JP3945633B2 - Optical pickup - Google Patents

Description

また、表中の記号は、以下の通りである。
「ＯＢＪ」は物点（光源としての半導体レーザー）を意味するが、光ピックアップ用対物レンズ２は「無限系」であり、曲率半径：ＲＤＹおよび厚さ：ＴＨＩの「ＩＮＦＩＮＩＴＹ（無限大）」は光源が無限遠にあることを意味する。また、「ＳＴＯ」は波長選択アパーチャ１の面であり、その曲率半径：ＲＤＹは「ＩＮＦＩＮＩＴＹ」で、厚さ：ＴＨＩは設計上「０」としている。なお、特に断らない限り、長さの次元を持つ量の単位は「ｍｍ」である。
【００４１】
「Ｓ１」は光ピックアップ用対物レンズの光源側面、「Ｓ２」は光記録媒体側面を意味する。実施例１における対物レンズ２の肉厚は２．３８１４６３ｍｍであり、Ｓ２の欄の曲率半径の右側に記載された厚さ０．４２５４９６ｍｍは「ワーキングディスタンス：ＷＤ」を示す。
【００４２】
「Ｓ３」は光記録媒体の光照射側基板３の光源側面、「Ｓ４」は同記録面に合致した面であり、これらの面Ｓ３，Ｓ４の間隔、すなわち、光照射側基板厚は０．１ｍｍ、ｎｄ：１．５１６３３０、νｄ：６４.１である。「ＥＰＤ：入射瞳径」は波長選択アパーチャ１の開口径（３ｍｍ）を表し、「ＷＬ：波長」は使用波長（４０７ｎｍ）を表す。
【００４３】
なお、非球面係数の表示において、例えば「Ｄ：０.３０５４７７Ｅ−０３」とあるのは、「Ｄ＝０．３０５４７７×１０^-3」を意味する。また、以下の各表の表示においても同様とする。
【００４４】
図３（ａ）に、実施例１に関する波長選択アパーチャ１、光ピックアップ用対物レンズ２、光照射側基板３の配置状態を示す。図３（ｂ），図３（ｃ）には、実施例１の光ピックアップ用対物レンズ２の非点収差、球面収差（縦軸の目盛は入射瞳半径を１に規格化した値である）を示す。両収差とも極めて良好に補正されている。また軸上、設計中央値の波面収差は０.００２２λである。
【００４５】
さらに、図３（ｄ）に、レンズの中心肉厚ずれが発生したときの収差劣化量を示す。破線は、使用波長：６５０ｎｍ、ＮＡ：０．７５、ｆ：２．００ｍｍ、ｎｄ：１.６９３３０、νｄ：５３.１７の従来の対物レンズにおける中心肉厚ずれに起因する収差劣化量に相当し、実線は本実施例１の同劣化量を示す。従来の対物レンズに比べ、±１μｍ程度の厚みずれがあっても波面劣化は０.００６λ以下で、製造が十分可能な範囲にある。
【００４６】
前記のように、実施例１の対物レンズは、光源側の近軸曲率半径：Ｒ１＝１．３７５９５ｍｍ、ｆ＝１.７６５ｍｍ、ｎｄ＝１．６９３５０、νｄ＝５３.２、ＷＤ＝０．４２５４９６ｍｍであるので、前記Ｒ１，ｔ，ＷＤ，ｆ，ｎｄ，νｄは、前記した条件１〜５を満足する範囲内にある。
【００４７】
次に、実施例２における光ピックアップ用の対物レンズは、前記実施例１とは、焦点距離：ｆが異なって、ＮＡ：０．８５、ｆ＝２.３５３ｍｍ、ｎｄ＝１．６９３５０、νｄ＝５３.２である。（表２）に、具体的データを（表１）に倣って示す。
【００４８】
【表２】

図４（ａ）に、実施例２に関する波長選択アパーチャ１、光ピックアップ用対物レンズ２、光照射側基板３の配置状態を示す。図４（ｂ），図４（ｃ）には、実施例２の光ピックアップ用対物レンズ２の非点収差、球面収差（縦軸の目盛は入射瞳半径を１に規格化した値である）を示す。両収差とも極めて良好に補正されている。また軸上、設計中央値の波面収差は０.００４３λである。
【００４９】
前記のように、実施例２の対物レンズは、Ｒ１＝１．８３３１ｍｍ、ｆ＝２．３５３ｍｍ、ｎｄ＝１．６９３５０、νｄ＝５３.２、ＷＤ＝０.５８８４５９ｍｍであるので、前記Ｒ１，ｔ、ＷＤ、ｆ、ｎｄ、νｄは、実施例１と同様に前記の条件１〜５を満足する範囲内にある。
【００５０】
続いて、本発明の使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０.８５±０.０５で光照射側基板厚：０.１ｍｍの光記録媒体光ピックアップ用対物レンズを用いて、ＤＶＤ系、ＣＤ系などの従来の光記録媒体にも所望の性能を実現するための条件としては、
条件６：−０.４２ｎｄ＋０.８２≦ＷＤ/ｆ≦−０.４２ｎｄ＋０.９５
条件７：−０.３５ｎｄ＋０.６４≦ＷＤ/ｆ≦−０.３５ｎｄ＋０.７２
であり、条件６の意味は条件７の意味と同じである。
【００５１】
ＤＶＤ系光記録媒体に集光させるためには、「使用波長：６６０ｎｍ±１０ｎｍ、ＮＡ０.６５±０.０５で光照射側基板厚：０.６ｍｍの光記録媒体に集光可能な光ピックアップ用対物レンズ」である必要がある。
【００５２】
同様にＣＤ系光記録媒体に集光させるためには、「使用波長：７８０ｎｍ±１０ｎｍ、ＮＡ０.５０±０.０５で光照射側基板厚：１.２ｍｍの光記録媒体に集光可能な光ピックアップ用対物レンズ」である必要がある。
【００５３】
本発明の対物レンズを、無限系対物レンズとして、前記ＤＶＤ系、ＣＤ系の使用波長，基板厚条件で使用した場合、基板厚の違い（０．１ｍｍ，０.６ｍｍ，１.２ｍｍ）、波長の違い（４０７ｎｍ，６６０ｎｍ，７８０ｎｍ）に伴う球面収差が発生する。この球面収差を抑制するためには、ＤＶＤ系、あるいはＣＤ系への記録，再生，消去を行うときには、対物レンズへの入射光束を発散光とすることにより補正可能である。すなわち、ＤＶＤ系、あるいはＣＤ系への記録，再生，消去を行うときは有限系対物レンズとして使用する。また、入射光を発散状態で入射させても、球面収差が僅かに残留するが、これは対物レンズ側に曲率の強い面を有するカップリングレンズを光源と対物レンズの間に配置することにより抑制できる。また、ＮＡの違い（０.８５，０.６５，０.５０）については、使用波長に応じて開口を制限できる素子を用いることで解消される。
【００５４】
前記の条件１〜５を満足する「使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０.８５±０.０５で光照射側基板厚：０.１ｍｍの光記録媒体光ピックアップ用対物レンズ」を、「使用波長：６６０ｎｍ±１０ｎｍ、ＮＡ：０.６５±０.０５で光照射側基板厚：０.６ｍｍの光記録媒体に集光可能な光ピックアップ用対物レンズ」（ＤＶＤ系）として、基板厚および使用波長の違いにより発生する球面収差を最小限に抑える条件のもとで、許容されるワーキングディスタンス：ＷＤとレンズ材質の屈折率：ｎｄとの関係を調べて見ると、焦点距離：ｆ＝1.８〜１.９ｍｍの例では、図５（ａ）における黒丸（●）のようになる。同様に、ｆ＝２.４〜２.５ｍｍ、ＮＡ：０.８５を例として求めて見ると、図５（ａ）における三角（△）のようになる。即ち、直線５ａ−１と直線５ａ−２上の範囲に収まる。材質の屈折率は、ｄ線の屈折率：ｎｄ以外にアッベ数：νｄにも依存するため、ＷＤとｎｄの関係は一位には決まらないが、直線５ａ−１と直線５ａ−２の範囲で定まるＷＤとｎｄの条件６を満足し、かつ条件１で定められたνｄを満足することにより、基板厚および使用波長が違いにより発生する球面収差を最小限に抑制できる。
【００５５】
同様に、前記条件１〜５を満足する「使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０.８５±０.０５で光照射側基板厚：０.１ｍｍの光記録媒体光ピックアップ用対物レンズ」を、「使用波長：７８０ｎｍ±１０ｎｍ、ＮＡ０.５０±０.０５で光照射側基板厚：１.２ｍｍの光記録媒体に集光可能な光ピックアップ用対物レンズ」（ＣＤ系）として、基板厚および使用波長の違いにより発生する球面収差を最小限に抑える条件のもとで、許容されるワーキングディスタンス：ＷＤとレンズ材質の屈折率：ｎｄとの関係を調べて見ると、焦点距離：ｆ＝1.８〜１.９ｍｍの例では、図５（ｂ）における黒丸（●）のようになる。同様に、ｆ＝２.４〜２.５ｍｍ、ＮＡ：０.８５を例として見ると、図５（ｂ）における三角（△）のようになる。
【００５６】
すなわち、直線５ｂ−１と直線５ｂ−２上の範囲に収まる。材質の屈折率は、ｄ線の屈折率：ｎｄ以外にアッベ数：νｄにも依存するため、ＷＤとｎｄの関係は一位には決まらないが、直線５ｂ−１と直線５ｂ−２上の範囲で定まるＷＤとｎｄの前記条件７を満足し、かつ前記条件１で定められたνｄを満足することにより、基板厚および使用波長が違いにより発生する球面収差を最小限に抑制できる。
【００５７】
このようにして、前記の条件６あるいは条件７を満足することにより、「使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０.８５±０.０５で光照射側基板厚：０.１ｍｍの光記録媒体に対して情報の記録，再生，消去の少なくともいずれか１以上を行う無限系の光ピックアップ」において、ＤＶＤ系あるいはＣＤ系といった従来の光記録媒体の記録，再生，消去の少なくともいずれか１以上を実現可能な光ピックアップを実現することができる。
【００５８】
そして、本実施の形態２として、使用波長：４０７ｎｍ、ＮＡ：０.８５の大容量光記録媒体と、ＤＶＤ系やＣＤ系といった従来の光記録媒体に記録，再生，消去を行うことができる、いわゆる互換型光ピックアップ用の対物レンズの具体的な実施例を２つ挙げる。また、図６（ａ），図７（ａ）においても、前記実施の形態１の図３（ａ），図４（ａ）と同様に、各構成部材に対応し同等機能のもには同一符号を付し、１は波長選択アパーチャ、２は対物レンズ、３は光照射側基板（厚さは、ＤＶＤ系は０．６ｍｍ、ＣＤ系は１.２ｍｍ）、４は光源、５は凹面形状を有するカップリングレンズである。
【００５９】
光源４から出射された光はカップリングレンズ５を介して、「発散光束」として波長選択アパーチャ１の開口（開口径：φ＝３.２４５７０ｍｍ）を通過し、対物レンズ２に入射し、この対物レンズ２により集光光束とされ、光記録媒体の光照射側基板３を透過して記録面（光照射側基板３の右側面に合致）に光スポットを形成する。
【００６０】
また、レンズ面の非球面形状は、光軸方向の座標：Ｘ、光軸直交方向の座標：Ｙ、近軸曲率半径：Ｒ、円錐定数：Ｋ、高次の係数：Ａ，Ｂ，Ｃ，Ｄ，Ｅ，Ｆ，…を用いて、周知の非球面式を（数２）で表し、
【００６１】
【数２】
Ｘ＝（Ｙ²／Ｒ）／［１＋√｛１−（１＋Ｋ）Ｙ／Ｒ²｝＋ＡＹ⁴＋ＢＹ⁶
＋ＣＹ⁸＋ＤＹ¹⁰＋ＥＹ¹²＋ＦＹ¹⁴＋ＧＹ¹⁶＋ＨＹ¹⁸＋ＪＹ²⁰＋・・
Ｒ、Ｋ、Ａ、Ｂ、Ｃ、Ｄ、・・を与えて形状を特定する。
【００６２】
実施例３として、前記実施の形態１の実施例１における対物レンズ２をＤＶＤ系で使用する場合について説明する。この光ピックアップ用の対物レンズは、使用波長：６６０ｎｍ、ＮＡ：０．６５、ｆ：２.４２３０ｍｍ、ｎｄ：１．５１６８０、νｄ：６４.２であり、（表３）に、具体的データを示す。
【００６３】
【表３】

また、表中の記号は、以下の通りである。
「ＯＢＪ」は物点（光源としての半導体レーザー）を意味し、対物レンズ２をＤＶＤ系では「有限系」として使用するものであり、ＲＤＹは曲率半径、ＴＨＩは厚さを意味する。また、「ＳＴＯ」は波長選択アパーチャ１の面であり、その曲率半径は「ＩＮＦＩＮＩＴＹ」で、厚さは設計上「０」としている。また、特に断らない限り、長さの次元を持つ量の単位は「ｍｍ」である。
【００６４】
「Ｓ２」はカップリングレンズ５の光源側面、「Ｓ３」は光記録媒体側面を意味する。また、「Ｓ５」は対物レンズ２の光源側面、「Ｓ７」は光記録媒体側面を意味する。
【００６５】
本実施例３における対物レンズ２の肉厚は３.１７４０７８ｍｍであり、「Ｓ６」の欄の曲率半径の右側に記載された厚さ０．５０１４５７ｍｍは「ワーキングディスタンス：ＷＤ」を示す。
【００６６】
「Ｓ７」は光記録媒体の光照射側基板３の光源側面、「Ｓ８」は同記録面に合致した面であり、これらの面Ｓ７，Ｓ８の間隔、即ち、光照射側基板厚は０．６ｍｍ、ｎｄ：１．５１６３３０、νｄ：６４.１である。「ＥＰＤ：入射瞳径」は波長選択アパーチャ１の開口径（３.２４５７０ｍｍ）を表し、「ＷＬ：波長」は使用波長（６６０ｎｍ）を表す。
【００６７】
図６（ａ）に、実施例３に関する波長選択アパーチャ１、光ピックアップ用対物レンズ２、光照射側基板３、カップリングレンズ５、光源４の配置状態を示す。また、図６（ｂ）には、実施例１で説明した対物レンズ２を、使用波長：６６０ｎｍ、基板厚：０.６ｍｍ、ＮＡ：０.６５として集光させたときの光学系構成と波面収差の関係として、▲１▼は無限系状態で入射させた場合、▲２▼は有限系状態で入射させた場合、▲３▼はカップリングレンズを介して有限系状態で入射させた場合における波面収差性能を示す。図６（ａ）に示す実施例３の形態で、収差は極めて良好に補正されている。
【００６８】
前記のように、実施例３の対物レンズ２は、ｎｄ：１．６９３５０、νｄ：５３.２、ｆ：２.４２９９ｍｍ、ＷＤ：０．５０１４５７ｍｍであるので、前記ＷＤ，ｆ，ｎｄ，νｄは、前記した条件１，条件２、および条件６を満足する範囲内にある。
【００６９】
本実施の形態２における実施例４として光ピックアップ用の対物レンズは、ＣＤ系の使用波長：７８０ｎｍであり、（表４）に、具体的データを（表３）に倣って示す。
【００７０】
【表４】

図７（ａ）に、実施例４に関する波長選択アパーチャ１、光ピックアップ用対物レンズ２、光照射側基板３、カップリングレンズ５、光源４の配置状態を示す。また、図７（ｂ）には、実施例１で説明した対物レンズ２を、使用波長：７８０ｎｍ、基板厚：１.２ｍｍ、ＮＡ：０.５０として集光させたときの光学系構成と波面収差の関係として、▲１▼は無限系状態で入射させた場合、▲２▼は有限系状態で入射させた場合、▲３▼はカップリングレンズを介して有限系状態で入射させた場合における波面収差性能を示す。図７（ａ）に示す実施例４の形態で、収差は極めて良好に補正されている。
【００７１】
前記のように、実施例４の対物レンズ２は、ｎｄ：１．６９３５０、νｄ：５３.２、ｆ：２．４４４５ｍｍ、ＷＤ：０．２３６００４ｍｍであるので、
前記ＷＤ，ｆ，ｎｄ，νｄは、前記した条件１，条件２、および条件７を満足する範囲内にある。
【００７２】
さらに、実施例３と実施例４は同時に実現することが可能である。
【００７３】
図８は本発明の実施の形態３における光ピックアップの概略構成を示すブロック図である。本実施の形態３は、前記実施の形態１の実施例１，２により説明した対物レンズを用いている。
【００７４】
図８の光ピックアップの要部は、半導体レーザー１０１、コリメートレンズ１０２、偏光ビームスプリッタ１０３、偏向プリズム１０４、１／４波長板１０５、光ピックアップ用の対物レンズ１０６、検出レンズ１０８、受光素子１０９より構成されている。
【００７５】
半導体レーザー１０１から放射されたレーザー光束はコリメートレンズ１０２により実質的な平行光束に変換され、偏光ビームスプリッタ１０３を透過し、偏向プリズム１０４により光路を９０度折り曲げられ、対物レンズ１０６を介して集光光束に変換され、光記録媒体１０７（光照射側基板厚：０．１ｍｍ）に照射され、光照射側基板を透過して記録面上に光スポットを形成する。
【００７６】
対物レンズ１０６の前段には１／４波長板１０５が配置され、光源側からの直線偏光を円偏光に変換する。光記録媒体１０７により反射された光束は「戻り光束」となって、照射時の光路を逆進し、対物レンズ１０６、１／４波長板１０５、偏向プリズム１０４を通って偏光ビームスプリッタ１０３に入射する。
【００７７】
１／４波長板１０５に入射する戻り光束は往路とは逆周りの円偏光であり、１／４波長板１０５を透過することにより、往路の偏光方向に直交する直線偏光となり、偏光ビームスプリッタ１０３で反射される。偏光ビームスプリッタ１０３で反射された戻り光束は、検出レンズ１０８を介して受光素子１０９に入射する。
【００７８】
受光素子１０９は、サーボ信号の生成方法に従って適宜に分割された受光面を有する。各受光面からの光電出力に基づき、トラッキング信号・フォーカシング信号が生成され、情報の再生時にはこれら信号と共に再生信号が生成される。また、これら信号は図示されない制御回路に向けて出力される。
【００７９】
図９（ａ）は本発明の実施の形態４における光ピックアップの概略構成を示すブロック図である。ここで、前記実施の形態３を示す図８において説明した構成部材に対応して同等機能のものには同一符号を付してこれを示し、以下の各図においても同様とする。
【００８０】
本実施の形態４は、前記実施の形態２の実施例３，４により説明した対物レンズを用いている。図９（ａ）に示す光ピックアップは、使用波長：４０７ｎｍ、ＮＡ：０.８５の大容量の光記録媒体と、使用波長：６６０ｎｍ、ＮＡ：０.６５のＤＶＤ系の光記録媒体をともに記録，再生，または消去できる。
【００８１】
まず、使用波長：４０７ｎｍ、ＮＡ：０.８５の大容量光記録媒体に記録、再生、または消去する場合について説明する。図９（ａ）において、１０１は光源である波長４０７ｎｍの半導体レーザーを示し、この半導体レーザー（光源）１０１から出射した直線偏光の発散光は、コリメートレンズ１０２で略平行光とされ、偏光ビームスプリッタ１０３、ダイクロイックプリズム２０３を透過し、偏向プリズム１０４で光路を９０度偏向され、１／４波長板１０５を通過し円偏光とされ、波長選択アパーチャ２０４を透過し、対物レンズ１０６に入射し、光記録媒体１０７上に微小スポットとして集光される。このスポットにより、情報の記録，再生，あるいは消去が行われる。
【００８２】
光記録媒体１０７から反射した光は、対物レンズ１０６、１／４波長板１０５を通過して往路とは反対回りの円偏光となり、再び略平行光とされ往路と直交した直線偏光になり、偏光ビームスプリッタ１０３で反射されて、検出レンズ１０８で収束光とされ、受光素子１０９に至る。受光素子１０９からは、情報信号、サーボ信号が検出される。
【００８３】
次に、使用波長：６６０ｎｍ、ＮＡ：０.６５のＤＶＤ系の光記録媒体に記録、再生、または消去する場合について説明する。近年、ＤＶＤ系の光ピックアップには受発光素子を１つのキャン（容器）の中に設置し、ホログラムを用いて光束の分離を行うホログラムユニットが一般的に用いられるようになってきた。
【００８４】
図９（ｃ）において、２０１は、半導体レーザー２０１ａのチップ、ホログラム２０１ｂ、および受光素子２０１ｃを一体化して構成されたホログラムユニットを示す。このホログラムユニット２０１の半導体レーザー２０１ａから出射された波長：６６０ｎｍの発散光はホログラム２０１ｂを透過し、図９（ａ）に示すようにカップリングレンズ２０２でカップリングされ、ダイクロイックプリズム２０３によって偏向プリズム１０４の方向に反射され、偏向プリズム１０４によって光路が９０度偏向され、１／４波長板１０５を通過して円偏光とされ、波長選択アパーチャ２０４を透過し、対物レンズ１０６に入射し、光記録媒体１０７上に微小スポットとして集光される。このスポットにより、情報の再生、記録または消去が行われる。
【００８５】
特に、波長選択アパーチャ２０４は、使用波長：６６０の光に対してはＮＡ：０.６５となるように通過光束を制限している。すなわち、図９（ｂ）に示すように波長選択アパーチャ２０４は同心円状の開口制限手段であって、波長：４０７ｎｍの光については作用せず、波長：６６０ｎｍの光はＮＡ：０.６５を満足するための中央部のみ透過する。
【００８６】
光記録媒体１０７から反射した光は、偏向プリズム１０４で偏向されて、ダイクロイックプリズム２０３で反射され、カップリングレンズ２０２で収束光とされ、図９（ｃ）に示すホログラム２０１ｂにより半導体レーザー２０１ａと同一キャン内にある受光素子２０１ｃ方向に回折されて受光される。受光素子２０１ｃからは、情報信号、サーボ信号が検出される。
【００８７】
図１０（ａ）は本発明の実施の形態５における光ピックアップの概略構成を示すブロック図である。本実施の形態５は、使用波長：４０７ｎｍ、ＮＡ：０.８５の大容量光記録媒体と、使用波長：６６０ｎｍ、ＮＡ：０.６５のＤＶＤ系の光記録媒体と、使用波長：７８０ｎｍ、ＮＡ：０.５０のＣＤ系の光記録媒体をともに記録、再生、または消去できる光ピックアップである。
【００８８】
前記実施の形態３と異なる点は、ＤＶＤ系とＣＤ系の波長の異なる２つの半導体レーザー２０１ａ，３０１ａのチップと、ＤＶＤ系とＣＤ系の各光記録媒体からの反射光を受光するための受光素子２０１ｃ，３０１ｃの２つの受光素子と、ＤＶＤ系とＣＤ系の各光記録媒体からの反射光を各受光素子２０１ｃ，３０１ｃのそれぞれに集光するためのホログラム３０１ｂからなるホログラムユニット３０１、および図１０（ｂ）に示すようなＤＶＤ系、ＣＤ系ではそれぞれがＮＡ：０.６５，０.５０となるように、波長：６６０ｎｍ、波長：７８０ｎｍの光を制限する波長選択アパーチャ３０４を用いた点であり、通過光路などは実施の形態４と同等である。
【００８９】
また、図１１は本発明の実施の形態６における光ピックアップの概略構成を示すブロック図である。本実施の形態６と前記実施の形態３〜５と異なる点は、対物レンズの製造公差に起因して発生する偶数次の収差成分を補正する補正手段４０１を備えた点である。
【００９０】
両面非球面のガラスモールドレンズの製造誤差としては、各面の近軸曲率半径ずれ、各面の非球面形状ずれ、厚みずれ、材質のばらつき、各面間のシフト、各面間のチルトが挙げられる。このうち、各面の近軸曲率半径ずれ、厚みずれ、材質のばらつきは、偶数次の収差の発生要因である。偶数次の収差があると記録面上に形成される光スポットの形状が劣化する。
【００９１】
本実施の形態６の偶数次の収差検出手段と偶数次の収差補正手段を持つ光ピックアップは、図１１に示すように、半導体レーザー１０１としては、発光波長：４０７ｎｍ±１０ｎｍのものが用いられ、対物レンズ１０６としては、前記実施の形態１の実施例１，２で説明した何れかの対物レンズが用いられる。
【００９２】
図１１において、４０１は偶数次の収差補正手段、４０２はレンズ製造誤差を検出する偶数次の収差検出手段であり、収差検出手段４０２は実際の構成を簡略化して描いたものである。
【００９３】
いま、レンズ製造誤差が存在すると偶数次の収差が発生し、記録面上に形成される光スポットの形状が劣化する。このように発生した収差は戻り光束の波面を歪ませることになり、検出レンズ１０８を介して受光素子１０９に向う光束にも収差が発生する。
【００９４】
図１２（ａ）はこの状態を示し、検出レンズ１０８に左側から入射する戻り光束に偶数次の収差が発生しているときには、戻り光束の基準波面に対して、光軸対称に「波面の遅れ」があり、基準波面を集光したときの集光点に対し遅れた波面が集光する位置はデフォーカスとなる。そこで、遅れた波面と進んだ波面の差を取り出してフォーカス状態を検出することで「波面収差の発生状況」を知ることができる。
【００９５】
例えば、図１１に示す収差検出手段４０２として、ホログラム，ビームスプリッタなどの光路分離手段、あるいは液晶シャッタなどによりタイミングをずらす素子と、図１２（ｂ）に示す如く、領域Ａと領域Ｂのように受光領域を分割された受光素子１０９を用い、各領域Ａ，Ｂの受光出力を調べることにより、戻り光束における偶数次の収差を検出することができる。
【００９６】
収差検出手段４０２により検出される偶数次の収差は、元をただせばレンズの製造誤差に起因するものであるから、検出される収差とレンズ製造誤差とは互いに対応関係があり、従って戻り光束の収差を前記の如く検出することによりレンズ製造誤差を知ることができる。このレンズ製造誤差に基づく偶数次の収差を補正して、記録面上に適正な光スポットを形成することが可能になる。本実施の形態６では、検出される収差は、受光素子１０９の各領域Ａ，Ｂからの光電出力信号を適宜に組み合わせて得られる「収差信号」として与えられる。
【００９７】
また、本実施の形態６における収差補正手段４０１は、２枚のレンズと、これらレンズの間隔を調整する間隔調整手段（図示せず）とにより構成されている。２枚のレンズは一方が正レンズ、他方が負レンズで、図１１に示す例では負レンズが光源側に配置されているが、正レンズを光源側に配置しても良い。
【００９８】
収差補正手段４０１を構成する正・負レンズの間隔を変化させると、収差補正手段４０１を対物レンズ１０６側へ透過する光束に偶数次の収差が発生するので、この偶数次の収差により対物レンズ１０６の製造誤差に伴い発生する偶数次の収差を相殺するようにすれば良い。
【００９９】
収差検出手段４０２により検出される対物レンズ１０６の製造誤差に起因して発生する偶数次の収差を与える波面収差が、例えば、図１２（ｃ）の如きものであったとする。この波面収差を２次元曲線として示したのが図１２（ｄ）である。このような波面収差に対し、対物レンズ１０６に光源側から入射する光束中で正・負レンズの間隔を変化させて、対物レンズへの入射光の発散状態を変化させると、図１２（ｅ）のような波面収差が補正後の波面収差として得られ、もとの波面収差よりも格段に小さくなる。
【０１００】
また、具体的な補正基準としては、収差補正手段４０１における２枚のレンズの間隔を基準値にして対物レンズ１０６が略設計中央値で収差が発生しない場合の前記「収差信号」が０となるように設定しておき、実際に使用する対物レンズ１０６を組付けて収差が発生したときには、収差信号を０とするようにレンズの間隔を調整すればよい。
【０１０１】
なお、収差補正手段４０１を構成する正レンズ・負レンズは、その一方もしくは双方を複数枚のレンズで構成しても良い。
【０１０２】
図１３（ａ）は本発明の実施の形態７における光ピックアップの概略構成を示すブロック図である。本実施の形態７が前記実施の形態６と異なる点は、偶数次の収差補正手段４０１を、液晶素子と、これを駆動する電圧制御手段（図示せず）から構成される偶数次の収差補正手段５０１とした点である。
【０１０３】
液晶素子は、図１３（ｂ）に示すように、少なくとも一方の透明電極が同心円状に分割され、各同心円帯の電極部分と共通電極との間に独立して電圧を印加できるように構成され、この電圧を制御することにより、各電極部分の液晶の屈折率：ｎをｎ１からｎ２まで自在に変えることができる。
【０１０４】
屈折率：ｎを変化させると、各領域を通過する光線に光路差：Δｎ・ｄ（Δｎは屈折率変化分、ｄは液晶のセル厚）、すなわち、波長をλとして、位相差：Δｎ・ｄ（２π／λ）を与えることができる。
【０１０５】
収差検出手段５０２により検出される対物レンズ１０６の製造誤差に起因して発生する偶数次の収差を与える波面収差が、例えば、図１２（ｃ）の如きものであったとする。この波面収差を２次元曲線として示したのが図１４（ａ）の上側部分の実線である。
【０１０６】
このような波面収差に対し、対物レンズ１０６に光源側から入射する光束に、図１４（ａ）の下側部分の破線に示す位相差が与えられるように、液晶素子の各同心円帯電極に印加する電圧を調整すると、液晶素子を透過する光束の各部での波面の遅れにより前記「波面収差」を打ち消すことができる。図１４（ｂ）は、図１４（ａ）における実線（波面収差）と破線（液晶素子による波面の遅れ）の和、すなわち補正後の波面収差を示す。もとの波面収差（図１４（ａ）の上側部分）よりも格段に小さくなる。
【０１０７】
なお、使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０．８５の光記録媒体に記録、再生、または消去をする光ピックアップの課題として、光記録媒体の基板厚みのずれに伴う球面収差の発生がある。すなわち、基板厚みのずれに伴う球面収差はＮＡの４乗、波長の１乗に比例して大きくなるが、基板厚みの製造誤差±１０μｍは光ピックアップとしては許容できないため、光記録媒体の厚みずれに伴う収差を補正する必要がある。このような基板厚みずれを補正する手段としては、特許第２５０２８８４号公報、特開２０００−１３１６０３号公報、特許第３０６７６６５号公報、特開平９−１２８７８５号公報などに記載されたものが知られており、従来から知られた基板厚誤差補正用の球面収差補正手段と共用することにより、前記レンズ製造誤差に起因する偶数次の収差を補正することも可能である。
【０１０８】
また、前記実施の形態６，７における収差補正手段４０１，５０１として、受光素子上で、収差検出信号を生成してフィードバックする構成を例に説明したが、これに限られるものでなく、予め対物レンズの透過光を組付時に観測しながら、収差補正手段の基準位置を合わせこむ構成も可能である。
【０１０９】
また、レンズ製造誤差に起因する収差の補正のタイミングは、電源投入時に行っても良く、光記録媒体の取り付け時に、光記録媒体の厚みずれに伴う球面収差と合わせて補正しても良く、あるいは、光記録媒体が記録、再生、消去の動作中に随時行っても良い。
【０１１０】
また、収差補正手段は、使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０．８５の光記録媒体を記録、再生、または消去をする光ピックアップに限られるものでなく、図９（ａ）、図１０（ａ）に示したＤＶＤ系やＣＤ系との互換を行う光ピックアップの途中光路中に配置しても良い。
【０１１１】
また、図１５は本発明の実施の形態８における光ピックアップの概略構成を示すブロック図である。本実施の形態８と実施の形態３〜５と異なる点は、対物レンズの製造公差に起因して発生する奇数次の収差成分を補正する補正手段６０１を備えた点である。
【０１１２】
両面非球面のガラスモールドレンズの製造誤差としては、各面の近軸曲率半径ずれ、各面の非球面形状ずれ、厚みずれ、材質のばらつき、各面間のシフト、各面間のチルトが挙げられる。このうち、各面間のシフト、チルトは、奇数次の収差の発生要因である。奇数次の収差があると記録面上に形成される光スポットの形状が劣化する。
【０１１３】
本実施の形態８の奇数次の収差検出手段と奇数次の収差補正手段を持つ光ピックアップは、図１５に示すように、半導体レーザー１０１としては、発光波長：４０７ｎｍ±１０ｎｍのものが用いられ、対物レンズ１０６としては、前記実施の形態１の実施例１，２で説明した何れかの対物レンズが用いられる。
【０１１４】
図１５において、６０１は奇数次の収差補正手段、６０２はレンズ製造誤差を検出する奇数次の収差検出手段であり、収差検出手段６０２は実際の構成を簡略化して描いたものである。
【０１１５】
いま、レンズ製造誤差が存在すると奇数次の収差が発生し、記録面上に形成される光スポットの形状が劣化する。このように発生した収差は戻り光束の波面を歪ませることになり、検出レンズ１０８を介して受光素子１０９に向う光束にも収差が発生する。
【０１１６】
図１６（ａ）はこの状態を示し、検出レンズ１０８に左側から入射する戻り光束に奇数次の収差が発生しているときには、戻り光束の基準波面に対して、光軸に反対称に「波面の遅れ」があり、基準波面を集光したときの集光点に対し遅れた波面が集光する位置はアンバランスなサイドローブを形成する。そこで、遅れた波面と進んだ波面の差を取り出してフォーカス状態を検出することで「波面収差の発生状況」を知ることができる。
【０１１７】
例えば、図１５に示す収差検出手段６０２として、ホログラム，ビームスプリッタなどの光路分離手段、あるいは液晶シャッタなどによるタイミングをずらす素子と、図１６（ｂ）に示す如く、領域Ａと領域Ｂのように受光領域を分割された受光素子１０９を用い、各領域Ａ，Ｂの受光出力を調べることにより、戻り光束における収差を検出することができる。
【０１１８】
収差検出手段５０２により検出される奇数次の収差は、元をただせばレンズの製造誤差に起因するものであるから、検出される収差とレンズ製造誤差とは互いに対応関係があり、従って戻り光束の収差を前記の如く検出することによりレンズ製造誤差を知ることができる。このレンズ製造誤差に基づく奇数次の収差を補正して、記録面上に適正な光スポットを形成することが可能になる。本実施の形態８では、検出される収差は、受光素子１０９の各領域Ａ，Ｂからの光電出力信号を適宜に組合せて得られる「収差信号」として与えられる。
【０１１９】
図１５の実施の形態８における収差補正手段６０１は、対物レンズをフォーカス・トラッキングの２方向制御に加えて、２軸周りのチルト制御可能な４軸アクチュエータを用いて対物レンズの光軸を、光学系の光軸から傾き調整する対物レンズ傾き調整手段により構成されている。
【０１２０】
収差補正手段６０１を構成する４軸アクチュエータで対物レンズの傾きを変化させると、収差補正手段６０１を対物レンズ１０６側へ透過する光束に奇数次の収差が発生するので、この奇数次の収差によって対物レンズの製造誤差に伴い発生する奇数次の収差を相殺するようにすればよい。
【０１２１】
収差検出手段６０２により検出される対物レンズ１０６の製造誤差に起因して発生する奇数次の収差を与える波面収差が、例えば、図１６（ｃ）の如きものであったとする。この波面収差を２次元曲線として示したのが図１６（ｄ）である。
【０１２２】
このような波面収差に対し、対物レンズ１０６に光源側から入射する光束に対して、対物レンズの傾きを変化させると、図１６（ｅ）のような波面収差が補正後の波面収差として得られる。もとの波面収差よりも格段に小さくなる。
【０１２３】
また、具体的な補正基準としては、収差補正手段６０１における対物レンズの傾きを基準値にして、対物レンズが略設計中央値で収差が発生しない場合に前記「収差信号」が０となるように設定しておき、実際に使用する対物レンズを組付けて収差が発生したときには、前記収差信号を０とするように、対物レンズの傾きを調整すればよい。
【０１２４】
なお、収差補正手段は、その４軸に限られずフォーカス・トラック・１軸方向のチルトのみ制御する３軸アクチュエータであっても良く、この場合は４軸に比べ、補正能力が落ちることは言うまでもない。
【０１２５】
図１７（ａ）は本発明の実施の形態９における光ピックアップの概略構成を示すブロック図である。本実施の形態９は前記実施の形態８と異なる点は、奇数次の収差補正手段６０１を、液晶素子と、これを駆動する電圧制御手段（図示せず）から構成される奇数次の収差補正手段７０１とした点である。
【０１２６】
液晶素子は、図１７（ｂ）に示すように、少なくとも一方の透明電極３１〜３８が左右上下対称に分割され、各電極部分と共通電極との間に独立して電圧を印加できるようになっており、この電圧を制御することにより、各電極部分の液晶の屈折率：ｎをｎ１からｎ２まで自在に変えることができる。
【０１２７】
屈折率：ｎを変化させると、各領域を通過する光線に光路差：Δｎ・ｄ（Δｎは屈折率変化分、ｄは液晶のセル厚）、すなわち、波長をλとして、位相差：Δｎ・ｄ（２π／λ）を与えることができる。
【０１２８】
収差検出手段７０２により検出される対物レンズ１０６の製造誤差に起因して発生する奇数次の収差を与える波面収差が、例えば、図１６（ｃ）の如きものであったとする。この波面収差を２次元曲線として示したのが図１８（ａ）の実線である。
【０１２９】
このような波面収差に対し、対物レンズ１０６に光源側から入射する光束に、図１８（ａ）の波線に示す位相差が与えられるように、液晶素子の各電極に印加する電圧を調整すると、液晶素子を透過する光束の各部での波面の遅れにより前記「波面収差」を打ち消すことができる。図１８（ｂ）は、図１８（ａ）における実線（波面収差）と破線（液晶素子による波面の遅れ）の和、すなわち補正後の波面収差を示す。もとの波面収差（図１８（ａ）の実線の部分）よりも格段に小さくなる。
【０１３０】
なお、光ピックアップの課題として、光記録媒体のチルトのずれに伴うコマ収差の発生がある。すなわち、基板の動作時チルトとして±１度程度を見込む必要があるが光ピックアップとしては許容できないため、光記録媒体のチルトに伴うコマ収差を補正する必要がある。このようなチルトに伴うコマ収差を補正する手段としては特開平１０−９１９９０号公報、特開２００１−１１００７５号公報、特許第３１４２２５１号公報、特開平９−１２８７８５号公報などによるものが知られている。したがって、従来から知られた記録媒体チルトのコマ収差補正手段と共用することにより、前記レンズ製造誤差に起因する奇数次の収差を補正することも可能である。
【０１３１】
また、前記実施の形態８，９における収差補正手段６０１，７０１として、受光素子上で、収差検出信号を生成してフィードバックする構成を説明したが、これに限られるものでなく、予め対物レンズの透過光を組付時に観測しながら、収差補正手段の基準位置を合わせこむ構成もある。
【０１３２】
また、レンズ製造誤差に起因する収差の補正のタイミングは、電源投入時に行っても良く、光記録媒体を取り付け時に、光記録媒体のチルトに伴うコマ収差と合わせて補正しても良く、あるいは、光記録媒体が記録、再生、消去の動作中に随時行ってもよい。
【０１３３】
また、収差補正手段は、使用波長：４０７ｎｍ±１０ｎｍ、ＮＡ：０．８５の光記録媒体を記録、再生、または消去をする光ピックアップに限られるものでなく、図９（ａ），図１０（ａ）に示したＤＶＤ系やＣＤ系との互換を行う光ピックアップの途中光路中に配置しても良い。
【０１３４】
特に、基板のチルトに伴うコマ収差は、ＮＡの３乗、基板厚みの１乗、波長の−１乗に比例して大きくなるが、ＣＤ系の世代では不要、ＤＶＤ系の世代では必要、「使用波長：４０７ｎｍ、基板厚：０.１ｍｍ、ＮＡ：０.８５」の世代ではＤＶＤ系の世代よりもコマ収差の影響が小さいため、不要になる可能性も高い。
【０１３５】
よって、図９（ａ）に示したようにＤＶＤ系の世代と、「使用波長：４０７ｎｍ、基板厚：０.１ｍｍ、ＮＡ：０.８５」の世代をともに記録，再生，消去する光ピックアップ装置においては、ＤＶＤ系の世代において記録，再生，消去時には基板のチルトに伴うコマ収差補正手段として機能し、「使用波長：４０７ｎｍ、基板厚：０.１ｍｍ、ＮＡ：０.８５」の世代の記録，再生，消去の時にはレンズ製造誤差を補正する手段として機能する構成にすれば良い。
【０１３６】
図１９は本発明の実施の形態１０における光情報処理装置のの概略構成を示す透過斜視図である。光情報処理装置１０は光記録媒体２０に対して、光ピックアップ１１を用いて情報の記録，再生，消去の少なくともいずれか１以上を行う装置である。本実施の形態１０において、光記録媒体２０はディスク状であって、保護ケースのカートリッジ２１内に格納されている。光記録媒体２０はカートリッジ２１ごと、挿入口１２から光情報処理装置１０に矢印「ディスク挿入」方向へ挿入セットされ、スピンドルモータ１３により回転され、光ピックアップ１１により情報の記録や再生、あるいは消去が行われる。
【０１３７】
光ピックアップ１１として、前述の光ピックアップを適宜用いることができ、光情報処理装置は前記使用波長の光記録媒体に対して良好に情報の記録，再生，および消去を行うことができる。
【０１３８】
【発明の効果】
以上説明したように、本発明によれば、単レンズ構成であり、部品点数の増加，重量の増加，組付精度の高精度化という問題が無く、従来の１枚構成のＮＡ：０.８５対物レンズでは達成できなかった数μｍ以上の厚みずれを、ガラスモールド材料により製造が容易なＮＡ：０.８５の光ピックアップ用対物レンズを実現でき、これを用いた光ピックアップは、高密度の情報処理に対応し、かつＤＶＤ系やＣＤ系といった従来の光記録媒体へも、収差を抑制した状態で集光でき、各光記録媒体を１つの光ピックアップにて互換を可能とし、さらに、対物レンズの製造誤差に起因して発生する軸対称の収差、光記録媒体の基板厚誤差に起因して発生する球面収差、対物レンズの製造誤差に起因して発生の反軸対称の収差、光記録媒体のチルトに起因して発生するコマ収差等を抑制するための補正手段を共用する構成で備えて、部品点数を増加させることなく、信頼性が高く各使用波長の光記録媒体に対して良好に情報の記録，再生，消去が可能な光ピックアップを実現できるという効果を奏する。
【図面の簡単な説明】
【図１】レンズ材料を、屈折率：ｎｄとアッベ数：νｄとの関係で表して見た図
【図２】（ａ）は近軸曲率半径と屈折率、（ｂ）はレンズの中心肉厚と屈折率、（ｃ）はワーキングディスタンスと屈折率の波面収差：０．０４λ以下を達成の条件における関係を示す図
【図３】本発明の実施の形態１における実施例１の波長選択アパーチャ、光ピックアップ用対物レンズ、光照射側基板の配置状態、（ｂ）は非点収差、（ｃ）は球面収差、（ｄ）はレンズの中心肉厚ずれが発生したときの収差劣化量を示す図
【図４】本発明の実施の形態１における実施例２の波長選択アパーチャ、光ピックアップ用対物レンズ、光照射側基板の配置状態、（ｂ）は非点収差、（ｃ）は球面収差、（ｄ）はレンズの中心肉厚ずれが発生したときの収差劣化量を示す図
【図５】（ａ）はＤＶＤ系、（ｂ）はＣＤ系のワーキングディスタンスとレンズ材質の屈折率との関係を示す図
【図６】（ａ）は本発明の実施の形態２における実施例３の波長選択アパーチャ、光ピックアップ用対物レンズ、光照射側基板、カップリングレンズ、光源の配置状態、（ｂ）はＤＶＤ系の光学系構成と波面収差の関係を示す図
【図７】（ａ）は本発明の実施の形態２における実施例４の波長選択アパーチャ、光ピックアップ用対物レンズ、光照射側基板、カップリングレンズ、光源の配置状態、（ｂ）はＣＤ系の光学系構成と波面収差の関係を示す図
【図８】本発明の実施の形態３における光ピックアップの概略構成を示すブロック図
【図９】（ａ）は本発明の実施の形態４における光ピックアップの概略構成を示すブロック図、（ｂ）は波長選択アパーチャ、（ｃ）はホログラムユニットの拡大図
【図１０】（ａ）は本発明の実施の形態５における光ピックアップの概略構成を示すブロック図、（ｂ）は波長選択アパーチャの波長開口制限を示す図
【図１１】本発明の実施の形態６における光ピックアップの概略構成を示すブロック図
【図１２】（ａ）は検出レンズに発生の偶数次の収差、（ｂ）は受光素子の分割領域、（ｃ）は波面収差の３次元曲線、（ｄ）は波面収差の２次元曲線、（ｅ）は補正後の２次元曲線を示す図
【図１３】（ａ）は本発明の実施の形態７における光ピックアップの概略構成を示すブロック図、（ｂ）は収差補正手段である液晶素子の透明電極を示す図
【図１４】（ａ）は補正前の波面収差、（ｂ）は補正後の波面収差を示す図
【図１５】本発明の実施の形態８における光ピックアップの概略構成を示すブロック図
【図１６】（ａ）は検出レンズに発生の奇数次の収差、（ｂ）は受光素子の分割領域、（ｃ）は波面収差の３次元曲線、（ｄ）は波面収差の２次元曲線、（ｅ）は補正後の２次元曲線を示す図
【図１７】（ａ）は本発明の実施の形態９における光ピックアップの概略構成を示すブロック図、（ｂ）は収差補正手段である液晶素子の透明電極を示す図
【図１８】（ａ）は補正前の波面収差、（ｂ）は補正後の波面収差を示す図
【図１９】本発明の実施の形態１０における光情報処理装置のの概略構成を示す透過斜視図
【図２０】従来例の対物レンズの厚み公差と波面収差の関係を示す図
【符号の説明】
１，２０４，３０４ 波長選択アパーチャ
２，１０６ 対物レンズ
３ 基板
４ 光源
５，２０２，３０２ カップリングレンズ
１０ 情報記録再生装置
１１ 光ピックアップ
１２ 挿入口
１３ スピンドルモータ
１４ キャリッジ
２０，１０７ 光記録媒体
２１ カートリッジ
２２ シャッタ
３１〜３８ 透明電極
１０１，２０１ａ，３０１ａ 半導体レーザー
１０２ コリメートレンズ
１０３ 偏光ビームスプリッタ
１０４ 偏向プリズム
１０５ １／４波長板
１０８ 検出レンズ
１０９，２０１ｃ，３０１ｃ 受光素子
２０１，３０１ ホログラムユニット
２０１ｂ、３０１ｂ ホログラム
２０３，３０３ ダイクロイックプリズム
４０１，５０１ 偶数次の収差補正手段
４０２，５０２ 偶数次の収差検出手段
６０１，７０１ 奇数次の収差補正手段
６０２，７０２ 奇数次の収差検出手段[0001]
BACKGROUND OF THE INVENTION
  The present invention provides an optical pickup.ToIt is related.
[0002]
[Prior art]
In an optical system used in an information recording / reproducing apparatus that records or reproduces information on an optical recording medium, it is required to reduce the spot that the objective lens collects on the recording medium in order to increase the recording information signal density. ing. For this reason, shortening of the wavelength of the semiconductor laser, which is a light source, and increasing the numerical aperture (hereinafter referred to as NA) of the objective lens are attempted.
[0003]
As a light source semiconductor laser, a semiconductor laser having an oscillation wavelength of about 400 nm has been put into practical use. As a high NA lens, for example, Japanese Patent Application Laid-Open No. 2001-83410, Japanese Patent Application Laid-Open No. 11-202194, and Japanese Patent Application Laid-Open No. 11-203711 disclose a high NA lens for pickup composed of two aspheric lenses. Has been. The high NA objective lens composed of these two lenses, compared with an objective lens that has conventionally been composed of a single lens in the low NA region, has an increased assembly process, increased accuracy and weight. Up is an issue.
[0004]
Further, when the two-lens configuration is used, the working distance (WD) corresponding to the distance between the objective lens and the information recording medium is reduced, and the information recording medium and the objective lens may be damaged due to the collision between the information recording medium and the objective lens. As a result, there was a problem in reliability. Japanese Patent Application Laid-Open No. 2001-324673 discloses an objective lens having a NA of 0.7 or more that solves such a problem.
[0005]
However, these conventional examples have low manufacturing feasibility. In order to achieve high NA and short wavelength with a single objective lens, select a glass type that can be press-molded using an ultra-precision machined mold, and ensure wavefront performance at the design median value. And manufacturing tolerances need to be in a feasible range. First, it is necessary to suppress the wavefront aberration at the design median value to 0.01λ or less.
[0006]
According to the inventor's calculations, for example, in the third embodiment described in Japanese Patent Application Laid-Open No. 2001-324673, use wavelength: 400 nm, NA: 0.85, f (focal length): 1.765 mm, nd (lens material) In the objective lens for an optical pickup having a refractive index with respect to the d-line) of 1.771667 and νd (Abbe number) of 53.2, the wavefront aberration is 0.037λ, and the feasibility is low. Even if the wavefront performance of the design median value is good, it is difficult to put it to practical use if the manufacturing tolerance is low. For example, the thickness deviation must be ± 1 μm or more, and the deterioration amount of the wavefront aberration must be about 0.015λ or less. As another example, FIG. 20 shows a thickness tolerance and wavefront aberration for an objective lens for an optical pickup having a use wavelength: 650 nm, NA: 0.75, f: 2.00 mm, nd: 1.69330, and νd: 53.17. The above condition cannot be satisfied.
[0007]
[Problems to be solved by the invention]
Therefore, it is desired to provide a lens having a small amount of wavefront deterioration due to manufacturing tolerances or an optical pickup capable of suppressing the amount of wavefront deterioration due to manufacturing tolerances.
[0008]
  In addition, while new standards with higher NA and shorter wavelengths have been realized in recent years, CDs and DVDs, which are conventional optical recording media, exist at the user's hand. It is desirable that both these optical recording media and the new standard optical recording media can be handled by the same optical information processing apparatus. The easiest way is to use a conventional optical pickup and a new standardofOptical pickupTheThere is a way to install. However, with this method, it is difficult to achieve downsizing and cost reduction.
[0009]
  The present invention is directed to solving the above-described problems of the prior art, and has a single lens configuration, a large NA effective for reducing the diameter of the light spot, and an optical pickup having a loose manufacturing tolerance.ofAn optical pickup using an objective lens can be recorded, reproduced, and erased on a conventional optical recording medium such as a DVD system or a CD system without a plurality of optical pickups, and corrects aberration components caused by manufacturing tolerances. The, ShinCan achieve reliabilityRuOptical pickupTheThe purpose is to provide.
[0010]
[Means for Solving the Problems]
  In order to achieve this object, the present inventionRepliesOptical pickup according to claim 1IsOptical recording medium with use wavelength: 407 nm ± 10 nm, NA: 0.85 ± 0.05, and light irradiation side substrate thickness: 0.1 mmAnd wavelength used: 660 nm ± 10 nm, numerical aperture: 0 . 65 ± 0 . 05: Light irradiation side substrate thickness: 0 . 6 mm optical recording mediumOptical pickup that performs at least one of information recording, reproduction, and erasingInIt is configured as a single lens, both surfaces are aspherical and convex, and the refractive index with respect to the d-line material: nd and Abbe number: νd, Lens center thickness: t, paraxial radius of curvature of light source side surface: R1, working distance at wavelength 407 nm: WD (λ = 407 nm), focal length at wavelength 407 nm: f (λ = 407 nm), wavelength 660 nm Working distance: WD (λ = 660 nm), focal length at wavelength 660 nm: f (λ = 660 nm)But the next6conditions,
  νd ≦ 65
  1.55 ≦ nd
  1 . 0nd-1 . 0 ≦ R1 / f (λ = 407 nm) ≦ 1 . 0nd-0 . 8
  1 . 2nd-0 . 75 ≦ t / f (λ = 407 nm) ≦ 1 . 2nd-0 . 5
  -0 . 35nd + 0 . 77 ≦ WD (λ = 407 nm) / f (λ = 407 nm) ≦ −0 . 35nd + 0 . 85
  -0 . 42nd + 0 . 82 ≦ WD (λ = 660 nm) / f (λ = 660 nm) ≦ −0 . 42nd + 0 . 95
SatisfiedUsed wavelength: 407 nm ± 10 nm, numerical aperture: 0 . 85 ± 0 . 05: Light irradiation side substrate thickness: 0 . As an infinite system lens for an optical recording medium of 1 mm, use wavelength: 660 nm ± 10 nm, numerical aperture: 0 . 65 ± 0 . 05: Light irradiation side substrate thickness: 0 . An objective lens used as a finite system lens is provided for a 6 mm optical recording medium..
[0011]
  Claims2The optical pick-up describedIs,Wavelength used: 407 nm ± 10 nm, numerical aperture: 0 . 85 ± 0 . 05: Light irradiation side substrate thickness: 0 . 1 mm optical recording medium, andWavelength used: 780 nm ± 10 nm, numerical aperture: 0.50 ± 0.05, light irradiation side substrate thickness: 1.2 mm At least one of information recording, reproduction, and erasing is performed on an optical recording mediumAn optical pickup configured as a single lens, having both aspherical surfaces and convex surfaces, a refractive index with respect to the d-line material: nd and Abbe number: νd, center thickness of the lens: t, paraxial curvature of the light source side surface Radius: R1, working distance at wavelength 407 nm: WD (λ = 407 nm), focal length at wavelength 407 nm: f (λ = 407 nm), working distance at wavelength 780 nm: WD (λ = 780 nm), wavelength 780 nm Focal length: f (λ = 780 nm) is the following 6 conditions
  νd ≦ 65
  1 . 55 ≦ nd
  1 . 0nd-1 . 0 ≦ R1 / f (λ = 407 nm) ≦ 1 . 0nd-0 . 8
  1 . 2nd-0 . 75 ≦ t / f (λ = 407 nm) ≦ 1 . 2nd-0 . 5
  -0 . 35nd + 0 . 77 ≦ WD (λ = 407 nm) / f (λ = 407 nm) ≦ −0 . 35nd + 0 . 85
  -0 . 35nd + 0 . 64 ≦ WD (λ = 780 nm) / f (λ = 780 nm) ≦ −0 . 35nd + 0 . 72
Satisfactory, use wavelength: 407 nm ± 10 nm, numerical aperture: 0 . 85 ± 0 . 05: Light irradiation side substrate thickness: 0 . For an optical recording medium of 1 mm, as an infinite system lens, wavelength used: 780 nm ± 10 nm, numerical aperture: 0 . 50 ± 0 . 05 for light irradiation side substrate thickness: 1 . Having an objective lens used as a finite lens for a 2 mm optical recording medium;
  The optical pickup according to claim 3 has a wavelength used: 407 nm ± 10 nm, a numerical aperture: 0 . 85 ± 0 . 05: Light irradiation side substrate thickness: 0 . 1 mm optical recording medium, wavelength used: 660 nm ± 10 nm, numerical aperture: 0 . 65 ± 0 . 05: Light irradiation side substrate thickness: 0 . 6 mm optical recording medium, wavelength used: 780 nm ± 10 nm, numerical aperture: 0 . 50 ± 0 . 05 for light irradiation side substrate thickness: 1 . An optical pickup that performs at least one of recording, reproduction, and erasing of information on a 2 mm optical recording medium, is configured as a single lens, has both aspherical surfaces and convex surfaces, and is refracted by the d-line material. Ratio: nd and Abbe number: νd, center thickness of lens: t, paraxial radius of curvature of light source side: R1, working distance at wavelength 407 nm: WD (λ = 407 nm), focal length at wavelength 407 nm: f ( λ = 407 nm), working distance at wavelength 660 nm: WD (λ = 660 nm), focal length at wavelength 660 nm: f (λ = 660 nm), working distance at wavelength 780 nm: WD (λ = 780 nm), wavelength 780 nm Focal length: f (λ = 780 nm) is the following seven conditions
  νd ≦ 65
  1 . 55 ≦ nd
  1 . 0nd-1 . 0 ≦ R1 / f (λ = 407 nm) ≦ 1 . 0nd-0 . 8
  1 . 2nd-0 . 75 ≦ t / f (λ = 407 nm) ≦ 1 . 2nd-0 . 5
  -0 . 35nd + 0 . 77 ≦ WD (λ = 407 nm) / f (λ = 407 nm) ≦ −0 . 35nd + 0 . 85
  -0 . 42nd + 0 . 82 ≦ WD (λ = 660 nm) / f (λ = 660 nm) ≦ −0 . 42nd + 0 . 95
  -0 . 35nd + 0 . 64 ≦ WD (λ = 780 nm) / f (λ = 780 nm) ≦ −0 . 35nd + 0 . 72
Satisfactory, use wavelength: 407 nm ± 10 nm, numerical aperture: 0 . 85 ± 0 . 05: Light irradiation side substrate thickness: 0 . As an infinite system lens for an optical recording medium of 1 mm, use wavelength: 660 nm ± 10 nm, numerical aperture: 0 . 65 ± 0 . 05: Light irradiation side substrate thickness: 0 . For a 6 mm optical recording medium, as a finite system lens, wavelength used: 780 nm ± 10 nm, numerical aperture: 0 . 50 ± 0 . 05 for light irradiation side substrate thickness: 1 . Since an objective lens used as a finite system lens is provided for a 2 mm optical recording medium, it has a single lens configuration, so that the number of parts, weight, and assembly accuracy are increased. NA of sheets: 0 . NA: 0 which can realize 85 objective lenses and is easy to manufacture . 85 objective lenses for recording, reproducing, and erasing information on a large-capacity optical recording medium (λ = 407 nm) and DVD (λ = 660 nm) and / or CD (λ = 780 nm) optical recording media Can do at least one or more.
[0012]
  And claims4,5The optical pick-up describedIsThe aperture limiting means for switching the numerical aperture according to the wavelength used and / or a lens having a surface with a strong curvature on the objective lens side between the objective lens and the light source is used in combination with the wavelength used: 407 nm, Condensation can be performed in a state where aberration is suppressed even for a large-capacity optical recording medium having an NA of 0.85 and an optical recording medium such as a DVD or CD.
[0015]
  Claims6~9The optical pickup according to claim1~5The optical pickup according to claim 1, further comprising a first correction unit that corrects even-order aberration components and a first detection unit that detects even-order aberration components. The correcting means is disposed between the objective lens and the light source, and is a correcting means for changing the divergence state of the incident light from the objective lens. The first correcting means is disposed between the objective lens and the light source, and the light flux Due to the fact that it is a correction means that concentrically gives a phase difference level when transmitting or reflecting, and the first correction means is an aberration correction means that corrects spherical aberration, it is caused by manufacturing errors of the objective lens. Can be provided with an optical pickup capable of good recording, reproduction, and erasing, including a correcting means for suppressing the axially symmetric aberration and the spherical aberration caused by the substrate thickness error of the optical recording medium, versus Manufacturing tolerances of the lens can be loosened.
[0016]
  Claims10~13The optical pickup according to claim1~5The optical pickup according to claim 1, further comprising: a second correction unit that corrects an odd-order aberration component; and a second detection unit that detects the odd-order aberration component; The second correcting means is disposed between the objective lens and the light source, and is an correcting means that makes incident light incident on the objective lens tilted with respect to the optical axis of the objective lens, and the second correcting means is an objective lens. By being a correction means that is arranged between the light sources and gives a phase difference level stepwise when the light beam is transmitted or reflected, and the second correction means is an aberration correction means that corrects coma aberration. , Equipped with correction means for suppressing anti-axisymmetric aberration caused by objective lens manufacturing error and coma aberration caused by tilt of optical recording medium, and good recording, reproduction and erasing Light picks It can provide up can loosen the manufacturing tolerances of the objective lens.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0021]
In general, the optical recording medium has a disk shape, and the light irradiation side substrate thickness of the optical recording medium: 0.1 mm is a standard value. Based on this standard value, an “optical pickup optical system” is designed, and in the optical recording medium actually used, the light irradiation side substrate thickness has an error with respect to the standard value.
[0022]
Here, refractive index: nd, Abbe number: νd, center thickness of lens: t, paraxial radius of curvature of light source side: R1, working distance: WD, refractive index of material for d-line: nd, focal length: f As
Condition 1: νd ≦ 65
Condition 2: 1.55 ≦ nd
Condition 3: 1.0 nd-1.0 ≦ R1 / f ≦ 1.0 nd−0.8
Condition 4: 1.2nd−0.75 ≦ t / f ≦ 1.2nd−0.5
Condition 5: -0.35nd + 0.77 ≦ WD / f ≦ −0.35nd + 0.85
These conditions 1 to 5 are conditions for the optical pickup objective lens to realize “desired performance”.
[0023]
The objective lens for an optical pickup used as an infinite system lens is a positive lens that collects a parallel light beam incident from the light source side, and the objective lens for an optical pickup according to the present invention has a single lens configuration and both surfaces are aspherical. As a form of the lens, a biconvex lens or a meniscus lens can be used. However, since the biconvex lens can relax the curvature on the light source side, the biconvex lens is preferable from the viewpoint of manufacturing feasibility.
[0024]
When forming a light spot with a "desired spot diameter" on the recording surface via a light source of a predetermined wavelength and a substrate of a predetermined thickness, "the upper limit value of wavefront aberration allowed to form a good light spot" ”Must be suppressed to 0.04λ (λ: wavelength) or less. In this wavefront aberration: 0.04λ, there is a wavefront deterioration due to a manufacturing error such as a curvature radius shift, a thickness shift, an aspherical shape shift, a shift of each surface, and a tilt of each surface of the first and second surfaces of the lens. included. Therefore, the upper limit guideline of the amount of wavefront deterioration associated with each manufacturing error is about 0.015λ.
[0025]
FIG. 1 shows a lens material that is allowed to realize a wavefront aberration of 0.04λ or less in terms of the relationship between the refractive index: nd and the Abbe number: νd. When the objective lens for optical pickup is configured as “a biconvex lens having a surface with a strong curvature facing the light source”, when the condition 2: 1.55 ≦ nd is not satisfied, the refractive index of the objective lens is too small, When realizing NA, the curvature of the lens surface on the light source side in particular must be increased, and it becomes difficult to form the objective lens surface with high accuracy, and the cost of the objective lens also increases.
[0026]
If the condition 1: νd ≦ 65 with respect to the Abbe number: νd is not satisfied, chromatic aberration due to wavelength fluctuations in the light source becomes too large. The conditions regarding the Abbe number: νd and the refractive index: nd are preferably satisfied particularly when the objective lens for an optical pickup is a “biconvex lens having a surface with a strong curvature facing the light source”.
[0027]
Further, in the case of being formed as “a biconvex lens with a convex surface having a strong curvature facing the light source side”, if the above conditions 3 and 4 are not satisfied, the required numerical aperture is achieved and the wavefront aberration is 0.04λ. The following cannot be realized.
[0028]
Consider the paraxial radius of curvature R1 of the conditions 3 and 4 above, the center thickness of the lens t and the refractive index nd. If the surface on the light source side of the optical pickup objective lens is “convex to the light source side”, increasing the paraxial radius of curvature R1 means that the positive refractive power on this surface is reduced. In the present invention, an object is to increase the NA of the optical pickup objective lens. To increase the NA, the positive refractive power of the lens must be increased. Accordingly, if the paraxial radius of curvature: R1 is increased and the NA is increased as described above, the refractive index of the lens material must be increased, and “the refractive index of the lens material: nd is the paraxial curvature. “Radius: increases as R1 increases”.
[0029]
On the other hand, when the center thickness t of the lens is increased, the region where light passes through the surface on the recording medium side is reduced. In the present invention, an object is to increase the NA of the optical pickup objective lens. To increase the NA, the positive refractive power of the lens must be increased. Therefore, if the center thickness of the lens: t is increased and the NA is increased as described above, the refractive index of the lens material must be increased, and “the refractive index of the lens material: nd “Center thickness: increases as t increases”.
[0030]
Under the condition that the above-mentioned “wavefront aberration: 0.04λ or less” can be achieved, the relationship in which the paraxial radius of curvature: R1 and the refractive index: nd are satisfied, “the surface with a strong curvature is directed to the light source side. The focal length: f = 1.765 mm and NA: 0.85 of the objective lens for optical pickup formed as a “biconvex lens” is obtained as an example, and a black circle (●) in FIG. Similarly, when f = 2.235 mm and NA: 0.85 are obtained as an example, a triangle (Δ) in FIG. 2A is obtained. That is, it falls within the range on the straight line 2a-1 and the straight line 2a-2. Since the refractive index of the material depends on the Abbe number: νd in addition to the refractive index of the d-line: nd, the relationship between R1 and nd is not determined first, but the range between the straight line 2a-1 and the straight line 2a-2. “Wavefront aberration: 0.04λ or less” can be achieved by satisfying condition 3 of R1 and nd determined by ## EQU1 ## and satisfying νd defined by condition 1.
[0031]
Similarly, under the condition that “wavefront aberration: 0.04λ or less” can be achieved, the relationship that the center thickness: t and the refractive index: nd are satisfied is expressed as “both surfaces with a strong curvature facing the light source side. The focal length: f = 1.765 mm and NA: 0.85 of the objective lens for an optical pickup formed as a “convex lens” are obtained as an example, and a black circle (●) in FIG. Similarly, when f = 2.235 mm and NA: 0.85 are obtained as an example, a triangle (Δ) in FIG. 2B is obtained. That is, it falls within the range on the straight line 2b-1 and the straight line 2b-2. Since the refractive index of the material depends on the Abbe number: νd in addition to the refractive index of the d-line: nd, the relationship between R1 and nd is not determined first, but the range of the straight line 2b-1 and the straight line 2b-2 “Wavefront aberration: 0.04λ or less” can be achieved by satisfying condition 4 of R1 and nd determined by ## EQU1 ## and satisfying νd defined by condition 1.
[0032]
Next, the objective lens for an optical pickup of the present invention secures a working distance: WD necessary for improving the reliability of the optical pickup. Working distance: In order to increase the WD, it is only necessary to increase the back focus. For this purpose, the refractive index of the optical pickup objective lens may be decreased to reduce the refractive power, but this leads to a decrease in NA. Therefore, in order to secure the required working distance: WD while ensuring the required NA, the NA and nd must be balanced.
[0033]
NA: 0.85 can be realized, and the allowable working distance under the condition of suppressing the wavefront aberration to 0.04λ or less is the relationship between WD and the refractive index of the lens material: nd. When examined with a focal length of an optical pickup objective lens formed as a “biconvex lens toward the light source side”: f = 1.765 mm, NA: 0.85, a black circle (● in FIG. 2C) )become that way. Similarly, when viewed and obtained under the condition of f = 2.235 mm and NA: 0.85, a triangle (Δ) in FIG. That is, it falls within the range on the straight line 2c-1 and the straight line 2c-2. Since the refractive index of the material depends not only on the refractive index of the d-line: nd but also on the Abbe number: νd, the relationship between WD and nd is not determined first, but on the straight lines 2c-1 and 2c-2. By satisfying condition 5 of WD and nd determined by the range, and satisfying νd defined by condition 1, the wavefront aberration can be 0.04λ or less. From the viewpoint of working distance and objective lens weight, the effective diameter of the side surface of the light source of the objective lens is appropriately in the range of φ3 mm to φ4 mm.
[0034]
If the conditions 3 to 5 are not satisfied, even if the aspherical shape of the lens surface on the light source side or the optical recording medium side is adjusted, the wavefront aberration of 0.04λ or less cannot be achieved at NA of 0.85.
[0035]
Thus, by satisfying the conditions 1 and 2, it is possible to realize an objective lens for an optical pickup having a numerical aperture in a required range and a wavefront aberration of 0.04λ or less. Moreover, when the conditions 3 to 5 are satisfied, manufacturing feasibility can be further improved.
[0036]
As the first embodiment of the present invention, two specific examples of an objective lens for an optical pickup are given. Here, in order to avoid complications, the same reference numerals are given to components having equivalent functions corresponding to the respective constituent members shown in FIGS. 3A and 4A, and 1 denotes a wavelength selection aperture, 2 Is an objective lens for optical pickup, and 3 is a light irradiation side substrate (thickness: 0.1 mm) of the optical recording medium. The laser beam from the light source side (not shown, but located on the left side of FIGS. 3A and 4A) is a “parallel beam” and has an opening (aperture diameter: φ = 3 mm or 4 mm) of the wavelength selection aperture 1. ), Is incident on the objective lens 2, and is converged by the objective lens 2, passes through the light irradiation side substrate 3 of the optical recording medium, and matches the recording surface (the right side surface of the light irradiation side substrate 3). ) To form a light spot.
[0037]
Further, the aspherical shape of the lens surface is: coordinate in the optical axis direction: X, coordinate in the optical axis orthogonal direction: Y, paraxial radius of curvature: R, conic constant: K, higher order coefficients: A, B, C, Using D, E, F,..., A well-known aspherical expression is expressed by (Expression 1)
[0038]
[Expression 1]
X = (Y²/ R) / [1 + √ {1- (1 + K) Y / R²} + AY^Four+ BY⁶
+ CY⁸+ DY^Ten+ EY¹²+ FY¹⁴+ GY¹⁶+ HY¹⁸+ JY²⁰+ ...
The shape is specified by giving R, K, A, B, C, D,.
[0039]
First, the objective lens for the optical pickup in Example 1 has a working wavelength: 407 nm, NA: 0.85, f: 1.765 mm, nd: 1.69350, and νd: 53.2. (Table 1) Specific data is shown.
[0040]
[Table 1]

The symbols in the table are as follows.
“OBJ” means an object point (semiconductor laser as a light source), but the objective lens 2 for optical pickup is “infinite system”, and “INFINITY (infinity)” with a radius of curvature: RDY and a thickness: THI is It means that the light source is at infinity. “STO” is the surface of the wavelength selection aperture 1, and its radius of curvature: RDY is “INFINITY” and the thickness: THI is “0” in design. Unless otherwise specified, the unit of the quantity having the dimension of length is “mm”.
[0041]
“S1” means the light source side surface of the optical pickup objective lens, and “S2” means the optical recording medium side surface. The thickness of the objective lens 2 in Example 1 is 2.38463 mm, and the thickness of 0.425496 mm described on the right side of the radius of curvature in the column of S2 indicates “working distance: WD”.
[0042]
“S3” is a light source side surface of the light irradiation side substrate 3 of the optical recording medium, and “S4” is a surface matching the recording surface, and the interval between these surfaces S3 and S4, that is, the light irradiation side substrate thickness is 0. 1 mm, nd: 1.516330, and νd: 64.1. “EPD: entrance pupil diameter” represents the aperture diameter (3 mm) of the wavelength selection aperture 1, and “WL: wavelength” represents the wavelength used (407 nm).
[0043]
In the display of the aspheric coefficient, for example, “D: 0.305477E-03” is “D = 0.305477 × 10.^-3"Means. The same applies to the display of each table below.
[0044]
FIG. 3A shows an arrangement state of the wavelength selection aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 relating to the first embodiment. FIGS. 3B and 3C show astigmatism and spherical aberration of the optical pickup objective lens 2 of Example 1 (the scale on the vertical axis is a value obtained by normalizing the entrance pupil radius to 1). Indicates. Both aberrations are corrected very well. On the axis, the wavefront aberration of the design median is 0.0022λ.
[0045]
Further, FIG. 3D shows the aberration deterioration amount when the lens center thickness shift occurs. The broken line corresponds to the amount of aberration deterioration caused by the deviation of the center thickness in the conventional objective lens of use wavelength: 650 nm, NA: 0.75, f: 2.00 mm, nd: 1.69330, νd: 53.17. The solid line shows the same deterioration amount of the first embodiment. Compared with the conventional objective lens, even if there is a thickness deviation of about ± 1 μm, the wavefront deterioration is 0.006λ or less, and it is in a range where the production is sufficiently possible.
[0046]
  As described above, the objective lens of Example 1 is close to the light source side.axisCurvature radius: R1 = 1.37595 mm, f = 1.765 mm, nd = 1.69350, νd = 53.2, WD = 0.254496 mm, R1, t, WD, f, nd, νd are It exists in the range which satisfies above-described conditions 1-5.
[0047]
Next, the objective lens for optical pickup in Example 2 is different from that in Example 1 in focal length: f, NA: 0.85, f = 2.353 mm, nd = 1.69350, νd = 53.2. Specific data is shown in (Table 2) following (Table 1).
[0048]
[Table 2]

FIG. 4A shows an arrangement state of the wavelength selection aperture 1, the optical pickup objective lens 2, and the light irradiation side substrate 3 regarding the second embodiment. 4 (b) and 4 (c) show astigmatism and spherical aberration of the optical pickup objective lens 2 of Example 2 (the scale on the vertical axis is a value obtained by normalizing the entrance pupil radius to 1). Indicates. Both aberrations are corrected very well. On the axis, the wavefront aberration of the design median is 0.0034λ.
[0049]
As described above, the objective lens of Example 2 has R1 = 1.8331 mm, f = 2.353 mm, nd = 1.69350, νd = 53.2, and WD = 0.5888459 mm. , WD, f, nd, and νd are in a range that satisfies the above conditions 1 to 5 as in the first embodiment.
[0050]
Subsequently, using the objective lens for an optical recording medium optical pickup having a working wavelength of 407 nm ± 10 nm, NA of 0.85 ± 0.05, and a light irradiation side substrate thickness of 0.1 mm, DVD system, CD system As a condition for realizing the desired performance of the conventional optical recording medium such as
Condition 6: -0.42nd + 0.82 ≦ WD / f ≦ −0.42nd + 0.95
Condition 7: -0.35nd + 0.64 ≦ WD / f ≦ −0.35nd + 0.72
And the meaning of condition 6 is the same as the meaning of condition 7.
[0051]
In order to collect light on a DVD-based optical recording medium, “For an optical pickup capable of condensing on an optical recording medium having a working wavelength: 660 nm ± 10 nm, NA 0.65 ± 0.05, and light irradiation side substrate thickness: 0.6 mm. It must be an “objective lens”.
[0052]
Similarly, in order to collect light on a CD-based optical recording medium, “light that can be condensed on an optical recording medium having a working wavelength of 780 nm ± 10 nm, NA of 0.50 ± 0.05, and a light irradiation side substrate thickness of 1.2 mm. It must be a pickup objective lens.
[0053]
When the objective lens of the present invention is used as an infinite system objective lens under the above-mentioned DVD system and CD system operating wavelength and substrate thickness conditions, differences in substrate thickness (0.1 mm, 0.6 mm, 1.2 mm), wavelength Spherical aberration due to the difference (407 nm, 660 nm, 780 nm) occurs. In order to suppress this spherical aberration, correction can be made by making the incident light beam on the objective lens into divergent light when recording, reproducing, or erasing data on a DVD system or CD system. That is, it is used as a finite objective lens when recording, reproducing, and erasing on a DVD system or a CD system. In addition, even when incident light is incident in a diverging state, a slight amount of spherical aberration remains, but this is suppressed by placing a coupling lens having a strong curvature surface on the objective lens side between the light source and the objective lens. it can. Also, the difference in NA (0.85, 0.65, 0.50) can be eliminated by using an element that can limit the aperture according to the wavelength used.
[0054]
“Used wavelength: 407 nm ± 10 nm, NA: 0.85 ± 0.05, light irradiation side substrate thickness: 0.1 mm objective lens for optical recording medium optical pickup” satisfying the above conditions 1 to 5 Thickness and use of optical pickup objective lens (DVD system) that can focus on an optical recording medium with wavelength: 660 nm ± 10 nm, NA: 0.65 ± 0.05, and light irradiation side substrate thickness: 0.6 mm Examining the relationship between the allowable working distance: WD and the refractive index of the lens material: nd under the condition of minimizing the spherical aberration caused by the wavelength difference, the focal length: f = 1. In the example of 8 to 1.9 mm, the black circle (●) in FIG. Similarly, when f = 2.4 to 2.5 mm and NA: 0.85 are obtained as an example, a triangle (Δ) in FIG. 5A is obtained. That is, it falls within the range on the straight line 5a-1 and the straight line 5a-2. Since the refractive index of the material depends on the Abbe number: νd in addition to the refractive index of the d-line: nd, the relationship between WD and nd is not fixed, but the range between the straight line 5a-1 and the straight line 5a-2. By satisfying the condition 6 of WD and nd determined by ## EQU1 ## and satisfying νd defined by condition 1, spherical aberration caused by the difference in substrate thickness and wavelength used can be suppressed to the minimum.
[0055]
Similarly, “an objective lens for an optical recording medium optical pickup having a working wavelength: 407 nm ± 10 nm, NA: 0.85 ± 0.05, and light irradiation side substrate thickness: 0.1 mm” satisfying the above conditions 1 to 5, “Used wavelength: 780 nm ± 10 nm, NA 0.50 ± 0.05 and light irradiation side substrate thickness: 1.2 mm optical pickup objective lens capable of focusing on optical recording medium” (CD system) Examining the relationship between the allowable working distance: WD and the refractive index of the lens material: nd under the condition of minimizing the spherical aberration caused by the wavelength difference, the focal length: f = 1. In the example of 8 to 1.9 mm, the black circle (●) in FIG. Similarly, when f = 2.4 to 2.5 mm and NA: 0.85 are taken as an example, a triangle (Δ) in FIG. 5B is obtained.
[0056]
That is, it falls within the range on the straight line 5b-1 and the straight line 5b-2. The refractive index of the material depends not only on the refractive index of the d-line: nd but also on the Abbe number: νd, so that the relationship between WD and nd is not determined first, but on the straight lines 5b-1 and 5b-2. By satisfying the condition 7 of WD and nd determined by the range, and satisfying the νd defined by the condition 1, it is possible to minimize the spherical aberration caused by the difference in the substrate thickness and the wavelength used.
[0057]
In this way, by satisfying the above condition 6 or 7, the optical recording medium having “use wavelength: 407 nm ± 10 nm, NA: 0.85 ± 0.05 and light irradiation side substrate thickness: 0.1 mm” Realizes at least one of the recording, reproduction and erasure of conventional optical recording media such as DVD and CD in "Infinite optical pickup that records at least one of information recording, reproduction and erasing" A possible optical pickup can be realized.
[0058]
As Embodiment 2, recording, reproduction, and erasing can be performed on a large-capacity optical recording medium having a used wavelength: 407 nm and NA: 0.85, and a conventional optical recording medium such as a DVD system or a CD system. Two specific examples of objective lenses for so-called compatible optical pickups will be given. 6 (a) and 7 (a) also correspond to the respective constituent members and have the same functions as in FIGS. 3 (a) and 4 (a) of the first embodiment. 1 is a wavelength selection aperture, 2 is an objective lens, 3 is a light irradiation side substrate (thickness is 0.6 mm for a DVD system, 1.2 mm for a CD system), 4 is a light source, and 5 is a concave shape A coupling lens having
[0059]
The light emitted from the light source 4 passes through the opening (opening diameter: φ = 3.2570 mm) of the wavelength selection aperture 1 as a “divergent light beam” through the coupling lens 5, enters the objective lens 2, and this objective The light is condensed by the lens 2 and passes through the light irradiation side substrate 3 of the optical recording medium to form a light spot on the recording surface (matching the right side surface of the light irradiation side substrate 3).
[0060]
Further, the aspherical shape of the lens surface is: coordinate in the optical axis direction: X, coordinate in the optical axis orthogonal direction: Y, paraxial radius of curvature: R, conic constant: K, higher order coefficients: A, B, C, Using D, E, F,..., A well-known aspherical expression is expressed by (Equation 2),
[0061]
[Expression 2]
X = (Y²/ R) / [1 + √ {1- (1 + K) Y / R²} + AY^Four+ BY⁶
+ CY⁸+ DY^Ten+ EY¹²+ FY¹⁴+ GY¹⁶+ HY¹⁸+ JY²⁰+ ...
The shape is specified by giving R, K, A, B, C, D,.
[0062]
As Example 3, a case where the objective lens 2 in Example 1 of the first embodiment is used in a DVD system will be described. The objective lens for this optical pickup has a working wavelength: 660 nm, NA: 0.65, f: 2.4230 mm, nd: 1.51680, and νd: 64.2. Specific data are shown in (Table 3). Show.
[0063]
[Table 3]

The symbols in the table are as follows.
“OBJ” means an object point (semiconductor laser as a light source), the objective lens 2 is used as a “finite system” in the DVD system, RDY means a radius of curvature, and THI means a thickness. “STO” is the surface of the wavelength selection aperture 1, the radius of curvature is “INFINITY”, and the thickness is “0” in design. Unless otherwise specified, the unit of the quantity having the dimension of length is “mm”.
[0064]
“S2” means the light source side surface of the coupling lens 5 and “S3” means the optical recording medium side surface. “S5” means the light source side surface of the objective lens 2 and “S7” means the optical recording medium side surface.
[0065]
The thickness of the objective lens 2 in Example 3 is 3.174078 mm, and the thickness of 0.501457 mm described on the right side of the radius of curvature in the “S6” column indicates “working distance: WD”.
[0066]
“S7” is a light source side surface of the light irradiation side substrate 3 of the optical recording medium, and “S8” is a surface matching the recording surface, and the distance between these surfaces S7 and S8, ie, the light irradiation side substrate thickness is 0. 6 mm, nd: 1.516330, and νd: 64.1. “EPD: entrance pupil diameter” represents the aperture diameter (3.245570 mm) of the wavelength selection aperture 1, and “WL: wavelength” represents the wavelength used (660 nm).
[0067]
FIG. 6A shows an arrangement state of the wavelength selection aperture 1, the optical pickup objective lens 2, the light irradiation side substrate 3, the coupling lens 5, and the light source 4 according to the third embodiment. FIG. 6B shows an optical system configuration and wavefront when the objective lens 2 described in the first embodiment is condensed with a use wavelength: 660 nm, a substrate thickness: 0.6 mm, and NA: 0.65. As for the aberration, (1) is incident in an infinite system state, (2) is incident in a finite system state, and (3) is incident in a finite system state via a coupling lens. Wavefront aberration performance is shown. In the embodiment 3 shown in FIG. 6A, the aberration is corrected extremely well.
[0068]
As described above, the objective lens 2 of Example 3 has nd: 1.69350, νd: 53.2, f: 2.4299 mm, and WD: 0.501457 mm. Therefore, the WD, f, nd, and νd are In the range satisfying the above-mentioned conditions 1, 2 and 6.
[0069]
The objective lens for an optical pickup as Example 4 in the present embodiment 2 has a CD system use wavelength: 780 nm, and (Table 4) shows specific data following (Table 3).
[0070]
[Table 4]

FIG. 7A shows an arrangement state of the wavelength selection aperture 1, the optical pickup objective lens 2, the light irradiation side substrate 3, the coupling lens 5, and the light source 4 according to the fourth embodiment. FIG. 7B shows an optical system configuration and wavefront when the objective lens 2 described in the first embodiment is condensed with a use wavelength: 780 nm, a substrate thickness: 1.2 mm, and NA: 0.50. As for the aberration, (1) is incident in an infinite system state, (2) is incident in a finite system state, and (3) is incident in a finite system state via a coupling lens. Wavefront aberration performance is shown. In the embodiment 4 shown in FIG. 7A, the aberration is corrected extremely well.
[0071]
As described above, the objective lens 2 of Example 4 has nd: 1.69350, νd: 53.2, f: 2.4445 mm, and WD: 0.236004 mm.
The WD, f, nd, and νd are in a range that satisfies the above-described condition 1, condition 2, and condition 7.
[0072]
Furthermore, Example 3 and Example 4 can be realized simultaneously.
[0073]
FIG. 8 is a block diagram showing a schematic configuration of the optical pickup according to the third embodiment of the present invention. The third embodiment uses the objective lens described in Examples 1 and 2 of the first embodiment.
[0074]
8 includes a semiconductor laser 101, a collimating lens 102, a polarizing beam splitter 103, a deflecting prism 104, a quarter wave plate 105, an optical pickup objective lens 106, a detection lens 108, and a light receiving element 109. It is configured.
[0075]
The laser beam emitted from the semiconductor laser 101 is converted into a substantially parallel beam by the collimator lens 102, passes through the polarization beam splitter 103, the optical path is bent by 90 degrees by the deflecting prism 104, and is condensed through the objective lens 106. The light beam is converted into a light beam, irradiated onto the optical recording medium 107 (light irradiation side substrate thickness: 0.1 mm), passes through the light irradiation side substrate, and forms a light spot on the recording surface.
[0076]
A quarter-wave plate 105 is disposed in front of the objective lens 106, and converts linearly polarized light from the light source side into circularly polarized light. The light beam reflected by the optical recording medium 107 becomes a “return light beam”, travels backward in the optical path at the time of irradiation, and enters the polarization beam splitter 103 through the objective lens 106, the quarter-wave plate 105, and the deflection prism 104. To do.
[0077]
The return light beam incident on the quarter-wave plate 105 is circularly polarized light that is opposite to the forward path, and is transmitted through the quarter-wave plate 105 to become linearly polarized light that is orthogonal to the polarization direction of the forward path. Reflected by. The return light beam reflected by the polarization beam splitter 103 is incident on the light receiving element 109 via the detection lens 108.
[0078]
The light receiving element 109 has a light receiving surface that is appropriately divided according to a servo signal generation method. Based on the photoelectric output from each light receiving surface, a tracking signal and a focusing signal are generated, and at the time of reproducing information, a reproduction signal is generated together with these signals. These signals are output to a control circuit (not shown).
[0079]
FIG. 9A is a block diagram showing a schematic configuration of the optical pickup according to the fourth embodiment of the present invention. Here, corresponding components having the same functions corresponding to the components described in FIG. 8 showing the third embodiment are denoted by the same reference numerals, and the same applies to the following drawings.
[0080]
In the fourth embodiment, the objective lens described in Examples 3 and 4 of the second embodiment is used. The optical pickup shown in FIG. 9A records both a large-capacity optical recording medium having a working wavelength: 407 nm and NA: 0.85 and a DVD optical recording medium having a working wavelength: 660 nm and NA: 0.65. , Play or erase.
[0081]
First, a case where recording, reproduction, or erasing is performed on a large-capacity optical recording medium having a working wavelength: 407 nm and NA: 0.85 will be described. In FIG. 9A, reference numeral 101 denotes a semiconductor laser having a wavelength of 407 nm, which is a light source, and linearly polarized divergent light emitted from the semiconductor laser (light source) 101 is converted into substantially parallel light by the collimator lens 102, and the polarization beam splitter. 103, transmitted through the dichroic prism 203, deflected by 90 degrees in the optical path by the deflecting prism 104, passed through the quarter-wave plate 105 to be circularly polarized, transmitted through the wavelength selection aperture 204, and incident on the objective lens 106, and It is condensed as a minute spot on the recording medium 107. Information is recorded, reproduced, or erased by this spot.
[0082]
The light reflected from the optical recording medium 107 passes through the objective lens 106 and the quarter-wave plate 105 and becomes circularly polarized light in the opposite direction to the forward path, becomes again substantially parallel light, becomes linearly polarized light orthogonal to the forward path, and is polarized. The light is reflected by the beam splitter 103, is converged by the detection lens 108, and reaches the light receiving element 109. An information signal and a servo signal are detected from the light receiving element 109.
[0083]
Next, a case where recording, reproduction, or erasing is performed on a DVD optical recording medium having a use wavelength: 660 nm and NA: 0.65 will be described. In recent years, a hologram unit that uses a hologram to separate a light beam by installing a light receiving and emitting element in one can (container) has been generally used for DVD optical pickups.
[0084]
In FIG. 9C, reference numeral 201 denotes a hologram unit configured by integrating the chip of the semiconductor laser 201a, the hologram 201b, and the light receiving element 201c. The divergent light having a wavelength of 660 nm emitted from the semiconductor laser 201 a of the hologram unit 201 is transmitted through the hologram 201 b, and is coupled by the coupling lens 202 as shown in FIG. 9A, and is deflected by the dichroic prism 203. , The optical path is deflected by 90 degrees by the deflecting prism 104, passes through the quarter-wave plate 105, becomes circularly polarized light, passes through the wavelength selection aperture 204, enters the objective lens 106, and is an optical recording medium. The light is condensed as a minute spot on 107. Information is reproduced, recorded or erased by this spot.
[0085]
In particular, the wavelength selection aperture 204 limits the passing light flux so that NA is 0.65 with respect to light having a working wavelength of 660. That is, as shown in FIG. 9B, the wavelength selection aperture 204 is a concentric aperture limiting means, which does not act on light having a wavelength of 407 nm, and satisfies NA: 0.65 for light having a wavelength of 660 nm. Only the central part for transmission is transmitted.
[0086]
  The light reflected from the optical recording medium 107 is deflected by the deflecting prism 104, reflected by the dichroic prism 203, and converged by the coupling lens 202, and the same as the semiconductor laser 201a by the hologram 201b shown in FIG. 9C. The light is diffracted and received in the direction of the light receiving element 201c in the can. From the light receiving element 201c, the informationNewsSignals and servo signals are detected.
[0087]
FIG. 10A is a block diagram showing a schematic configuration of the optical pickup according to the fifth embodiment of the present invention. In the fifth embodiment, a large-capacity optical recording medium having a used wavelength of 407 nm and NA: 0.85, a DVD-based optical recording medium having a used wavelength of 660 nm and NA of 0.65, a used wavelength of 780 nm, and an NA. : An optical pickup capable of recording, reproducing or erasing both 0.50 CD optical recording media.
[0088]
The difference from the third embodiment is that the two semiconductor lasers 201a and 301a having different wavelengths for the DVD system and the CD system and the light reception for receiving the reflected light from the DVD and CD optical recording media. A hologram unit 301 including two light receiving elements 201c and 301c, a hologram 301b for condensing the reflected light from each of the DVD and CD optical recording media on each of the light receiving elements 201c and 301c, and FIG. In the DVD system and the CD system as shown in FIG. 10B, the wavelength selection aperture 304 that restricts the light with the wavelength of 660 nm and the wavelength of 780 nm is used so that NA is 0.65 and 0.50, respectively. The passing light path and the like are the same as those in the fourth embodiment.
[0089]
FIG. 11 is a block diagram showing a schematic configuration of the optical pickup according to the sixth embodiment of the present invention. The difference between the sixth embodiment and the third to fifth embodiments is that a correction means 401 for correcting even-order aberration components generated due to manufacturing tolerances of the objective lens is provided.
[0090]
Manufacturing errors of double-sided aspherical glass mold lenses include deviations in paraxial curvature radius of each surface, aspherical shape deviation of each surface, thickness deviation, material variation, shift between surfaces, and tilt between surfaces. It is done. Among these, the paraxial curvature radius deviation, thickness deviation, and material variation of each surface are the causes of even-order aberrations. If there is even-order aberration, the shape of the light spot formed on the recording surface deteriorates.
[0091]
As shown in FIG. 11, the optical pickup having the even-order aberration detecting unit and the even-order aberration correcting unit of the sixth embodiment uses a semiconductor laser 101 having an emission wavelength of 407 nm ± 10 nm. As the objective lens 106, any of the objective lenses described in Examples 1 and 2 of the first embodiment is used.
[0092]
In FIG. 11, 401 is an even-order aberration correction means, 402 is an even-order aberration detection means for detecting a lens manufacturing error, and the aberration detection means 402 is a simplified illustration of the actual configuration.
[0093]
Now, when there is a lens manufacturing error, even-order aberration occurs, and the shape of the light spot formed on the recording surface deteriorates. The aberration generated in this manner distorts the wavefront of the returning light beam, and aberration also occurs in the light beam that travels toward the light receiving element 109 via the detection lens 108.
[0094]
FIG. 12A shows this state. When even-numbered aberration is generated in the return beam incident on the detection lens 108 from the left side, the “wavefront delay” is symmetric with respect to the reference wavefront of the return beam. The position where the wavefront delayed with respect to the condensing point when the reference wavefront is condensed is defocused. Therefore, by extracting the difference between the delayed wavefront and the advanced wavefront and detecting the focus state, the “occurrence state of wavefront aberration” can be known.
[0095]
For example, as the aberration detection means 402 shown in FIG. 11, optical path separation means such as a hologram and a beam splitter, or an element whose timing is shifted by a liquid crystal shutter, and the like, as shown in FIG. By using the light receiving element 109 in which the light receiving area is divided and examining the light receiving outputs of the areas A and B, it is possible to detect even-order aberrations in the return light flux.
[0096]
Since the even-order aberration detected by the aberration detection means 402 is caused by a lens manufacturing error if the original is taken, the detected aberration and the lens manufacturing error have a corresponding relationship with each other. A lens manufacturing error can be known by detecting aberration as described above. By correcting even-order aberrations based on this lens manufacturing error, it becomes possible to form an appropriate light spot on the recording surface. In the sixth embodiment, the detected aberration is given as an “aberration signal” obtained by appropriately combining photoelectric output signals from the regions A and B of the light receiving element 109.
[0097]
In addition, the aberration correction unit 401 according to the sixth embodiment includes two lenses and an interval adjustment unit (not shown) that adjusts the interval between these lenses. One of the two lenses is a positive lens and the other is a negative lens. In the example shown in FIG. 11, the negative lens is disposed on the light source side, but the positive lens may be disposed on the light source side.
[0098]
When the distance between the positive and negative lenses constituting the aberration correction unit 401 is changed, even-order aberration is generated in the light beam transmitted through the aberration correction unit 401 to the objective lens 106 side. It is only necessary to cancel even-order aberrations that occur due to the manufacturing error.
[0099]
It is assumed that the wavefront aberration that gives even-order aberration caused by the manufacturing error of the objective lens 106 detected by the aberration detection unit 402 is as shown in FIG. This wavefront aberration is shown as a two-dimensional curve in FIG. With respect to such wavefront aberration, if the distance between the positive and negative lenses in the light beam incident on the objective lens 106 from the light source side is changed to change the divergence state of the incident light to the objective lens, FIG. Is obtained as corrected wavefront aberration, which is much smaller than the original wavefront aberration.
[0100]
Further, as a specific correction reference, the “aberration signal” when the aberration of the objective lens 106 is approximately the design median value and no aberration occurs is set to 0 with the distance between the two lenses in the aberration correction unit 401 as a reference value. In this way, when an aberration occurs when the objective lens 106 actually used is assembled, the distance between the lenses may be adjusted so that the aberration signal becomes zero.
[0101]
One or both of the positive lens and the negative lens constituting the aberration correction unit 401 may be composed of a plurality of lenses.
[0102]
FIG. 13A is a block diagram showing a schematic configuration of the optical pickup according to the seventh embodiment of the present invention. The seventh embodiment is different from the sixth embodiment in that even-order aberration correction means 401 is composed of a liquid crystal element and voltage control means (not shown) for driving the liquid crystal element. The point is the means 501.
[0103]
As shown in FIG. 13B, the liquid crystal element is configured such that at least one of the transparent electrodes is concentrically divided and a voltage can be independently applied between the electrode portion of each concentric zone and the common electrode. By controlling this voltage, the refractive index n of the liquid crystal of each electrode portion can be freely changed from n1 to n2.
[0104]
When the refractive index: n is changed, the optical path difference: Δn · d (Δn is the change in refractive index, d is the cell thickness of the liquid crystal), that is, the wavelength is λ, and the phase difference is Δn · d (2π / λ) can be given.
[0105]
It is assumed that the wavefront aberration that gives even-order aberration caused by the manufacturing error of the objective lens 106 detected by the aberration detector 502 is, for example, as shown in FIG. This wavefront aberration is shown as a two-dimensional curve in the solid line in the upper part of FIG.
[0106]
For such wavefront aberration, the light beam incident on the objective lens 106 from the light source side is applied to each concentric band electrode of the liquid crystal element so that the phase difference shown by the broken line in the lower part of FIG. When the voltage to be adjusted is adjusted, the “wavefront aberration” can be canceled by the delay of the wavefront at each part of the light beam transmitted through the liquid crystal element. FIG. 14B shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 14A, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (upper part in FIG. 14A).
[0107]
Incidentally, as an issue of an optical pickup for recording, reproducing, or erasing on an optical recording medium having a used wavelength: 407 nm ± 10 nm and NA: 0.85, there is generation of spherical aberration due to deviation of the substrate thickness of the optical recording medium. That is, the spherical aberration associated with the deviation of the substrate thickness increases in proportion to the fourth power of NA and the first power of the wavelength. However, the manufacturing error of the substrate thickness of ± 10 μm is unacceptable as an optical pickup. It is necessary to correct the aberrations associated with. As means for correcting such a substrate thickness deviation, those described in Japanese Patent No. 2502884, Japanese Patent Laid-Open No. 2000-131603, Japanese Patent No. 3067665, Japanese Patent Laid-Open No. 9-128785 are known. In addition, it is also possible to correct even-order aberrations caused by the lens manufacturing error by sharing with a conventionally known spherical aberration correcting means for correcting the substrate thickness error.
[0108]
In addition, as the aberration correction units 401 and 501 in the sixth and seventh embodiments, the configuration in which the aberration detection signal is generated and fed back on the light receiving element has been described as an example. However, the present invention is not limited to this. A configuration in which the reference position of the aberration correction means is adjusted while observing the transmitted light of the lens at the time of assembly is also possible.
[0109]
In addition, the correction timing of the aberration due to the lens manufacturing error may be performed when the power is turned on, and may be corrected together with the spherical aberration accompanying the thickness deviation of the optical recording medium when the optical recording medium is attached, or The optical recording medium may be performed at any time during the recording, reproduction, and erasing operations.
[0110]
The aberration correction means is not limited to an optical pickup that records, reproduces, or erases an optical recording medium having a used wavelength: 407 nm ± 10 nm and NA: 0.85. FIG. 9A and FIG. You may arrange | position in the optical path in the middle of the optical pick-up which performs compatibility with the DVD type | system | group shown to a), or CD type | system | group.
[0111]
FIG. 15 is a block diagram showing a schematic configuration of the optical pickup according to the eighth embodiment of the present invention. The difference between the eighth embodiment and the third to fifth embodiments is that a correction means 601 for correcting an odd-order aberration component generated due to the manufacturing tolerance of the objective lens is provided.
[0112]
Manufacturing errors of double-sided aspherical glass mold lenses include deviations in paraxial curvature radius of each surface, aspherical shape deviation of each surface, thickness deviation, material variation, shift between surfaces, and tilt between surfaces. It is done. Of these, the shift and tilt between the surfaces are the factors that cause odd-order aberrations. If there is an odd-order aberration, the shape of the light spot formed on the recording surface deteriorates.
[0113]
As shown in FIG. 15, the optical pickup having the odd-order aberration detecting unit and the odd-order aberration correcting unit of the eighth embodiment uses a semiconductor laser 101 having an emission wavelength of 407 nm ± 10 nm. As the objective lens 106, any of the objective lenses described in Examples 1 and 2 of the first embodiment is used.
[0114]
In FIG. 15, 601 is an odd-order aberration correction unit, 602 is an odd-order aberration detection unit that detects a lens manufacturing error, and the aberration detection unit 602 is a simplified illustration of the actual configuration.
[0115]
Now, if there is a lens manufacturing error, odd-order aberrations occur, and the shape of the light spot formed on the recording surface deteriorates. The aberration generated in this manner distorts the wavefront of the returning light beam, and aberration also occurs in the light beam that travels toward the light receiving element 109 via the detection lens 108.
[0116]
FIG. 16A shows this state, and when an odd-order aberration is generated in the return beam incident on the detection lens 108 from the left side, the “wavefront” is antisymmetric with respect to the optical axis with respect to the reference wavefront of the return beam. The position where the wavefront delayed with respect to the focal point when the reference wavefront is condensed forms an unbalanced side lobe. Therefore, by extracting the difference between the delayed wavefront and the advanced wavefront and detecting the focus state, the “occurrence state of wavefront aberration” can be known.
[0117]
For example, as the aberration detection means 602 shown in FIG. 15, optical path separation means such as a hologram and a beam splitter, or an element that shifts the timing by a liquid crystal shutter, and the like, as shown in FIG. By using the light receiving element 109 in which the light receiving area is divided and examining the light receiving outputs of the areas A and B, it is possible to detect the aberration in the returning light flux.
[0118]
Since the odd-order aberration detected by the aberration detector 502 is caused by a manufacturing error of the lens if the original is taken, the detected aberration and the lens manufacturing error have a corresponding relationship with each other. A lens manufacturing error can be known by detecting aberration as described above. It is possible to correct an odd-order aberration based on this lens manufacturing error and form an appropriate light spot on the recording surface. In the eighth embodiment, the detected aberration is given as an “aberration signal” obtained by appropriately combining photoelectric output signals from the regions A and B of the light receiving element 109.
[0119]
The aberration correction means 601 in Embodiment 8 of FIG. 15 optically changes the optical axis of the objective lens by using a four-axis actuator capable of tilt control around two axes in addition to the two-direction control of the objective lens for focus and tracking. An objective lens tilt adjusting means for adjusting the tilt from the optical axis of the system is used.
[0120]
When the inclination of the objective lens is changed by the four-axis actuator constituting the aberration correction unit 601, odd-order aberration is generated in the light beam transmitted through the aberration correction unit 601 to the objective lens 106 side. What is necessary is just to cancel the odd-order aberration which occurs with the manufacturing error of the lens.
[0121]
It is assumed that the wavefront aberration that gives an odd-order aberration caused by the manufacturing error of the objective lens 106 detected by the aberration detector 602 is as shown in FIG. This wavefront aberration is shown as a two-dimensional curve in FIG.
[0122]
When the inclination of the objective lens is changed with respect to the light beam incident on the objective lens 106 from the light source side, the wavefront aberration as shown in FIG. 16E is obtained as the corrected wavefront aberration. . It is much smaller than the original wavefront aberration.
[0123]
Further, as a specific correction reference, the “aberration signal” is set to 0 when the objective lens has a substantially designed median value and no aberration occurs with the inclination of the objective lens in the aberration correction unit 601 as a reference value. It is necessary to adjust the inclination of the objective lens so that the aberration signal is zero when aberration is generated by assembling the objective lens actually used.
[0124]
The aberration correction means is not limited to the four axes, and may be a three-axis actuator that controls only the focus, the track, and the tilt in one axis direction. In this case, it goes without saying that the correction capability is lower than that of the four axes. .
[0125]
FIG. 17A is a block diagram showing a schematic configuration of the optical pickup according to the ninth embodiment of the present invention. The ninth embodiment is different from the eighth embodiment in that the odd-order aberration correction means 601 is composed of a liquid crystal element and a voltage control means (not shown) for driving the liquid crystal element. The point is the means 701.
[0126]
In the liquid crystal element, as shown in FIG. 17B, at least one of the transparent electrodes 31 to 38 is divided symmetrically in the left-right and up-down directions so that a voltage can be applied independently between each electrode portion and the common electrode. By controlling this voltage, the refractive index n of the liquid crystal at each electrode portion can be freely changed from n1 to n2.
[0127]
When the refractive index: n is changed, the optical path difference: Δn · d (Δn is the change in refractive index, d is the cell thickness of the liquid crystal), that is, the wavelength is λ, and the phase difference is Δn · d (2π / λ) can be given.
[0128]
It is assumed that the wavefront aberration that gives the odd-order aberration caused by the manufacturing error of the objective lens 106 detected by the aberration detector 702 is as shown in FIG. This wavefront aberration is shown as a two-dimensional curve as a solid line in FIG.
[0129]
When the voltage applied to each electrode of the liquid crystal element is adjusted so that the phase difference shown by the wavy line in FIG. 18A is given to the light beam incident on the objective lens 106 from the light source side against such wavefront aberration, The “wavefront aberration” can be canceled out by the wavefront delay in each part of the light beam transmitted through the liquid crystal element. FIG. 18B shows the sum of the solid line (wavefront aberration) and the broken line (wavefront delay due to the liquid crystal element) in FIG. 18A, that is, the corrected wavefront aberration. It is much smaller than the original wavefront aberration (the solid line portion in FIG. 18A).
[0130]
An issue with optical pickups is the occurrence of coma aberration associated with the tilt shift of the optical recording medium. That is, it is necessary to allow about ± 1 degree as the tilt during the operation of the substrate, but it is not acceptable as an optical pickup, so it is necessary to correct the coma due to the tilt of the optical recording medium. As means for correcting such coma due to tilt, those disclosed in JP-A-10-91990, JP-A-2001-110075, JP-A-3142251, JP-A-9-128785 are known. Yes. Therefore, it is also possible to correct odd-order aberrations caused by the lens manufacturing error by sharing with a conventionally known recording medium tilt coma aberration correcting means.
[0131]
Further, as the aberration correction units 601 and 701 in the eighth and ninth embodiments, the configuration in which the aberration detection signal is generated and fed back on the light receiving element has been described. There is also a configuration in which the reference position of the aberration correction means is adjusted while observing the transmitted light during assembly.
[0132]
In addition, the correction timing of the aberration due to the lens manufacturing error may be performed when the power is turned on, and may be corrected together with the coma accompanying the tilt of the optical recording medium when the optical recording medium is attached, or The optical recording medium may be performed at any time during the recording, reproduction, and erasing operations.
[0133]
The aberration correction means is not limited to an optical pickup that records, reproduces, or erases an optical recording medium having a working wavelength: 407 nm ± 10 nm and NA: 0.85, and is not limited to FIGS. You may arrange | position in the optical path in the middle of the optical pick-up which performs compatibility with the DVD type | system | group shown to a), or CD type | system | group.
[0134]
In particular, the coma accompanying the tilt of the substrate increases in proportion to the third power of NA, the first power of the substrate thickness, and the first power of the wavelength, but is not necessary for the CD generation and necessary for the DVD generation. In the generation of “use wavelength: 407 nm, substrate thickness: 0.1 mm, NA: 0.85”, since the influence of coma aberration is smaller than that of the DVD generation, it is highly likely that it becomes unnecessary.
[0135]
Therefore, as shown in FIG. 9A, an optical pickup device for recording, reproducing, and erasing both the DVD generation and the generation of “use wavelength: 407 nm, substrate thickness: 0.1 mm, NA: 0.85”. In the DVD generation, it functions as a coma aberration correcting means accompanying the tilt of the substrate during recording, reproduction, and erasing, and the recording of the generation of “use wavelength: 407 nm, substrate thickness: 0.1 mm, NA: 0.85” , A structure that functions as a means for correcting a lens manufacturing error at the time of reproduction and erasing may be used.
[0136]
FIG. 19 is a transparent perspective view showing a schematic configuration of the optical information processing apparatus according to Embodiment 10 of the present invention. The optical information processing apparatus 10 is an apparatus that performs at least one of information recording, reproduction, and erasing with respect to the optical recording medium 20 using the optical pickup 11. In the tenth embodiment, the optical recording medium 20 has a disk shape and is stored in a cartridge 21 of a protective case. The optical recording medium 20 is inserted and set together with the cartridge 21 from the insertion port 12 into the optical information processing apparatus 10 in the arrow “disc insertion” direction, rotated by the spindle motor 13, and recorded, reproduced, or erased by the optical pickup 11. Done.
[0137]
  As an optical pickup 11,AboveThe optical information processing apparatus can appropriately record, reproduce, and erase information with respect to the optical recording medium having the used wavelength.
[0138]
【The invention's effect】
  As described above, according to the present invention, it has a single lens configuration, and there is no problem of an increase in the number of parts, an increase in weight, and an increase in assembly accuracy. A thickness deviation of several μm or more that could not be achieved with an objective lens can be realized with an NA: 0.85 optical pickup objective lens that can be easily manufactured using a glass mold material. It can be focused on conventional optical recording media such as DVD and CD systems with reduced aberrations, and each optical recording medium can be compatible with a single optical pickup. Axisymmetric aberration caused by manufacturing errors of the optical disc, spherical aberration caused by errors in the substrate thickness of the optical recording medium, anti-axisymmetric aberration caused by manufacturing errors of the objective lens, optical recording medium Due to tilt With a configuration that shares a correction means to suppress coma aberration, etc., and reliability without increasing the number of partsButHighTheAn optical pickup that can record, reproduce, and erase information on optical recording media of each wavelength.TheThere is an effect that it can be realized.
[Brief description of the drawings]
FIG. 1 is a view of a lens material represented by the relationship between refractive index: nd and Abbe number: νd.
2A is a paraxial radius of curvature and refractive index, FIG. 2B is a lens center thickness and refractive index, and FIG. 2C is a condition for achieving a working distance and a refractive index wavefront aberration of 0.04λ or less. Diagram showing the relationship
3 shows the arrangement of the wavelength selective aperture, the optical pickup objective lens, and the light irradiation side substrate of Example 1 according to Embodiment 1 of the present invention, (b) astigmatism, (c) spherical aberration, ( d) is a diagram showing the amount of aberration deterioration when the lens center thickness deviation occurs.
4 shows the arrangement of the wavelength selective aperture, the optical pickup objective lens, and the light irradiation side substrate of Example 2 in Embodiment 1 of the present invention, (b) astigmatism, (c) spherical aberration, ( d) is a diagram showing the amount of aberration deterioration when the lens center thickness deviation occurs.
FIGS. 5A and 5B are diagrams showing a relationship between a DVD system and FIG. 5B a CD system working distance and a refractive index of a lens material.
6A is a wavelength selection aperture, an optical pickup objective lens, a light irradiation side substrate, a coupling lens, and a light source arrangement state of Example 3 in Embodiment 2 of the present invention, and FIG. 6B is a DVD system. Of the relationship between the optical system configuration and wavefront aberration
7A is a wavelength selection aperture, an optical pickup objective lens, a light irradiation side substrate, a coupling lens, and a light source arrangement state of Example 4 in Embodiment 2 of the present invention, and FIG. 7B is a CD system. Of the relationship between the optical system configuration and wavefront aberration
FIG. 8 is a block diagram showing a schematic configuration of an optical pickup according to a third embodiment of the present invention.
9A is a block diagram showing a schematic configuration of an optical pickup according to a fourth embodiment of the present invention, FIG. 9B is a wavelength selection aperture, and FIG. 9C is an enlarged view of a hologram unit.
10A is a block diagram illustrating a schematic configuration of an optical pickup according to a fifth embodiment of the present invention, and FIG. 10B is a diagram illustrating wavelength aperture limitation of a wavelength selection aperture.
FIG. 11 is a block diagram showing a schematic configuration of an optical pickup according to a sixth embodiment of the present invention.
12A is an even-order aberration generated in the detection lens, FIG. 12B is a divided region of the light receiving element, FIG. 12C is a three-dimensional curve of wavefront aberration, and FIG. 12D is a two-dimensional curve of wavefront aberration; (E) is a figure which shows the two-dimensional curve after correction | amendment.
13A is a block diagram illustrating a schematic configuration of an optical pickup according to a seventh embodiment of the present invention, and FIG. 13B is a diagram illustrating a transparent electrode of a liquid crystal element that is aberration correction means.
14A is a diagram showing wavefront aberration before correction, and FIG. 14B is a diagram showing wavefront aberration after correction.
FIG. 15 is a block diagram showing a schematic configuration of an optical pickup according to an eighth embodiment of the present invention.
16A is an odd-order aberration generated in the detection lens, FIG. 16B is a divided region of the light receiving element, FIG. 16C is a three-dimensional curve of wavefront aberration, and FIG. 16D is a two-dimensional curve of wavefront aberration; (E) is a figure which shows the two-dimensional curve after correction | amendment.
17A is a block diagram illustrating a schematic configuration of an optical pickup according to a ninth embodiment of the present invention, and FIG. 17B is a diagram illustrating a transparent electrode of a liquid crystal element that is an aberration correction unit.
18A is a diagram showing wavefront aberration before correction, and FIG. 18B is a diagram showing wavefront aberration after correction.
FIG. 19 is a transparent perspective view showing a schematic configuration of the optical information processing apparatus in the tenth embodiment of the present invention.
FIG. 20 is a diagram showing a relationship between thickness tolerance and wavefront aberration of a conventional objective lens;
[Explanation of symbols]
1,204,304 Wavelength selection aperture
2,106 Objective lens
3 Substrate
4 Light source
5,202,302 Coupling lens
10 Information recording and playback device
11 Optical pickup
12 insertion slot
13 Spindle motor
14 Carriage
20, 107 Optical recording medium
21 cartridge
22 Shutter
31-38 Transparent electrode
101, 201a, 301a Semiconductor laser
102 Collimating lens
103 Polarizing beam splitter
104 Deflection prism
105 1/4 wave plate
108 Detection lens
109, 201c, 301c Light receiving element
201, 301 Hologram unit
201b, 301b hologram
203, 303 Dichroic prism
401, 501 Even-order aberration correction means
402, 502 Even-order aberration detection means
601,701 Odd-order aberration correction means
602, 702 Odd-order aberration detection means

Claims (13)

Use Wavelength: 407 nm ± 10 nm, numerical aperture: 0.85 Light irradiation-side substrate thickness by ± 0.05: 0.1 mm of the optical recording medium, and the use wavelength: 660 nm ± 10 nm, numerical aperture:. 0 65 ± 0. light irradiation-side substrate thickness by 05:. 0 6 mm of the information on an optical recording medium recording, reproducing, an optical pickup for performing at least any one or more erased,
Constructed as a single lens, both surfaces are aspherical and convex, refractive index with respect to d-line material: nd and Abbe number: νd , lens center thickness: t, paraxial radius of curvature of light source side surface: R1,
Working distance at wavelength 407 nm: WD (λ = 407 nm), focal length at wavelength 407 nm: f (λ = 407 nm),
Working distance at a wavelength of 660 nm: WD (λ = 660 nm), focal length at a wavelength of 660 nm: f (λ = 660 nm) are the following six conditions νd ≦ 65
1.55 ≦ nd
1. 0nd-1. 0 ≦ R1 / f (λ = 407nm) ≦ 1. 0nd-0. 8
1. 2nd-0. 75 ≦ t / f (λ = 407nm) ≦ 1. 2nd-0. 5
-0. 35nd + 0. 77 ≦ WD (λ = 407nm) / f (λ = 407nm) ≦ -0. 35nd + 0. 85
-0. 42nd + 0. 82 ≦ WD (λ = 660nm) / f (λ = 660nm) ≦ -0. 42nd + 0. 95
Satisfied ,
Use Wavelength: 407 nm ± 10 nm, numerical aperture:.. 0 85 ± 0 light irradiation side substrate thickness by 05: as an infinite system lens for 0 1 mm of the optical recording medium.
Use Wavelength: 660 nm ± 10 nm, numerical aperture:.. 0 65 ± 0 05 by light irradiation side substrate thickness:. 0 and having an objective lens used as the finite lens for 6mm optical recording medium light pickup. Use Wavelength: 407 nm ± 10 nm, numerical aperture:.. 0 85 ± 0 05 by light irradiation side substrate thickness:. 0 1 mm of the optical recording medium, and the use wavelength: 780 nm ± 10 nm, numerical aperture:. 0 50 ± 0. light irradiation-side substrate thickness by 05:. 1 2 mm of the information on an optical recording medium recording, reproducing, an optical pickup for performing at least any one or more erased,
Constructed as a single lens, both surfaces are aspherical and convex, refractive index with respect to d-line material: nd and Abbe number: νd , lens center thickness: t, paraxial radius of curvature of light source side surface: R1,
Working distance at wavelength 407 nm : WD (λ = 407 nm), focal length at wavelength 407 nm : f (λ = 407 nm),
Working distance at a wavelength of 780 nm: WD (λ = 780 nm), focal length at a wavelength of 780 nm: f (λ = 780 nm) are the following six conditions:
νd ≦ 65
1. 55 ≦ nd
1.0nd-1.0 ≦ R1 / f (λ = 407 nm) ≦ 1.0nd−0.8
1.2nd−0.75 <t / f (λ = 407 nm) ≦ 1.2nd−0.5
−0.35nd + 0.77 ≦ WD (λ = 407 nm) / f (λ = 407 nm) ≦ −0.35nd + 0.85
-0. 35nd + 0. 64 ≦ WD (λ = 780nm) / f (λ = 780nm) ≦ -0. 35nd + 0. 72
Satisfied ,
Use Wavelength: 407 nm ± 10 nm, numerical aperture:.. 0 85 ± 0 light irradiation side substrate thickness by 05: as an infinite system lens for 0 1 mm of the optical recording medium.
Use Wavelength: 780 nm ± 10 nm, numerical aperture:.. 0 50 ± 0 05 by light irradiation side substrate thickness:. 1 and having an objective lens used as the finite lens for 2mm optical recording medium light pickup. Use Wavelength: 407 nm ± 10 nm, numerical aperture:.. 0 85 ± 0 05 by light irradiation side substrate thickness:. 0 1 mm of the optical recording medium, and the use wavelength: 660 nm ± 10 nm, numerical aperture:. 0 65 ± 0. light irradiation-side substrate thickness by 05:. 0 6 mm of the optical recording medium, and the use wavelength: 780 nm ± 10 nm, numerical aperture:.. 0 50 ± 0 05 by light irradiation side substrate thickness: to 1 2 mm of the optical recording medium. An optical pickup that performs at least one of recording, reproducing, and erasing information .
Constructed as a single lens, both surfaces are aspherical and convex, refractive index with respect to d-line material: nd and Abbe number: νd, lens center thickness: t, paraxial radius of curvature of light source side surface: R1,
Working distance at wavelength 407 nm : WD (λ = 407 nm), focal length at wavelength 407 nm: f (λ = 407 nm),
Working distance at wavelength 660 nm: WD (λ = 660 nm), focal length at wavelength 660 nm: f (λ = 660 nm),
Working distance at wavelength 780 nm: WD (λ = 780 nm), focal length at wavelength 780 nm: f (λ = 780 nm)
But the following 7 conditions
νd ≦ 65
1. 55 ≦ nd
1. 0nd-1. 0 ≦ R1 / f (λ = 407nm) ≦ 1. 0nd-0. 8
1. 2nd-0. 75 ≦ t / f (λ = 407nm) ≦ 1. 2nd-0. 5
-0. 35nd + 0. 77 ≦ WD (λ = 407nm) / f (λ = 407nm) ≦ -0. 35nd + 0. 85
−0.42nd + 0.82 ≦ WD (λ = 660 nm) / f (λ = 660 nm) ≦ −0.42nd + 0.95
-0. 35nd + 0. 64 ≦ WD (λ = 780nm) / f (λ = 780nm) ≦ -0. 35nd + 0. 72
Satisfied ,
Use Wavelength: 407 nm ± 10 nm, numerical aperture:.. 0 85 ± 0 light irradiation side substrate thickness by 05: as an infinite system lens for 0 1 mm of the optical recording medium.
Use Wavelength: 660 nm ± 10 nm, numerical aperture: 0.65 Light irradiation-side substrate thickness by ± 0.05: as the finite lens for 0.6mm optical recording medium,
Use Wavelength: 780 nm ± 10 nm, numerical aperture:.. 0 50 ± 0 05 by light irradiation side substrate thickness:. 1 and having an objective lens used as the finite lens for 2mm optical recording medium light pickup. Any one optical pickup according to claim 1, wherein the use together aperture limiting means for switching the numerical aperture according to the wavelength used. Wherein between the objective lens and the light source, any one light pickup according to claim 1, wherein the use in conjunction a lens having the curvature strong surface on the objective lens side. First correction means and any one of claims 1-5, characterized in that further comprising a first detecting means for detecting the even-order aberration component for correcting the even-order aberration component of the light pickup. Wherein the first correction means is arranged between the objective lens and the light source, the light pickup according to claim 6, characterized in that a correcting means for changing the divergence state of the objective lens incident light. 7. The light according to claim 6, wherein the first correction means is a correction means that is disposed between the objective lens and the light source and that gives a phase difference level concentrically when the light beam is transmitted or reflected. pick up. The optical pickup according to claim 6, wherein the first correction unit is an aberration correction unit that corrects spherical aberration . And second correction means for correcting the odd-order aberration components, according to any one of claims 1 to 5, further comprising a second detection means for detecting said odd-order aberration component the optical pick-up of. 11. The correction means according to claim 10, wherein the second correction means is disposed between an objective lens and a light source and makes the incident light incident on the objective lens tilted with respect to the optical axis of the objective lens . Optical pickup. 11. The light according to claim 10, wherein the second correction means is a correction means that is disposed between the objective lens and the light source and gives a phase difference level in a stepped manner when a light beam is transmitted or reflected. pick up. It said second correction means, any one optical pickup according to claim 10-12, characterized in that the aberration correcting means for correcting the coma.

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