JP4218096B2

JP4218096B2 - Optical head

Info

Publication number: JP4218096B2
Application number: JP33719098A
Authority: JP
Inventors: 照弘塩野; 圭一松▲ざき▼; 定夫水野
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-11-27
Filing date: 1998-11-27
Publication date: 2009-02-04
Anticipated expiration: 2018-11-27
Also published as: JP2000163791A

Description

【０００１】
【発明の属する技術分野】
本発明は、光学的記録再生装置の光学ヘッドに関し、特に、複数の種類の情報記録媒体に対応でき、互いに近傍に配置した２波長の光源を具備する小型・薄型・軽量の光学ヘッドに関する。
【０００２】
【従来の技術】
コンパクトディスク（ＣＤ）、ＤＶＤ等の光ディスクや光カードメモリ等の情報記録媒体の信号を読み出すための重要な構成部品として光学ヘッドがある。光学ヘッドは、光学的記録媒体から信号を取り出すために、信号検出機能だけでなくフォーカスサーボ、トラッキングサーボ等の制御機構を備える必要がある。
【０００３】
ＤＶＤやＣＤまたはＣＤ-Ｒの複数の情報記録媒体に対応するために、光源を２つ搭載した光学ヘッドがあった。従来の２波長の光源を有する光学ヘッドを図８に示す。
【０００４】
ＤＶＤに対応した第１の波長λ1を出射する第１の光源１’ａと、ＣＤやＣＤ−Ｒに対応した第２の波長λ2を出射する第２の光源１’ｂは、それぞれ別々の光源・光検出器ユニット１７’ａ、１７’ｂに内蔵されており、それらから出射されたレーザ光２’ａ、２’ｂはビームスプリッタ１４により合波され、コリメータレンズ３’で平行になり、立ち上げミラー１５で光軸を９０°折り曲げられ、対物レンズ４’により、光ディスク１１（ＤＶＤは１１ａ、ＣＤは１１ｂ）に集光される。
【０００５】
光ディスク１１で反射された信号光は、逆向きに折り返し、ビームスプリッタ１４により分波され、光源・光検出器ユニット１７’ａ、１７’ｂの窓に設けられたフォーカス／トラック誤差信号検出器８’ａ、８’ｂにより、光検出器１３’上に集光され、再生信号が読み出される。また、フォーカス／トラックサーボ等の制御が行われ、安定して信号が読み出せるようにしている。
【０００６】
【発明が解決しようとする課題】
しかしながら、ＤＶＤやＣＤまたはＣＤ-Ｒ等の複数の情報記録媒体に対応するために、光源を別々のパッケージ（光源・光検出器ユニット）に内蔵し、ビームスプリッタ等で合成するような従来の構成では、光学ヘッドの小型・薄型・軽量化に限界があり、しかも位置合わせが複雑で、さらなる簡素化、組立の簡単化ができないという課題があった。
【０００７】
本発明は、従来技術における前記課題を解決するためになされたものであり、特に、複数の種類の情報記録媒体に対応でき、互いに近傍に配置した２波長の光源を具備する小型・薄型・軽量の光学ヘッドを提供することを目的とする。
【０００８】
【課題を解決するための手段】
前記目的を達成するため、本発明の請求項１に記載の発明は、第１の波長の光を出射する第１の光源と、上記第１の光源の近傍に配置された、第２の波長の光を出射する第２の光源と、上記第１と第２の波長の光を分離する波長分離手段と、分離された上記第２の波長の光を、分離された上記第１の波長の光と光軸が実質上平行になるように偏向を行う光偏向手段と、上記光偏向手段から出射された上記第１の波長の光と上記第２の波長の光を情報記録媒体にそれぞれ集光する対物レンズとを具備し、透明基板上に上記波長分離手段を設け、その上に上記光偏向手段を設け、上記第１及び第２の波長の光は、上記透明基板のその対向面側から入射し、上記波長分離手段は上記第１の波長の光を実質上反射させ、上記第２の波長の光を実質上透過させ、上記光偏向手段は表面レリーフ型の回折光学素子であり、その溝の底部から上記波長分離手段までの距離は、上記第１の波長よりも大きいことを特徴とする光学ヘッドである。これにより、例えば、互いに近傍に配置された２波長の光源を用いた、小型軽量で、複数の種類の情報記録媒体に対応できる光学ヘッドを得ることができる。例えば、コンパクトな構成を実現することができる。例えば、光学部品の位置合わせが簡単になり、構造が安定化するとともに、実質上平行になる第１と第２の波長の光の最大強度の中心位置を近づけ、光ディスク上で良好な集光スポットを形成することができる。例えば、波長分離手段からしみ出す、光偏向手段への第１の波長の光の影響を無くし、第１の波長の光の光利用効率を良くすることができる。
【０００９】
また、本発明の請求項２に記載の発明は、上記波長分離手段は波長分離多層膜である請求項１に記載の光学ヘッドである。これにより、例えば、薄型で他の光学部品に集積化することができ、構造が安定になる。
【００１０】
また、本発明の請求項３に記載の発明は、上記対物レンズに入射する上記第１の波長の光の光軸に垂直となる光学ヘッドの下面を基準面とし、上記透明基板は上記基準面に対して、実質上４５°に配置することを特徴とする請求項１に記載の光学ヘッドである。これにより、例えば、透明基板と一体化した光学部品は立ち上げミラーを兼ねることができる。
【００１１】
また、本発明の請求項４に記載の発明は、上記回折光学素子は反射形の直線状グレーティングであることを特徴とする請求項１に記載の光学ヘッドである。これにより、例えば、光偏向手段の製造が簡単で、位置合わせが容易な光学ヘッドを得ることができる。
【００１２】
また、本発明の請求項５に記載の発明は、上記対物レンズに入射する上記第１の波長の光の光軸に垂直となる光学ヘッドの下面を基準面とし、上記第１の光源と上記第２の光源は、上記基準面に対して、実質上同一高さに配置することを特徴とする請求項１に記載の光学ヘッドである。これにより、例えば、第１と第２の光源の配置が容易になる。
【００１３】
また、本発明の請求項６に記載の発明は、上記光偏向手段は反射形の直線状グレーティングであって、上記基準面に対して上記グレーティングの溝方向に傾けて配置することを特徴とする請求項５に記載の光学ヘッドである。これにより、例えば、グレーティングの１次回折効率を高くできる構成が可能である。
【００１４】
また、本発明の請求項７に記載の発明は、上記グレーティングは断面形状が鋸歯形状であり、上記基準面の法線からの、溝方向に傾けた傾斜角をθ 1 とし、その屈折率をｎとしたとき、上記第２の波長λ 2 に対して、上記グレーティングの溝深さＬが、Ｌ = λ 2 ／（２ｎ cos θ 1 ）の関係を実質上満たすことを特徴とする請求項６に記載の光学ヘッドである。これにより、例えば、グレーティングの１次回折効率を最も高くできる。
【００１５】
また、本発明の請求項８に記載の発明は、上記グレーティングは断面形状がレベル数ｐのマルチレベル形状であり、上記基準面の法線からの、溝方向に傾けた傾斜角をθ 1 とし、その屈折率をｎとしたとき、上記第２の波長λ 2 に対して、上記グレーティングの溝深さＬが、Ｌ = （ｐ−１）λ 2 ／（２ｐｎ cos θ 1 ）の関係を実質上満たすことを特徴とする請求項６に記載の光学ヘッドである。これにより、例えば、グレーティングの製造が容易で、１次回折効率を最も高くすることができる。
【００１６】
また、本発明の請求項９に記載の発明は、上記対物レンズに入射する上記第１の波長の光の光軸に垂直となる光学ヘッドの下面を基準面とし、上記第１の光源と上記第２の光源は、実質上上記基準面に対して高さ方向に配置することを特徴とする請求項１に記載の光学ヘッドである。これにより、例えば、第１と第２の光源の配置が容易になる。
【００１７】
また、本発明の請求項１０に記載の発明は、上記光偏向手段は反射形の直線状グレーティングであって、上記基準面に対して、上記グレーティングの溝に垂直な方向に傾けて配置することを特徴とする請求項９に記載の光学ヘッドである。これにより、例えば、対物レンズに入射する第１の波長の光と第２の波長の光の光軸の、側面図における奥行き方向のずれを実質上無くすことができる。
【００１８】
また、本発明の請求項１１に記載の発明は、上記第１の波長は、上記第２の波長より小さいことを特徴とする請求項１に記載の光学ヘッドである。これにより、例えば、一般的に光源の出射効率が悪いという波長が小さい方の第１の波長の光利用効率を、第２の波長の光利用効率より大きくすることができる。
【００１９】
また、本発明の請求項１２に記載の発明は、上記波長分離手段と上記光偏向手段の間にバッファ層を設けることを特徴とする請求項１記載の光学ヘッドである。これにより、例えば、波長分離手段からしみ出す、光偏向手段への第１の波長の光の影響を無くし、第１の波長の光の光利用効率を良くすることができる。
【００２０】
また、本発明の請求項１３に記載の発明は、第１の波長の光を出射する第１の光源と、上記第１の光源の近傍に配置された、第２の波長の光を出射する第２の光源と、上記第１と第２の波長の光を分離する波長分離手段と、分離された上記第２の波長の光を、分離された上記第１の波長の光と光軸が実質上平行になるように偏向を行う光偏向手段と、上記光偏向手段から出射された上記第１の波長の光と上記第２の波長の光を情報記録媒体にそれぞれ集光する対物レンズとを具備し、上記対物レンズに入射する上記第１の波長の光の光軸に垂直となる光学ヘッドの下面を基準面とし、上記情報記録媒体側を第１面、上記光源側を第２面、上記基準面側を第３面とする３つの光学面を有するプリズムの上記第３面に上記波長分離手段を設け、その下面に上記光偏向手段を設け、上記第１及び第２の波長の光は、上記第２面から入射し、上記第１面、第３面、第１面の順に通過し、上記波長分離手段は上記第１の波長の光を実質上反射させ、上記第２の波長の光を実質上透過させることを特徴とする光学ヘッドである。これにより、例えば、互いに近傍に配置された２波長の光源を用いた、小型軽量で、複数の種類の情報記録媒体に対応できる光学ヘッドを得ることができる。例えば、コンパクトな構成を実現することができる。例えば、光路をプリズム内のジグザグ伝搬をとる構成により光学ヘッドを薄型にすることができる。
【００２１】
また、本発明の請求項１４に記載の発明は、少なくとも上記第１の波長の光の光路中に、プリズムの色分散を低減する色収差補正グレーティングを設けることを特徴とする請求項１３に記載の光学ヘッドである。これにより、例えば、光源からの出射光として半導体レーザ光を用いた場合、高周波モジュールや自励発振による数 nm 程度の波長帯域の広がりや環境温度の変化によって出射光の中心波長が変化しても、プリズムの色分散を低減して光ディスク面で良好な集光スポットを得ることができる。
【００２２】
また、本発明の請求項１５に記載の発明は、第１の波長の光を出射する第１の光源と、上記第１の光源の近傍に配置された、第２の波長の光を出射する第２の光源と、上記第１と第２の波長の光を分離する波長分離手段と、分離された上記第２の波長の光を、分離された上記第１の波長の光と光軸が実質上平行になるように偏向を行う光偏向手段とを具備し、上記光偏向手段は反射形の直線状グレーティングであり、上記グレーティングは、上記第１の光源と上記第２の光源の距離が大きいほど、その周期を小さくすることを特徴とする光学ヘッドである。これにより、例えば、互いに近傍に配置された２波長の光源を用いた、小型軽量で、複数の種類の情報記録媒体に対応できる光学ヘッドを得ることができる。例えば、光偏向手段の製造が簡単で、位置合わせが容易な光学ヘッドを得ることができる。例えば、第１の光源と第２の光源の任意の距離に対して２波長の光源の光軸を実質上平行にすることが可能である。
【００３１】
【発明の実施の形態】
（第１の実施の形態）
本発明の第１の実施の形態の光学ヘッドについて、図１から図３までを用い、座標軸を図のようにとって詳細に説明する。
【００３２】
図１（ａ）は本発明の第１の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図、図１（ｂ）は本発明の第１の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す裏面図、図２（ａ）は同実施の形態の光学ヘッドにおける波長分離手段、光偏向手段の説明図、図２（ｂ）は同実施の形態のさらに他の光学ヘッドにおける波長分離手段、光偏向手段の説明図、図３（ａ）は本発明の第１の実施の形態の光学ヘッドにおける第１の波長に対する３ビームグレーティングの回折効率と溝深さの関係図、図３（ｂ）は本発明の第１の実施の形態の光学ヘッドにおける第２の波長に対する３ビームグレーティングの回折効率と溝深さの関係図である。
【００３３】
本実施の形態の光学ヘッドは、互いに近傍に配置された２波長の光源を搭載し、例えば、ＤＶＤやＣＤ、ＣＤ−Ｒ等の複数の情報記録媒体に対応できる、小型・薄型・軽量の光学ヘッドを実現する。
【００３４】
図１に示すように、光源・光検出器ユニット１７内に、２波長の光源１と光検出器１３が内蔵されており、光源として、例えば、第１の波長λ1＝0.658μmの光２ａを出射する半導体レーザチップ１ａと、例えば、第２の波長λ2＝0.8μmの光２ｂを出射する半導体レーザチップ１ｂが、それらの中心位置の距離ｇが、例えば、４００μm程度離れた近傍に配置されている。
【００３５】
光源１ａと１ｂは、通常同時に発光するものではなく、光ディスク１１の種類に応じて選択的に光を出射するものである。本実施の形態では、基準面１８（ｘｙ平面に平行な光学ヘッドの下面）に対して、２波長の光源１は実質上同一高さになるように配置してある。このような配置にすることにより、配置が容易となる。２波長の光源１となる半導体レーザチップを互いに近傍に配置することにより、従来例のようなビームスプリッタ等の光学部品が省略できるため、光学ヘッドが簡素化・小型・薄型・軽量化でき、また組立の際の位置合わせが容易になる。
【００３６】
光源１から選択的に出射されたレーザ光２ａまたは２ｂは、光源・光検出器ユニット１７の窓側に設けた、３ビームグレーティング２４を透過し、それと一体化した、例えば、ホログラム素子であるフォーカス／トラック誤差信号検出素子８を透過（０次回折光利用）して、例えば、焦点距離２０ｍｍのコリメータレンズ３により、ビーム径が例えば、第１の波長の光は３ｍｍ程度、第２の波長の光は２．２ｍｍ程度の略平行光６ａ、６ｂとなる。このとき、光源１ａとコリメータレンズ３の中心を結ぶ第１の波長の光２ａ、６ａの光軸は、ｙ軸に平行となるように配置し、光源１ｂとコリメータレンズ３の中心を結ぶ２ｂ、６ｂの光軸は、基準面１８に平行でｙ軸方向に対して、例えば、１．１５°傾いている（図１（ｂ）参照）。
【００３７】
３ビームグレーティング２４は、第２の波長の光２ｂに対してのみ回折して３ビーム（０次、±１次回折光）になり、トラッキング検出できるように設けたもので、第１の波長の光２ａに対しては、透明基板のようにただ通過するだけである。特に、ＣＤ−Ｒの光ディスクを第２の波長の光で読み出す際のトラッキング検出法は、３ビーム法が好ましく、ＤＶＤの光ディスクを第１の波長の光で読み出す際のトラッキング検出法は、位相差法が好ましいためにそのような構成にすると、それらの光ディスクに対して、有効にトラッキング検出ができる。
【００３８】
本発明者らは、３ビームグレーティング２４の断面を実質上矩形または台形形状である２レベルグレーティングとすると、図３に示すように、例えば、第１の波長λ1＝0.658μm、屈折率ｎ＝1.5に対して、その溝深さは、実質上λ1／（ｎ−１）＝1.3２μmのとき、第１の波長の光に関しては、ほとんどすべて透過する（0次回折光〜１００％）が、このとき、例えば、波長λ2＝0.8μmの第２の波長の光に対しては、０次回折光と1次回折光の比が最適なほぼ７：１程度になることを見い出した。さらに、本発明者らは、第１の波長の第２の波長に対する大きさの比Ｒは０．７５≦Ｒ≦０．９を実質上満たし（上記の記述では、Ｒ＝０．８２）、その溝深さは、実質上λ1／（ｎ−１）であれば、第１の波長の光利用効率をほとんど落とさずに、第２の波長に対してのみ、有効に３ビームトラッキング制御ができることを見い出した。
【００３９】
第１の波長の光６ａは、基準面１８に対して実質上４５°で配置された、例えば、厚さ１ｍｍ程度のガラス等である透明基板９の、無反射コート（図示なし）が設けられた表面を透過し、その裏面に形成された、例えば、波長分離多層膜である波長分離手段１２により実質上反射され、光軸を実質上９０°折り曲げて、ｚ軸方向の平行光１０ａとなり、対物レンズ４に入射し、収束光７ａとなって光ディスクであるＤＶＤ１１ａ上に集光される。
【００４０】
第２の波長の光６ｂも、透明基板９内を透過するが、さらに波長分離手段１２も実質上通過し、その上に形成された（図１(a)では下面）、例えば、反射形の直線状ブレーズ化グレーティング（例えば、周期が４０μm）である反射形の光偏向手段５に入射し、偏向、反射されて（偏向はｘ軸方向成分のみ）、光軸が実質上ｚ軸に平行になり、同じく対物レンズ４に入射し、ＣＤ１１ｂに集光される。第１の波長の光１０ａの光軸と第２の波長の光１０ｂの光軸が平行になった結果、対物レンズ４に入射する光軸が垂直になり、どちらの波長に対しても、コマ収差や非点収差が生じることなく良好に対物レンズ４で集光することが可能である。また、透明基板９と一体化された波長分離手段１２と光偏向手段５は、１つの集積部品となり、構造が安定で位置合わせが容易となり、しかも立ち上げミラーを兼ねることができる。
【００４１】
波長分離手段１２と光偏向手段５を組み合わせて設けたことにより、光偏向手段５であるグレーティングの周期は大きくでき、製造が容易である。
【００４２】
光ディスク１１によって反射されたレーザ光７は、逆方向に折り返し、対物レンズ４、透明基板９を通過し、第２の波長の光１０ｂのみ光偏向手段５によりｘ軸成分のみ偏向されて、コリメータレンズ３を通過して、フォーカス／トラック誤差信号検出素子８によって分割されて（１次あるいは２次回折光利用）、光検出器１３で検出される。
【００４３】
波長分離手段１２は、本実施の形態においては、例えば、ＳｉＯ2とＴｉＯ2の誘電体薄膜を透明基板９上に交互に堆積した構造の波長分離多層膜を用いたが、このような多層膜構成では波長分離手段を数μm以内の薄さにでき、透明基板と集積一体化可能で、構造が安定になるという効果があった。また、波長分離手段１２は非常に薄くできるため、対物レンズ４に入射する第１の波長の光１０aと第２の波長の光１０ｂの最大強度位置は、ほぼ中央部に設定することができる（なお、図１(a)では、波長分離手段１２を誇張して厚く描いているため、ずれているようになっている）。
【００４４】
また、光偏向手段５は、回折光学素子である、反射形の直線状グレーティングを用いた。回折光学素子の光偏向手段を用いることにより、光学ヘッドを薄型化、軽量化、低価格化を図ることができる。
【００４５】
本実施の形態においては、基準面１８に対して、グレーティング５をその溝方向に傾けて配置した。このように配置することによって、実効的に垂直入射した場合と同じ高い１次回折効率が得られるという効果がある（例えば、後述する図６のグラフでθ2＝0の相当する高い１次回折効率、例えば、９５％が得られる）。
【００４６】
図２に示すように、グレーティング５または５’は、表面レリーフ型で、表面に反射層１６が形成され、それぞれ、断面形状が鋸歯形状（図２(a)）、マルチレベル形状（図２（ｂ）は４レベル形状）であり、基準面１８の法線（ｚ軸）からの、溝方向に傾けた傾斜角をθ1とし、その屈折率をｎとしたとき、第２の波長λ2に対して、上記グレーティングの溝深さＬが、Ｌ= λ2／（２ｎcosθ1）（鋸歯形状の場合）、Ｌ= （ｐ−１）λ2／（２ｐｎcosθ1）（マルチレベル形状で、ｐはレベル数）の関係を実質上満たすようにした。このような傾斜角に依存した溝深さにすることにより、１次回折効率を最大（例えば、９５％から９８％）にすることができた。反射層１６としては、ＡｇやＡｕ、Ａｌ等の金属層、または誘電体の多層膜を用いることが可能である。
【００４７】
また、グレーティング５または５’の溝の底面から波長分離手段までの距離ｓは、第１の波長λ1よりも大きくした。第１の波長の光６ａが波長分離手段１２で反射する際、ごくわずかにそこからしみ出す現象がおこるが、このような構成により、グレーティング５または５’の溝部へのしみ出しを無くし、第１の波長の光６ａは全く回折しなくなり、光利用効率を良くすることができる。また、波長分離手段１２と光偏向手段５の間に、例えば、第１の波長よりも厚いＳｉＯ2層等のバッファ層を設けても同じ効果が得られる。
【００４８】
グレーティング５の周期Λは、例えば、４０μmであり、このときの波長λ2に対する１次回折角は、λ2=0.8μmの場合、θd＝１．１５°となり、ちょうど第２の波長の光の光軸ずれの角度を補正することができる。なお、回折角θdは、第２の波長の光の光軸ずれの角度（コリメータレンズ３の焦点距離ｆと光源の中心距離ｇにより、ｔａｎ-1（ｇ／ｆ）で表される）と同じにすることにより、両波長に対する光軸を平行にすることが可能であり、回折角は、θd=sｉｎー1（λ2/Λ）で表されるので、この式を実質上満足するように、グレーティング５の周期Λを設定すれば良い。本実施の形態の光偏向手段５であるグレーティングは、波長分離手段９の形成された透明基板１２上に、例えば、公知の２Ｐ法により、紫外線硬化樹脂を用いて金型から転写して作製した。
【００４９】
また、本実施の形態では、波長が大きい方の光を第２の波長の光とし、光偏向手段５により偏向させたが、一般に、波長が大きい光を出射する半導体レーザ光源のほうが出射効率が良いため、光のパワに余裕があり、光偏向手段５で多少損失があっても問題なく使用できるためである。なお、波長が小さい方の光を第２の波長の光としてももちろん動作は可能である。
【００５０】
（第２の実施の形態）
本発明の第２の実施の形態の光学ヘッドについて、図４を用いて、上記第１の実施の形態と異なる点を中心に説明する。
【００５１】
図４（ａ）は本発明第２の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図、図４（ｂ）は本発明の第２の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す裏面図である。
【００５２】
図４に示すように、本実施の形態の光学ヘッドにおいては、透明基板９の表面に波長分離手段１２を設け、その対向面に光偏向手段５を設け、第１及び第２の波長の光６は、波長分離手段１２側から入射する構成である。本実施の形態でも透明基板９と一体化された波長分離手段１２と光偏向手段５は、１つの集積部品となり、構造が安定で位置合わせが容易となり、しかも立ち上げミラーを兼ねることができる。
【００５３】
第１の波長の光６ａは、基準面１８に対して実質上４５°で配置された、例えば、厚さ１ｍｍ程度のガラス等である透明基板９の表面に設けた例えば、波長分離多層膜である波長分離手段１２で実質上反射され、光軸を実質上９０°折り曲げて、ｚ軸方向の平行光１０ａとなり、対物レンズ４に入射し、収束光７ａとなって光ディスクであるＤＶＤ１１ａ上に集光される。
【００５４】
第２の波長の光６ｂは、波長分離手段１２も実質上透過し、透明基板９内を通って、その対向面に形成された、例えば、反射形の直線状ブレーズ化グレーティング（例えば、周期が４０μm）である反射形の光偏向手段５に入射し、ｘ軸方向成分のみ偏向、反射されて、光軸が実質上ｚ軸に平行になり、同じく対物レンズ４に入射し、ＣＤ１１ｂに集光される。
【００５５】
本実施の形態の光学ヘッドでは、第１の波長の光６ａが、透明基板９を通ることなく、波長分離手段１２表面で反射されるので、光利用効率が多少向上する。しかしながら、第１の実施形態の光学ヘッドに比べて、透明基板９の厚さがあるため、対物レンズ４に入射する第１の波長の光１０ａと第２の波長の光１０ｂの最大強度の中心位置のずれ量が大きくなるという課題が発生する。
【００５６】
（第３の実施の形態）
本発明の第３の実施の形態の光学ヘッドについて、図５と図６を用いて、上記第１の実施の形態と異なる点を中心に説明する。
【００５７】
図５は本発明の第３の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図、図６は本発明の第３の実施の形態の光学ヘッドにおけるグレーティング（光偏向手段）への入射角θ2と１次回折効率の関係図である。
【００５８】
図５に示すように、本実施の形態においては、第１の光源１ａと第２の光源１ｂは、実質上基準面１８に対して高さ方向（ｚ軸方向）に、例えば、４００μm離れて配置している。これにより、第１と第２の光源の配置が容易になる。
【００５９】
また、例えば、周期がΛ＝４０μmの反射形の直線状グレーティングである光偏向手段５ａは、基準面１８に対して、グレーティングの溝（ｘ方向）に垂直な方向に、例えば、４５°傾けて配置している。これにより、対物レンズ４に入射する第１の波長の光１０ａと第２の波長の光１０ｂの光軸の、側面図における奥行き方向（ｘ軸方向）のずれを実質上無くすことができる。
【００６０】
図６に示すように、本実施の形態の光学ヘッドの光偏向手段５ａである反射形グレーティング（周期Λ＝４０μm、溝深さＬ＝０．２６７μm、Ａｕの反射膜）の１次回折効率は、入射角θ2に依存しており、グレーティング５ａに対する第２の波長の光６ｂの入射角θ2は、-５０°≦θ2≦５０°の関係を実質上満たす範囲であれば、ほぼ９０％以上の高い１次回折効率を実現できることが分かった。本実施の形態では、入射角θ2は例えば、４５°であるから、９２％の回折効率が得られた。
【００６１】
（第４の実施の形態）
本発明の第４の実施の形態の光学ヘッドについて、図７を用いて、上記第１の実施の形態と異なる点を中心に説明する。
【００６２】
図７（ａ）は本発明の第４の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図、図７（ｂ）は本発明の第４の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す裏面図である。
【００６３】
本実施の形態の光学ヘッドは、例えば、９．５ｍｍ厚の超薄型構成の光学ヘッドを実現する。
【００６４】
図７に示すように、光源・光検出器ユニット１７の窓側に、３ビームグレーティング、フォーカス／トラック誤差信号検出素子８、色収差補正グレーティング２０をこの順に配置している。立ち上げミラーの代わりに、３つの光学面を有するプリズム１９を用いている。
【００６５】
プリズム１９は、情報記録媒体１１側を第１面（斜面）２１、光源１側を第２面（側面）２２、基準面１８側を第３面（底面）２３としたとき、プリズムの第３面２３に波長分離手段１２を設け、その下面に光偏向手段５を設けている。
【００６６】
光源１からの出射光２は、３ビームグレーティング２４、フォーカス／トラック誤差信号検出素子８を透過し、色収差補正グレーティング２０で、例えば、1°程度、ｚ軸方向に回折され、コリメータレンズ３に入射し、略平行光６になる。
【００６７】
第１及び第２の波長の光６ａ、６ｂは、プリズム１９の第２面２２を透過して、第１面２１で全反射して、第３面１４の順に入射する。第１の波長の光６ａは、波長分離手段１２で反射され、第１面２１を透過して対物レンズ４に入射する。第２の波長の光６ｂは、波長分離手段１２を透過し、光偏向手段５で、偏向、反射され、光軸が平行になり、第１面２１を透過して対物レンズ４に入射する。
【００６８】
このようにジグザグ状にプリズム１９内を伝搬させ、光軸を９０°折り曲げる構成により、大幅に光学ヘッドの高さ（z軸方向サイズ）を小さくし、超薄型構成が可能になる。
【００６９】
プリズム１９の仕様は、例えば、θr＝５．０°、θp＝２９．３°、θq＝１１４．３°で、底面２３の長さを４．４mmとし、硝材としてＢＫ７を用いた。この場合、プリズム１９に入射するビーム径と出射するビーム径は等しいとしたビーム整形無しの構成であり、プリズム１９の硝材の屈折率をｎとし、底面の設置角度をθrとすると、そのプリズムの底角の一方の角度のθpが、ｓin（θp−θr）＝ｎ・sin（４θp−２θr−９０°−θ’）と、ｎ・sinθ’=sin（θp−θr）とを実質上満足し、底角の他方の角度θqが、θq=θ＋９０°−２θrを実質上満たす関係にあるものとする。プリズム１９の設置角度は、例えば、θr＝５°としたが、実質上２°から８°の範囲内であれば、対物レンズ４の左端とプリズム１９との間隔に十分余裕が生まれ、好ましいことが分かった。
【００７０】
本実施の形態では、光源１に半導体レーザを用いているため、高周波モジュールまたは自励発振により、典型的に１nm程度の波長帯域の広がりや環境温度の変化によって出射光の中心波長が変化するという現象が生じる。
【００７１】
本実施の形態では、プリズム１９の側面２２と斜面２１に光軸が斜めに入射するため、波長帯域に広がりがあると、屈折角が異なるという色分散が生じる。光路中に、回折光の回折角の変化が、プリズム１９での屈折角の変化と互いに相殺する方向に生じるように、色収差補正グレーティング２０を配置すると、色分散がうち消されて、光ディスク１１上に良好に集光させることが可能である。
【００７２】
本発明者らは、プリズム１９を構成するガラスの硝材が低分散であるほうが良く、そのような場合、幅広い波長領域で、色収差をほぼ問題ならない程度まで相殺でき、同時に、色収差を補正するグレーティング２０の周期も大きくできるため、素子の製造が容易で高い回折効率が得られる効果があることを発見した。また波長変動は、第１の波長で±１０nmの範囲内であることが、現実的にはほとんどであり、その場合硝材のアッベ数は６４以上であれば、光ディスク１１上に色収差の影響の少ない光スポットを形成することができ、効果的であることも分かった。従って、硝材としては、ＢＫ７、ＦＣ５、ＦＫ５、ＦＣＤ１、ＦＣＤ１０、ＦＣＤ１００等が好ましい。
【００７３】
本実施の形態の光学ヘッドは、色収差補正グレーティング２０として、均一周期のグレーティングを、光源１から、コリメータレンズ３までの収束光光路または発散光光路中に配置した。本発明者らは、このような収束光光路または発散光光路中に、色収差補正用のグレーティング２０を配置した場合、入射角により補正効果が異なる（光が傾いて入射した場合ほど、色収差補正効果が大きくなる）ことが分かったので、厳密には、出射光２の収束角にあわせて、ｚ軸方向のグレーティング２０の周期分布を変化させる必要があったが、開口数が０．３９以下の収束光光路中、または発散光光路中に配置されていた場合、対物レンズ４での光ディスク１１上のスポットは色収差で問題にならないことが分かり、均一周期のグレーティング２０を用いることが可能で、位置合わせや製造が楽であるという効果があった。
【００７４】
以上、本発明の第１〜第４の実施の形態の光学ヘッドについて述べてきたが、これらの実施の形態の光学ヘッド以外に、それぞれの光学ヘッドの構成を組み合わせた光学ヘッドも構成可能であり、同様の効果を有するのは言うまでもない。
【００７５】
なお、実施の形態は光ディスクで説明したが、同様の情報記録再生装置で厚みや記録密度など複数の仕様の異なる媒体を再生できるように設計されたカード状やドラム状、テープ状の製品に応用することは本発明の範囲である。また、実施の形態の説明に用いた対物レンズとコリメータレンズは便宜上名付けたものであり、一般にいうレンズと同じである。
【００７６】
【発明の効果】
以上説明したように、本発明によれば、複数の種類の情報記録媒体に対応でき、互いに近傍に配置した２波長の光源を具備する小型・薄型・軽量の光学ヘッドを実現することができる。
【図面の簡単な説明】
【図１】本発明の第１の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図と裏面図
【図２】本発明の第１の実施の形態の光学ヘッドにおける波長分離手段、光偏向手段の説明図
【図３】本発明の第１の実施の形態の光学ヘッドにおける第１と第２の波長に対する３ビームグレーティングの回折効率と溝深さの関係図
【図４】本発明の第２の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図と裏面図
【図５】本発明の第３の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図
【図６】本発明の第３の実施の形態の光学ヘッドにおけるグレーティング（光偏向手段）への入射角θ2と１次回折効率の関係図
【図７】本発明の第４の実施の形態における光学ヘッドの基本構成と光の伝搬の様子を示す側面図と裏面図
【図８】従来の光学ヘッドの基本構成と光の伝搬の様子を示す側面図と上面図
【符号の説明】
１光源
２出射光
３コリメータレンズ
４対物レンズ
５グレーティング（光偏向手段）
６平行光
７収束光
８フォーカス／トラック誤差信号検出素子
９透明基板
１０平行光
１１情報記録媒体
１２波長分離手段
１３光検出器
１４ビームスプリッタ
１５立ち上げミラー
１６反射膜
１７光源・光検出器ユニット
１８基準面
１９プリズム
２０色収差補正グレーティング
２１プリズムの斜面（第１面）
２２プリズムの測面（第２面）
２３プリズムの底面（第３面）
２４３ビームグレーティング[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical head of an optical recording / reproducing apparatus, and more particularly, to a small, thin, and lightweight optical head that is compatible with a plurality of types of information recording media and includes two-wavelength light sources arranged in the vicinity of each other.
[0002]
[Prior art]
There is an optical head as an important component for reading a signal of an information recording medium such as an optical disk such as a compact disk (CD) or DVD or an optical card memory. The optical head needs to have not only a signal detection function but also a control mechanism such as a focus servo and a tracking servo in order to extract a signal from the optical recording medium.
[0003]
In order to cope with a plurality of information recording media such as DVD, CD or CD-R, there has been an optical head equipped with two light sources. A conventional optical head having a light source of two wavelengths is shown in FIG.
[0004]
A first light source 1′a that emits a first wavelength λ1 corresponding to DVD and a second light source 1′b that emits a second wavelength λ2 corresponding to CD or CD-R are respectively separate light sources. Built in the photodetector units 17'a and 17'b, the laser beams 2'a and 2'b emitted from them are combined by the beam splitter 14 and made parallel by the collimator lens 3 '. The optical axis is bent by 90 ° by the rising mirror 15, and the light is condensed on the optical disc 11 (11a for DVD and 11b for CD) by the objective lens 4 ′.
[0005]
The signal light reflected by the optical disk 11 is folded in the opposite direction, demultiplexed by the beam splitter 14, and the focus / track error signal detector 8 provided in the windows of the light source / photodetector units 17′a and 17′b. By “a, 8′b”, the light is condensed on the photodetector 13 ′, and the reproduction signal is read out. In addition, control such as focus / track servo is performed so that signals can be read out stably.
[0006]
[Problems to be solved by the invention]
However, in order to support a plurality of information recording media such as DVD, CD, or CD-R, a conventional configuration in which a light source is built in a separate package (light source / photodetector unit) and combined by a beam splitter or the like. However, there is a limit to the reduction in size, thickness, and weight of the optical head, and the alignment is complicated, and further simplification and assembly cannot be simplified.
[0007]
The present invention has been made to solve the above-described problems in the prior art, and in particular, can be applied to a plurality of types of information recording media, and is small, thin, and lightweight equipped with two-wavelength light sources arranged in the vicinity of each other. It is an object of the present invention to provide an optical head.
[0008]
[Means for Solving the Problems]
  In order to achieve the object, the invention according to claim 1 of the present invention includes a first light source that emits light having a first wavelength and a second wavelength that is disposed in the vicinity of the first light source. A second light source that emits the first light, a wavelength separation means that separates the light of the first and second wavelengths, and the separated light of the second wavelength that has been separated. Optical deflection means for deflecting light so that the optical axis is substantially parallelAnd an objective lens for condensing the light of the first wavelength and the light of the second wavelength emitted from the light deflecting means on the information recording medium, respectively, and the wavelength separating means on the transparent substrate. And the light deflecting means is provided thereon, the light of the first and second wavelengths is incident from the opposite surface side of the transparent substrate, and the wavelength separating means substantially emits the light of the first wavelength. The light deflecting means is a surface relief type diffractive optical element, and the distance from the bottom of the groove to the wavelength separating means is the first reflecting light. An optical head characterized by being larger than the wavelength. Accordingly, for example, an optical head that is compatible with a plurality of types of information recording media can be obtained using a light source having two wavelengths arranged in the vicinity of each other and being small and light. For example, a compact configuration can be realized. For example, the alignment of the optical components is simplified, the structure is stabilized, and the central positions of the maximum intensities of the first and second wavelengths that are substantially parallel are brought close to each other, so that a good condensing spot on the optical disc Can be formed. For example, it is possible to improve the light utilization efficiency of the light of the first wavelength by eliminating the influence of the light of the first wavelength that oozes out from the wavelength separation means to the light deflecting means.
[0009]
  The invention according to claim 2 of the present invention is2. The optical head according to claim 1, wherein the wavelength separation means is a wavelength separation multilayer film. Thereby, for example, it is thin and can be integrated into another optical component, and the structure becomes stable.
[0010]
  The invention according to claim 3 of the present invention isThe lower surface of the optical head perpendicular to the optical axis of the first wavelength light incident on the objective lens is used as a reference surface, and the transparent substrate is disposed at substantially 45 ° with respect to the reference surface. The optical head according to claim 1. Thereby, for example, the optical component integrated with the transparent substrate can also serve as a rising mirror.
[0011]
  According to a fourth aspect of the present invention, there is provided the optical head according to the first aspect, wherein the diffractive optical element is a reflective linear grating. Thereby, for example, it is possible to obtain an optical head that is easy to manufacture and can be easily aligned.
[0012]
  According to a fifth aspect of the present invention, the lower surface of the optical head perpendicular to the optical axis of the light having the first wavelength incident on the objective lens is used as a reference surface, and the first light source and the The optical head according to claim 1, wherein the second light source is disposed at substantially the same height with respect to the reference surface. Thereby, for example, the arrangement of the first and second light sources is facilitated.
[0013]
  The invention according to claim 6 of the present invention is characterized in that the light deflecting means is a reflective linear grating, and is inclined with respect to the groove direction of the grating with respect to the reference plane. The optical head according to claim 5. Thereby, for example, a configuration capable of increasing the first-order diffraction efficiency of the grating is possible.
[0014]
  In the invention according to claim 7 of the present invention, the grating has a sawtooth cross-sectional shape, and an inclination angle inclined in the groove direction from the normal line of the reference plane is θ. 1 When the refractive index is n, the second wavelength λ 2 In contrast, the groove depth L of the grating is L = λ 2 / (2n cos θ 1 The optical head according to claim 6, wherein the relationship is substantially satisfied. Thereby, for example, the first-order diffraction efficiency of the grating can be maximized.
[0015]
  In the invention according to claim 8 of the present invention, the grating has a multi-level shape with a cross section of the number of levels p, and an inclination angle inclined in the groove direction from the normal line of the reference plane is θ. 1 When the refractive index is n, the second wavelength λ 2 In contrast, the groove depth L of the grating is L = (P-1) λ 2 / (2pn cos θ 1 The optical head according to claim 6, wherein the relationship is substantially satisfied. Thereby, for example, the grating can be easily manufactured, and the first-order diffraction efficiency can be maximized.
[0016]
  According to a ninth aspect of the present invention, the lower surface of the optical head perpendicular to the optical axis of the light having the first wavelength incident on the objective lens is used as a reference surface, and the first light source and the The optical head according to claim 1, wherein the second light source is disposed substantially in a height direction with respect to the reference surface. Thereby, for example, the arrangement of the first and second light sources is facilitated.
[0017]
  According to a tenth aspect of the present invention, the light deflecting means is a reflective linear grating, and is inclined with respect to the reference plane in a direction perpendicular to the groove of the grating. The optical head according to claim 9. Thereby, for example, the shift in the depth direction in the side view of the optical axes of the first wavelength light and the second wavelength light incident on the objective lens can be substantially eliminated.
[0018]
  The invention according to claim 11 of the present invention is the optical head according to claim 1, wherein the first wavelength is smaller than the second wavelength. As a result, for example, the light utilization efficiency of the first wavelength, which has a smaller wavelength, which is generally the poor emission efficiency of the light source, can be made larger than the light utilization efficiency of the second wavelength.
[0019]
  According to a twelfth aspect of the present invention, in the optical head according to the first aspect, a buffer layer is provided between the wavelength separation means and the light deflection means. Thereby, for example, it is possible to eliminate the influence of the light having the first wavelength that oozes out from the wavelength separating unit and to improve the light use efficiency of the light having the first wavelength.
[0020]
  According to a thirteenth aspect of the present invention, there is provided a first light source that emits light having a first wavelength, and light having a second wavelength that is disposed in the vicinity of the first light source. A second light source, wavelength separation means for separating the light of the first and second wavelengths, the separated light of the second wavelength, the separated light of the first wavelength and the optical axis An optical deflector that deflects the light so as to be substantially parallel; and an objective lens that condenses the light of the first wavelength and the light of the second wavelength emitted from the light deflector on the information recording medium, respectively. The lower surface of the optical head perpendicular to the optical axis of the first wavelength light incident on the objective lens is a reference surface, the information recording medium side is a first surface, and the light source side is a second surface. The wavelength separation means is provided on the third surface of the prism having three optical surfaces with the reference surface side as the third surface. The light deflecting means is provided on the lower surface, and the light beams having the first and second wavelengths are incident on the second surface and pass through the first surface, the third surface, and the first surface in this order, and the wavelength separating device. Is an optical head that substantially reflects the light having the first wavelength and substantially transmits the light having the second wavelength. Accordingly, for example, an optical head that is compatible with a plurality of types of information recording media can be obtained using a light source having two wavelengths arranged in the vicinity of each other and being small and light. For example, a compact configuration can be realized. For example, the optical head can be made thin by a configuration in which the optical path takes a zigzag propagation in the prism.
[0021]
  The invention according to claim 14 of the present invention is characterized in that a chromatic aberration correction grating for reducing chromatic dispersion of the prism is provided at least in the optical path of the light having the first wavelength. It is an optical head. Thus, for example, when semiconductor laser light is used as emitted light from the light source, the number of high frequency modules and self-excited oscillation nm Even if the center wavelength of the emitted light changes due to a broadening of the wavelength band or a change in the environmental temperature, it is possible to reduce the chromatic dispersion of the prism and obtain a good focused spot on the optical disk surface.
[0022]
  According to a fifteenth aspect of the present invention, there is provided a first light source that emits light having a first wavelength, and light having a second wavelength that is disposed in the vicinity of the first light source. A second light source, wavelength separation means for separating the light of the first and second wavelengths, the separated light of the second wavelength, the separated light of the first wavelength and the optical axis Light deflecting means for deflecting so as to be substantially parallel, the light deflecting means is a reflective linear grating, and the grating has a distance between the first light source and the second light source. The optical head is characterized in that the larger the size is, the shorter the cycle is. Accordingly, for example, an optical head that is compatible with a plurality of types of information recording media can be obtained using a light source having two wavelengths arranged in the vicinity of each other and being small and light. For example, it is possible to obtain an optical head that is simple to manufacture and can be easily aligned. For example, the optical axes of the two-wavelength light sources can be substantially parallel to an arbitrary distance between the first light source and the second light source.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
The optical head according to the first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 3 and coordinate axes as shown in the drawing.
[0032]
FIG. 1A is a side view showing the basic configuration of the optical head and the state of light propagation in the first embodiment of the present invention, and FIG. 1B is the optical head in the first embodiment of the present invention. FIG. 2A is an explanatory view of wavelength separation means and light deflection means in the optical head according to the embodiment, and FIG. 2B is an illustration of the basic configuration of FIG. Further, FIG. 3A is an explanatory diagram of wavelength separation means and light deflection means in another optical head, and FIG. 3A shows the diffraction efficiency and groove depth of the three-beam grating for the first wavelength in the optical head of the first embodiment of the present invention. FIG. 3B is a diagram showing the relationship between the diffraction efficiency of the three-beam grating and the groove depth with respect to the second wavelength in the optical head according to the first embodiment of the present invention.
[0033]
The optical head of the present embodiment is equipped with two-wavelength light sources arranged in the vicinity of each other, and can be used for a plurality of information recording media such as DVDs, CDs, and CD-Rs. Realize the head.
[0034]
As shown in FIG. 1, a two-wavelength light source 1 and a photodetector 13 are built in a light source / photodetector unit 17, and for example, a light 2a having a first wavelength λ1 = 0.658 μm is used as the light source. A semiconductor laser chip 1a that emits light and a semiconductor laser chip 1b that emits light 2b having a second wavelength λ2 = 0.8 μm, for example, are disposed in the vicinity of a distance g between their central positions, for example, about 400 μm away. Yes.
[0035]
The light sources 1 a and 1 b do not normally emit light at the same time, but selectively emit light according to the type of the optical disk 11. In the present embodiment, the two-wavelength light sources 1 are arranged so as to have substantially the same height with respect to the reference surface 18 (the lower surface of the optical head parallel to the xy plane). Such an arrangement facilitates the arrangement. By arranging the semiconductor laser chips to be the two-wavelength light source 1 in the vicinity of each other, optical components such as a beam splitter as in the conventional example can be omitted, so that the optical head can be simplified, small, thin, and lightweight. Positioning during assembly is facilitated.
[0036]
The laser light 2a or 2b selectively emitted from the light source 1 passes through a three-beam grating 24 provided on the window side of the light source / photodetector unit 17, and is integrated with it, for example, a focus / For example, the collimator lens 3 having a focal length of 20 mm transmits the track error signal detection element 8 (using 0th-order diffracted light). The parallel light 6a and 6b is about 2.2 mm. At this time, the optical axes of the first wavelength lights 2a and 6a connecting the light source 1a and the center of the collimator lens 3 are arranged so as to be parallel to the y-axis, and 2b connecting the light source 1b and the center of the collimator lens 3 to each other. The optical axis 6b is parallel to the reference plane 18 and is inclined, for example, 1.15 ° with respect to the y-axis direction (see FIG. 1B).
[0037]
The three-beam grating 24 is provided so as to be diffracted only into the light 2b of the second wavelength to become three beams (0th order and ± 1st order diffracted light) and to be able to detect the tracking. For 2a, it just passes like a transparent substrate. In particular, the tracking detection method for reading a CD-R optical disc with light of the second wavelength is preferably a three-beam method, and the tracking detection method for reading a DVD optical disc with light of the first wavelength is a phase difference. Since the method is preferable, such a configuration enables effective tracking detection for these optical discs.
[0038]
Assuming that the cross section of the three-beam grating 24 is a two-level grating having a substantially rectangular or trapezoidal shape, the inventors have, for example, a first wavelength λ1 = 0.658 μm and a refractive index n = 1.5, as shown in FIG. On the other hand, when the groove depth is substantially λ1 / (n−1) = 1.32 μm, almost all the light of the first wavelength is transmitted (0th order diffracted light to 100%). For example, it has been found that the optimum ratio of 0th-order diffracted light to 1st-order diffracted light is about 7: 1 with respect to light of the second wavelength of wavelength λ2 = 0.8 μm. Furthermore, the present inventors have found that the ratio R of the magnitude of the first wavelength to the second wavelength substantially satisfies 0.75 ≦ R ≦ 0.9 (in the above description, R = 0.82), If the groove depth is substantially λ1 / (n−1), three-beam tracking control can be effectively performed only for the second wavelength without substantially reducing the light utilization efficiency of the first wavelength. I found out.
[0039]
The light 6a of the first wavelength is provided with a non-reflective coating (not shown) of the transparent substrate 9 which is disposed at substantially 45 ° with respect to the reference surface 18, for example, glass having a thickness of about 1 mm. Is reflected by the wavelength separation means 12 formed on the back surface thereof, for example, a wavelength separation multilayer film, and the optical axis is bent by 90 ° to become parallel light 10a in the z-axis direction, The light enters the objective lens 4 and is converged on the DVD 11a, which is an optical disk, as convergent light 7a.
[0040]
The light 6b having the second wavelength is also transmitted through the transparent substrate 9, but the wavelength separating means 12 is also substantially passed therethrough and formed thereon (the lower surface in FIG. 1 (a)). The light is incident on the reflective light deflecting means 5 having a linear blazed grating (for example, the period is 40 μm), deflected and reflected (the deflection is only in the x-axis direction component), and the optical axis is substantially parallel to the z-axis. Similarly, the light enters the objective lens 4 and is focused on the CD 11b. As a result of the optical axis of the first wavelength light 10a and the optical axis of the second wavelength light 10b being parallel, the optical axis incident on the objective lens 4 becomes vertical, and the coma for both wavelengths is It is possible to condense with the objective lens 4 satisfactorily without causing aberration or astigmatism. Further, the wavelength separating means 12 and the light deflecting means 5 integrated with the transparent substrate 9 become one integrated component, the structure is stable and the alignment becomes easy, and it can also serve as a rising mirror.
[0041]
By providing the wavelength separating means 12 and the light deflecting means 5 in combination, the period of the grating that is the light deflecting means 5 can be increased, and manufacturing is easy.
[0042]
The laser light 7 reflected by the optical disk 11 is turned back in the opposite direction, passes through the objective lens 4 and the transparent substrate 9, and only the light 10b of the second wavelength is deflected by the light deflecting means 5, and the collimator lens is deflected. 3 is divided by the focus / track error signal detection element 8 (using the first-order or second-order diffracted light) and detected by the photodetector 13.
[0043]
In the present embodiment, the wavelength separation means 12 uses, for example, a wavelength separation multilayer film having a structure in which dielectric thin films of SiO2 and TiO2 are alternately deposited on the transparent substrate 9, but in such a multilayer film configuration, The wavelength separating means can be made thin within several μm, and can be integrated and integrated with the transparent substrate, which has the effect of stabilizing the structure. In addition, since the wavelength separation means 12 can be made very thin, the maximum intensity positions of the first wavelength light 10a and the second wavelength light 10b incident on the objective lens 4 can be set substantially at the center ( In FIG. 1 (a), the wavelength separating means 12 is exaggerated and drawn so as to be shifted.
[0044]
The light deflecting means 5 is a reflective linear grating, which is a diffractive optical element. By using the light deflecting means of the diffractive optical element, the optical head can be reduced in thickness, weight, and cost.
[0045]
In the present embodiment, the grating 5 is inclined with respect to the reference plane 18 in the groove direction. Such an arrangement has the effect of obtaining the same high first-order diffraction efficiency as that obtained when effectively perpendicularly incident (for example, a high first-order diffraction efficiency corresponding to θ2 = 0 in the graph of FIG. 6 described later). For example, 95% is obtained).
[0046]
As shown in FIG. 2, the grating 5 or 5 ′ is a surface relief type, and a reflection layer 16 is formed on the surface, and the cross-sectional shape is a sawtooth shape (FIG. 2A) and a multilevel shape (FIG. b) is a four-level shape), and the inclination angle tilted in the groove direction from the normal line (z-axis) of the reference surface 18 is θ1, and the refractive index is n, with respect to the second wavelength λ2. The groove depth L of the grating is such that L = λ2 / (2ncosθ1) (in the case of a sawtooth shape), L = (p−1) λ2 / (2pncosθ1) (in a multilevel shape, p is the number of levels) Was substantially satisfied. By setting the groove depth depending on such an inclination angle, the first-order diffraction efficiency could be maximized (for example, 95% to 98%). As the reflective layer 16, a metal layer such as Ag, Au, or Al, or a dielectric multilayer film can be used.
[0047]
Further, the distance s from the bottom surface of the groove of the grating 5 or 5 'to the wavelength separating means is made larger than the first wavelength λ1. When the light 6a having the first wavelength is reflected by the wavelength separation means 12, a phenomenon that the light oozes out slightly there occurs. However, with such a configuration, the oozing into the groove portion of the grating 5 or 5 ′ is eliminated, and the first The light 6a having the first wavelength is not diffracted at all, and the light utilization efficiency can be improved. Further, even if a buffer layer such as a SiO2 layer thicker than the first wavelength is provided between the wavelength separating unit 12 and the light deflecting unit 5, the same effect can be obtained.
[0048]
The period Λ of the grating 5 is, for example, 40 μm, and the first-order diffraction angle with respect to the wavelength λ 2 at this time is θd = 1.15 ° when λ 2 = 0.8 μm, and the optical axis deviation of the light of the second wavelength is just right. Can be corrected. The diffraction angle θd is the same as the angle of the optical axis deviation of the light of the second wavelength (expressed as tan −1 (g / f) by the focal length f of the collimator lens 3 and the center distance g of the light source). It is possible to make the optical axes parallel to both wavelengths, and the diffraction angle is expressed by θd = sin−1 (λ2 / Λ), so that this equation is substantially satisfied, The period Λ of the grating 5 may be set. The grating, which is the light deflecting means 5 of the present embodiment, was produced by transferring from a mold using an ultraviolet curable resin, for example, by a known 2P method on the transparent substrate 12 on which the wavelength separating means 9 was formed. .
[0049]
In the present embodiment, the light having the larger wavelength is used as the light having the second wavelength, and is deflected by the light deflecting unit 5. In general, however, a semiconductor laser light source that emits light having a larger wavelength has higher emission efficiency. This is because there is a margin in light power and the light deflecting means 5 can be used without any problem even if there is some loss. Of course, the operation is possible even if the light having the smaller wavelength is used as the light having the second wavelength.
[0050]
(Second Embodiment)
The optical head according to the second embodiment of the present invention will be described with reference to FIG. 4 focusing on differences from the first embodiment.
[0051]
FIG. 4A is a side view showing the basic configuration of the optical head and the state of light propagation in the second embodiment of the present invention, and FIG. 4B is the optical head in the second embodiment of the present invention. It is a back view which shows the mode of a basic composition and light propagation.
[0052]
As shown in FIG. 4, in the optical head of the present embodiment, the wavelength separating means 12 is provided on the surface of the transparent substrate 9, the light deflecting means 5 is provided on the opposite surface, and light of the first and second wavelengths is provided. Reference numeral 6 denotes a configuration in which the light enters from the wavelength separation means 12 side. Also in this embodiment, the wavelength separating means 12 and the light deflecting means 5 integrated with the transparent substrate 9 become one integrated component, the structure is stable and the alignment is easy, and it can also serve as a rising mirror.
[0053]
The light 6a of the first wavelength is, for example, a wavelength separation multilayer film provided on the surface of the transparent substrate 9 that is disposed at substantially 45 ° with respect to the reference surface 18, for example, glass having a thickness of about 1 mm. The light is substantially reflected by a certain wavelength separation means 12, and the optical axis is bent by substantially 90 ° to become parallel light 10a in the z-axis direction, which is incident on the objective lens 4 and becomes convergent light 7a, which is collected on the DVD 11a which is an optical disk. Lighted.
[0054]
The light 6b having the second wavelength is also substantially transmitted through the wavelength separation means 12, passes through the transparent substrate 9, and is formed on the opposite surface, for example, a reflective linear blazed grating (for example, having a period of 40 [mu] m) is reflected on the reflective light deflecting means 5 and only the x-axis direction component is deflected and reflected so that the optical axis is substantially parallel to the z-axis and is also incident on the objective lens 4 and condensed on the CD 11b. Is done.
[0055]
In the optical head of the present embodiment, the light 6a having the first wavelength is reflected on the surface of the wavelength separation means 12 without passing through the transparent substrate 9, so that the light utilization efficiency is somewhat improved. However, since the transparent substrate 9 is thicker than the optical head of the first embodiment, the center of the maximum intensity of the first wavelength light 10a and the second wavelength light 10b incident on the objective lens 4 is obtained. There arises a problem that the amount of positional deviation increases.
[0056]
(Third embodiment)
An optical head according to a third embodiment of the present invention will be described with reference to FIGS. 5 and 6 focusing on differences from the first embodiment.
[0057]
FIG. 5 is a side view showing the basic configuration of the optical head and the state of light propagation in the third embodiment of the present invention, and FIG. 6 is a grating (light deflecting means) in the optical head of the third embodiment of the present invention. Is a relationship diagram between the incident angle θ2 and the first-order diffraction efficiency.
[0058]
As shown in FIG. 5, in the present embodiment, the first light source 1a and the second light source 1b are substantially separated from the reference plane 18 in the height direction (z-axis direction), for example, by 400 μm. It is arranged. Thereby, arrangement | positioning of the 1st and 2nd light source becomes easy.
[0059]
Further, for example, the light deflecting means 5a, which is a reflective linear grating with a period of Λ = 40 μm, is inclined with respect to the reference plane 18 in a direction perpendicular to the grating groove (x direction), for example, 45 °. It is arranged. Thereby, the shift | offset | difference of the depth direction (x-axis direction) in a side view of the optical axis of the light 10a of the 1st wavelength and the light 10b of the 2nd wavelength which injects into the objective lens 4 can be eliminated substantially.
[0060]
As shown in FIG. 6, the first-order diffraction efficiency of the reflective grating (period Λ = 40 μm, groove depth L = 0.267 μm, Au reflective film) which is the light deflecting means 5a of the optical head of the present embodiment is The incident angle θ2 of the second wavelength light 6b with respect to the grating 5a is approximately 90% or more as long as the relationship of −50 ° ≦ θ2 ≦ 50 ° is substantially satisfied. It was found that high first-order diffraction efficiency can be realized. In the present embodiment, since the incident angle θ2 is 45 °, for example, a diffraction efficiency of 92% was obtained.
[0061]
(Fourth embodiment)
An optical head according to a fourth embodiment of the present invention will be described with reference to FIG. 7, focusing on differences from the first embodiment.
[0062]
FIG. 7A is a side view showing the basic configuration of the optical head and the state of light propagation in the fourth embodiment of the present invention, and FIG. 7B is the optical head in the fourth embodiment of the present invention. It is a back view which shows the mode of a basic structure, and the mode of light propagation.
[0063]
The optical head according to the present embodiment realizes, for example, an optical head having an ultra-thin configuration having a thickness of 9.5 mm.
[0064]
As shown in FIG. 7, the three-beam grating, the focus / track error signal detection element 8, and the chromatic aberration correction grating 20 are arranged in this order on the window side of the light source / photodetector unit 17. Instead of the rising mirror, a prism 19 having three optical surfaces is used.
[0065]
The prism 19 has a first surface (slope) 21 on the information recording medium 11 side, a second surface (side surface) 22 on the light source 1 side, and a third surface (bottom surface) 23 on the reference surface 18 side. The wavelength separation means 12 is provided on the surface 23, and the light deflection means 5 is provided on the lower surface thereof.
[0066]
The outgoing light 2 from the light source 1 passes through the three-beam grating 24 and the focus / track error signal detection element 8, and is diffracted in the z-axis direction by, for example, about 1 ° by the chromatic aberration correction grating 20 and enters the collimator lens 3. Thus, the light becomes substantially parallel light 6.
[0067]
The light beams 6 a and 6 b having the first and second wavelengths are transmitted through the second surface 22 of the prism 19, totally reflected by the first surface 21, and incident on the third surface 14 in this order. The light 6 a having the first wavelength is reflected by the wavelength separation unit 12, passes through the first surface 21, and enters the objective lens 4. The second wavelength light 6 b is transmitted through the wavelength separation unit 12, is deflected and reflected by the light deflecting unit 5, the optical axis is parallel, passes through the first surface 21, and enters the objective lens 4.
[0068]
In this way, the configuration in which the optical axis is bent by 90 ° while propagating through the prism 19 in a zigzag manner can significantly reduce the height (size in the z-axis direction) of the optical head and enable an ultra-thin configuration.
[0069]
The specification of the prism 19 is, for example, θr = 5.0 °, θp = 29.3 °, θq = 11.4 °, the length of the bottom surface 23 is 4.4 mm, and BK7 is used as the glass material. In this case, the beam diameter incident on the prism 19 is equal to the beam diameter emitted and the beam diameter is not formed. When the refractive index of the glass material of the prism 19 is n and the installation angle of the bottom surface is θr, Θp of one of the base angles substantially satisfies sin (θp−θr) = n · sin (4θp−2θr−90 ° −θ ′) and n · sinθ ′ = sin (θp−θr). Suppose that the other angle θq of the base angle substantially satisfies θq = θ + 90 ° −2θr. The installation angle of the prism 19 is, for example, θr = 5 °. However, if the angle is substantially within the range of 2 ° to 8 °, a sufficient margin is created in the interval between the left end of the objective lens 4 and the prism 19, which is preferable. I understood.
[0070]
In the present embodiment, since a semiconductor laser is used as the light source 1, the center wavelength of the emitted light changes due to a broadening of the wavelength band of about 1 nm or a change in environmental temperature due to a high-frequency module or self-excited oscillation. A phenomenon occurs.
[0071]
In the present embodiment, since the optical axis is obliquely incident on the side surface 22 and the inclined surface 21 of the prism 19, chromatic dispersion occurs in which the refraction angle is different when the wavelength band is widened. If the chromatic aberration correction grating 20 is disposed in the optical path so that the change in the diffraction angle of the diffracted light occurs in a direction that cancels out the change in the refraction angle at the prism 19, chromatic dispersion is eliminated and the optical disk 11 is It is possible to condense well.
[0072]
The inventors of the present invention should preferably have a low dispersion of the glass material of the glass constituting the prism 19, and in such a case, the chromatic aberration can be canceled out to an almost non-problem in a wide wavelength region, and at the same time, the grating 20 for correcting the chromatic aberration. It has been found that the device can be manufactured easily and has an effect of obtaining high diffraction efficiency. Further, it is practically almost that the wavelength variation is within a range of ± 10 nm at the first wavelength. In this case, if the Abbe number of the glass material is 64 or more, there is little influence of chromatic aberration on the optical disk 11. It was found that a light spot can be formed and is effective. Accordingly, BK7, FC5, FK5, FCD1, FCD10, FCD100, etc. are preferable as the glass material.
[0073]
In the optical head of the present embodiment, a grating having a uniform period is arranged as a chromatic aberration correction grating 20 in a convergent light path or a divergent light path from the light source 1 to the collimator lens 3. When the grating 20 for correcting chromatic aberration is disposed in such a convergent light path or divergent light path, the present inventors have different correction effects depending on the incident angle (the chromatic aberration correction effect is greater as the light is incident at an angle). Strictly speaking, it is necessary to change the periodic distribution of the grating 20 in the z-axis direction in accordance with the convergence angle of the outgoing light 2, but the numerical aperture is 0.39 or less. It can be seen that the spot on the optical disk 11 at the objective lens 4 does not cause a problem due to chromatic aberration when it is arranged in the convergent light path or the divergent light path, and it is possible to use a grating 20 having a uniform period, There was an effect that it was easy to combine and manufacture.
[0074]
As described above, the optical heads according to the first to fourth embodiments of the present invention have been described. However, in addition to the optical heads according to these embodiments, an optical head in which the configurations of the respective optical heads are combined can be configured. Needless to say, it has the same effect.
[0075]
Although the embodiment has been described with reference to an optical disc, it is applied to a card-shaped, drum-shaped, or tape-shaped product designed to be able to reproduce a plurality of media having different specifications such as thickness and recording density with a similar information recording / reproducing apparatus. It is within the scope of the present invention. Further, the objective lens and the collimator lens used in the description of the embodiments are named for convenience, and are the same as the lenses generally called.
[0076]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a small, thin, and lightweight optical head that is compatible with a plurality of types of information recording media and includes two-wavelength light sources arranged in the vicinity of each other.
[Brief description of the drawings]
FIGS. 1A and 1B are a side view and a rear view showing a basic configuration of an optical head and a state of light propagation in a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of wavelength separation means and light deflection means in the optical head according to the first embodiment of the invention.
FIG. 3 is a diagram showing the relationship between the diffraction efficiency and groove depth of a three-beam grating for the first and second wavelengths in the optical head according to the first embodiment of the present invention.
FIGS. 4A and 4B are a side view and a rear view showing a basic configuration of an optical head and a state of light propagation in a second embodiment of the present invention. FIGS.
FIG. 5 is a side view showing a basic configuration of an optical head and a state of light propagation in a third embodiment of the present invention.
FIG. 6 is a graph showing the relationship between the incident angle θ2 to the grating (light deflecting means) and the first-order diffraction efficiency in the optical head according to the third embodiment of the present invention.
FIGS. 7A and 7B are a side view and a back view showing a basic configuration of an optical head and a state of light propagation in a fourth embodiment of the present invention. FIGS.
FIGS. 8A and 8B are a side view and a top view showing a basic configuration of a conventional optical head and a state of light propagation. FIGS.
[Explanation of symbols]
1 Light source
2 outgoing light
3 Collimator lens
4 Objective lens
5 Grating (light deflection means)
6 Parallel light
7 convergent light
8 Focus / track error signal detector
9 Transparent substrate
10 Parallel light
11 Information recording media
12 Wavelength separation means
13 Photodetector
14 Beam splitter
15 Launch mirror
16 Reflective film
17 Light source / detector unit
18 Reference plane
19 Prism
20 Chromatic aberration correction grating
21 Slope of the prism (first surface)
22 Surface measurement of prism (second surface)
23 Bottom surface of prism (third surface)
24 3-beam grating

Claims

A first light source that emits light of a first wavelength;
A second light source arranged near the first light source and emitting light of a second wavelength;
Wavelength separation means for separating the light of the first and second wavelengths;
Light deflecting means for deflecting the separated light of the second wavelength so that the separated light of the first wavelength and the optical axis are substantially parallel;
An objective lens for condensing the light of the first wavelength and the light of the second wavelength emitted from the light deflecting unit on the information recording medium, respectively.
The wavelength separation means is provided on a transparent substrate, the light deflection means is provided thereon, and the light of the first and second wavelengths is incident from the opposite surface side of the transparent substrate,
The wavelength separation means substantially reflects the light of the first wavelength, substantially transmits the light of the second wavelength;
The optical head is characterized in that the light deflecting means is a surface relief type diffractive optical element, and the distance from the bottom of the groove to the wavelength separating means is larger than the first wavelength .

The optical head according to claim 1 , wherein the wavelength separation means is a wavelength separation multilayer film.

Wherein the lower surface of the optical head becomes perpendicular to the optical axis of the first wavelength light incident on the objective lens as a reference surface, the transparent substrate is to be disposed with respect to the reference plane, substantially 45 ° The optical head according to claim 1 .

2. The optical head according to claim 1 , wherein the diffractive optical element is a reflective linear grating.

The lower surface of the optical head is perpendicular to the optical axis of the light of the first wavelength incident on the objective lens as a reference plane, the first light source and the second light source, with respect to the reference plane, substantially The optical head according to claim 1, wherein the optical head is disposed at the same height.

It is the light deflecting means a linear grating of the reflection type optical head according to claim 5, characterized in that arranged inclined in the groove direction of the grating with respect to the reference plane.

The grating cross-sectional shape is a saw-tooth shape, from the normal line of the reference plane, when the tilt angle tilted in the groove direction and .theta.1, and the refractive index n, with respect to the second wavelength .lambda.2, 7. The optical head according to claim 6 , wherein the groove depth L of the grating substantially satisfies the relationship of L = λ2 / (2n cos θ1).

Said grating is a multi-level form of the number of levels p is the cross-sectional shape, from a normal line of the reference plane, the tilt angle tilted in the groove direction is .theta.1, when the refractive index n, the second wavelength against .lambda.2, groove depth L of the grating, L = (p-1) λ2 / optical f head according to claim 6, characterized in that satisfies substantially the relationship (2pncosθ1).

The lower surface of the optical head is perpendicular to the optical axis of the light of the first wavelength incident on the objective lens as a reference plane, the first light source and the second light source, with respect to substantially the reference plane The optical head according to claim 1, wherein the optical head is arranged in a height direction.

Is the light deflecting means a linear grating of the reflection type optical head according to claim 9, with respect to the reference plane, characterized in that it arranged to be inclined in a direction perpendicular to the grooves of the grating.

The first wavelength, the optical head according to claim 1, wherein less than the second wavelength.

It said wavelength separating means and the optical head according to claim 1, characterized by providing a buffer layer between the light deflecting means.

A first light source that emits light of a first wavelength;
A second light source arranged near the first light source and emitting light of a second wavelength;
Wavelength separation means for separating the light of the first and second wavelengths;
Light deflecting means for deflecting the separated light of the second wavelength so that the separated light of the first wavelength and the optical axis are substantially parallel;
An objective lens for condensing the light of the first wavelength and the light of the second wavelength emitted from the light deflecting unit on the information recording medium, respectively.
Above the reference plane lower surface of the optical head becomes perpendicular to the optical axis of the first wavelength light incident on the objective lens, the information recording medium side of the first surface, the light source-side second surface, said reference surface said wavelength separating means to said third surface of the prism having three optical surfaces and a side third surface is provided, the light deflecting means, on its top surface, the light of the first and second wavelengths, the Incident from the second surface, passing through the first surface, the third surface, the first surface in this order ,
It said wavelength separating means is not substantially reflect light of said first wavelength, an optical head according to claim Rukoto not substantially transmit light of said second wavelength.

At least above a first optical path of the light wavelength, the optical head according to claim 13, characterized by providing a chromatic aberration correction grating to reduce color dispersion prism.

A first light source that emits light of a first wavelength;
A second light source arranged near the first light source and emitting light of a second wavelength;
Wavelength separation means for separating the light of the first and second wavelengths;
Optical deflection means for deflecting the separated light of the second wavelength so that the separated light of the first wavelength and the optical axis are substantially parallel;
The light deflecting means is a reflective linear grating,
The optical head is characterized in that the period of the grating is reduced as the distance between the first light source and the second light source is increased.