JP2004127473A - Optical pickup and optical information processing apparatus using the same - Google Patents

Optical pickup and optical information processing apparatus using the same Download PDF

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JP2004127473A
JP2004127473A JP2003003525A JP2003003525A JP2004127473A JP 2004127473 A JP2004127473 A JP 2004127473A JP 2003003525 A JP2003003525 A JP 2003003525A JP 2003003525 A JP2003003525 A JP 2003003525A JP 2004127473 A JP2004127473 A JP 2004127473A
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recording medium
liquid crystal
light
optical
optical recording
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JP4278989B2 (en
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Hideaki Hirai
平井　秀明
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Ricoh Co Ltd
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Ricoh Co Ltd
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Priority to DE60321414T priority patent/DE60321414D1/en
Priority to EP08006364A priority patent/EP1965380B1/en
Priority to DE60330817T priority patent/DE60330817D1/en
Priority to EP03251102A priority patent/EP1341166B1/en
Priority to US10/372,916 priority patent/US7142497B2/en
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Priority to US11/580,019 priority patent/US7848209B2/en
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Abstract

<P>PROBLEM TO BE SOLVED: To form a favorable spot on an information recording plane of a blue system optical recording medium, a DVD system optical recording medium, or a CD system optical recording medium without increasing the number of parts. <P>SOLUTION: A liquid crystal element for correcting spherical aberration is constituted by forming metallic electrodes 12a-14a, 12b-14b on transparent electrodes 10a, 10b with a pair of continuous transparent electrodes 10a, 10b as a unit. A metallic electrode 13a is formed at a pupil radius position where the spherical aberration generated when recording and reproducing the DVD system optical recording medium is a maximum, and a metallic electrode 13b is formed at a pupil radius position where the spherical aberration generated when recording and reproducing the CD system optical recording medium is a maximum. Voltage is applied to the metallic electrode 13a at the position where an additive phase amount is maximized in recognizing the insertion of the DVD system optical recording medium of an optical recording medium discrimination means to the liquid crystal element, and voltage is applied to the metallic electrode 13b at the position where an additive phase amount is maximized in recognizing the CD system optical recording medium. Moreover, in the recognition of insertion of a blue optical recording medium, the liquid crystal element does not play any role at all. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、光源からの通過光束に印加電圧に応じて位相変化を与える液晶素子を備えた光ピックアップ及びこれを用いる光情報処理装置に関するものである。
【０００２】
【従来の技術】
映像情報、音声情報、またはコンピュータ上のデータを保存する手段として、記録容量０．６５ＧＢのＣＤ、記録容量４．７ＧＢのＤＶＤなどの光記録媒体が普及しつつある。そして、近年、さらなる記録密度の向上及び大容量化の要求が強くなっている。
【０００３】
このような光記録媒体の記録密度を上げる手段としては、光記録媒体に情報の書き込みまたは呼び出しを行う光ピックアップにおいて、対物レンズの開口数（以下、ＮＡという）を大きくすること、あるいは、光源の波長を短くすることにより、この対物レンズによって集光され、光記録媒体上に形成されるビームスポットの小径化が有効である。そこで、例えば、「ＣＤ系光記録媒体」では、対物レンズのＮＡが０．５０、光源の波長が７８０ｎｍとされているのに対して、「ＣＤ系光記録媒体」よりも高記録密度化がなされた「ＤＶＤ系光記録媒体」では、対物レンズのＮＡが０．６５、光源の波長が６６０ｎｍとされている。そして、光記録媒体は、前述したように、さらなる記録密度の向上及び大容量化が望まれており、そのためには、対物レンズのＮＡを０．６５よりもさらに大きく、あるいは、光源の波長を６６０ｎｍよりもさらに短くすることが望まれている。
【０００４】
このような大容量の光記録媒体及び光情報処理装置として、例えば、非特許文献１などに挙げられている、青色の波長領域の光源とＮＡ０．８５の対物レンズを用いて、２２ＧＢ相当の容量確保を満足するシステム提案がある。
【０００５】
前記高ＮＡ化、あるいは短波長化による新規格が近年提案される一方、利用者の手元には、従来の光記録媒体であるＣＤ，ＤＶＤが存在する。これらの光記録媒体と前記新規格の光記録媒体をともに同一の光情報処理装置で取り扱えることが望ましい。これを実現する最も簡単な方法としては、従来の光ピックアップと、新規格用光ピックアップの両方の光ピックアップを搭載する方法がある。しかし、この方法では、小型化、低コスト化を達成することは難しい。
【０００６】
そこで、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として、図３２に概略構成を示すように青色用光源１００，ＤＶＤ用光源２００，ＣＤ用光源３００の各光源と、各光源からの出射光を所定の光記録媒体に集光させるための１つの対物レンズを備えた構成が望ましい。ところで、このように１つの対物レンズで、青色，ＤＶＤ，ＣＤの異なる規格の光記録媒体に集光させるためには、次のような課題が存在する。
【０００７】
波長（λ１）：４００ｎｍ、ＮＡ（λ１）：０．６５、光照射側基板厚（ｔ１）：０．６ｍｍの青色系光記録媒体に対して、無限系入射（対物レンズへの入射光が平行光で入射する状態を意味する）により球面収差の波面が最小となる単一の対物レンズを用いて、波長（λ２）：６６０ｎｍ、ＮＡ（λ２）：０．６５、光照射側基板厚（ｔ２）：０．６ｍｍのＤＶＤ系光記録媒体に無限系入射でスポット形成させた場合、あるいは波長（λ３）：７８０ｎｍ、ＮＡ（λ３）：０．５０、光照射側基板厚（ｔ３）：１．２ｍｍのＣＤ系光記録媒体に無限系入射で集光させた場合、図３３，図３４に示すように波長の違いあるいは基板厚みの違いに伴う球面収差が発生する。
【０００８】
このような課題は、ＤＶＤ／ＣＤ互換型光ピックアップでも同様にあった。すなわち、波長（λ２）：６６０ｎｍ、ＮＡ（λ２）：０．６５、基板厚（ｔ２）：０．６ｍｍのＤＶＤ系光記録媒体に無限系入射で球面収差の波面が最小となる単一の対物レンズを用いて、波長（λ３）：７８０ｎｍ、ＮＡ（λ３）：０．５０、基板厚（ｔ３）：１．２ｍｍのＣＤ系光記録媒体に無限系入射で集光させた場合、波長の違いと基板厚みの違いに伴う球面収差が発生する。
【０００９】
このときの対応方法として、例えば、特許文献１，特許文献２に記載がある。すなわち、波長の異なる２つの半導体レーザーと、波長選択性の液晶素子とを有し、一方の半導体レーザーから出射された波長６６０ｎｍの光を用いて厚さ０．６ｍｍのＤＶＤ系光記録媒体に対して記録や再生を行い、他方の半導体レーザーから出射された波長７８０ｎｍの光を用いて厚さ１．２ｍｍのＣＤ系光記録媒体に対して記録や再生を行うように構成し、波長選択性の液晶素子については、波長６６０ｎｍの光に対しては位相分布を変化させず、他方の波長７８０ｎｍの光に対しては位相分布を変化させて基板厚さの違いに伴う球面収差を補正するという手法を提案している。
【００１０】
また、他の方法として、対物レンズに対し波長６６０ｎｍのＤＶＤ側入射光が無限系、ＣＤ側入射光が有限系（いわゆる、発散光で入射する状態を意味する）とすることにより（図３５参照）、ＤＶＤ系光記録媒体とＣＤ系光記録媒体の基板厚及び波長の差に起因する球面収差を補正する手段が一般に知られている。
【００１１】
さて、以上のような従来例を用いて、青色系光記録媒体／ＤＶＤ系光記録媒体の互換型光ピックアップを提案しているものとして非特許文献２に記載がある。この非特許文献２の記載には、青色系光記録媒体／ＤＶＤ系光記録媒体／ＣＤ系光記録媒体の３種類の光記録媒体を１つの対物レンズで記録あるいは再生する方法が提案されている。波長４０５ｎｍ，６５０ｎｍ，７８０ｎｍの異なる３つの半導体レーザーと、波長選択性の位相補正素子とを有し、波長４０５ｎｍ、無限系入射の光を用いて厚さ０．１ｍｍの青色系光記録媒体に対して照射を行い、波長６５０ｎｍ、有限系入射の光を用いて厚さ０．６ｍｍのＤＶＤ系光記録媒体に対して照射を行い、波長７８０ｎｍ、有限系入射の光を用いて厚さ１．２ｍｍのＣＤ系光記録媒体に対して照射を行う構成とし、波長選択位相板は波長４０５ｎｍの光に対しては位相分布を変化させずに、他方の波長６５０ｎｍ，７８０ｎｍの光に対しては位相分布を変化させている。この構成では、基板厚さの違いに伴う球面収差を補正する方法として、波長選択性の位相補正素子とＤＶＤ／ＣＤの２波長を有限系入射にするという２種類の波面補正手段を併用している。
【００１２】
さらに、別の課題として、対物レンズのＮＡをより大きく、あるいは光源の波長をより短くして大容量化を図ると、光記録媒体の透明基板の厚み誤差によって発生する球面収差の影響が大きくなり、その影響を抑制する補正手段が必要となる。光記録媒体の透明基板の厚み誤差によって発生する球面収差は、一般的に（数１）で与えられる。
【００１３】
【数１】
Ｗ４０＝（（ｎ２−１）／（８ｎ３））×（ｄ×ＮＡ４／λ）
ここで、ｎは光記録媒体の透明基板の屈折率、ｄは透明基板の厚み、ＮＡは対物レンズの開口数、λは光源の波長を意味する。
【００１４】
この（数１）から、短波長、高ＮＡほど収差が大きくなることがわかる。ＣＤ，ＤＶＤといった従来の光記録媒体への情報の書き込み、読み出しを行う光情報処理装置においては、この球面収差による波面劣化はとくに補正を必要としなかったが、非特許文献１の記載などに挙げられている青色波長の光源とＮＡ０．８５の対物レンズを用いたシステムでは光記録媒体の厚み誤差に伴う波面劣化は、例えば、０．０７λ以上となり補正が要求される。
【００１５】
さらに、近年、さらなる大容量化の方法として情報記録面を２層以上にする多層型光記録媒体が提案されているが、このような場合でも層間距離に伴う波面劣化が問題となることは言うまでもない。これらの補正手段としては、特許文献３、特許文献４、特許文献５に挙げられている複数のレンズ群の移動により対物レンズへ入射する光束の発散状態を変化させる手段、あるいは特許文献６、特許文献７に挙げられている対物レンズへの入射光束の位相状態を変化させる手段が知られている。
【００１６】
【特許文献１】
特許第２７２５６５３号公報
【特許文献２】
特開平１０−３３４５０４号公報
【特許文献３】
特開２０００−１３１６０３号公報
【特許文献４】
特開２０００−２４２９６３号公報
【特許文献５】
特開２００１−２８１４７号公報
【特許文献６】
特開平９−１２８７８５号公報
【特許文献７】
特開平１０−２０２６３号公報
【特許文献８】
特開２００１−１４３３０３号公報
【非特許文献１】
ＩＳＯＭ２００１　予稿集「Ｎｅｘｔ　Ｇｅｎｅｒａｔｉｏｎ　Ｏｐｔｉｃａｌ　Ｄｉｓｃ」Ｈｉｒｏｓｈｉ　Ｏｇａｗａ、ｐ６〜７
【非特許文献２】
ＩＳＯＭ２００１　予稿集「ＢＬＵＥ／ＤＶＤ／ＣＤ　ＣＯＭＰＡＴＩＢＬＥ　ＯＰＴＩＣＡＬ　ＨＥＡＤ　ＷＩＴＨ　ＴＨＲＥＥＷＡＶＥＬＥＮＧＴＨＳ　ＡＮＤ　Ａ　ＷＡＶＥＬＥＮＧＴＨ　ＳＥＬＥＣＴＩＶＥ　ＦＩＬＴＥＲ」Ｒｙｕｉｃｈｉ　Ｋａｔａｙａｍａ　ａｎｄ　Ｙｕｉｃｈｉ　Ｋｏｍａｔｓｕ　ｐ３０〜３１
【非特許文献３】
山田英明、「レーザー＆オプティクスガイドＩＶ（２）」メレスグリオ社、第１版、１９９６．６発行　ｐ２２−７〜８
【００１７】
【発明が解決しようとする課題】
このように、今後の光ピックアップに要求される課題としては、高ＮＡ化あるいは短波長化に伴い発生する収差の補償、及び従来の光記録媒体との互換性が課題として挙げられる。前述のように、それぞれ対策案が開示されているが、別々に補正手段を設置する方法では、光ピックアップの大型化、高コスト化を招くことになる。そこで、各機能の集約、小型化が望まれる。
【００１８】
また、非特許文献２の方法では、ＤＶＤ系光記録媒体／ＣＤ系光記録媒体の互換時に十分な波面性能が得られない。一般に、回折限界の球面収差として、マーシャル・クライテリオン：０．０７λｒｍｓが基準値として用いられることがあるが、光ピックアップでは、光記録媒体の厚み誤差、光記録媒体のチルト誤差、光記録媒体と対物レンズ位置のずれに伴うデフォーカス誤差などをはじめとする様々な誤差要因が存在し、これらの誤差に伴う波面劣化の確立的な積上げを考えると、誤差を含まない状態での球面収差の波面（中央値）は０．０３λｒｍｓ以下であることが望まれるが、これに対して、非特許文献２では、ＤＶＤ系光記録媒体の球面（中央値）は、約０．０５λｒｍｓもある。一つの素子で、ＤＶＤ系とＣＤ系いずれの球面収差も最小とすることは不可能である。すなわち、ＤＶＤ系とＣＤ系の球面収差の波面が最小となる液晶素子条件の中間値を狙った設計を行わざるを得なくなり、結果、十分に球面収差を抑制することはできないという課題があった。
【００１９】
本発明は、前記従来技術の問題を解決することに指向するものであり、その目的は、部品点数を増加させることなく、青色波長帯域：４００ｎｍを用いる青色系光記録媒体、または赤色波長帯域：６６０ｎｍを用いるＤＶＤ系光記録媒体、または赤外波長帯域：７８０ｎｍを用いるＣＤ系光記録媒体の３種類の情報記録面上に、一枚の対物レンズで良好なスポットを照射可能な構成を実現することにあり、特に、青色／ＤＶＤ／ＣＤ系の各光学系で球面収差を十分に抑制し、具体的には設計中央値で残留球面収差０．０３０λｒｍｓ以下とする光ピックアップ及びこれを用いる光情報処理装置を提供することにある。
【００２０】
【課題を解決するための手段】
この目的を達成するために、本発明に係る請求項１に記載の光ピックアップは、光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、各々波長の異なる複数の光源と、光記録媒体に光源からの出射光を集光させるための対物レンズと、電圧印加により通過光束に位相変化を与える液晶素子とを備え、液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、同心円状の位相変化が最大となる瞳半径位置、及び付加位相量を各光源の点灯に応じて切り換える構成によって、複数の光記録媒体に光源からの出射光を最良の状態で集光でき、最良の記録，再生を行うことができる。
【００２１】
また、請求項２，３に記載の光ピックアップは、請求項１記載の光ピックアップにおいて、複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡｉ）により光記録媒体１，２，…ｉに記録，再生，消去のうちいずれか１以上を行い、液晶素子が、位相変化の最大となる瞳半径位置：ｒ１，ｒ２，…ｒｉを有し、瞳半径位置が次の条件「ｒ１≧ｒ２≧…≧ｒｉ」を満足すること、または、対物レンズを、光記録媒体１において球面収差の波面が最小となるように設計されたとき、液晶素子が、位相変化の最大となる瞳半径位置：ｒ２，ｒ３…ｒｉを有し、瞳半径位置が次の条件「ｒ２≧ｒ３≧…≧ｒｉ」を満足する構成によって、単一の対物レンズにより複数の光記録媒体に光源からの出射光を最良の状態で集光でき、最良の記録，再生を行うことができる。
【００２２】
また、請求項４に記載の光ピックアップは、請求項１記載の光ピックアップにおいて、複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡｉ）により光記録媒体１，２，…ｉに記録，再生，消去のうちいずれか１以上を行い、光記録媒体１，２，…ｉ上に発生する球面収差が最大となる瞳半径位置をＲ１，Ｒ２，…Ｒｇ，Ｒｈ，…Ｒｉ（Ｒ１≧Ｒ２≧…≧Ｒｇ≧Ｒｈ…≧Ｒｉ）としたとき、液晶素子が、位相変化の最大となる瞳半径位置：ｒ１，ｒ２，…ｒｘ，…ｒｊ（ｘ＜ｊ＜ｉ）を有し、瞳半径位置：ｒｘが次の条件「ｒｘ＝（Ｒｇ＋Ｒｈ）／２」を満足する構成によって、想定される各球面収差が最大となる各瞳半径位置に対して、その中間の瞳半径位置で付加位相が最大となるように液晶素子を構成し、液晶素子の電極パターンを単純化できる。
【００２３】
また、請求項５に記載の光ピックアップは、請求項１記載の光ピックアップにおいて、複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡａ≧ＮＡｂ≧ＮＡｃ…≧ＮＡｉ）により光記録媒体１，２，…ａ，ｂ，ｃ，…ｉに記録，再生，消去のうちいずれか１以上を行い、対物レンズが、光記録媒体ｂに対しては有限系により使用されるとき、液晶素子が、位相変化の最大となる瞳半径位置：ｒ１，ｒ２，…ｒａ，ｒｃ，…ｒｉを有し、瞳半径位置が次の条件「ｒ１≧ｒ２≧…ｒａ≧ｒｃ…≧ｒｉ」を満足する構成によって、対物レンズを複数の光源の少なくともいずれか１に対して有限系で使用するとき、液晶素子が、有限系光路を除く光路に対して位相変化を与えて、液晶素子の電極パターンを単純化することができる。
【００２４】
また、請求項６，７に記載の光ピックアップは、光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、波長：λ１，λ２，λ３（λ１≦λ２≦λ３）の光を出射する３つの光源と、光記録媒体に光源からの出射光を集光させるための対物レンズと、開口数：ＮＡ１，ＮＡ２，ＮＡ３（ＮＡ１≧ＮＡ２≧ＮＡ３）を切り換える開口制限手段と、電圧印加により通過光束に位相分布の変化を与える液晶素子とを備え、液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、同心円状の位相変化が最大となる瞳半径位置ｒ２，ｒ３をもち、瞳半径位置ｒ２と瞳半径位置ｒ３は対向電極のそれぞれ異なる電極面にあり、瞳半径位置ｒ２は略開口数：ＮＡ２〜ＮＡ３の領域に、瞳半径位置ｒ３は略開口数：ＮＡ３以内の領域に形成されてなる構成によって、また液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、同心円状の位相変化が最大となる瞳半径位置ｒ２，ｒ３をもち、瞳半径位置ｒ２と瞳半径位置ｒ３は対向電極の同一電極面上にあり、瞳半径位置ｒ２は略開口数：ＮＡ２〜ＮＡ３の領域に、瞳半径位置ｒ３は略開口数：ＮＡ３以内の領域に形成されてなる構成によって、波長の違いあるいは基板厚みの違いに伴い発生する球面収差とは逆極性の球面収差を発生させる液晶素子により、発生の球面収差を解決し、また球面収差とは逆極性の球面収差を同一電極面上で発生させ液晶素子を小型化し、複数の光記録媒体に光源からの出射光を最良の状態で集光し、記録，再生を行うことができる。
【００２５】
さらに、請求項８に記載の光ピックアップは、請求項６，７記載の光ピックアップにおいて、対物レンズを、３つの光源の波長：λ１，λ２，λ３（λ１≦λ２≦λ３）のうち、波長：λ２の光源点灯時は有限系で使用する構成によって、液晶素子のλ２とλ３の位相補正領域を異ならせることができ、同一電極面上に形成すること、また液晶素子の位相補正量を低減して、収差補正時の駆動時間を短縮できる。
【００２６】
また、請求項９に記載の光ピックアップは、光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、波長：λ１，λ２，λ３（λ１≦λ２≦λ３）の光を出射する３つの光源と、光記録媒体に光源からの出射光を集光させるための対物レンズと、開口数：ＮＡ１，ＮＡ２，ＮＡ３（ＮＡ１≧ＮＡ２≧ＮＡ３）を切り換える開口制限手段と、電圧印加により通過光束に位相分布の変化を与える液晶素子とを備え、液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、同心円状の位相変化が最大となる瞳半径位置ｒ２をもち、瞳半径位置ｒ２は略開口数：ＮＡ２〜ＮＡ３の領域に形成されてなる構成によって、波長あるいは基板厚みの違いに伴い発生の球面収差とは逆極性の球面収差を同一電極面上で発生させ、複数の光記録媒体に光源からの出射光を最良の状態で集光し、記録，再生を行うことができる。
【００２７】
さらに、請求項１０に記載の光ピックアップは、請求項９記載の光ピックアップにおいて、対物レンズを、３つの光源の波長：λ１，λ２，λ３（λ１≦λ２≦λ３）のうち、波長：λ２及び波長：λ３の光源点灯時は有限系で使用する構成によって、液晶素子の位相補正量を低減して収差補正時の駆動時間を短縮でき、光記録媒体に光源からの出射光を最良の状態で集光し、記録，再生を行うことができる。
【００２８】
また、請求項１１，１２に記載の光ピックアップは、請求項１〜１０記載の光ピックアップにおいて、光記録媒体を判別する光記録媒体判別手段を備え、光記録媒体判別手段からの信号に応じて、液晶素子の付加位相量、及び付加位相量が最大となる瞳半径位置を切り換えること、さらに、光記録媒体上に発生する球面収差を検出する球面収差検出手段を備え、球面収差検出手段からの信号に応じて、液晶素子の付加位相量を変化させる構成によって、各光記録媒体に応じて光源からの出射光を最良の状態で集光し、記録，再生を行うことができる。
【００２９】
また、請求項１３に記載の光ピックアップは、請求項７，９記載の光ピックアップの液晶素子において、同心円状の位相付加面の対向電極面が、光軸中心に対称分割された２ｎ領域（ｎは整数）からなる構成によって、球面収差，コマ収差の収差補正を液晶素子の同一電極面上に形成することができ、光記録媒体に光源からの出射光を最良の状態で集光し、記録，再生を行うことができる。
【００３０】
さらに、請求項１４，１５に記載の光ピックアップは、請求項１３記載の光ピックアップにおいて、光記録媒体からの反射光の干渉パターンからコマ収差信号を生成する手段を備え、このコマ収差信号に基づいて、液晶素子の付加位相量を制御すること、対物レンズの略光軸中心からの位置ずれ量を検知する手段を備え、検知した位置ずれ量の信号に基づいて、液晶素子の付加位相量を制御する構成によって、液晶素子と対物レンズとの位置ずれを補正し光記録媒体に光源からの出射光を最良の状態で集光し、記録，再生を行うことができる。
【００３１】
また、請求項１６に記載の光ピックアップは、請求項１〜１５記載の光ピックアップにおいて、複数の光記録媒体における少なくともいずれか１つは、情報記録層が多重形成された多層型光記録媒体であって、多層型光記録媒体の記録，再生を行う情報記録層の位置に応じて、液晶素子の付加位相量を変化させる構成によって、複数の光記録媒体に応じた光源からの出射光を最良の状態で集光して記録，再生を行うことができる。
【００３２】
また、請求項１７〜１９に記載の光ピックアップは、請求項１〜１６記載の光ピックアップにおいて、光源の使用波長に応じて、光源からの出射光の開口数を切り換える開口制限手段を備え、開口制限手段が液晶素子と一体化されたこと、さらに、光源の使用波長に応じて、光源からの出射光の偏光状態を変化させる偏光素子を備え、偏光素子が液晶素子と一体化されたこと、さらに、液晶素子が、対物レンズと一体で可動する構成によって、光ピックアップの構成を各機能の集約、小型化でき複数の光記録媒体に光源からの出射光を最良の状態で集光して記録，再生を行うことができる。
【００３３】
また、請求項２０記載の光情報処理装置は、請求項１〜１９のいずれか１項記載の光ピックアップを用いて、複数の光記録媒体に光源からの出射光を最良の状態で集光して、光記録媒体に対して情報の記録，再生，消去の少なくとも１以上を行うことができる。
【００３４】
【発明の実施の形態】
以下、図面を参照して本発明における実施の形態を詳細に説明する。
【００３５】
図１は本発明の実施の形態１における「使用波長４００ｎｍ、ＮＡ０．６５、光照射側基板厚０．６ｍｍの青色系光記録媒体」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。
【００３６】
図１に示すように光ピックアップの要部は、波長４００ｎｍの半導体レーザー１０１、コリメートレンズ１０２、偏光ビームスプリッタ１０３、ダイクロイックプリズム２０３，３０３、プリズム１０４、液晶素子１０５、波長板１０６、開口制限素子１０７、対物レンズ１０８、検出レンズ１１０、光束分割手段１１１、受光素子１１２より構成される波長４００ｎｍの光が通過する青色光学系が構成されている。
【００３７】
また、ホログラムユニット２０１、カップリングレンズ２０２、ダイクロイックプリズム２０３，３０３、プリズム１０４、液晶素子１０５、波長板１０６、開口制限素子１０７、対物レンズ１０８から構成される波長６６０ｎｍの光が通過するＤＶＤ光学系が構成されている。
【００３８】
さらに、ホログラムユニット３０１、カップリングレンズ３０２、ダイクロイックプリズム３０３、プリズム１０４、液晶素子１０５、波長板１０６、開口制限素子１０７、対物レンズ１０８から構成される波長７８０ｎｍの光が通過するＣＤ光学系から構成されている。すなわち、ダイクロイックプリズム２０３，３０３、プリズム１０４、液晶素子１０５、波長板１０６、開口制限素子１０７、対物レンズ１０８は２ないし３つの光学系に用いられる共通部品である。
【００３９】
ここで、本実施の形態１において、対物レンズ１０８は、「使用波長４００ｎｍ、ＮＡ０．６５、光照射側基板厚０．６ｍｍの青色系光記録媒体」に対し、無限系入射において球面収差の波面が最小になるように設計されている。
【００４０】
また、光記録媒体１０９ａ、１０９ｂ及び１０９ｃはそれぞれ基板厚さ、使用波長が異なる光記録媒体で、光記録媒体１０９ａは基板厚さが０．６ｍｍの青色系光記録媒体で、光記録媒体１０９ｂは基板厚さが０．６ｍｍのＤＶＤ系光記録媒体で、光記録媒体１０９ｃは基板厚さが１．２ｍｍのＣＤ系光記録媒体である。記録、あるいは再生時にはいずれかの光記録媒体のみが図示しない回転機構にセットされて高速回転される。
【００４１】
さらに、本実施の形態１では、青色系光記録媒体は情報記録面を２層有する２層型光記録媒体にも対応可能な光ピックアップの形態についても説明する。２層型光記録媒体は、基板厚０．６ｍｍの透明基板を介して１層目の情報記録面をもち、この１層目の情報記録面のさらに奥側に２層目の情報記録面をもつ。１層目と２層目の間にはスペーサ層と呼ばれる層が形成されていて、その厚みは３０μｍ程度である。
【００４２】
また、本実施の形態１において、対物レンズ１０８は、「使用波長４００ｎｍ、ＮＡ０．６５、光照射側基板厚０．６ｍｍの青色系光記録媒体の１層目」に対し、無限系入射において球面収差の波面が最小になるように設計されている。
【００４３】
以上のように構成される光ピックアップの動作について、まず、「使用波長４００ｎｍ、ＮＡ０．６５、光照射側基板厚０．６ｍｍの青色系光記録媒体」を記録、再生、または消去する場合について説明する。波長４００ｎｍの半導体レーザー１０１から出射した直線偏光の発散光は、コリメートレンズ１０２で略平行光とされ、偏光ビームスプリッタ１０３、ダイクロイックプリズム２０３，３０３を透過し、プリズム１０４で光路を９０度偏向され、液晶素子１０５を透過し、波長板１０６を通過し円偏光とされ、開口制限素子１０７でＮＡ０．６５に制限され、対物レンズ１０８に入射し、光記録媒体１０９ａ上に微小スポットとして集光される。このスポットにより、情報の再生、記録あるいは消去が行われる。
【００４４】
また、光記録媒体１０９ａから反射した光は、往路とは反対回りの円偏光となり、再び略平行光とされ、波長板１０６を通過して往路と直交した直線偏光になり、偏光ビームスプリッタ１０３で反射され、検出レンズ１１０で収束光とされ、光束分割手段１１１により複数の光路に偏向分割され受光素子１１２に至る。受光素子１１２からは、収差信号、情報信号、サーボ信号が検出される。
【００４５】
次に、「使用波長６６０ｎｍ、ＮＡ０．６５、光照射側基板厚０．６ｍｍのＤＶＤ系光記録媒体」を記録、再生、または消去する場合について説明する。近年、ＤＶＤのピックアップには受発光素子を１つのキャンの中に設置し、ホログラムを用いて光束の分離を行うホログラムユニットが一般的に用いられるようになってきた。図２に、半導体レーザー２０１ａ、ホログラム２０１ｂ及び受光素子２０１ｃを一体化して構成されたホログラムユニット２０１を示す。
【００４６】
このホログラムユニット２０１の半導体レーザー２０１ａから出射された６６０ｎｍの光は、ホログラム２０１ｂを透過し、カップリングレンズ２０２で所定の発散状ビームに変換され、波長４００ｎｍの光は透過し波長６６０ｎｍの光は反射させるダイクロイックプリズム２０３によってプリズム１０４の方向に反射され、プリズム１０４によって光路が９０度偏向され、液晶素子１０５において所定の位相が付加され、波長板１０６を通過し円偏光あるいは楕円偏光とされ、開口制限素子１０７では何ら作用を受けず、対物レンズ１０８に入射し、光記録媒体１０９ｂ上に微小スポットとして集光される。このスポットにより、情報の再生、記録あるいは消去が行われる。
【００４７】
光記録媒体１０９ｂから反射した光は、プリズム１０４で偏向され、ダイクロイックプリズム２０３で反射され、カップリングレンズ２０２で収束光とされ、図２に示すようにホログラム２０１ｂにより半導体レーザー２０１ａと同一キャン内にある受光素子２０１ｃ方向に回折されて受光素子２０１ｃに受光される。受光素子２０１ｃからは、収差信号、情報信号、サーボ信号が検出される。
【００４８】
引き続き、「使用波長７８０ｎｍ、ＮＡ０．５０、光照射側基板厚１．２ｍｍのＣＤ系光記録媒体」を記録、再生、または消去する場合について説明する。ＤＶＤ系同様にＣＤ系のピックアップも受発光素子を１つのキャンの中に設置した、ホログラムを用いて光束の分離を行うホログラムユニットが一般的に用いられる。図１に示すように、３０１は、半導体レーザー３０１ａ、ホログラム３０１ｂ及び受光素子３０１ｃを一体化して構成されたホログラムユニットを示す。
【００４９】
このホログラムユニット３０１の半導体レーザー３０１ａから出射された７８０ｎｍの光は、ホログラム３０１ｂを透過し、カップリングレンズ３０２で所定の発散状ビームに変換され、青色と赤色波長帯域の光は透過し赤外波長帯域の光は反射させるダイクロイックプリズム３０３によってプリズム１０４の方向に反射され、プリズム１０４によって光路が９０度偏向され、液晶素子１０５では何ら作用を受けず透過し、波長板１０６を通過し楕円偏光あるいは円偏光とされ、開口制限素子１０７でＮＡ０．５０に制限され、対物レンズ１０８に入射し、光記録媒体１０９ｃ上に微小スポットとして集光される。このスポットにより、情報の再生、記録あるいは消去が行われる。
【００５０】
光記録媒体１０９ｃから反射した光は、プリズム１０４で偏向され、ダイクロイックプリズム３０３で反射され、カップリングレンズ３０２で収束光とされ、受光素子３０１ｃ方向に回折されて受光素子３０１ｃに受光される。受光素子３０１ｃからは、収差信号、情報信号、サーボ信号が検出される。
【００５１】
図３は本実施の形態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であり、図４（ａ），（ｂ）は液晶素子の電極パターンの例を示す図である。以下に、図３，図４（ａ），（ｂ）を用いて構成、動作原理を説明する。
【００５２】
図３に示す本実施の形態１の液晶素子は、特許文献８に記載されている公知の構成であり、ガラス基板１ａ，１ｂが、導電性スペーサ２により接着され液晶セルを形成している。ガラス基板１ａの内側表面には、内側表面から電極４ａ、絶縁膜５、配向膜６の順に、またガラス基板１ｂの内側表面には、内側表面から電極４ｂ、絶縁膜５、配向膜６の順に被膜されている。
【００５３】
電極４ａは電極引出部７で接続線によって制御回路と接続できるようパターン配線されている。また電極４ｂは導電性スペーサ２によりガラス基板１ａ上に形成された電極４ａと電気的に接続されている。したがって、電極４ｂは電極引出部７で接続線によって位相補正素子制御回路と接続できる。液晶セル内部には液晶３が充填されている。
【００５４】
前述した液晶素子を構成し液晶層を挟持する基板上の電極に形成される電極は、特許文献８の段落番号［００２６］〜［００３６］で開示されているような一様電極内に給電部が設けられた電圧降下型の方法、あるいは特許文献６で開示されているセグメント型の構成を用いればよい。本実施の形態１では、電極パターンが光軸中心に同心円状に形成されてなり、前者の方法を用いたときの電極パターンの概念図を図４（ａ）に、後者の方法を用いたときの電極パターンの概念図を図４（ｂ）に示す。
【００５５】
また、本実施の形態１の光ピックアップでは、回転機構にセットされる光記録媒体に応じて、ＮＡ（開口数）を切り換える必要がある。対物レンズの焦点距離をｆ、集光に利用される光束の有効径をφとしたとき、ＮＡは（数２）で与えられる。
【００５６】
【数２】
ＮＡ＝φ／２／ｆ
よって、使用波長に応じて、通過光束径を切り換える手段を用いればよい。点灯光源に応じて、光束径を切り換える手段として、開口制限素子１０５（図１参照）を用いている。開口制限素子は、波長帯域あるいは偏光方向に応じて、反射，回折，吸収のいずれかの光学特性を利用して光束径の切り換えを行うものであればよい。
【００５７】
すなわち、波長４００ｎｍで最良の波面を有する対物レンズに、同一光束径の波長６６０ｎｍの光を無限系入射させた場合、屈折力が低下し、ＮＡが低くなる。そのため、本発明では波長６６０ｎｍについては、波長４００ｎｍでの入射光束径φ１に比べ、僅かに大きめの光束径φ２で入射させる。図５（ａ）は、後述する（表１）の特性を有する対物レンズにおいて、ＮＡ０．６５となる有効径と波長の関係を示すものである。
【００５８】
この図５（ａ）から、波長６６０ｎｍを使用するＤＶＤ系光記録媒体の記録、再生時には光束径φ２を４．０２ｍｍ程度にする必要があることがわかる。また、光束径φ１とφ２の関係は、対物レンズの硝種によっても異なる。図５（ｂ）は図５（ａ）の対物レンズと同じφ１、焦点距離、ＮＡの対物レンズで、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の関係を示したものであり、対物レンズの硝種に応じて適当なφ２を選択してやればよい。
【００５９】
一方、ＣＤ系光記録媒体を記録、再生するときの最適なＮＡは０．５０程度であるが、図５（ａ）と同様の方法により、最適な有効径φ３を見積もると、φ３：３．２ｍｍ程度とすればよいことがわかる。
【００６０】
例えば、本実施の形態１における点灯光源に応じて光束径を切り換える手段である反射特性を利用した開口制限素子として、光源から出射される光束の波長に応じ、図６（ａ）に示すように反射によって光束径を切り換える手段を用いればよく、また、回折特性を利用した開口制限素子として、光源から出射される光束の波長に応じ、図６（ｂ）に示すように回折によって光束径を切り換える手段でもよく、さらに、吸収特性を利用した開口制限素子として、光源から出射される光束の波長に応じ、図６（ｃ）のように吸収によって光束径を切り換える手段でもよい。
【００６１】
さらに、本実施の形態１では波長４００ｎｍの光を直線偏光から円偏光、あるいは円偏光から直線偏光に変換できるとともに、波長６６０ｎｍと波長７８０ｎｍの光については直線偏光から円偏光もしくは楕円偏光、あるいはその逆の変換が行える波長板を備えている。この波長板は、波長４００ｎｍの光と波長６６０ｎｍの光と波長７８０ｎｍの光をともに直線偏光から円偏光、あるいは円偏光から直線偏光に変換できる。いわゆる波長板の構成としては、ある厚さｔにおいて常光線（屈折率ｎｏ）と異常光線（屈折率ｎｅ）の位相差が波長４００ｎｍと波長６６０ｎｍと波長７８０ｎｍの１／４となるような結晶からなる波長板を採用すればよい。すなわち以下の（数３），（数４），（数５）の条件を満たす結晶であればよい。
【００６２】
【数３】
Δｎ１×ｔ＝｛（２ｐ＋１）／４｝×４００（ｐ＝０，１…）
Δｎ１；波長４００ｎｍの光源からの光に対する（ｎｏ−ｎｅ）
【００６３】
【数４】
Δｎ２×ｔ＝｛（２ｑ＋１）／４｝×６６０（ｑ＝０，１…）
Δｎ２；波長６６０ｎｍの光源からの光に対する（ｎｏ−ｎｅ）
【００６４】
【数５】
Δｎ３×ｔ＝｛（２ｒ＋１）／４｝×７８０（ｒ＝０，１…）
Δｎ３；波長７８０ｎｍの光源からの光に対する（ｎｏ−ｎｅ）
例えば、ＤＶＤ光学系の光路中に配置されてなるホログラム２０１ｂ（図１参照）として、無偏光性のホログラムを用いた場合、往路と復路の光路分離は十分に行なえず、およそ光記録媒体からの戻り光の約３０％が、光源に戻ってきてしまう。一般にこのような戻り光は、ノイズ成分として半導体レーザーの発振状態を不安定化させてしまう。
【００６５】
しかしながら、本実施の形態１は、前述のような特性をもつ波長板を配置することにより、例えば、図１のＤＶＤ光学系のホログラムユニット２０１の出射光と光記録媒体からホログラムユニット２０１へ向かう光の偏光方向を直交させることができる。このように往路の光と復路の光の偏光方向を直交させることにより半導体レーザー２０１ａへの戻り光によるノイズ発生を防止できる。
【００６６】
また、このような特性をもつ波長板を配置することにより、例えば、図１の青色系光記録媒体に対しては偏光ビームスプリッタ１０３と波長板１０６が、組み合わされた偏光分離光学系が実現されており、十分な光量を得られるとともに、半導体レーザー１０１への戻り光によるノイズ発生も低減可能としている。同様に、ＤＶＤ光学系の光路に対しても、ホログラムとして偏光選択性のホログラムを使用することにより偏光分離光学系が実現可能である。
【００６７】
具体的には、波長４００ｎｍの光と波長６６０ｎｍの光をともに直線偏光から円偏光、あるいは円偏光から直線偏光に変換し、波長７８０ｎｍの光については楕円偏光に変換する波長板の構成としては、（数３），（数４）の条件を満足すればよい。
【００６８】
さらに、波長４００ｎｍの光を直線偏光から円偏光、あるいは円偏光から直線偏光に変換し、波長６６０ｎｍと波長７８０ｎｍの光については楕円偏光に変換する波長板の構成としては、（数３）の条件を満足すればよい。
【００６９】
なお、波長板は（数３），（数４），（数５）を満足する結晶に限られない。例えば、有機材料の位相差素子を積層配置させたものをガラス板で挟み込んだ構成であってもよい。あるいは、液晶素子などの電気光学素子を用いてもよい。
【００７０】
また、図１において、光束分割手段１１１と受光素子１１２の組み合わせにより「球面収差検出手段」を構成し、液晶素子１０６が「球面収差補正手段」に相当する。前述のとおり、光記録媒体の厚み誤差が存在すると記録面上に形成される光スポットの形状が劣化する。このように発生した収差は戻り光束の波面を歪ませることになり、検出レンズ１１０を介して受光素子１１２に向かう光束にも収差が発生する。図７はこの状態を示している。
【００７１】
検出レンズ１１０を通過する戻り光束に球面収差が発生しているときには、戻り光束の基準波面に対して、光軸中心に同心円状に「波面の遅れ」があり、基準波面を集光したときの集光点に対し遅れた波面が集光する位置はデフォーカスとなる。そこで、遅れた波面と進んだ波面の差を取り出してフォーカス状態を検出することで「球面収差の波面の発生状況」を知ることができる。
【００７２】
例えば、図８に示すように、光束分割手段１１１としてホログラムを配置し、分割された各々の光束を検知できるように受光領域が分割された受光素子１１２を準備すればよい。光速分割手段１１１は、光軸直交面内でジッタ方向に対称分割された半分の領域を同心円に内側、外側の２領域に分割されたホログラムとする。受光素子１１２は、ホログラムで回折された各々の光束を検知する２分割の受光素子とする。そして、ホログラム回折光の光点像の移動量を検知して、各受光素子で生成される差分（Ｓａ−Ｓｂ）、（Ｓｃ−Ｓｄ）の差分：Ｗ１（数６）が球面収差信号に相当する。
【００７３】
【数６】
Ｗ１＝（Ｓａ−Ｓｂ−Ｓｃ＋Ｓｄ）
Ｗ１＝０で収差がないことを意味する。
【００７４】
また、液晶素子１０５は、図４（ａ），（ｂ）に示すような給電部１１あるいは分割電極１５に所定の電圧を印加して、液晶の屈折率：ｎをｎ１からｎ２まで、同心円状に自在に変えることを可能としている。屈折率：ｎを変化させると、各領域を通過する光束に光路差：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。
【００７５】
検出された基板厚誤差に起因して発生する球面収差が、例えば、図９の如きものであったとする。この球面収差の波面を２次元曲線として示したのが図１０（ａ），図１１（ａ）の上側部分の実線である。図４（ａ）の電極を用いた場合、このような球面収差に対し、対物レンズに光源側から入射する光束に、図１０（ａ）の下側部分の破線に示すような位相差が与えられるように、液晶素子の各同心円帯給電部１１に印加する電圧を調整すると、液晶素子を透過する光束の各部での波面の遅れにより前記「球面収差の波面」を打ち消すことができる。
【００７６】
また、図４（ｂ）の分割電極を用いた場合、このような球面収差に対し、対物レンズに光源側から入射する光束に、図１１（ａ）の下側部分の破線に示すような位相差が与えられるように、液晶素子の各分割電極に印加する電圧を調整すると、液晶素子を透過する光束の各部での波面の遅れにより前記「球面収差の波面」を打ち消すことができる。図１０（ｂ）は、図１０（ａ）における実線（球面収差の波面）と破線（液晶素子による波面の遅れ）の和、すなわち補正後の球面収差の波面を示す。もとの球面収差の波面（図１０（ａ）の上側部分の実線）よりも格段に小さくなる。図１１（ｂ）は、図１１（ａ）における実線（球面収差の波面）と破線（液晶素子による波面の遅れ）の和、すなわち補正後の球面収差の波面を示す。もとの球面収差の波面（図１１（ａ）の上側部分の実線）よりも格段に小さくなる。
【００７７】
また、本実施の形態１では、青色系光記録媒体，ＤＶＤ系光記録媒体，ＣＤ系光記録媒体の記録、再生も行うことから、青色系光記録媒体とＤＶＤ系光記録媒体とＣＤ系光記録媒体を判別する手段としては、いわゆるＤＶＤ／ＣＤの２世代互換型の情報記録再生装置（コンボドライブなどと呼ばれている）において用いられている手法を用いればよい。すなわち、光記録媒体の挿入時に、青色、赤色のいずれかの光源を点灯させてフォーカスサーチさせたときの戻り光量レベルなどにより判別する構成などを用いればよい。
【００７８】
前述したように、ＤＶＤの記録再生時に、この光源からの光束を対物レンズに入射させると、波長や基板厚みの違いに伴う球面収差が発生し、記録面上に形成される光スポットの形状が劣化する。この発生する球面収差を打ち消す逆極性の球面収差量を、光記録媒体ごとに予め記憶させておき、光記録媒体判別手段から検知された光記録媒体の種類に応じて、この逆極性の球面収差を与えるようにすればよい。
【００７９】
いま、図１に示す光ピックアップにおいて、波長４００ｎｍで球面収差の波面が最小となる単一の対物レンズ１０８に、波長６６０ｎｍの光を無限系で入射させてＤＶＤ系光記録媒体１０９ｂにスポット形成させた場合、あるいは波長７８０ｎｍの光を無限系で入射させてＣＤ系光記録媒体１０９ｃにスポット形成させた場合、図１２，図１３に示すような、波長の違いあるいは基板厚みの違いに伴う球面収差が発生する。
【００８０】
図１２，図１３のように発生する球面収差と逆極性の球面収差を発生させるために、図１に示す液晶素子１０５を備えてなる。また、図１４に示すように発生する青色系光記録媒体１０９ａとして２層の光記録媒体の記録再生時に発生する球面収差と逆極性の球面収差も発生させる。
【００８１】
そこで、以下の球面収差と逆極性の球面収差を与えるため、
▲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
のそれぞれにおいて、前述した同様の手法により、光記録媒体の判別を行うことができる。そして、この光記録媒体の光記録媒体判別信号に応じて、所定の位相形状（各瞳半径位置での付加位相量）を与えるように予め記憶されている。また、２層の青色系光記録媒体では、記録再生する情報層位置に応じて所定の位相形状を与える。
【００８２】
前記の２つの異なる球面収差を補正するための液晶素子の電極構成としては、例えば、図１５のようにすればよい。すなわち、連続した透明電極１０ａ，１０ｂを１対となし、透明電極１０ａ，１０ｂのそれぞれにメタル電極１２ａ〜１４ａ，１２ｂ〜１４ｂを形成してなる。メタル電極はメタル配線によりそれぞれ外部の信号源に接続されており、外部信号により各々任意の電圧を供給できる。そして、本実施の形態１では、メタル電極１３ａとしてＤＶＤ色系光記録媒体（及び、２層型青色系光記録媒体においては２層目）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、メタル電極１３ｂ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いる。
【００８３】
具体的には、図１７に概観図、（表１）に形状データが示される対物レンズを用いた場合、青色、ＤＶＤ、ＣＤ各光路の対物レンズの入射ビーム径はφ：３．９ｍｍ、φ：４．０２ｍｍ、φ：３．２ｍｍであり、液晶素子の光束通過径は、ＤＶＤ系光路と略同等のφ：４．０２ｍｍで作製される（実際には０．１〜０．２ｍｍのマージンをもたせる）。このときメタル電極１３ａの瞳半径位置は１．２ｍｍ〜１．６ｍｍ、メタル電極１３ｂの瞳半径位置は１．０ｍｍ〜１．２ｍｍとすればよい（図１２，図１３，図１４に相当する）。
【００８４】
【表１】

Figure 2004127473
【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５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５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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical pickup including a liquid crystal element that changes the phase of a light beam passing from a light source in accordance with an applied voltage, and an optical information processing apparatus using the same.
[0002]
[Prior art]
Optical storage 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 as means for storing video information, audio information, or data on a computer. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity.
[0003]
Means for increasing the recording density of such an optical recording medium include increasing the numerical aperture (hereinafter, referred to as NA) of an objective lens in an optical pickup for writing or retrieving information on the optical recording medium, or using a light source. By shortening the wavelength, it is effective to reduce the diameter of the beam spot collected 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, but the recording density is higher than that in the “CD optical recording medium”. In the "DVD optical recording medium", 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 be shorter than 660 nm.
[0004]
As such a large-capacity optical recording medium and optical information processing apparatus, for example, using a light source in a blue wavelength region and an objective lens with an NA of 0.85, which is described in Non-Patent Document 1, a capacity equivalent to 22 GB There is a system proposal that satisfies the security.
[0005]
While new standards based on higher NA or shorter wavelength have been proposed in recent years, users have CDs and DVDs as conventional optical recording media. It is desirable that both of these optical recording media and the optical recording media of the new standard can be handled by the same optical information processing device. The simplest way to achieve this is to mount both a conventional optical pickup and an optical pickup for a new standard. However, with this method, it is difficult to achieve size reduction and cost reduction.
[0006]
Therefore, as a large-capacity optical recording medium using a blue wavelength band light source and an optical pickup compatible with an existing DVD or CD, a blue light source 100 and a DVD light source as schematically shown in FIG. It is desirable to provide a configuration including each light source of the light source 200 and the CD light source 300 and one objective lens for condensing the light emitted from each light source onto a predetermined optical recording medium. By the way, in order to converge light on optical recording media of different standards of blue, DVD, and CD with one objective lens as described above, there are the following problems.
[0007]
Wavelength (λ1): 400 nm, NA (λ1): 0.65, light-irradiation side substrate thickness (t1): Infinite system incidence (parallel to the objective lens) The wavelength (λ2): 660 nm, NA (λ2): 0.65, and the light irradiation side substrate thickness (t2) ): When spots are formed on a 0.6 mm DVD optical recording medium with infinite system incidence, or wavelength (λ3): 780 nm, NA (λ3): 0.50, light irradiation side substrate thickness (t3): 1. When light is condensed on a 2 mm CD-based optical recording medium at infinite system incidence, spherical aberration occurs due to a difference in wavelength or a difference in substrate thickness as shown in FIGS.
[0008]
Such a problem also occurred in a DVD / CD compatible optical pickup. That is, a single objective in which the wavefront of spherical aberration is minimized at infinite system 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 the light is focused on a CD-based optical recording medium having a wavelength (λ3): 780 nm, NA (λ3): 0.50, and substrate thickness (t3): 1.2 mm using a lens, the wavelength is different. And a spherical aberration occurs due to a difference in substrate thickness.
[0009]
For example, Patent Literature 1 and Patent Literature 2 describe methods for dealing with this case. That is, a DVD-based optical recording medium having two semiconductor lasers having different wavelengths and a wavelength-selective liquid crystal element and having a thickness of 0.6 mm using light having a wavelength of 660 nm emitted from one of the semiconductor lasers. Recording and reproduction by using the light of wavelength 780 nm emitted from the other semiconductor laser to perform recording and reproduction on a CD-based optical recording medium having a thickness of 1.2 mm. For a liquid crystal element, a method of correcting the spherical aberration caused by the difference in the substrate thickness by changing the phase distribution for the light of the wavelength 660 nm without changing the phase distribution for the light of the wavelength 660 nm. Has been proposed.
[0010]
As another method, the DVD-side incident light having a wavelength of 660 nm with respect to the objective lens is set to an infinite system, and the CD-side incident light is set to a finite system (meaning a state in which the incident light is divergent light) (see FIG. 35). Means for correcting spherical aberration caused by the difference in substrate thickness and wavelength between DVD-based optical recording media and CD-based optical recording media are generally known.
[0011]
Non-Patent Document 2 describes a proposal of a compatible optical pickup for a blue optical recording medium / DVD optical recording medium using the above conventional example. Non-Patent Document 2 proposes a method of 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. . It has three semiconductor lasers having different wavelengths of 405 nm, 650 nm, and 780 nm, and a wavelength-selective phase correction element. Irradiation is performed on a DVD optical recording medium having a thickness of 0.6 mm using 650 nm wavelength, finite system incident light, and 1.2 mm thickness using a 780 nm wavelength, finite system incident light. The wavelength selective phase plate does not change the phase distribution for light having a wavelength of 405 nm, and the phase distribution does not change for the other light having a wavelength of 650 nm or 780 nm. Is changing. In this configuration, as a method of correcting spherical aberration due to a difference in substrate thickness, a wavelength-selective phase correction element and two types of wavefront correction means of setting two wavelengths of DVD / CD to finite system incidence are used in combination. I have.
[0012]
Further, as another problem, when 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 a thickness error of the transparent substrate of the optical recording medium increases. , 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]
(Equation 1)
W 40 = ((N 2 -1) / (8n 3 )) × (d × NA 4 / 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 aberration increases as the wavelength becomes shorter and the NA becomes higher. In an optical information processing apparatus for writing and reading 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 need to be particularly corrected. In a system using a light source of a blue wavelength and an objective lens with an NA of 0.85, the wavefront deterioration due to the thickness error of the optical recording medium is, for example, 0.07λ or more, and correction is required.
[0015]
Further, in recent years, a multilayer optical recording medium having an information recording surface of two or more layers has been proposed as a method for further increasing the capacity. However, it is needless to say that even in such a case, the wavefront deterioration due to the interlayer distance becomes a problem. No. As these correction means, means for changing a divergence state of a light beam incident on an objective lens by moving a plurality of lens groups described in Patent Literature 3, Patent Literature 4, and Patent Literature 5, or Patent Literature 6, Patent Literature Means for changing the phase state of a light beam incident on an objective lens described in Document 7 is known.
[0016]
[Patent Document 1]
Japanese Patent No. 2725653
[Patent Document 2]
JP-A-10-334504
[Patent Document 3]
JP 2000-131603 A
[Patent Document 4]
JP-A-2000-242963
[Patent Document 5]
JP 2001-28147 A
[Patent Document 6]
JP-A-9-128785
[Patent Document 7]
JP-A-10-20263
[Patent Document 8]
JP 2001-143303 A
[Non-patent document 1]
Proceedings of ISOM2001 "Next Generation Optical Disc" Hiroshi Ogawa, p6-7
[Non-patent document 2]
Preliminary collection of ISOM2001 "BLUE / DVD / CD COMPATIBLE OPTICAL HEAD WITH THREEWAVELENGTHS AND A WAVELENGTH SELECTIVE FILTER"
[Non-Patent Document 3]
Hideaki Yamada, "Laser & Optics Guide IV (2)", Melles Griot, 1st Edition, 1996.6, pages 22-7-8
[0017]
[Problems to be solved by the invention]
As described above, problems required for the optical pickup in the future include the compensation of aberrations caused by the increase in NA or the shortening of the wavelength, and the compatibility with conventional optical recording media. As described above, countermeasures have been disclosed, but the method of separately providing the correction means leads to an increase in the size and cost of the optical pickup. Therefore, it is desired to consolidate and miniaturize each function.
[0018]
Further, according to the method of Non-Patent Document 2, sufficient wavefront performance cannot be obtained when the DVD-based optical recording medium / CD-based optical recording medium is interchangeable. In general, a marshall criterion: 0.07 λrms may be used as a reference value as a diffraction-limited spherical aberration, but in an optical pickup, a thickness error of an optical recording medium, a tilt error of an optical recording medium, an optical recording medium and an objective There are various error factors including a defocus error due to a shift in the lens position. Considering the probable accumulation of the wavefront degradation caused by these errors, the wavefront of the spherical aberration in a state that does not include the error is considered. The median value is desirably 0.03λrms or less, whereas in Non-Patent Document 2, the spherical surface (median value) of the DVD-based optical recording medium is about 0.05λrms. With one element, it is impossible to minimize the spherical aberration of both DVD and CD systems. In other words, there is a problem that the design must aim at an intermediate value between the liquid crystal element conditions where the wavefront of the spherical aberration of the DVD system and the CD system is minimized, and as a result, the spherical aberration cannot be sufficiently suppressed. .
[0019]
The present invention is directed to solving the above-mentioned problems of the related art, and has as its object to increase the number of parts without increasing the number of components, and to use a blue-based optical recording medium using a blue wavelength band: 400 nm, or a red wavelength band: A configuration in which a single objective lens can irradiate a good spot on three types of information recording surfaces of a DVD optical recording medium using 660 nm or a CD optical recording medium using an infrared wavelength band: 780 nm is realized. In particular, an optical pickup in which the spherical aberration is sufficiently suppressed in each of the blue / DVD / CD optical systems, and specifically, the residual spherical aberration is 0.030λrms or less at the design median value, and optical information using the optical pickup. An object of the present invention is to provide a processing device.
[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 at least one of recording, reproducing, and erasing information on an optical recording medium, A plurality of light sources having different wavelengths, an objective lens for condensing the light emitted from the light source on the optical recording medium, and a liquid crystal element that changes the phase of the passing light beam by applying a voltage are provided. By providing a concentric phase change at the center of the optical axis, the pupil radius position at which the concentric phase change is maximum, and a configuration in which the amount of additional phase is switched according to the lighting of each light source, a plurality of optical recording media can be switched from the light source to the light source. Can be collected in the best condition, and the best recording and reproduction can be performed.
[0021]
The optical pickup according to the second or third aspect of the present invention is the optical pickup according to the first aspect, wherein the plurality of light sources have openings corresponding to wavelengths: λ1, λ2,... Λi (λ1 <λ2 <. Number: NA1, NA2,... NAi (NA1 ≧ NA2 ≧... ≧ NAi) performs at least one of recording, reproduction, and erasing on the optical recording media 1, 2,. Pupil radius position: r1, r2,... Ri, and the pupil radius position satisfies the following condition “r1 ≧ r2 ≧. , The liquid crystal element has pupil radius positions r2, r3... Ri at which the phase change becomes maximum, and the pupil radius positions satisfy the following condition “r2 ≧ r3 ≧. a single objective lens Ri light emitted from the light source into a plurality of optical recording media in the best condition possible condensing, best recording, can be reproduced.
[0022]
An optical pickup according to a fourth aspect of the present invention is the optical pickup according to the first aspect, wherein a plurality of light sources have wavelengths: λ1, λ2,... Λi (λ1 <λ2 <. At least one of recording, reproduction, and erasing is performed on the optical recording media 1, 2,... I according to NA1, NA2,. When the pupil radius positions at which the spherical aberration generated at the maximum is R1, R2, ..., Rg, Rh, ... Ri (R1 ≥ R2 ≥ ... ≥ Rg ≥ Rh ... ≥ Ri), the liquid crystal element has the maximum phase change. Pupil radius position: r1, r2,... Rx,... Rj (x <j <i), and the pupil radius position: rx satisfies the following condition “rx = (Rg + Rh) / 2”. For each pupil radius position where the assumed spherical aberration is the maximum, Additional phase at the pupil radius position of the constitutes the liquid crystal element so that the maximum, can be simplified electrode pattern of the liquid crystal element.
[0023]
An optical pickup according to a fifth aspect of the present invention is the optical pickup according to the first aspect, wherein a plurality of light sources have wavelengths: λ1, λ2,... Λi (λ1 <λ2 <. NA1, NA2,... NAi (NA1 ≧ NA2 ≧... ≧ NAa ≧ NAb ≧ NAc. Performing the above, when the objective lens is used in a finite system for the optical recording medium b, the liquid crystal element determines the pupil radius positions at which the phase change becomes maximum: r1, r2,..., Ra, rc,. When the objective lens is used in a finite system with respect to at least one of the plurality of light sources, the pupil radius position satisfies the following condition “r1 ≧ r2 ≧... Ra ≧ rc. The liquid crystal element is By giving a phase change Te, it is possible to simplify the electrode pattern of the liquid crystal element.
[0024]
The optical pickup according to the sixth and seventh aspects is an optical pickup that performs at least one of recording, reproducing, and erasing of information on an optical recording medium, and has a wavelength of λ1, λ2, λ3 (λ1 .Ltoreq..lambda.2.ltoreq..lambda.3), an objective lens for converging the light emitted from the light source on the optical recording medium, and a numerical aperture: NA1, NA2, NA3 (NA1.gtoreq.NA2.gtoreq.NA3). An aperture limiting means for switching, and a liquid crystal element for giving a change in phase distribution to a passing light beam by applying a voltage, wherein the liquid crystal element gives a concentric phase change to the optical axis center of the passing light beam, and the concentric phase change is generated. The pupil radius position r2 has a maximum pupil radius position r3, and the pupil radius position r3 is at a different electrode surface of the opposing electrode. The pupil radius position r2 is substantially in the area of the numerical aperture: NA2 to NA3. Position r3 is almost open Number: Due to the configuration formed in the area within NA3, the liquid crystal element gives a concentric phase change to the optical axis center of the passing light beam, and pupil radius positions r2 and r3 at which the concentric phase change becomes maximum. The pupil radius position r2 and the pupil radius position r3 are on the same electrode surface of the counter electrode, the pupil radius position r2 is substantially in the area of numerical aperture: NA2 to NA3, and the pupil radius position r3 is substantially in the numerical aperture: NA3. The liquid crystal element that generates spherical aberration of the opposite polarity to the spherical aberration that occurs due to the difference in wavelength or the difference in substrate thickness by the configuration formed in the area of Can generate a spherical aberration of opposite polarity on the same electrode surface to reduce the size of the liquid crystal element, collect light emitted from a light source on a plurality of optical recording media in the best condition, and perform recording and reproduction.
[0025]
Further, in the optical pickup according to the eighth aspect, in the optical pickup according to the sixth or seventh aspect, the objective lens is formed by changing the wavelength of the three light sources: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3). When the light source of λ2 is turned on, the phase correction regions of λ2 and λ3 of the liquid crystal element can be made different by the configuration used in a finite system, and they can be formed on the same electrode surface, and the amount of phase correction of the liquid crystal element can be reduced. As a result, the driving time during aberration correction can be reduced.
[0026]
An optical pickup according to a ninth aspect of the present invention is an optical pickup that performs at least one of recording, reproducing, and erasing of information on an optical recording medium, and has a wavelength of λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3), an objective lens for condensing the light emitted from the light source on the optical recording medium, and an aperture for switching the numerical aperture: NA1, NA2, NA3 (NA1 ≧ NA2 ≧ NA3). Limiting means, and a liquid crystal element that changes the phase distribution of the passing light beam by applying a voltage, the liquid crystal element gives a concentric phase change at the optical axis center of the passing light beam, and the concentric phase change is maximized. Pupil radius position r2, which is formed in a region of approximately numerical aperture: NA2 to NA3, has a spherical aberration having a polarity opposite to that of spherical aberration generated due to a difference in wavelength or substrate thickness. Same electricity Is generated on the surface, the light emitted from the light source into a plurality of optical recording medium is condensed in the best condition, the recording can be reproduced.
[0027]
Further, in the optical pickup according to the tenth aspect, in the optical pickup according to the ninth aspect, the objective lens is configured such that the wavelength: λ2 and λ2 among λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3). When the light source of wavelength: λ3 is turned on, the driving time for aberration correction can be reduced by reducing the phase correction amount of the liquid crystal element by using a finite system, and the light emitted from the light source can be optimally recorded on the optical recording medium. Light can be collected and recorded and reproduced.
[0028]
The optical pickup according to claims 11 and 12 is the optical pickup according to claims 1 to 10, further comprising an optical recording medium discriminating means for discriminating the optical recording medium, and according to a signal from the optical recording medium discriminating means. An additional phase amount of the liquid crystal element, and a pupil radius position at which the additional phase amount is maximum, and a spherical aberration detecting unit for detecting a spherical aberration generated on the optical recording medium. With the configuration in which the amount of additional phase of the liquid crystal element is changed according to the signal, the light emitted from the light source can be condensed in the best condition for each optical recording medium, and recording and reproduction can be performed.
[0029]
According to a thirteenth aspect of the present invention, in the liquid crystal element of the optical pickup according to the seventh or ninth aspect, the opposing electrode surface of the concentric phase adding surface is a 2n region (n) symmetrically divided about the optical axis center. (Integer), spherical aberration and coma aberration can be corrected on the same electrode surface of the liquid crystal element, and the light emitted from the light source is condensed on the optical recording medium in the best condition for recording. , Playback can be performed.
[0030]
Further, the optical pickup according to claim 14 or 15 is the optical pickup according to claim 13, further comprising means for generating a coma aberration signal from an interference pattern of light reflected from the optical recording medium, and based on the coma aberration signal. Means for controlling the amount of additional phase of the liquid crystal element, and means for detecting the amount of misalignment of the objective lens from substantially the center of the optical axis, and detecting the amount of additional phase of the liquid crystal element based on a signal of the detected amount of misalignment. With the configuration for controlling, it is possible to correct the positional deviation between the liquid crystal element and the objective lens, converge the light emitted from the light source on the optical recording medium in the best condition, and perform recording and reproduction.
[0031]
An optical pickup according to a sixteenth aspect is the optical pickup according to the first to fifteenth aspects, wherein at least one of the plurality of optical recording media is a multilayer optical recording medium in which information recording layers are multiplexed. In addition, the configuration in which the amount of additional phase of the liquid crystal element is changed according to the position of the information recording layer for performing recording and reproduction of the multilayer optical recording medium makes it possible to optimize the light emitted from the light source corresponding to the plurality of optical recording media. In this state, recording and reproduction can be performed by condensing light.
[0032]
The optical pickup according to the seventeenth to nineteenth aspects is the optical pickup according to the first to sixteenth aspects, further comprising an aperture limiting unit that switches a numerical aperture of light emitted from the light source according to a wavelength used by the light source. That the limiting means is integrated with the liquid crystal element, further comprising a polarizing element that changes the polarization state of the light emitted from the light source according to the wavelength used by the light source, wherein the polarizing element is integrated with the liquid crystal element, In addition, the liquid crystal element can be moved integrally with the objective lens, so that the configuration of the optical pickup can be integrated and downsized, and the light emitted from the light source can be collected and recorded on multiple optical recording media in the best condition. , Playback can be performed.
[0033]
According to a twentieth aspect of the present invention, an optical information processing apparatus uses the optical pickup according to any one of the first to nineteenth aspects to collect light emitted from a light source on a plurality of optical recording media in the best condition. Thus, at least one of recording, reproducing, and erasing of information can be performed on the optical recording medium.
[0034]
BEST MODE FOR CARRYING OUT 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 working wavelength of 400 nm, NA of 0.65 and a light-irradiation-side substrate of 0.6 mm” according to Embodiment 1 of the present invention, and “a working wavelength of 660 nm, NA of 0.65, and a light-irradiation-side substrate. Outline of an optical pickup capable of recording, reproducing, or erasing both a DVD optical recording medium having a thickness of 0.6 mm and a CD optical recording medium having a working wavelength of 780 nm, NA of 0.50 and a light-irradiation side substrate of 1.2 mm. FIG. 3 is a diagram illustrating a configuration.
[0036]
As shown in FIG. 1, the main parts of the optical pickup include 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. , An objective lens 108, a detection lens 110, a light beam splitting means 111, and a light receiving element 112.
[0037]
A DVD optical system including a hologram unit 201, a coupling lens 202, dichroic prisms 203 and 303, a prism 104, a liquid crystal element 105, a wavelength plate 106, an aperture limiting element 107, and an objective lens 108 through which light having a wavelength of 660 nm passes. Is configured.
[0038]
Furthermore, a hologram unit 301, a coupling lens 302, a dichroic prism 303, a prism 104, a liquid crystal element 105, a wavelength plate 106, an aperture limiting element 107, and a CD optical system through which light having a wavelength of 780 nm passes are constituted. Have been. That is, the dichroic prisms 203 and 303, the prism 104, the liquid crystal element 105, the wavelength plate 106, the aperture limiting element 107, and the objective lens 108 are common components used in two or three optical systems.
[0039]
Here, in the first embodiment, the objective lens 108 has a wavefront of spherical aberration at infinite system incidence with respect to “a blue optical recording medium having a wavelength of 400 nm, NA of 0.65, and a light-irradiation side substrate 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 operating wavelengths. The optical recording medium 109a is a blue optical recording medium having a substrate thickness of 0.6 mm. The DVD-type optical recording medium having 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. During recording or reproduction, only one of the optical recording media is set on a rotating mechanism (not shown) and rotated at high speed.
[0041]
Further, in the first embodiment, a description will be given of an embodiment of an optical pickup which can correspond to a two-layer type optical recording medium having a blue optical recording medium having two information recording surfaces. The two-layer optical recording medium has a first-layer information recording surface via a transparent substrate having a substrate thickness of 0.6 mm, and a second-layer information recording surface further deeper than the first-layer information recording surface. Have. A layer called a spacer layer is formed between the first layer and the second layer, and has a thickness of about 30 μm.
[0042]
In the first embodiment, the objective lens 108 has a spherical surface at infinite system incidence with respect to “the first layer of the blue optical recording medium having a wavelength of 400 nm, NA of 0.65, and a light-irradiation side substrate of 0.6 mm”. It is designed to minimize the wavefront of aberration.
[0043]
First, the operation of the optical pickup configured as described above will be described for the case of recording, reproducing, or erasing a “blue optical recording medium with a wavelength of 400 nm, NA of 0.65, and a light-irradiation side substrate of 0.6 mm”. I do. The divergent light of linearly polarized light emitted from the semiconductor laser 101 having a wavelength of 400 nm is converted into substantially parallel light by a collimating lens 102, passes through a polarizing beam splitter 103, dichroic prisms 203 and 303, and is deflected by 90 degrees in an optical path by a prism 104. The light passes through the liquid crystal element 105, passes through the wavelength plate 106, is converted into circularly polarized light, is limited to NA 0.65 by the aperture limiting element 107, is incident on the objective lens 108, and is focused on the optical recording medium 109a as a minute spot. . The reproduction, recording, or erasing of information is performed by the spot.
[0044]
The light reflected from the optical recording medium 109a becomes circularly polarized light in the opposite direction to the outward path, becomes substantially parallel light again, passes through the wave plate 106, becomes linearly polarized light orthogonal to the outward path, and is reflected by the polarization beam splitter 103. The light is reflected, converted into convergent light by the detection lens 110, deflected and divided into a plurality of optical paths by the light beam splitting means 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 case of recording, reproducing, or erasing a “DVD-based optical recording medium having a wavelength of 660 nm, an NA of 0.65, and a substrate thickness of 0.6 mm on the light irradiation side” will be described. In recent years, a hologram unit in which a light receiving / emitting element is installed in one can and a light beam is separated using a hologram has been generally used for a DVD pickup. FIG. 2 shows a hologram unit 201 formed by integrating a semiconductor laser 201a, a hologram 201b, and a light receiving element 201c.
[0046]
The light of 660 nm emitted from the semiconductor laser 201a of the hologram unit 201 passes through the hologram 201b and is converted into a predetermined divergent beam by the coupling lens 202. The light of wavelength 400nm is transmitted and the light of wavelength 660nm is reflected. The light is reflected by the dichroic prism 203 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, the light passes through the wave plate 106, and is converted into circularly polarized light or elliptically polarized light. The element 107 is not affected at all, enters the objective lens 108, and is focused as a minute spot on the optical recording medium 109b. The reproduction, recording, or erasing of information is performed by the spot.
[0047]
The light reflected from the optical recording medium 109b is deflected by the prism 104, reflected by the dichroic prism 203, is converged by the coupling lens 202, and is converged by the hologram 201b as shown in FIG. The light is diffracted in 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]
Subsequently, the case of recording, reproducing, or erasing a “CD-based 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” will be described. A hologram unit that separates a light beam using a hologram, in which a light emitting and receiving element is installed in one can, is generally used for a pickup of a CD system as well as a DVD system. 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 passes through the hologram 301b and is converted into a predetermined divergent beam by the coupling lens 302, and the light in the blue and red wavelength bands is transmitted and transmitted in the infrared wavelength range. The light in the band is reflected in the direction of the prism 104 by the dichroic prism 303 that reflects the light, the optical path is deflected by 90 degrees by the prism 104, passes through the liquid crystal element 105 without any action, passes through the wave plate 106, and passes through the wave plate 106 to obtain elliptically polarized light or circular light. The light is polarized, is limited to an NA of 0.50 by the aperture limiting element 107, is incident on the objective lens 108, and is focused on the optical recording medium 109c as a minute spot. The reproduction, recording, or erasing of information is performed by the spot.
[0050]
The light reflected from the optical recording medium 109c is deflected by the prism 104, reflected by the dichroic prism 303, converted into convergent light 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 a liquid crystal element in the optical pickup according to the first embodiment. FIGS. 4A and 4B are diagrams illustrating examples of electrode patterns of the liquid crystal element. The configuration and operation principle will be described below with reference to FIGS. 3, 4A and 4B.
[0052]
The liquid crystal element according to the first embodiment shown in FIG. 3 has a known configuration described in Patent Document 8, in which glass substrates 1a and 1b are adhered by conductive spacers 2 to form a liquid crystal cell. On the inner surface of the glass substrate 1a, the electrode 4a, the insulating film 5, and the alignment film 6 are arranged in this order from the inner surface. On the inner surface of the glass substrate 1b, the electrode 4b, the insulating film 5, and the alignment film 6 are arranged in order. Coated.
[0053]
The electrode 4a is patterned so that it can be connected to a 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 section 7. Liquid crystal 3 is filled inside the liquid crystal cell.
[0054]
The electrodes formed on the substrate that constitutes the above-described liquid crystal element and sandwich the liquid crystal layer are provided with a power supply portion within a uniform electrode as disclosed in paragraphs [0026] to [0036] of Patent Document 8. May be used, or a segment type configuration disclosed in Patent Document 6 may be used. In the first embodiment, the electrode pattern is formed concentrically about the center of the optical axis. FIG. 4A is a conceptual diagram of the electrode pattern when the former method is used, and FIG. FIG. 4B is a conceptual diagram of the electrode pattern of FIG.
[0055]
Further, in the optical pickup according to the first embodiment, it is necessary to switch the NA (numerical aperture) according to the optical recording medium set in the rotating mechanism. When the focal length of the objective lens is f and the effective diameter of the light beam used for light collection is φ, NA is given by (Equation 2).
[0056]
(Equation 2)
NA = φ / 2 / f
Therefore, means for switching the passing light beam diameter according to the wavelength used may be used. An aperture limiting element 105 (see FIG. 1) is used as means for switching the light beam diameter according to the lighting light source. The aperture limiting element may be any element that switches the beam diameter using any one of the optical characteristics of reflection, diffraction, and absorption according to the wavelength band or the polarization direction.
[0057]
That is, when light having the same light beam diameter and a wavelength of 660 nm is incident on an objective lens having the best wavefront at a wavelength of 400 nm, the refractive power is reduced and the NA is reduced. For this reason, in the present invention, light having a wavelength 660 nm is incident with a light beam diameter φ2 slightly larger than the incident light beam diameter φ1 at a wavelength of 400 nm. FIG. 5 (a) shows the relationship between the effective diameter and the wavelength of NA 0.65 in an objective lens having the characteristics described in (Table 1) described later.
[0058]
From FIG. 5A, it can be seen that the luminous flux diameter φ2 needs to be about 4.02 mm at the time of recording and reproduction of a DVD optical recording medium using a wavelength of 660 nm. The relationship between the luminous flux diameters φ1 and φ2 also differs 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 of FIG. 5A, and φ2 / φ1 when the glass type is changed, and the refractive index nd at d-line of the glass type used. And an appropriate φ2 may be selected according to the glass type of the objective lens.
[0059]
On the other hand, the optimum NA for recording and reproducing information on and from a CD optical recording medium is about 0.50, but when the optimum effective diameter φ3 is estimated by the same method as in FIG. It can be seen that the distance should be about 2 mm.
[0060]
For example, as an aperture limiting element utilizing reflection characteristics, which 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. Means for switching the light beam diameter by reflection may be used, and as an aperture limiting element utilizing diffraction characteristics, the light beam diameter is switched by diffraction according to the wavelength of the light beam emitted from the light source as shown in FIG. Means may be used, and further, as an aperture limiting element utilizing absorption characteristics, means for switching the light beam diameter by absorption as shown in FIG. 6C 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 circularly polarized light to linearly polarized light, and light having wavelengths of 660 nm and 780 nm can be converted from linearly polarized light to circularly polarized light or elliptically polarized light, or the like. A wave plate capable of performing reverse conversion is provided. This wave plate can convert both 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 so-called wave plate is formed of a crystal in which the phase difference between the ordinary ray (refractive index no) and the extraordinary ray (refractive index ne) at a certain thickness t is 1/4 of the wavelength of 400 nm, 660 nm and 780 nm. What is necessary is just to employ the wave plate which becomes. That is, any crystal that satisfies 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; for light from a light source having a wavelength of 400 nm (no-ne)
[0063]
(Equation 4)
Δn2 × t = {(2q + 1) / 4} × 660 (q = 0, 1,...)
Δn2; for light from a light source having a wavelength of 660 nm (no-ne)
[0064]
(Equation 5)
Δn3 × t = {(2r + 1) / 4} × 780 (r = 0, 1,...)
Δn3; for light from a light source having a wavelength of 780 nm (no-ne)
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, and the optical path from the optical recording medium cannot be sufficiently determined. About 30% of the returned light returns to the light source. Generally, such return light destabilizes the oscillation state of the semiconductor laser as a noise component.
[0065]
However, in the first embodiment, by disposing 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 disposing a wavelength plate having such characteristics, for example, for the blue optical recording medium of FIG. 1, a polarization separation optical system in which the polarization beam splitter 103 and the wavelength plate 106 are combined is realized. As a result, a sufficient amount of light can be obtained, and noise generation due to light returning to the semiconductor laser 101 can be reduced. Similarly, for 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, as a configuration of a wave 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 from circularly polarized light to linearly polarized light, and converting light having a wavelength of 780 nm to elliptically polarized light, It is sufficient that the conditions of (Equation 3) and (Equation 4) are satisfied.
[0068]
Further, the configuration of the wave 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 wavelengths of 660 nm and 780 nm to elliptically polarized light is as follows: Should be satisfied.
[0069]
The wavelength plate is not limited to a crystal satisfying (Equation 3), (Equation 4), and (Equation 5). For example, a configuration in which phase difference elements of organic materials are stacked and arranged may be sandwiched between glass plates. 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 light beam splitting unit 111 and the light receiving element 112, and the liquid crystal element 106 corresponds to a “spherical aberration correcting unit”. As described above, when there is a thickness error in the optical recording medium, the shape of the light spot formed on the recording surface deteriorates. The aberration thus generated distorts the wavefront of the returning light beam, and the light beam traveling toward the light receiving element 112 via the detection lens 110 also has an aberration. FIG. 7 shows this state.
[0071]
When a 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. The position where the wavefront delayed with respect to the focal point converges is defocused. Therefore, by detecting the difference between the delayed wavefront and the advanced wavefront and detecting the focus state, it is possible to know the “state of occurrence 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 as to detect each of the split light beams may be prepared. The light speed splitting unit 111 converts a half area symmetrically split in the jitter direction in the plane orthogonal to the optical axis into a hologram split into two concentric inner and outer areas. The light receiving element 112 is a two-divided light receiving element that detects each light beam diffracted by the hologram. Then, the moving amount 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. I do.
[0073]
(Equation 6)
W1 = (Sa−Sb−Sc + Sd)
W1 = 0 means no aberration.
[0074]
In addition, the liquid crystal element 105 applies a predetermined voltage to the power supply unit 11 or the divided electrode 15 as shown in FIGS. 4A and 4B, and changes the refractive index of the liquid crystal from n1 to n2 in a concentric manner. 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 phase difference: 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 upper part of FIGS. 10 (a) and 11 (a). When the electrode shown in FIG. 4A is used, a phase difference as shown by a broken line in a lower portion of FIG. As described above, by adjusting the voltage applied to each of the concentric band feeding portions 11 of the liquid crystal element, the "wavefront of spherical aberration" can be canceled due to the delay of the wavefront at each part of the light beam transmitted through the liquid crystal element.
[0076]
In addition, when the split electrode shown in FIG. 4B is used, the light flux incident on the objective lens from the light source side is not affected by such spherical aberration 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 provide a phase difference, the "wavefront of spherical aberration" can be canceled due to 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 (wavefront of spherical aberration) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 10A, that is, the corrected wavefront of spherical aberration. It becomes much smaller than the wavefront of the original spherical aberration (the solid line in the upper part of FIG. 10A). FIG. 11B shows the sum of the solid line (wavefront of spherical aberration) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 11A, that is, the corrected wavefront of spherical aberration. It becomes much smaller than the wavefront of the original spherical aberration (the solid line in the upper part of FIG. 11A).
[0077]
In the first embodiment, recording and reproduction of a blue optical recording medium, a DVD optical recording medium, and a CD optical recording medium are also performed. As a means for determining a 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. In other words, a configuration may be used in which, when an optical recording medium is inserted, one of the blue and red light sources is turned on and discrimination is performed based on a return light amount level when a focus search is performed.
[0078]
As described above, when a light beam from this light source is made incident on an objective lens during recording / reproduction of a DVD, spherical aberration occurs due to a difference in wavelength or substrate thickness, and the shape of a light spot formed on the recording surface is reduced. to degrade. The amount of spherical aberration of the opposite polarity that cancels out the generated spherical aberration is stored in advance for each optical recording medium, and the spherical aberration of the opposite polarity is stored in accordance with the type of the optical recording medium detected by the optical recording medium discriminating means. Should be given.
[0079]
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 minimum wavefront of spherical aberration at a wavelength of 400 nm to form a spot on a DVD-based optical recording medium 109b. When the light having a wavelength of 780 nm is incident in an infinite system to form a spot on the CD-based optical recording medium 109c, the spherical aberration caused by the difference in wavelength or the difference in substrate thickness as shown in FIGS. Occurs.
[0080]
The liquid crystal device 105 shown in FIG. 1 is provided to generate a spherical aberration having a polarity opposite to that of the generated spherical aberration as shown in FIGS. In addition, as shown in FIG. 14, the blue optical recording medium 109a also generates a spherical aberration having a polarity opposite to that of the spherical aberration generated during recording and reproduction of a two-layer optical recording medium.
[0081]
Therefore, in order to give spherical aberration of the opposite polarity to the following spherical aberration,
(1) Spherical aberration generated due to the difference in wavelength used when compatible with DVD
(2) Spherical aberration caused by differences in wavelength used and substrate thickness when compatible with CD
{Circle around (3)} As a blue optical recording medium, spherical aberration caused by a difference in interlayer distance between two-layer optical recording media
In each case, the optical recording medium can be determined 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 the optical recording medium. Further, in a two-layer blue optical recording medium, a predetermined phase shape is given according to the position of the information layer for recording and reproduction.
[0082]
The electrode configuration of the liquid crystal element for correcting the two different spherical aberrations may be, for example, as shown in FIG. That is, the continuous transparent electrodes 10a and 10b are paired, and the metal electrodes 12a to 14a and 12b to 14b are formed on the transparent electrodes 10a and 10b, respectively. The metal electrodes are connected to external signal sources by metal wiring, respectively, and can supply arbitrary voltages by external signals. In the first embodiment, the spherical aberration generated when recording / reproducing a DVD color optical recording medium (and a second layer in a two-layer type blue optical recording medium) as the metal electrode 13a is maximized. The metal electrode 13b is formed at the pupil radius position where the spherical aberration generated when trying to record / reproduce a CD optical recording medium is maximized.
[0083]
Specifically, when the objective lens whose outline data is shown in FIG. 17 and the shape data is shown in (Table 1) is used, the incident beam diameter of the objective lens in each of the optical paths of blue, DVD, and CD 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 with φ: 4.02 mm, which is substantially equal to that of 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]
Figure 2004127473
[0085]
In the first embodiment, there are roughly three types of spherical aberration, that is,
(1) Spherical aberration generated due to the difference in wavelength used when compatible with DVD
(2) Spherical aberration caused by differences in wavelength used and substrate thickness when compatible with CD
{Circle around (3)} As a blue optical recording medium, spherical aberration caused by a difference in interlayer distance between two-layer optical recording media
12 and FIG. 14, as is clear from FIGS. 12 and 14, the positions where the spherical aberration is maximized in (1) and (3) substantially coincide with each other. The patterns 13a and 13b may be used (see FIG. 15). This is because the blue optical path has the same NA and substrate thickness as those of the DVD system.
[0086]
Then, for example, when the optical recording medium discriminating means recognizes that the DVD-based optical recording medium has been inserted into the liquid crystal element having such an electrode pattern, the additional phase amount becomes maximum. When a pre-stored applied voltage is applied to each electrode so that the position becomes the metal electrode 13a, and it is recognized that the CD-based optical recording medium has been inserted, the position where the amount of additional phase becomes maximum becomes the metal electrode 13b. A pre-stored applied voltage is applied to each electrode such that Also, when it is recognized that the medium is a blue optical recording medium, in the case of a two-layer type blue optical recording medium, at the time of recording / reproducing of the first layer, the liquid crystal element does not act at all, and focus jump is performed to the second layer. When the recording / reproduction is started in step (1), an applied voltage stored in advance is applied to each electrode so that the position where the amount of additional phase becomes maximum is the metal electrode 13a.
[0087]
Note that the electrode configuration of the liquid crystal element is not limited to FIG. Metal electrodes 22 to 25 are formed on one continuous transparent electrode 20 (a pair of transparent electrodes 10a and 10b in FIG. 15) as shown in FIG. When a DVD optical recording medium is formed as an optical path and formed at a pupil radius position where the amount of additional phase is maximized during recording / reproducing as a metal electrode 23, and recording / reproducing of a CD optical recording medium is attempted as a metal electrode 24. It may be formed at the pupil radius position where the generated spherical aberration is maximized.
[0088]
Also, a divided electrode region 26 is formed as a divided electrode on the transparent electrode 20 (a pair of the transparent electrodes 10a and 10b in FIG. 15) as shown in FIG. Divided electrode regions 27 and 28 are formed on the inner periphery of 26 (1 <divided electrode region 28 <divided electrode region 27 <divided electrode region 26). The divided electrode region 27 is formed at the pupil radius position where the spherical aberration generated when recording / reproducing the second layer of the two-layer type blue optical recording medium or the DVD color optical recording medium is maximized. The region 28 may be formed at a pupil radius position at which spherical aberration generated when recording / reproducing on a CD-based optical recording medium is maximized.
[0089]
Further, in the first embodiment, as shown in FIG. 19A, the aperture limiting element 107, the liquid crystal element 105, and the wavelength plate 106 may be integrally formed as a composite element. Thereby, the assembly process can be simplified. Further, the structure of another composite element 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. Is also good. As described above, it is possible to further reduce the thickness and weight of the element, for example, by unifying components and mounting the actuator.
[0090]
Further, in the optical pickup according to the first embodiment, as another electrode pattern of the liquid crystal element, for example, a plurality of power supply units are provided so that spherical aberration is maximized at different pupil radius positions as shown in FIG. On the other hand, even if the electrode is configured such that the peak position always occurs at the approximate center position (arrow C in FIG. 20) of the spherical aberration occurring at different peak positions as shown in FIGS. 12, 13, and 14. Good. Then, a predetermined phase amount is added according to the optical recording medium determination signal and the spherical aberration signal, and a predetermined phase amount is determined according to the switching of the first / second recording / reproducing layer by the optical recording medium determination signal. May be added. With this configuration, the electrode pattern can be simplified.
[0091]
Making the optical path of the DVD system a finite system means that the light beam incident on the objective lens is in a divergent state or a convergent state. In general, changing the divergence state of the light beam incident on the objective lens is equivalent to changing the spherical aberration, so that a divergence state capable of reducing the spherical aberration may be selected. The spherical aberration of the DVD optical path can be suppressed by such a finite system method (see FIG. 35). In the first embodiment, when the DVD optical path is constituted by a finite system, the substrate thickness error of the blue optical recording medium is reduced. The electrode pattern of the liquid crystal element may be configured so as to suppress only the spherical aberration generated due to the above. The phase addition region of the liquid crystal element includes a DVD-based NA: 0.65 and a CD-based NA: 0 of the outer peripheral portion. It may be specialized 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 optical path, an aberration correction area was formed in a range of NA: 0.50 or less for the CD system.
[0092]
Next, FIG. 21 shows an optical pickup having another configuration according to the second embodiment. As with the configuration of the optical pickup described in the first embodiment, “use wavelength 400 nm, NA 0.65, light irradiation side substrate” A 0.6-mm thick blue (large capacity) optical recording medium, a DVD-based optical recording medium with a working wavelength of 660 nm, NA of 0.65, and a light-irradiation side substrate of 0.6 mm, and a working wavelength of 780 nm, NA 0. 50 is a diagram showing a schematic configuration of an optical pickup capable of recording, reproducing, or erasing a CD-based optical recording medium having a thickness of 1.2 mm on a light irradiation side substrate. The difference from the first embodiment is that the hologram unit 401 in which the light source, the light receiving element, and the optical path separating means are housed in a single package is also used for the blue light path. This makes it possible to reduce the size of the optical system and simplify the assembly.
[0093]
Similarly, FIG. 22A is a diagram illustrating a schematic configuration of another optical pickup according to the first embodiment. As in the optical pickup of the first embodiment described above, a “blue (large capacity) 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” and a working wavelength of 660 nm, NA of 0.65, Light capable of recording, reproducing, or erasing both a DVD-based optical recording medium having a light-irradiation-side substrate thickness of 0.6 mm and a CD-based 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. It is a pickup. The difference from the first embodiment is that the light source, light receiving element, and optical path separating means of the DVD / CD are integrated into a single package. Thus, the three-wavelength optical system is realized by a small optical pickup. Note that the hologram 301b may have a structure including a layer having a hologram surface for DVD and a layer having a hologram surface for CD as shown in FIG.
[0094]
Further, as Embodiment 2 of the present invention, a configuration of an optical pickup described below may be adopted. The optical pickup according to the second embodiment is different from the optical pickup described in the first embodiment in that the optical pickup also has a finite optical path in the CD optical path. By using a finite system in the CD optical path, it is possible to sufficiently suppress the wavefront aberration. For this reason, the spherical aberration of the optical path of the CD system can be suppressed, so that the liquid crystal element does not need to operate on the optical path. That is, it is possible to reduce the number of electrode patterns for the CD optical path formed on the liquid crystal element as compared with the configuration of the first embodiment.
[0095]
Further, as the third embodiment of the present invention, in the liquid crystal element used in each of the above-described embodiments, when the center axis of the objective lens coincides with the optical axis, a pattern capable of performing optimal aberration correction is provided. Designed. Therefore, when a displacement 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 deviation between the aberration distribution requiring correction and the correction pattern formed on the liquid crystal element occurs. A position shift occurs, and the function of aberration correction deteriorates. A simple explanation will be given using FIGS. 23 (a), 23 (b) and 23 (c). When the wavefront of the spherical aberration generated at the time of DVD or CD compatibility is in the upper part of FIG. 23A, the light beam incident on the objective lens from the light source side has the same shape as shown in the lower part of FIG. As described above, it is possible to provide a phase difference and cancel a wavefront of an unnecessary aberration. Here, when a position shift occurs between the liquid crystal element and the objective lens as shown in FIG. 23B, an unnecessary aberration wavefront as shown in FIG. 23C is generated.
[0096]
In order to improve the function deterioration of aberration correction based on the objective lens shift, there is a method of mounting a liquid crystal element on a movable part (actuator) and driving the liquid crystal element integrally with the objective lens. However, it is desired that the liquid crystal element having this configuration be installed outside the objective lens actuator from the viewpoint of an increase in weight and an increase in the number of signal lead wires.
[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 which is anti-symmetric with respect to the optical axis. This shape shows a shape equivalent to the coma aberration described in Non-Patent Document 3, for example. In the third embodiment, unnecessary aberrations generated during DVD and CD compatibility can be corrected by devising the electrode pattern of the liquid crystal element as coma aberration correcting means as described later.
[0098]
As described above, the relative positional displacement between the liquid crystal element that corrects the wavefront shape symmetrically with respect to the optical axis and the objective lens causes unnecessary coma aberration. The third embodiment includes such a coma aberration detecting optical system that mainly includes the detection lens 110 and the light receiving element 112 (see FIG. 1), so that such unnecessary coma aberration can be detected.
[0099]
Guide grooves are formed in the optical recording medium 109 as shown in FIG. The reflected light from the guide groove includes the 0th-order light, which is directly reflected light, and the diffracted ± 1st-order diffracted light, and these lights interfere with each other. FIG. 24B is a diagram of the 0th-order light (straight traveling light) and ± 1st-order diffracted light received on the light receiving surface of the light receiving unit when viewed from above the light receiving surface of the light receiving element 112. The zero-order light (straight-forward light) and the ± first-order diffracted lights have overlapping portions, and the overlapping portions are called interference regions.
[0100]
How this interference region changes with coma will be described with reference to FIG. FIG. 25 shows how the interference area changes as the objective lens 108 shifts with respect to the liquid crystal element that suppresses spherical aberration. The shift of the objective lens 108 causes a bias in the amount of light on the left and right in the figure. This is because coma aberration occurs in a spot projected on the optical recording medium 109 due to a relative positional shift between the objective lens 108 and the liquid crystal element 105. This deviation occurs in the opposite direction between the one interference region and the other interference region. In FIG. 25, it can be seen that the larger the displacement, the stronger the area on the right in the figure and the weaker the area on the left.
[0101]
In the third embodiment, the coma 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 in the rotation direction (tangential direction) of the optical recording medium 109. I have. 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 rotation direction. The light amount signals output from the a region 112a, the b region 112b, and the c region 112c are denoted by A, B, and C, respectively. Of the two areas in the radial direction of the optical recording medium 109, three areas included in the other are defined as a d area 112d, an e area 112e, and an f area 112f. The light intensity signals output from the d region 112d, the e region 112e, and the f region 112f are D, E, and F, respectively. The calculation means 113 is composed of an addition means and a subtraction means.
[0102]
The light amount signals output from the respective regions of the light receiving element 112 are input to the calculating means 113, where a predetermined calculation is performed, and the calculation result is a signal indicating the coma in the radial direction (radial direction) of the optical recording medium: COMA is output from the arithmetic means 113. When the calculation by the calculation means 113 is expressed by an equation, it becomes (Equation 7).
[0103]
(Equation 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 shift between the objective lens 108 and the liquid crystal element 105 using the calculating means 113 of (Formula 7). In FIG. 27, the horizontal axis represents the relative displacement 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 driving the liquid crystal element 105 by detecting coma, 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 control of the element 105 may be performed. To detect the amount of displacement, a well-known PSD (Position Sensor Device) may be arranged on the pickup fixed optical system to detect the distance between the objective lens and the PSD. Then, the detected positional deviation amount is converted into a coma aberration amount based on a table (not shown) stored in advance. The driving of the liquid crystal element 105 is controlled in accordance with the amount of coma.
[0105]
As shown in FIG. 28, the coma aberration correcting means is arranged to face a DVD / CD compatible pattern (see FIGS. 4A and 4B) of the liquid crystal element 105 having a predetermined electrode pattern. As shown in FIG. 28, in the liquid crystal element 105, at least one of the transparent electrodes is divided symmetrically so that a voltage can be independently applied to each electrode portion (and between the common electrode). By controlling the voltage, the refractive index n of the liquid crystal at 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 a change in the refractive index, d is the cell thickness of the liquid crystal), that is, the phase difference Δn · d (2π / λ).
[0106]
For example, it is assumed that coma as shown in FIG. 29 has occurred. The upper part of FIG. 30A shows this wavefront aberration as a three-dimensional curve. The liquid crystal element 105 shown in FIG. 28 is provided so that a light beam incident on the objective lens 108 from the light source side has a phase difference as shown in the lower part of FIG. By adjusting the voltage applied to each of the electrodes, it is possible to cancel out the “aberration wavefront” due to the delay of the wavefront of each part of the light beam transmitted through the liquid crystal element 105. FIG. 30B shows the sum of the solid line (wavefront of coma aberration) 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 portion indicated by the solid line in FIG. 30A).
[0107]
In particular, such a coma aberration correcting electrode surface may be formed on a counter electrode surface of a liquid crystal element having a spherical aberration correcting electrode pattern on only 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 according to Embodiment 4 of the present invention.
[0109]
The information recording / reproducing device 30 is a device that performs at least one of recording, reproducing, and erasing of information on the optical recording medium 40 using the optical pickup 31. In the fifth embodiment, the optical recording medium 40 has a disk shape and is stored in a cartridge 41 in a protective case. The optical recording medium 40 is inserted into the information recording / reproducing apparatus 30 through the insertion port 32 in the direction of the arrow “disc insertion” together with the cartridge 41, is driven to rotate by the spindle motor 33, and records, reproduces, or deletes information by the optical pickup 31. Is performed.
[0110]
As the optical pickup 31, the optical pickup described in the first to third embodiments can be appropriately used.
[0111]
Also, the fifth embodiment is an optical information processing apparatus that performs multi-level recording with an information recording density multiplication degree: P1> 1.8 on an optical recording medium at a used wavelength λ: 400 nm and NA: 0.65. Is also good. Thus, for example, an optical information processing apparatus of 22 GB or more can be realized without using an objective lens having a high NA of 0.85. That is, the recording capacity of the optical recording medium is determined by the spot diameter. Compared with DVD-based optical recording media (4.7 GB), if the blue wavelength band is used, the spot diameter ratio (λ / NA) 2 , The capacity is increased to about 12 GB. By applying the multi-value recording under the above conditions, 22 GB equivalent can be obtained. As a result, it is possible to expand a margin accompanying fluctuations and the like. Since the depth of focus of the objective lens becomes stricter in proportion to the square of NA, the margin of the lens of NA 0.65 can be expanded 1.7 times as compared with the objective lens of NA 0.85.
[0112]
In the above-described embodiments, the wavelengths are limited to 400 nm, 660 nm, and 780 nm for simplicity, but the present invention is applied to the following ranges of optical recording media defined as standards. It is possible.
[0113]
-Blue wavelength band: wavelength 397 nm to 417 nm
・ Red wavelength band: wavelength 650 nm to 670 nm
-Infrared wavelength band: wavelength 770 nm to 790 nm
Similarly, it has been described that each NA (numerical aperture) is limited to 0.65 and 0.50.
· NA of blue optical recording medium: 0.60 to 0.70
· NA of DVD-based optical recording medium: 0.60 to 0.65
· NA of CD optical recording medium: 0.45 to 0.50
Applicable to the range.
[0114]
【The invention's effect】
As described above, according to the present invention, the spherical aberration that occurs when recording and reproduction are performed on a DVD or CD optical recording medium with a blue objective lens, and the substrate thickness variation of the blue optical recording medium. In order to suppress the spherical aberration caused by the interlayer distance of the multilayer type blue optical recording medium with a single liquid crystal element, the information of the large-capacity blue optical recording medium and the information of the conventional DVD-based and CD-based optical recording media is obtained. An advantageous effect is obtained that a good spot can be formed on the recording surface, and a signal can be recorded and reproduced with a high S / N on any of the three-generation optical recording media without increasing the number of components.
[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 configured by integrating a semiconductor laser, a hologram, and a light receiving element.
FIG. 3 is a 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 an electrode pattern of a liquid crystal element.
FIG. 5 (a) shows the relationship between the effective diameter and the wavelength of the objective lens at NA of 0.65, and FIG. 5 (b) shows the relationship 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 type used
FIGS. 6A and 6B are diagrams showing a configuration of an aperture limiting element for switching a light 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 via a detection lens.
FIG. 8 is a view showing a divided light receiving element 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 generated due to a detected substrate thickness error.
10A is a diagram illustrating a wavefront of a spherical aberration (solid line) and a delay of the wavefront due to a liquid crystal element (broken line), and FIG. 10B is a diagram illustrating a wavefront of the corrected spherical aberration as a two-dimensional curve.
11A is a diagram illustrating a wavefront of a spherical aberration (solid line) and a delay of a wavefront due to a liquid crystal element (broken line), and FIG. 11B is a diagram illustrating a wavefront of the spherical aberration after correction as a two-dimensional curve.
FIG. 12 is a diagram illustrating a case where light having a wavelength of 660 nm is incident in an infinite system on a single objective lens having a wavelength of 400 nm and an NA of 0.65 and having a minimum wavefront of spherical aberration to form a spot on a DVD-based 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 in an infinite system on a single objective lens having a minimum wavefront of spherical aberration at a wavelength of 400 nm and NA of 0.65 to form a spot on a CD optical recording medium. Diagram showing spherical aberration
FIG. 14 is a diagram showing spherical aberration generated when recording / reproducing information on / from a second information recording layer of a 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 an objective lens according to the first embodiment.
FIG. 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 diagram showing a configuration of an aperture limiting element, a liquid crystal element, and a composite element integrally formed with a wavelength plate, and FIG. 19B is a view showing a configuration of another composite element.
FIG. 20 is a diagram illustrating an electrode configuration in which a peak position occurs at a substantially central position of spherical aberration occurring at different peak positions as an electrode pattern of the liquid crystal element of the first embodiment.
FIG. 21 is a diagram showing a schematic configuration of an optical pickup having another configuration according to the second embodiment 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. Diagram showing a hologram configuration provided with
23 (a) shows the generated spherical aberration (upper side) and the phase difference added thereto (lower side), FIG. 23 (b) shows the state where the added phase difference is shifted due to the objective lens shift, and FIG. 23 (c) shows the objective lens Diagram showing unnecessary wavefront aberration (residual aberration) generated by shifting
FIG. 24 (a) shows the 0th-order light of the reflected light directly from the guide groove of the optical recording medium, interference with diffracted ± 1st-order diffracted light, and FIG. 24 (b) shows the 0th-order light as viewed from the light receiving surface of the light receiving means. The figure which shows the interference area of (straight-forward light) and 1st-order diffracted light
FIG. 25 is a diagram showing an interference area that changes with a liquid crystal element due to an objective lens shift.
FIG. 26 is a diagram showing a schematic configuration for detecting a generated coma aberration by a light receiving element and an arithmetic unit;
FIG. 27 is a diagram illustrating a result of calculation by a calculation unit of a change in an interference area due to a relative position shift between an objective lens and a liquid crystal element.
FIG. 28 illustrates an electrode pattern of a liquid crystal element.
FIG. 29 is a diagram showing coma aberration generated due to an objective lens shift.
30A is a diagram showing a wavefront (solid line) of a coma aberration and a phase difference (dashed line) given thereto, and FIG. 30B is a diagram showing a corrected wavefront.
FIG. 31 is a transparent perspective view showing a schematic configuration of an information recording / reproducing apparatus which is an optical information processing apparatus according to Embodiment 4 of the present invention.
FIG. 32 is a diagram showing a schematic configuration of a large-capacity optical recording medium using a light source in a blue wavelength band and an optical pickup compatible with an existing DVD or CD.
FIG. 33 is a diagram showing a wavefront of spherical aberration when light is focused on a DVD optical recording medium having a wavelength of 660 nm with infinite system incidence.
FIG. 34 is a diagram showing the wavefront of spherical aberration when light is focused on a CD-based optical recording medium having a wavelength of 780 nm with infinite system incidence.
FIG. 35 is a diagram showing a wavefront of spherical aberration when light is condensed on a DVD-based optical recording medium having a wavelength of 660 nm with finite system incidence.
[Explanation of symbols]
1a, 1b Glass substrate
2 Conductive spacer
3 liquid crystal
4a, 4b electrode
5 Insulating film
6 Alignment film
7 Electrode extraction part
10, 10a, 10b, 20 Transparent electrode
11 Power supply unit
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 device
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 to 112f, a to f area
113 arithmetic means
200 Light source for DVD
201,301 Hologram unit
201b, 301b hologram
202, 302, 502 Coupling lens
203,303 Dichroic prism
Light source for 300 CD

Claims (20)

光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、各々波長の異なる複数の光源と、前記光記録媒体に前記光源からの出射光を集光させるための対物レンズと、電圧印加により通過光束に位相変化を与える液晶素子とを備え、
前記液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、前記同心円状の位相変化が最大となる瞳半径位置、及び付加位相量を前記各光源の点灯に応じて切り換えることを特徴とする光ピックアップ。An optical pickup for performing at least one of recording, reproducing, and erasing of information on an optical recording medium, wherein a plurality of light sources having different wavelengths from each other and light emitted from the light sources are condensed on the optical recording medium. An objective lens, and a liquid crystal element that changes the phase of a passing light beam by applying a voltage.
The liquid crystal element gives a concentric phase change to the center of the optical axis of the passing light beam, and switches the pupil radius position where the concentric phase change is maximum, and the additional phase amount according to the lighting of each light source. An optical pickup characterized by the following. 前記複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡｉ）により光記録媒体１，２，…ｉに記録，再生，消去のうちいずれか１以上を行い、液晶素子が、位相変化の最大となる瞳半径位置：ｒ１，ｒ２，…ｒｉを有し、前記瞳半径位置が次の条件
ｒ１≧ｒ２≧…≧ｒｉ
を満足することを特徴とする請求項１記載の光ピックアップ。.. Λi (λ1 <λ2 <... <Λi) in the plurality of light sources, and the numerical aperture: NA1, NA2,... NAi (NA1 ≧ NA2 ≧... ≧ NAi). , 2,... I, one or more of recording, reproduction, and erasing are performed, and the liquid crystal element has pupil radius positions r1, r2,. Condition r1≥r2≥ ... ≥ri
2. The optical pickup according to claim 1, wherein the following condition is satisfied. 前記複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡｉ）により光記録媒体１，２，…ｉに記録，再生，消去のうちいずれか１以上を行い、対物レンズを、前記光記録媒体１において球面収差の波面が最小となるように設計されたとき、液晶素子が、位相変化の最大となる瞳半径位置：ｒ２，ｒ３…ｒｉを有し、前記瞳半径位置が次の条件
ｒ２≧ｒ３≧…≧ｒｉ
を満足することを特徴とする請求項１記載の光ピックアップ。.. Λi (λ1 <λ2 <... <Λi) in the plurality of light sources, and the numerical aperture: NA1, NA2,... NAi (NA1 ≧ NA2 ≧... ≧ NAi). , 2,... I, one or more of recording, reproduction, and erasure are performed, and when the objective lens is designed so that the wavefront of the spherical aberration in the optical recording medium 1 is minimized, The pupil radius position at which the change is maximum: r2, r3... Ri, and the pupil radius position satisfies the following condition: r2 ≧ r3 ≧.
2. The optical pickup according to claim 1, wherein the following condition is satisfied. 前記複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡｉ）により光記録媒体１，２，…ｉに記録，再生，消去のうちいずれか１以上を行い、光記録媒体１，２，…ｉ上に発生する球面収差が最大となる瞳半径位置をＲ１，Ｒ２，…Ｒｇ，Ｒｈ，…Ｒｉ（Ｒ１≧Ｒ２≧…≧Ｒｇ≧Ｒｈ…≧Ｒｉ）としたとき、液晶素子が、位相変化の最大となる瞳半径位置：ｒ１，ｒ２，…ｒｘ，…ｒｊ（ｘ＜ｊ＜ｉ）を有し、前記瞳半径位置：ｒｘが次の条件
ｒｘ＝（Ｒｇ＋Ｒｈ）／２
を満足することを特徴とする請求項１記載の光ピックアップ。.. Λi (λ1 <λ2 <... <Λi) in the plurality of light sources, and the numerical aperture: NA1, NA2,... NAi (NA1 ≧ NA2 ≧... ≧ NAi). , 2,... I, one or more of recording, reproduction, and erasing are performed, and the pupil radius positions at which the spherical aberration occurring on the optical recording media 1, 2,. .., (R1 ≧ R2 ≧... ≧ Rg ≧ Rh... ≧ Ri), the pupil radius position at which the phase change becomes maximum: r1, r2,. i), wherein the pupil radius position: rx is the following condition: rx = (Rg + Rh) / 2
2. The optical pickup according to claim 1, wherein the following condition is satisfied. 前記複数の光源における、波長：λ１，λ２，…λｉ（λ１＜λ２＜…＜λｉ）に対して、開口数：ＮＡ１，ＮＡ２，…ＮＡｉ（ＮＡ１≧ＮＡ２≧…≧ＮＡａ≧ＮＡｂ≧ＮＡｃ…≧ＮＡｉ）により光記録媒体１，２，…ａ，ｂ，ｃ，…ｉに記録，再生，消去のうちいずれか１以上を行い、対物レンズが、光記録媒体ｂに対しては有限系により使用されるとき、晶素子が、位相変化の最大となる瞳半径位置：ｒ１，ｒ２，…ｒａ，ｒｃ，…ｒｉを有し、前記瞳半径位置が次の条件
ｒ１≧ｒ２≧…ｒａ≧ｒｃ…≧ｒｉ
を満足することを特徴とする請求項１記載の光ピックアップ。Numerical aperture: NA1, NA2,... NAi (NA1 ≧ NA2 ≧... ≧ NAa ≧ NAb ≧ NAc... ≧ NAi) performs at least one of recording, reproduction, and erasure on the optical recording media 1, 2,... A, b, c,. Then, the crystal element has a pupil radius position at which the phase change is maximum: r1, r2,..., Ra, rc,. ≧ ri
2. The optical pickup according to claim 1, wherein the following condition is satisfied. 光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、波長：λ１，λ２，λ３（λ１≦λ２≦λ３）の光を出射する３つの光源と、前記光記録媒体に前記光源からの出射光を集光させるための対物レンズと、開口数：ＮＡ１，ＮＡ２，ＮＡ３（ＮＡ１≧ＮＡ２≧ＮＡ３）を切り換える開口制限手段と、電圧印加により通過光束に位相分布の変化を与える液晶素子とを備え、
前記液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、前記同心円状の位相変化が最大となる瞳半径位置ｒ２，ｒ３をもち、前記瞳半径位置ｒ２と瞳半径位置ｒ３は対向電極のそれぞれ異なる電極面にあり、前記瞳半径位置ｒ２は略開口数：ＮＡ２〜ＮＡ３の領域に、前記瞳半径位置ｒ３は略開口数：ＮＡ３以内の領域に形成されてなることを特徴とする光ピックアップ。An optical pickup for performing at least one of recording, reproducing, and erasing of information on an optical recording medium, comprising: three light sources that emit light of wavelengths: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3); An objective lens for converging the light emitted from the light source on the optical recording medium, an aperture limiting means for switching the numerical aperture: NA1, NA2, NA3 (NA1 ≧ NA2 ≧ NA3); A liquid crystal element that changes the phase distribution,
The liquid crystal element gives concentric phase changes to the optical axis center of the passing light beam, and has pupil radius positions r2 and r3 at which the concentric phase changes become maximum, and the pupil radius positions r2 and r3 Are located on different electrode surfaces of the opposing electrode, the pupil radius position r2 is formed in a region of approximately NA2 to NA3, and the pupil radius position r3 is formed in a region of approximately within NA3. Optical pickup. 光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、波長：λ１，λ２，λ３（λ１≦λ２≦λ３）の光を出射する３つの光源と、前記光記録媒体に前記光源からの出射光を集光させるための対物レンズと、開口数：ＮＡ１，ＮＡ２，ＮＡ３（ＮＡ１≧ＮＡ２≧ＮＡ３）を切り換える開口制限手段と、電圧印加により通過光束に位相分布の変化を与える液晶素子とを備え、
前記液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、前記同心円状の位相変化が最大となる瞳半径位置ｒ２，ｒ３をもち、前記瞳半径位置ｒ２と瞳半径位置ｒ３は対向電極の同一電極面上にあり、前記瞳半径位置ｒ２は略開口数：ＮＡ２〜ＮＡ３の領域に、前記瞳半径位置ｒ３は略開口数：ＮＡ３以内の領域に形成されてなることを特徴とする光ピックアップ。An optical pickup for performing at least one of recording, reproducing, and erasing of information on an optical recording medium, comprising: three light sources that emit light of wavelengths: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3); An objective lens for converging the light emitted from the light source on the optical recording medium, an aperture limiting means for switching the numerical aperture: NA1, NA2, NA3 (NA1 ≧ NA2 ≧ NA3); A liquid crystal element that changes the phase distribution,
The liquid crystal element gives concentric phase changes to the optical axis center of the passing light beam, and has pupil radius positions r2 and r3 at which the concentric phase changes become maximum, and the pupil radius positions r2 and r3 Are located on the same electrode surface of the opposing electrode, and the pupil radius position r2 is formed in a region of approximately NA2 to NA3, and the pupil radius position r3 is formed in a region of approximately within NA3. Optical pickup. 前記対物レンズを、３つの光源の波長：λ１，λ２，λ３（λ１≦λ２≦λ３）のうち、波長：λ２の光源点灯時は有限系で使用することを特徴とする請求項６または７記載の光ピックアップ。8. The finite system according to claim 6, wherein the objective lens is used in a finite system when a light source of wavelength: λ2 is turned on among three wavelengths of light sources: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3). Optical pickup. 光記録媒体に対して情報の記録，再生，消去のうちいずれか１以上を行う光ピックアップであって、波長：λ１，λ２，λ３（λ１≦λ２≦λ３）の光を出射する３つの光源と、前記光記録媒体に前記光源からの出射光を集光させるための対物レンズと、開口数：ＮＡ１，ＮＡ２，ＮＡ３（ＮＡ１≧ＮＡ２≧ＮＡ３）を切り換える開口制限手段と、電圧印加により通過光束に位相分布の変化を与える液晶素子とを備え、
前記液晶素子が、通過光束の光軸中心に同心円状の位相変化を与えて、前記同心円状の位相変化が最大となる瞳半径位置ｒ２をもち、前記瞳半径位置ｒ２は略開口数：ＮＡ２〜ＮＡ３の領域に形成されてなることを特徴とする光ピックアップ。An optical pickup for performing at least one of recording, reproducing, and erasing of information on an optical recording medium, comprising: three light sources that emit light of wavelengths: λ1, λ2, λ3 (λ1 ≦ λ2 ≦ λ3); An objective lens for converging the light emitted from the light source on the optical recording medium, an aperture limiting means for switching the numerical aperture: NA1, NA2, NA3 (NA1 ≧ NA2 ≧ NA3); A liquid crystal element that changes the phase distribution,
The liquid crystal element has a pupil radius position r2 at which the concentric phase change is maximized by giving a concentric phase change to the optical axis center of the passing light beam, and the pupil radius position r2 is substantially equal to the numerical aperture: NA2 An optical pickup formed in the area of NA3. 前記対物レンズを、３つの光源の波長：λ１，λ２，λ３（λ１≦λ２≦λ３）のうち、波長：λ２及び波長：λ３の光源点灯時は有限系で使用することを特徴とする請求項９記載の光ピックアップ。3. The method according to claim 1, wherein the objective lens is used in a finite system when the light sources of the wavelengths: .lambda.2 and .lambda.3 (.lambda.1.ltoreq..lambda.2.ltoreq..lambda.3) of the three light sources are turned on. 9. The optical pickup according to item 9. 前記光記録媒体を判別する光記録媒体判別手段を備え、前記光記録媒体判別手段からの信号に応じて、液晶素子の付加位相量、及び付加位相量が最大となる瞳半径位置を切り換えることを特徴とする請求項１〜１０のいずれか１項記載の光ピックアップ。An optical recording medium discriminating means for discriminating the optical recording medium, wherein the additional phase amount of the liquid crystal element and a pupil radius position at which the additional phase amount is maximum are switched according to a signal from the optical recording medium discriminating means. The optical pickup according to any one of claims 1 to 10, wherein: 前記光記録媒体上に発生する球面収差を検出する球面収差検出手段を備え、前記球面収差検出手段からの信号に応じて、液晶素子の付加位相量を変化させることを特徴とする請求項１〜１１のいずれか１項記載の光ピックアップ。2. The apparatus according to claim 1, further comprising: a spherical aberration detecting unit configured to detect a spherical aberration generated on the optical recording medium, wherein an additional phase amount of the liquid crystal element is changed according to a signal from the spherical aberration detecting unit. 12. The optical pickup according to any one of items 11 to 11. 前記液晶素子において、同心円状の位相付加面の対向電極面が、光軸中心に対称分割された２ｎ領域（ｎは整数）からなることを特徴とする請求項７または９記載の光ピックアップ。10. The optical pickup according to claim 7, wherein, in the liquid crystal element, a counter electrode surface of the concentric phase addition surface is formed of a 2n region (n is an integer) symmetrically divided about an optical axis center. 光記録媒体からの反射光の干渉パターンからコマ収差信号を生成する手段を備え、前記コマ収差信号に基づいて、液晶素子の付加位相量を制御することを特徴とする請求項１３記載の光ピックアップ。14. The optical pickup according to claim 13, further comprising means for generating a coma aberration signal from an interference pattern of light reflected from the optical recording medium, and controlling an additional phase amount of the liquid crystal element based on the coma aberration signal. . 対物レンズの略光軸中心からの位置ずれ量を検知する手段を備え、検知した前記位置ずれ量の信号に基づいて、液晶素子の付加位相量を制御することを特徴とする請求項１３記載の光ピックアップ。14. The apparatus according to claim 13, further comprising means for detecting a displacement amount of the objective lens from the center of the optical axis, and controlling an additional phase amount of the liquid crystal element based on the detected signal of the displacement amount. Optical pickup. 前記複数の光記録媒体における少なくともいずれか１つは、情報記録層が多重形成された多層型光記録媒体であって、前記多層型光記録媒体の記録、再生を行う前記情報記録層の位置に応じて、液晶素子の付加位相量を変化させることを特徴とする請求項１〜１５のいずれか１項記載の光ピックアップ。At least one of the plurality of optical recording media is a multilayer optical recording medium in which an information recording layer is multiplexed, and the information recording layer performs recording and reproduction at a position of the information recording layer. 16. The optical pickup according to claim 1, wherein the amount of additional phase of the liquid crystal element is changed accordingly. 前記光源の使用波長に応じて、前記光源からの出射光の開口数を切り換える開口制限手段を備え、前記開口制限手段が液晶素子と一体化されたことを特徴とする請求項１〜１６のいずれか１項記載の光ピックアップ。17. The liquid crystal device according to claim 1, further comprising an aperture limiting unit that switches a numerical aperture of light emitted from the light source according to a wavelength used by the light source, wherein the aperture limiting unit is integrated with a liquid crystal element. 2. The optical pickup according to claim 1. 前記光源の使用波長に応じて、前記光源からの出射光の偏光状態を変化させる偏光素子を備え、前記偏光素子が液晶素子と一体化されたことを特徴とする請求項１〜１７のいずれか１項記載の光ピックアップ。The liquid crystal device according to any one of claims 1 to 17, further comprising: a polarizing element that changes a polarization state of light emitted from the light source in accordance with a wavelength used by the light source. 2. The optical pickup according to claim 1. 前記液晶素子が、対物レンズと一体で可動することを特徴とする請求項１〜１８のいずれか１項記載の光ピックアップ。19. The optical pickup according to claim 1, wherein the liquid crystal element is movable integrally with an objective lens. 請求項１〜１９のいずれか１項記載の光ピックアップを用いて、光記録媒体に対して情報の記録，再生，消去の少なくとも１以上を行うことを特徴とする光情報処理装置。20. An optical information processing apparatus, comprising: performing at least one of recording, reproducing, and erasing information on an optical recording medium using the optical pickup according to claim 1.
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JP2003003525A JP4278989B2 (en) 2002-08-02 2003-01-09 Optical pickup and optical information processing apparatus using the same
EP08006364A EP1965380B1 (en) 2002-02-27 2003-02-25 Optical pickup and optical information processing apparatus
DE60330817T DE60330817D1 (en) 2002-02-27 2003-02-25 Optical read head and optical information processing device
EP03251102A EP1341166B1 (en) 2002-02-27 2003-02-25 Optical pickup for different wavelengths
DE60321414T DE60321414D1 (en) 2002-02-27 2003-02-25 Optical scanning head for different wavelengths
US10/372,916 US7142497B2 (en) 2002-02-27 2003-02-26 Optical pickup and optical information processing apparatus with light sources of three different wavelengths
US11/580,019 US7848209B2 (en) 2002-02-27 2006-10-13 Optical pickup and optical information processing apparatus with light sources of three different wavelengths

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JP2006012391A (en) * 2004-05-28 2006-01-12 Ricoh Co Ltd Optical pickup and optical information processing apparatus using the same
JP2006209881A (en) * 2005-01-28 2006-08-10 Canon Inc Optical information recording and reproducing apparatus
US7414950B2 (en) 2002-12-11 2008-08-19 Pioneer Corporation Aberration correction liquid crystal device and optical pickup apparatus
EP1998330A1 (en) * 2007-05-28 2008-12-03 Funai Electric Co., Ltd. Discrimination method for optical disc types and optical disc apparatus
US20210263198A1 (en) * 2020-02-26 2021-08-26 Beijing Voyager Technology Co., Ltd. Liquid crystal-based laser beam scanners and laser signal receivers

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JPH10124921A (en) * 1996-08-30 1998-05-15 Sanyo Electric Co Ltd Optical reproducing device
JP2000276766A (en) * 1999-01-19 2000-10-06 Matsushita Electric Ind Co Ltd Optical pickup, optical information recording and reproducing device equipped therewith, and variable phase type wavelength plate used therefor
JP2001318231A (en) * 2000-02-29 2001-11-16 Asahi Glass Co Ltd Polarization phase compensating element and optical head device
JP2002050068A (en) * 2000-05-24 2002-02-15 Matsushita Electric Ind Co Ltd Optical pickup device

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JPH09128785A (en) * 1995-08-31 1997-05-16 Pioneer Electron Corp Optical pickup
JPH09211460A (en) * 1996-01-30 1997-08-15 Asahi Glass Co Ltd Light modulator and optical head device using the same
JPH10124921A (en) * 1996-08-30 1998-05-15 Sanyo Electric Co Ltd Optical reproducing device
JP2000276766A (en) * 1999-01-19 2000-10-06 Matsushita Electric Ind Co Ltd Optical pickup, optical information recording and reproducing device equipped therewith, and variable phase type wavelength plate used therefor
JP2001318231A (en) * 2000-02-29 2001-11-16 Asahi Glass Co Ltd Polarization phase compensating element and optical head device
JP2002050068A (en) * 2000-05-24 2002-02-15 Matsushita Electric Ind Co Ltd Optical pickup device

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7414950B2 (en) 2002-12-11 2008-08-19 Pioneer Corporation Aberration correction liquid crystal device and optical pickup apparatus
JP2006012391A (en) * 2004-05-28 2006-01-12 Ricoh Co Ltd Optical pickup and optical information processing apparatus using the same
JP2006209881A (en) * 2005-01-28 2006-08-10 Canon Inc Optical information recording and reproducing apparatus
US7706227B2 (en) 2005-01-28 2010-04-27 Canon Kabushiki Kaisha Information recording/reproduction apparatus
JP4642492B2 (en) * 2005-01-28 2011-03-02 キヤノン株式会社 Optical information recording / reproducing apparatus
EP1998330A1 (en) * 2007-05-28 2008-12-03 Funai Electric Co., Ltd. Discrimination method for optical disc types and optical disc apparatus
US7920450B2 (en) 2007-05-28 2011-04-05 Funai Electric Co., Ltd. Discrimination method for optical disc types and optical disc apparatus
US20210263198A1 (en) * 2020-02-26 2021-08-26 Beijing Voyager Technology Co., Ltd. Liquid crystal-based laser beam scanners and laser signal receivers

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