JP4621964B2 - Optical pickup device, recording / reproducing device, and correction method of spherical aberration fluctuation in optical pickup device - Google Patents

Description

【００８８】
球面収差誤差信号ΔＳＡは、多分割光検出器１５の各受光部での受光量に基づいて以下の演算により検出される。
【００８９】
ΔＳＡ＝（Ａ２＋Ｂ１）−（Ａ１＋Ｂ２）
【００９０】
表１より、アンダー状態においてΔＳＡ＜０、オーバー状態においてΔＳＡ＞０となることが分かる。
【００９１】
図１の多分割光検出器１５において、ΔＳＡ＜０と検出された場合には、ビームエキスパンダ５の駆動手段である１軸アクチュエータ１１によって、基準状態と比較して負レンズ５ａと正レンズ５ｂの間隔を広げるように負レンズ５ａを光軸方向に沿ってΔＳＡ＝０となるように変移させる。これに対し、ΔＳＡ＞０と検出された場合には、ビームエキスパンダ５の駆動手段である１軸アクチュエータ１１によって、基準状態と比較して負レンズ５ａと正レンズ５ｂの間隔を狭めるように負レンズ５ａを光軸方向に沿ってΔＳＡ＝０となるように変移させる。
【００９２】
なお、多分割光検出器１５の受光面の配置は、上記のように第１の光束１６ａおよび第２の光束１６ｂの近軸焦点位置に限らずその内側もしくは外側でもよく、上述した方法と同様の原理で球面収差の変動を検出・補正できる。
次に、図４により、図１の光ピックアップ装置の変形例を説明する。図４の光ピックアップ装置は、球面収差補正手段としてカップリングレンズを光軸方向に沿って変移可能としたものであり、図１と同様の効果を得ることができる。
【００９３】
図４に示すように、光源１からの光束が偏光ビームスプリッタ４、４’、１／４波長板６、カップリングレンズ２、及び絞り７を通過し、対物レンズ８によって光情報記録媒体の透明基板９を介して情報記録面９’に集光される。情報記録面９’からの反射光は、対物レンズ８及びカップリングレンズ２等を通過した後、一部が偏光ビームスプリッタ４’によって反射され球面収差付加素子１２を通過して多分割光検出器１５に向かい、残りが偏光ビームスプリッタ４’を通過した後、偏光ビームスプリッタ４によって反射されトラッキング／フォーカシング誤差検出手段１９に向かう。
【００９４】
また、球面収差補正手段としてのカップリングレンズ２は、球面収差補正手段の駆動手段としての１軸アクチュエータ１１により図４の光軸方向に沿って変移可能に構成されている。なお、図１，図４において、ビームエキスパンダ５やカップリングレンズ２の駆動手段（１軸アクチュエータ１１）は、ボイスコイルアクチュエータやピエゾアクチュエータなどを用いることができる。
【００９５】
また、情報記録面９'からの反射光を多分割光検出器１５に集光させる図１の集光レンズ１３はカップリングレンズ２と同一の光学素子とされ省略されている。これにより、光ピックアップ装置の小型化、部品数の少量化等が達成できる。
【００９６】
図４の光ピックアップ装置の多分割光検出器１５において、球面収差誤差信号ΔＳＡ＜０と検出された場合には、カップリングレンズ２の駆動手段１１によって、基準状態と比較してカップリングレンズ２と対物レンズ８の間隔を狭めるようにカップリングレンズ２を光軸方向に沿ってΔＳＡ＝０となるように変移させる。これに対し、ΔＳＡ＞０と検出された場合には、カップリングレンズ２の駆動手段１１によって、基準状態と比較してカップリングレンズ２と対物レンズ８の間隔を広げるようにカップリングレンズ２を光軸方向に沿ってΔＳＡ＝０となるように変移させる。
【００９７】
次に、図５により、図１の光ピックアップ装置の別の変形例を説明する。図５の光ピックアップ装置は、球面収差補正手段として図１のビームエキスパンダ５の代わりに屈折率分布可変素子を用いたものであり、図１と同様の効果を得ることができる。
【００９８】
図５に示すように、光源１からの光束が偏光ビームスプリッタ４、４’、屈折率分布可変素子１７等を通過し、対物レンズ８によって光情報記録媒体の透明基板９を介して情報記録面９’に集光される。情報記録面９’からの反射光は、対物レンズ８及び屈折率分布可変素子１７等を通過した後、一部が偏光ビームスプリッタ４’によって反射され球面収差付加素子１２及び集光レンズ１３を通過して多分割光検出器１５に向かい、残りが偏光ビームスプリッタ４’を通過した後、偏光ビームスプリッタ４によって反射されトラッキング／フォーカシング誤差検出手段１９に向かう。
【００９９】
図５に示す球面収差補正手段としての屈折率分布が可変である屈折率分布可変素子１７は、例えば、電気的に互いに接続された光学的に透明な電極層１７ａ、１７ｂ、１７ｃと、電極層１７ａ、１７ｂ、１７ｃに対し電気的に絶縁され、駆動手段１８から印加される電圧に応じて屈折率分布が変化する屈折率分布可変層１７ｄ、１７ｅとが交互に積層され、電極層１７ａ、１７ｂ、１７ｃが複数の領域に分割された素子などを用いることができる。
【０１００】
図５の光ピックアップ装置の多分割光検出器１５において球面収差誤差信号ΔＳＡが検出された場合には、屈折率分布可変素子１７の駆動手段１８により電極層１７ａ、１７ｂ、１７ｃに電圧を印加し、屈折率分布可変層１７ｄ、１７ｅの屈折率を場所によって変化させ、屈折率分布可変素子１７からの射出光の位相をΔＳＡが零となるように制御する。
【０１０１】
また、屈折率分布が可変である素子として、液晶分子を光軸に垂直な面内で、任意のＸ方向にそろえて配列させた液晶素子ａと、液晶分子を光軸に垂直な面内で、Ｘ方向とは垂直なＹ方向にそろえて配列させた液晶素子ｂを用いることもできる。液晶素子ａと液晶素子ｂとをガラス基板ｃをはさんで交互に積層させ、液晶素子ａと液晶素子ｂとのそれぞれに電圧を印加することで、球面収差補正手段からの射出光の位相のＸ方向成分、およびＹ方向成分を独立に制御することにより球面収差の変動を補正することができる。
【０１０２】
また、集光レンズ１３を回折レンズとすることで、集光レンズ１３に球面収差付加素子１２の機能を持たせても良い。球面収差付加素子１２と集光レンズ１３とを共通化することで光ピックアップ光学系の構成要素を減らすことができ、より簡素な構成とすることができる。
【０１０３】
〈第２の実施の形態〉
【０１０４】
図１２は第２の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【０１０５】
図１２に示す本実施の形態による光ピックアップ装置は、光源１から情報記録面９'に至る光路と、情報記録面９'から多分割光検出器１５に至る光路とが共有され、図１の偏光ビームスプリッタ４’が省略され、光源１と多分割光検出器１５とが同一の基板上に形成され、さらにビームエキスパンダ５の正レンズ５ｂを１軸アクチュエータ１１により光軸方向に沿って変移させることで球面収差の変動を補正する以外は図１と基本的に同様の構成であるので、同一部分には同じ符号を付し、その説明を省略する。
【０１０６】
図１２に示すように、光源／多分割光検出器集積ユニット２４’内に光源１、多分割光検出器１５、ホログラム２０及び球面収差付加素子１２がユニット化されている。
【０１０７】
光源１から出射された光束は、ホログラム２０、カップリングレンズ２、ビーム整形プリズムペア３、偏光ビームスプリッタ４、ビームエキスパンダ５、１／４波長板６、絞り７を通過した後、対物レンズ８によって光情報記録媒体の透明基板９を介して情報記録面９'に集光される。情報記録面９'からの反射光は再び対物レンズ８、絞り７，１／４波長板６、ビームエキスパンダ５を通過した後、一部が偏光ビームスプリッタ４によって反射されトラッキング誤差／フォーカシング誤差検出手段１９に向かい、残りが偏光ビームスプリッタ４を通過した後、ビーム整形プリズムペア３、カップリングレンズ２を通過し、ホログラム２０によって回折され球面収差検出手段に向かう。このような図１２の光ピックアップ装置によれば、図１と同様の効果を得ることができる。
【０１０８】
また、情報記録面９'からの反射光を多分割光検出器１５に集光させる図１の集光レンズ１３はカップリングレンズ２と同一の光学素子とされ省略されている。これにより、光ピックアップ装置の小型化、部品数の少量化等が達成できる。
【０１０９】
図１、図５、図６及び図１２の各光ピックアップ装置にあるように、光源から出射された光束の非点隔差を緩和するためのビーム整形プリズムペア３を用いる場合、ビーム整形プリズムペア３による非点収差の発生を防ぐために、ビーム整形プリズムペア３に入射する光束の発散度は常に一定に保たれる必要がある。このため、カップリングレンズ２はガラスレンズであることが好ましい。これにより、温度変化及び／または湿度変化がおきた場合でもビーム整形プリズムペア３に入射する光束の発散度を一定に保つことができる。さらにこのガラスカップリングレンズを回折レンズとし、光源の波長が微少変動したときのカップリングレンズの焦点の移動を小さく抑えることで、光源の波長が微少変動した場合でもビーム整形プリズムペア３に入射する光束の発散度を一定に保つことができるのでより好ましい。
【０１１０】
また、温度変化及び／または湿度変化がおきた場合、カップリングレンズ２を保持する鏡枠の形状変化によって光源からカップリングレンズ２までの距離が変化し、カップリングレンズ２からの射出光の発散度が変化してしまう場合がある。カップリングレンズ２を、屈折作用をもつガラスレンズと、一方の面で前記ガラスレンズに接合され、他方の面に光学面が形成されたプラスチック材料及び／または紫外線硬化樹脂からなる光学素子とから構成される複合レンズとすると、上述の発散度の変化と、カップリングレンズ２自身の焦点距離の変化によるカップリングレンズ２からの射出光の発散度の変化とを、互いに打ち消すことができるので、温度変化及び／または湿度変化に対してカップリングレンズ２から常に一定の発散度の光束を出射することができる。このような複合レンズ型のカップリングレンズ２としては同一出願人による特願２０００−０５３８５８号にあるようなカップリングレンズを用いることができる。
【０１１１】
〈第３の実施の形態〉
【０１１２】
図１３は第３の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【０１１３】
図１３に示す本実施の形態による光ピックアップ装置は、図４と同様に情報記録面９'からの反射光を多分割光検出器１５に集光させる図１の集光レンズ１３とカップリングレンズ２とが同一の光学素子とされており、図４と比べて、光源１とカップリングレンズ２との光路中に、光源１から射出された光束の非点隔差を緩和するためのビーム整形レンズ２１を配置した以外は図４と基本的に同様の構成であるので、同一部分には同じ符号を付し、その説明を省略する。
【０１１４】
図１３に示すビーム整形レンズ２１としては、アナモルフィッックレンズを用いることができる。アナモルフィックレンズの面形状は光源から出射する光束の非点隔差の大きさにより決定される。
【０１１５】
図１３に示すように、光源１から出射された光束は、ビーム整形レンズ２１、偏光ビームスプリッタ４'、偏光ビームスプリッタ４、カップリングレンズ２、ビームエキスパンダ５、１／４波長板６、絞り７を通過した後、対物レンズ８によって光情報記録媒体の透明基板９を介して情報記録面９'に集光される。情報記録面９'からの反射光は再び対物レンズ８、１／４波長板６、ビームエキスパンダ５、カップリングレンズ２を通過した後、一部が偏光ビームスプリッタ４'によって反射されトラッキング誤差／フォーカシング誤差検出手段１９に向かい、残りが偏光ビームスプリッタ４'を通過した後、偏光ビームスプリッタ４によって反射され球面収差検出手段に向かう。このような図１３の光ピックアップ装置によれば、図４と同様の効果を得ることができる。
【０１１６】
更に、図１３の光ピックアップ装置では、光源１とカップリングレンズ２との光路中にビーム整形素子を配置したので、カップリングレンズ２をプラスチックレンズとすることが可能である。温度変化及び湿度変化や光源の微少な波長変動が起きたときに、カップリングレンズ２から出射される光束の発散度が変化することにより発生する球面収差は、カップリングレンズ２を１軸アクチュエータにより光軸方向に変移させることで補正可能である。
【０１１７】
図１、図５、図６、図１２及び図１３の各光ピックアップ装置のように、光源１から出射された光束の非点隔差を緩和するためのビーム整形プリズムペア３あるいはビーム整形レンズ２１を使用すると、光源からの光束を、光量を損失することなく、カップリングレンズ２によって全て取り込むことができるので、低出力型の光源であっても適用可能となるので好ましい。また、光源の駆動電圧が小さくて済むので、光源の寿命を延ばすことができる。
【０１１８】
〈第４の実施の形態〉
【０１１９】
図１４は第４の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【０１２０】
図１４に示す本実施の形態による光ピックアップ装置は、図４と同様に情報記録面９'からの反射光を多分割光検出器１５に集光させる図１の集光レンズ１３とカップリングレンズ２とが同一の光学素子とされており、図４と基本的に同様の構成であるので、同一部分には同じ符号を付し、その説明を省略する。
【０１２１】
図１４に示すように、情報記録面９'からトラッキング誤差／フォーカシング誤差検出用の第２の光検出器１９に至る光路と情報記録面９'から多分割光検出器１５に至る光路とが共有され、トラッキング誤差／フォーカシング誤差検出用の第２の光検出器と多分割光検出器１５とを同一の基板上に形成している。多分割光検出器／第２の光検出器集積ユニット２５’内に多分割光検出器１５、第２の光検出器１９、ホログラム２０及び球面収差付加素子１２がユニット化されている。
【０１２２】
また、対物レンズ８を光源１からの発散光束を情報記録面９'上に集光する有限共役型とすることで、ワーキングディスタンスを大きく確保し、光情報記録媒体と対物レンズ８との衝突を防いでいる。また、球面収差変動の補正は、光源１と対物レンズ８との光路中に配置した、光軸方向に沿って変移可能なカップリングレンズ２によって行う。
【０１２３】
図１４に示すように、光源１から出射された光束は、偏光ビームスプリッタ４、カップリングレンズ２、１／４波長板６、絞り７を通過した後、対物レンズ８によって光情報記録媒体の透明基板９を介して情報記録面９'に集光される。情報記録面９'からの反射光は再び対物レンズ８、１／４波長板６、カップリングレンズ２を通過した後、偏光ビームスプリッタ４によって反射されホログラム２０に入射する。ホログラム２０によって生成される回折光のうちｍ次回折は球面収差検出手段に向かい、ｎ次回折光（ただし、ｍ≠ｎ）はトラッキング誤差／フォーカシング誤差検出手段１９に向かう。このような図１４の光ピックアップ装置によれば、図４と同様の効果を得ることができる。
【０１２４】
〈第５の実施の形態〉
【０１２５】
図１５は第５の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【０１２６】
図１５に示す本実施の形態による光ピックアップ装置は、対物レンズ８を２枚の正レンズ２２，２３から構成される２群構成とし、それぞれのレンズ２２，２３を光軸方向及び／または光軸に垂直方向に沿って変移可能とし、図４のカップリングレンズ２を省略した以外は図４と基本的に同様の構成であるので、同一部分には同じ符号を付し、その説明を省略する。
【０１２７】
光源側の第１レンズ２２を球面収差変動を補正するために１軸アクチュエータ１１によって変移させ、光情報記録媒体側の第２レンズ２３をトラッキング誤差／フォーカシング誤差の低減のために２軸アクチュエータ１０によって変移させる。
【０１２８】
図１５に示すように、光源１から出射された光束は、偏光ビームスプリッタ４、偏光ビームスプリッタ４'、１／４波長板６、絞り７を通過した後、対物レンズ８によって光情報記録媒体の透明基板を介して情報記録面９'に集光される。情報記録面９'からの反射光は再び対物レンズ８、１／４波長板６を通過した後、一部が偏光ビームスプリッタ４'によって反射されトラッキング誤差／フォーカシング誤差検出手段１９に向かい、残りが偏光ビームスプリッタ４'を通過した後、偏光ビームスプリッタ４によって反射され球面収差検出手段に向かう。このような図１４の光ピックアップ装置によれば、図４と同様の効果を得ることができる。
【０１２９】
上述の図１、図５、図６、図１２及び図１３の各光ピックアップ装置において、光源１として、高出力型の半導体レーザあるいは、略円形のほぼ非点隔差のない光束を出射可能な光源を用いる場合、光源１から出射された光束の非点隔差を緩和するためのビーム整形プリズムペア３あるいはビーム整形レンズ２１を省略することができ、さらにカップリングレンズをプラスチックレンズとすることができるので好ましい。
【０１３０】
また、高出力型の半導体レーザを光源とする場合は、光源から出射された楕円形の光束をカップリングレンズ２での光線のけられ効果を利用して円形に整形するが、このとき、広がり角が小さい方向の光量を充分に取り込むためにカップリングレンズ２の開口数を０．１３以下とすることが好ましい。
【０１３１】
また、略円形のほぼ非点隔差のない光束を出射可能な光源としては、半導体レーザの前方にＳＨＧ（Second Harmonic Generation：第２次高調波発生）素子を形成した光源を用いることができる。
【０１３２】
〈第６の実施の形態〉
【０１３３】
図６は第６の実施の形態による光ピックアップ装置の概略的構成を示す図であり、図７は図６の多分割光検出器の受光面を図６の方向ＡＡから見た概略的な平面図である。
【０１３４】
図６に示すように、本実施の形態の光ピックアップ装置は、球面収差補正手段として図１と同様に正レンズ５ａと負レンズ５ｂとから構成されたビームエキスパンダを用いており、多分割光検出器の受光面が更に多数に分割されている以外は同様の構成であるので、同一部分には同じ符号を付し、その説明を省略する。
【０１３５】
本実施の形態における球面収差の変動の検出及び球面収差の変動の補正の原理について図７により説明する。図７（ａ）に示すように、多分割光検出器２５の受光面２４は分割線２１、２２によって受光面２４ａおよび受光面２４ｂに分割され、受光面２４ａおよび受光面２４ｂは分割線２３によってさらに受光部ａ１、ａ２、ａ１’、ａ２’及びｂ１、ｂ２、ｂ１’、ｂ２’に分割される。受光部ａ１、ａ２と受光部ａ１’、ａ２’及び受光部ｂ１、ｂ２と受光部ｂ１’、ｂ２’はそれぞれ互いに対向する位置にある。
【０１３６】
図６の光ピックアップ装置において、情報記録面９'からの反射光は球面収差付加素子１２を通過する際に、図７（ａ）のＸ−Ｚ面内の光線に対し、すなわち受光面２４ｂに受光される光線に対しオーバーな球面収差成分が付加され、Ｙ−Ｚ面内の光線に対し、すなわち受光面２４ａに受光される光線に対しアンダーな球面収差成分が付加される。このとき、Ｘ−Ｚ面内の光線とＹ−Ｚ面内の光線のべストフォーカス位置は同一にされ、多分割光検出器２５の受光面２４は、Ｘ−Ｚ面内の光線およびＹ−Ｚ面内の光線のべストフォーカス位置よりも外側に配置される。
【０１３７】
図７（ｂ）に、基準状態における受光面２４の情報記録面からの反射光の受光パターンを示す。受光部ａ１、ａ２、ｂ１、ｂ２、ａ１’、ａ２’、ｂ１’、ｂ２’の大きさ及び球面収差付加素子１２の形状は、基準状態において、各々の受光部の受光量ａ１、ａ２、ｂ１、ｂ２、ａ１’、ａ２’、ｂ１’、ｂ２’（各受光量を各受光部と同じ符号で表す）が、
ａ１＝ａ２、ａ１’＝ａ２’
ｂ１＝ｂ２、ｂ１’＝ｂ２’
もしくは、
（ａ２＋ｂ１）−（ａ１＋ｂ２）＝０
（ａ２’＋ｂ１’）−（ａ１’＋ｂ２’）＝０
の関係式が成り立つように決定される。
【０１３８】
受光面２４ａで受光されるスポットは球面収差がアンダーの状態、すなわち中心に比較的光線密度の大きい核を形成し、周辺に光線密度の小さいフレアを形成する。受光面２４ｂで受光されるスポットは球面収差がオーバーの状態、すなわち周辺に比較的光線密度の大きいリング状のスポットを形成する。
【０１３９】
アンダー状態では、受光パターンは図７（ｃ）のようになる。受光面２４ａで受光されるスポットはアンダーな球面収差が強調され、基準状態と比較して周辺のフレアの強度は大きく、中心の核の強度は小さくなる。それに対し、受光面２４ｂで受光されるスポットはオーバーな球面収差が低減され、周辺のリング状のスポットは一様な強度分布に近づく。
【０１４０】
また、オーバー状態では、受光パターンは図７（ｄ）のようになる。受光面２４ａで受光されるスポットはアンダーな球面収差が低減され、一様な強度分布に近づく。それに対し、受光面２４ｂで受光されるスポットはオーバーな球面収差が強調され、基準状態と比較して周辺のリング状のスボットの強度は大きくなる。
【０１４１】
上述の各受光面２４ａ、２４ｂの各受光部で受光する光量の基準状態に対する変化を次の表２に示す。表２において、「＋」は基準状態と比較して光量が増大することを、「−」は基準状態と比較して光量が減少することを表す。
【０１４２】
【表２】

【０１４３】
球面収差誤差信号ΔＳＡは、多分割光検出器２５の各受光部での受光量に基づいて以下の演算により検出される。
ΔＳＡ＝（ａ２＋ｂ１）−（ａ１＋ｂ２）
または、
ΔＳＡ＝（ａ２’＋ｂ１’）−（ａ１’＋ｂ２’）
または、
ΔＳＡ＝（ａ２＋ｂ１＋ａ２’＋ｂ１’）−（ａ１＋ｂ２＋ａ１’＋ｂ２’）
【０１４４】
表２より、アンダー状態においてΔＳＡ＜０、オーバー状態においてΔＳＡ＞０となることが分かる。
【０１４５】
多分割光検出器２５において、ΔＳＡ＜０と検出された場合には、ビームエキスパンダ５の駆動手段１１によって、基準状態と比較して負レンズ５ａと正レンズ５ｂの間隔を広げるように負レンズ５ａを光軸方向に沿ってΔＳＡ＝０となるように変移させる。これに対し、ΔＳＡ＞０と検出された場合には、ビームエキスパンダの駆動手段１１によって、基準状態と比較して負レンズ５ａと正レンズ５ｂの間隔を狭めるように負レンズ５ａを光軸方向に沿ってΔＳＡ＝０となるように変移させる。
【０１４６】
また、多分割光検出器１５の受光面１４がＸ−Ｚ面内の光線とＹ−Ｚ面内の光線のべストフォーカス位置より内側に配置される場合においても上述した方法と同様の原理で球面収差の変動を検出・補正できる。
【０１４７】
なお、図４，図５と同様に、図６の光ピックアップ装置における球面収差補正手段として、光軸方向に沿って変移可能としたカップリングレンズあるいは屈折率分布可変素子を用いても良い。
【０１４８】
【実施例】
次に、本発明を実施例１、２により更に具体的に説明する。なお、本実施例のレンズにおける非球面は光軸方向をＸ軸、光軸に垂直な方向の高さをｈ、屈折面の曲率半径をｒとするとき次の数１で表す。但し、κを円すい係数、Ａ２ｉを非球面係数とする。
【０１４９】
【数１】

【０１５０】
また、本実施例のレンズに設けた輪帯状の回折面は光路差関数Φｂとして次の数２により表すことができる。ここで、ｈは光軸に垂直な高さであり、ｂ２ｉは光路差関数の係数である。
【０１５１】
【数２】

【０１５２】
〈実施例１〉
【０１５３】
表３に、上述の図１の光ピックアップ装置に用いられるのに好ましい光学系のデータを示す。本実施例では、対物レンズの像側開口数は０．８５、情報の記録または再生を行う光源の発振波長は４０５ｎｍとし、すべての構成要素を短波長領域での内部透過率の高いプラスチック材料から形成した。球面収差補正手段として１枚の負レンズと１枚の正レンズで構成されたビームエキスパンダを用いており、光学系で発生する球面収差の変動を負レンズを光軸に沿って変移させることで補正した。なお、本実施例では、ビームエキスパンダの構成レンズのうち、球面収差の変動の補正のため、正レンズを変移させてもよいし、正レンズ及び負レンズの両方を変移させてもよい。
【０１５４】
【表３】

【０１５５】
表４に実施例１における±１０ｎｍの光源の発振波長変動、±３０℃の温度変化、±０．０２ｍｍの透明基板厚さ誤差に起因して発生した球面収差の変動を補正した結果を示す。また、発振波長４００ｎｍほどの短波長レーザ光源を用いた場合に問題となる色収差は、ビームエキスパンダの正レンズを両面回折レンズとすることで補正した。図８に実施例１に関する光路図、図９に実施例１に関する球面収差図を示す。
【０１５６】
【表４】

【０１５７】
〈実施例２〉
【０１５８】
表５に、上述の図４の光ピックアップ装置に用いられるのに好ましい光学系のデータを示す。本実施例では、対物レンズの像側開口数は０．８５、情報の記録または再生を行う光源の発振波長は４０５ｎｍとし、すベての構成要素を短波長領域での内部透過率の高いプラスチック材料から形成した。球面収差補正手段としてカップリングレンズを用いており、光学系で発生する球面収差の変動をカップリングレンズを光軸に沿って変移させることで補正した。なお、本実施例では、カップリングレンズを１群構成としたが、複数のレンズ群からなる構成としてもよい。
【０１５９】
【表５】

【０１６０】
表６に実施例２における±１０ｎｍの光源の発振波長変動、±３０℃の温度変化、±０．０２ｍｍの透明基板厚さ誤差に起因して発生した球面収差の変動を補正した結果を示す。また、発振波長４００ｎｍほどの短波長レーザ光源を用いた場合に問題となる色収差は、カップリングレンズの光源側の面を回折面とすることで補正した。図１０に実施例２に関する光路図、図１１に実施例２に関する球面収差図を示す。
【０１６１】
【表６】

【０１６２】
なお、上述の表では、１０のべき乗の表現にＥ（またはｅ）を用いて、例えば、Ｅ−０２（＝１０^−２）のように表している。
【０１６３】
【発明の効果】
以上述べたように、本発明における光ピックアップ装置では、球面収差検出手段により、少なくとも温度及び／または湿度変化に対して、プラスチックレンズの形状及び屈折率の少なくとも一方の変化及び／または光源の発振波長変動により生じる球面収差の変動を検出し、駆動手段によって球面収差補正手段を駆動させ、この球面収差の変動を補正するようにしたので、高開口数の対物レンズを有する光ピックアップ装置であっても、温度や湿度変化の影響を受けやすいプラスチックレンズを使うことが可能である。
【０１６４】
さらに、本発明の光ピックアップ装置は、温度や湿度変化による球面収差の変動だけでなく、光ディスクの保護層の厚み誤差、光源の微少な発振波長変動、集光光学系に含まれる光学素子の製造誤差等に起因して発生する球面収差の変動も良好に補正できるので、
1. 集光光学系にプラスチックレンズを用いることが可能となり、大幅なコストダウン及び軽量化が図れる。
2. レーザ光源の選別が必要なくなるので、レーザ光源への製造精度の要求が厳しくなりすぎないので、レーザ光源の量産性を高めることができる。また、光ピックアップ装置の製造時間の短縮を図れる。
3. 光情報記録媒体の製造誤差に対する要求精度が厳しくなりすぎないので、光情報記録媒体の量産性を高めることができる。
4. 集光光学系に含まれる光学素子への製造精度の要求が厳しくなりすぎないので、集光光学系に含まれる光学素子の量産性を高めることができる。
等の利点があり、それでいて良好な集光特性を常に維持できる集光光学系を得ることができる。
【０１６５】
また、本発明による光ピックアップ装置では、光軸に沿って変移可能な光学素子は、全てプラスチック材料から形成されることが好ましい。これにより、アクチュエータの負担を軽減することができるので、アクチュエータの駆動電力が小さくて済み、また、より小型のアクチュエータでの変移が可能となるので、光ピックアップ装置を小型化できる。光軸方向に沿って変移可能な光学素子とは、例えばトラッキング誤差／フォーカシング誤差を低減するために２軸アクチュエータにより変移される対物レンズ、球面収差の変動を補正するために光軸方向に沿って変移される球面収差補正手段に含まれる光学素子である。
【０１６６】
また、本発明による光ピックアップ装置では、軽量化、コスト上の観点から、集光光学系に含まれる光学素子のうち少なくとも１つがプラスチック材料から形成されていることが好ましいが、対物レンズ、ビームエキスパンダ、球面収差補正手段としてのカップリングレンズのうち少なくとも１つがプラスチック材料から形成されることがより好ましい。さらに、上述の光学素子の全てがプラスチック材料から形成されることが特に好ましい。
【０１６７】
また、本発明による光ピックアップ装置に用いられる対物レンズは、上述の式（３）あるいは式（４）を満たすことが好ましい。式（３）あるいは式（４）を満たすことで、高開口数の対物レンズであっても、ワーキングディスタンスの充分な確保、レンズ径の小型化と製造誤差感度の低減を両立することができる。また、この対物レンズを、無限遠物体からの平行光束に対して収差が最小となるように収差補正する場合は、トラッキング誤差／フォーカシング誤差の低減のために対物レンズを動かしても対物レンズへの入射条件の変化が少ないので、収差変化が少ない。また、この対物レンズを、有限距離にある物体からの発散光束に対して収差が最小となるように収差補正する場合は、ワーキングディスタンスをより大きく確保できるので、対物レンズと光情報記録媒体との衝突を防ぐことができる。また、この対物レンズを、像側物体に向かう収斂光束に対して収差が最小となるように収差補正する場合は、対物レンズへの光線の入射角が小さくなるので、製造時の偏芯誤差による収差劣化を抑えることができ、製造し易い対物レンズとすることができる。
【０１６８】
また、本発明による光ピックアップ装置では、集光光学系中に、輪帯状の回折構造を少なくとも１つの面に有する回折光学素子を有することが好ましい。これにより、発振波長が５００ｎｍ以下の光源を用いたときに問題となる軸上色収差を補正することができる。この回折光学素子は、集光光学系中に含まれる、対物レンズ、ビームエキスパンダ、カップリングレンズ等の光学素子であってもよいし、上述の光学素子とは別途に設けてもよい。
【０１６９】
なお、本明細書中において、光源と対物レンズとの光路中に配置された球面収差補正手段とは、ビームエキスパンダやカップリングレンズや屈折率分布可変素子のほかに、光源や対物レンズも含むものとする。従って、球面収差補正手段が有する光軸に沿って変移可能な光学素子には、ビームエキスパンダやカップリングレンズに含まれるレンズ群、あるいはビームエキスパンダやカップリングレンズとは別途に設けたレンズ群のほかに、光軸に沿って変移可能な光源や対物レンズに含まれるレンズ群も含まれる。
【０１７０】
また、本明細書中において、ビームエキスパンダとは、少なくとも１つの正屈折力を有するレンズ群と、少なくとも１つの負屈折力を有するレンズ群とから構成され、光束径ａ（ｍｍ）の略平行光束が入射した場合に、光束径ｂ（ｍｍ）（ａ≠ｂ）の略平行光束を出射することのできる、一般的によく知られた光学素子を指し、光束径を拡大するものだけでなく、光束径を縮小するものも含まれるものとする。
【０１７１】
また、本明細書中において、カップリングレンズとは光源からの発散光束の発散度を変換する光学素子を指し、出射される光束が発散光束であるもの、出射される光束が平行光束であるもの（コリメートレンズ）、出射される光束が収斂光束であるもののいずれの場合も含まれるものとする。また、１つのレンズ群から構成されるものだけでなく、複数のレンズ群から構成されるものも含まれるとする。
【０１７２】
また、本明細書中において、光情報記録媒体とは表面に透明基板を有するものだけでなく、透明基板を有さないものも含まれるとする。光情報記録媒体が透明基板を有する場合には、本発明の光ピックアップ装置に用いられる対物レンズは、ある特定の厚みの透明基板との組み合わせのもとに収差が最小となるように収差補正されていることが好ましい。
【０１７３】
また、本明細書中において、光源の発振波長の微少変動とは、光源の発振波長に対して、±１０ｎｍの範囲内での波長変動を指すものとする。また、本明細書中において、各種の収差を（良好に）補正するとは、波面収差を求めたときにいわゆる回折限界性能である０．０７λｒｍｓ以下（ここで、λは使用する光源の発振波長）であることが好ましい。
【図面の簡単な説明】
【図１】第１の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【図２】図２（ａ），（ｂ）は図１の多分割光検出器の受光面１４ａ、１４ｂを図１の方向Ａから見た概略的な平面図であり、図２（ｃ），（ｄ）は基準状態における受光面１４ａ、１４ｂでの受光パターンを模式的に示す平面図であり、図２（ｅ），（ｆ）は同じくアンダー状態における受光面１４ａ、１４ｂでの受光パターンを模式的に示す平面図であり、図２（ｇ），（ｈ）は同じオーバー状態における受光面１４ａ、１４ｂでの受光パターンを模式的に示す平面図である。
【図３】図１の球面収差付加素子の例としてのホログラム素子を示す斜視図である。
【図４】図１の光ピックアップ装置の変形例を示す図である。
【図５】図１の光ピックアップ装置の別の変形例を示す図である。
【図６】第６の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【図７】図７（ａ）は図６の多分割光検出器２５の分割された受光面２４を図６の方向ＡＡから見た概略的な平面図であり、図７（ｂ）は基準状態における受光面２４での受光パターンを模式的に示す平面図であり、図７（ｃ）はアンダー状態における受光面２４での受光パターンを模式的に示す平面図であり、図７（ｄ）はオーバー状態における受光面２４での受光パターンを模式的に示す平面図である。
【図８】実施例１に関する光路図である。
【図９】実施例１に関する球面収差図である。
【図１０】実施例２に関する光路図である。
【図１１】実施例２に関する球面収差図である。
【図１２】第２の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【図１３】第３の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【図１４】第４の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【図１５】第５の実施の形態による光ピックアップ装置の概略的構成を示す図である。
【符号の説明】
１ レーザ半導体、光源
２ カップリングレンズ
３ ビーム整形プリズム
４ 偏光ビームスプリッタ
４’ 偏光ビームスプリッタ
５ ビームエキスパンダ
６ １／４波長板
７ 絞り
８ 対物レンズ
９ 光情報記録媒体の透明基板
９’ 光情報記録媒体の情報記録面
１０ ２軸アクチュエ一タ（対物レンズ駆動手段）
１１ １軸アクチュエータ（球面収差補正手段駆動手段）
１２ 球面収差付加素子
１２ａ ホログラム素子
１３ 集光レンズ
１４ａ，１４ｂ 受光面
２４ 受光面
２４ａ，２４ｂ 受光面
１５、２５ 多分割光検出器
１６ 反射光
１６ａ 多分割光検出器１５の受光面１４ａに受光される第１の光束
１６ｂ 多分割光検出器１５の受光面１４ｂに受光される第２の光束
１７ 屈折率分布可変素子
１８ 屈折率分布可変素子１７の駆動手段
１９ トラッキング誤差／フォーカシング誤差検出手段、第２の光検出器
２０ ホログラム
２１ ビーム整形レンズ
２２ 第１レンズ
２３ 第２レンズ
２４’ 光源／多分割光検出器集積ユニット
２５’ 多分割光検出器／第２の光検出器集積ユニット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup device for recording / reproducing information on / from an optical information recording medium, a recording / reproducing device equipped with the optical pickup device, and a method for correcting spherical aberration fluctuations in the optical pickup device.
[0002]
[Prior art]
In recent years, with the practical application of short-wave different red semiconductor lasers, high-capacity, high-capacity, high-capacity optical disks (also called “optical information recording media”), which are the same size as conventional CDs (compact disks). DVD (digital versatile disc), which is an optical disc, has been developed and commercialized, but it is expected that next-generation optical discs with higher density will appear in the near future. In the optical system of the optical information recording / reproducing apparatus using such a next-generation optical disk as a medium, in order to increase the recording signal density or to reproduce the high-density recording signal, the objective lens is shortened with the wavelength of the laser as the light source. Of high numerical aperture (Nurmerical Aperture: NA). However, if the NA of the objective lens is increased, it is expected that problems that can be almost ignored when recording or reproducing an optical disk having a relatively low density such as a CD or DVD will become more apparent.
[0003]
For example, since the spherical aberration caused by the thickness error of the protective layer (also referred to as “transparent substrate”) of the optical disk is generated in proportion to the fourth power of the numerical aperture of the objective lens, the protective layer increases as the numerical aperture of the objective lens increases. There is a possibility that the influence of the thickness error becomes large, and stable information recording or reproduction cannot be performed.
[0004]
  In addition, semiconductor lasers used as light sources in optical pickup devices have individual oscillation variations of about ± 10 nm. Semiconductor laser with oscillation wavelength deviated from the reference wavelengthTheWhen the is used as a light source, the spherical aberration that occurs in the objective lens increases as the numerical aperture increases, so semiconductor lasers with oscillation wavelengths that deviate from the reference wavelength cannot be used, and it is necessary to select a semiconductor laser to be used as the light source. It becomes.
[0005]
Also, plastic lenses generally used in optical pickup devices are easily deformed by changes in temperature and humidity, and their refractive index changes greatly. The refractive index change with respect to the temperature change of the plastic lens is approximately −10 × 10.^-5/ ° C. The spherical aberration caused by the change in the refractive index is generated in proportion to the fourth power of the numerical aperture of the objective lens. Therefore, the fluctuation of the spherical aberration due to the change in the refractive index, which is not so much a problem in the optical system used in the conventional optical pickup device, is also caused. When the numerical aperture of the objective lens is increased, the amount is not negligible.
[0006]
[Problems to be solved by the invention]
The present invention has been proposed in view of the above-described problems, and is an optical pickup device having a condensing optical system including an objective lens having a high numerical aperture and at least one plastic lens. / Or optical pickup device which can effectively correct fluctuation of spherical aberration caused by humidity change and can always maintain a good condensing state, recording / reproducing device equipped with this optical pickup device, and optical pickup device An object of the present invention is to provide a correction method for spherical aberration fluctuations in
[0007]
Furthermore, it effectively corrects the variation of spherical aberration caused by the thickness error of the protective layer of the optical disc, the slight oscillation wavelength variation of the light source, the manufacturing error of the optical element included in the condensing optical system, etc. It is an object of the present invention to provide an optical pickup device capable of maintaining a good condensing state, and a spherical aberration variation correcting method in the optical pickup device.
[0008]
[Means for Solving the Problems]
To achieve the above objective,Reference exampleThe first optical pickup device according to the invention is disposed in the optical path of the light source, the objective lens for condensing the light beam from the light source on the information recording surface of the optical information recording medium, and the spherical surface of the light source and the objective lens. An optical pickup device including a condensing optical system including a spherical aberration correcting means for correcting aberration fluctuations, wherein the condensing optical system includes at least one plastic lens, A spherical surface that detects reflected light to detect a change in spherical aberration caused by a change in at least one of the shape and refractive index of the plastic lens and / or a change in the oscillation wavelength of the light source, at least with respect to temperature and / or humidity changes. An aberration detection means; and a drive means for driving the spherical aberration correction means to correct a variation in the spherical aberration detected by the spherical aberration detection means. Characterized in that it obtain.
[0009]
According to this optical pickup device, the spherical aberration detection means detects at least one of the shape and refractive index of the plastic lens and / or the spherical aberration caused by the oscillation wavelength variation of the light source at least with respect to temperature and / or humidity changes. Since the fluctuation is detected and the spherical aberration correction means is driven by the driving means to correct the fluctuation of the spherical aberration, even in an optical pickup device having a high numerical aperture objective lens, the temperature and humidity change It is possible to use sensitive plastic lenses.
[0010]
  A second optical pickup device according to the present invention includes a light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens. Arranged,Occurs due to changes in temperature and / or humidityAn optical pickup device including a condensing optical system including a spherical aberration correcting unit for correcting the fluctuation of the spherical aberration, and detecting the reflected light from the information recording surface to detect the fluctuation of the spherical aberration. A spherical aberration detecting means for detecting, and a driving means for driving the spherical aberration correcting means in accordance with a detection result of the spherical aberration detecting means, wherein the spherical aberration detecting means has an amplitude at least with respect to an incident light beam. Splitting means for performing splitting or wavefront splitting, and spherical aberrations of different sizes or different signs on the split luminous flux or wavefront, respectively.AddAn optical element,Incident on the dividing means.Spherical aberration by the optical elementIs addedWasReflected lightAnd a multi-segment photodetector for receiving the light.
[0011]
According to this optical pickup device, spherical aberration can be accurately detected by applying spherical aberrations of different magnitudes or different signs to the light beams or wavefronts divided by the spherical aberration detection means, and the spherical aberration can be detected by the drive means. By driving the aberration correcting means, it is possible to accurately correct the variation of the spherical aberration.
[0012]
  A third optical pickup device according to the present invention includes a light source, an objective lens that focuses a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens. Arranged,Occurs due to changes in temperature and / or humidityAn optical pickup device including a condensing optical system including a spherical aberration correcting unit for correcting the fluctuation of the spherical aberration, and detecting the reflected light from the information recording surface to detect the fluctuation of the spherical aberration. A spherical aberration detecting means for detecting, and a driving means for driving the spherical aberration correcting means in accordance with the detection result of the spherical aberration detecting means, wherein the spherical aberration detecting means detects the spherical aberration of the incident light beam.FluctuationA multi-segment photodetector having a first light-receiving surface and a second light-receiving surface whose areas are distributed so as to cause a change in the amount of light received according to the above, the spherical aberration correcting means, and the multi-segment photodetector And the first light beam received by the first light receiving surface with the reflected light from the information recording surface, and the first light beam and the paraxial focal position or the best focus position are the same. And splitting it into a second light beam received by the second light receiving surface, and over-spherical aberration in the first light beam.AppendUnder spherical aberration in the second light fluxAddThe first light-receiving surface has two light-receiving portions, and when the two light-receiving portions have received light amounts A1 and A2 in the respective light-receiving portions, A1 = A2 in the reference state And the second light receiving surface has two light receiving parts, and when the two light receiving parts have received light amounts B1 and B2 in the respective light receiving parts, B1 = B2 is satisfied in the reference state,Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in an under direction, the received light amount A1 on the first light receiving surface increases from the reference state, the received light amount A2 decreases, and the received light amount B1 on the second light receiving surface. Decreases from the reference state and the received light amount B2 increases,Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in the over direction, the received light amount A1 on the first light receiving surface decreases from the reference state and the received light amount A2 increases, and the received light amount B1 on the second light receiving surface. Increases from the reference state, and the amount of received light B1 decreases, and the amount of received light according to the following equation generated due to the difference in the magnitude or sign of the spherical aberration between the first light flux and the second light flux. By detecting the difference ΔSA, the variation amount of the spherical aberration is detected, and the driving unit is driven to reduce the variation amount of the spherical aberration.
ΔSA = (A2 + B1) − (A1 + B2)
[0013]
  According to this optical pickup device, in the first light receiving surface generated due to the difference in magnitude or sign of the spherical aberration between the first light flux and the second light flux in the spherical aberration detection means.Each received light amountAnd in the second light receiving surfaceAbove for each received light quantitydifferenceΔS, The spherical aberration can be accurately detected, and the spherical aberration correcting means is driven by the driving means, so that the variation of the spherical aberration can be accurately corrected.
[0014]
The first light receiving surface and the second light receiving surface are preferably formed on the same substrate.
[0015]
  A fourth optical pickup device according to the present invention includes a light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens. Arranged,Occurs due to changes in temperature and / or humidityAn optical pickup device including a condensing optical system including a spherical aberration correcting unit for correcting the fluctuation of the spherical aberration, and detecting the reflected light from the information recording surface to detect the fluctuation of the spherical aberration. A spherical aberration detecting means for detecting, and a driving means for driving the spherical aberration correcting means in accordance with a detection result of the spherical aberration detecting means, wherein the spherical aberration detecting means sequentially enters in a clockwise direction. Of spherical aberration of luminous fluxFluctuationA first light receiving surface, a second light receiving surface, a third light receiving surface facing the first light receiving surface, and the second light receiving surface, the areas of which are distributed so as to change the amount of light received according to A multi-segment photodetector having a light-receiving surface divided into at least four regions of a fourth light-receiving surface facing the surface, and an optical path between the spherical aberration correcting means and the multi-segment photodetector, and information The wavefront of the reflected light from the recording surface is received by the respective light receiving surfaces of the multi-divided photodetector, and is divided into four regions where the paraxial focus position or the best focus position is the same, and the first Spherical aberration over the wave front received by the first light receiving surface and the third light receiving surfaceAppendUnder-spherical aberration in the wavefronts received by the second light receiving surface and the fourth light receiving surfaceAddThe first light receiving surface is divided into two light receiving portions, the light receiving amounts at the respective light receiving portions are a1 and a2, and the second light receiving surface is two light receiving portions. The third light receiving surface is divided into two light receiving parts, and the light receiving amounts at the respective light receiving parts are a1 ′ and a2 ′. The light receiving surface 4 is divided into two light receiving portions, and the amount of light received by each light receiving portion is b1 ′ and b2 ′, and each light receiving portion of each light receiving surface is expressed by the following formula (1) or (2) The filling,
a1 = a2, b1 = b2, a1 '= a2', b1 '= b2' (1)
(a2 + b1) − (a1 + b2) = 0, (a2 ′ + b1 ′) − (a1 ′ + b2 ′) = 0 (2)
Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in an under direction, the received light amounts a1, a1 ′, b2, b2 ′ on the respective light receiving surfaces increase from the reference state, and the received light amounts a2, a2 ′, b1, b1. 'Decrease,Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in the over direction, the received light amounts a1, a1 ′, b2, b2 ′ at the respective light receiving surfaces are reduced from the reference state, and the received light amounts a2, a2 ′, b1, b1. ′ Increases, and the following expression (3) on each light receiving surface of the multi-segment photodetector generated due to the difference in the magnitude or sign of the spherical aberration of the wavefront divided into the four regions, By detecting the difference ΔSA in the amount of received light according to (4) or (5), the variation amount of the spherical aberration is detected, and the driving means is driven so as to reduce the variation amount of the spherical aberration. To do.
ΔSA = (a2 + b1) − (a1 + b2) (3)
ΔSA = (a2 ′ + b1 ′) − (a1 ′ + b2 ′) (4)
ΔSA = (a2 + b1 + a2 ′ + b1 ′) − (a1 + b2 + a1 ′ + b2 ′) (5)
[0016]
  According to this optical pickup device, in each light receiving surface of the multi-segment photodetector generated due to the difference in the magnitude or sign of the spherical aberration of the wavefront divided into four regions in the spherical aberration detection means.Above for each received light amountdifferenceΔS, The spherical aberration can be accurately detected, and the spherical aberration correcting means is driven by the driving means, so that the variation of the spherical aberration can be accurately corrected.
[0017]
Further, it is preferable that an optical path from the light source to the information recording surface of the optical information recording medium and an optical path from the information recording surface to the multi-divided photodetector are shared. In this case, the light source and the multi-divided It is preferable that the photodetector is formed on the same substrate.
[0018]
Further, the optical pickup device detects a reflected light from the information recording surface by a driving means for driving the objective lens and a tracking error and / or focusing of the objective lens by detecting the reflected light from the second optical detector. Error detection means for detecting an error, and an optical path from the information recording surface to the second photodetector and an optical path from the information recording surface to the multi-segment photodetector are shared. It is preferable. In this case, it is preferable that the second photodetector and the multi-segment photodetector are formed on the same substrate.
[0019]
  In addition, the optical pickup device collects the reflected light from the information recording surface on the light receiving surface of the multi-divided photodetector in the optical path between the spherical aberration correcting means and the multi-divided photodetector. The condensing lens includes:Combined with the optical element,It is preferable to give spherical aberrations having different sizes or different signs to at least the incident light beam and to perform amplitude division or wavefront division.
[0020]
  Also,The condensing lens preferably has an annular diffractive structure on at least one surface.
  The optical element preferably has an annular diffractive structure on at least one surface.
[0021]
  Also,Reference exampleThe fifth optical pickup device according to the present invention includes a light source, a coupling lens for converting the divergence of the light beam emitted from the light source, and an object for condensing the light beam from the light source on the information recording surface of the optical information recording medium. An optical pickup device including a lens and a condensing optical system that is disposed in an optical path between the light source and the objective lens, and includes a spherical aberration correction unit that corrects a variation in spherical aberration. A spherical aberration detector that detects a change in the spherical aberration by detecting reflected light from the recording surface; and a drive unit that drives the spherical aberration corrector according to the detection result of the spherical aberration detector. And a condensing lens included in the coupling lens and the spherical aberration detection unit, and disposed in an optical path between the photodetector included in the spherical aberration detection unit and the spherical aberration correction unit. And the lens, characterized in that substantially matches the characteristic with respect to wavelength variations and temperature changes of the light source.
[0022]
According to this optical pickup device, the coupling lens against the spherical aberration of the reflected light from the information recording surface detected by the photodetector of the spherical aberration detection means when the temperature change or the oscillation wavelength fluctuation of the light source occurs. The contribution can be canceled by the condenser lens. Thereby, the variation of the spherical aberration generated between the spherical aberration correcting means and the optical information recording medium can be detected with high accuracy by the spherical aberration detecting means.
[0023]
In this case, it is preferable that the coupling lens and the condenser lens are optically the same optical element.
[0024]
  Also,Reference exampleThe sixth optical pickup device according to the present invention is an optical pickup device provided with a condensing optical system including a light source and an objective lens that condenses the light beam from the light source on the information recording surface of the optical information recording medium. The condensing optical system includes at least two lens groups that can be shifted independently along the optical axis direction, and the shiftable lens groups are all made of a plastic material, and the shiftable lens groups are arranged in the optical axis direction. It has the drive means for changing along.
[0025]
According to this optical pickup device, since all the optical elements that can be displaced along the optical axis are made of a plastic material, the burden on the driving means can be reduced, so that the driving power of the driving means can be reduced. In addition, since the displacement by a smaller driving means is possible, the optical pickup device can be miniaturized.
[0026]
Further, the optical pickup device detects a reflected light from the information recording surface, and a spherical aberration correcting means for correcting a variation of spherical aberration arranged in an optical path between the light source and the objective lens. A spherical aberration detecting means for detecting the variation of the spherical aberration, and the spherical aberration correcting means has at least one movable element that can be displaced along the optical axis direction and can be displaced along the optical axis direction; At least one lens group among the lens groups is the movable element, and the lens group is movable along the optical axis direction, and at least one lens group other than the movable element is the lens group. An objective lens is preferred.
[0027]
  Further, the spherical aberration fluctuation amount that can be detected by the spherical aberration detector is calculated.ΔSA 'It is preferable to satisfy the following formula (1).
[0028]
  ΔSA '≧ 0.030λrms (1)
Where λ: oscillation wavelength of the light source (nm)
[0029]
  Further, the spherical aberration fluctuation amount that can be detected by the spherical aberration detector is calculated.ΔSA 'It is preferable that the following expression (2) is satisfied.
[0030]
  ΔSA '≧ 0.010λrms (2)
[0031]
The spherical aberration detection means generates a spherical aberration error signal corresponding to a variation amount of the spherical aberration generated in the condensing optical system, and drives the driving means so that the spherical aberration error signal becomes substantially zero. It is preferable to make it.
[0032]
In addition, it is preferable that a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information on the information recording surface of the optical information recording medium is 0.65 or more.
[0033]
Further, it is preferable that a predetermined numerical aperture on the image side of the objective lens necessary for recording or reproducing information on the information recording surface of the optical information recording medium is 0.75 or more.
[0034]
The objective lens is preferably composed of a first lens having a positive refractive power and a second lens having a positive refractive power, which are sequentially arranged from the light source side, and preferably satisfies the following expression (3).
[0035]
0.07 <NA.WD / f <0.35 (3)
NA: a predetermined image-side numerical aperture required for recording and / or reproduction on an optical information recording medium
WD: Working distance of the objective lens (mm)
f: Focal length (mm) of the entire system of the objective lens
[0036]
The objective lens is a single lens, and preferably satisfies the following expression (4).
[0037]
0.10 <NA.WD / f <0.40 (4)
NA: a predetermined image-side numerical aperture required for recording and / or reproduction on an optical information recording medium
WD: Working distance of the objective lens (mm)
f: Focal length (mm) of the entire system of the objective lens
[0038]
In addition, it is preferable that the objective lens is corrected for aberration so as to minimize aberration with respect to a parallel light beam from an object at infinity.
[0039]
In addition, it is preferable that the objective lens is corrected for aberration so as to minimize aberration with respect to a divergent light beam from an object at a finite distance.
[0040]
In addition, it is preferable that the objective lens is corrected for aberration so as to minimize the aberration with respect to the convergent light beam toward the image side object.
[0041]
The light source preferably generates light having a wavelength of 500 nm or less.
[0042]
The condensing optical system may include a coupling lens that converts a divergence angle of a divergent light beam from the light source in an optical path between the light source and the objective lens, and the coupling lens is made of a glass material. preferable.
[0043]
Further, the condensing optical system has a coupling lens for converting a divergence angle of a divergent light beam from the light source in an optical path between the light source and the objective lens, and the coupling lens has a refractive action. And a compound lens composed of a plastic material and / or an optical element made of an ultraviolet curable resin having one surface bonded to the glass lens and the other surface formed with an optical surface. As a result, the change in divergence and the change in the divergence of the emitted light from the coupling lens due to the change in the focal length of the coupling lens can be canceled out with respect to temperature change and / or humidity change. Therefore, a light beam with a constant divergence can always be emitted from the coupling lens.
[0044]
The coupling lens is a collimating lens that converts a divergent light beam from a light source into a parallel light beam, and the optical pickup device includes a light beam emitted from the light source in an optical path between the collimating lens and the objective lens. It is preferable to have a beam shaping element for reducing the astigmatic difference.
[0045]
Moreover, it is preferable that all optical elements other than the coupling lens included in the condensing optical system are formed of a plastic material.
[0046]
The condensing optical system may include a coupling lens for converting a divergence angle of a divergent light beam from the light source in an optical path between the light source and the objective lens, and the coupling lens may be made of a plastic material. preferable.
[0047]
The light source preferably emits a substantially circular light beam.
[0048]
The light source includes a semiconductor laser and a wavelength conversion element that converts a wavelength of light emitted from the semiconductor laser, and the condensing optical system converts light emitted from the wavelength conversion element into the information. When the wavelength of the light condensed from the recording surface and emitted from the semiconductor laser is λ0 nm and the wavelength of the light after wavelength conversion by the wavelength conversion element is λnm, the following equation (5) is satisfied. preferable.
[0049]
λ = λ0 / m (m = 2, 3,...) (5)
[0050]
The numerical aperture of the coupling lens is preferably 0.13 or less.
[0051]
Moreover, it is preferable that the said optical pick-up apparatus has a beam shaping element for relieving the astigmatic difference of the light beam inject | emitted from the light source in the optical path of the said light source and the said coupling lens.
[0052]
Moreover, it is preferable that all the optical elements included in the condensing optical system are formed of a plastic material.
[0053]
The condensing optical system preferably includes at least one diffractive optical element having an annular diffractive structure on at least one surface.
[0054]
Further, the diffractive optical element can be included in the spherical aberration correcting means.
[0055]
The diffractive optical element may be included in a coupling lens that is disposed in an optical path between the light source and the objective lens and converts a divergence angle of a divergent light beam from the light source.
[0056]
The diffractive optical element may be included in the objective lens.
[0057]
Further, it is preferable that the spherical aberration correcting means has at least one movable element that can be displaced along the optical axis direction.
[0058]
The spherical aberration correction means is a coupling lens that is disposed in an optical path between the light source and the objective lens and changes a divergence angle of a divergent light beam from the light source, and includes at least one constituting the coupling lens. It is preferable that one lens group is the movable element.
[0059]
The condensing optical system includes a collimating lens disposed in an optical path between the light source and the objective lens, and converts a divergent light beam from the light source into parallel light, and the spherical aberration correcting unit includes the collimating lens A beam expander disposed in an optical path between the lens and the objective lens, wherein at least one lens group constituting the beam expander is preferably the movable element.
[0060]
The driving means for driving the movable element can be constituted by a voice coil actuator or a piezo actuator.
[0061]
The spherical aberration correcting means can be configured such that the refractive index distribution along the direction perpendicular to the optical axis is variable.
[0062]
In addition, an audio and / or image recording / reproducing apparatus according to the present invention is equipped with the above-described optical pickup devices.
[0063]
  A first spherical aberration variation correction method according to the present invention includes a light source, an objective lens that focuses a light beam from the light source on an information recording surface of an optical information recording medium, and the light source and the objective lens. Placed in the light path,Occurs due to changes in temperature and / or humidityA condensing optical system including a spherical aberration correcting unit for correcting the variation of the spherical aberration, and a spherical aberration detecting unit for detecting the variation of the spherical aberration by detecting the reflected light from the information recording surface; And a driving means for driving the spherical aberration correcting means in accordance with a detection result of the spherical aberration detecting means. A method for correcting spherical aberration fluctuation in an optical pickup device, wherein the spherical aberration detecting means includes at least an incident light beam. Amplitude division or wavefront division is performed on the divided light flux or wavefront, and spherical aberrations of different sizes or different signsAddAnd an optical element through the optical elementAdded spherical aberrationA multi-split photodetector for receiving the split light beam, and the light splitting surface of the multi-split photodetector generated due to a difference in the magnitude or sign of the spherical aberration of the split light flux or wavefront. A variation amount of the spherical aberration is detected by detecting a difference in light amount, and the driving unit is driven so as to reduce the variation amount of the spherical aberration.
[0064]
According to the correction method of the spherical aberration fluctuation in this optical pickup device, by detecting the difference in the amount of light on the light receiving surface caused by the difference in the magnitude or sign of the spherical aberration of the divided light beam or wavefront. Spherical aberration can be detected with high accuracy. Thereby, the spherical aberration correcting means is driven by the driving means, and the variation of the spherical aberration can be accurately corrected.
[0065]
  A second spherical aberration variation correction method according to the present invention includes a light source, an objective lens that focuses a light beam from the light source on an information recording surface of an optical information recording medium, and the light source and the objective lens. Placed in the light path,Occurs due to changes in temperature and / or humidityA condensing optical system including a spherical aberration correcting unit for correcting the variation of the spherical aberration, and a spherical aberration detecting unit for detecting the variation of the spherical aberration by detecting the reflected light from the information recording surface; A spherical aberration variation correcting method in an optical pickup device having a driving means for driving the spherical aberration correcting means in accordance with a detection result of the spherical aberration detecting means, wherein the spherical aberration detecting means Spherical aberrationFluctuationA multi-segment photodetector having a first light-receiving surface and a second light-receiving surface, the areas of which are distributed so as to cause a change in the amount of light received in accordance with, the spherical aberration correcting means, and the multi-segment photodetector. The first light beam disposed between and receiving the reflected light from the information recording surface by the first light receiving surface, and the first light beam and the paraxial focal position or the best focus position are the same, The light beam is divided into a second light beam received by the second light receiving surface and an over spherical aberration is applied to the first light beam.AppendUnder spherical aberration in the second light fluxAddThe first light-receiving surface has two light-receiving portions, and when the two light-receiving portions have received light amounts A1 and A2 in the respective light-receiving portions, A1 = A2 in the reference state And the second light receiving surface has two light receiving parts, and when the two light receiving parts have received light amounts B1 and B2 in the respective light receiving parts, B1 = B2 is satisfied in the reference state,Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in an under direction, the received light amount A1 on the first light receiving surface increases from the reference state, the received light amount A2 decreases, and the received light amount B1 on the second light receiving surface. Decreases from the reference state and the received light amount B2 increases,Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in the over direction, the received light amount A1 on the first light receiving surface decreases from the reference state and the received light amount A2 increases, and the received light amount B1 on the second light receiving surface. Increases from the reference state, and the amount of received light B1 decreases, and the amount of received light according to the following equation generated due to the difference in the magnitude or sign of the spherical aberration between the first light flux and the second light flux. By detecting the difference ΔSA, the variation amount of the spherical aberration is detected, and the driving unit is driven to reduce the variation amount of the spherical aberration.
ΔSA = (A2 + B1) − (A1 + B2)
[0066]
  According to the correction method of the spherical aberration variation in the optical pickup device, the first light receiving surface that is generated due to the difference in the magnitude or sign of the spherical aberration between the first light flux and the second light flux.Each received light amountAnd in the second light receiving surfaceAbove for each received light quantitydifferenceΔSBy detecting this, it is possible to accurately detect spherical aberration. Thereby, the spherical aberration correcting means is driven by the driving means, and the variation of the spherical aberration can be accurately corrected.
[0067]
  A third spherical aberration variation correction method according to the present invention includes a light source, an objective lens that focuses a light beam from the light source on an information recording surface of an optical information recording medium, and the light source and the objective lens. Placed in the light path,Occurs due to changes in temperature and / or humidityA condensing optical system including a spherical aberration correcting unit for correcting the variation of the spherical aberration, and a spherical aberration detecting unit for detecting the variation of the spherical aberration by detecting the reflected light from the information recording surface; And a driving means for driving the spherical aberration correcting means according to a detection result of the spherical aberration detecting means. A correction method for spherical aberration fluctuations in an optical pickup device, wherein the spherical aberration detecting means is a clockwise direction. In order of the spherical aberration of the incident light beamFluctuationA first light receiving surface, a second light receiving surface, a third light receiving surface facing the first light receiving surface, and the second light receiving surface, the areas of which are distributed so as to change the amount of light received according to A multi-divided photodetector having a light-receiving surface divided into at least four regions of a fourth light-receiving surface facing the surface, and disposed between the spherical aberration correcting means and the multi-divided photodetector; The wavefront of the reflected light from the surface is received by the respective light receiving surfaces of the multi-split photodetector, and is divided into wavefronts of four regions in which the paraxial focus position or the best focus position is the same, and the first Over spherical aberration on the wavefront received by the light receiving surface and the third light receiving surface.AppendUnder-spherical aberration in the wavefronts received by the second light receiving surface and the fourth light receiving surfaceAddThe first light receiving surface is divided into two light receiving portions, the light receiving amounts at the respective light receiving portions are a1 and a2, and the second light receiving surface is two light receiving portions. The third light receiving surface is divided into two light receiving parts, and the light receiving amounts at the respective light receiving parts are a1 ′ and a2 ′. The light receiving surface 4 is divided into two light receiving portions, and the amount of light received by each light receiving portion is b1 ′ and b2 ′, and each light receiving portion of each light receiving surface is expressed by the following formula (1) or (2) The filling,
a1 = a2, b1 = b2, a1 '= a2', b1 '= b2' (1)
(a2 + b1) − (a1 + b2) = 0, (a2 ′ + b1 ′) − (a1 ′ + b2 ′) = 0 (2)
Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in an under direction, the received light amounts a1, a1 ′, b2, b2 ′ on the respective light receiving surfaces increase from the reference state, and the received light amounts a2, a2 ′, b1, b1. 'Decrease,Includes spherical aberration added by the optical elementWhen the spherical aberration of the reflected light fluctuates in the over direction, the received light amounts a1, a1 ′, b2, b2 ′ at the respective light receiving surfaces are reduced from the reference state, and the received light amounts a2, a2 ′, b1, b1. ′ Increases, and the following expression (3) on each light receiving surface of the multi-segment photodetector generated due to the difference in the magnitude or sign of the spherical aberration of the wavefront divided into the four regions, By detecting the difference ΔSA in the amount of received light according to (4) or (5), the variation amount of the spherical aberration is detected, and the driving means is driven so as to reduce the variation amount of the spherical aberration. To do.
ΔSA = (a2 + b1) − (a1 + b2) (3)
ΔSA = (a2 ′ + b1 ′) − (a1 ′ + b2 ′) (4)
ΔSA = (a2 + b1 + a2 ′ + b1 ′) − (a1 + b2 + a1 ′ + b2 ′) (5)
[0068]
  According to the correction method of the spherical aberration variation in this optical pickup device, the light reception of each of the multi-segment photodetectors caused by the difference in the magnitude or sign of the spherical aberration of the wavefront divided into the four regions. In terms ofAbove for each received light amountdifferenceΔSBy detecting this, it is possible to accurately detect spherical aberration. Thereby, the spherical aberration correcting means is driven by the driving means, and the variation of the spherical aberration can be accurately corrected.
[0069]
The spherical aberration fluctuation correction method is a spherical aberration fluctuation correction method in an optical pickup device including at least one plastic lens in the condensing optical system, and at least with respect to temperature and / or humidity changes. It is preferable to correct a change in spherical aberration caused by a change in at least one of the shape and refractive index of the plastic lens and / or a change in oscillation wavelength of the light source.
[0070]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, optical pickup devices according to first to sixth embodiments of the present invention will be described with reference to the drawings.
[0071]
<First Embodiment>
[0072]
FIG. 1 is a diagram showing a schematic configuration of the optical pickup device according to the first embodiment, and FIG. 2 is a schematic plan view of the light receiving surface of the multi-segment photodetector shown in FIG. FIG. 3 is a perspective view showing a hologram element as an example of the spherical aberration adding element of FIG.
[0073]
As shown in FIG. 1, the optical pickup apparatus according to the present embodiment uses a beam expander 5 composed of a negative lens 5a and a positive lens 5b as spherical aberration correction means.
[0074]
  In the optical pickup device of FIG. 1, a light beam emitted from a light source 1 composed of a semiconductor laser is coupled with a coupling lens 2, a beam shaping prism pair 3, a polarization beam.lightAfter passing through the beam splitters 4, 4 ′, the beam expander 5, the quarter wavelength plate 6 and the diaphragm 7, the light is condensed by the objective lens 8 onto the information recording surface 9 ′ via the transparent substrate 9 of the optical information recording medium. It is comprised so that.
[0075]
  Further, the reflected light from the information recording surface 9 ′ passes again through the objective lens 8, the beam expander 5, etc., and then partly polarized.lightReflected by the beam splitter 4 ′, passes through the spherical aberration adding element 12 and the condenser lens 13, travels to the multi-segment photodetector 15, and the rest is polarized.lightAfter passing through the beam splitter 4 'lightThe beam is reflected by the beam splitter 4 and directed to the tracking / focusing error detection means 19.
[0076]
1 includes a biaxial actuator 10 that drives the objective lens 8 in biaxial directions for tracking / focusing as objective lens driving means, and a beam expander as driving means for spherical aberration correction means. And a uniaxial actuator 11 for driving the negative lens 5a in the optical axis direction.
[0077]
Further, after detecting the focusing error by the tracking error / focusing error detecting means 19 and performing the focus servo pull-in operation by the biaxial actuator 10, the multi-segment photodetector 15 detects the variation of the spherical aberration. The detection of the tracking error / focusing error can be performed using a known push-pull method, astigmatism method, or the like, and will not be described.
[0078]
Next, the principle of detection of spherical aberration variation and correction of spherical aberration variation in the present embodiment will be described.
[0079]
As shown in FIGS. 2A and 2B, the multi-segment photodetector 15 has a light receiving surface 14a and a light receiving surface 14b having a predetermined area, and the light receiving surface 14a and the light receiving surface 14b are on the same substrate. It is the structure formed in. The light receiving surface 14a is divided into light receiving portions A1 and A2 having a predetermined area by a dividing line 19, and the light receiving surface 14b is divided into light receiving portions B1 and B2 having a predetermined area by a dividing line 20.
[0080]
  As shown in FIG. 1, the light is reflected by the information recording surface 9 ', passes through the objective lens 8 and the beam expander 5 of the spherical aberration correcting means, and is deflected.lightBeam splitter4 'The first light beam 16a received by the light receiving surface 14a when one surface passes through the spherical aberration adding element 12 having one surface formed as a hologram surface, and the light beam 16 reflected by the light beam (hereinafter referred to as "reflected light 16"); The light beam is split into two light beams of the second light beam 16b received by the light receiving surface 14b, and the spherical aberration adding element 12 causes an under spherical aberration component in the first light beam 16a, while the second light beam 16b has an under spherical aberration component. An excessive spherical aberration component is added. This spherical aberration component is preferably equal to the spherical aberration component generated by the thickness error of the transparent substrate 9 of the optical information recording medium, and the size is the maximum amount including the spherical aberration component due to temperature change and wavelength variation. Is preferred. At this time, the paraxial focal positions of the first light beam 16a and the second light beam 16b are the same, and the light receiving surfaces 14a and 14b of the multi-split photodetector 15 are arranged at this position.
[0081]
As the spherical aberration adding element 12, a hologram element 12a as shown in FIG. 3 can be used. When the pattern of the hologram surface 12b is determined from a predetermined spherical aberration amount at the light source wavelength and a predetermined light beam separation amount on the multi-segmented photodetector 15, one of ± first-order diffracted light has an under spherical aberration and the other is an over. The spherical aberrations are respectively added. The hologram surface 12b is preferably configured as a sine wave or rectangular wave type grating having a phase difference of λ / 2 of the light source wavelength (λ).
[0082]
2C and 2D, the reflected light from the information recording surface 9 ′ on the light receiving surface 14a and the light receiving surface 14b when the reflected light 16 has no variation in spherical aberration (hereinafter referred to as “reference state”). The light receiving pattern is shown. The sizes of the light receiving portions A1, A2, B1, and B2 and the shape of the spherical aberration adding element 12 are the light receiving amounts A1, A2, B1, and B2 of the respective light receiving portions in the reference state (each light receiving amount is the same as each light receiving portion (Represented by a sign)
A1 = A2
B1 = B2
It is determined to satisfy.
[0083]
In the above-described reference state, the spot received by the light receiving surface 14a has an under spherical aberration, and the spot received by the light receiving surface 14b has an over spherical aberration. That is, a nucleus having a relatively high light density is formed at the center, and a flare having a low light density is formed at the periphery.
[0084]
Here, when the spherical aberration of the reflected light 16 fluctuates in an under direction (hereinafter referred to as an “under state”), the light receiving pattern is as shown in FIGS.
That is, as shown in the figure, the spot received by the light receiving surface 14a is emphasized by an under spherical aberration, and the intensity of the peripheral flare is large and the intensity of the central nucleus is small compared to the reference state. On the other hand, the spot received by the light receiving surface 14b has reduced over-spherical aberration, the intensity of the peripheral flare is smaller than that of the reference state, and the intensity of the central nucleus is increased.
[0085]
  Also reflected light16When the spherical aberration of the lens fluctuates in the over direction (hereinafter referred to as “over state”), the light receiving pattern is as shown in FIGS. In other words, as shown in the figure, the spot received by the light receiving surface 14a is reduced in under spherical aberration, the intensity of the peripheral flare is smaller than that in the reference state, and the intensity of the central nucleus is increased. On the other hand, the spot received by the light receiving surface 14b is emphasized by excessive spherical aberration, and the intensity of the peripheral flare is large and the intensity of the central nucleus is small compared to the reference state.
[0086]
Table 1 shows changes in the light amounts A1, A2, B1, and B2 received by the light receiving portions of the light receiving surfaces 14a and 14b with respect to the reference state. In Table 1, “+” indicates that the amount of light increases compared to the reference state, and “−” indicates that the amount of light decreases compared to the reference state.
[0087]
[Table 1]

[0088]
The spherical aberration error signal ΔSA is detected by the following calculation based on the amount of light received by each light receiving portion of the multi-segment photodetector 15.
[0089]
ΔSA = (A2 + B1) − (A1 + B2)
[0090]
From Table 1, it can be seen that ΔSA <0 in the under state and ΔSA> 0 in the over state.
[0091]
When ΔSA <0 is detected in the multi-segment photodetector 15 in FIG. 1, the negative lens 5a and the positive lens 5b are compared with the reference state by the uniaxial actuator 11 which is a driving unit of the beam expander 5. The negative lens 5a is shifted along the optical axis direction so that ΔSA = 0. On the other hand, when ΔSA> 0 is detected, the uniaxial actuator 11 which is the driving means of the beam expander 5 is negatively adjusted so as to narrow the distance between the negative lens 5a and the positive lens 5b as compared with the reference state. The lens 5a is shifted along the optical axis direction so that ΔSA = 0.
[0092]
The arrangement of the light receiving surfaces of the multi-segment photodetector 15 is not limited to the paraxial focal position of the first light beam 16a and the second light beam 16b as described above, and may be on the inner side or the outer side. It is possible to detect and correct the variation of spherical aberration by the principle of.
Next, a modification of the optical pickup device of FIG. 1 will be described with reference to FIG. The optical pickup device shown in FIG. 4 has a coupling lens that can be displaced along the direction of the optical axis as spherical aberration correction means, and can achieve the same effect as that of FIG.
[0093]
  As shown in FIG. 4, the light flux from the light source 1 is deviated.lightIt passes through the beam splitters 4 and 4 ′, the quarter-wave plate 6, the coupling lens 2, and the diaphragm 7, and is focused on the information recording surface 9 ′ by the objective lens 8 through the transparent substrate 9 of the optical information recording medium. The The reflected light from the information recording surface 9 ′ is partially polarized after passing through the objective lens 8 and the coupling lens 2.lightReflected by the beam splitter 4 ′, passes through the spherical aberration adding element 12, goes to the multi-segment photodetector 15, and the rest is polarized.lightAfter passing through the beam splitter 4 'lightThe light is reflected by the beam splitter 4 and travels toward the tracking / focusing error detection means 19.
[0094]
  Further, the coupling lens 2 as the spherical aberration correcting unit is illustrated by a uniaxial actuator 11 as the driving unit of the spherical aberration correcting unit.4It is configured to be movable along the optical axis direction. 1 and 4, a voice coil actuator, a piezo actuator, or the like can be used as the driving means (uniaxial actuator 11) for the beam expander 5 or the coupling lens 2.
[0095]
Further, the condensing lens 13 in FIG. 1 that condenses the reflected light from the information recording surface 9 ′ on the multi-divided photodetector 15 is the same optical element as the coupling lens 2 and is omitted. As a result, it is possible to reduce the size of the optical pickup device and to reduce the number of components.
[0096]
If the spherical aberration error signal ΔSA <0 is detected by the multi-segment photodetector 15 of the optical pickup device of FIG. 4, the coupling lens 2 is compared with the reference state by the driving means 11 of the coupling lens 2. The coupling lens 2 is shifted so that ΔSA = 0 along the optical axis direction so that the distance between the objective lens 8 and the objective lens 8 is reduced. On the other hand, when ΔSA> 0 is detected, the coupling lens 2 is moved by the driving means 11 of the coupling lens 2 so that the distance between the coupling lens 2 and the objective lens 8 is increased as compared with the reference state. A shift is made along the optical axis direction so that ΔSA = 0.
[0097]
Next, another modification of the optical pickup device of FIG. 1 will be described with reference to FIG. The optical pickup device of FIG. 5 uses a refractive index distribution variable element instead of the beam expander 5 of FIG. 1 as spherical aberration correction means, and can obtain the same effect as FIG.
[0098]
  As shown in FIG. 5, the light flux from the light source 1 is deviated.lightThe light passes through the beam splitters 4, 4 ′, the refractive index distribution variable element 17, etc., and is focused on the information recording surface 9 ′ by the objective lens 8 through the transparent substrate 9 of the optical information recording medium. The reflected light from the information recording surface 9 ′ is partially polarized after passing through the objective lens 8 and the refractive index distribution variable element 17.lightReflected by the beam splitter 4 ′, passes through the spherical aberration adding element 12 and the condenser lens 13, travels to the multi-segment photodetector 15, and the rest is polarized.lightAfter passing through the beam splitter 4 'lightThe light is reflected by the beam splitter 4 and travels toward the tracking / focusing error detection means 19.
[0099]
The refractive index distribution variable element 17 having a variable refractive index distribution as the spherical aberration correcting means shown in FIG. 5 includes, for example, optically transparent electrode layers 17a, 17b, and 17c that are electrically connected to each other, and an electrode layer. Refractive index distribution variable layers 17d and 17e that are electrically insulated from 17a, 17b, and 17c, and whose refractive index distribution changes according to the voltage applied from the driving means 18, are alternately stacked to form electrode layers 17a, 17b. , 17c can be used.
[0100]
When the spherical aberration error signal ΔSA is detected by the multi-segment photodetector 15 of the optical pickup device of FIG. 5, a voltage is applied to the electrode layers 17a, 17b, and 17c by the driving means 18 of the refractive index distribution variable element 17. Then, the refractive indexes of the refractive index distribution variable layers 17d and 17e are changed depending on the location, and the phase of the light emitted from the refractive index distribution variable element 17 is controlled so that ΔSA becomes zero.
[0101]
Further, as an element having a variable refractive index distribution, a liquid crystal element a in which liquid crystal molecules are aligned in an X direction in a plane perpendicular to the optical axis, and a liquid crystal molecule in a plane perpendicular to the optical axis. The liquid crystal elements b aligned in the Y direction perpendicular to the X direction can also be used. The liquid crystal element a and the liquid crystal element b are alternately stacked with the glass substrate c interposed therebetween, and a voltage is applied to each of the liquid crystal element a and the liquid crystal element b, so that the phase of the light emitted from the spherical aberration correcting unit is adjusted. By controlling the X direction component and the Y direction component independently, it is possible to correct the variation of the spherical aberration.
[0102]
Further, by using the condensing lens 13 as a diffractive lens, the condensing lens 13 may have the function of the spherical aberration adding element 12. By using the spherical aberration adding element 12 and the condenser lens 13 in common, the components of the optical pickup optical system can be reduced, and a simpler configuration can be achieved.
[0103]
<Second Embodiment>
[0104]
FIG. 12 is a diagram showing a schematic configuration of an optical pickup device according to the second embodiment.
[0105]
  The optical pickup device according to the present embodiment shown in FIG. 12 shares an optical path from the light source 1 to the information recording surface 9 ′ and an optical path from the information recording surface 9 ′ to the multi-divided photodetector 15, and FIG. sidelightThe beam splitter 4 ′ is omitted, the light source 1 and the multi-split photodetector 15 are formed on the same substrate, and the positive lens 5 b of the beam expander 5 is moved along the optical axis direction by the uniaxial actuator 11. Since the configuration is basically the same as that of FIG. 1 except that the variation of the spherical aberration is corrected, the same parts are denoted by the same reference numerals and the description thereof is omitted.
[0106]
As shown in FIG. 12, the light source 1, the multi-segment photodetector 15, the hologram 20 and the spherical aberration adding element 12 are unitized in the light source / multi-segment photodetector integrated unit 24 '.
[0107]
  A light beam emitted from the light source 1 is transmitted through a hologram 20, a coupling lens 2, a beam shaping prism pair 3, a polarization beam.lightAfter passing through the beam splitter 4, the beam expander 5, the quarter wavelength plate 6 and the diaphragm 7, the light is condensed by the objective lens 8 onto the information recording surface 9 ′ through the transparent substrate 9 of the optical information recording medium. The reflected light from the information recording surface 9 ′ passes again through the objective lens 8, the diaphragm 7, the quarter wavelength plate 6, and the beam expander 5, and then partially polarized.lightReflected by the beam splitter 4 toward the tracking error / focusing error detecting means 19 and the rest is biased.lightAfter passing through the beam splitter 4, it passes through the beam shaping prism pair 3 and the coupling lens 2, and is diffracted by the hologram 20 toward the spherical aberration detecting means. According to such an optical pickup device in FIG. 12, the same effect as in FIG. 1 can be obtained.
[0108]
Further, the condensing lens 13 in FIG. 1 that condenses the reflected light from the information recording surface 9 ′ on the multi-divided photodetector 15 is the same optical element as the coupling lens 2 and is omitted. As a result, it is possible to reduce the size of the optical pickup device and to reduce the number of components.
[0109]
When using the beam shaping prism pair 3 for reducing the astigmatic difference of the light beam emitted from the light source as in each of the optical pickup devices of FIGS. 1, 5, 6 and 12, the beam shaping prism pair 3 In order to prevent the generation of astigmatism due to, the divergence of the light beam incident on the beam shaping prism pair 3 must always be kept constant. For this reason, it is preferable that the coupling lens 2 is a glass lens. Thereby, even when a temperature change and / or a humidity change occur, the divergence of the light beam incident on the beam shaping prism pair 3 can be kept constant. Further, this glass coupling lens is used as a diffractive lens, and the movement of the focal point of the coupling lens when the wavelength of the light source slightly changes is suppressed, so that the light enters the beam shaping prism pair 3 even when the wavelength of the light source slightly changes. This is more preferable because the divergence of the luminous flux can be kept constant.
[0110]
When the temperature change and / or the humidity change occur, the distance from the light source to the coupling lens 2 changes due to the shape change of the lens frame that holds the coupling lens 2, and the emission light from the coupling lens 2 diverges. The degree may change. The coupling lens 2 is composed of a glass lens having a refractive action and an optical element made of a plastic material and / or an ultraviolet curable resin having an optical surface formed on the other surface bonded to the glass lens. When the composite lens is used, the above-described change in divergence and the change in the divergence of the emitted light from the coupling lens 2 due to the change in the focal length of the coupling lens 2 itself can cancel each other. A light flux having a constant divergence can always be emitted from the coupling lens 2 with respect to changes and / or humidity changes. As such a compound lens type coupling lens 2, a coupling lens as disclosed in Japanese Patent Application No. 2000-053858 by the same applicant can be used.
[0111]
<Third Embodiment>
[0112]
FIG. 13 is a diagram showing a schematic configuration of an optical pickup device according to the third embodiment.
[0113]
The optical pickup device according to the present embodiment shown in FIG. 13 is similar to FIG. 4 in that the condensing lens 13 and the coupling lens shown in FIG. 1 condense the reflected light from the information recording surface 9 ′ on the multi-segment photodetector 15. 2 is the same optical element, and compared with FIG. 4, a beam shaping lens for reducing the astigmatic difference of the light beam emitted from the light source 1 in the optical path between the light source 1 and the coupling lens 2. Since the configuration is basically the same as that of FIG. 4 except that 21 is arranged, the same parts are denoted by the same reference numerals, and the description thereof is omitted.
[0114]
An anamorphic lens can be used as the beam shaping lens 21 shown in FIG. The surface shape of the anamorphic lens is determined by the magnitude of the astigmatism difference of the light beam emitted from the light source.
[0115]
  As shown in FIG. 13, the light beam emitted from the light source 1 is reflected by the beam shaping lens 21 and the polarization.lightBeam splitter 4 ', biaslightAfter passing through the beam splitter 4, the coupling lens 2, the beam expander 5, the quarter wavelength plate 6, and the diaphragm 7, the objective lens 8 collects it on the information recording surface 9 ′ via the transparent substrate 9 of the optical information recording medium. Lighted. The reflected light from the information recording surface 9 ′ passes again through the objective lens 8, the quarter-wave plate 6, the beam expander 5, and the coupling lens 2, and a part thereof is polarized.lightReflected by the beam splitter 4 ′ and directed to the tracking error / focusing error detecting means 19, and the rest is biased.lightAfter passing through the beam splitter 4 'lightThe light is reflected by the beam splitter 4 and travels toward the spherical aberration detection means. According to such an optical pickup device of FIG. 13, the same effect as that of FIG. 4 can be obtained.
[0116]
Furthermore, in the optical pickup device of FIG. 13, since the beam shaping element is disposed in the optical path between the light source 1 and the coupling lens 2, the coupling lens 2 can be a plastic lens. Spherical aberration that occurs due to a change in the divergence of the light beam emitted from the coupling lens 2 when a temperature change, a humidity change, or a slight wavelength fluctuation of the light source occurs, causes the coupling lens 2 to be moved by the uniaxial actuator. Correction is possible by shifting in the direction of the optical axis.
[0117]
A beam shaping prism pair 3 or a beam shaping lens 21 for reducing the astigmatic difference of the light beam emitted from the light source 1 is provided as in each of the optical pickup devices of FIGS. 1, 5, 6, 12, and 13. If used, the entire luminous flux from the light source can be taken in by the coupling lens 2 without losing the amount of light, which is preferable because even a low-output light source can be applied. Further, since the driving voltage of the light source can be small, the life of the light source can be extended.
[0118]
<Fourth embodiment>
[0119]
FIG. 14 is a diagram showing a schematic configuration of an optical pickup device according to the fourth embodiment.
[0120]
The optical pickup device according to the present embodiment shown in FIG. 14 has a condensing lens 13 and a coupling lens in FIG. 1 for condensing the reflected light from the information recording surface 9 ′ on the multi-segment photodetector 15 as in FIG. 2 are the same optical elements and have basically the same configuration as that of FIG. 4, and thus the same parts are denoted by the same reference numerals and the description thereof is omitted.
[0121]
As shown in FIG. 14, the optical path from the information recording surface 9 ′ to the second optical detector 19 for tracking error / focusing error detection and the optical path from the information recording surface 9 ′ to the multi-segment optical detector 15 are shared. Thus, the second photodetector for detecting the tracking error / focusing error and the multi-segment photodetector 15 are formed on the same substrate. In the multi-divided photodetector / second photodetector integrated unit 25 ′, the multi-divided photodetector 15, the second photodetector 19, the hologram 20, and the spherical aberration adding element 12 are unitized.
[0122]
Further, by making the objective lens 8 a finite conjugate type that condenses the divergent light beam from the light source 1 on the information recording surface 9 ′, a large working distance is secured, and the collision between the optical information recording medium and the objective lens 8 is prevented. It is preventing. Further, the correction of the spherical aberration fluctuation is performed by the coupling lens 2 that is arranged in the optical path between the light source 1 and the objective lens 8 and can be shifted along the optical axis direction.
[0123]
  As shown in FIG. 14, the light beam emitted from the light source 1 is polarized.lightAfter passing through the beam splitter 4, the coupling lens 2, the quarter wavelength plate 6 and the diaphragm 7, the light is condensed by the objective lens 8 onto the information recording surface 9 ′ via the transparent substrate 9 of the optical information recording medium. The reflected light from the information recording surface 9 ′ passes again through the objective lens 8, the quarter wavelength plate 6, and the coupling lens 2, and then is deflected.lightIt is reflected by the beam splitter 4 and enters the hologram 20. Of the diffracted light generated by the hologram 20, the m-th order diffraction is directed to the spherical aberration detection means, and the n-th order diffracted light (where m ≠ n) is directed to the tracking error / focusing error detection means 19. According to such an optical pickup device in FIG. 14, the same effect as in FIG. 4 can be obtained.
[0124]
<Fifth embodiment>
[0125]
FIG. 15 is a diagram showing a schematic configuration of an optical pickup device according to the fifth embodiment.
[0126]
In the optical pickup device according to the present embodiment shown in FIG. 15, the objective lens 8 has a two-group configuration including two positive lenses 22 and 23, and the lenses 22 and 23 are arranged in the optical axis direction and / or optical axis. Since the configuration is basically the same as that of FIG. 4 except that the coupling lens 2 of FIG. 4 is omitted, the same parts are denoted by the same reference numerals and description thereof is omitted. .
[0127]
The first lens 22 on the light source side is displaced by the uniaxial actuator 11 in order to correct the spherical aberration variation, and the second lens 23 on the optical information recording medium side is moved by the biaxial actuator 10 in order to reduce the tracking error / focusing error. Change.
[0128]
  As shown in FIG. 15, the light beam emitted from the light source 1 is polarized.lightBeam splitter 4lightAfter passing through the beam splitter 4 ′, the quarter-wave plate 6, and the diaphragm 7, the light is condensed on the information recording surface 9 ′ by the objective lens 8 through the transparent substrate of the optical information recording medium. The reflected light from the information recording surface 9 ′ passes again through the objective lens 8 and the quarter-wave plate 6 and is partially polarized.lightReflected by the beam splitter 4 ′ and directed to the tracking error / focusing error detecting means 19, and the rest is biased.lightAfter passing through the beam splitter 4 'lightThe light is reflected by the beam splitter 4 and travels toward the spherical aberration detection means. According to such an optical pickup device in FIG. 14, the same effect as in FIG. 4 can be obtained.
[0129]
In each of the optical pickup devices shown in FIGS. 1, 5, 6, 12, and 13, the light source 1 is a high-power semiconductor laser or a light source that can emit a light beam that is substantially circular and has almost no astigmatic difference. , The beam shaping prism pair 3 or the beam shaping lens 21 for reducing the astigmatism of the light beam emitted from the light source 1 can be omitted, and the coupling lens can be a plastic lens. preferable.
[0130]
When a high-power semiconductor laser is used as a light source, an elliptical light beam emitted from the light source is shaped into a circular shape by utilizing the effect of the light beam from the coupling lens 2. In order to capture a sufficient amount of light in a direction with a small angle, it is preferable that the numerical aperture of the coupling lens 2 is 0.13 or less.
[0131]
As a light source capable of emitting a substantially circular light beam having substantially no astigmatic difference, a light source in which an SHG (Second Harmonic Generation) element is formed in front of the semiconductor laser can be used.
[0132]
<Sixth embodiment>
[0133]
FIG. 6 is a diagram showing a schematic configuration of the optical pickup device according to the sixth embodiment, and FIG. 7 is a schematic plan view of the light receiving surface of the multi-segment photodetector shown in FIG. 6 viewed from the direction AA in FIG. FIG.
[0134]
As shown in FIG. 6, the optical pickup device of the present embodiment uses a beam expander composed of a positive lens 5a and a negative lens 5b as spherical aberration correction means, as in FIG. Since the configuration is the same except that the light receiving surface of the detector is further divided into a large number, the same parts are denoted by the same reference numerals, and the description thereof is omitted.
[0135]
The principle of detecting the variation of spherical aberration and correcting the variation of spherical aberration in this embodiment will be described with reference to FIG. As shown in FIG. 7A, the light receiving surface 24 of the multi-split photodetector 25 is divided into light receiving surfaces 24a and 24b by dividing lines 21 and 22, and the light receiving surfaces 24a and 24b are divided by dividing lines 23. Furthermore, it is divided into light receiving parts a1, a2, a1 ′, a2 ′ and b1, b2, b1 ′, b2 ′. The light receiving portions a1 and a2 and the light receiving portions a1 'and a2' and the light receiving portions b1 and b2 and the light receiving portions b1 'and b2' are in positions facing each other.
[0136]
In the optical pickup device of FIG. 6, when the reflected light from the information recording surface 9 ′ passes through the spherical aberration adding element 12, the reflected light from the XZ plane of FIG. An over spherical aberration component is added to the received light beam, and an under spherical aberration component is added to the light beam in the YZ plane, that is, the light beam received by the light receiving surface 24a. At this time, the best focus position of the light beam in the XZ plane and the light beam in the YZ plane is made the same, and the light receiving surface 24 of the multi-divided photodetector 25 receives the light beam in the XZ plane and the Y- It is arranged outside the best focus position of the light beam in the Z plane.
[0137]
FIG. 7B shows a light receiving pattern of reflected light from the information recording surface of the light receiving surface 24 in the reference state. The sizes of the light receiving portions a1, a2, b1, b2, a1 ′, a2 ′, b1 ′, b2 ′ and the shape of the spherical aberration adding element 12 are the light receiving amounts a1, a2, b1 of the respective light receiving portions in the reference state. , B2, a1 ′, a2 ′, b1 ′, b2 ′ (each received light amount is represented by the same symbol as each light receiving unit),
a1 = a2, a1 '= a2'
b1 = b2, b1 ′ = b2 ′
Or
(A2 + b1) − (a1 + b2) = 0
(A2 '+ b1')-(a1 '+ b2') = 0
It is determined so that
[0138]
The spot received by the light receiving surface 24a has a spherical aberration under, that is, forms a nucleus having a relatively high light density at the center and forms a flare having a low light density at the periphery. The spot received by the light receiving surface 24b is in a state where the spherical aberration is over, that is, a ring-shaped spot having a relatively high light density is formed in the periphery.
[0139]
In the under state, the light receiving pattern is as shown in FIG. The spot received by the light receiving surface 24a is enhanced by under spherical aberration, and the intensity of the peripheral flare is large and the intensity of the central nucleus is small compared to the reference state. On the other hand, the spot received by the light receiving surface 24b is reduced in excessive spherical aberration, and the surrounding ring-shaped spots approach a uniform intensity distribution.
[0140]
In the over state, the light receiving pattern is as shown in FIG. The spot received by the light receiving surface 24a is reduced in under spherical aberration and approaches a uniform intensity distribution. On the other hand, the spot received by the light receiving surface 24b is emphasized by excessive spherical aberration, and the intensity of the peripheral ring-shaped sbot is increased compared to the reference state.
[0141]
Table 2 below shows changes in the amount of light received by the light receiving portions of the light receiving surfaces 24a and 24b with respect to the reference state. In Table 2, “+” indicates that the amount of light increases compared to the reference state, and “−” indicates that the amount of light decreases compared to the reference state.
[0142]
[Table 2]

[0143]
  The spherical aberration error signal ΔSA is detected by the following calculation based on the amount of light received by each light receiving unit of the multi-segment photodetector 25.
ΔSA = (a2 + b1) − (a1 + b2)
Or
ΔSA = (a2 ′ + b1 ′) − (a1 ′ + b2 ′)
Or
ΔSA = (a2 + b1 + a2 ′ + b1 ′) − (a1 + b2 + a1 ′ + b2 ′)
[0144]
From Table 2, it can be seen that ΔSA <0 in the under state and ΔSA> 0 in the over state.
[0145]
When the multi-divided light detector 25 detects ΔSA <0, the driving means 11 of the beam expander 5 causes the negative lens to widen the interval between the negative lens 5a and the positive lens 5b as compared with the reference state. 5a is shifted along the optical axis direction so that ΔSA = 0. On the other hand, when ΔSA> 0 is detected, the beam expander driving means 11 moves the negative lens 5a in the direction of the optical axis so as to narrow the distance between the negative lens 5a and the positive lens 5b as compared with the reference state. And shift so that ΔSA = 0.
[0146]
Further, even when the light receiving surface 14 of the multi-segment photodetector 15 is disposed inside the best focus position of the light beam in the XZ plane and the light beam in the YZ plane, the same principle as described above is used. It is possible to detect and correct variations in spherical aberration.
[0147]
4 and 5, a coupling lens or a refractive index distribution variable element that can be shifted along the optical axis direction may be used as the spherical aberration correction means in the optical pickup device of FIG. 6.
[0148]
【Example】
Next, the present invention will be described more specifically with reference to Examples 1 and 2. The aspherical surface in the lens of the present embodiment is expressed by the following equation 1 where the optical axis direction is the X axis, the height perpendicular to the optical axis is h, and the curvature radius of the refractive surface is r. Here, κ is a cone coefficient, and A2i is an aspheric coefficient.
[0149]
[Expression 1]

[0150]
Further, the annular diffractive surface provided in the lens of the present embodiment can be expressed by the following formula 2 as an optical path difference function Φb. Here, h is a height perpendicular to the optical axis, and b2i is a coefficient of an optical path difference function.
[0151]
[Expression 2]

[0152]
<Example 1>
[0153]
Table 3 shows data of an optical system preferable for use in the optical pickup device shown in FIG. In this embodiment, the image side numerical aperture of the objective lens is 0.85, the oscillation wavelength of the light source for recording or reproducing information is 405 nm, and all the components are made of a plastic material having a high internal transmittance in the short wavelength region. Formed. A beam expander composed of one negative lens and one positive lens is used as spherical aberration correction means, and the fluctuation of spherical aberration generated in the optical system is shifted along the optical axis. Corrected. In this embodiment, among the constituent lenses of the beam expander, the positive lens may be shifted or both the positive lens and the negative lens may be shifted in order to correct the variation of the spherical aberration.
[0154]
[Table 3]

[0155]
Table 4 shows the result of correcting the variation of the spherical aberration caused by the variation in oscillation wavelength of the light source of ± 10 nm, the temperature variation of ± 30 ° C., and the transparent substrate thickness error of ± 0.02 mm in Example 1. Further, the chromatic aberration which becomes a problem when using a short wavelength laser light source having an oscillation wavelength of about 400 nm was corrected by using a double-sided diffractive lens as the positive lens of the beam expander. FIG. 8 is an optical path diagram related to Example 1, and FIG. 9 is a spherical aberration diagram related to Example 1.
[0156]
[Table 4]

[0157]
<Example 2>
[0158]
Table 5 shows data of an optical system preferable for use in the optical pickup device shown in FIG. In this embodiment, the image side numerical aperture of the objective lens is 0.85, the oscillation wavelength of the light source for recording or reproducing information is 405 nm, and all the components are plastics having high internal transmittance in the short wavelength region. Made from material. A coupling lens is used as the spherical aberration correction means, and the fluctuation of the spherical aberration generated in the optical system is corrected by shifting the coupling lens along the optical axis. In the present embodiment, the coupling lens is configured as one group, but may be configured as a plurality of lens groups.
[0159]
[Table 5]

[0160]
Table 6 shows the result of correcting the variation in spherical aberration caused by the oscillation wavelength variation of ± 10 nm light source, the temperature variation of ± 30 ° C., and the transparent substrate thickness error of ± 0.02 mm in Example 2. Further, the chromatic aberration which becomes a problem when using a short wavelength laser light source with an oscillation wavelength of about 400 nm was corrected by making the light source side surface of the coupling lens a diffractive surface. FIG. 10 is an optical path diagram related to Example 2, and FIG. 11 is a spherical aberration diagram related to Example 2.
[0161]
[Table 6]

[0162]
In the above table, E (or e) is used to express a power of 10, for example, E-02 (= 10^-2).
[0163]
【The invention's effect】
As described above, in the optical pickup device according to the present invention, the spherical aberration detector means at least one change in the shape and refractive index of the plastic lens and / or the oscillation wavelength of the light source with respect to at least a temperature and / or humidity change. Even when an optical pickup device having an objective lens with a high numerical aperture is used, the variation in spherical aberration caused by the variation is detected, the spherical aberration correction unit is driven by the driving unit, and the variation in spherical aberration is corrected. It is possible to use plastic lenses that are susceptible to changes in temperature and humidity.
[0164]
Furthermore, the optical pickup device of the present invention is not only for variations in spherical aberration due to temperature and humidity changes, but also for optical disk protective layer thickness errors, slight oscillation wavelength fluctuations in the light source, and production of optical elements included in the condensing optical system. Because it is possible to satisfactorily correct the variation in spherical aberration caused by errors, etc.,
1. A plastic lens can be used for the condensing optical system, which can greatly reduce the cost and weight.
2. Since it is not necessary to select the laser light source, the requirement of manufacturing accuracy for the laser light source does not become too strict, and the mass productivity of the laser light source can be increased. In addition, the manufacturing time of the optical pickup device can be shortened.
3. The required accuracy for manufacturing errors of the optical information recording medium is not too strict, so the mass productivity of the optical information recording medium can be improved.
4. Since manufacturing requirements for optical elements included in the condensing optical system are not too strict, mass productivity of the optical elements included in the condensing optical system can be increased.
Thus, it is possible to obtain a condensing optical system that can always maintain good condensing characteristics.
[0165]
In the optical pickup device according to the present invention, it is preferable that all the optical elements that can be displaced along the optical axis are made of a plastic material. As a result, the burden on the actuator can be reduced, so that the driving power of the actuator can be reduced, and the displacement can be achieved with a smaller actuator, so that the optical pickup device can be downsized. An optical element that can be displaced along the optical axis direction includes, for example, an objective lens that is displaced by a biaxial actuator to reduce tracking errors / focusing errors, and an optical element along the optical axis direction to correct variations in spherical aberration. It is an optical element included in the shifted spherical aberration correction means.
[0166]
In the optical pickup device according to the present invention, it is preferable that at least one of the optical elements included in the condensing optical system is made of a plastic material from the viewpoint of weight reduction and cost. It is more preferable that at least one of the panda and the coupling lens as spherical aberration correction means is made of a plastic material. Furthermore, it is particularly preferred that all of the optical elements described above are formed from a plastic material.
[0167]
Moreover, it is preferable that the objective lens used in the optical pickup device according to the present invention satisfies the above formula (3) or formula (4). By satisfying the formula (3) or the formula (4), it is possible to achieve both a sufficient working distance, a reduction in lens diameter and a reduction in manufacturing error sensitivity even with an objective lens having a high numerical aperture. In addition, when this objective lens is corrected so that the aberration is minimized with respect to a parallel light beam from an object at infinity, even if the objective lens is moved to reduce the tracking error / focusing error, Since the change in the incident condition is small, the change in aberration is small. In addition, when the objective lens is corrected for aberration so that the aberration is minimized with respect to a divergent light beam from an object at a finite distance, a larger working distance can be secured, so the objective lens and the optical information recording medium Collisions can be prevented. In addition, when the objective lens is corrected for aberration so that the aberration is minimized with respect to the convergent light beam directed toward the image side object, the incident angle of the light beam to the objective lens becomes small. Aberration deterioration can be suppressed, and the objective lens can be easily manufactured.
[0168]
In the optical pickup device according to the present invention, it is preferable that the condensing optical system includes a diffractive optical element having an annular diffractive structure on at least one surface. As a result, it is possible to correct axial chromatic aberration which becomes a problem when a light source having an oscillation wavelength of 500 nm or less is used. The diffractive optical element may be an optical element such as an objective lens, a beam expander, or a coupling lens included in the condensing optical system, or may be provided separately from the above-described optical element.
[0169]
In this specification, the spherical aberration correction means arranged in the optical path between the light source and the objective lens includes the light source and the objective lens in addition to the beam expander, the coupling lens, and the refractive index distribution variable element. Shall be. Therefore, the optical element that can be shifted along the optical axis of the spherical aberration correction means includes a lens group included in the beam expander and the coupling lens, or a lens group provided separately from the beam expander and the coupling lens. In addition to the above, a light source that can be shifted along the optical axis and a lens group included in the objective lens are also included.
[0170]
In this specification, the beam expander is composed of at least one lens group having a positive refractive power and at least one lens group having a negative refractive power, and is substantially parallel with a light beam diameter a (mm). A generally well-known optical element capable of emitting a substantially parallel light beam having a light beam diameter b (mm) (a ≠ b) when a light beam is incident, and not only an element that expands the light beam diameter. Also included are those that reduce the beam diameter.
[0171]
In this specification, a coupling lens refers to an optical element that converts the divergence of a divergent light beam from a light source. The emitted light beam is a divergent light beam, and the emitted light beam is a parallel light beam. (Collimate lens) and the case where the emitted light beam is a convergent light beam are included. It is assumed that not only one lens group but also a plurality of lens groups are included.
[0172]
Further, in this specification, the optical information recording medium includes not only those having a transparent substrate on the surface but also those having no transparent substrate. In the case where the optical information recording medium has a transparent substrate, the objective lens used in the optical pickup device of the present invention is corrected for aberration so that the aberration is minimized in combination with the transparent substrate having a specific thickness. It is preferable.
[0173]
Further, in this specification, the slight fluctuation of the oscillation wavelength of the light source refers to a wavelength fluctuation within a range of ± 10 nm with respect to the oscillation wavelength of the light source. Further, in this specification, correcting various aberrations (good) means that the wavefront aberration is 0.07λ rms or less, which is a so-called diffraction-limited performance (where λ is the oscillation wavelength of the light source used). It is preferable that
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an optical pickup device according to a first embodiment.
2 (a) and 2 (b) are schematic plan views of the light receiving surfaces 14a and 14b of the multi-segment photodetector shown in FIG. 1 as viewed from the direction A in FIG. 1, and FIG. 2 (c). , (D) are plan views schematically showing light receiving patterns on the light receiving surfaces 14a, 14b in the reference state, and FIGS. 2 (e), (f) are light receiving patterns on the light receiving surfaces 14a, 14b in the under state. 2 (g) and 2 (h) are plan views schematically showing light receiving patterns on the light receiving surfaces 14a and 14b in the same over state.
3 is a perspective view showing a hologram element as an example of the spherical aberration adding element of FIG. 1. FIG.
4 is a diagram showing a modification of the optical pickup device in FIG. 1. FIG.
FIG. 5 is a diagram showing another modification of the optical pickup device in FIG. 1;
FIG. 6 is a diagram showing a schematic configuration of an optical pickup device according to a sixth embodiment.
7A is a schematic plan view of the divided light receiving surface 24 of the multi-segment photodetector 25 in FIG. 6 as viewed from the direction AA in FIG. 6, and FIG. FIG. 7C is a plan view schematically showing a light receiving pattern on the light receiving surface 24 in the state, and FIG. 7C is a plan view schematically showing a light receiving pattern on the light receiving surface 24 in the under state. FIG. 5 is a plan view schematically showing a light receiving pattern on a light receiving surface 24 in an over state.
8 is an optical path diagram related to Example 1. FIG.
9 is a spherical aberration diagram for Example 1. FIG.
10 is an optical path diagram related to Example 2. FIG.
11 is a spherical aberration diagram for Example 2. FIG.
FIG. 12 is a diagram showing a schematic configuration of an optical pickup device according to a second embodiment.
FIG. 13 is a diagram showing a schematic configuration of an optical pickup device according to a third embodiment.
FIG. 14 is a diagram showing a schematic configuration of an optical pickup device according to a fourth embodiment.
FIG. 15 is a diagram showing a schematic configuration of an optical pickup device according to a fifth embodiment.
[Explanation of symbols]
1 Laser semiconductor, light source
2 Coupling lens
3 Beam shaping prism
4 Polarizing beam splitter
4 'polarization beam splitter
5 Beam expander
6 1/4 wave plate
7 Aperture
8 Objective lens
9 Transparent substrate for optical information recording media
Information recording surface of 9 'optical information recording medium
10 2-axis actuator (objective lens driving means)
11 Single-axis actuator (spherical aberration correction means driving means)
12 Spherical aberration adding element
12a Hologram element
13 Condensing lens
14a, 14b Photosensitive surface
24 Photosensitive surface
24a, 24b Photosensitive surface
15, 25 Multi-splitting photodetector
16 Reflected light
16a 1st light beam received by the light-receiving surface 14a of the multi-split photodetector 15
16b Second light beam received by the light receiving surface 14b of the multi-split photodetector 15
17 Refractive index distribution variable element
18 Driving means for refractive index distribution variable element 17
19 Tracking error / focusing error detection means, second photodetector
20 hologram
21 Beam shaping lens
22 First lens
23 Second lens
24 'light source / multi-segment photodetector integrated unit
25 'multi-segment photodetector / second photodetector integrated unit

Claims (24)

A light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens, and resulting from changes in temperature and / or humidity An optical pickup device including a condensing optical system including spherical aberration correcting means for correcting fluctuations in spherical aberration generated by
Spherical aberration detection means for detecting the variation of the spherical aberration by detecting reflected light from the information recording surface; drive means for driving the spherical aberration correction means according to the detection result of the spherical aberration detection means; Have
The spherical aberration detection means includes an optical element you added a division unit for performing amplitude division or wavefront splitting the light flux at least incident, a different size or a different spherical aberration of the code to split light beams or wavefront, An optical pickup device comprising: a multi-segment photodetector that receives the reflected light that is incident on the splitting unit and has spherical aberration added thereto by the optical element. A light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens, and resulting from changes in temperature and / or humidity An optical pickup device including a condensing optical system including spherical aberration correcting means for correcting fluctuations in spherical aberration generated by
Spherical aberration detection means for detecting the variation of the spherical aberration by detecting reflected light from the information recording surface; drive means for driving the spherical aberration correction means according to the detection result of the spherical aberration detection means; Have
The spherical aberration detecting means has a first light receiving surface and a second light receiving surface which have a first light receiving surface and a second light receiving surface, the areas of which are distributed so as to change the amount of light received according to the variation of the spherical aberration of the incident light beam. And a first light beam disposed in an optical path between the spherical aberration correcting means and the multi-divided photodetector and receiving reflected light from the information recording surface on the first light receiving surface, and the first And the paraxial focal position or the best focus position are the same, and the light beam is divided into a second light beam received by the second light receiving surface, and an over spherical aberration is added to the first light beam, anda optical element you added under spherical aberration on the second light flux,
The first light receiving surface has two light receiving portions, and the two light receiving portions satisfy A1 = A2 in a reference state when the light receiving amounts in the respective light receiving portions are A1 and A2,
The second light receiving surface has two light receiving portions, and the two light receiving portions satisfy B1 = B2 in the reference state when the light receiving amount in each light receiving portion is B1 and B2,
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in an under direction, the received light amount A1 on the first light receiving surface increases from the reference state and the received light amount A2 decreases. , The amount of received light B1 on the second light receiving surface decreases from the reference state and the amount of received light B2 increases,
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in the over direction, the amount of received light A1 on the first light receiving surface decreases from the reference state and the amount of received light A2 increases. , The amount of received light B1 on the second light receiving surface increases from the reference state, and the amount of received light B1 decreases,
By detecting the difference ΔSA in the amount of received light according to the following equation that is caused by the difference in the magnitude or sign of the spherical aberration between the first light flux and the second light flux, the fluctuation amount of the spherical aberration can be reduced. An optical pickup device that detects and drives the drive means so as to reduce a variation amount of the spherical aberration.
ΔSA = (A2 + B1) − (A1 + B2) The optical pickup device according to claim 2, wherein the first light receiving surface and the second light receiving surface are formed on the same substrate. A light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens, and resulting from changes in temperature and / or humidity An optical pickup device including a condensing optical system including spherical aberration correcting means for correcting fluctuations in spherical aberration generated by
Spherical aberration detection means for detecting the variation of the spherical aberration by detecting reflected light from the information recording surface; drive means for driving the spherical aberration correction means according to the detection result of the spherical aberration detection means; Have
The spherical aberration detecting means has a first light receiving surface and a second light receiving surface, in which areas are distributed so as to change the amount of light received in accordance with the variation of the spherical aberration of the incident light beam in order in the clockwise direction. A multi-divided photodetector having a light receiving surface divided into at least four regions: a surface, a third light receiving surface facing the first light receiving surface, and a fourth light receiving surface facing the second light receiving surface; The wavefront of the reflected light from the information recording surface is received by the respective light receiving surfaces of the multi-divided photodetector and arranged in the optical path between the spherical aberration correcting means and the multi-divided photodetector, and the paraxial focus The wavefront is divided into four regions having the same position or the best focus position, and an over spherical aberration is added to the wavefronts received by the first light receiving surface and the third light receiving surface. Light receiving surface and the fourth light receiving surface Has an optical element you added under spherical aberration in the wavefront, and
The first light receiving surface is divided into two light receiving parts, and the amount of light received by each light receiving part is a1 and a2,
The second light receiving surface is divided into two light receiving parts, and the amount of light received by each light receiving part is b1 and b2,
The third light receiving surface is divided into two light receiving parts, and the amount of light received by each light receiving part is a1 ′, a2 ′,
The fourth light receiving surface is divided into two light receiving parts, and the amount of light received in each light receiving part is b1 ′ and b2 ′,
Each light receiving portion of each light receiving surface satisfies the following formula (1) or (2) in the reference state,
a1 = a2, b1 = b2, a1 ′ = a2 ′, b1 ′ = b2 ′ (1)
(a2 + b1) − (a1 + b2) = 0, (a2 ′ + b1 ′) − (a1 ′ + b2 ′) = 0 (2)
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in an under direction, the received light amounts a1, a1 ′, b2, b2 ′ on the respective light receiving surfaces increase from the reference state. , The amount of received light a2, a2 ′, b1, b1 ′ decreases,
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in the over direction, the received light amounts a1, a1 ′, b2, b2 ′ on the respective light receiving surfaces are reduced from the reference state. , The amount of received light a2, a2 ′, b1, b1 ′ increases,
The following equations (3), (4) or (4) on the respective light receiving surfaces of the multi-divided photodetector generated due to the difference in the magnitude or sign of the spherical aberration of the wavefront divided into the four regions: 5. An optical pickup device characterized by detecting the amount of variation of the spherical aberration by detecting the difference ΔSA in the amount of received light according to 5) and driving the driving means so as to reduce the amount of variation of the spherical aberration.
ΔSA = (a2 + b1) − (a1 + b2) (3)
ΔSA = (a2 ′ + b1 ′) − (a1 ′ + b2 ′) (4)
ΔSA = (a2 + b1 + a2 ′ + b1 ′) − (a1 + b2 + a1 ′ + b2 ′) (5) 5. The optical path from the light source to the information recording surface of the optical information recording medium and the optical path from the information recording surface to the multi-split photodetector are shared. The optical pickup device described in 1. The optical pickup device according to claim 5, wherein the light source and the multi-split photodetector are formed on the same substrate. The optical pickup device detects a tracking error and / or a focusing error of the objective lens by detecting drive light for driving the objective lens and reflected light from the information recording surface by a second photodetector. Error detection means for detecting, and an optical path from the information recording surface to the second photodetector and an optical path from the information recording surface to the multi-segment photodetector are shared. The optical pickup device according to claim 1, wherein the optical pickup device is characterized. The optical pickup device according to claim 7, wherein the second photodetector and the multi-segment photodetector are formed on the same substrate. A condensing lens for condensing the reflected light from the information recording surface on the light receiving surface of the multi-divided photodetector in the optical path between the spherical aberration correcting means and the multi-divided photodetector; The optical pickup device according to claim 1, wherein: A condensing lens for condensing the reflected light from the information recording surface on the light receiving surface of the multi-divided photodetector in the optical path between the spherical aberration correcting means and the multi-divided photodetector;
9. The light collecting lens according to claim 2, wherein the condensing lens also serves as the optical element, gives spherical aberration of a different size or a different sign to at least an incident light beam, and performs amplitude division or wavefront division. 2. An optical pickup device according to item 1.   The optical pickup device according to claim 10, wherein the condenser lens has an annular diffractive structure on at least one surface. The optical pickup device according to claim 1, wherein the optical element has an annular diffractive structure on at least one surface. The spherical aberration detection unit generates a spherical aberration error signal corresponding to a variation amount of the spherical aberration generated in the condensing optical system, and drives the driving unit so that the spherical aberration error signal becomes substantially zero. the optical pickup device according to any one of claims 1 to 12, wherein the. Claims 1 to 13 prescribed numerical aperture on the image side of the optical information recording medium of recording information on the information recording plane or the objective lens necessary for conducting reproducing and wherein the at least 0.75 The optical pickup device according to any one of the above. It said light source optical pickup device according to any one of claims 1 to 14, wherein the generating light of a wavelength 500 nm. The spherical aberration correction means, the optical pickup apparatus according to any one of claims 1 to 15, characterized in that it has a transition moveable element along at least one direction of the optical axis. The spherical aberration correction means is a coupling lens arranged in an optical path between the light source and the objective lens, and changes a divergence angle of a divergent light beam from the light source, and at least one lens constituting the coupling lens The optical pickup device according to claim 16 , wherein a group is the movable element. The condensing optical system includes a collimating lens that is disposed in an optical path between the light source and the objective lens and converts a divergent light beam from the light source into parallel light,
The spherical aberration correcting means is a beam expander disposed in an optical path between the collimating lens and the objective lens, and at least one lens group constituting the beam expander is the movable element. The optical pickup device according to claim 16 , wherein The spherical aberration correction means, the optical pickup device written in any one of claims 1 to 18, wherein the refractive index along the direction perpendicular to the optical axis distribution is variable. 20. A sound and / or image recording device and / or a sound and / or image reproducing device, wherein the optical pickup device according to any one of claims 1 to 19 is mounted. A light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens, and resulting from changes in temperature and / or humidity A condensing optical system including spherical aberration correcting means for correcting fluctuations in spherical aberration generated by
Spherical aberration detection means for detecting fluctuations in the spherical aberration by detecting reflected light from the information recording surface;
And a driving means for driving the spherical aberration correcting means in accordance with the detection result of the spherical aberration detecting means, and a correction method for spherical aberration fluctuations in an optical pickup device comprising:
The spherical aberration detection means may be amplitude divided or wavefront splitting to a light flux of at least incident, an optical element you added size or different spherical aberration code different to the split light beam or wavefront, the optical element A multi-segment photodetector for receiving a light beam with spherical aberration added thereto ,
By detecting the difference in the amount of light on the light receiving surface of the multi-segment photodetector caused by the difference in the magnitude or sign of the spherical aberration of the divided light beam or wavefront, the amount of variation in the spherical aberration And correcting the spherical aberration fluctuation in the optical pickup device, wherein the driving means is driven so as to reduce the fluctuation amount of the spherical aberration. A light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens, and resulting from changes in temperature and / or humidity A condensing optical system including spherical aberration correcting means for correcting fluctuations in spherical aberration generated by
Spherical aberration detection means for detecting fluctuations in the spherical aberration by detecting reflected light from the information recording surface;
And a driving means for driving the spherical aberration correcting means in accordance with the detection result of the spherical aberration detecting means, and a correction method for spherical aberration fluctuations in an optical pickup device comprising:
The spherical aberration detector includes a first and second light-receiving surfaces having a first light-receiving surface and a second light-receiving surface, the areas of which are distributed so as to change the amount of light received according to a change in spherical aberration of an incident light beam. And a first light beam disposed between the spherical aberration correcting means and the multi-segmented light detector and receiving reflected light from the information recording surface on the first light receiving surface, and the first light beam. And the paraxial focus position or the best focus position are the same, and the second light receiving surface receives the second light beam, and an over spherical aberration is added to the first light beam. It has an optical element 2 of the light beam you added under spherical aberration, and
The first light receiving surface has two light receiving portions, and the two light receiving portions satisfy A1 = A2 in a reference state when the light receiving amounts in the respective light receiving portions are A1 and A2,
The second light receiving surface has two light receiving portions, and the two light receiving portions satisfy B1 = B2 in the reference state when the light receiving amount in each light receiving portion is B1 and B2,
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in an under direction, the received light amount A1 on the first light receiving surface increases from the reference state and the received light amount A2 decreases. , The amount of received light B1 on the second light receiving surface decreases from the reference state and the amount of received light B2 increases,
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in the over direction, the amount of received light A1 on the first light receiving surface decreases from the reference state and the amount of received light A2 increases. , The amount of received light B1 on the second light receiving surface increases from the reference state, and the amount of received light B1 decreases,
By detecting the difference ΔSA in the amount of received light according to the following equation that is caused by the difference in the magnitude or sign of the spherical aberration between the first light flux and the second light flux, the fluctuation amount of the spherical aberration can be reduced. A method for correcting spherical aberration fluctuations in an optical pickup device, wherein the driving means is driven to detect and reduce the fluctuation amount of the spherical aberration.
ΔSA = (A2 + B1) − (A1 + B2) A light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, and an optical path between the light source and the objective lens, and resulting from changes in temperature and / or humidity A condensing optical system including spherical aberration correcting means for correcting fluctuations in spherical aberration generated by
Spherical aberration detection means for detecting fluctuations in the spherical aberration by detecting reflected light from the information recording surface;
And a driving means for driving the spherical aberration correcting means in accordance with the detection result of the spherical aberration detecting means, and a correction method for spherical aberration fluctuations in an optical pickup device comprising:
The spherical aberration detecting means has a first light receiving surface and a second light receiving surface, in which areas are distributed so as to change the amount of light received in accordance with the variation of the spherical aberration of the incident light beam in order in the clockwise direction. A multi-divided photodetector having a light receiving surface divided into at least four regions: a surface, a third light receiving surface facing the first light receiving surface, and a fourth light receiving surface facing the second light receiving surface; The wavefront of the reflected light from the information recording surface is received by the respective light receiving surfaces of the multi-divided photodetector and disposed between the spherical aberration correcting means and the multi-divided photodetector, and the paraxial focal position Alternatively, the wavefront is divided into four regions having the same best focus position, and an over spherical aberration is added to the wavefronts received by the first light receiving surface and the third light receiving surface. Light is received by the light receiving surface and the fourth light receiving surface. Has an optical element you added under spherical aberration in the wavefront, and
The first light receiving surface is divided into two light receiving parts, and the amount of light received by each light receiving part is a1 and a2,
The second light receiving surface is divided into two light receiving parts, and the amount of light received by each light receiving part is b1 and b2,
The third light receiving surface is divided into two light receiving parts, and the amount of light received by each light receiving part is a1 ′, a2 ′,
The fourth light receiving surface is divided into two light receiving parts, and the amount of light received in each light receiving part is b1 ′ and b2 ′,
Each light receiving portion of each light receiving surface satisfies the following formula (1) or (2) in the reference state,
a1 = a2, b1 = b2, a1 ′ = a2 ′, b1 ′ = b2 ′ (1)
(a2 + b1) − (a1 + b2) = 0, (a2 ′ + b1 ′) − (a1 ′ + b2 ′) = 0 (2)
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in an under direction, the received light amounts a1, a1 ′, b2, b2 ′ on the respective light receiving surfaces increase from the reference state. , The amount of received light a2, a2 ′, b1, b1 ′ decreases,
When the spherical aberration of the reflected light including the spherical aberration added by the optical element fluctuates in the over direction, the received light amounts a1, a1 ′, b2, b2 ′ on the respective light receiving surfaces are reduced from the reference state. , The amount of received light a2, a2 ′, b1, b1 ′ increases,
The following equations (3), (4), or (4) on the respective light receiving surfaces of the multi-divided photodetector generated due to the difference in the magnitude or sign of the spherical aberration of the wavefront divided into the four regions: In the optical pickup device, the amount of received light difference ΔSA in step 5) is detected to detect the amount of variation of the spherical aberration, and the driving unit is driven to reduce the amount of variation of the spherical aberration. Correction method for spherical aberration fluctuations.
ΔSA = (a2 + b1) − (a1 + b2) (3)
ΔSA = (a2 ′ + b1 ′) − (a1 ′ + b2 ′) (4)
ΔSA = (a2 + b1 + a2 ′ + b1 ′) − (a1 + b2 + a1 ′ + b2 ′) (5) The spherical aberration fluctuation correction method is a spherical aberration fluctuation correction method in an optical pickup device including at least one plastic lens in the condensing optical system, wherein the plastic lens is at least for temperature and / or humidity changes. The spherical aberration fluctuation according to any one of claims 21 to 23 , wherein a spherical aberration fluctuation caused by a change in at least one of the shape and refractive index of the light source and / or a fluctuation in oscillation wavelength of the light source is corrected. Correction method.

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