JP2004171709A - Objective optical element of optical pickup system, and the optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective element and an optical pickup that can conduct appropriate recording and reproduction, without degrading its temperature characteristics. <P>SOLUTION: By providing a diffraction structure, acting to excessively increase the 3rd spherical aberration components of the waveform aberration around the objective lens 16, when the wavelength changes higher than a first wavelength λ1 in the light flux inputted from a first light source 111, when using a DVD, the light flux passing such a peripheral area turns into an appropriate flare light and can be prevented from being detected as the error signals in the photodetector, even though it is an appropriate recording or reproducing signal, when using a CD. <P>COPYRIGHT: (C)2004,JPO

Description

【０００３】
ここで、記録密度が異なる光情報記録媒体同士の互換性が要求されるものとして、ＤＶＤとＣＤとがある。これらの光情報記録媒体は、［表１］にもあるように、透明基板厚さがそれぞれ異なっている。互換性を確保するためにはこの透明基板厚さの違いによって発生する球面収差を、何らかの手段によって補正する必要がある。更に、ＤＶＤとＣＤとでは、要求開口数（ＤＶＤ：０．６５程度、ＣＤ：０．４５程度）が異なるので、これに対しても何らかの対応策が必要となる。
【０００４】
ＤＶＤ／ＣＤの互換性のある光ピックアップ装置を実現するために、回折構造を設けた対物レンズが開発されている。そのような対物レンズとしては、例えば、対物レンズの一方の面において、光軸から特定の高さｈの内外で異なる回折構造を設け、内側の領域では各々の透明基板厚さに対して球面収差を補正し、外側の領域ではＤＶＤの使用時のみ球面収差を補正し、ＣＤの使用時には球面収差を補正せずにフレア化させたものがある。このように対物レンズを構成することで、各々の光情報記録媒体上で、それぞれ情報の記録又は再生時に要求される集光スポットを適切に形成することが可能となる。
【０００５】
【発明が解決しようとする課題】
しかしながら、対物レンズに形成した回折構造のみでは、ＣＤの使用時にフレア光の調整が不十分となり、場合によっては、光検出器の受光面にフレア光がかかることで、エラー信号として検出されてしまう恐れがあることがわかった。
【０００６】
かかる問題の一因としては、環境温度が変化することに起因してレーザ光源の波長が変化してもＤＶＤに対する情報の記録又は再生を適切に行えるよう、波長変化に対する収差特性（温度特性という）を向上させることを主眼として、回折構造の設計がなされていることが考えられる。このような設計思想により設計された対物レンズを用いては、ＣＤ使用時に、フレア光を適切な位置に照射させることができず、光ピックアップ装置によっては光検出器の受光面にかかってしまう恐れが生じる。しかしながら、フレア光の照射位置を任意に設定すると、ＤＶＤ使用時における温度特性が劣化するという本来的な問題が生じてしまう。
【０００７】
本発明は、かかる従来技術の問題点に鑑みなされたものであり、温度特性を犠牲にすることなく、情報の適切な記録又は再生を行える光ピックアップ装置の対物光学素子及び光ピックアップ装置を提供することを目的とする。
【０００８】
【課題を解決するための手段】
請求項１に記載の光ピックアップ装置の光学素子は、透明基板の厚さがｔ１である第１の光情報記録媒体に対して光束を照射することで情報の記録又は再生を行うようになっている第１波長λ１の第１の光源と、透明基板の厚さがｔ２（ｔ１＜ｔ２）である第２の光情報記録媒体に対して光束を照射することで情報の記録又は再生を行うようになっている第２波長λ２（λ１＜λ２）である第２の光源と、前記第１の光源から出射された光束を、前記第１の光情報記録媒体の透明基板を介して情報記録面に集光させ、且つ前記第２の光源から出射された光束を、前記第２の光情報記録媒体の透明基板を介して情報記録面に集光させる対物光学素子を含む集光光学系と、を有する光ピックアップ装置の対物光学素子であって、前記対物光学素子は、前記第１又は前記第２の光源からの光束を集光する対物レンズと、前記光束に光学的作用を与える光学機能面とを有し、前記対物光学素子の光学機能面は、光軸を含み且つ前記第１の光情報記録媒体及び前記第２の光情報記録媒体の両方に対して情報の記録及び／又は再生のために用いられる中央領域と、該中央領域の外側に設けられ且つ主に前記第１の光情報記録媒体に対して情報の記録及び／又は再生のために用いられる周辺領域とを有し、前記周辺領域には、前記第１の光源から入射する光束において、前記第１波長λ１より高くなるように波長変化を生じた場合、波面収差の３次球面収差成分をオーバーにするように作用する回折構造が設けられていることを特徴とする。
【０００９】
上述した従来技術の問題に対し、鋭意研究の結果、本発明者らは、前記第１の光情報記録媒体（たとえばＤＶＤ）使用時（すなわち情報の記録又は再生時）における外側の領域を通過した光束について、３次球面収差の変動に着目し、これを調整することで、前記第１の光情報記録媒体使用時の温度特性を犠牲にすることなく、前記第２の光情報記録媒体（たとえばＣＤ）に対しても適切に情報の記録又は再生を行えることを見いだした。すなわち、前記第１の光源から入射する光束において、前記第１波長λ１より高くなるように波長変化を生じた場合、波面収差の３次球面収差成分をオーバーにするように作用する回折構造を前記周辺領域に設けることで、前記第２の光情報記録媒体使用時には、かかる周辺領域を通過する光束が適切なフレア光になり、適切な記録又は再生信号でありながら光検出器においてエラー信号として検出される不具合を抑制できるという新たな設計思想を見いだしたのである。
【００１０】
尚、「前記第１の光源から入射する光束において、前記第１波長λ１より高くなるように波長変化を生じた場合、波面収差の３次球面収差成分をオーバーにするように作用する回折構造を設ける」とは、前記第２の光情報記録媒体使用時において、縦球面収差図を描いたときに存在する「波長特性」の閾値・境界を、大幅に超えた設計をすることを意味する。ここで、波長特性の閾値・境界とは、たとえば「温度特性が悪化する領域の境界」、「波長特性の符号が悪化する領域の境界」、「温度変化によって球面収差の変化量が大きくなる領域の境界」、「光源波長の変化に応じて変化する球面収差の変化量の符号が変わる境界」、「光源波長長さの増減に応じて変化する、球面収差の変化量の符号が変わる境界」等を意味するものとする。
【００１１】
「アンダーな球面収差もしくは／オーバーな球面収差」については、図１に示すように、近軸像点位置を原点とする球面収差において、近軸像点よりも手前側で光軸と交わる場合を「アンダー」、近軸像点よりも遠い位置で光軸と交わる場合を「オーバー」とする。
【００１２】
ここで、「光学機能面」とは、各光源からの光束が通過する前記対物光学素子のレンズ面範囲のことを意味する。本明細書では、前記第１光情報記録媒体使用時の絞り開口径で制限される光束が通過するレンズ面範囲とする。「中央領域の外側」とは、中央領域に対し、光軸に交差する方向において光軸から離れる側という意味である。
【００１３】
又、「主に前記第１の光情報記録媒体に対して情報の記録及び／又は再生のために用いられる」における、「主に」の意義ついて説明する。前記第１の光情報記録媒体使用時に周辺領域を通過する光束は、光情報記録媒体面上で対物レンズの合焦デフォーカス時に結像させている。ここで、前記第２の光情報記録媒体使用時で周辺領域を通過する光束は、前記第２の光情報記録媒体面上では前記対物レンズの合焦デフォーカス時にはスポット光から離れた場所でフレアー光となる。ここで、「主に」という言葉を使用しているのは、次の２点の理由からによる。まず、第１の理由としては、光ピックアップ装置に通常設けられている信号検出用のセンサー（光検出器ともいう）に着目すると、センサーの開口サイズによっては、このフレアー光がセンサー開口内に入射する場合も生じる。この場合はフレアー光も含めた上で前記対物レンズのデフォーカス制御を実用上行うことなり、広義な意味では第２の光情報記録媒体使用時でも、この周辺領域を通過する光束の影響を実使用上受けることがある。また、第２の理由としては、波動光学的には光情報記録媒体でのフレアー光とスポット光との位相差を制御することでスポット光のエアリーディスクのピーク強度を高めることも可能になることがある。このような理由から、本発明では無用な限定を避けるべく、「主に」という語句を用いたものである。
【００１４】
更に、「対物光学素子」とは、前記対物レンズの光学面に前記光学機能面を設けたものであっても良く、前記対物レンズの他に、前記光学機能面を設けた光学素子を別個に設けても良い。
【００１５】
請求項２に記載の光ピックアップ装置の対物光学素子は、前記回折構造において、前記第１波長λ１±２０ｎｍの範囲をブレイズ化波長として取り扱うので、前記周辺領域において前記第１の光源からの光束が通過する場合における回折効率を高く維持できる。尚、「ブレイズ化波長」とは、その波長の光束が前記回折構造に入射したときに、最も高い回折光が出射される波長をいうが、これに限られない。
【００１６】
請求項３に記載の光ピックアップ装置の対物光学素子は、前記第１の光源からの光束を、前記光学機能面の前記中央領域と前記周辺領域とを通過させ、前記第１の光情報記録媒体に対して情報の記録及び／又は再生を行うにあたり、波面収差の３次球面収差成分をＳＡ３としたときに、温度変化ΔＴに対する３次球面収差成分ＳＡ３の標準偏差値の変化量Δ（（ＳＡ３ｔ）ｒｍｓ）が、以下の関係を満たすので、前記第１の光情報記録媒体使用時における温度特性の劣化を抑制でき、いずれの媒体に対しても適切な情報の記録又は再生を行える。
Δ（（ＳＡ３ｔ）ｒｍｓ）／ΔＴ ≦ １／７５０（λ１’／℃） （１）
１／６ ≦ Δλ１／ΔＴ ≦ １／３（ｎｍ／℃） （２）
但し、λ１’は、標準状態から温度がΔＴ変化した際の前記第１の光源の波長変化量をΔλ１としたときに、λ１’＝λ１＋Δλ１である。
【００１７】
請求項４に記載の光ピックアップ装置の対物光学素子は、前記第１の光源からの光束を、前記光学機能面の前記中央領域と前記周辺領域とを通過させ、前記第１の光情報記録媒体に対して情報の記録及び／又は再生を行うにあたり、波面収差の３次球面収差成分をＳＡ３としたときに、波長変化Δλに対する３次球面収差成分ＳＡ３の標準偏差値の変化量Δ（（ＳＡ３λ）ｒｍｓ）が、以下の関係を満たすので、前記第１の光情報記録媒体使用時における温度特性の劣化を抑制でき、いずれの媒体に対しても適切な情報の記録又は再生を行える。
Δ（（ＳＡ３λ）ｒｍｓ）／Δλ１ ≦ １／１０００（λ１’／ｎｍ） （３）
但し、λ１’は、標準状態から温度がΔＴ変化した際の前記第１の光源の波長変化量をΔλ１としたときに、λ１’＝λ１＋Δλ１である。
【００１８】
請求項５に記載の光ピックアップ装置は、透明基板の厚さがｔ１である第１の光情報記録媒体に対して光束を照射することで情報の記録又は再生を行うようになっている第１波長λ１の第１の光源と、透明基板の厚さがｔ２（ｔ１＜ｔ２）である第２の光情報記録媒体に対して光束を照射することで情報の記録又は再生を行うようになっている第２波長λ２（λ１＜λ２）である第２の光源と、前記第１の光源から出射された光束を、前記第１の光情報記録媒体の透明基板を介して情報記録面に集光させ、且つ前記第２の光源から出射された光束を、前記第２の光情報記録媒体の透明基板を介して情報記録面に集光させる対物光学素子を含む集光光学系と、を有する光ピックアップ装置であって、前記対物光学素子は、前記第１又は前記第２の光源からの光束を集光する対物レンズと、前記光束に光学的作用を与える光学機能面とを有し、前記対物光学素子の光学機能面は、光軸を含み且つ前記第１の光情報記録媒体及び前記第２の光情報記録媒体の両方に対して情報の記録及び／又は再生のために用いられる中央領域と、該中央領域の外側に設けられ且つ主に前記第１の光情報記録媒体に対して情報の記録及び／又は再生のために用いられる周辺領域とを有し、前記周辺領域には、前記第１の光源から入射する光束において、前記第１波長λ１より高くなるように波長変化を生じた場合、波面収差の３次球面収差成分をオーバーにするように作用する回折構造が設けられているので、請求項１に記載の発明と同様な作用効果を発揮できる。
【００１９】
請求項６に記載の光ピックアップ装置は、前記回折構造において、前記第１波長λ１±２０ｎｍの範囲をブレイズ化波長として取り扱うので、請求項２に記載の発明と同様な作用効果を発揮できる。
【００２０】
請求項７に記載の光ピックアップ装置は、前記第１の光源からの光束を、前記光学機能面の前記中央領域と前記周辺領域とを通過させ、前記第１の光情報記録媒体に対して情報の記録及び／又は再生を行うにあたり、波面収差の３次球面収差成分をＳＡ３としたときに、温度変化ΔＴに対する３次球面収差成分ＳＡ３の標準偏差値の変化量Δ（（ＳＡ３ｔ）ｒｍｓ）が、以下の関係を満たすので、請求項３に記載の発明と同様な作用効果を発揮できる。
Δ（（ＳＡ３ｔ）ｒｍｓ）／ΔＴ ≦ １／７５０（λ１’／℃） （４）
１／６ ≦ Δλ１／ΔＴ ≦ １／３（ｎｍ／℃） （５）
但し、λ１’は、標準状態から温度がΔＴ変化した際の前記第１の光源の波長変化量をΔλ１としたときに、λ１’＝λ１＋Δλ１である。
【００２１】
請求項８に記載の光ピックアップ装置は、前記第１の光源からの光束を、前記光学機能面の前記中央領域と前記周辺領域とを通過させ、前記第１の光情報記録媒体に対して情報の記録及び／又は再生を行うにあたり、波面収差の３次球面収差成分をＳＡ３としたときに、波長変化Δλに対する３次球面収差成分ＳＡ３の標準偏差値の変化量Δ（（ＳＡ３λ）ｒｍｓ）が、以下の関係を満たすので、請求項４に記載の発明と同様な作用効果を発揮できる。
Δ（（ＳＡ３λ）ｒｍｓ）／Δλ１ ≦ １／１０００（λ１’／ｎｍ） （６）
但し、λ１’は、標準状態から温度がΔＴ変化した際の前記第１の光源の波長変化量をΔλ１としたときに、λ１’＝λ１＋Δλ１である。
【００２２】
本明細書中で用いる「回折構造」とは、対物レンズの表面に、レリーフを設けて、回折によって光束を集光あるいは発散させる作用を持たせた部分のことをいう。レリーフの形状としては、例えば、対物レンズの表面に、光軸を中心とする略同心円状の輪帯として形成され、光軸を含む平面でその断面をみれば各輪帯は鋸歯のような形状が知られているが、そのような形状を含むものであり、そのような形状を特に「回折輪帯」という。
【００２３】
本明細書中において、対物レンズとは、狭義には光ピックアップ装置に光情報記録媒体を装填した状態において、最も光情報記録媒体側の位置で、これと対向すべく配置される集光作用を有するレンズを指し、広義にはそのレンズと共に、アクチュエータによって少なくともその光軸方向に作動可能なレンズ群を指すものとする。ここで、かかるレンズ群とは、少なくとも１枚以上（例えば２枚）のレンズを指すものである。従って、本明細書中において、対物レンズの光情報記録媒体側（像側）の開口数ＮＡとは、対物レンズの最も光情報記録媒体側に位置するレンズ面の開口数ＮＡを指すものである。また、本明細書中では必要開口数ＮＡは、それぞれの光情報記録媒体の規格で規定されている開口数、あるいはそれぞれの光情報記録媒体に対して、使用する光源の波長に応じ、情報の記録または再生をするために必要なスポット径を得ることができる回折限界性能の対物レンズの開口数を示す。
【００２４】
本明細書中において、第２の光情報記録媒体とは、例えば、ＣＤ−Ｒ，ＣＤ−ＲＷ，ＣＤ−Ｖｉｄｅｏ，ＣＤ−ＲＯＭ等の各種ＣＤ系の光ディスクをいい、第１の光情報記録媒体とは、ＤＶＤ−ＲＯＭ，ＤＶＤ−ＲＡＭ，ＤＶＤ−Ｒ，ＤＶＤ−ＲＷ，ＤＶＤ−Ｖｉｄｅｏ等の各種ＤＶＤ系の光ディスクを意味するものである。更に、本明細書中で透明基板の厚さｔといった時は、ｔ＝０を含むものである。
【００２５】
【発明の実施の形態】
以下、図面を参照して、本発明をさらに詳細に説明する。図２は、本実施の形態にかかる光情報記録再生装置又は光ピックアップ装置（２レーザ１パッケージモジュールタイプの光源を含む）の概略構成図である。図２においては、第１光源としての第１半導体レーザ１１１と第２光源としての第２半導体レーザ１１２とが、光軸に対して直交する同一基板の面上に取り付けられ１ユニットとして構成されている。第１半導体レーザ１１１（波長λ１＝６１０ｎｍ〜６７０ｎｍ）から出射されたビームは、光合波手段であるビームスプリッタ１２０を透過し、さらに絞り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。
【００２６】
そして情報記録面２２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１６、絞り１７を透過して、ビームスプリッタ１２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２０に情報記録された情報の読み取り信号が得られる。
【００２７】
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（不図示）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１６を移動させる。
【００２８】
第２半導体レーザ１１２（波長λ１＝７４０ｎｍ〜８７０ｎｍ）から出射されたビームは、光合波手段であるビームスプリッタ１２０を透過し、さらに絞り１７、対物レンズ１６を介して第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。
【００２９】
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、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上へ入射して、その出力信号を用いて、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。
【００３０】
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い、２次元アクチュエータ（不図示）により、合焦、トラッキングのために対物レンズ１６を移動させるようになっている。
【００３１】
以下、上述の実施の形態に好適な実施例について説明する。
対物レンズの両面は［数１］で示される非球面である。ただし、Ｚは光軸方向の軸で、ｈは光軸と垂直方向の軸、ｒは近軸曲率半径、κは円錐係数、Ａは非球面係数、Ｐは非球面のべき数である。
【数１】

【００３２】
更に、対物レンズの光源側非球面の表面には回折構造が一体で形成されている。この回折構造は、ブレーズ化波長λＢに対する光路差関数Φにより単位をｍｍとして［数２］で表される。この２次係数が回折部分の近軸的なパワーが表される。また、２次以外の係数、例えば４次、６次係数等で球面収差を制御できる。ここで制御できるとは、屈折部分が有する球面収差を回折部分で逆特性の球面収差を持たせてトータルとして球面収差を補正したり、回折部分の球面収差を操作してトータルの球面収差を所望のフレア量にすることを意味する。この場合、温度変化時の球面収差も、屈折部分の球面収差の温度変化と回折部分の球面収差変化のトータルと考えることが出来る。
【数２】

【００３３】
（実施例）
本実施例においては、対物光学素子としての対物レンズの光源側の面に２つの光学機能面が形成されている。光軸を含む光学機能面は、ＤＶＤ、ＣＤそれぞれの使用時における球面収差を補正した内側光学機能面（中央領域）が形成され、その外側の光学機能面は、ＤＶＤで球面収差補正され且つＣＤベストフォーカス時にはかかる光学機能面を通過した光束が光情報記録媒体面上でフレアー光となる周辺領域が形成されている。表２に、本実施例にかかる対物レンズのレンズデータを示す。表３は、対物レンズの素材と光源波長との組み合わせによる屈折率を示す。
【表２】

【表３】

【００３４】
なお、本発明は上記実施の形態に限定されない。２レーザー１パッケージモジュール光源としたが、モジュールされていないディスクリート光ピックアップ装置についても適用は可能である。更に、対物レンズの光情報記録媒体側の光学面を同一の非球面で構成しているが、これに限らない。この面も２つの光学機能面を設けて、周辺領域共有領域それぞれの球面収差設計、正弦条件不満足量設計を行っても良い。
【００３５】
【発明の効果】
本発明によれば、温度特性を犠牲にすることなく、情報の適切な記録又は再生を行える光ピックアップ装置の対物光学素子及び光ピックアップ装置を提供することができる。
【図面の簡単な説明】
【図１】球面収差がアンダーかオーバーかを示す図である。
【図２】本実施の形態にかかる光情報記録再生装置又は光ピックアップ装置（２レーザ１パッケージモジュールタイプの光源を含む）の概略構成図である。
【符号の説明】
１１１ 第１半導体レーザ
１１２ 第２半導体レーザ
１６ 対物レンズ
１７ 絞り
２０ 光情報記録媒体（ＤＶＤ又はＣＤ）
３０ 光検出器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an objective optical element and an optical pickup device used in an optical pickup device that performs recording / reproducing of an optical information recording medium having different wavelengths and different thicknesses of a transparent substrate with one objective optical element.
[0002]
[Prior art]
At present, there are many types of optical information recording media, and the specifications of these optical information recording media are determined as shown in [Table 1]. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented by using E (for example, 2.5 × E−3).
[Table 1]

[0003]
Here, DVDs and CDs are required to have compatibility between optical information recording media having different recording densities. These optical information recording media have different thicknesses of the transparent substrate as shown in Table 1. In order to ensure compatibility, it is necessary to correct the spherical aberration caused by the difference in the thickness of the transparent substrate by some means. Furthermore, since the required numerical aperture (DVD: about 0.65, CD: about 0.45) differs between DVD and CD, some countermeasure is required for this as well.
[0004]
In order to realize a DVD / CD compatible optical pickup device, an objective lens provided with a diffraction structure has been developed. As such an objective lens, for example, on one surface of the objective lens, different diffractive structures are provided inside and outside a specific height h from the optical axis, and in an inner region, spherical aberration is caused with respect to each transparent substrate thickness. In some cases, the spherical aberration is corrected only when the DVD is used in the outer region, and the spherical aberration is corrected without correcting the spherical aberration when the CD is used. By configuring the objective lens in this manner, it becomes possible to appropriately form a condensed spot required at the time of recording or reproducing information on each optical information recording medium.
[0005]
[Problems to be solved by the invention]
However, the use of only the diffractive structure formed on the objective lens causes insufficient adjustment of the flare light when the CD is used, and in some cases, the flare light is applied to the light receiving surface of the photodetector, which is detected as an error signal. I knew it was afraid.
[0006]
One cause of such a problem is an aberration characteristic (referred to as temperature characteristic) with respect to a wavelength change so that information can be appropriately recorded or reproduced on a DVD even if the wavelength of the laser light source changes due to a change in the environmental temperature. It is conceivable that the diffraction structure is designed with the main purpose of improving the diffraction efficiency. If an objective lens designed according to such a design concept is used, flare light cannot be applied to an appropriate position when a CD is used, and depending on the optical pickup device, there is a possibility that the light will strike the light receiving surface of a photodetector. Occurs. However, if the irradiating position of the flare light is set arbitrarily, there is an inherent problem that the temperature characteristics when using the DVD are deteriorated.
[0007]
The present invention has been made in view of the problems of the related art, and provides an objective optical element and an optical pickup device of an optical pickup device capable of appropriately recording or reproducing information without sacrificing temperature characteristics. The purpose is to:
[0008]
[Means for Solving the Problems]
The optical element of the optical pickup device according to the first aspect records or reproduces information by irradiating a first optical information recording medium having a transparent substrate with a thickness of t1 with a light beam. The first light source of the first wavelength λ1 and the second optical information recording medium having a thickness of the transparent substrate of t2 (t1 <t2) are irradiated with a light beam to record or reproduce information. A second light source having a second wavelength λ2 (λ1 <λ2) and a light beam emitted from the first light source are transmitted through a transparent substrate of the first optical information recording medium to an information recording surface. A condensing optical system including an objective optical element that condenses the light flux emitted from the second light source onto an information recording surface via a transparent substrate of the second optical information recording medium; An objective optical element of an optical pickup device having: An objective lens for condensing a light beam from the first or second light source, and an optical function surface for giving an optical action to the light beam, wherein the optical function surface of the objective optical element includes an optical axis. A central area used for recording and / or reproducing information on both the first optical information recording medium and the second optical information recording medium; and a central area provided outside the central area and mainly A peripheral region used for recording and / or reproducing information on the first optical information recording medium, wherein the peripheral region includes the first light source in a light beam incident from the first light source; When a wavelength change occurs so as to be higher than the wavelength λ1, a diffraction structure is provided which acts to make the third-order spherical aberration component of wavefront aberration over.
[0009]
As a result of earnest research on the above-mentioned problem of the prior art, as a result of the present inventors, the present inventors have passed the outer region when the first optical information recording medium (for example, DVD) is used (that is, when recording or reproducing information). By focusing on the fluctuation of the third-order spherical aberration with respect to the light flux, and adjusting the fluctuation, the second optical information recording medium (for example, without sacrificing the temperature characteristics when the first optical information recording medium is used). It has been found that information can be appropriately recorded or reproduced on a CD). That is, when a wavelength change occurs in the light beam incident from the first light source so as to be higher than the first wavelength λ1, the diffraction structure acting to make the third-order spherical aberration component of the wavefront aberration exceed When the second optical information recording medium is used, the luminous flux passing through the peripheral area becomes an appropriate flare light when the second optical information recording medium is used, and is detected as an error signal by the photodetector while being an appropriate recording or reproduction signal. They found a new design philosophy that could reduce the inconvenience that would occur.
[0010]
It should be noted that, in the case where a light beam incident from the first light source undergoes a wavelength change so as to be higher than the first wavelength λ1, a diffractive structure acting to make the third-order spherical aberration component of wavefront aberration over. "Providing" means that, when the second optical information recording medium is used, a design that greatly exceeds the threshold / boundary of "wavelength characteristics" existing when a longitudinal spherical aberration diagram is drawn. Here, the threshold / boundary of the wavelength characteristic is, for example, “a boundary of a region where the temperature characteristic is deteriorated”, “a boundary of a region where the sign of the wavelength characteristic is deteriorated”, or “a region where the amount of change of the spherical aberration increases due to the temperature change”. Boundary "," the boundary where the sign of the change amount of the spherical aberration that changes according to the change of the light source wavelength "," the boundary where the sign of the change amount of the spherical aberration changes which changes as the length of the light source wavelength changes " And so on.
[0011]
As for “under spherical aberration or / over spherical aberration”, as shown in FIG. 1, in the spherical aberration having the origin at the paraxial image point position, a case where the optical axis intersects the near side of the paraxial image point is shown. "Under", and the case where the optical axis intersects at a position farther than the paraxial image point are "over".
[0012]
Here, the “optically functional surface” means a lens surface area of the objective optical element through which a light beam from each light source passes. In the present specification, a lens surface range through which a light beam limited by the aperture diameter of the stop when the first optical information recording medium is used passes. “Outside the central region” means a side away from the optical axis in a direction intersecting the optical axis with respect to the central region.
[0013]
The meaning of "mainly" in "mainly used for recording and / or reproducing information on the first optical information recording medium" will be described. The light beam passing through the peripheral area when the first optical information recording medium is used forms an image on the surface of the optical information recording medium when the objective lens is defocused. Here, when the second optical information recording medium is used, the light beam passing through the peripheral area is flare on the surface of the second optical information recording medium at a position away from the spot light at the time of defocusing of the objective lens. It becomes light. Here, the word "mainly" is used for the following two reasons. First, as a first reason, focusing attention on a signal detection sensor (also referred to as a photodetector) usually provided in an optical pickup device, depending on the opening size of the sensor, this flare light enters the sensor opening. In some cases. In this case, the defocus control of the objective lens is performed in practice including the flare light. In a broad sense, even when the second optical information recording medium is used, the influence of the light beam passing through the peripheral area is actually measured. May be subject to use. The second reason is that, in terms of wave optics, it is possible to increase the peak intensity of the spotlight Airy disk by controlling the phase difference between the flare light and the spotlight in the optical information recording medium. There is. For this reason, the present invention uses the phrase "mainly" to avoid unnecessary limitation.
[0014]
Furthermore, the “objective optical element” may be one in which the optical function surface is provided on the optical surface of the objective lens, and in addition to the objective lens, an optical element provided with the optical function surface is separately provided. It may be provided.
[0015]
The objective optical element of the optical pickup device according to claim 2, wherein in the diffraction structure, the range of the first wavelength λ1 ± 20 nm is treated as a blazed wavelength, so that the light flux from the first light source in the peripheral region is used. Diffraction efficiency in the case of passing through can be kept high. The “blazed wavelength” refers to a wavelength at which the highest diffracted light is emitted when a light beam of that wavelength enters the diffraction structure, but is not limited thereto.
[0016]
The objective optical element of the optical pickup device according to claim 3, wherein the light beam from the first light source passes through the central area and the peripheral area of the optical function surface, and the first optical information recording medium is provided. When recording and / or reproducing information with respect to temperature, when the third-order spherical aberration component of the wavefront aberration is SA3, the change amount Δ ((SA3t) of the standard deviation value of the third-order spherical aberration component SA3 with respect to the temperature change ΔT Since rms) satisfies the following relationship, deterioration of the temperature characteristic when the first optical information recording medium is used can be suppressed, and appropriate information can be recorded or reproduced on any medium.
Δ ((SA3t) rms) / ΔT ≦ 1/750 (λ1 ′ / ° C.) (1)
1/6 ≦ Δλ1 / ΔT ≦ 1/3 (nm / ° C) (2)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state.
[0017]
The objective optical element of the optical pickup device according to claim 4, wherein the light beam from the first light source passes through the central area and the peripheral area of the optical function surface, and the first optical information recording medium is provided. When recording and / or reproducing information with respect to, when the tertiary spherical aberration component of the wavefront aberration is SA3, the change amount Δ ((SA3λ) of the standard deviation value of the tertiary spherical aberration component SA3 with respect to the wavelength change Δλ Since rms) satisfies the following relationship, deterioration of the temperature characteristic when the first optical information recording medium is used can be suppressed, and appropriate information can be recorded or reproduced on any medium.
Δ ((SA3λ) rms) / Δλ1 ≦ 1/1000 (λ1 ′ / nm) (3)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state.
[0018]
In the optical pickup device according to the fifth aspect, information is recorded or reproduced by irradiating the first optical information recording medium having a transparent substrate with a thickness of t1 with a light beam. The recording or reproduction of information is performed by irradiating a first light source having a wavelength λ1 and a second optical information recording medium having a thickness of a transparent substrate of t2 (t1 <t2) with a light beam. A second light source having a second wavelength λ2 (λ1 <λ2) and a light beam emitted from the first light source are condensed on an information recording surface via a transparent substrate of the first optical information recording medium. And a condensing optical system including an objective optical element for converging a light beam emitted from the second light source onto an information recording surface via a transparent substrate of the second optical information recording medium. In the pickup device, the objective optical element may be the first or the second. An objective lens for condensing a light beam from a source; and an optically functional surface for giving an optical effect to the light beam, wherein the optically functional surface of the objective optical element includes an optical axis and the first optical information recording. A central area used for recording and / or reproducing information on both the medium and the second optical information recording medium, and the first optical information recording medium provided outside the central area and mainly provided And a peripheral region used for recording and / or reproducing information with respect to the peripheral region. The peripheral region has a wavelength so that a light beam incident from the first light source is higher than the first wavelength λ1. When a change occurs, a diffractive structure that acts to make the third-order spherical aberration component of the wavefront aberration over is provided, so that the same operation and effect as the first aspect of the invention can be exhibited.
[0019]
In the optical pickup device according to the sixth aspect, in the diffraction structure, the range of the first wavelength λ1 ± 20 nm is treated as a blazed wavelength, so that the same operation and effect as the invention according to the second aspect can be exhibited.
[0020]
8. The optical pickup device according to claim 7, wherein the light flux from the first light source passes through the central area and the peripheral area of the optical function surface, and information is transmitted to the first optical information recording medium. In performing recording and / or reproduction of, when the tertiary spherical aberration component of the wavefront aberration is defined as SA3, the change amount Δ (((SA3t) rms) of the standard deviation value of the tertiary spherical aberration component SA3 with respect to the temperature change ΔT is Since the following relationship is satisfied, the same function and effect as the third aspect of the invention can be exerted.
Δ ((SA3t) rms) / ΔT ≦ 1/750 (λ1 ′ / ° C.) (4)
1/6 ≦ Δλ1 / ΔT ≦ 1/3 (nm / ° C) (5)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state.
[0021]
9. The optical pickup device according to claim 8, wherein the light flux from the first light source passes through the central area and the peripheral area of the optical function surface, and information is transmitted to the first optical information recording medium. In performing recording and / or reproduction of, when the tertiary spherical aberration component of the wavefront aberration is set to SA3, the change amount Δ (((SA3λ) rms) of the standard deviation value of the tertiary spherical aberration component SA3 with respect to the wavelength change Δλ is Since the following relationship is satisfied, the same operation and effect as the invention according to claim 4 can be exerted.
Δ ((SA3λ) rms) / Δλ1 ≦ 1/1000 (λ1 ′ / nm) (6)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state.
[0022]
As used herein, the term "diffraction structure" refers to a portion provided with a relief on the surface of an objective lens so as to condense or diverge a light beam by diffraction. As the shape of the relief, for example, on the surface of the objective lens, it is formed as a substantially concentric annular zone centered on the optical axis, and when viewed in cross section on a plane including the optical axis, each annular zone is shaped like a sawtooth. Is known, but includes such a shape, and such a shape is particularly called “diffraction ring zone”.
[0023]
In the present specification, in the narrow sense, the objective lens is a light condensing function that is arranged to face the optical information recording medium at the position closest to the optical information recording medium when the optical information recording medium is loaded in the optical pickup device. And, in a broad sense, together with the lens, a lens group operable at least in the optical axis direction by an actuator. Here, such a lens group refers to at least one or more (for example, two) lenses. Accordingly, in this specification, the numerical aperture NA of the objective lens on the optical information recording medium side (image side) indicates the numerical aperture NA of the lens surface of the objective lens closest to the optical information recording medium. . Further, in the present specification, the required numerical aperture NA is a numerical aperture defined by the standard of each optical information recording medium, or the information of each optical information recording medium, according to the wavelength of the light source used. This shows the numerical aperture of an objective lens having diffraction-limited performance capable of obtaining a spot diameter necessary for recording or reproduction.
[0024]
In this specification, the second optical information recording medium refers to, for example, various CD-type optical discs such as CD-R, CD-RW, CD-Video, and CD-ROM, and the first optical information recording medium. The term means various DVD-type optical disks such as DVD-ROM, DVD-RAM, DVD-R, DVD-RW, and DVD-Video. Further, in the present specification, the term “thickness t” of the transparent substrate includes t = 0.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 2 is a schematic configuration diagram of an optical information recording / reproducing device or an optical pickup device (including a two-laser one-package module type light source) according to the present embodiment. In FIG. 2, a first semiconductor laser 111 as a first light source and a second semiconductor laser 112 as a second light source are mounted on a surface of the same substrate orthogonal to the optical axis and configured as one unit. I have. A beam emitted from the first semiconductor laser 111 (wavelength λ1 = 610 nm to 670 nm) passes through a beam splitter 120 which is an optical multiplexing unit, is further narrowed down by a diaphragm 17, and is transparent by a first lens 20 by an objective lens 16. The light is focused on the information recording surface 22 via the substrate 21.
[0026]
The light flux modulated and reflected by the information bit on the information recording surface 22 passes through the objective lens 16 and the aperture 17 again, enters the beam splitter 12, is reflected there, and is given astigmatism by the cylindrical lens 180. Then, the light is incident on the photodetector 301 via the concave lens 50, and a read signal of information recorded on the first optical disc 20 is obtained using the output signal.
[0027]
In addition, by detecting a change in the light amount due to a change in the shape and position of the spot on the photodetector 30, focus detection and track detection are performed. Based on this detection, a two-dimensional actuator (not shown) moves the objective lens 16 so that the light beam from the first semiconductor laser 111 is focused on the recording surface 22 of the first optical disc 20, and the semiconductor laser 111 The objective lens 16 is moved so that the light flux from the lens is focused on a predetermined track.
[0028]
The beam emitted from the second semiconductor laser 112 (wavelength λ1 = 740 nm to 870 nm) passes through the beam splitter 120 which is an optical multiplexing unit, and further passes through the aperture 17 and the objective lens 16 to the transparent substrate of the second optical disk 20. The light is condensed on the information recording surface 22 via 21.
[0029]
The light flux modulated and reflected by the information pits on the information recording surface 22 is reflected again by the objective lens 16, the aperture 17, and the beam splitter 120, is given astigmatism by the cylindrical lens 180, and is transmitted through the concave lens 50. The signal is incident on the detector 301, and a read signal of information recorded on the second optical disc 20 is obtained using the output signal.
[0030]
Further, a change in the light amount due to a change in the shape and position of the spot on the photodetector 30 is detected to detect focus and track, and a two-dimensional actuator (not shown) is used for focusing and tracking. The lens 16 is moved.
[0031]
Hereinafter, an example suitable for the above-described embodiment will be described.
Both surfaces of the objective lens are aspherical surfaces represented by [Equation 1]. Here, Z is the axis in the optical axis direction, h is the axis perpendicular to the optical axis, r is the paraxial radius of curvature, κ is the conic coefficient, A is the aspheric coefficient, and P is the power of the aspheric surface.
(Equation 1)

[0032]
Further, a diffractive structure is integrally formed on the surface of the aspherical surface on the light source side of the objective lens. This diffractive structure is represented by [Equation 2] with a unit of mm by an optical path difference function Φ with respect to the blazed wavelength λB. This second-order coefficient represents the paraxial power of the diffraction portion. Further, the spherical aberration can be controlled by a coefficient other than the second order, for example, a fourth order or sixth order coefficient. Controlling here means that the spherical aberration of the refracting portion is corrected by adding the spherical aberration of the inverse characteristic to the diffractive portion, or the spherical aberration of the diffractive portion is manipulated to obtain the total spherical aberration. Means the amount of flare. In this case, the spherical aberration at the time of temperature change can be considered as the total of the temperature change of the spherical aberration of the refraction part and the spherical aberration change of the diffraction part.
(Equation 2)

[0033]
(Example)
In the present embodiment, two optical functional surfaces are formed on the light source side surface of the objective lens as the objective optical element. On the optical function surface including the optical axis, an inner optical function surface (center region) is formed in which spherical aberration is corrected when each of DVD and CD is used, and the outer optical function surface is corrected in spherical aberration in DVD and CD. At the time of the best focus, there is formed a peripheral area where the light beam passing through the optical function surface becomes flare light on the optical information recording medium surface. Table 2 shows lens data of the objective lens according to the present example. Table 3 shows the refractive index depending on the combination of the material of the objective lens and the wavelength of the light source.
[Table 2]

[Table 3]

[0034]
Note that the present invention is not limited to the above embodiment. Although a two-laser, one-package module light source is used, the present invention can also be applied to a discrete optical pickup device that is not modular. Further, the optical surface of the objective lens on the side of the optical information recording medium is constituted by the same aspherical surface, but is not limited to this. This surface may also be provided with two optical function surfaces, and the spherical aberration design and the sine condition unsatisfaction amount design of each of the peripheral region shared regions may be performed.
[0035]
【The invention's effect】
According to the present invention, it is possible to provide an objective optical element and an optical pickup device of an optical pickup device capable of appropriately recording or reproducing information without sacrificing temperature characteristics.
[Brief description of the drawings]
FIG. 1 is a diagram showing whether spherical aberration is under or over.
FIG. 2 is a schematic configuration diagram of an optical information recording / reproducing device or an optical pickup device (including a two-laser one-package module type light source) according to the present embodiment;
[Explanation of symbols]
111 First semiconductor laser 112 Second semiconductor laser 16 Objective lens 17 Aperture 20 Optical information recording medium (DVD or CD)
30 Photodetector

Claims (8)

A first light source of a first wavelength λ1 for recording or reproducing information by irradiating a first optical information recording medium having a transparent substrate with a thickness of t1 with a light beam; At a second wavelength λ2 (λ1 <λ2) in which information is recorded or reproduced by irradiating a second optical information recording medium having a thickness of t2 (t1 <t2) with a light beam. A second light source, and a light beam emitted from the first light source is condensed on an information recording surface via a transparent substrate of the first optical information recording medium, and is emitted from the second light source. A focusing optical system including an objective optical element that focuses the light flux on the information recording surface via the transparent substrate of the second optical information recording medium.
The objective optical element has an objective lens that collects a light beam from the first or second light source, and an optical function surface that gives an optical effect to the light beam,
The optically functional surface of the objective optical element includes an optical axis and a center used for recording and / or reproducing information on both the first optical information recording medium and the second optical information recording medium. An area, and a peripheral area provided outside the central area and mainly used for recording and / or reproducing information with respect to the first optical information recording medium,
In the peripheral area, when a wavelength change occurs in the light beam incident from the first light source so as to be higher than the first wavelength λ1, the light acts to make the third-order spherical aberration component of wavefront aberration over. An objective optical element for an optical pickup device, comprising a diffraction structure. 2. The objective optical element according to claim 1, wherein in the diffraction structure, a range of the first wavelength λ1 ± 20 nm is treated as a blaze wavelength. 3. In passing the light flux from the first light source through the central region and the peripheral region of the optical function surface, and performing recording and / or reproduction of information on the first optical information recording medium, a wavefront When the tertiary spherical aberration component of the aberration is SA3, the variation Δ ((SA3t) rms) of the standard deviation value of the tertiary spherical aberration component SA3 with respect to the temperature change ΔT satisfies the following relationship. An objective optical element of the optical pickup device according to claim 1.
Δ ((SA3t) rms) / ΔT ≦ 1/750 (λ1 ′ / ° C.) (1)
1/6 ≦ Δλ1 / ΔT ≦ 1/3 (nm / ° C) (2)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state. In passing the light flux from the first light source through the central region and the peripheral region of the optical function surface, and performing recording and / or reproduction of information on the first optical information recording medium, a wavefront When the third-order spherical aberration component of the aberration is represented by SA3, the variation Δ ((SA3λ) rms) of the standard deviation of the third-order spherical aberration component SA3 with respect to the wavelength change Δλ satisfies the following relationship. An objective optical element of the optical pickup device according to claim 1.
Δ ((SA3λ) rms) / Δλ1 ≦ 1/1000 (λ1 ′ / nm)
(3)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state. A first light source of a first wavelength λ1 for recording or reproducing information by irradiating a first optical information recording medium having a transparent substrate with a thickness of t1 with a light beam; At a second wavelength λ2 (λ1 <λ2) in which information is recorded or reproduced by irradiating a second optical information recording medium having a thickness of t2 (t1 <t2) with a light beam. A second light source, and a light beam emitted from the first light source is condensed on an information recording surface via a transparent substrate of the first optical information recording medium, and is emitted from the second light source. A light-collecting optical system including an objective optical element that focuses the collected light beam on an information recording surface via a transparent substrate of the second optical information recording medium,
The objective optical element has an objective lens that collects a light beam from the first or second light source, and an optical function surface that gives an optical effect to the light beam,
The optically functional surface of the objective optical element includes an optical axis and a center used for recording and / or reproducing information on both the first optical information recording medium and the second optical information recording medium. An area, and a peripheral area provided outside the central area and mainly used for recording and / or reproducing information with respect to the first optical information recording medium,
In the peripheral area, when a wavelength change occurs in the light beam incident from the first light source so as to be higher than the first wavelength λ1, the light acts to make the third-order spherical aberration component of wavefront aberration over. An optical pickup device comprising a diffraction structure. 6. The optical pickup device according to claim 5, wherein in the diffraction structure, a range of the first wavelength λ1 ± 20 nm is treated as a blaze wavelength. In passing the light flux from the first light source through the central region and the peripheral region of the optical function surface, and performing recording and / or reproduction of information on the first optical information recording medium, a wavefront When the tertiary spherical aberration component of the aberration is SA3, the variation Δ ((SA3t) rms) of the standard deviation value of the tertiary spherical aberration component SA3 with respect to the temperature change ΔT satisfies the following relationship. The optical pickup device according to claim 5.
Δ ((SA3t) rms) / ΔT ≦ 1/750 (λ1 ′ / ° C.) (4)
1/6 ≦ Δλ1 / ΔT ≦ 1/3 (nm / ° C) (5)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state. In passing the light flux from the first light source through the central region and the peripheral region of the optical function surface, and performing recording and / or reproduction of information on the first optical information recording medium, a wavefront When the third-order spherical aberration component of the aberration is represented by SA3, the variation Δ ((SA3λ) rms) of the standard deviation of the third-order spherical aberration component SA3 with respect to the wavelength change Δλ satisfies the following relationship. The optical pickup device according to claim 5.
Δ ((SA3λ) rms) / Δλ1 ≦ 1/1000 (λ1 ′ / nm) (6)
Here, λ1 ′ is λ1 ′ = λ1 + Δλ1, where Δλ1 is the wavelength change amount of the first light source when the temperature changes by ΔT from the standard state.

Images