reproducing method, and an objective lens that are stable against changes can be obtained. In addition, at least the optical system can be reduced in size and weight and cost. Further, when the optical element has a diffractive surface that maximizes the diffraction efficiency of diffracted light of the same order with respect to light of at least two different wavelengths, the diffraction efficiency of diffracted light of different orders is maximized. The loss of light quantity can be reduced as compared with the case of doing so.
[Brief description of the drawings]
FIG. 1 is an optical path diagram of a diffractive optical lens according to a first embodiment of the present invention.
FIG. 2 is a spherical aberration diagram for the wavelength λ = 635 nm by the diffractive optical lens according to Example 1 of the present invention;
FIG. 3 is a spherical aberration diagram up to NA 0.45 for wavelength λ = 780 nm by the diffractive optical lens according to Example 1 of the present invention;
FIG. 4 is a spherical aberration diagram up to NA 0.60 for wavelength λ = 780 nm by the diffractive optical lens according to Example 1 of the present invention;
FIG. 5 is a wavefront aberration diagram with respect to a wavelength λ = 635 nm by the diffractive optical lens according to Example 1 of the present invention;
6 is a wavefront aberration diagram with respect to a wavelength λ = 780 nm by the diffractive optical lens according to Example 1 of the present invention; FIG.
FIG. 7 is an optical path diagram for a wavelength λ = 405 nm by the diffractive optical lens according to Example 2 of the present invention;
FIG. 8 is an optical path diagram with respect to a wavelength λ = 635 nm by the diffractive optical lens according to Example 2 of the present invention;
FIG. 9 is a spherical aberration diagram with respect to a wavelength λ = 405 nm by the diffractive optical lens according to Example 2 of the present invention;
FIG. 10 is a spherical aberration diagram for the wavelength λ = 635 nm by the diffractive optical lens according to Example 2 of the present invention;
FIG. 11 is a wavefront aberration diagram with respect to a wavelength λ = 405 nm by the diffractive optical lens according to Example 2 of the present invention;
12 is a wavefront aberration diagram with respect to a wavelength λ = 635 nm by the diffractive optical lens according to Example 2 of the present invention; FIG.
FIG. 13 is an optical path diagram for a wavelength λ = 405 nm by the diffractive optical lens according to Example 3 of the present invention;
FIG. 14 is an optical path diagram for a wavelength λ = 635 nm by the diffractive optical lens according to Example 3 of the present invention;
FIG. 15 is a spherical aberration diagram for the wavelength λ = 405 nm by the diffractive optical lens according to Example 3 of the present invention;
FIG. 16 is a spherical aberration diagram for the wavelength λ = 635 nm by the diffractive optical lens according to Example 3 of the present invention;
FIG. 17 is a wavefront aberration diagram at the wavelength λ = 405 nm by the diffractive optical lens according to Example 3 of the present invention;
FIG. 18 is a wavefront aberration diagram with respect to a wavelength λ = 635 nm by the diffractive optical lens according to Example 3 of the present invention;
FIG. 19 is an optical path diagram of the diffractive optical lens according to Example 4 of the present invention.
20 is a spherical aberration diagram with respect to wavelengths λ = 635 nm, 650 nm, and 780 nm by the diffractive optical lens according to Example 4 of the present invention; FIG.
FIG. 21 is an optical path diagram of the diffractive optical lens according to Example 5 of the present invention.
22 is a spherical aberration diagram with respect to wavelengths λ = 635 nm, 650 nm, and 780 nm by the diffractive optical lens of Example 5 of the present invention. FIG.
FIG. 23 is an optical path diagram for a wavelength λ = 650 nm by the diffractive optical lens according to Example 6 of the present invention;
FIG. 24 is an optical path diagram for the wavelength λ = 780 nm (NA = 0.5) by the diffractive optical lens according to Example 6 of the present invention;
FIG. 25 is a spherical aberration diagram up to numerical aperture 0.60 for wavelength λ = 650 ± 10 nm by the diffractive optical lens according to Example 6 of the present invention.
FIG. 26 is a spherical aberration diagram up to numerical aperture 0.50 for wavelength λ = 780 ± 10 nm by the diffractive optical lens according to Example 6 of the present invention.
FIG. 27 is a spherical aberration diagram up to numerical aperture 0.60 for wavelength λ = 780 nm by the diffractive optical lens according to Example 6 of the present invention;
FIG. 28 is a wavefront aberration rms diagram with respect to wavelength λ = 650 nm by the diffractive optical lens according to Example 6 of the present invention;
FIG. 29 is a wavefront aberration rms diagram with respect to wavelength λ = 780 nm by the diffractive optical lens according to Example 6 of the present invention;
30 is an optical path diagram for a wavelength λ = 650 nm by the diffractive optical lens according to Example 7 of the present invention; FIG.
FIG. 31 is an optical path diagram for a wavelength λ = 780 nm (NA = 0.5) by the diffractive optical lens according to Example 7 of the present invention;
FIG. 32 is a spherical aberration diagram up to numerical aperture 0.60 for wavelength λ = 650 ± 10 nm by the diffractive optical lens according to Example 7 of the present invention;
FIG. 33 is a spherical aberration diagram up to numerical aperture 0.50 for wavelength λ = 780 ± 10 nm by the diffractive optical lens according to Example 7 of the present invention.
FIG. 34 is a spherical aberration diagram up to numerical aperture 0.60 for wavelength λ = 780 nm by the diffractive optical lens of Example 7 of the present invention.
FIG. 35 is a wavefront aberration rms diagram with respect to wavelength λ = 650 nm by the diffractive optical lens according to Example 7 of the present invention;
FIG. 36 is a wavefront aberration rms diagram with respect to wavelength λ = 780 nm by the diffractive optical lens according to Example 7 of the present invention;
FIG. 37 is an optical path diagram for the wavelength λ = 650 nm by the diffractive optical lens according to Example 8 of the present invention;
FIG. 38 is an optical path diagram for the wavelength λ = 780 nm (NA = 0.5) by the diffractive optical lens according to Example 8 of the present invention;
FIG. 39 is a spherical aberration diagram up to numerical aperture 0.60 for wavelength λ = 650 ± 10 nm by the diffractive optical lens according to Example 8 of the present invention.
40 is a spherical aberration diagram up to numerical aperture 0.50 for wavelength λ = 780 ± 10 nm by the diffractive optical lens according to Example 8 of the present invention. FIG.
FIG. 41 is a spherical aberration diagram up to numerical aperture 0.60 for wavelength λ = 780 nm by the diffractive optical lens according to Example 8 of the present invention;
FIG. 42 is a wavefront aberration rms diagram with respect to wavelength λ = 650 nm by the diffractive optical lens according to Example 8 of the present invention;
FIG. 43 is a wavefront aberration rms diagram with respect to wavelength λ = 780 nm by the diffractive optical lens according to Example 8 of the present invention;
FIG. 44 is a graph showing the relationship between the number of diffraction ring zones and the height from the optical axis for the diffractive optical lens according to Example 6 of the present invention;
FIG. 45 is a graph showing the relationship between the number of diffraction ring zones and the height from the optical axis for the diffractive optical lens according to Example 7 of the present invention;
FIG. 46 is a graph showing the relationship between the number of diffraction ring zones and the height from the optical axis for the diffractive optical lens according to Example 8 of the present invention;
FIG. 47 is a diagram schematically showing the relationship between the diffractive lens power and the lens shape for the diffractive optical lens according to the working example of the present invention.
FIG. 48 is an optical path diagram showing the configuration of the optical pickup apparatus according to the second embodiment of the present invention.
FIG. 49 is an optical path diagram showing the configuration of the optical pickup apparatus according to the third embodiment of the present invention.
FIG. 50 is an optical path diagram for the wavelength λ = 650 nm of the objective lens according to Example 9 of the present invention;
FIG. 51 is an optical path diagram with respect to wavelength λ = 780 nm of an objective lens according to Example 9 of the present invention;
FIG. 52 is a spherical aberration diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 9 of the present invention.
FIG. 53 is a spherical aberration diagram up to NA0.45 for wavelength λ = 780 nm for the objective lens according to Example 9 of the present invention.
54 is a spherical aberration diagram up to NA 0.60 for wavelength λ = 780 nm for the objective lens according to Example 9 of the present invention. FIG.
FIG. 55 is a wavefront aberration diagram at a wavelength λ = 650 nm for the objective lens according to Example 9 of the present invention.
FIG. 56 is a wavefront aberration diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 9 of the present invention;
FIG. 57 is an optical path diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 10 of the present invention;
FIG. 58 is an optical path diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 10 of the present invention;
FIG. 59 is an optical path diagram for the wavelength λ = 780 nm with respect to the objective lens according to Example 10 of the present invention.
FIG. 60 is a spherical aberration diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 10 of the present invention;
61 is a spherical aberration diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 10 of the present invention. FIG.
FIG. 62 is a spherical aberration diagram up to NA0.45 for wavelength λ = 780 nm for the objective lens according to Example 10 of the present invention;
FIG. 63 is a spherical aberration diagram up to NA0.65 for wavelength λ = 780 nm for the objective lens according to Example 10 of the present invention;
FIG. 64 is a wavefront aberration diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 10 of the present invention;
FIG. 65 is a wavefront aberration diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 10 of the present invention;
FIG. 66 is a wavefront aberration diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 10 of the present invention;
FIG. 67 is a diagram showing a configuration of an optical pickup device according to a fourth embodiment of the present invention.
FIG. 68 is an optical path diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 11 of the present invention;
FIG. 69 is an optical path diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 11 of the present invention;
FIG. 70 is an optical path diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 11 of the present invention;
FIG. 71 is a spherical aberration diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 11 of the present invention;
72 is a spherical aberration diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 11 of the present invention; FIG.
FIG. 73 is a spherical aberration diagram up to numerical aperture 0.45 for wavelength λ = 780 nm for the objective lens according to Example 11 of the present invention;
74 is a spherical aberration diagram up to numerical aperture 0.65 for wavelength λ = 780 nm, concerning the objective lens according to Example 11 of the present invention. FIG.
FIG. 75 is a wavefront aberration diagram at a wavelength λ = 650 nm for the objective lens according to Example 11 of the present invention;
FIG. 76 is a wavefront aberration diagram at the wavelength λ = 400 nm for the objective lens according to Example 11 of the present invention;
77 is a wavefront aberration diagram at the wavelength λ = 780 nm for the objective lens according to Example 11 of the present invention. FIG.
FIG. 78 is an optical path diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 12 of the present invention;
FIG. 79 is an optical path diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 12 of the present invention;
FIG. 80 is an optical path diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 12 of the present invention;
81 is a spherical aberration diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 12 of the present invention; FIG.
FIG. 82 is a spherical aberration diagram with respect to a wavelength λ = 400 nm for the objective lens according to Example 12 of the present invention.
83 is a spherical aberration diagram up to numerical aperture 0.45 for wavelength λ = 780 nm, concerning the objective lens according to Example 12 of the present invention. FIG.
84 is a spherical aberration diagram up to numerical aperture 0.65 for wavelength λ = 780 nm, concerning the objective lens according to Example 12 of the present invention. FIG.
FIG. 85 is a wavefront aberration diagram at a wavelength λ = 650 nm for the objective lens according to Example 12 of the present invention;
FIG. 86 is a wavefront aberration diagram at the wavelength λ = 400 nm for the objective lens according to Example 12 of the present invention.
FIG. 87 is a wavefront aberration diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 12 of the present invention;
FIG. 88 is an optical path diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 13 of the present invention;
FIG. 89 is an optical path diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 13 of the present invention;
FIG. 90 is an optical path diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 13 of the present invention;
FIG. 91 is a spherical aberration diagram with respect to wavelength λ = 650 nm for the objective lens according to Example 13 of the present invention;
FIG. 92 is a spherical aberration diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 13 of the present invention;
93 is a spherical aberration diagram up to numerical aperture 0.45 for wavelength λ = 780 nm, for the objective lens according to Example 13 of the present invention. FIG.
FIG. 94 is a spherical aberration diagram up to numerical aperture 0.65 for wavelength λ = 780 nm, concerning the objective lens according to Example 13 of the present invention.
FIG. 95 is a wavefront aberration diagram at a wavelength λ = 650 nm for the objective lens according to Example 13 of the present invention;
FIG. 96 is a wavefront aberration diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 13 of the present invention;
FIG. 97 is a wavefront aberration diagram with respect to wavelength λ = 780 nm for the objective lens according to Example 13 of the present invention;
FIG. 98 is an optical path diagram with respect to wavelength λ = 400 nm for the objective lens according to Example 13 of the present invention;
FIG. 99 is a spherical aberration diagram with respect to wavelength λ = 400 nm ± 10 nm for the objective lens according to Example 13 of the present invention;
FIG. 100 is a spherical aberration diagram with respect to wavelength λ = 650 nm ± 10 nm for the objective lens according to Example 13 of the present invention;
FIG. 101 is a spherical aberration diagram with respect to wavelength λ = 780 nm ± 10 nm for the objective lens according to Example 13 of the present invention;
FIG. 102 is an optical path diagram showing a first configuration of the optical pickup apparatus according to the eighth embodiment of the present invention.
FIG. 103 is an optical path diagram showing a second configuration of the optical pickup apparatus according to the eighth embodiment of the present invention;
FIG. 104 is an optical path diagram showing a third configuration of the optical pickup apparatus according to the eighth embodiment of the present invention.
FIG. 105 is an optical path diagram showing a fourth configuration of the optical pickup apparatus according to the eighth embodiment of the present invention.
FIG. 106 is an optical path diagram showing a fifth configuration of the optical pickup apparatus according to the eighth embodiment of the present invention.
FIG. 107 is an optical path diagram showing a sixth configuration of the optical pickup apparatus according to the eighth embodiment of the present invention;
FIG. 108 is an optical path diagram showing a seventh configuration of the optical pickup apparatus according to the eighth embodiment of the present invention.
FIG. 109 is a schematic diagram showing the structure of a Super RENS optical disc.
110 is a graph showing the relationship between the imaging magnification m2 and the wavefront aberration of the objective lens according to Example 15 according to the eighth embodiment of the present invention. FIG.
FIG. 111 is a cross sectional view of Example 15 according to the eighth embodiment of the present invention;
112 is a spherical aberration diagram of Example 15; FIG.
FIG. 113 is an explanatory diagram of the action of a diffraction pattern.
FIG. 114 is a schematic diagram showing the influence of chromatic aberration on the spherical aberration of the objective lens according to the eighth embodiment of the present invention.
FIG. 115 is a schematic diagram showing the influence of + 1st order diffraction on the spherical aberration of the objective lens according to the eighth embodiment of the present invention.
FIG. 116 is a schematic diagram showing the influence of −1st order diffraction on the spherical aberration of the objective lens according to the eighth embodiment of the present invention.
FIG. 117 is an optical path diagram showing the configuration of the optical pickup apparatus according to the seventh embodiment of the present invention;
FIG. 118 is an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is an objective lens according to Example 15 according to the seventh embodiment of the invention.
119 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths (λ) = 640, 650, and 660 nm of the diffractive optical lens in FIG. 118;
120 is an optical path diagram of the diffractive optical lens in Example 15 when the transparent substrate of the optical information recording medium is thicker than FIG. 118. FIG.
121 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths λ = 770, 780, and 790 nm of the diffractive optical lens in FIG. 120;
FIG. 122 is an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is an objective lens according to Example 16 according to the seventh embodiment of the invention;
123 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths (λ) = 640, 650, and 660 nm of the diffractive optical lens in FIG. 122;
124 is an optical path diagram of the diffractive optical lens in Example 16 when the transparent substrate of the optical information recording medium is thicker than FIG. 122. FIG.
125 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths λ = 770, 780, and 790 nm of the diffractive optical lens in FIG. 124;
FIG. 126 is an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is an objective lens according to Example 17 according to the seventh embodiment of the invention.
127 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths (λ) = 640, 650, and 660 nm of the diffractive optical lens in FIG. 126;
128 is an optical path diagram of the diffractive optical lens in Example 17 when the transparent substrate of the optical information recording medium is thicker than that in FIG. 126. FIG.
129 is a spherical aberration diagram up to numerical aperture 0.60 for wavelengths λ = 770, 780, and 790 nm of the diffractive optical lens in FIG. 128;
FIG. 130 is an optical path diagram of a diffractive optical lens (objective lens having a diffractive surface) which is an objective lens according to Example 18 according to the seventh embodiment of the invention.
131 is a spherical aberration diagram up to numerical aperture 0.70 for wavelengths (λ) = 390, 400, and 410 nm of the diffractive optical lens in FIG. 130;
132 is an optical path diagram of the diffractive optical lens in Example 18 when the transparent substrate of the optical information recording medium is thicker than FIG. 130. FIG.
133 is a spherical aberration diagram up to numerical aperture 0.70 for wavelengths λ = 640, 650, and 660 nm of the diffractive optical lens in FIG. 132. FIG.
FIG. 134 is a diagram for explaining the pitch of a diffraction ring zone and the depth of a step in the present invention.
[Explanation of symbols]
1 Objective lens
2 Collimator lens
3 Aperture
4 optical axes
5 Condensing optical system
6,7 Beam splitter
10 Optical pickup device
11 First semiconductor laser
12 Blue laser
13 Second semiconductor laser
16 Objective lens
16a Flange part
20 Optical disc
21 Transparent substrate
22 Information recording surface
111, 112 semiconductor laser
120, 121, 122 Polarizing beam splitter
130, 131, 132 collimator
140, 141, 142 1/4 wave plate
150 Two-dimensional actuator
160 Objective lens
170 aperture
180 Cylindrical lens
190 Beam splitter
200 optical disc
210 Transparent substrate
220 Information recording surface
230,231,232 hologram
240 First protective film
250 Nonlinear optical film
260 Second protective film
270 Third protective film
300, 301, 302, 305 photodetector
400, 410, 420, 430 Laser / detector integrated unit
50 concave lens
60 coupling ring lens
90 condenser lens

Claims (38)

In an optical pickup device for reproducing information from an optical information recording medium or recording information on an optical information recording medium,
Information is reproduced from a first optical information recording medium having a first transparent substrate, or a first light beam having a first wavelength for recording information on the first optical information recording medium is emitted. A first light source;
The information for reproducing information from a second optical information recording medium having a second transparent substrate having a thickness different from that of the first transparent substrate, or for recording information on the second optical information recording medium A second light source that emits a second light flux having a second wavelength different from the first wavelength;
A condensing optical system having an objective lens, an optical axis, and a diffraction part;
A photodetector for receiving a light beam reflected from the information recording surface of the first optical information recording medium or the information recording surface of the second optical information recording medium,
In the condensing optical system, when the first light flux passes through at least a part of the diffractive portion, the amount of light of the n-th order diffracted light (where n is an integer other than 0) of the first light flux is Generating at least one order of diffracted light that is greater than the amount of light of any other order of diffracted light in order to reproduce information from the first optical information recording medium, or In order to record information on the optical information recording medium, the n-th order diffracted light of the first light flux is collected on the information recording surface of the first optical information recording medium via the first transparent substrate. Can light,
In the condensing optical system, when the second light flux passes through at least a part of the diffractive portion, the amount of light of the n-order diffracted light (where n is an integer other than 0) of the second light flux is In order to generate at least one order of diffracted light that is larger than the amount of light of any other order of diffracted light in order to reproduce information from the second optical information recording medium, or the second In order to record information on the optical information recording medium, the n-th order diffracted light of the second light beam is collected on the information recording surface of the second optical information recording medium via the second transparent substrate. An optical pickup device capable of emitting light and satisfying the following conditional expression :
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Here, ΔT (° C.): temperature change Δn: change in refractive index of the objective lens when there is a temperature change ΔT
Δλ1 (nm) : Amount of change in wavelength of the first light flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux  The condensing optical system causes the n-th order diffracted light in the first light flux to be on the information recording surface of the first optical information recording medium, on the image side of the objective lens, on a predetermined aperture in the first light flux. The focusing optical system can focus the n-order diffracted light in the second light flux on the information recording surface of the second optical information recording medium. 2. The optical pickup device according to claim 1, wherein the light can be condensed in a state of 0.07 λ rms or less within a predetermined numerical aperture of the second light flux on the image side of the lens.  The optical pickup device according to claim 1, wherein the nth-order diffracted light is + 1st-order diffracted light. The optical pickup device according to claim 1, wherein the following conditional expression is satisfied.
0.55mm <t1 <0.65mm
1.1mm <t2 <1.3mm
630 nm <λ1 <670 nm
760 nm <λ2 <820 nm
0.55 <NA1 <0.68
0.40 <NA2 <0.55 The optical pickup device according to claim 4, wherein the following conditional expression is satisfied.
t1 = 0.6mm
t2 = 1.2mm
λ1 = 650 nm
λ2 = 780 nm
NA1 = 0.6
NA2 = 0.45 When the diffraction efficiency of the n-th order diffracted light of the first light flux in the diffractive portion is A% and the diffraction efficiency of other diffracted light of a certain order is B%, A−B ≧ 10.
A′−B ′ ≧ 10 when the diffraction efficiency of the n-th order diffracted light of the second light flux in the diffractive portion is A ′% and the diffraction efficiency of another certain order of diffracted light is B ′%. The optical pickup device according to claim 1, wherein the optical pickup device is an optical pickup device.  The diffraction part has a plurality of annular zones when viewed from the direction of the optical axis, and the plurality of annular zones are formed on substantially concentric circles centered on the optical axis or a point in the vicinity of the optical axis. The optical pickup device according to claim 1, wherein: The diffraction part has a first diffraction pattern and a second diffraction pattern,
The optical pickup device according to claim 7, wherein the second diffraction pattern is further away from the optical axis than the first diffraction pattern.  2. The optical pickup device according to claim 1, wherein the n-order diffracted light is + 1st-order diffracted light or -1st-order diffracted light. When the second light flux is used, the second light flux within a predetermined numerical aperture on the image side of the objective lens has zero wavefront aberration on the information recording surface of the second optical information recording medium. .07λrms or less in the focused state,
Using the second light beam, the second light beam that has passed outside the predetermined numerical aperture has a wavefront aberration greater than 0.07λrms on the information recording surface of the second optical information recording medium. And
Using the first light flux, both the first light flux that has passed through the predetermined numerical aperture and the first light flux that has passed outside the predetermined numerical aperture are both the first optical information recording medium. The optical pickup device according to claim 1, wherein the optical pickup device is focused on the information recording surface with a wavefront aberration of 0.07 λrms or less.  The optical pickup device according to claim 1, wherein the condensing optical system includes a lens having a refracting surface, and the diffraction unit is provided on the lens.  The optical pickup device according to claim 11, wherein the lens is the objective lens.  The optical pickup device according to claim 12, wherein the objective lens has a flange portion on an outer periphery.  The optical pickup device according to claim 12, wherein the refractive surface of the objective lens is an aspherical surface.  The optical pickup device according to claim 11, wherein the lens is made of a material having an Abbe number νd larger than 50.  The optical pickup device according to claim 11, wherein the lens is a plastic lens.  The optical pickup device according to claim 11, wherein the lens is a glass lens.  18. The optical pickup device according to claim 1, wherein a wavelength difference between the first light flux and the second light flux is 80 nm to 400 nm. An objective lens used in an optical pickup device for reproducing information from an optical information recording medium or recording information on an optical information recording medium,
Having an optical axis and a diffraction part,
A first light beam having a first wavelength for reproducing information from a first optical information recording medium having a first transparent substrate or recording information on the first optical information recording medium is diffracted. By passing at least a part of the part, the light quantity of the nth-order diffracted light (where n is an integer other than 0) of the first light flux is any light quantity of any other order of the first light flux. In order to generate at least one order of diffracted light that is greater than and reproduce information from the first optical information recording medium or to record information on the first optical information recording medium. The n-th order diffracted light of one luminous flux can be condensed on the information recording surface of the first optical information recording medium via the first transparent substrate;
The information for reproducing information from a second optical information recording medium having a second transparent substrate having a thickness different from that of the first transparent substrate, or for recording information on the second optical information recording medium A second light beam having a second wavelength different from the first wavelength passes through at least a part of the diffractive portion, whereby the nth-order diffracted light of the second light beam (where n is an integer other than 0). For generating at least one order of diffracted light that is greater than the amount of light of any other order of diffracted light in the second light flux, and for reproducing information from the second optical information recording medium, or In order to record information on the second optical information recording medium, the n-th order diffracted light of the second light beam is transmitted to the information recording medium of the second optical information recording medium via the second transparent substrate. Can focus on the surface,
An objective lens for an optical pickup device that satisfies the following conditional expression:
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Here, ΔT (° C.): temperature change Δn: change in refractive index of the objective lens when there is a temperature change ΔT
Δλ1 (nm) : Amount of change in wavelength of the first light flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux The objective lens has the n-th order diffracted light in the first light flux on the information recording surface of the first optical information recording medium within a predetermined numerical aperture in the first light flux on the image side of the objective lens. Then, it can collect light in a state of 0.07λrms or less,
The objective lens has the n-th order diffracted light in the second light flux on the information recording surface of the second optical information recording medium within a predetermined numerical aperture in the second light flux on the image side of the objective lens. The objective lens according to claim 19, wherein the light can be condensed in a state of 0.07 λrms or less.  The objective lens according to claim 19 or 20, wherein the nth-order diffracted light is + 1st-order diffracted light. The objective lens according to claim 19, wherein the following conditional expression is satisfied.
0.55mm <t1 <0.65mm
1.1mm <t2 <1.3mm
630 nm <λ1 <670 nm
760 nm <λ2 <820 nm
0.55 <NA1 <0.68
0.40 <NA2 <0.55 The objective lens according to claim 22, wherein the following conditional expression is satisfied.
t1 = 0.6mm
t2 = 1.2mm
λ1 = 650 nm
λ2 = 780 nm
NA1 = 0.6
NA2 = 0.45 When the diffraction efficiency of the n-th order diffracted light of the first light flux in the diffractive portion is A% and the diffraction efficiency of other diffracted light of a certain order is B%, A−B ≧ 10.
A′−B ′ ≧ 10 when the diffraction efficiency of the n-th order diffracted light of the second light flux in the diffractive portion is A ′% and the diffraction efficiency of another certain order of diffracted light is B ′%. The objective lens according to any one of claims 19 to 23, wherein:  The diffraction part has a plurality of annular zones when viewed from the direction of the optical axis, and the plurality of annular zones are formed on substantially concentric circles centered on the optical axis or a point in the vicinity of the optical axis. The objective lens according to any one of claims 19 to 24, wherein: The diffraction part has a first diffraction pattern and a second diffraction pattern,
The objective lens according to claim 25, wherein the second diffraction pattern is further away from the optical axis than the first diffraction pattern.  The objective lens according to claim 19, wherein the nth-order diffracted light is + 1st-order diffracted light or −1st-order diffracted light. When the second light flux is used, the second light flux within a predetermined numerical aperture on the image side of the objective lens has zero wavefront aberration on the information recording surface of the second optical information recording medium. .07λrms or less in the focused state,
Using the second light beam, the second light beam that has passed outside the predetermined numerical aperture has a wavefront aberration greater than 0.07λrms on the information recording surface of the second optical information recording medium. And
Using the first light flux, both the first light flux that has passed through the predetermined numerical aperture and the first light flux that has passed outside the predetermined numerical aperture are both the first optical information recording medium. The objective lens according to claim 19, wherein the objective lens is focused on the information recording surface in a state where the wavefront aberration is 0.07 λrms or less.  The objective lens according to claim 19, wherein the objective lens has a refractive surface.  The objective lens according to claim 29, further comprising a flange portion on an outer periphery.  The objective lens according to claim 29, wherein the refractive surface is an aspherical surface.  30. Objective lens according to claim 29, characterized in that it is made of a material with an Abbe number νd greater than 50.  The objective lens according to claim 29, wherein the objective lens is a plastic lens.  It is a glass lens, The objective lens of any one of Claims 29-32 characterized by the above-mentioned.  The objective lens according to any one of claims 19 to 34, wherein a wavelength difference between the first light flux and the second light flux is 80 nm to 400 nm.  An apparatus for reproducing information from an optical information recording medium or recording information on an optical information recording medium, comprising the optical pickup device according to any one of claims 1 to 18. Recording / playback device. An apparatus for reproducing information from an optical information recording medium or recording information on an optical information recording medium,
Equipped with an optical pickup device,
The optical pickup device is:
Information is reproduced from a first optical information recording medium having a first transparent substrate, or a first light beam having a first wavelength for recording information on the first optical information recording medium is emitted. A first light source;
The information for reproducing information from a second optical information recording medium having a second transparent substrate having a thickness different from that of the first transparent substrate, or for recording information on the second optical information recording medium A second light source that emits a second light flux having a second wavelength different from the first wavelength;
A condensing optical system having an objective lens, an optical axis, and a diffraction part;
A photodetector for receiving a light beam reflected from the information recording surface of the first optical information recording medium or the information recording surface of the second optical information recording medium,
In the condensing optical system, when the first light flux passes through at least a part of the diffractive portion, the amount of light of the n-th order diffracted light (where n is an integer other than 0) of the first light flux is Generating at least one order of diffracted light that is greater than the amount of light of any other order of diffracted light in order to reproduce information from the first optical information recording medium, or In order to record information on the optical information recording medium, the n-th order diffracted light of the first light flux is collected on the information recording surface of the first optical information recording medium via the first transparent substrate. Can light,
In the condensing optical system, when the second light flux passes through at least a part of the diffractive portion, the amount of light of the n-order diffracted light (where n is an integer other than 0) of the second light flux is In order to generate at least one order of diffracted light that is larger than the amount of light of any other order of diffracted light in order to reproduce information from the second optical information recording medium, or the second In order to record information on the optical information recording medium, the n-th order diffracted light of the second light beam is collected on the information recording surface of the second optical information recording medium via the second transparent substrate. A recording / reproducing apparatus capable of emitting light and satisfying the following conditional expression :
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Here, ΔT (° C.): temperature change Δn: change in refractive index of the objective lens when there is a temperature change ΔT
Δλ1 (nm) : Amount of change in wavelength of the first light flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux A recording / reproducing method for reproducing or recording information on at least two types of optical information recording media by an optical pickup device,
The optical pickup device includes a first light source, a second light source, a condensing optical system having an objective lens that satisfies the following conditional expression, an optical axis, and a diffraction unit, and a photodetector, Emitting a first light flux from the first light source or a second light flux different from the wavelength of the first light flux from the second light source;
Diffracting light of at least one order of the first light flux or diffracting light of at least one order of the second light flux by allowing the first light flux or the second light flux to pass through at least a part of the diffraction section. (Where n is an integer other than 0 in the diffracted light of at least one order of the first light beam) If the amount of diffracted light of the second order is greater than the amount of diffracted light of the second order, the amount of light of nth order diffracted light among the diffracted light of at least one order of the second light flux Larger than the amount of light)
The condensing optical system causes the n-th order diffracted light of the first light flux to pass through the first transparent substrate to the information recording surface of the first optical information recording medium or the n-th order diffracted light of the second light flux. The optical pickup device is connected to the first optical information recording medium or the second optical information recording surface of the second optical information recording medium through a second transparent substrate having a thickness different from that of the first transparent substrate. Condensing to record information on or reproduce information from the optical information recording medium of
The first reflected light from the information recording surface of the first optical information recording medium of the collected nth-order diffracted light or the second of the collected nth-order diffracted light by the photodetector. Detecting the second reflected light from the information recording surface of the optical information recording medium, and satisfying the following conditional expression:
−0.0002 / ° C. <Δn / ΔT <−0.00005 / ° C.
0.05nm / ° C <Δλ1 / ΔT <0.5nm / ° C
λ1 <λ2
t1 <t2
NA1> NA2
Here, ΔT (° C.): temperature change Δn: change in refractive index of the objective lens when there is a temperature change ΔT
Δλ1 (nm) : Amount of change in wavelength of the first light flux when there is a temperature change ΔT
λ1: wavelength of the first light beam
λ2: wavelength of the second light flux
t1: thickness of the first transparent substrate
t2: thickness of the second transparent substrate
NA1: A predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the first optical information recording medium using the first light flux.
NA2: a predetermined numerical aperture on the image side of the objective lens when information is reproduced or recorded on the second optical information recording medium using the second light flux

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