JP4278989B2 - Optical pickup and optical information processing apparatus using the same - Google Patents

Description

【００８５】
本実施の形態１では、大きく３種類の球面収差、すなわち、
▲１▼ＤＶＤ互換時に、使用波長の違いに伴い発生する球面収差
▲２▼ＣＤ互換時に、使用波長及び基板厚の違いに伴い発生する球面収差
▲３▼青色系光記録媒体として、２層光記録媒体の層間距離の違いに伴い発生する球面収差
を補正するが、図１２，図１４を見れば明らかなとおり、▲１▼と▲３▼で球面収差が最大となる位置は略一致しているため、２種類のピーク位置を出すような電極パターン１３ａ，１３ｂを用いればよい（図１５参照）。これは、青色系光路をＤＶＤ系と同様のＮＡ，基板厚で構成したためである。
【００８６】
そして、このような電極パターンを有する液晶素子に対して、例えば、前記のような光記録媒体判別手段でＤＶＤ系光記録媒体が挿入されたことが認識されると、付加位相量が最大となる位置がメタル電極１３ａとなるように予め記憶された印加電圧が各電極に加えられ、ＣＤ系光記録媒体が挿入されたことが認識されると、付加位相量が最大となる位置がメタル電極１３ｂとなるように予め記憶された印加電圧が各電極に加えられる。また、青色系光記録媒体であることが認識されると、２層型青色系光記録媒体の場合に１層目の記録再生時には、液晶素子は何ら作用せず、フォーカスジャンプして２層目で記録再生を開始すると、付加位相量が最大となる位置がメタル電極１３ａとなるように予め記憶された印加電圧が各電極に加えられる。
【００８７】
なお、液晶素子の電極構成は図１５に限られるものではない。図１６に示すような連続した１枚の透明電極２０（図１５の透明電極１０ａ、１０ｂを１対とした）にメタル電極２２〜２５を形成してなり、ＤＶＤ系用の光源点灯時に有限系光路として構成し、かつメタル電極２３としてＤＶＤ系光記録媒体を記録再生時に付加位相量が最大となる瞳半径位置に形成し、メタル電極２４としてＣＤ系光記録媒体の記録再生しようとしたときに発生する球面収差が最大となる瞳半径位置に形成してもよい。
【００８８】
また、図１８に示すような透明電極２０（図１５の透明電極１０ａ、１０ｂを１対とした）に、分割電極として、外縁部から中心部へ分割電極領域２６が形成され、さらに分割電極領域２６より内周に分割電極領域２７，２８が形成されてなる（１＜分割電極領域２８＜分割電極領域２７＜分割電極領域２６）。分割電極領域２７として２層型青色系光記録媒体の２層目、あるいはＤＶＤ色系光記録媒体を記録再生しようとしたときに発生する球面収差が最大となる瞳半径位置に形成し、分割電極領域２８としてＣＤ系光記録媒体の記録再生しようとしたときに発生する球面収差が最大となる瞳半径位置に形成してもよい。
【００８９】
さらに、本実施の形態１は図１９（ａ）に示すように、複合素子として開口制限素子１０７、液晶素子１０５、波長板１０６を一体形成してもよい。これにより、組付工程の簡素化が図れる。また、図１９（ｂ）に示すような別の複合素子の構成、すなわち、液晶素子１０５、波長板１０６の順に一体形成され、液晶素子表面もしくは波長板表面に開口制限素子１０７が形成されていてもよい。このように、部品の単一化や、アクチュエータへの搭載など、さらに素子の薄型化、重量の低減が可能となる。
【００９０】
また、本実施の形態１の光ピックアップにおいて、液晶素子の別の電極パターンとして、例えば、図１５に示すような異なる瞳半径位置で球面収差が最大となるように複数の給電部を設けたのに対し、図１２，図１３，図１４に示すような異なるピーク位置に発生する球面収差の略中心位置（図２０中の矢印Ｃ）に常にピーク位置が発生するように電極が構成されてもよい。そして、光記録媒体判別信号、球面収差信号応じて所定の位相量を付加する構成、また光記録媒体判別信号により、１層目／２層目の記録再生層の切り換えに応じて所定の位相量を付加する構成であってもよい。この構成により、電極パターンを単純化することができる。
【００９１】
また、ＤＶＤ系光路を有限系とすることは、対物レンズへの入射光束を発散状態あるいは収束状態とすることを意味する。一般に対物レンズへの入射光束の発散状態を変化させることは、球面収差を変化させることと等価であるため、球面収差を低減可能な発散状態を選べばよい。このような有限系の手法によりＤＶＤ系光路の球面収差が抑制でき（図３５参照）、実施の形態１において、ＤＶＤ系光路を有限系で構成した場合は、青色系光記録媒体の基板厚誤差に伴い発生する球面収差のみを抑制するように液晶素子の電極パターンを構成してやればよく、液晶素子の位相付加領域としては、外周部のＤＶＤ系のＮＡ：０.６５〜ＣＤ系のＮＡ：０.５０の範囲に特化すればよい。そして、ＣＤ系光路において、液晶素子による位相補正効果を用いて収差補正を行うため、ＣＤ系のＮＡ：０.５０以下の範囲に収差補正領域を形成した。
【００９２】
次に、図２１は本実施の形態２における別の構成の光ピックアップであり、前述の実施の形態１で説明した光ピックアップの構成と同じく、「使用波長４００ｎｍ、ＮＡ０.６５、光照射側基板厚０.６ｍｍの青色系（大容量）光記録媒体」と、「使用波長６６０ｎｍ、ＮＡ０.６５、光照射側基板厚０.６ｍｍのＤＶＤ系光記録媒体」と、「使用波長７８０ｎｍ、ＮＡ０.５０、光照射側基板厚１.２ｍｍのＣＤ系光記録媒体」をともに記録、再生、または消去できる光ピックアップの概略構成を示す図である。実施の形態１と異なる点は、青色系光路も光源と受光素子と光路分離手段を単一パッケージに収めたホログラムユニット４０１を使用している点である。これにより、光学系の小型化、組付の簡素化が図れる。
【００９３】
同様に、図２２（ａ）は本実施の形態１におけるもう一つ別の光ピックアップの概略構成を示す図である。前述した実施の形態１の光ピックアップと同じく、「使用波長４００ｎｍ、ＮＡ０.６５、光照射側基板厚０.６ｍｍの青色系（大容量）光記録媒体」と「使用波長６６０ｎｍ、ＮＡ０.６５、光照射側基板厚０.６ｍｍのＤＶＤ系光記録媒体」と「使用波長７８０ｎｍ、ＮＡ０.５０、光照射側基板厚１.２ｍｍのＣＤ系光記録媒体」をともに記録、再生、または消去できる光ピックアップである。そして、実施の形態１と異なる点は、ＤＶＤ／ＣＤの光源、受光素子、光路分離手段を単一パッケージに集約した点である。これにより、３波長光学系を小型な光ピックアップで実現したものである。なお、ホログラム３０１ｂとしては、図２２（ｂ）に示すようにＤＶＤ用のホログラム面をもつ層とＣＤ用のホログラム面をもつ層を備えた構成を用いればよい。
【００９４】
また、本発明の実施の形態２として、以下に説明する光ピックアップの構成としてもよい。そして、本実施の形態２の光ピックアップは、前述の実施の形態１で説明した光ピックアップと構成の異なる点は、ＣＤ系光路においても有限系で構成した点である。ＣＤ系光路において、有限系とすることにより、波面の収差を十分に抑制することができる。このためＣＤ系光路の球面収差が抑制できることから、同光路では液晶素子を作用させずに済むことになる。すなわち、実施の形態１の構成に対して、液晶素子に形成するＣＤ系光路用の電極パターンを減らすことが可能となる。
【００９５】
また、本発明の実施の形態３として、前述の各実施の形態に用いる液晶素子においては、対物レンズの中心軸が光軸に一致しているときに、最適な収差補正ができるようなパターンが設計されている。したがって、光記録媒体のトラッキングサーボにより対物レンズがラジアル方向（光記録媒体の半径方向）に移動するずれが生じると、補正を必要とする収差分布と液晶素子に形成された補正パターンとの間に位置ずれが生じ、収差補正の機能が劣化する。図２３（ａ），（ｂ），（ｃ）を用いて簡易的に説明する。ＤＶＤやＣＤ互換時に発生する球面収差の波面が、図２３（ａ）の上側部分であるときに、対物レンズに光源側から入射する光束に、図２３（ａ）の下側部分に示すような位相差を与え、不要な収差の波面を打ち消すことができることは前述のとおりである。ここで、図２３（ｂ）のように液晶素子と、対物レンズの間に位置ずれが生じた場合、図２３（ｃ）に示すような不要な収差の波面が発生する。
【００９６】
この対物レンズシフトに基づく、収差補正の機能劣化を改善するためには液晶素子を可動部（アクチュエータ）に搭載し、対物レンズと一体に駆動させる方法がある。しかしながら、この方法とした構成の液晶素子では重量増加、信号引出線の配線本数増加などの観点から、対物レンズアクチュエータの外部に設置することが望まれる。
【００９７】
ここで、図２３（ｃ）に示す不要な収差形状に着目すると、光軸反対称な３次関数状の形状を示していることがわかる。この形状は、例えば、非特許文献３で説明されているコマ収差と同等の形状を示すものである。本実施の形態３は、コマ収差補正手段として液晶素子の電極パターンを、後述のとおり工夫することにより、ＤＶＤ、ＣＤ互換時に発生する不要収差を補正可能とする。
【００９８】
前述したように、光軸対称に波面形状を補正する液晶素子と、対物レンズとの相対位置ずれは、不要なコマ収差を発生させる。本実施の形態３は、検出レンズ１１０と受光素子１１２（図１参照）を主として形成されるコマ収差検出光学系を備えることにより、このような不要なコマ収差を検知することができる。
【００９９】
図２４（ａ）に示すような光記録媒体１０９には案内溝が形成されている。この案内溝からの反射光には、直接の反射光である０次光と、回折された±１次回折光とが含まれ、これらの光が干渉し合っている。図２４（ｂ）は、受光手段の受光面で受光される０次光（直進光）と±１次回折光とを、受光素子１１２の受光面の上から見た図である。０次光（直進光）と±１次回折光とは、重なる部分があり、この重なる部分を干渉領域と呼ぶ。
【０１００】
この干渉領域が、コマ収差に伴いどのように変化するかを、図２５を用いて説明する。図２５は、球面収差を抑制している液晶素子に対し、対物レンズ１０８がシフト移動していくことにより、干渉領域がどのように変化するかを示している。対物レンズ１０８のシフトに伴い図の左右で光量に偏りが生じる。これは、対物レンズ１０８と液晶素子１０５の相対位置ずれにより、光記録媒体１０９上に投影されるスポットにコマ収差が発生するためである。この偏りは、一方の干渉領域と、もう一方の干渉領域とで、逆方向に生じる。図２５では、位置ずれが大きくなるほど図中右側の領域が強くなり、左側の領域が徐々に弱くなっていくのがわかる。
【０１０１】
本実施の形態３では、図２６のような６つの領域に分割された受光素子１１２と、演算手段１１３により、このコマ収差を検知する。すなわち、受光素子１１２の受光面は、光記録媒体１０９の半径方向（ラジアル方向）に２領域を有し、この２領域は光記録媒体１０９の回転方向（タンジェンシャル方向）にそれぞれ３分割されている。光記録媒体１０９の半径方向（ラジアル方向）の２領域のうちの一方に含まれる３つの領域を回転方向順にａ領域１１２ａ，ｂ領域１１２ｂ，ｃ領域１１０ｃとする。そして、ａ領域１１２ａ，ｂ領域１１２ｂ，ｃ領域１１２ｃから出力される光量信号を、それぞれＡ，Ｂ，Ｃとする。光記録媒体１０９のラジアル方向２領域のうち、もう一方に含まれる３つの領域をｄ領域１１２ｄ，ｅ領域１１２ｅ，ｆ領域１１２ｆとする。そして、ｄ領域１１２ｄ，ｅ領域１１２ｅ，ｆ領域１１２ｆから出力される光量信号を、それぞれＤ，Ｅ，Ｆとする。演算手段１１３は、加算手段及び減算手段から構成されている。
【０１０２】
受光素子１１２の各領域から出力された光量信号は、演算手段１１３に入力され、所定の演算が行われ、この演算結果が、光記録媒体の半径方向（ラジアル方向）のコマ収差を示す信号：ＣＯＭＡが演算手段１１３から出力される。演算手段１１３による演算を式で表すと、（数７）となる。
【０１０３】
【数７】
ＣＯＭＡ＝（Ａ＋Ｃ＋Ｅ）-（Ｂ＋Ｄ＋Ｆ）
対物レンズ１０８と、液晶素子１０５の相対位置ずれに伴う干渉領域の変化を、（数７）の演算手段１１３を用いて演算した結果を図２７に示す。図２７の横軸は対物レンズ１０８と液晶素子１０５の相対位置ずれ量、縦軸は出力信号Ａ〜Ｆの和信号で規格化したコマ収差信号である。
【０１０４】
また、本実施の形態３では、コマ収差を検出して液晶素子１０５を駆動する方法の代わりに、対物レンズ１０８あるいは対物レンズアクチュエータと液晶素子１０５との相対位置ずれ量を直接検知して、液晶素子１０５の制御を行ってもよい。位置ずれ量の検知は、よく知られたＰＳＤ（Ｐosition Ｓensor Ｄevice）をピックアップ固定光学系上に配置して、対物レンズとＰＳＤ間の距離を検出すればよい。そして、検知された位置ずれ量は、予め記憶されているテーブル（表記せず）に基づきコマ収差量に変換される。そして、そのコマ収差量に応じて、液晶素子１０５は駆動制御される。
【０１０５】
コマ収差補正手段は、図２８に示すように所定の電極パターンを有する液晶素子１０５のＤＶＤ/ＣＤ互換用パターン（図４（ａ），（ｂ）参照）に対向して配置する。液晶素子１０５は、図２８に示すように、少なくとも一方の透明電極が左右対称に分割され、各電極部分（と共通電極との間）に独立して電圧を印加できるようになっており、前記電圧を制御することにより、各電極部分の液晶の屈折率：ｎをｎ1 からｎ２ まで自在に変えることができる。屈折率：ｎを変化させると、各領域を通過する光線に光路差：Δｎ・ｄ（Δｎは屈折率変化分、ｄは液晶のセル厚）、すなわち、波長をλとして、位相差Δｎ・ｄ（２π／λ）を与えることができる。
【０１０６】
例えば、図２９の如きコマ収差が発生したとする。この波面収差を３次元曲線として示したのが図３０（ａ）の上の部分である。このようなコマ収差の波面に対し、対物レンズ１０８に光源側から入射する光束に、図３０（ａ）の下側部分に示すような位相差が与えられるように、図２８に示す液晶素子１０５の各電極に印加する電圧を調整すると、液晶素子１０５を透過する光束の各部での波面の遅れにより前記「収差の波面」を打ち消すことができる。図３０（ｂ）は、図３０（ａ）における実線（コマ収差の波面）と破線（液晶素子による波面の遅れ）の和、すなわち補正後の波面を示す。もとの波面（図３０（ａ）の実線の部分）よりも格段に小さくなる。
【０１０７】
特に、このようなコマ収差補正用電極面は図１６，図１８に示したような片側にのみ球面収差補正用電極パターンを有する液晶素子の対向電極面に形成すればよい。
【０１０８】
図３１は本発明の実施の形態４における光情報処理装置である情報記録再生装置の概略構成を示す透過斜視図である。
【０１０９】
情報記録再生装置３０は、光記録媒体４０に対して光ピックアップ３１を用いて情報の記録，再生，消去の少なくともいずれか１以上を行う装置である。本実施の形態４において、光記録媒体４０はディスク状であって、保護ケースのカートリッジ４１内に格納されている。光記録媒体４０はカートリッジ４１ごと、挿入口３２から情報記録再生装置３０に矢印「ディスク挿入」方向へ挿入セットされ、スピンドルモータ３３により回転駆動され、光ピックアップ３１により情報の記録や再生、あるいは消去が行われる。
【０１１０】
この光ピックアップ３１として、前述の実施の形態１〜３に記載の光ピックアップを適宜用いることができる。
【０１１１】
また本実施の形態４は、使用波長λ：４００ｎｍ、ＮＡ：０.６５で光記録媒体上に情報記録密度増倍度：Ｐ１＞１.８の多値記録を行う光情報処理装置であってもよい。これにより、例えば、２２ＧＢ以上の光情報処理装置をＮＡ０.８５の高ＮＡの対物レンズを用いることなく実現できる。すなわち、光記録媒体への記録容量はスポット径で定まる。ＤＶＤ系光記録媒体（４.７ＧＢ）に比べ、青色波長帯域を利用すれば、スポット径比（λ／ＮＡ）²で容量が上げられ、１２ＧＢ相当となる。これに前記条件の多値記録を適用することにより、２２ＧＢ相当が得られる。この結果、変動などに伴うマージンを拡大できる。そして、対物レンズの焦点深度は、ＮＡの２乗に比例して厳しくなるため、ＮＡ０.８５の対物レンズに比べＮＡ０.６５のレンズは１.７倍マージンを広げられる。
【０１１２】
なお、前述の各実施の形態では、簡単のため、波長として４００ｎｍ、６６０ｎｍ、７８０ｎｍに限定して述べてきたが、本発明は、以下のような各光記録媒体が規格として定める範囲に適用することが可能である。
【０１１３】
・青色波長帯域：波長３９７ｎｍ〜４１７ｎｍ
・赤色波長帯域：波長６５０ｎｍ〜６７０ｎｍ
・赤外波長帯域：波長７７０ｎｍ〜７９０ｎｍ
同様に、それぞれのＮＡ（開口数）として、０.６５、０.５０に限定して述べてきたが、
・青色系光記録媒体のＮＡ：０.６０〜０.７０
・ＤＶＤ系光記録媒体のＮＡ：０.６０〜０.６５
・ＣＤ系光記録媒体のＮＡ：０.４５〜０.５０
の範囲に適用できる。
【０１１４】
【発明の効果】
以上説明したように、本発明によれば、青色系対物レンズによりＤＶＤ系，ＣＤ系光記録媒体に対して記録，再生を行うときに発生する球面収差、及び青色系光記録媒体の基板厚ばらつき、多層型青色系光記録媒体の層間距離に伴い発生する球面収差を１枚の液晶素子で抑制するため、大容量の青色系光記録媒体と、従来のＤＶＤ系，ＣＤ系光記録媒体の情報記録面上に良好なスポットを形成でき、かつ部品点数を増加させることなく、３世代いずれの光記録媒体に対しても高Ｓ／Ｎで信号を記録、再生することができるという効果を奏する。
【図面の簡単な説明】
【図１】本発明の実施の形態１における光ピックアップの概略構成を示す図
【図２】半導体レーザー、ホログラム及び受光素子を一体化して構成されたホログラムユニットを示す図
【図３】本実施の形態１の光ピックアップにおける液晶素子の概略構成を示す断面図
【図４】（ａ），（ｂ）は液晶素子の電極パターンの例を示す図
【図５】（ａ）は対物レンズのＮＡ０.６５となる有効径と波長の関係、（ｂ）は（ａ）の対物レンズと同じφ１、焦点距離、ＮＡにおいて、硝種を変化させたときのφ２／φ１と、使用硝種のｄ線での屈折率ｎｄの関係を示す図
【図６】本実施の形態１における（ａ）は反射、（ｂ）は回折、（ｃ）は吸収の光学特性を利用して光束径を切り換える開口制限素子の構成を示す図
【図７】検出レンズを介して受光素子に向かう光束に発生する球面収差を示す図
【図８】光束分割手段により分割された各々の光束を検知する受光領域の分割された受光素子を示す図
【図９】検出された基板厚誤差に起因して発生する球面収差を示す図
【図１０】（ａ）は球面収差の波面（実線）と液晶素子による波面の遅れ（破線）、（ｂ）は補正後の球面収差の波面を２次元曲線として示す図
【図１１】（ａ）は球面収差の波面（実線）と液晶素子による波面の遅れ（破線）、（ｂ）は補正後の球面収差の波面を２次元曲線として示す図
【図１２】波長４００ｎｍ、ＮＡ０.６５で球面収差の波面が最小となる単一の対物レンズに、波長６６０ｎｍの光を無限系で入射させてＤＶＤ系光記録媒体にスポット形成させたとき発生の球面収差を示す図
【図１３】波長４００ｎｍ、ＮＡ０.６５で球面収差の波面が最小となる単一の対物レンズに、波長７８０ｎｍの光を無限系で入射させてＣＤ系光記録媒体にスポット形成させたとき発生の球面収差を示す図
【図１４】青色系光記録媒体の２層目の情報記録層への記録再生時に発生する球面収差を示す図
【図１５】本実施の形態１における球面収差を補正するための液晶素子の２つの透明電極におけるメタル電極構成を示す図
【図１６】本実施の形態１における球面収差を補正するための液晶素子の１つの透明電極におけるメタル電極構成を示す図
【図１７】本実施の形態１における対物レンズの概観図を示す図
【図１８】本実施の形態１における球面収差を補正するための液晶素子の透明電極における分割電極構成を示す図
【図１９】（ａ）は開口制限素子、液晶素子、波長板を一体形成した複合素子、（ｂ）は別の複合素子の構成を示す図
【図２０】本実施の形態１の液晶素子の電極パターンとして、異なるピーク位置に発生する球面収差の略中心位置にピーク位置が発生する電極構成を説明する図
【図２１】本発明の実施の形態２における別の構成の光ピックアップの概略構成を示す図
【図２２】（ａ）は本発明の実施の形態１におけるもう一つ別の構成の光ピックアップの概略構成、（ｂ）はＤＶＤ用のホログラム面をもつ層とＣＤ用のホログラム面をもつ層を備えたホログラム構成を示す図
【図２３】（ａ）は発生の球面収差（上側）とこれに付加する位相差（下側）、（ｂ）は対物レンズシフトにより付加する位相差がずれた状態、（ｃ）は対物レンズシフトにより発生の不要な波面の収差（残留収差）を示す図
【図２４】（ａ）は光記録媒体の案内溝から直接の反射光の０次光、回折された±１次回折光との干渉、（ｂ）は受光手段の受光面から見た０次光（直進光）と１次回折光との干渉領域を示す図
【図２５】液晶素子に対して対物レンズシフトにより変化する干渉領域を示す図
【図２６】受光素子と演算手段により、発生したコマ収差を検知する概略構成を示す図
【図２７】対物レンズと液晶素子の相対位置ずれに伴う干渉領域の変化の演算手段により演算した結果を示す図
【図２８】液晶素子の電極パターンを示す図
【図２９】対物レンズシフトに起因し発生のコマ収差を示す図
【図３０】（ａ）はコマ収差の波面（実線）と付与される位相差（破線）、（ｂ）は補正後の波面を示す図
【図３１】本発明の実施の形態４における光情報処理装置である情報記録再生装置の概略構成を示す透過斜視図
【図３２】青色波長帯域の光源を用いた大容量光記録媒体と、既存のＤＶＤ、あるいはＣＤとの互換が可能な光ピックアップの概略構成を示す図
【図３３】波長６６０ｎｍのＤＶＤ系光記録媒体に無限系入射で集光させたときの球面収差の波面を示す図
【図３４】波長７８０ｎｍのＣＤ系光記録媒体に無限系入射で集光させたときの球面収差の波面を示す図
【図３５】波長６６０ｎｍのＤＶＤ系光記録媒体に有限系入射で集光させたときの球面収差の波面を示す図
【符号の説明】
１ａ，１ｂ ガラス基板
２ 導電性スペーサ
３ 液晶
４ａ，４ｂ 電極
５ 絶縁膜
６ 配向膜
７ 電極引出部
１０，１０ａ，１０ｂ，２０ 透明電極
１１ 給電部
１２ａ，１２ｂ，１３ａ，１３ｂ，１４ａ，１４ｂ，２２，２３，２４，２５ メタル電極
１５ 分割電極
２６，２７，２８ 分割電極領域
３０ 情報記録再生装置
３１ 光ピックアップ
３２ 挿入口
３３ スピンドルモータ
４０ 光記録媒体
２１ カートリッジ
１００ 青色用光源
１０１，２０１ａ，３０１ａ 半導体レーザー
１０２ コリメートレンズ
１０３ 偏光ビームスプリッタ
１０４ プリズム
１０５ 液晶素子
１０６ 波長板
１０７ 開口制限素子
１０８ 対物レンズ
１０９ａ，１０９ｂ，１０９ｃ 光記録媒体
１１０ 検出レンズ
１１１ 光束分割手段
１１２，２０１ｃ，３０１ｃ 受光素子
１１２ａ〜１１２ｆ， ａ〜ｆ領域
１１３ 演算手段
２００ ＤＶＤ用光源
２０１，３０１ ホログラムユニット
２０１ｂ，３０１ｂ ホログラム
２０２，３０２，５０２ カップリングレンズ
２０３，３０３ ダイクロイックプリズム
３００ ＣＤ用光源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup including a liquid crystal element that gives a phase change to a passing light beam from a light source according to an applied voltage, and an optical information processing apparatus using the same.
[0002]
[Prior art]
As means for storing video information, audio information, or data on a computer, optical recording media such as a CD with a recording capacity of 0.65 GB and a DVD with a recording capacity of 4.7 GB are becoming widespread. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity.
[0003]
As means for increasing the recording density of such an optical recording medium, in an optical pickup that writes or calls information on the optical recording medium, the numerical aperture of the objective lens (hereinafter referred to as NA) is increased, or the light source By shortening the wavelength, it is effective to reduce the diameter of the beam spot condensed by the objective lens and formed on the optical recording medium. Therefore, for example, in the “CD optical recording medium”, the NA of the objective lens is 0.50 and the wavelength of the light source is 780 nm, whereas the recording density is higher than that of the “CD optical recording medium”. In the “DVD optical recording medium” made, the NA of the objective lens is 0.65 and the wavelength of the light source is 660 nm. As described above, the optical recording medium is desired to further improve the recording density and increase the capacity. For this purpose, the NA of the objective lens is set to be larger than 0.65 or the wavelength of the light source is increased. It is desired to make it shorter than 660 nm.
[0004]
As such a large-capacity optical recording medium and optical information processing apparatus, for example, a capacity equivalent to 22 GB using a light source in a blue wavelength region and an objective lens with NA 0.85 listed in Non-Patent Document 1, etc. There is a system proposal that satisfies the requirements.
[0005]
While new standards with higher NA or shorter wavelengths have recently been proposed, there are CDs and DVDs that are conventional optical recording media at hand. It is desirable that both these optical recording media and the new standard optical recording media can be handled by the same optical information processing apparatus. As the simplest method for realizing this, there is a method of mounting both the conventional optical pickup and the optical pickup for the new standard. However, with this method, it is difficult to achieve downsizing and cost reduction.
[0006]
Therefore, as an optical pickup capable of being compatible with a large-capacity optical recording medium using a light source in the blue wavelength band and an existing DVD or CD, as shown in a schematic configuration in FIG. 32, a blue light source 100 and a DVD light source. It is desirable that each of the 200 and CD light sources 300 and a single objective lens for condensing the light emitted from each light source on a predetermined optical recording medium are desirable. By the way, there are the following problems in order to focus light onto optical recording media of different standards such as blue, DVD, and CD with one objective lens.
[0007]
Infinite system incidence (incident light on the objective lens is parallel to a blue optical recording medium having a wavelength (λ1): 400 nm, NA (λ1): 0.65, and light irradiation side substrate thickness (t1): 0.6 mm. The wavelength (λ2): 660 nm, NA (λ2): 0.65, and the light irradiation side substrate thickness (t2) using a single objective lens that minimizes the wavefront of spherical aberration. ): When a spot is formed on a 0.6 mm DVD optical recording medium with infinite incidence, or wavelength (λ3): 780 nm, NA (λ3): 0.50, light irradiation side substrate thickness (t3): 1. When focused on a 2 mm CD optical recording medium with infinite incidence, spherical aberration due to a difference in wavelength or a difference in substrate thickness occurs as shown in FIGS.
[0008]
Such a problem is also present in the DVD / CD compatible optical pickup. That is, a single objective that minimizes the wavefront of spherical aberration upon infinite incidence on a DVD optical recording medium having a wavelength (λ2): 660 nm, NA (λ2): 0.65, and substrate thickness (t2): 0.6 mm. When a lens is used to collect light with an infinite incidence on a CD optical recording medium having a wavelength (λ3): 780 nm, NA (λ3): 0.50, and substrate thickness (t3): 1.2 mm, the difference in wavelength And spherical aberration due to the difference in substrate thickness.
[0009]
As a handling method at this time, for example, Patent Document 1 and Patent Document 2 are described. That is, for a DVD optical recording medium having a thickness of 0.6 mm using two semiconductor lasers having different wavelengths and a wavelength-selective liquid crystal element and using light having a wavelength of 660 nm emitted from one of the semiconductor lasers. Recording and reproduction are performed, and recording and reproduction are performed on a CD-based optical recording medium having a thickness of 1.2 mm using light having a wavelength of 780 nm emitted from the other semiconductor laser. For the liquid crystal element, the phase distribution is not changed for light having a wavelength of 660 nm, and the spherical aberration due to the difference in substrate thickness is corrected by changing the phase distribution for light having the other wavelength of 780 nm. Has proposed.
[0010]
As another method, DVD-side incident light with a wavelength of 660 nm is an infinite system and CD-side incident light is a finite system (referred to as a divergent light incident state) with respect to the objective lens (see FIG. 35). ), A means for correcting spherical aberration caused by the difference in substrate thickness and wavelength between the DVD optical recording medium and the CD optical recording medium is generally known.
[0011]
Non-Patent Document 2 describes that a blue type optical recording medium / DVD type optical recording medium compatible optical pickup is proposed by using the conventional example as described above. In the description of Non-Patent Document 2, a method for recording or reproducing three types of optical recording media of a blue optical recording medium / DVD optical recording medium / CD optical recording medium with one objective lens is proposed. . For a blue-based optical recording medium having three semiconductor lasers having different wavelengths of 405 nm, 650 nm, and 780 nm and a wavelength-selective phase correction element, and having a wavelength of 405 nm and an infinite system incident light and a thickness of 0.1 mm The DVD-type optical recording medium having a wavelength of 650 nm and a finite system incident is used to irradiate a DVD optical recording medium having a wavelength of 650 nm and the thickness is 1.2 mm using a 780 nm wavelength and finite system incident light. The wavelength-selective phase plate does not change the phase distribution for light with a wavelength of 405 nm, and the phase distribution for light with other wavelengths of 650 nm and 780 nm. Is changing. In this configuration, as a method of correcting the spherical aberration due to the difference in substrate thickness, two types of wavefront correction means for making the wavelength selective phase correction element and DVD / CD two wavelengths finite system incident are used in combination. Yes.
[0012]
Furthermore, as another problem, if the NA of the objective lens is increased or the wavelength of the light source is shortened to increase the capacity, the influence of spherical aberration caused by the thickness error of the transparent substrate of the optical recording medium increases. Therefore, a correction means for suppressing the influence is required. The spherical aberration caused by the thickness error of the transparent substrate of the optical recording medium is generally given by (Equation 1).
[0013]
[Expression 1]
W ₄₀ = ((N ² -1) / (8n ^Three )) X (d x NA ^Four / Λ)
Here, n is the refractive index of the transparent substrate of the optical recording medium, d is the thickness of the transparent substrate, NA is the numerical aperture of the objective lens, and λ is the wavelength of the light source.
[0014]
From this (Equation 1), it can be seen that the shorter the wavelength and the higher the NA, the larger the aberration. In an optical information processing apparatus that writes and reads information on and from a conventional optical recording medium such as a CD and a DVD, the wavefront deterioration due to the spherical aberration does not particularly require correction, but is described in Non-Patent Document 1, etc. In a system using a blue light source and an NA 0.85 objective lens, the wavefront deterioration accompanying the thickness error of the optical recording medium is, for example, 0.07λ or more, and correction is required.
[0015]
Furthermore, in recent years, a multilayer optical recording medium having two or more information recording surfaces has been proposed as a method for further increasing the capacity, but it goes without saying that the wavefront deterioration accompanying the interlayer distance becomes a problem even in such a case. Yes. As these correction means, means for changing the divergence state of the light beam incident on the objective lens by movement of a plurality of lens groups listed in Patent Document 3, Patent Document 4, and Patent Document 5, or Patent Document 6, Patent Means for changing the phase state of a light beam incident on an objective lens described in Document 7 are known.
[0016]
[Patent Document 1]
Japanese Patent No. 2725653
[Patent Document 2]
JP 10-334504 A
[Patent Document 3]
JP 2000-131603 A
[Patent Document 4]
JP 2000-242963 A
[Patent Document 5]
JP 2001-28147 A
[Patent Document 6]
Japanese Patent Laid-Open No. 9-128785
[Patent Document 7]
Japanese Patent Laid-Open No. 10-20263
[Patent Document 8]
JP 2001-143303 A
[Non-Patent Document 1]
ISOM2001 Proceedings "Next Generation Optical Disc" Hiroshi Ogawa, p6-7
[Non-Patent Document 2]
ISOM2001 Proceedings "BLUE / DVD / CD COMPATIBLE OPTICAL HEAD WITH THREE WAVELENGTHS AND A WAVELENGTH SELECTIVE FILTER" Ryuichi Katayama and Yuichi Komatsu p30 ~ 31
[Non-Patent Document 3]
Hideaki Yamada, "Laser & Optics Guide IV (2)" Melles Griot, 1st edition, published 1996.6 p22-7-8
[0017]
[Problems to be solved by the invention]
As described above, problems that will be required for future optical pickups include compensation for aberrations that occur with higher NA or shorter wavelengths, and compatibility with conventional optical recording media. As described above, countermeasures are disclosed, but the method of separately installing the correction means leads to an increase in the size and cost of the optical pickup. Therefore, it is desired to integrate each function and reduce the size.
[0018]
Further, in the method of Non-Patent Document 2, sufficient wavefront performance cannot be obtained when the DVD optical recording medium / CD optical recording medium is compatible. In general, Marshall Criterion: 0.07λrms is sometimes used as a reference value as a diffraction-limited spherical aberration. In an optical pickup, an optical recording medium thickness error, an optical recording medium tilt error, an optical recording medium and an objective lens are used. There are various error factors such as defocus error due to lens position shift. Considering the cumulative accumulation of wavefront deterioration due to these errors, the wavefront of spherical aberration without error ( On the other hand, in Non-Patent Document 2, the spherical surface (median value) of a DVD-based optical recording medium is about 0.05 λrms. It is impossible to minimize the spherical aberration of both the DVD system and the CD system with one element. That is, there is a problem that the design must be aimed at an intermediate value of the liquid crystal element conditions that minimize the wavefront of spherical aberration of the DVD system and the CD system, and as a result, there is a problem that the spherical aberration cannot be sufficiently suppressed. .
[0019]
The present invention is directed to solving the above-described problems of the prior art, and the object thereof is to increase the number of components without increasing the number of components, and the blue optical recording medium using the blue wavelength band: 400 nm, or the red wavelength band: A configuration in which a good spot can be irradiated with one objective lens on three types of information recording surfaces of a DVD optical recording medium using 660 nm or a CD optical recording medium using infrared wavelength band: 780 nm is realized. In particular, an optical pickup that sufficiently suppresses spherical aberration in each blue / DVD / CD optical system, specifically, a design median value of residual spherical aberration of 0.030 λrms or less, and optical information using the optical pickup It is to provide a processing apparatus.
[0020]
[Means for Solving the Problems]
In order to achieve this object, an optical pickup according to claim 1 of the present invention is an optical pickup that performs one or more of recording, reproducing, and erasing information on an optical recording medium, and has a wavelength : Three light sources that emit light of λ1, λ2, and λ3 (λ1 ≦ λ2 ≦ λ3), an objective lens that focuses the light emitted from the light source on the optical recording medium, and numerical apertures: NA1, NA2, and NA3 Aperture limiting means for switching (NA1 ≧ NA2 ≧ NA3), and a liquid crystal element that changes the phase distribution of the passing light beam by applying a voltage, Wavelength: λ1, λ2, λ3, NA: NA1, NA2, NA3 are 397 nm ≦ λ1 ≦ 417 nm, 650 nm ≦ λ2 ≦ 670 nm, 770 nm ≦ λ3 ≦ 790 nm, 0.60 ≦ NA1 ≦ 0.70, 0.60 ≦ NA2 ≦ 0.65, 0.45 ≦ NA3 ≦ 0.50, When using light of wavelength λ1, the numerical aperture is NA1, when using light of wavelength: λ2, the numerical aperture is NA2, and when using light of wavelength: λ3, the numerical aperture is NA3. The optical recording medium for wavelength: λ1 and numerical aperture: NA1 is a two-layer optical recording medium having two information recording surfaces, The liquid crystal element gives a concentric phase change at the center of the optical axis of the passing light beam, When using light of wavelength: λ1 or wavelength: λ2 Concentric The eyes of Radial position r2 Concentric pupil radius position when the phase change of is maximized and the wavelength: λ3 is used r3 The phase change of The pupil radius position r2 and the pupil radius position r3 are different electrode surfaces of the counter electrode. above Yes, the pupil radius position r2 is formed in a region of approximately numerical aperture: NA2 to NA3, and the pupil radius position r3 is generated in a region of approximately numerical aperture: NA3 or less, which occurs with a difference in wavelength or substrate thickness. By using a liquid crystal element that generates spherical aberration of the opposite polarity to the spherical aberration that occurs, the generated spherical aberration can be solved, and the light emitted from the light source can be focused on the optical recording medium in the best condition, and the best recording and reproduction can be performed. Can do.
[0024]
The optical pickup according to claim 2 is an optical pickup that performs any one or more of recording, reproducing, and erasing information with respect to an optical recording medium, and has wavelengths: λ1, λ2, λ3 (λ1 ≦ λ2). ≦ λ3) three light sources for emitting light, an objective lens for condensing the light emitted from the light source on the optical recording medium, and apertures for switching numerical apertures: NA1, NA2, NA3 (NA1 ≧ NA2 ≧ NA3) A limiting means, and a liquid crystal element that changes the phase distribution of the passing light flux by applying a voltage, Wavelength: λ1, λ2, λ3, numerical aperture: NA1, NA2, NA3 are 397 nm ≦ λ1 ≦ 417 nm, 650 nm ≦ λ2 ≦ 670 nm, 770 nm ≦ λ3 ≦ 790 nm, 0.60 ≦ NA1 ≦ 0.70, 0.60 ≦ NA2 ≦ 0.65, 0.45 ≦ NA3 ≦ 0.50, When using light of wavelength λ1, the numerical aperture is NA1, when using light of wavelength: λ2, the numerical aperture is NA2, and when using light of wavelength: λ3, the numerical aperture is NA3. The optical recording medium for wavelength: λ1 and numerical aperture: NA1 is a two-layer optical recording medium having two information recording surfaces, The liquid crystal element gives a concentric phase change at the center of the optical axis of the passing light beam, When using light of wavelength: λ1 or wavelength: λ2 Concentric The eyes of Radial position r2 Concentric pupil radius position when the phase change of is maximized and the wavelength: λ3 is used r3 The phase change of The pupil radius position r2 and the pupil radius position r3 are either the same electrode surface of the counter electrode. above Yes, the pupil radius position r2 is formed in a region of approximately numerical aperture: NA2 to NA3, and the pupil radius position r3 is generated in a region of approximately numerical aperture: NA3 or less, which occurs with a difference in wavelength or substrate thickness. A spherical aberration of the opposite polarity to the spherical aberration that occurs is generated on the same electrode surface, miniaturizing the liquid crystal element, and collecting and reproducing the light emitted from the light source in the best condition on multiple optical recording media Can do.
[0025]
And claims 3 The optical pickup according to claim 1, 2 In the described optical pickup, the objective lens is configured to be used in a finite system when the light source of the wavelength: λ2 among the wavelengths: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3) of the three light sources is used. The phase correction regions of λ2 and λ3 can be made different, and they can be formed on the same electrode surface, and the phase correction amount of the liquid crystal element can be reduced, so that the driving time for aberration correction can be shortened.
[0026]
The optical pickup according to claim 4 is an optical pickup that performs any one or more of information recording, reproduction, and erasing with respect to an optical recording medium, and has wavelengths: λ1, λ2, λ3 (λ1 ≦ λ2). ≦ λ3) three light sources for emitting light, an objective lens for condensing the light emitted from the light source on the optical recording medium, and apertures for switching numerical apertures: NA1, NA2, NA3 (NA1 ≧ NA2 ≧ NA3) A limiting means, and a liquid crystal element that changes the phase distribution of the passing light flux by applying a voltage, Wavelength: λ1, λ2, λ3, numerical aperture: NA1, NA2, NA3 are 397 nm ≦ λ1 ≦ 417 nm, 650 nm ≦ λ2 ≦ 670 nm, 770 nm ≦ λ3 ≦ 790 nm, 0.60 ≦ NA1 ≦ 0.70, 0.60 ≦ NA2 ≦ 0.65, 0.45 ≦ NA3 ≦ 0.50, When using light of wavelength λ1, the numerical aperture is NA1, when using light of wavelength: λ2, the numerical aperture is NA2, and when using light of wavelength: λ3, the numerical aperture is NA3. The optical recording medium for wavelength: λ1 and numerical aperture: NA1 is a two-layer optical recording medium having two information recording surfaces, The liquid crystal element gives a concentric phase change at the center of the optical axis of the passing light beam, When using light of wavelength: λ1 or wavelength: λ2 Concentric The eyes of Radial position r2 The phase change at the concentric pupil radius position r3 is maximized when using light of wavelength λ3. The pupil radius position r2 is formed in a region of approximately numerical apertures NA2 to NA3, so that a spherical aberration having a polarity opposite to the generated spherical aberration is generated on the same electrode surface with a difference in wavelength or substrate thickness. The light emitted from the light source can be condensed in a best condition on a plurality of optical recording media, and recording and reproduction can be performed.
[0027]
And claims 5 The optical pickup according to claim 4 In the optical pickup described above, the objective lens may be used in a finite system when the light source having the wavelength of λ2 and the wavelength of λ3 among the wavelengths of the three light sources: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3) is turned on. In addition, the phase correction amount of the liquid crystal element can be reduced to shorten the drive time for correcting the aberration, and the light emitted from the light source can be condensed onto the optical recording medium in the best condition for recording and reproduction.
[0028]
Claims 6,7 The optical pickup according to claim 1, wherein 5 The optical pickup according to claim 1, further comprising an optical recording medium determining unit that determines an optical recording medium, and an additional phase amount of the liquid crystal element and a pupil radius position at which the additional phase amount is maximized according to a signal from the optical recording medium determining unit. And a spherical aberration detector that detects spherical aberration generated on the optical recording medium, and changes the additional phase amount of the liquid crystal element in accordance with a signal from the spherical aberration detector. Depending on the recording medium, the light emitted from the light source can be condensed in the best condition for recording and reproduction.
[0029]
Claims 8 The optical pickup according to claim 2, 4 In the liquid crystal element of the optical pickup described above, the counter electrode surface of the concentric phase addition surface is Left and right Symmetry In Divided Transparent electrode With this configuration, aberration correction for spherical aberration and coma aberration can be formed on the same electrode surface of the liquid crystal element, and the light emitted from the light source is focused on the optical recording medium in the best condition for recording and reproduction. It can be carried out.
[0030]
And claims 9, 10 The optical pickup according to claim 8 The optical pickup described above includes means for generating a coma aberration signal from an interference pattern of reflected light from the optical recording medium, and controls the additional phase amount of the liquid crystal element based on the coma aberration signal. A means for detecting the amount of misalignment from the center of the optical axis is provided, and the misalignment between the liquid crystal element and the objective lens is corrected by controlling the additional phase amount of the liquid crystal element based on the detected misalignment amount signal. The light emitted from the light source can be collected in the best condition on the optical recording medium for recording and reproduction.
[0032]
Claims 11-13 The optical pickup according to claim 1, wherein 10 The optical pickup described above includes an aperture limiting unit that switches the numerical aperture of the light emitted from the light source according to the wavelength used by the light source, the aperture limiting unit being integrated with the liquid crystal element, and further, Accordingly, a polarizing element that changes the polarization state of the light emitted from the light source is provided. The polarizing element is integrated with the liquid crystal element, and the liquid crystal element is movable integrally with the objective lens. The structure can be integrated and miniaturized, and the light emitted from the light source can be collected and recorded on a plurality of optical recording media in the best condition.
[0033]
Claims 14 The optical information processing apparatus according to claim 1. 13 Using the optical pickup according to any one of the above, at least one of recording, reproducing, and erasing information on the optical recording medium by converging light emitted from the light source on a plurality of optical recording media in the best state. The above can be performed.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0035]
FIG. 1 shows a “blue optical recording medium having a used wavelength of 400 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” and a “use wavelength of 660 nm, NA of 0.66, a light irradiation side substrate in Embodiment 1 of the present invention. Outline of optical pickup capable of recording, reproducing or erasing both “DVD optical recording medium with a thickness of 0.6 mm” and “CD optical recording medium with a working wavelength of 780 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm”. It is a figure which shows a structure.
[0036]
As shown in FIG. 1, the main parts of the optical pickup are a semiconductor laser 101 having a wavelength of 400 nm, a collimating lens 102, a polarizing beam splitter 103, dichroic prisms 203 and 303, a prism 104, a liquid crystal element 105, a wavelength plate 106, and an aperture limiting element 107. A blue optical system through which light having a wavelength of 400 nm passes, which is composed of the objective lens 108, the detection lens 110, the light beam splitting means 111, and the light receiving element 112, is configured.
[0037]
In addition, a DVD optical system through which light having a wavelength of 660 nm, which includes the hologram unit 201, the coupling lens 202, the dichroic prisms 203 and 303, the prism 104, the liquid crystal element 105, the wave plate 106, the aperture limiting element 107, and the objective lens 108 passes. Is configured.
[0038]
Furthermore, it is composed of a CD optical system through which light having a wavelength of 780 nm passes, comprising a hologram unit 301, a coupling lens 302, a dichroic prism 303, a prism 104, a liquid crystal element 105, a wave plate 106, an aperture limiting element 107, and an objective lens 108. Has been. That is, the dichroic prisms 203 and 303, the prism 104, the liquid crystal element 105, the wave plate 106, the aperture limiting element 107, and the objective lens 108 are common components used in two to three optical systems.
[0039]
Here, in the first embodiment, the objective lens 108 has a spherical aberration wavefront at an infinite incidence relative to “a blue optical recording medium having a working wavelength of 400 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm”. Is designed to be minimal.
[0040]
The optical recording media 109a, 109b, and 109c are optical recording media having different substrate thicknesses and wavelengths used, the optical recording medium 109a is a blue optical recording medium having a substrate thickness of 0.6 mm, and the optical recording medium 109b is The DVD-type optical recording medium has a substrate thickness of 0.6 mm, and the optical recording medium 109c is a CD-type optical recording medium having a substrate thickness of 1.2 mm. At the time of recording or reproducing, only one of the optical recording media is set in a rotating mechanism (not shown) and rotated at a high speed.
[0041]
Further, in the first embodiment, a description will be given of a form of an optical pickup that can be applied to a two-layer optical recording medium in which the blue-based optical recording medium has two information recording surfaces. The two-layer type optical recording medium has a first information recording surface through a transparent substrate having a substrate thickness of 0.6 mm, and a second information recording surface further on the back side of the first information recording surface. Have. A layer called a spacer layer is formed between the first layer and the second layer, and the thickness thereof is about 30 μm.
[0042]
Further, in the first embodiment, the objective lens 108 has a spherical surface at infinite incidence relative to “the first layer of a blue optical recording medium having a working wavelength of 400 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm”. Designed to minimize the wavefront of aberrations.
[0043]
Regarding the operation of the optical pickup configured as described above, first, a case where “a blue optical recording medium having a used wavelength of 400 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” is recorded, reproduced or erased will be described. To do. The linearly polarized divergent light emitted from the semiconductor laser 101 having a wavelength of 400 nm is converted into substantially parallel light by the collimator lens 102, passes through the polarization beam splitter 103 and the dichroic prisms 203 and 303, and the optical path is deflected by 90 degrees by the prism 104. The light passes through the liquid crystal element 105, passes through the wave plate 106, becomes circularly polarized light, is limited to NA 0.65 by the aperture limiting element 107, enters the objective lens 108, and is condensed as a minute spot on the optical recording medium 109 a. . Information is reproduced, recorded or erased by this spot.
[0044]
In addition, the light reflected from the optical recording medium 109 a becomes circularly polarized light opposite to the outward path, becomes again substantially parallel light, passes through the wave plate 106 and becomes linearly polarized light orthogonal to the forward path, and is polarized by the polarization beam splitter 103. The light is reflected and converged by the detection lens 110, and is deflected and divided into a plurality of optical paths by the light beam dividing unit 111, and reaches the light receiving element 112. From the light receiving element 112, an aberration signal, an information signal, and a servo signal are detected.
[0045]
Next, a description will be given of a case where “DVD-based optical recording medium having a used wavelength of 660 nm, NA of 0.65, and light irradiation side substrate thickness of 0.6 mm” is recorded, reproduced or erased. In recent years, a hologram unit in which a light receiving and emitting element is installed in one can and a light beam is separated using a hologram has come to be generally used for a DVD pickup. FIG. 2 shows a hologram unit 201 configured by integrating a semiconductor laser 201a, a hologram 201b, and a light receiving element 201c.
[0046]
The 660 nm light emitted from the semiconductor laser 201a of the hologram unit 201 is transmitted through the hologram 201b, converted into a predetermined divergent beam by the coupling lens 202, the light having a wavelength of 400 nm is transmitted, and the light having a wavelength of 660 nm is reflected. The dichroic prism 203 is reflected in the direction of the prism 104, the optical path is deflected by 90 degrees by the prism 104, a predetermined phase is added in the liquid crystal element 105, and the light passes through the wave plate 106 to be circularly polarized or elliptically polarized. The element 107 receives no action and enters the objective lens 108 and is condensed as a minute spot on the optical recording medium 109b. Information is reproduced, recorded or erased by this spot.
[0047]
The light reflected from the optical recording medium 109b is deflected by the prism 104, reflected by the dichroic prism 203, and converged by the coupling lens 202. As shown in FIG. 2, the light is reflected in the same can as the semiconductor laser 201a by the hologram 201b. The light is diffracted in the direction of a certain light receiving element 201c and received by the light receiving element 201c. An aberration signal, an information signal, and a servo signal are detected from the light receiving element 201c.
[0048]
Next, a case where “CD optical recording medium having a used wavelength of 780 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm” is recorded, reproduced or erased will be described. Similar to the DVD system, a CD-type pickup generally uses a hologram unit in which a light emitting / receiving element is installed in one can and which separates a light beam using a hologram. As shown in FIG. 1, reference numeral 301 denotes a hologram unit configured by integrating a semiconductor laser 301a, a hologram 301b, and a light receiving element 301c.
[0049]
The light of 780 nm emitted from the semiconductor laser 301a of the hologram unit 301 is transmitted through the hologram 301b and converted into a predetermined divergent beam by the coupling lens 302, and the light in the blue and red wavelength bands is transmitted through the infrared wavelength. The light in the band is reflected in the direction of the prism 104 by the reflecting dichroic prism 303, the optical path is deflected by 90 degrees by the prism 104, is transmitted through the liquid crystal element 105 without any action, passes through the wave plate 106, and is elliptically polarized or circular. The polarized light is limited to NA 0.50 by the aperture limiting element 107, enters the objective lens 108, and is condensed as a minute spot on the optical recording medium 109c. Information is reproduced, recorded or erased by this spot.
[0050]
The light reflected from the optical recording medium 109c is deflected by the prism 104, reflected by the dichroic prism 303, converged by the coupling lens 302, diffracted in the direction of the light receiving element 301c, and received by the light receiving element 301c. An aberration signal, an information signal, and a servo signal are detected from the light receiving element 301c.
[0051]
FIG. 3 is a cross-sectional view illustrating a schematic configuration of the liquid crystal element in the optical pickup according to the first embodiment, and FIGS. 4A and 4B are diagrams illustrating examples of electrode patterns of the liquid crystal element. Hereinafter, the configuration and operation principle will be described with reference to FIGS. 3, 4A and 4B.
[0052]
The liquid crystal element of the first embodiment shown in FIG. 3 has a known configuration described in Patent Document 8, and glass substrates 1a and 1b are bonded by a conductive spacer 2 to form a liquid crystal cell. The inner surface of the glass substrate 1a is in the order of the electrode 4a, the insulating film 5 and the alignment film 6 from the inner surface, and the inner surface of the glass substrate 1b is in the order of the electrode 4b, the insulating film 5 and the alignment film 6 from the inner surface. It is coated.
[0053]
The electrode 4a is wired in a pattern so that it can be connected to the control circuit by a connection line at the electrode lead-out portion 7. The electrode 4b is electrically connected to the electrode 4a formed on the glass substrate 1a by the conductive spacer 2. Therefore, the electrode 4b can be connected to the phase correction element control circuit by the connection line at the electrode lead-out portion 7. Liquid crystal 3 is filled inside the liquid crystal cell.
[0054]
An electrode formed on the electrode on the substrate that constitutes the liquid crystal element and sandwiches the liquid crystal layer is provided in the uniform electrode as disclosed in paragraphs [0026] to [0036] of Patent Document 8. A voltage drop type method provided with the above or a segment type configuration disclosed in Patent Document 6 may be used. In the first embodiment, the electrode pattern is formed concentrically around the center of the optical axis. FIG. 4A shows a conceptual diagram of the electrode pattern when the former method is used, and FIG. FIG. 4B shows a conceptual diagram of the electrode pattern.
[0055]
In the optical pickup of the first embodiment, it is necessary to switch the NA (numerical aperture) according to the optical recording medium set in the rotation mechanism. When the focal length of the objective lens is f and the effective diameter of the light beam used for condensing is φ, NA is given by (Expression 2).
[0056]
[Expression 2]
NA = φ / 2 / f
Therefore, a means for switching the passing beam diameter may be used according to the wavelength used. An aperture limiting element 105 (see FIG. 1) is used as means for switching the beam diameter according to the lighting light source. The aperture limiting element may be any element that switches the beam diameter using one of the optical characteristics of reflection, diffraction, and absorption according to the wavelength band or the polarization direction.
[0057]
That is, when an infinite system light having the same luminous flux diameter is incident on an objective lens having the best wavefront at a wavelength of 400 nm, the refractive power decreases and the NA decreases. Therefore, in the present invention, the wavelength 660 nm is made incident with a slightly larger beam diameter φ2 than the incident beam diameter φ1 at the wavelength of 400 nm. FIG. 5A shows the relationship between the effective diameter and the wavelength for NA 0.65 in the objective lens having the characteristics described later (Table 1).
[0058]
From FIG. 5 (a), it is understood that the diameter of the light beam φ2 needs to be about 4.02 mm at the time of recording and reproduction of the DVD optical recording medium using the wavelength of 660 nm. Further, the relationship between the beam diameters φ1 and φ2 varies depending on the glass type of the objective lens. FIG. 5B is an objective lens having the same φ1, focal length, and NA as the objective lens in FIG. 5A. When the glass type is changed, φ2 / φ1 and the refractive index nd at the d-line of the used glass type. It is only necessary to select an appropriate φ2 according to the glass type of the objective lens.
[0059]
On the other hand, the optimum NA for recording and reproducing the CD optical recording medium is about 0.50, but when the optimum effective diameter φ3 is estimated by the same method as in FIG. 5A, φ3: 3. It can be seen that it may be about 2 mm.
[0060]
For example, as an aperture limiting element using a reflection characteristic that is a means for switching the light beam diameter according to the lighting light source in the first embodiment, as shown in FIG. 6A according to the wavelength of the light beam emitted from the light source. A means for switching the beam diameter by reflection may be used, and as the aperture limiting element utilizing the diffraction characteristics, the beam diameter is switched by diffraction as shown in FIG. 6B according to the wavelength of the beam emitted from the light source. Further, as the aperture limiting element using the absorption characteristic, a means for switching the light beam diameter by absorption as shown in FIG. 6C may be used according to the wavelength of the light beam emitted from the light source.
[0061]
Furthermore, in the first embodiment, light having a wavelength of 400 nm can be converted from linearly polarized light to circularly polarized light, or from circularly polarized light to linearly polarized light, and for light having a wavelength of 660 nm and wavelength 780 nm, linearly polarized light is converted to circularly polarized light or elliptically polarized light, or A wave plate capable of reverse conversion is provided. This wave plate can convert light having a wavelength of 400 nm, light having a wavelength of 660 nm, and light having a wavelength of 780 nm from linearly polarized light to circularly polarized light, or from circularly polarized light to linearly polarized light. The structure of the so-called wave plate is a crystal in which the phase difference between an ordinary ray (refractive index no) and an extraordinary ray (refractive index ne) is 1/4 of a wavelength of 400 nm, a wavelength of 660 nm, and a wavelength of 780 nm at a certain thickness t. A wave plate may be employed. That is, any crystal satisfying the following (Equation 3), (Equation 4), and (Equation 5) may be used.
[0062]
[Equation 3]
Δn1 × t = {(2p + 1) / 4} × 400 (p = 0, 1,...)
Δn1; (no-ne) for light from a light source having a wavelength of 400 nm
[0063]
[Expression 4]
Δn2 × t = {(2q + 1) / 4} × 660 (q = 0, 1,...)
Δn2; for light from a light source with a wavelength of 660 nm (no-ne)
[0064]
[Equation 5]
Δn3 × t = {(2r + 1) / 4} × 780 (r = 0, 1,...)
Δn3; (no-ne) for light from a light source having a wavelength of 780 nm
For example, when a non-polarizing hologram is used as the hologram 201b (see FIG. 1) arranged in the optical path of the DVD optical system, the optical path separation between the forward path and the return path cannot be sufficiently performed, About 30% of the return light returns to the light source. In general, such return light destabilizes the oscillation state of the semiconductor laser as a noise component.
[0065]
However, in the first embodiment, by arranging the wave plate having the above-described characteristics, for example, the light emitted from the hologram unit 201 of the DVD optical system in FIG. Can be orthogonalized. In this way, by making the polarization directions of the forward light and the backward light orthogonal to each other, it is possible to prevent the generation of noise due to the return light to the semiconductor laser 201a.
[0066]
Further, by arranging the wave plate having such characteristics, for example, a polarization separation optical system in which the polarization beam splitter 103 and the wave plate 106 are combined is realized for the blue optical recording medium of FIG. Therefore, it is possible to obtain a sufficient amount of light and to reduce the generation of noise due to the return light to the semiconductor laser 101. Similarly, with respect to the optical path of the DVD optical system, a polarization separation optical system can be realized by using a polarization selective hologram as the hologram.
[0067]
Specifically, the wavelength plate that converts both light having a wavelength of 400 nm and light having a wavelength of 660 nm from linearly polarized light to circularly polarized light, or circularly polarized light to linearly polarized light, and converting light having a wavelength of 780 nm to elliptically polarized light, What is necessary is just to satisfy the conditions of (Equation 3) and (Equation 4).
[0068]
Furthermore, the configuration of the wavelength plate that converts light having a wavelength of 400 nm from linearly polarized light to circularly polarized light or from circularly polarized light to linearly polarized light, and converts light having a wavelength of 660 nm and wavelength of 780 nm to elliptically polarized light is as follows: Should be satisfied.
[0069]
The wave plate is not limited to a crystal that satisfies (Equation 3), (Equation 4), and (Equation 5). For example, a configuration in which organic material retardation elements are stacked and sandwiched between glass plates may be used. Alternatively, an electro-optical element such as a liquid crystal element may be used.
[0070]
In FIG. 1, a “spherical aberration detecting unit” is configured by a combination of the beam splitting unit 111 and the light receiving element 112, and the liquid crystal element 106 corresponds to the “spherical aberration correcting unit”. As described above, when there is a thickness error of the optical recording medium, the shape of the light spot formed on the recording surface deteriorates. The aberration generated in this manner distorts the wavefront of the returning light beam, and aberration also occurs in the light beam that travels toward the light receiving element 112 via the detection lens 110. FIG. 7 shows this state.
[0071]
When spherical aberration occurs in the return light beam passing through the detection lens 110, there is a “wavefront delay” concentrically around the optical axis with respect to the reference wavefront of the return light beam, and the reference wavefront is condensed. The position where the wavefront delayed with respect to the condensing point is defocused. Therefore, by extracting the difference between the delayed wavefront and the advanced wavefront and detecting the focus state, it is possible to know the “occurrence state of the spherical aberration wavefront”.
[0072]
For example, as shown in FIG. 8, a hologram may be arranged as the light beam splitting means 111, and a light receiving element 112 having a light receiving area divided so that each divided light beam can be detected may be prepared. light bundle The dividing unit 111 sets a half area symmetrically divided in the jitter direction in the plane orthogonal to the optical axis as a hologram divided into two areas inside and outside concentrically. The light receiving element 112 is a two-divided light receiving element that detects each light beam diffracted by the hologram. Then, the amount of movement of the light spot image of the hologram diffracted light is detected, and the difference (Sa−Sb) and (Sc−Sd) generated by each light receiving element: W1 (Equation 6) corresponds to the spherical aberration signal. To do.
[0073]
[Formula 6]
W1 = (Sa−Sb−Sc + Sd)
W1 = 0 means no aberration.
[0074]
Further, the liquid crystal element 105 applies a predetermined voltage to the power feeding section 11 or the split electrode 15 as shown in FIGS. 4A and 4B, and the refractive index of the liquid crystal: n is concentric from n1 to n2. It is possible to change freely. When the refractive index: n is changed, the optical path difference: Δn · d (Δn is the refractive index change, d is the cell thickness of the liquid crystal), that is, the wavelength is λ, and the phase difference is Δn · d (2π / λ) can be given.
[0075]
It is assumed that the spherical aberration generated due to the detected substrate thickness error is, for example, as shown in FIG. The wavefront of this spherical aberration is shown as a two-dimensional curve in the solid lines in the upper part of FIGS. 10 (a) and 11 (a). When the electrode of FIG. 4A is used, a phase difference as shown by the broken line in the lower part of FIG. 10A is given to the light beam incident on the objective lens from the light source side against such spherical aberration. As described above, by adjusting the voltage applied to each concentric-band power supply unit 11 of the liquid crystal element, the “wavefront of spherical aberration” can be canceled by the delay of the wavefront at each part of the light beam passing through the liquid crystal element.
[0076]
In addition, when the split electrode of FIG. 4B is used, against such spherical aberration, the light beam incident on the objective lens from the light source side has a position as shown by the broken line in the lower part of FIG. When the voltage applied to each divided electrode of the liquid crystal element is adjusted so as to give a phase difference, the “spherical aberration wavefront” can be canceled by the delay of the wavefront at each part of the light beam transmitted through the liquid crystal element. FIG. 10B shows the sum of the solid line (spherical aberration wavefront) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 10A, that is, the corrected spherical aberration wavefront. It becomes much smaller than the wavefront of the original spherical aberration (solid line in the upper part of FIG. 10A). FIG. 11B shows the sum of the solid line (spherical aberration wavefront) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 11A, that is, the corrected spherical aberration wavefront. It becomes much smaller than the wavefront of the original spherical aberration (solid line in the upper part of FIG. 11A).
[0077]
In the first embodiment, recording and reproduction are also performed on a blue optical recording medium, a DVD optical recording medium, and a CD optical recording medium, so that the blue optical recording medium, the DVD optical recording medium, and the CD optical light are recorded. As a means for discriminating the recording medium, a method used in a so-called DVD / CD two-generation compatible information recording / reproducing apparatus (called a combo drive or the like) may be used. That is, a configuration in which, for example, a determination is made based on a return light amount level when a focus search is performed by turning on one of the blue and red light sources when an optical recording medium is inserted.
[0078]
As described above, when a light beam from this light source is incident on the objective lens during recording / reproduction of a DVD, spherical aberration due to a difference in wavelength or substrate thickness occurs, and the shape of the light spot formed on the recording surface is to degrade. A reverse-polarity spherical aberration amount that cancels the generated spherical aberration is stored in advance for each optical recording medium, and this reverse-polarity spherical aberration is determined according to the type of optical recording medium detected by the optical recording medium discriminating means. Should be given.
[0079]
Now, in the optical pickup shown in FIG. 1, light having a wavelength of 660 nm is incident in an infinite system on a single objective lens 108 having a wavelength of 400 nm that minimizes the wavefront of spherical aberration, and is spot-formed on a DVD-based optical recording medium 109b. Or when a light beam having a wavelength of 780 nm is incident in an infinite system to form a spot on the CD-type optical recording medium 109c, as shown in FIGS. 12 and 13, spherical aberration due to a difference in wavelength or a difference in substrate thickness Will occur.
[0080]
The liquid crystal element 105 shown in FIG. 1 is provided in order to generate spherical aberration having the opposite polarity to the spherical aberration that occurs as shown in FIGS. Further, as shown in FIG. 14, a spherical aberration having a polarity opposite to that of the spherical aberration generated during recording / reproduction of the two-layer optical recording medium is also generated as the blue optical recording medium 109a.
[0081]
Therefore, in order to give the following spherical aberration and the opposite spherical aberration,
(1) Spherical aberration caused by the difference in wavelength used when compatible with DVD
(2) Spherical aberration that occurs due to differences in operating wavelength and substrate thickness when compatible with CD
(3) Spherical aberration that occurs due to the difference in interlayer distance between two-layer optical recording media as blue optical recording media
In each of the above, the optical recording medium can be discriminated by the same method as described above. Then, it is stored in advance so as to give a predetermined phase shape (additional phase amount at each pupil radius position) according to the optical recording medium discrimination signal of this optical recording medium. Further, in a two-layer blue optical recording medium, a predetermined phase shape is given according to the information layer position to be recorded / reproduced.
[0082]
The electrode configuration of the liquid crystal element for correcting the two different spherical aberrations may be as shown in FIG. That is, a pair of continuous transparent electrodes 10a and 10b is formed, and metal electrodes 12a to 14a and 12b to 14b are formed on the transparent electrodes 10a and 10b, respectively. The metal electrodes are each connected to an external signal source by metal wiring, and can each supply an arbitrary voltage by an external signal. In the first embodiment, the spherical aberration that occurs when attempting to record / reproduce the DVD color optical recording medium (and the second layer in the case of a two-layer blue optical recording medium) as the metal electrode 13a is maximum. Is formed at the pupil radius position where the spherical aberration that occurs when recording and reproduction of the CD optical recording medium as the metal electrode 13b is maximized.
[0083]
Specifically, when the objective lens whose outline data is shown in FIG. 17 and whose shape data is shown in (Table 1) is used, the incident beam diameter of the objective lens in each of the blue, DVD, and CD optical paths is φ: 3.9 mm, φ : 4.02 mm, φ: 3.2 mm, and the light beam passage diameter of the liquid crystal element is manufactured at φ: 4.02 mm which is substantially the same as the DVD optical path (actually a margin of 0.1 to 0.2 mm) ). At this time, the pupil radius position of the metal electrode 13a may be 1.2 mm to 1.6 mm, and the pupil radius position of the metal electrode 13b may be 1.0 mm to 1.2 mm (corresponding to FIGS. 12, 13, and 14). .
[0084]
[Table 1]

[0085]
In the first embodiment, three types of spherical aberration, that is,
(1) Spherical aberration caused by the difference in wavelength used when compatible with DVD
(2) Spherical aberration that occurs due to differences in operating wavelength and substrate thickness when compatible with CD
(3) Spherical aberration that occurs due to the difference in interlayer distance between two-layer optical recording media as blue optical recording media
12 and 14, as is clear from FIGS. 12 and 14, the positions where the spherical aberration becomes maximum in (1) and (3) are substantially the same. Patterns 13a and 13b may be used (see FIG. 15). This is because the blue optical path is configured with the same NA and substrate thickness as the DVD system.
[0086]
For the liquid crystal element having such an electrode pattern, for example, when the optical recording medium discriminating means as described above recognizes that the DVD optical recording medium is inserted, the additional phase amount becomes maximum. When an applied voltage stored in advance so that the position is the metal electrode 13a is applied to each electrode, and it is recognized that the CD optical recording medium is inserted, the position where the additional phase amount is maximized is the metal electrode 13b. An applied voltage stored in advance is applied to each electrode. Also, when it is recognized that the recording medium is a blue optical recording medium, the liquid crystal element does not act at the time of recording / reproduction of the first layer in the case of the two-layer blue optical recording medium, and the focus jumps to the second layer. When recording / reproduction is started, an applied voltage stored in advance is applied to each electrode so that the position where the additional phase amount is maximum is the metal electrode 13a.
[0087]
The electrode configuration of the liquid crystal element is not limited to FIG. A metal electrode 22 to 25 is formed on one continuous transparent electrode 20 (a pair of the transparent electrodes 10a and 10b in FIG. 15) as shown in FIG. When a DVD optical recording medium is configured as an optical path and a DVD optical recording medium is formed as a metal electrode 23 at a pupil radius position where the additional phase amount is maximized during recording and reproduction, and a CD optical recording medium is recorded and reproduced as the metal electrode 24 You may form in the pupil radius position where the generated spherical aberration becomes the maximum.
[0088]
Further, a divided electrode region 26 is formed as a divided electrode from the outer edge portion to the central portion on the transparent electrode 20 (a pair of the transparent electrodes 10a and 10b in FIG. 15) as shown in FIG. 26, divided electrode regions 27 and 28 are formed on the inner periphery (1 <divided electrode region 28 <divided electrode region 27 <divided electrode region 26). The divided electrode region 27 is formed in the second layer of the two-layer blue optical recording medium, or at the pupil radius position where the spherical aberration that occurs when recording or reproducing the DVD color optical recording medium is maximized. The region 28 may be formed at a pupil radius position where the spherical aberration that occurs when recording / reproduction of the CD optical recording medium is to be maximized.
[0089]
Further, in the first embodiment, as shown in FIG. 19A, an aperture limiting element 107, a liquid crystal element 105, and a wave plate 106 may be integrally formed as a composite element. Thereby, the assembly process can be simplified. Further, another composite element configuration as shown in FIG. 19B, that is, the liquid crystal element 105 and the wave plate 106 are integrally formed in this order, and the aperture limiting element 107 is formed on the liquid crystal element surface or the wave plate surface. Also good. In this way, it is possible to make the device thinner and reduce the weight, such as unification of components and mounting on an actuator.
[0090]
Further, in the optical pickup of the first embodiment, as another electrode pattern of the liquid crystal element, for example, a plurality of power feeding portions are provided so that the spherical aberration becomes maximum at different pupil radius positions as shown in FIG. On the other hand, even if the electrode is configured so that the peak position always occurs at the substantially central position (arrow C in FIG. 20) of spherical aberration occurring at different peak positions as shown in FIGS. Good. A configuration in which a predetermined phase amount is added according to the optical recording medium discrimination signal and the spherical aberration signal, and a predetermined phase amount according to the switching of the first recording layer / second recording layer by the optical recording medium discrimination signal. May be added. With this configuration, the electrode pattern can be simplified.
[0091]
In addition, making the DVD optical path a finite system means that the light beam incident on the objective lens is diverged or converged. In general, changing the divergence state of the light beam incident on the objective lens is equivalent to changing the spherical aberration. Therefore, a divergence state that can reduce the spherical aberration may be selected. The spherical aberration of the DVD optical path can be suppressed by such a finite system technique (see FIG. 35). In the first embodiment, when the DVD optical path is configured by a finite system, the substrate thickness error of the blue optical recording medium The electrode pattern of the liquid crystal element may be configured so as to suppress only the spherical aberration that occurs along with this, and the phase addition region of the liquid crystal element has a DVD-based NA of the outer peripheral portion: 0.65 to a NA of CD-based NA: 0. Specialize in the range of .50. Then, in order to perform aberration correction using the phase correction effect of the liquid crystal element in the CD system optical path, an aberration correction region was formed in a range of CD system NA: 0.50 or less.
[0092]
Next, FIG. 21 shows an optical pickup having another configuration according to the second embodiment. As in the configuration of the optical pickup described in the first embodiment, “use wavelength 400 nm, NA 0.65, light irradiation side substrate”. “Blue-based (large capacity) optical recording medium having a thickness of 0.6 mm”, “DVD-based optical recording medium having a used wavelength of 660 nm, NA of 0.65, and light irradiation side substrate thickness of 0.6 mm”, and “Used wavelength of 780 nm, NA of 0.8. 50 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, or erasing “50, CD-based optical recording medium having a light irradiation side substrate thickness of 1.2 mm”. The difference from the first embodiment is that a blue light path uses a hologram unit 401 in which a light source, a light receiving element, and an optical path separating means are housed in a single package. As a result, the optical system can be miniaturized and the assembly can be simplified.
[0093]
Similarly, FIG. 22A is a diagram showing a schematic configuration of another optical pickup according to the first embodiment. Similar to the optical pickup of the first embodiment described above, “a blue (large capacity) optical recording medium having a used wavelength of 400 nm, NA of 0.65, and a light irradiation side substrate thickness of 0.6 mm” and “used wavelength of 660 nm, NA of 0.66, Light capable of recording, reproducing, or erasing both a DVD-type optical recording medium having a light irradiation side substrate thickness of 0.6 mm and a “CD type optical recording medium having a working wavelength of 780 nm, NA of 0.50, and a light irradiation side substrate thickness of 1.2 mm”. Pick up. The difference from the first embodiment is that the DVD / CD light source, light receiving element, and optical path separating means are integrated into a single package. As a result, the three-wavelength optical system is realized with a small optical pickup. As the hologram 301b, as shown in FIG. 22B, a configuration having a layer having a DVD hologram surface and a layer having a CD hologram surface may be used.
[0094]
Further, as a second embodiment of the present invention, the configuration of an optical pickup described below may be adopted. The difference between the configuration of the optical pickup of the second embodiment and the optical pickup described in the first embodiment is that the optical path of the optical pickup is configured as a finite system in the CD optical path. By using a finite system in the CD optical path, the wavefront aberration can be sufficiently suppressed. For this reason, since the spherical aberration of the CD optical path can be suppressed, the liquid crystal element does not need to act on the optical path. That is, the electrode pattern for the CD optical path formed in the liquid crystal element can be reduced with respect to the configuration of the first embodiment.
[0095]
Further, as a third embodiment of the present invention, in the liquid crystal element used in each of the above-described embodiments, a pattern capable of optimal aberration correction when the central axis of the objective lens coincides with the optical axis. Designed. Therefore, when a deviation occurs in which the objective lens moves in the radial direction (radial direction of the optical recording medium) due to the tracking servo of the optical recording medium, the difference between the aberration distribution requiring correction and the correction pattern formed on the liquid crystal element is generated. Misalignment occurs, and the aberration correction function deteriorates. This will be briefly described with reference to FIGS. 23 (a), (b), and (c). When the wavefront of spherical aberration that occurs when DVD or CD is compatible is the upper part of FIG. 23 (a), the light beam incident on the objective lens from the light source side is shown in the lower part of FIG. 23 (a). As described above, it is possible to cancel the wavefront of the unnecessary aberration by giving a phase difference. Here, when a displacement occurs between the liquid crystal element and the objective lens as shown in FIG. 23B, an unnecessary wavefront of aberration as shown in FIG. 23C is generated.
[0096]
In order to improve the aberration correction function deterioration based on the objective lens shift, there is a method in which a liquid crystal element is mounted on a movable part (actuator) and is driven integrally with the objective lens. However, it is desirable that the liquid crystal element configured as described above be installed outside the objective lens actuator from the viewpoint of an increase in weight and an increase in the number of signal lead lines.
[0097]
Here, paying attention to the unnecessary aberration shape shown in FIG. 23 (c), it can be seen that the shape shows a cubic function shape that is antisymmetric to the optical axis. This shape shows the shape equivalent to the coma aberration demonstrated in the nonpatent literature 3, for example. In the third embodiment, the electrode pattern of the liquid crystal element is devised as a coma aberration correcting means as described later, thereby making it possible to correct unnecessary aberrations that occur during DVD and CD compatibility.
[0098]
As described above, the relative displacement between the liquid crystal element that corrects the wavefront shape symmetrically to the optical axis and the objective lens generates unnecessary coma. The third embodiment can detect such an unnecessary coma aberration by including a coma aberration detection optical system mainly including a detection lens 110 and a light receiving element 112 (see FIG. 1).
[0099]
Guide grooves are formed in the optical recording medium 109 as shown in FIG. The reflected light from the guide groove includes 0th-order light that is directly reflected light and diffracted ± 1st-order diffracted light, and these lights interfere with each other. FIG. 24B is a view of the 0th-order light (straight-ahead light) and ± 1st-order diffracted light received by the light-receiving surface of the light-receiving unit as viewed from above the light-receiving surface of the light-receiving element 112. The zero-order light (straight-ahead light) and the ± first-order diffracted light have overlapping portions, and this overlapping portion is called an interference region.
[0100]
How this interference region changes with coma will be described with reference to FIG. FIG. 25 shows how the interference region changes as the objective lens 108 shifts and moves with respect to the liquid crystal element that suppresses spherical aberration. As the objective lens 108 is shifted, the light quantity is biased on the left and right sides of the figure. This is because coma aberration occurs in the spot projected on the optical recording medium 109 due to the relative positional deviation between the objective lens 108 and the liquid crystal element 105. This deviation occurs in the opposite direction between one interference region and the other interference region. In FIG. 25, it can be seen that the area on the right side of the figure becomes stronger and the area on the left side gradually becomes weaker as the positional deviation increases.
[0101]
In the third embodiment, the coma aberration is detected by the light receiving element 112 divided into six regions as shown in FIG. That is, the light receiving surface of the light receiving element 112 has two regions in the radial direction (radial direction) of the optical recording medium 109, and these two regions are divided into three parts in the rotational direction (tangential direction) of the optical recording medium 109. Yes. Three regions included in one of the two regions in the radial direction (radial direction) of the optical recording medium 109 are referred to as a region 112a, b region 112b, and c region 110c in the order of the rotation direction. The light amount signals output from the a region 112a, b region 112b, and c region 112c are A, B, and C, respectively. Of the two regions in the radial direction of the optical recording medium 109, three regions included in the other region are referred to as a d region 112d, an e region 112e, and an f region 112f. The light amount signals output from the d region 112d, the e region 112e, and the f region 112f are D, E, and F, respectively. The computing means 113 is composed of an adding means and a subtracting means.
[0102]
The light quantity signal output from each area of the light receiving element 112 is input to the calculation means 113, and a predetermined calculation is performed. The calculation result is a signal indicating the coma aberration in the radial direction (radial direction) of the optical recording medium: COMA is output from the calculation means 113. When the calculation by the calculation means 113 is expressed by an equation, (Expression 7) is obtained.
[0103]
[Expression 7]
COMA = (A + C + E) − (B + D + F)
FIG. 27 shows the result of calculating the change in the interference area due to the relative positional deviation between the objective lens 108 and the liquid crystal element 105 using the calculating means 113 of (Equation 7). In FIG. 27, the horizontal axis represents the relative positional deviation amount between the objective lens 108 and the liquid crystal element 105, and the vertical axis represents the coma aberration signal normalized by the sum signal of the output signals A to F.
[0104]
In the third embodiment, instead of the method of detecting the coma aberration and driving the liquid crystal element 105, the relative displacement between the objective lens 108 or the objective lens actuator and the liquid crystal element 105 is directly detected, and the liquid crystal element 105 is detected. The element 105 may be controlled. To detect the amount of displacement, a well-known PSD (Position Sensor Device) may be placed on the pickup fixing optical system to detect the distance between the objective lens and the PSD. The detected positional deviation amount is converted into a coma aberration amount based on a previously stored table (not shown). The liquid crystal element 105 is driven and controlled according to the coma aberration amount.
[0105]
As shown in FIG. 28, the coma aberration correcting means is arranged to face the DVD / CD compatible pattern (see FIGS. 4A and 4B) of the liquid crystal element 105 having a predetermined electrode pattern. In the liquid crystal element 105, as shown in FIG. 28, at least one of the transparent electrodes is divided symmetrically so that a voltage can be applied independently to each electrode portion (between the common electrode), By controlling the voltage, the refractive index n of the liquid crystal in each electrode portion can be freely changed from n1 to n2. When the refractive index: n is changed, the optical path difference: Δn · d (Δn is the refractive index change, d is the cell thickness of the liquid crystal), that is, the wavelength is λ, and the phase difference Δn · d (2π / λ) can be given.
[0106]
For example, assume that coma aberration as shown in FIG. 29 occurs. This wavefront aberration is shown as a three-dimensional curve in the upper part of FIG. The liquid crystal element 105 shown in FIG. 28 is provided so that the phase difference shown in the lower part of FIG. 30A is given to the light beam incident on the objective lens 108 from the light source side with respect to the wavefront of such coma aberration. By adjusting the voltage applied to each of the electrodes, the “aberration wavefront” can be canceled out by the delay of the wavefront at each part of the light beam passing through the liquid crystal element 105. FIG. 30B shows the sum of the solid line (coma aberration wavefront) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 30A, that is, the corrected wavefront. It is much smaller than the original wavefront (the solid line portion in FIG. 30A).
[0107]
In particular, such a coma aberration correcting electrode surface may be formed on the counter electrode surface of the liquid crystal element having the spherical aberration correcting electrode pattern only on one side as shown in FIGS.
[0108]
FIG. 31 is a transparent perspective view showing a schematic configuration of an information recording / reproducing apparatus which is an optical information processing apparatus in Embodiment 4 of the present invention.
[0109]
The information recording / reproducing apparatus 30 is an apparatus that performs at least one of information recording, reproduction, and erasing with respect to the optical recording medium 40 using the optical pickup 31. This embodiment 4 The optical recording medium 40 has a disk shape and is stored in a cartridge 41 of a protective case. The optical recording medium 40, together with the cartridge 41, is inserted and set from the insertion port 32 into the information recording / reproducing apparatus 30 in the arrow “disc insertion” direction, is driven to rotate by the spindle motor 33, and information is recorded, reproduced or erased by the optical pickup 31. Is done.
[0110]
As the optical pickup 31, the optical pickup described in the first to third embodiments can be used as appropriate.
[0111]
This embodiment 4 May be an optical information processing apparatus that performs multi-level recording with an information recording density multiplication factor P1> 1.8 on an optical recording medium at a use wavelength λ: 400 nm and NA: 0.65. Thereby, for example, an optical information processing apparatus of 22 GB or more can be realized without using a high NA objective lens with NA 0.85. That is, the recording capacity to the optical recording medium is determined by the spot diameter. Compared to DVD optical recording medium (4.7 GB), if the blue wavelength band is used, the spot diameter ratio (λ / NA) ² The capacity is increased by 12GB. By applying the multi-value recording of the above condition to this, 22 GB equivalent can be obtained. As a result, it is possible to expand the margin associated with fluctuations. Since the focal depth of the objective lens becomes stricter in proportion to the square of NA, the NA 0.65 lens has a 1.7 times wider margin than the NA 0.85 objective lens.
[0112]
In each of the above-described embodiments, for simplicity, the wavelengths have been described as being limited to 400 nm, 660 nm, and 780 nm. However, the present invention is applied to the ranges defined as standards by the following optical recording media. It is possible.
[0113]
Blue wavelength band: wavelength 397nm to 417nm
・ Red wavelength band: Wavelength 650nm-670nm
Infrared wavelength band: wavelength 770 nm to 790 nm
Similarly, each NA (numerical aperture) has been limited to 0.65 and 0.50.
-NA of blue optical recording medium: 0.60 to 0.70
-NA of DVD optical recording medium: 0.60 to 0.65
-NA of CD optical recording medium: 0.45 to 0.50
Applicable to a range of
[0114]
【The invention's effect】
As described above, according to the present invention, spherical aberration generated when recording / reproducing is performed on a DVD / CD optical recording medium by a blue objective lens, and variation in substrate thickness of the blue optical recording medium. In order to suppress the spherical aberration caused by the interlayer distance of the multilayer blue optical recording medium with one liquid crystal element, information on a large capacity blue optical recording medium and conventional DVD and CD optical recording media A good spot can be formed on the recording surface, and the signal can be recorded and reproduced with high S / N on any of the three generation optical recording media without increasing the number of parts.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an optical pickup according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a hologram unit formed by integrating a semiconductor laser, a hologram, and a light receiving element.
FIG. 3 is a cross-sectional view showing a schematic configuration of a liquid crystal element in the optical pickup according to the first embodiment.
FIGS. 4A and 4B are diagrams showing examples of electrode patterns of a liquid crystal element.
FIG. 5A shows the relationship between the effective diameter and wavelength of the objective lens with NA of 0.65, and FIG. 5B shows the result when the glass type is changed at the same φ1, focal length, and NA as the objective lens of FIG. Diagram showing the relationship between φ2 / φ1 and the refractive index nd at the d-line of the glass used
6A and 6B are diagrams showing the configuration of an aperture limiting element that switches the beam diameter using optical characteristics of (a) reflection, (b) diffraction, and (c) absorption in the first embodiment.
FIG. 7 is a diagram illustrating spherical aberration generated in a light beam traveling toward a light receiving element through a detection lens.
FIG. 8 is a diagram showing a light receiving element divided in a light receiving region for detecting each light beam divided by the light beam dividing means;
FIG. 9 is a diagram illustrating spherical aberration caused by a detected substrate thickness error
10A is a diagram showing a spherical aberration wavefront (solid line) and a wavefront delay due to a liquid crystal element (broken line), and FIG. 10B is a diagram showing a corrected spherical aberration wavefront as a two-dimensional curve.
11A is a diagram showing a spherical aberration wavefront (solid line) and a wavefront delay due to a liquid crystal element (broken line), and FIG. 11B is a diagram showing a corrected spherical aberration wavefront as a two-dimensional curve.
FIG. 12 is generated when a light beam having a wavelength of 660 nm is incident on an infinite system on a single objective lens having a wavelength of 400 nm and NA of 0.66 to minimize the wavefront of spherical aberration to form a spot on a DVD optical recording medium. Diagram showing spherical aberration
FIG. 13 is a diagram showing a case where light having a wavelength of 780 nm is incident on a single objective lens having a wavelength of 400 nm and NA of 0.65 to minimize the wavefront of spherical aberration and is spot-formed on a CD optical recording medium. Diagram showing spherical aberration
FIG. 14 is a diagram showing spherical aberration occurring at the time of recording / reproducing on the second information recording layer of the blue optical recording medium.
FIG. 15 is a diagram showing a metal electrode configuration of two transparent electrodes of a liquid crystal element for correcting spherical aberration in the first embodiment.
FIG. 16 is a diagram showing a metal electrode configuration in one transparent electrode of a liquid crystal element for correcting spherical aberration in the first embodiment.
FIG. 17 is a diagram showing an overview of the objective lens according to the first embodiment.
18 is a diagram showing a divided electrode configuration in a transparent electrode of a liquid crystal element for correcting spherical aberration in the first embodiment. FIG.
19A is a composite element in which an aperture limiting element, a liquid crystal element, and a wave plate are integrally formed, and FIG. 19B is a diagram showing the configuration of another composite element.
FIG. 20 is a diagram illustrating an electrode configuration in which a peak position is generated at a substantially central position of spherical aberration occurring at different peak positions as an electrode pattern of the liquid crystal element according to the first embodiment.
FIG. 21 is a diagram showing a schematic configuration of an optical pickup having another configuration according to Embodiment 2 of the present invention;
22A is a schematic configuration of an optical pickup having another configuration according to Embodiment 1 of the present invention, and FIG. 22B is a layer having a hologram surface for DVD and a layer having a hologram surface for CD. Showing a hologram configuration with
23A shows a generated spherical aberration (upper side) and a phase difference to be added thereto (lower side), FIG. 23B shows a state in which the phase difference added by the objective lens shift is shifted, and FIG. 23C shows an objective lens. The figure which shows the aberration (residual aberration) of the wave front which is unnecessary due to the shift
FIG. 24A is the 0th-order light reflected directly from the guide groove of the optical recording medium and interference with the diffracted ± 1st-order diffracted light, and FIG. 24B is the 0th-order light viewed from the light receiving surface of the light receiving means. The figure which shows the interference area | region of (straight-ahead light) and 1st-order diffracted light
FIG. 25 is a diagram showing an interference region that changes due to an objective lens shift with respect to a liquid crystal element;
FIG. 26 is a diagram showing a schematic configuration for detecting the generated coma aberration by the light receiving element and the calculation means.
FIG. 27 is a diagram illustrating a result of calculation performed by a calculation unit for a change in an interference area caused by a relative positional shift between the objective lens and the liquid crystal element.
FIG. 28 is a diagram showing an electrode pattern of a liquid crystal element.
FIG. 29 is a diagram showing coma aberration generated due to the objective lens shift.
30A shows a wavefront (solid line) of coma aberration and a phase difference (dashed line) to be applied, and FIG. 30B shows a wavefront after correction.
FIG. 31 is a transparent perspective view showing a schematic configuration of an information recording / reproducing apparatus which is an optical information processing apparatus in Embodiment 4 of the present invention.
FIG. 32 is a diagram showing a schematic configuration of an optical pickup capable of being compatible with a large-capacity optical recording medium using a blue wavelength band light source and an existing DVD or CD.
FIG. 33 is a diagram showing a wavefront of spherical aberration when focused on an infinite system incident on a DVD-based optical recording medium having a wavelength of 660 nm.
FIG. 34 is a diagram showing a wavefront of spherical aberration when focused on an infinite system incident on a CD optical recording medium having a wavelength of 780 nm.
FIG. 35 is a diagram showing the wavefront of spherical aberration when focused on a DVD optical recording medium with a wavelength of 660 nm with a finite incidence.
[Explanation of symbols]
1a, 1b glass substrate
2 Conductive spacer
3 LCD
4a, 4b electrode
5 Insulating film
6 Alignment film
7 Electrode extraction part
10, 10a, 10b, 20 Transparent electrode
11 Feeder
12a, 12b, 13a, 13b, 14a, 14b, 22, 23, 24, 25 Metal electrode
15 Split electrode
26, 27, 28 Split electrode area
30 Information recording / reproducing apparatus
31 Optical pickup
32 insertion slot
33 Spindle motor
40 Optical recording media
21 cartridge
100 Blue light source
101, 201a, 301a Semiconductor laser
102 Collimating lens
103 Polarizing beam splitter
104 prism
105 Liquid crystal element
106 Wave plate
107 aperture limiting element
108 Objective lens
109a, 109b, 109c optical recording medium
110 detection lens
111 Beam splitting means
112, 201c, 301c light receiving element
112a-112f, af region
113 Calculation means
200 Light source for DVD
201, 301 Hologram unit
201b, 301b hologram
202, 302, 502 coupling lens
203, 303 Dichroic prism
300 CD light source

Claims (14)

An optical pickup that performs one or more of information recording, reproduction, and erasing with respect to an optical recording medium, and includes three light sources that emit light having wavelengths λ1, λ2, and λ3 (λ1 ≦ λ2 ≦ λ3) An objective lens for condensing the light emitted from the light source on the optical recording medium, aperture limiting means for switching numerical apertures: NA1, NA2 and NA3 (NA1 ≧ NA2 ≧ NA3), and passing light flux by applying voltage. A liquid crystal element that changes the phase distribution,
Wavelength: λ1, λ2, λ3, numerical aperture: NA1, NA2, NA3
397 nm ≦ λ1 ≦ 417 nm,
650 nm ≦ λ2 ≦ 670 nm,
770 nm ≦ λ3 ≦ 790 nm,
0.60 ≦ NA1 ≦ 0.70,
0.60 ≦ NA2 ≦ 0.65,
0.45 ≦ NA3 ≦ 0.50,
And
When using light of wavelength λ1, the numerical aperture is NA1, when using light of wavelength: λ2, the numerical aperture is NA2, and when using light of wavelength: λ3, the numerical aperture is NA3.
The optical recording medium for wavelength: λ1 and numerical aperture: NA1 is a two-layer optical recording medium having two information recording surfaces,
When the liquid crystal element gives a concentric phase change at the center of the optical axis of the passing light beam and uses light of wavelength: λ1 or wavelength: λ2, the phase change of the concentric pupil radius position r2 is maximized, and the wavelength: When the light of λ3 is used, the phase change of the concentric pupil radius position r3 is maximized , the pupil radius position r2 and the pupil radius position r3 are on different electrode surfaces of the counter electrode , and the pupil radius position r2 is substantially the same. An optical pickup characterized in that the pupil radius position r3 is formed in a region substantially within the numerical aperture: NA3 in a numerical aperture: NA2-NA3 region. An optical pickup that performs one or more of information recording, reproduction, and erasing with respect to an optical recording medium, and includes three light sources that emit light having wavelengths λ1, λ2, and λ3 (λ1 ≦ λ2 ≦ λ3) An objective lens for condensing the light emitted from the light source on the optical recording medium, aperture limiting means for switching numerical apertures: NA1, NA2 and NA3 (NA1 ≧ NA2 ≧ NA3), and passing light flux by applying voltage. A liquid crystal element that changes the phase distribution,
Wavelength: λ1, λ2, λ3, numerical aperture: NA1, NA2, NA3
397 nm ≦ λ1 ≦ 417 nm,
650 nm ≦ λ2 ≦ 670 nm,
770 nm ≦ λ3 ≦ 790 nm,
0.60 ≦ NA1 ≦ 0.70,
0.60 ≦ NA2 ≦ 0.65,
0.45 ≦ NA3 ≦ 0.50,
And
When using light of wavelength λ1, the numerical aperture is NA1, when using light of wavelength: λ2, the numerical aperture is NA2, and when using light of wavelength: λ3, the numerical aperture is NA3.
The optical recording medium for wavelength: λ1 and numerical aperture: NA1 is a two-layer optical recording medium having two information recording surfaces,
When the liquid crystal element gives a concentric phase change at the center of the optical axis of the passing light beam and uses light of wavelength: λ1 or wavelength: λ2, the phase change of the concentric pupil radius position r2 is maximized, and the wavelength: When the light of λ3 is used, the phase change of the concentric pupil radius position r3 is maximized, and the pupil radius position r2 and the pupil radius position r3 are on the same electrode surface of the counter electrode , and the pupil radius position r2 Is formed in a region of substantially numerical aperture: NA2 to NA3, and the pupil radial position r3 is formed in a region of substantially numerical aperture: NA3 or less.   3. The objective lens according to claim 1, wherein the objective lens is used in a finite system when the light source of the wavelength: [lambda] 2 among the wavelengths of the three light sources: [lambda] 1, [lambda] 2, [lambda] 3 ([lambda] 1≤ [lambda] 2≤ [lambda] 3). Optical pickup. An optical pickup that performs one or more of information recording, reproduction, and erasing with respect to an optical recording medium, and includes three light sources that emit light having wavelengths λ1, λ2, and λ3 (λ1 ≦ λ2 ≦ λ3) An objective lens for condensing the light emitted from the light source on the optical recording medium, aperture limiting means for switching numerical apertures: NA1, NA2 and NA3 (NA1 ≧ NA2 ≧ NA3), and passing light flux by applying voltage. A liquid crystal element that changes the phase distribution,
Wavelength: λ1, λ2, λ3, numerical aperture: NA1, NA2, NA3
397 nm ≦ λ1 ≦ 417 nm,
650 nm ≦ λ2 ≦ 670 nm,
770 nm ≦ λ3 ≦ 790 nm,
0.60 ≦ NA1 ≦ 0.70,
0.60 ≦ NA2 ≦ 0.65,
0.45 ≦ NA3 ≦ 0.50,
And
When using light of wavelength λ1, the numerical aperture is NA1, when using light of wavelength: λ2, the numerical aperture is NA2, and when using light of wavelength: λ3, the numerical aperture is NA3.
The optical recording medium for wavelength: λ1 and numerical aperture: NA1 is a two-layer optical recording medium having two information recording surfaces,
When the liquid crystal element gives a concentric phase change at the center of the optical axis of the passing light beam and uses light of wavelength: λ1 or wavelength: λ2, the phase change of the concentric pupil radius position r2 is maximized, and the wavelength: An optical pickup characterized in that when the light of λ3 is used, the phase change of the concentric pupil radius position r3 is maximized, and the pupil radius position r2 is formed in a region of approximately numerical apertures NA2 to NA3.   The objective lens is used in a finite system when the light sources having wavelengths of λ2 and λ3 among the wavelengths of the three light sources: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3) are turned on. 4. The optical pickup according to 4.   An optical recording medium discriminating unit for discriminating the optical recording medium, and switching an additional phase amount of the liquid crystal element and a pupil radius position at which the additional phase amount is maximum according to a signal from the optical recording medium discriminating unit; The optical pickup according to claim 1, wherein the optical pickup is characterized in that:   2. A spherical aberration detector for detecting a spherical aberration generated on the optical recording medium, wherein an additional phase amount of the liquid crystal element is changed in accordance with a signal from the spherical aberration detector. 6. The optical pickup according to any one of 6 above.   5. The optical pickup according to claim 2, wherein in the liquid crystal element, the counter electrode surface of the concentric phase addition surface is made of a transparent electrode divided symmetrically.   9. The optical pickup according to claim 8, further comprising means for generating a coma aberration signal from an interference pattern of reflected light from the optical recording medium, and controlling an additional phase amount of the liquid crystal element based on the coma aberration signal. .   A means for detecting a displacement amount of the liquid crystal element from a substantially optical axis center of the objective lens is provided, and an additional phase amount of the liquid crystal element is controlled based on the detected signal of the displacement amount. 8. The optical pickup according to 8. The aperture limiting means for switching the numerical aperture of the light emitted from the light source according to the wavelength used by the light source is provided, and the aperture limiting means is integrated with the liquid crystal element. The optical pickup according to claim 1. 12. The polarizing element according to claim 1, further comprising a polarizing element that changes a polarization state of light emitted from the light source according to a wavelength used by the light source, and the polarizing element is integrated with a liquid crystal element. 1. An optical pickup according to item 1. The optical pickup according to claim 1 , wherein the liquid crystal element is movable integrally with an objective lens . An optical information processing apparatus that performs at least one of recording, reproduction, and erasing of information on an optical recording medium using the optical pickup according to claim 1 .

Images