JP3881956B2 - Optical integrated unit and optical pickup device - Google Patents

Description

また、ピット情報が記録された光ディスクの再生時には、ＳｈとＳｉの位相差の変化を検出して、位相差（ＤＰＤ）法によるトラッキング誤差信号ＴＥＳ３も検出可能となっている。
【００１６】
そして、記録された情報信号（ＲＦ）は、次式（２３）により検出される。
ＲＦ＝Ｓｈ＋Ｓｇ＋Ｓｉ … （２３）
【００１７】
【特許文献１】
特開２００１−２７３６６６号公報
【００１８】
【非特許文献１】
大里潔著「新しいトラッキングサーボ方式」光メモリシンポジウム’８６、１９８６年１２月１８日、Ｐ．１２７〜Ｐ．１３２
【００１９】
【発明が解決しようとする課題】
特許文献１に記載の光ピックアップ装置では、半導体レーザ１０５から出射された光は、光ディスク側に進行するにつれてビーム径が太くなる（図７（ｂ）参照）。このため、図７（ｂ）において、３ビーム回折格子１０６よりも図の上方においては、メインビームとサブビームＡ、Ｂがほぼ重なり合う状態で存在しており、ビームの外形が光１２０であると考えても大差はない。
【００２０】
しかしながら、ビーム径の小さい領域では、メインビームとサブビームＡ、Ｂのずれが顕著になり上述と異なる状況を呈す。図９にホログラム素子１０９上のビーム形状を示す。図９を参照して、ホログラム素子１０９上で、メインビームＭ１２１ａ、サブビームＡ１２１ｂ、サブビームＢ１２１ｃがずれていることが分かる。
【００２１】
ホログラム素子１０９と受光素子１１０の間、例えば図７（ｂ）中のＸ’−Ｘ’線断面で、光路の光線の状態を調べると、ホログラム素子１０９を図９の状態で通過するメインビームＭおよびサブビームＡ，Ｂそれぞれが、ホログラム素子１０９の３領域１０９ａ〜１０９ｃで回折され、それら各回折光は図１０に示すごとくなる。なお、図中符号を記したビームは、サーボ信号生成、再生信号生成等に利用される光を示し、符号不記載ビームは光ピックアップ装置として利用されない光を示している。サブビームＡは領域１０９ｂ並びに１０９ｃで回折されて＋１次回折光１３０ｅ、１３０ｃとなり、サブビームＢは領域１０９ｂ並びに１０９ｃで回折されて＋１次回折光１３０ｆ、１３０ｄとなることが示されている。サブビームＡとサブビームＢの回折光同士で形状の違いが顕著であるため、光量が異なる。これは、３ビーム回折格子１０６でのサブビームＡとサブビームＢの回折効率は同じであるため、ホログラム通過後のビーム形状が異なると、光量が異なることによる。サブビームＡ，Ｂにおける光量の相違は、図９に示したように、サブビームＡ１２１ｂと、サブビームＢ１２１ｃがホログラム素子１０９の分割線１０９ｌによって中央で分割されないことに起因する。
【００２２】
サブビームＡ，Ｂ間の光量の違いが生じると、次のような問題が発生する。サブビームＡ、Ｂの光量に違いがある構成、すなわち、分割線１０９ｌで切られることによるサブビームＡ、Ｂの光量のアンバランスがあっても、そのアンバランスが常に一定であれば、定数ｋを適当な値に設定することにより、ピックアップ装置によらず安定したトラッキングサーボが可能となる。すなわち、メインビームとサブビームＡ、Ｂの強度比が、Ｍ：Ａ：Ｂ＝ａ：ｂ１：ｂ２なので、式（３）における定数ｋをｋ＝ａ／（ｂ１＋ｂ２）とすればよい。
【００２３】
しかしながら実際の光ピックアップ装置では、半導体レーザ１０５の取り付け誤差や、パッケージ、ステム、ハウジング等筐体部分に関する製造誤差、ビームスプリッタや反射ミラー等光ピックアップに用いられる光学部品の製造誤差及び取り付け誤差などの影響で、ホログラム素子１０９上のメインビームとサブビームＡ、Ｂの位置および間隔が光ピックアップ装置ごとに異なってしまう。したがって、定数ｋを定めることにより本来有するメインビームＭとサブビームＡ，Ｂの光強度の違いを補正しようとしても、光ピックアップ装置の有する個体差を考慮すると、光ピックアップ装置ごとにサブビームＡ，Ｂの強度比が異なるため、十分補正しきれないという問題があった。このため、特許文献１に記載の光ピックアップ装置では、安定なトラッキングサーボが困難なものが発生するという課題があった。
【００２４】
この発明は上述の問題点を解決するためになされたもので、この発明の目的の１つは、ＤＰＰ法による安定したトラッキング誤差信号を生成するための信号を容易に出力させることが可能な光集積化ユニットを提供することである。
【００２５】
この発明の他の目的は、ＤＰＰ法による安定したトラッキング誤差信号を生成することが可能な光ピックアップ装置を提供することである。
【００２６】
【課題を解決するための手段】
上述の目的を達成するためにこの発明のある局面によれば、光集積化ユニットは、光記録媒体に光を照射する光源と、光源の光をメインビーム、第１のサブビームおよび第２のサブビームに分岐する光分岐手段と、光記録媒体からの戻り光を検出する光検出器と、戻り光を少なくとも光記録媒体のラジアル方向に分割する第１の光分割手段と、戻り光を少なくとも光記録媒体のタンジェンシャル方向に分割する第２の光分割手段を備え、第１の光分割手段と第２の光分割手段とは、所定の距離を隔てて配置されることを特徴とする。
【００２７】
好ましくは、第１の光分割手段は、戻り光を透過光と、透過光から僅かにそれる第１および第２の分割光とに分割することを特徴とする。
【００２８】
好ましくは、第１の光分割手段は、第１および第２のサブビームそれぞれの第１および第２の分割光の光量が略等しくなる位置に配置され、光検出器は、トラッキング誤差信号を生成するために第１および第２の分割光を検出することを特徴とする。
【００２９】
好ましくは、第１の光分割手段は、第１および第２のサブビームそれぞれの第１および第２の分割光の形状が略等しくなる位置に配置され、光検出器は、トラッキング誤差信号を生成するために第１および第２の分割光を検出することを特徴とする。
【００３０】
好ましくは、第１の光分割手段は、第１および第２のサブビームと、メインビームそれぞれの第１および第２の分割光の形状が略等しくなる位置に配置され、光検出器は、トラッキング誤差信号を生成するために第１および第２の分割光を検出することを特徴とする。
【００３１】
好ましくは、第１の光分割手段は、透過光の効率が、第１および第２の分割光の効率より大きいことを特徴とする。
【００３２】
好ましくは、第１の光分割手段は、第２の光分割手段より光記録媒体側に配置されることを特徴とする。
【００３３】
好ましくは、第２の光分割手段は、第１の光分割手段を透過した透過光をに分岐することを特徴とする。
【００３４】
好ましくは、第１の光分割手段は、回折格子であることを特徴とする。
好ましくは、第２の光分割手段は、回折格子であることを特徴とする。
【００３５】
この発明の他の局面によれば、光ピックアップ装置は、上述した光集積化ユニットと、光源の光を光記録媒体に集光する対物レンズとを備える。
【００３６】
好ましくは、第１の光分割手段でラジアル方向に分割された第１および第２の分割光の光検出器による出力信号に基づきトラッキング誤差信号を生成するトラッキング誤差信号生成手段をさらに備える。
【００３７】
好ましくは、光検出器は、メインビームが第１の光分割手段により分割された第１および第２の分割光それぞれの光検出器による出力信号の差信号の第１の差信号と、第１のサブビームが第１の光分割手段により分割された第１および第２の分割光それぞれの光検出器による出力信号の差信号の第２の差信号と、第２のサブビームが第１の光分割手段により分割された第１および第２の分割光それぞれの光検出器による出力信号の差信号の第３の差信号を検出し、トラッキング誤差信号生成手段は、第１の差信号、第２の差信号および第３の差信号に基づき、トラッキング誤差信号を生成する。
【００３８】
【発明の実施の形態】
以下、本発明の実施の形態について、図面を参照して説明する。なお、図中において、同一符号は同一または相当する部材を示し、重複する説明は繰返さない。
【００３９】
図１は、本発明の実施の形態における光ピックアップ装置の概略構成図である。図１を参照して、光ピックアップ装置は、光集積化ユニット１７と、コリメートレンズ１１と、対物レンズ１０とを含む。光集積化ユニット１７は、半導体レーザ１８と、複合プリズム１４と、光学基板１５と、１／４波長板１３と、光検出器７とを含む。光学基板は、３ビーム回折格子１と、ラジアル方向分割回折格子２と、タンジェンシャル方向分割回折格子３とを含む。
【００４０】
光源なる半導体レーザ１８から出射された直線偏光（Ｐ偏光）は光分岐手段なる３ビーム回折格子１で回折されることにより０次回折光なるメインビームＭと、±１次回折光なる第１のサブビームＡおよび第２のサブビームＢとの３本の光に略タンジェンシャル方向（図中のＹ方向）に分岐される。なお、分岐の方向は図面略奥行き方向となるので、図面ではメインビームで代表して表記している。
【００４１】
図２は、３ビーム回折格子１の平面図である。図２を参照して、３ビーム回折格子１は直線格子状の形状を有している。
【００４２】
図１に戻って、３ビーム回折格子１を通過した上記３本の光は複合プリズム１４の偏光ビームスプリッタ（以下「ＰＢＳ面」と称す）１４ａを透過する。ＰＢＳ１４ａを透過した上記３本の光は、複合プリズム１４上に配置された１／４波長板１３により円偏光となりコリメートレンズ１１に入射する。コリメートレンズ１１で平行光となった３本の光は、対物レンズ１０で集光され光記録媒体なる光ディスク１２に照射される。光ディスク１２からの３本の戻り光は、対物レンズ１０、コリメートレンズ１１、１／４波長板１３を順に戻り、１／４波長板１３を通過することにより直線偏光（Ｓ偏光）になり、ＰＢＳ１４ａで図面右方向に反射される。さらに、３本の戻り光は、ＰＢＳ面１４ａと平行に配置された反射面１４ｂで図面下方向に反射され、第１の光分割手段なるラジアル方向分割回折格子２に入射する。
【００４３】
図３は、ラジアル方向分割回折格子２の平面図である。図３を参照して、ラジアル方向分割回折格子２は、タンジェンシャル方向に延在する分割線２ａによりラジアル方向に分割された２つの領域２ｂ，２ｃを有する回折格子である。領域２ｂ，２ｃは異なる回折格子からなっており、それぞれ入射する光を透過光（０次回折光）および所定の方向に第１および第２の分割光（以下「回折光」ともいう）として回折する。それぞれの領域２ｂ，２ｃでの０次回折光と±１次回折光の回折効率は一定である。
【００４４】
後述するように領域２ｂ，２ｃの０次回折光は、フォーカス誤差信号（ＦＥＳ）および情報信号（ＲＦ）の検出に用いられるため、ラジアル方向分割回折格子２は、０次回折光（透過光）の回折効率が±１次回折光の回折効率より大きい。
【００４５】
メインビームＭ、サブビームＡ，Ｂの３つの戻り光は、ラジアル方向分割回折格子２を通過することで、それぞれが透過光なる０次回折光６とラジアル方向に分割され半円形状となった回折光に分割される。このうち図１では、メインビームＭの０次回折光６と領域２ｂで生じた＋１次回折光４、ならびに領域２ｃで生じた−１次回折光５を記載している。
【００４６】
なお、領域２ｂで生じる−１次回折光、ならびに領域２ｃで生じる＋１次回折光については本実施例では利用しない光であるので、図面の煩雑を防ぐために記載を省略している。
【００４７】
図１に戻って、これら±１次回折光は、次に説明するタンジェンシャル方向分割回折格子３に掛からない位置を通過し、＋１次回折光４及び−１次回折光５はそのまま光検出器７に入射する。したがって、ラジアル方向分割回折格子２とタンジェンシャル方向分割回折格子３とは、所定の距離を隔てた位置に配置される。また、ラジアル方向分割回折格子２は、領域２ｂで生じる−１次回折光、ならびに領域２ｃで生じる＋１次回折光が、＋１次回折光４及び−１次回折光５を受光する受光部（図５を参照）にて検出されない位置に向かうように適宜設計される。
【００４８】
一方、ラジアル方向分割回折格子２を透過した０次回折光６は第２の光分割手段なるタンジェンシャル方向分割回折格子３に入射する。
【００４９】
図４は、タンジェンシャル方向分割回折格子３の平面図である。図４を参照して、タンジェンシャル方向分割回折格子３は、ラジアル方向に延在する分割線３ａによりタンジェンシャル方向に２つの領域３ｂ、３ｃを有する回折格子である。領域３ｂ、３ｃは異なる回折格子からなっており、それぞれ入射する光を所定の方向に＋１次回折光８、−１次回折光９として回折する。
【００５０】
すなわち、メインビームＭ、サブビームＡ，Ｂの０次回折光６はタンジェンシャル方向分割回折格子３を通過することで、それぞれが±１次回折光８，９に分岐され、光検出器７に入射する。ここでは±１次回折光８，９の回折効率を向上するために、タンジェンシャル方向分割回折格子３での０次回折光を略０とする構成になっている。
【００５１】
図４では、タンジェンシャル方向分割回折格子３はメインビームＭ、サブビームＡ，Ｂの３つの０次回折光６のすべて覆う領域に形成されているが、これに限るものではなく、少なくともメインビームＭの０次回折光を覆う領域に形成されていれば良い。メインビームＭの０次回折光の内、領域３ｂで回折された半円状の回折光は、後に説明するように、ナイフエッジ法にてフォーカス誤差信号検出用の光として用いられる。この半円状の回折光は、組立て公差、製造公差等でラジアル方向分割回折格子２上の光がタンジェンシャル方向にずれる場合、たとえば後述する図６（ｃ）で表される状況等の場合は、半円でなく弓形となる場合もあるが、フォーカス誤差信号の検出には問題はない。
【００５２】
図１に戻って、３ビーム回折格子１、ラジアル方向分割回折格子２およびタンジェンシャル方向分割回折格子３は、光学基板１５の上面および下面に形成される。すなわち、３ビーム回折格子１とタンジェンシャル方向分割回折格子３は面１５ａ、ラジアル方向分割回折格子２は面１５ｂに形成されている。このため、３ビーム回折格子１ならびにラジアル方向分割回折格子２、タンジェンシャル方向分割回折格子３は、硝材を光学基板１５として用い、フォトリソグラフィー工程を用いて形成する方法や、樹脂材料を光学基板１５として用いて成形することにより作成する方法などで、光学基板１５の両面の図１に示す上下方向および水平方向の位置に精度よくかつ簡単に形成することができる。また、ラジアル方向分割回折格子２およびタンジェンシャル方向分割回折格子３を１つの光学基板１５に形成することにより、ラジアル方向分割回折格子２とタンジェンシャル方向分割回折格子３との間の距離（図１中のＺ方向の距離）および水平方向（図１中のＸ方向およびＹ方向）の位置決めを正確にすることができる。さらに、フォトリソ工程または成形工程で位置決めがされるので、組立工程で位置決めをする必要がない。
【００５３】
また、ラジアル方向分割回折格子２とタンジェンシャル方向分割回折格子３とを光学基板１５の相対する面に形成するようにしたので、ラジアル方向分割回折光子２の領域２ｂにおけるメインビームＭ、サブビームＡ，Ｂの形状または光量と、領域２ｃにおけるメインビームＭ、サブビームＡ，Ｂの形状または光量とが略同じとなる位置にラジアル方向分割回折格子２の位置を定めることができる。
【００５４】
図５は、光検出器７上の光の配置を示す図である。図５を参照して、図面最右列の光群は、ラジアル方向分割回折格子２の領域２ｂで回折された＋１次回折光４を示し、最左列の光群はラジアル方向分割回折格子２の領域２ｃで回折された−１次回折光５を示している。また、図中、光群４の左側の光群はラジアル方向分割回折格子２の０次回折光６がタンジェンシャル方向分割回折格子３で回折された＋１次回折光８を示し、光群５の右側の光群はラジアル方向分割回折格子２の０次回折光６がタンジェンシャル方向分割回折格子３で回折された−１次回折光９を示している。
【００５５】
各光を示す符号の付け方は主に以下のようになっている。ラジアル方向分割回折格子２に関連しては、領域２ｂ、２ｃの中の符号ｂ、ｃならびに＋１次回折光４、−１次回折光５とメインビームＭ、サブビームＡ，Ｂを表すＭ、Ａ、Ｂを複合して表している。タンジェンシャル方向分割回折格子３に関連しては、＋１次回折光を示す「８」、−１次回折光を示す「９」、メインビーム、サブビームを表す「Ｍ」、「Ａ」、「Ｂ」、タンジェンシャル方向分割回折格子３の分割領域３ｂ、３ｃの符号「ｂ」、「ｃ」を複合して表している。光検出器７の各受光部の符号にＳを付した符号で、その出力信号を表すものとする。なお、（ ）を付記した符号で示される光は、本実施の形態においては信号検出に用いていない光を示しているが、これに限るものではなく各光は適宜利用されてもかまわない。
【００５６】
次に、トラッキング誤差信号の検出形態について説明する。ラジアル方向分割回折格子２の領域２ｂ、２ｃによる半円状の＋１次回折光４、−１次回折光５には光ディスク１２の案内溝で生じる光の回折によるＡＣ成分が含まれている。メインビームＭの＋１次回折光４Ｍ，５Ｍが検出される受光部７１、７６の出力信号をＳ７１、Ｓ７６と表せば、これら出力信号の差信号（第１の差信号）によりメインビームのプシュプル信号（ＭＰＰ）が次式（１）で検出される。
【００５７】
ＭＰＰ＝Ｓ７１−Ｓ７６ …（１）
さらに、サブビームＡ，Ｂは、メインビームＭの＋１次回折光４ＭのＡＣ成分の位相に対し、サブビームＡ，Ｂの＋１次回折光４Ａ，４ＢのＡＣ成分の位相が１８０°異なるよう光ディスク１２上の案内溝（不図示）に配置されるので、これらが検出される受光部７０、７２、７５、７７の出力をＳ７０、Ｓ７２、Ｓ７５、Ｓ７７と表せば、（Ｓ７０−Ｓ７５）、および（Ｓ７２−Ｓ７７）はＭＰＰに対し逆相のＡＣ成分となる。一方で、対物レンズ１０がトラッキングの際にラジアル方向に移動することによって生ずるオフセット成分（ＤＣ成分）は、メインビームＭの＋１次回折光４Ｍ、サブビームＡ，Ｂの＋１次回折光４Ａ，４Ｂ同士で同様に生じる。、また、メインビームＭの−１次回折光５Ｍ、サブビームの−１次回折光５Ａ，５Ｂ同士でも同様に生ずる。以上のことから、（Ｓ７０−Ｓ７５）および（Ｓ７２−Ｓ７７）はＭＰＰに対しＡＣ成分が逆相で、オフセット成分が同符号なる第２、第３の差信号となる。
【００５８】
したがって、ＤＰＰ法によるトラッキング誤差信号（ＴＥＳ）は（１）式も利用して、次式（２）で検出できる。
【００５９】
ＴＥＳ＝（Ｓ７１−Ｓ７６）−ｋ｛（Ｓ７０−Ｓ７５）＋（Ｓ７２−Ｓ７７）｝ … （２）
次に、式（２）の定数ｋについて説明する。定数ｋはメインビームＭとサブビームＡ，Ｂの強度比を補正する定数である。本実施の形態においては、３ビーム回折格子１でのメインビームＭ：サブビームＡ：サブビームＢの強度比が１０：１：１であるとともに、回折効率が同様に設定された２つ領域２ｂ、２ｃの回折光を用いているため、ｋ＝１０／（１＋１）＝５となる。これによって、（２）式ではＭＰＰに生ずる対物レンズ移動によるＤＣオフセットを相殺できる。
【００６０】
タンジェンシャル方向分割回折格子３の少なくとも領域３ｂはホログラムで構成されており、該領域３ｂによるメインビームＭの＋１次回折光８Ｍｂは受光部７３、７４の分割線上に集光するよう構成されている（図５では便宜上デフォーカスさせて記載している）。したがって、フォーカス誤差信号（ＦＥＳ）は、タンジェンシャル方向分割回折格子３の領域３ｂによるメインビームＭの＋１次回折光８Ｍｂを受光部７３、７４の分割線上で受光し、それらの出力信号の差信号として次式（３）により検出できる。
【００６１】
ＦＥＳ＝Ｓ７３−Ｓ７４ … （３）
記録媒体に記録された情報信号（ＲＦ）は、タンジェンシャル方向分割回折格子３の全領域（３ｂと３ｃ）によるメインビームＭの−１次回折光９Ｍｂ、９Ｍｃを受光部７８、７９で検出し、それらの出力信号の和信号として、次式（４）により検出できる。
【００６２】
ＲＦ＝Ｓ７８＋Ｓ７９ … （４）
なお、ＲＦ信号は−１次回折光９Ｍｂ，９Ｍｃを用いないで、＋１次回折光８Ｍｂ，８Ｍｃを検出して和信号とすることでも検出可能であるが、＋１次回折光８Ｍｂはフォーカス誤差信号検出にも用いるため、ＲＦ信号は別の回折光を用いて検出する方が光検出器の設計の自由度が増す。
【００６３】
本実施の形態では、ラジアル方向分割回折格子２とタンジェンシャル方向分割回折格子３をそれぞれ独立に配置している（光学基板１５の上面１５ｂおよび下面１５ａ）。このため、図６（ａ）〜（ｃ）に示すように、実際に製造される光ピックアップ装置が有する半導体レーザ１８の取り付け誤差や、パッケージ１６や、ステム、ハウジング等筐体部分（不図示）に関する製造誤差、取付け誤差、ビームスプリッタや反射ミラー等光ピックアップに用いられる光学部品の製造誤差及び取り付け誤差などの影響で、ラジアル方向分割回折格子２上のメインビームとサブビームＡ，Ｂの位置および間隔やサイズ等が光ピックアップ装置ごとに異なってしまうような場合であっても、回折光４Ｍ，４Ａ，４Ｂ，５Ｍ，５Ａ，５Ｂは半円形状を維持（同形状を維持）することができる。このため、＋１次回折光４、−１次回折光５におけるメインビームとサブビームの光量比が常に一定となるので、光ピックアップ装置ごとに定数ｋの値がばらつくことがなくなり、ＤＰＰ法による安定したトラッキング誤差信号を得る光ピックアップ装置を製造可能となる。
【００６４】
さらに本実施の形態では、初めの回折格子（ラジアル方向分割回折格子２）の０次回折光を次の回折格子（タンジェンシャル方向分割回折格子３）に入射させる構成としている。このように、初めの回折格子の１次回折光ではなく０次回折光を次の回折格子に入射させるのが好ましい。１次回折光は温度変化による波長変動や、格子ピッチ等の製造ばらつき等により、回折光の角度にばらつきを生じやすいため、それを利用することで後の回折格子による回折光の状況も上述したばらつきによる影響を引きずることになるからである。一方で０次回折光は温度変化による波長変動や、格子ピッチ等の製造ばらつきには影響されない利点があり、上述したばらつきが後の回折格子による回折状況に影響を与えない効果がある。
【００６５】
さらに本実施の形態では、ラジアル方向分割回折格子２を光ディスク１２に近い側に配置し、タンジェンシャル方向分割回折格子３を光検出器７に近い側に配置している。初めの回折格子の±１次回折光は、不要な回折等によるビームの欠け等をさけるために後の回折格子を避けて光検出器７に到達させる必要がある。このため、初めの回折格子の±１次回折光は光軸Ｚ１から概ね１０°以上曲げる必要があり（設計により幾分の相違は存在する）、光検出器７上では収差を発生してスポット形状が拡大および変形する。ただし、図５では表記の便宜上収差による光の変形は記載せず、半円形状で記載している。その拡大や変形に対応して、受光部７０、７１、７２、７５、７６、７７は面積を広く構成する必要がある。
【００６６】
受光部面積を広くすると狭い場合に比べて一般に光検出器の応答速度が遅くなる傾向にある。一方、トラッキング誤差信号はＲＦ信号等に比べ周波数帯域が低い。したがって、トラッキング誤差信号生成に用いる光は光検出器上でのそのスポットがやや拡大していてもなんら問題ない。むしろ、高速の応答を必要とするＲＦ信号ようの光９Ｍｃ，９Ｍｂ等を受光する受光部７８、７９を狭く形成することが光ピックアップ全体の特性向上に対し好ましい。したがって、ラジアル方向分割回折格子２を光ディスク１２側に配置し、タンジェンシャル方向分割回折格子３を光検出器７に近い側に配置するのはそのような点で好ましい。
【００６７】
以上説明したように本実施の形態における光集積化ユニット１７は、光記録媒体からの戻り光は、ラジアル方向分割回折格子２（第１の光分割手段）により光記録媒体のラジアル方向（第１の方向）に分割されるとともに、タンジェンシャル方向分割回折格子３（第２の光分割手段）により光記録媒体のタンジェンシャル方向（第２の方向）に分割されて光検出器７により検出される。ラジアル方向分割回折格子２とタンジェンシャル方向分割回折格子３とは、所定の距離を隔てて配置されているので、ラジアル方向分割回折格子２とタンジェンシャル方向分割回折格子３とは別々に戻り光を分割することができ、ラジアル方向分割回折格子２によってトラッキング誤差信号生成に係わるメインビームＭとサブビームＡ，Ｂを、従来のようにビームの一部分がアンバランスに欠けることなく分岐できる。このため、光集積化ユニットを用いた光ピックアップ装置が構成部品の寸法公差、組立公差の影響で個体差を有してばらついた場合であってもＤＰＰ法による安定したトラッキング誤差信号を得る光ピックアップ装置を製造することができる。
【００６８】
また、ラジアル方向分割回折格子２（第１の光分割手段）は、メインビームＭ、サブビームＡ，Ｂの戻り光を０次回折光（透過光）と、±１次回折光（透過光から光記録媒体のラジアル方向に僅かにそれる第１および第２の分割光）とに分割するので、±１次回折光を信号検出用の光に利用することができる。このため、信号検出に独立した光を利用でき、信号検出に係わる設計の自由度が向上する。
【００６９】
さらに、ラジアル方向分割回折格子２（第１の光分割手段）は、サブビームＡ，Ｂそれぞれの領域２ｂの＋１次回折光と領域２ｃの−１次回折光の光量または形状が略等しくなる位置に配置され、光検出器７は、トラッキング誤差信号を生成するためにサブビームＡ，Ｂそれぞれの領域２ｂの＋１次回折光と領域２ｃの−１次回折光を検出する。このため、サブビームＡ，Ｂそれぞれの領域２ｂの＋１次回折光と領域２ｃの−１次回折光とをトラッキング誤差信号検出用の光とできると共に、ＤＰＰ信号のサブプシュプル信号を安定して得ることができる。
【００７０】
さらに、ラジアル方向分割回折格子２（第１の光分割手段）は、メインビームＭ、サブビームＡ，Ｂそれぞれの領域２ｂの＋１次回折光と領域２ｃの−１次回折光の光量または形状が略等しくなる位置に配置され、光検出器７は、トラッキング誤差信号を生成するためにメインビームＭ、サブビームＡ，Ｂそれぞれの領域２ｂの＋１次回折光と領域２ｃの−１次回折光を検出する。このため、メインビームＭ、サブビームＡ，Ｂそれぞれの領域２ｂの＋１次回折光と領域２ｃの−１次回折光とをトラッキング誤差信号検出用の光とできると共に、サブプシュプル信号とＭＰＰ信号の強度比を常に一定に保てるため、ＤＰＰ信号を安定して得ることができる。
【００７１】
さらに、ラジアル方向分割回折格子２（第１の光分割手段）は、０次回折光（透過光）の効率が、±１次回折光（第１および第２の分割光）の効率より大きいので、ラジアル方向分割回折格子２（第１の光分割手段）の０次回折光（透過光）をトラッキング誤差信号以外のフォーカス誤差信号（ＦＥＳ）および情報信号（ＲＦ）の検出等に利用することができる。
【００７２】
さらに、ラジアル方向分割回折格子２（第１の光分割手段）を、タンジェンシャル方向分割回折格子３（第２の光分割手段）より光記録媒体側に配置したので、ラジアル方向分割回折格子２（第１の光分割手段）により分割された戻り光の光検出器７でのスポット形状が、タンジェンシャル方向分割回折格子３（第２の光分割手段）により分割された戻り光の光検出器７でのスポット形状よりも大きくなる。このため、光検出器７上でスポットが拡大あるいは変形し大面積の受光部を必要とする回折光を比較的応答速度の緩やかなトラッキング誤差信号用の光として適用でき、速い応答速度が要求されるＲＦ信号用の受光部を小さく構成でき、トラッキング誤差信号検出に弊害を発生することなく、ＲＦ信号をも高速で安定して検出できる。
【００７３】
さらに、タンジェンシャル方向分割回折格子３（第２の光分割手段）は、ラジアル方向分割回折格子２（第１の光分割手段）を透過した０次回折光（透過光）を光記録媒体のタンジェンシャル方向に分岐するので、ラジアル方向分割回折格子２（第１の光分割手段）のばらつき要因の影響をうけない光をタンジェンシャル方向分割回折格子３（第２の光分割手段）で利用でき、タンジェンシャル方向分割回折格子３（第２の光分割手段）による安定した信号を得ることができる。
【００７４】
さらに、ラジアル方向分割回折格子２（第１の光分割手段）を回折格子としたので、ラジアル方向分割回折格子２（第１の光分割手段）を簡単な製法で構成できると共に、３ビーム回折格子１（光分岐手段）、タンジェンシャル方向分割回折格子３（第２の光分割手段）等も回折格子で作製できる設計の自由度を与え、さらにそれらを一体的な光学基板に形成できるという、製法上の利点がある。
【００７５】
さらに、タンジェンシャル方向分割回折格子３（第２の光分割手段）を回折格子としたので、タンジェンシャル方向分割回折格子３（第２の光分割手段）を簡単な製法で構成できると共に、３ビーム回折格子１（光分岐手段）、ラジアル方向分割回折格子２（第１の光分割手段）等も回折格子で作製できる設計の自由度を与え、さらにそれらを一体的な光学基板に形成できるという、製法上の利点がある。
【００７６】
本実施の形態における光ピックアップ装置は、上述した光集積化ユニットと、光源の光を光記録媒体に集光する対物レンズとを備えたため、安定したＤＰＰ法によるトラッキング誤差信号生成できる。
【００７７】
さらに、ラジアル方向分割回折格子２（第１の光分割手段）は、メインビームＭ、サブビームＡ，Ｂの戻り光を０次回折光（透過光）と、±１次回折光（透過光から光記録媒体のラジアル方向に僅かにそれる第１および第２の分割光）とに分割し、分割された±１次回折光の光検出器７による出力信号に基づきトラッキング誤差信号が生成されるので、トラッキング誤差信号の検出に独立した光を利用でき、信号検出に係わる設計の自由度が向上する。
【００７８】
さらに、光検出器７は、メインビームがラジアル方向分割回折格子２（第１の光分割手段）により分割された±１次回折光（第１および第２の分割光）４Ｍ，５Ｍそれぞれの光検出器７による出力信号Ｓ７１，Ｓ７６の差信号の第１の差信号と、サブビームＡ（第１のサブビーム）がラジアル方向分割回折格子２（第１の光分割手段）により分割された±１次回折光（第１および第２の分割光）４Ａ，５Ａそれぞれの光検出器７による出力信号Ｓ７０，Ｓ７５の差信号の第２の差信号と、サブビームＢ（第２のサブビーム）がラジアル方向分割回折格子２（第１の光分割手段）により分割された±１次回折光（第１および第２の分割光）４Ｂ，５Ｂそれぞれの光検出器７による出力信号Ｓ７２、Ｓ７７の差信号の第３の差信号が検出され、第１の差信号、第２の差信号および第３の差信号に基づきトラッキング誤差信号が生成される。このため、ＤＰＰ法に基づくトラッキング誤差信号を安定して得ることができる。
【００７９】
今回開示された実施の形態はすべての点で例示であって制限的なものではないと考えられるべきである。本発明の範囲は上記した説明ではなくて特許請求の範囲によって示され、特許請求の範囲と均等の意味および範囲内でのすべての変更が含まれることが意図される。
【００８０】
【発明の効果】
（１） この発明に従えば、光源の光がメインビーム、第１のサブビームおよび第２のサブビームに分岐されて光記録媒体に照射される。光記録媒体からの戻り光は、第１の光分割手段により少なくとも光記録媒体のラジアル方向に分割されるとともに、第２の光分割手段により少なくとも光記録媒体のタンジェンシャル方向に分割されて光検出器により検出される。第１の光分割手段と第２の光分割手段とは、所定の距離を隔てて配置されているので、第１の光分割手段と第２の分割手段とは別々に戻り光を分割することができ、分割する戻り光の形状を容易に設定することができる。その結果、光集積化ユニットが構成部品の寸法公差、組立公差の影響で個体差を有してばらついた場合であってもＤＰＰ法による安定したトラッキング誤差信号を生成するための信号を容易に出力させることができる。
【００８１】
（２） 第１の光分割手段により、戻り光が、透過光と、透過光から光記録媒体のラジアル方向に僅かにそれる第１および第２の分割光とに分割される。このため、透過光から光記録媒体のラジアル方向に僅かにそれる第１および第２の分割光を信号検出用の光に利用することができる。その結果、信号検出に独立した光を利用でき、信号検出に係わる設計の自由度が向上する。
【００８２】
（３） 第１の光分割手段が、第１および第２のサブビームそれぞれの第１および第２の分割光の光量が略等しくなる位置に配置されるので、ＤＰＰ信号のサブプシュプル信号を安定して得ることができる。
【００８３】
（４） 第１の光分割手段が、第１および第２のサブビームそれぞれの第１および第２の分割光の形状が略等しくなる位置に配置されので、分割光によりトラッキング誤差信号検出用の光を得ることができると共に、ＤＰＰ信号のサブプシュプル信号を安定して得ることができる。
【００８４】
（５） 第１の光分割手段は、第１および第２のサブビームと、メインビームそれぞれの第１および第２の分割光の形状が略等しくなる位置に配置されるので、サブプシュプル信号とメインプッシュプル信号（ＭＰＰ）の強度比を一定に保つことができる。このため、ＤＰＰ信号を安定して得ることができる。
【００８５】
（６） 第１の光分割手段は、透過光の効率が、第１および第２の分割光の効率より大きいので、第１の光分割手段の透過光を、トラッキング誤差信号以外の信号検出に利用することができる。
【００８６】
（７） 第１の光分割手段は、第２の光分割手段より光記録媒体側に配置されるので、第１の光分割手段により分割された戻り光の光検出器でのスポット形状が、第２の光分割手段により分割された戻り光の光検出器でのスポット形状よりも大きくなる。このため、第２の光分割手段により分割された戻り光を検出するための光検出器の受光部を、第１の光分割手段により分割された戻り光を検出するための光検出器の受光部よりも小さくすることができる。受光部の大きさが小さいほど検出速度が速くなるので、第１の光分割手段により分割された戻り光を応答速度の緩やかなトラッキング誤差信号用の光として適用でき、第２の光分割手段により分割された戻り光を速い応答速度が要求されるＲＦ信号用に適用することができる。その結果、トラッキング誤差信号の検出に弊害をおよぼすことなく、ＲＦ信号を高速で安定して検出できる。
【００８７】
（８） 第２の光分割手段は、第１の光分割手段を透過した透過光を光記録媒体のタンジェンシャル方向に分岐するので、第１の光分割手段のばらつき要因の影響を受けない光を第２の光分割手段で分割することができる。その結果、第２の光分割手段で分割された分割光を光検出器に安定して受光させることができる。
【００８８】
（９） 第１の光分割手段は、回折格子なので、簡単な製法で製造することができる。さらに、第２の光分割手段または光分岐手段を回折格子とした場合には、それらとともに光学基板に一体的に形成することができる。
【００８９】
（１０） 第２の光分割手段は、回折格子なので、簡単な製法で製造することができる。また、第１の光分割手段または光分岐手段を回折格子とした場合には、それらとともに光学基板に一体的に形成することができる。
【００９０】
（１１） この発明の他の局面によれば、光ピックアップ装置は、上述した光集積化ユニットと、光源の光を光記録媒体に集光する対物レンズとを備える。このため、ＤＰＰ法による安定したトラッキング誤差信号を生成することが可能な光ピックアップ装置を提供することができる。
【００９１】
（１２） 第１の光分割手段によりラジアル方向に分割された第１および第２の分割光の光検出器による出力信号に基づきトラッキング誤差信号が生成される。トラッキング誤差信号の検出に独立した光を利用でき、信号検出に係わる設計の自由度が向上する。
【００９２】
（１３） 光検出器は、メインビームが第１の光分割手段により分割された第１および第２の分割光それぞれの光検出器による出力信号の差信号の第１の差信号と、第１のサブビームが第１の光分割手段により分割された第１および第２の分割光それぞれの光検出器による出力信号の差信号の第２の差信号と、第２のサブビームが第１の光分割手段により分割された第１および第２の分割光それぞれの光検出器による出力信号の差信号の第３の差信号が検出され、第１の差信号、第２の差信号および第３の差信号に基づきトラッキング誤差信号が生成される。このため、ＤＰＰ法に基づくトラッキング誤差信号を安定して得ることができる。
【図面の簡単な説明】
【図１】 本発明の実施の形態における光ピックアップ装置の概略構成図である。
【図２】 本実施の形態に係る光ピックアップ装置の３ビーム回折格子の平面図である。
【図３】 本実施の形態に係る光ピックアップ装置のラジアル方向分割回折格子の平面図である。
【図４】 本実施の形態に係る光ピックアップ装置のタンジェンシャル方向分割回折格子３の平面図である。
【図５】 本実施の形態に係る光ピックアップ装置の光検出器上の光の配置を示す図である。
【図６】 本実施の形態に係る光ピックアップ装置のラジアル方向分割回折格子上の光の配置例を示す図である。
【図７】 従来の光ピックアップ装置の概略構成を示す図である。
【図８】 従来の光ピックアップ装置のホログラム素子と受光素子の素子形状、並びにホログラム素子１０９の各領域により回折される光が受光素子で受光される領域を示す図である。
【図９】 従来の光ピックアップ装置のホログラム素子上のビーム形状を示す図である。
【図１０】 図７（ｂ）中のＸ’−Ｘ’線断面におけるメインビームＭおよびサブビームＡ，Ｂそれぞれがホログラム素子で回折されたビーム形状を示す図である。
【符号の説明】
１ ３ビーム回折格子、２ ラジアル方向分割回折光子、３ タンジェンシャル方向分割回折格子、７ 光検出器、１０ 対物レンズ、１１ コリメートレンズ、１２ 光ディスク、１３ １／４波長板、１４ 複合プリズム、１５ 光学基板、１６ パッケージ、１８ 半導体レーザ。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical integrated unit and an optical pickup device, and more particularly to an optical pickup device for optically recording or reproducing information on an information recording medium such as an optical disc and an optical integrated unit used therefor.
[0002]
[Prior art]
As a tracking servo system of an optical disk apparatus, a 3-beam method and a push-pull method are mainly known. When these methods are used in an optical disc apparatus, an offset is caused by recording, reproduction, access, or disc tilt. As a method for removing this offset, a differential push-pull (DPP) method has been proposed (see, for example, Non-Patent Document 1).
[0003]
In recent years, optical pickup devices using the DPP method are used in high-density optical disk devices such as DVD players. The present applicant has proposed an optical pickup device using an optical integrated unit capable of using the DPP method in Japanese Patent Application Laid-Open No. 2001-273666.
[0004]
FIG. 7 shows a schematic configuration of the optical pickup device disclosed in the above publication. FIG. 7A shows a top view and FIG. 7B shows a side view. The light 120 emitted from the semiconductor laser 105 is divided into a main beam (0th-order light) and two sub-beams (± 1st-order diffracted light) by the three-beam diffraction grating 106, and the polarization beam splitter (PBS) surface 107 a of the composite prism 107 is applied. The light passes through the ¼ wavelength plate 108 and travels toward a collimator lens (not shown). In order to avoid complication of the figure, the sub beam is not shown. Return light 121 from an optical disk (not shown) is transmitted through the quarter-wave plate 108, reflected by the PBS surface 107 a and the reflection mirror surface 107 b, and enters the hologram element 109. The return light 121 incident on the hologram element 109 is diffracted and incident on the light receiving element 110.
[0005]
Here, the polarized light of the light emitted from the semiconductor laser 105 is linearly polarized light (P-polarized light) in the X direction shown in the figure, is transmitted through the PBS surface 107a, is circularly polarized by the quarter wavelength plate 108, and is incident on the optical disk. To do. The return light again enters the quarter-wave plate 108 and becomes Y-direction polarized light (S-polarized light) shown in the figure, and is reflected by the PBS surface 107a.
[0006]
Accordingly, almost all of the light emitted from the semiconductor laser 105 can be guided to the optical disk, and almost all of the return light can be guided to the detector side, so that the light utilization efficiency is improved. .
[0007]
Next, the hologram element 109, the light receiving element 110, and the servo signal detection method will be described. FIG. 8 shows the element shapes of the hologram element 109 and the light receiving element 110 and in which area of the light receiving element 110 the light diffracted by each area of the hologram element 109 is received.
[0008]
The hologram element 109 is divided into three regions 109a to 109c by a dividing line 109l in the X direction corresponding to the radial direction of the optical disk and a dividing line 109m in the Y direction corresponding to the tangential direction of the optical disk.
[0009]
The light receiving element 110 includes six light receiving areas 110a to 110f that receive the + 1st order diffracted light from the hologram element 109 and three light receiving areas 110g to 110i that receive the −1st order diffracted light. In the following description, the outputs of the light receiving regions 110a to 110i are Sa to Si, respectively.
[0010]
The + 1st order diffracted light diffracted in the region 109a of the hologram element 109 in the return light of the main beam is detected on the dividing line 110l of the regions 110a and 110b of the light receiving element 110, and the −1st order diffracted light is detected in the region 110g. Further, the −1st order diffracted light in the region 109b of the hologram element 109 is detected in the region 110h of the light receiving element 110, and the −1st order diffracted light in the region 109c is detected in the region 110i.
[0011]
If one of the two sub beams is represented by sub beam A and the other is represented by sub beam B, for sub beam A, the + 1st order diffracted light diffracted in region 109b is detected in region 110e, and the + 1st order diffracted light diffracted in region 109c is detected. Detected in region 110c. For the sub-beam B, the + 1st order diffracted light diffracted in the region 109b is detected in the region 110f, and the + 1st order diffracted light diffracted in the region 109c is detected in the region 110d.
[0012]
The calculation processing of various signals detected by the hologram element 109 and the light receiving element 110 configured as described above is performed as follows.
[0013]
The focus error signal (FES) is detected by the following equation (20).
FES = Sa−Sb (20)
The tracking error signal (TES1) is detected by the following equation (21) based on the push-pull method using Si and Sh.
[0014]
TES1 = Sh-Si (21)
For the reasons already described, the DPP (differential push-pull) method using the push-pull signals (sub-push-pull) TES (A) and TES (B) of the sub-beam A and sub-beam B is mainly used. In this case, the tracking error signal (TES2) by the DPP method is detected by the equation (22). In equation (22), the constant k is for correcting the difference in intensity between the main beam and the sub beams A and B. If the intensity ratio is main beam: sub beam A: sub beam B = a: b: b, k = a / (2b).
[0015]

Further, when reproducing an optical disc on which pit information is recorded, a change in the phase difference between Sh and Si can be detected, and a tracking error signal TES3 by the phase difference (DPD) method can also be detected.
[0016]
The recorded information signal (RF) is detected by the following equation (23).
RF = Sh + Sg + Si (23)
[0017]
[Patent Document 1]
JP 2001-273666 A
[0018]
[Non-Patent Document 1]
Osato Kiyoshi, “New Tracking Servo System” Optical Memory Symposium '86, December 18, 1986, P.M. 127-P. 132
[0019]
[Problems to be solved by the invention]
In the optical pickup device described in Patent Document 1, the beam diameter of the light emitted from the semiconductor laser 105 increases as it travels toward the optical disk (see FIG. 7B). For this reason, in FIG. 7B, the main beam and the sub-beams A and B exist in a state of being substantially overlapped above the three-beam diffraction grating 106 in the figure, and the outer shape of the beam is considered to be the light 120. But there is no big difference.
[0020]
However, in the region where the beam diameter is small, the deviation between the main beam and the sub-beams A and B becomes prominent, resulting in a situation different from the above. FIG. 9 shows the beam shape on the hologram element 109. Referring to FIG. 9, it can be seen that the main beam M121a, the sub beam A121b, and the sub beam B121c are shifted on the hologram element 109.
[0021]
When the state of the light beam in the optical path is examined between the hologram element 109 and the light receiving element 110, for example, at the X′-X ′ line cross section in FIG. 7B, the main beam M passing through the hologram element 109 in the state of FIG. Each of the sub beams A and B is diffracted by the three regions 109a to 109c of the hologram element 109, and each diffracted light is as shown in FIG. In the figure, a beam indicated by a symbol indicates light used for servo signal generation, reproduction signal generation, and the like, and a beam without reference symbol indicates light that is not used as an optical pickup device. It is shown that the sub beam A is diffracted by the regions 109b and 109c to become + 1st order diffracted light 130e and 130c, and the sub beam B is diffracted by the regions 109b and 109c to become + 1st order diffracted light 130f and 130d. Since the difference in shape between the diffracted lights of the sub-beam A and the sub-beam B is remarkable, the amount of light is different. This is because the diffraction efficiency of the sub-beam A and the sub-beam B in the three-beam diffraction grating 106 is the same, so that the amount of light differs if the beam shape after passing through the hologram is different. The difference in light quantity between the sub beams A and B is due to the fact that the sub beam A 121 b and the sub beam B 121 c are not divided at the center by the dividing line 109 l of the hologram element 109 as shown in FIG.
[0022]
When the difference in the amount of light between the sub beams A and B occurs, the following problem occurs. If there is a difference in the light amounts of the sub-beams A and B, that is, even if there is an imbalance in the light amounts of the sub-beams A and B due to being cut at the dividing line 109l, the constant k is appropriate if the unbalance is always constant. By setting to a small value, stable tracking servo can be performed regardless of the pickup device. That is, since the intensity ratio between the main beam and the sub beams A and B is M: A: B = a: b1: b2, the constant k in equation (3) may be set to k = a / (b1 + b2).
[0023]
However, in an actual optical pickup device, there are mounting errors of the semiconductor laser 105, manufacturing errors related to a housing part such as a package, stem, and housing, manufacturing errors and mounting errors of optical components used in the optical pickup such as a beam splitter and a reflection mirror, etc. Due to the influence, the positions and intervals of the main beam and the sub beams A and B on the hologram element 109 differ for each optical pickup device. Therefore, even if an attempt is made to correct the difference in light intensity between the main beam M and the sub-beams A and B inherently determined by determining the constant k, considering the individual differences of the optical pickup device, the sub-beams A and B for each optical pickup device. Since the intensity ratios are different, there is a problem that the correction cannot be performed sufficiently. For this reason, the optical pickup device described in Patent Document 1 has a problem that it is difficult to perform stable tracking servo.
[0024]
The present invention has been made to solve the above-described problems, and one of the objects of the present invention is an optical signal that can easily output a signal for generating a stable tracking error signal by the DPP method. It is to provide an integrated unit.
[0025]
Another object of the present invention is to provide an optical pickup device capable of generating a stable tracking error signal by the DPP method.
[0026]
[Means for Solving the Problems]
In order to achieve the above object, according to one aspect of the present invention, an optical integration unit includes a light source for irradiating light to an optical recording medium, and the light from the light source as a main beam, a first sub beam, and a second sub beam. A light branching means for branching into the optical recording medium, a photodetector for detecting the return light from the optical recording medium, a first light splitting means for splitting the return light at least in the radial direction of the optical recording medium, and at least optically recording the return light. A second light splitting unit for splitting the medium in the tangential direction is provided, and the first light splitting unit and the second light splitting unit are arranged at a predetermined distance.
[0027]
Preferably, the first light splitting means splits the return light into transmitted light and first and second split light slightly deviating from the transmitted light.
[0028]
Preferably, the first light splitting unit is arranged at a position where the amounts of the first and second split lights of the first and second sub beams are approximately equal, and the photodetector generates a tracking error signal. Therefore, the first and second split lights are detected.
[0029]
Preferably, the first light dividing means is arranged at a position where the shapes of the first and second divided lights of the first and second sub beams are approximately equal, and the photodetector generates a tracking error signal. Therefore, the first and second split lights are detected.
[0030]
Preferably, the first light splitting unit is arranged at a position where the shapes of the first and second sub beams and the first and second split beams of the main beam are substantially equal, and the photodetector has a tracking error. A first and second split lights are detected to generate a signal.
[0031]
Preferably, the first light splitting means is characterized in that the efficiency of transmitted light is larger than the efficiency of the first and second split lights.
[0032]
Preferably, the first light splitting unit is arranged closer to the optical recording medium than the second light splitting unit.
[0033]
Preferably, the second light dividing means branches the transmitted light that has passed through the first light dividing means.
[0034]
Preferably, the first light splitting means is a diffraction grating.
Preferably, the second light splitting means is a diffraction grating.
[0035]
According to another aspect of the present invention, an optical pickup device includes the above-described optical integrated unit and an objective lens that condenses light from a light source onto an optical recording medium.
[0036]
Preferably, the apparatus further includes tracking error signal generation means for generating a tracking error signal based on output signals from the photodetectors of the first and second divided lights divided in the radial direction by the first light dividing means.
[0037]
Preferably, the photodetector includes a first difference signal of a difference signal of an output signal from each photodetector of the first and second divided lights obtained by dividing the main beam by the first light dividing means, The second difference signal of the difference signal of the output signal by the photodetector of each of the first and second divided lights obtained by dividing the first sub-beam by the first light dividing means, and the second sub-beam is the first light divided Detecting a third difference signal of the difference signal of the output signal by the photodetector of each of the first and second split lights divided by the means, and the tracking error signal generating means includes the first difference signal, the second difference signal, and the second difference signal. A tracking error signal is generated based on the difference signal and the third difference signal.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same reference numerals indicate the same or corresponding members, and redundant description will not be repeated.
[0039]
FIG. 1 is a schematic configuration diagram of an optical pickup device according to an embodiment of the present invention. Referring to FIG. 1, the optical pickup device includes an optical integration unit 17, a collimating lens 11, and an objective lens 10. The optical integrated unit 17 includes a semiconductor laser 18, a composite prism 14, an optical substrate 15, a quarter wavelength plate 13, and a photodetector 7. The optical substrate includes a three-beam diffraction grating 1, a radial direction division diffraction grating 2, and a tangential direction division diffraction grating 3.
[0040]
The linearly polarized light (P-polarized light) emitted from the semiconductor laser 18 serving as the light source is diffracted by the three-beam diffraction grating 1 serving as the light branching means, whereby the main beam M serving as the 0th-order diffracted light and the first sub-beam A serving as the ± 1st-order diffracted light. In addition, the light is branched into approximately three tangential directions (Y direction in the figure) into three lights with the second sub-beam B. Since the branching direction is substantially the depth direction of the drawing, it is represented by the main beam in the drawing.
[0041]
FIG. 2 is a plan view of the three-beam diffraction grating 1. Referring to FIG. 2, the three-beam diffraction grating 1 has a linear grating shape.
[0042]
Returning to FIG. 1, the three lights that have passed through the three-beam diffraction grating 1 pass through a polarization beam splitter (hereinafter referred to as “PBS plane”) 14 a of the composite prism 14. The three lights transmitted through the PBS 14 a are circularly polarized by the quarter wavelength plate 13 disposed on the composite prism 14 and enter the collimating lens 11. The three lights converted into parallel light by the collimator lens 11 are collected by the objective lens 10 and applied to the optical disk 12 serving as an optical recording medium. The three return lights from the optical disk 12 return in order through the objective lens 10, the collimating lens 11, and the quarter wavelength plate 13 and pass through the quarter wavelength plate 13 to become linearly polarized light (S polarized light). Is reflected in the right direction of the drawing. Further, the three return lights are reflected downward in the drawing by the reflecting surface 14b arranged in parallel with the PBS surface 14a, and enter the radial direction division diffraction grating 2 serving as the first light dividing means.
[0043]
FIG. 3 is a plan view of the radial direction division diffraction grating 2. Referring to FIG. 3, the radial direction division diffraction grating 2 is a diffraction grating having two regions 2b and 2c divided in the radial direction by a division line 2a extending in the tangential direction. The regions 2b and 2c are made of different diffraction gratings, and each diffracts incident light as transmitted light (0th order diffracted light) and first and second divided light (hereinafter also referred to as “diffracted light”) in a predetermined direction. . The diffraction efficiencies of the 0th order diffracted light and the ± 1st order diffracted light in the respective regions 2b and 2c are constant.
[0044]
As will be described later, since the 0th-order diffracted light in the regions 2b and 2c is used to detect the focus error signal (FES) and the information signal (RF), the radial direction division diffraction grating 2 diffracts the 0th-order diffracted light (transmitted light). Efficiency is greater than the diffraction efficiency of ± first order diffracted light.
[0045]
The three return lights of the main beam M and the sub-beams A and B pass through the radial direction split diffraction grating 2, so that each of the zero-order diffracted light 6 that is transmitted light and the diffracted light that is split in the radial direction into a semicircular shape It is divided into. Among these, FIG. 1 shows the 0th-order diffracted light 6 of the main beam M, the + 1st-order diffracted light 4 generated in the region 2b, and the −1st-order diffracted light 5 generated in the region 2c.
[0046]
Note that the −1st order diffracted light generated in the region 2b and the + 1st order diffracted light generated in the region 2c are light that is not used in the present embodiment, and thus are not described in order to prevent the drawing from being complicated.
[0047]
Returning to FIG. 1, these ± 1st order diffracted lights pass through a position not applied to the tangential direction division diffraction grating 3 described below, and the + 1st order diffracted light 4 and the −1st order diffracted light 5 enter the photodetector 7 as they are. To do. Therefore, the radial direction divisional diffraction grating 2 and the tangential direction divisional diffraction grating 3 are arranged at positions separated by a predetermined distance. Further, the radial direction division diffraction grating 2 is a light receiving unit in which the −1st order diffracted light generated in the region 2b and the + 1st order diffracted light generated in the region 2c receive the + 1st order diffracted light 4 and the −1st order diffracted light 5 (see FIG. 5). It is designed as appropriate so as to go to a position not detected by
[0048]
On the other hand, the 0th-order diffracted light 6 transmitted through the radial direction division diffraction grating 2 is incident on the tangential direction division diffraction grating 3 serving as the second light division means.
[0049]
FIG. 4 is a plan view of the tangential direction division diffraction grating 3. Referring to FIG. 4, the tangential direction division diffraction grating 3 is a diffraction grating having two regions 3b and 3c in the tangential direction by a division line 3a extending in the radial direction. The regions 3b and 3c are made of different diffraction gratings, and each diffracts incident light as + 1st order diffracted light 8 and −1st order diffracted light 9 in a predetermined direction.
[0050]
That is, the 0th-order diffracted light 6 of the main beam M and the sub-beams A and B passes through the tangential direction division diffraction grating 3, and is branched into ± 1st-order diffracted lights 8 and 9 and enters the photodetector 7. Here, in order to improve the diffraction efficiency of the ± 1st-order diffracted beams 8 and 9, the 0th-order diffracted beam in the tangential direction division diffraction grating 3 is set to substantially zero.
[0051]
In FIG. 4, the tangential direction division diffraction grating 3 is formed in a region that covers all three zero-order diffracted lights 6 of the main beam M and sub-beams A and B, but is not limited to this. What is necessary is just to form in the area | region which covers 0th-order diffracted light. Of the 0th order diffracted light of the main beam M, the semicircular diffracted light diffracted in the region 3b is used as focus error signal detection light by the knife edge method, as will be described later. This semicircular diffracted light is used when the light on the radial direction division diffraction grating 2 is shifted in the tangential direction due to assembly tolerance, manufacturing tolerance, etc., for example, in the case of the situation shown in FIG. In some cases, the shape may be a bow instead of a semicircle, but there is no problem in detecting the focus error signal.
[0052]
Returning to FIG. 1, the three-beam diffraction grating 1, the radial direction division diffraction grating 2, and the tangential direction division diffraction grating 3 are formed on the upper surface and the lower surface of the optical substrate 15. That is, the three-beam diffraction grating 1 and the tangential direction division diffraction grating 3 are formed on the surface 15a, and the radial direction division diffraction grating 2 is formed on the surface 15b. Therefore, the three-beam diffraction grating 1, the radial direction division diffraction grating 2, and the tangential direction division diffraction grating 3 are formed by using a glass material as the optical substrate 15 and using a photolithography process, or using a resin material as the optical substrate 15. 1 can be formed accurately and easily at the vertical and horizontal positions shown in FIG. 1 on both sides of the optical substrate 15. Further, by forming the radial direction division diffraction grating 2 and the tangential direction division diffraction grating 3 on one optical substrate 15, the distance between the radial direction division diffraction grating 2 and the tangential direction division diffraction grating 3 (FIG. 1). (Distance in the Z direction in the middle) and positioning in the horizontal direction (X direction and Y direction in FIG. 1) can be made accurate. Furthermore, since positioning is performed in the photolithography process or the molding process, it is not necessary to perform positioning in the assembly process.
[0053]
Further, since the radial direction division diffraction grating 2 and the tangential direction division diffraction grating 3 are formed on opposite surfaces of the optical substrate 15, the main beam M, the sub beam A, and the sub beam A in the region 2b of the radial direction division diffraction photon 2 are formed. The position of the radial direction division diffraction grating 2 can be determined at a position where the shape or light quantity of B and the shape or light quantity of the main beam M and sub beams A and B in the region 2c are substantially the same.
[0054]
FIG. 5 is a diagram showing the arrangement of light on the photodetector 7. Referring to FIG. 5, the light group in the rightmost column in the drawing shows the + 1st order diffracted light 4 diffracted in the region 2 b of the radial direction division diffraction grating 2, and the light group in the leftmost column is the radial direction division diffraction grating 2. The first-order diffracted light 5 diffracted in the region 2c is shown. Further, in the figure, the light group on the left side of the light group 4 shows the + 1st order diffracted light 8 obtained by diffracting the zeroth order diffracted light 6 of the radial direction division diffraction grating 2 by the tangential direction division diffraction grating 3. The light group shows −1st order diffracted light 9 obtained by diffracting the 0th order diffracted light 6 of the radial direction divided diffraction grating 2 by the tangential direction divided diffraction grating 3.
[0055]
The method of attaching symbols indicating each light is mainly as follows. In relation to the radial direction division diffraction grating 2, the symbols b and c in the regions 2b and 2c, and the + 1st order diffracted light 4, the −1st order diffracted light 5, the main beam M, and the sub beams A and B, M, A, B Is represented in a composite manner. In relation to the tangential direction division diffraction grating 3, "8" indicating + 1st order diffracted light, "9" indicating -1st order diffracted light, "M", "A", "B" indicating main beam and sub beam, The symbols “b” and “c” of the divided regions 3 b and 3 c of the tangential direction divided diffraction grating 3 are shown in combination. It is assumed that the output signal is represented by a symbol with S added to the symbol of each light receiving unit of the photodetector 7. The light indicated by the reference numerals with () indicates light that is not used for signal detection in the present embodiment, but is not limited to this, and each light may be used as appropriate.
[0056]
Next, a detection form of the tracking error signal will be described. The semicircular + 1st order diffracted light 4 and −1st order diffracted light 5 by the regions 2b and 2c of the radial direction division diffraction grating 2 contain an AC component due to light diffraction generated in the guide groove of the optical disk 12. If the output signals of the light receiving units 71 and 76 from which the + 1st order diffracted lights 4M and 5M of the main beam M are detected are represented as S71 and S76, the main signal push-pull signal (first difference signal) is expressed by the difference signal (first difference signal) of these output signals. MPP) is detected by the following equation (1).
[0057]
MPP = S71−S76 (1)
Further, the sub beams A and B are guided on the optical disc 12 so that the phase of the AC components of the + 1st order diffracted lights 4A and 4B of the subbeams A and B is 180 ° different from the phase of the AC component of the + 1st order diffracted light 4M of the main beam M. Since they are arranged in grooves (not shown), the outputs of the light receiving units 70, 72, 75, 77 from which these are detected are expressed as S70, S72, S75, S77, (S70-S75), and (S72-S77). ) Is an AC component having a phase opposite to that of MPP. On the other hand, the offset component (DC component) generated by the objective lens 10 moving in the radial direction during tracking is the same for the + 1st order diffracted light 4M of the main beam M and the + 1st order diffracted lights 4A and 4B of the sub beams A and B. To occur. Further, the -1st order diffracted light 5M of the main beam M and the -1st order diffracted lights 5A and 5B of the sub-beams are similarly generated. From the above, (S70-S75) and (S72-S77) are the second and third difference signals in which the AC component is opposite in phase to the MPP and the offset component has the same sign.
[0058]
Therefore, the tracking error signal (TES) by the DPP method can be detected by the following equation (2) using the equation (1).
[0059]
TES = (S71−S76) −k {(S70−S75) + (S72−S77)} (2)
Next, the constant k in Expression (2) will be described. The constant k is a constant for correcting the intensity ratio between the main beam M and the sub beams A and B. In the present embodiment, the intensity ratio of the main beam M: sub-beam A: sub-beam B in the three-beam diffraction grating 1 is 10: 1: 1, and the two regions 2b and 2c are set similarly in diffraction efficiency. Therefore, k = 10 / (1 + 1) = 5. Thereby, in the formula (2), the DC offset caused by the objective lens movement generated in the MPP can be canceled.
[0060]
At least the region 3b of the tangential direction division diffraction grating 3 is constituted by a hologram, and the + 1st order diffracted light 8Mb of the main beam M by the region 3b is constituted to be condensed on the dividing lines of the light receiving portions 73 and 74 ( In FIG. 5, it is defocused for convenience). Therefore, the focus error signal (FES) receives the + 1st order diffracted light 8Mb of the main beam M by the region 3b of the tangential direction division diffraction grating 3 on the dividing line of the light receiving units 73 and 74, and as a difference signal of their output signals. It can be detected by the following equation (3).
[0061]
FES = S73−S74 (3)
The information signal (RF) recorded on the recording medium is detected by the light receiving portions 78 and 79 by detecting the first-order diffracted light beams 9Mb and 9Mc of the main beam M by the entire region (3b and 3c) of the tangential direction division diffraction grating 3, The sum signal of these output signals can be detected by the following equation (4).
[0062]
RF = S78 + S79 (4)
The RF signal can also be detected by detecting the + 1st order diffracted light 8Mb, 8Mc as a sum signal without using the -1st order diffracted light 9Mb, 9Mc, but the + 1st order diffracted light 8Mb is also used for focus error signal detection. Therefore, the degree of freedom in designing the photodetector increases when the RF signal is detected using another diffracted light.
[0063]
In the present embodiment, the radial direction division diffraction grating 2 and the tangential direction division diffraction grating 3 are independently arranged (the upper surface 15b and the lower surface 15a of the optical substrate 15). For this reason, as shown in FIGS. 6A to 6C, the mounting error of the semiconductor laser 18 included in the optical pickup device that is actually manufactured, the housing portion such as the package 16, the stem, and the housing (not shown). The position and spacing of the main beam and sub-beams A and B on the radial-direction split diffraction grating 2 due to the effects of manufacturing errors, mounting errors, manufacturing errors and mounting errors of optical components used in optical pickups such as beam splitters and reflecting mirrors, etc. Even in the case where the size or the size of each optical pickup device is different, the diffracted light 4M, 4A, 4B, 5M, 5A, 5B can maintain a semicircular shape (maintain the same shape). For this reason, since the light quantity ratio between the main beam and the sub beam in the + 1st order diffracted light 4 and the −1st order diffracted light 5 is always constant, the value of the constant k does not vary for each optical pickup device, and stable tracking error by the DPP method is prevented. An optical pickup device for obtaining a signal can be manufactured.
[0064]
Further, in the present embodiment, the 0th-order diffracted light of the first diffraction grating (radial direction division diffraction grating 2) is made incident on the next diffraction grating (tangential direction division diffraction grating 3). In this way, it is preferable to make the 0th-order diffracted light enter the next diffraction grating instead of the first-order diffracted light of the first diffraction grating. Since the first-order diffracted light tends to cause variations in the angle of the diffracted light due to variations in wavelength due to temperature changes, manufacturing variations such as the grating pitch, and so on, the situation of the diffracted light due to the subsequent diffraction grating can also be changed by using this. This is because the influence of the is dragged. On the other hand, the 0th-order diffracted light has the advantage that it is not affected by wavelength variations due to temperature changes and manufacturing variations such as the grating pitch, and has the effect that the above-described variations do not affect the diffraction status of the subsequent diffraction grating.
[0065]
Further, in the present embodiment, the radial direction division diffraction grating 2 is arranged on the side close to the optical disk 12, and the tangential direction division diffraction grating 3 is arranged on the side close to the photodetector 7. The ± 1st-order diffracted light of the first diffraction grating needs to reach the photodetector 7 while avoiding the subsequent diffraction grating in order to avoid beam breakage due to unnecessary diffraction or the like. For this reason, the ± 1st-order diffracted light of the first diffraction grating needs to be bent by approximately 10 ° or more from the optical axis Z1 (there is some difference depending on the design), and aberration is generated on the photodetector 7 to generate a spot shape. Expands and deforms. However, in FIG. 5, the deformation of light due to aberration is not described for convenience of description, and is illustrated in a semicircular shape. Corresponding to the expansion and deformation, the light receiving portions 70, 71, 72, 75, 76, and 77 need to be configured with a wide area.
[0066]
When the area of the light receiving part is increased, the response speed of the photodetector generally tends to be lower than that in the case where the area is small. On the other hand, the tracking error signal has a lower frequency band than the RF signal or the like. Therefore, there is no problem with the light used for generating the tracking error signal even if the spot on the photodetector is slightly enlarged. Rather, it is preferable to narrow the light receiving portions 78 and 79 for receiving the light 9Mc, 9Mb and the like as RF signals that require a high-speed response in order to improve the characteristics of the entire optical pickup. Therefore, it is preferable in that respect to arrange the radial direction division diffraction grating 2 on the optical disc 12 side and arrange the tangential direction division diffraction grating 3 on the side close to the photodetector 7.
[0067]
As described above, in the optical integrated unit 17 in the present embodiment, the return light from the optical recording medium is transmitted in the radial direction (first direction) of the optical recording medium by the radial direction division diffraction grating 2 (first optical dividing means). Are divided in the tangential direction (second direction) of the optical recording medium by the tangential direction division diffraction grating 3 (second light dividing means) and detected by the photodetector 7. . Since the radial direction division diffraction grating 2 and the tangential direction division diffraction grating 3 are arranged at a predetermined distance, the radial direction division diffraction grating 2 and the tangential direction division diffraction grating 3 separately transmit return light. The main beam M and the sub beams A and B related to the tracking error signal generation can be branched by the radial direction division diffraction grating 2 without a part of the beam being unbalanced as in the conventional case. For this reason, even if the optical pickup device using the optical integrated unit varies due to individual differences due to the dimensional tolerance and assembly tolerance of the component parts, an optical pickup that obtains a stable tracking error signal by the DPP method The device can be manufactured.
[0068]
Further, the radial direction split diffraction grating 2 (first light splitting means) is configured such that the return light of the main beam M and the sub beams A and B is converted into 0th order diffracted light (transmitted light) and ± 1st order diffracted light (transmitted light to optical recording medium) The first and second split lights slightly deviating in the radial direction of the first and second split light beams can be used as signal detection light. For this reason, independent light can be used for signal detection, and the degree of freedom in design related to signal detection is improved.
[0069]
Further, the radial direction split diffraction grating 2 (first light splitting means) is disposed at a position where the light amounts or shapes of the + 1st order diffracted light in the regions 2b and the -1st order diffracted light in the regions 2c of the sub beams A and B are substantially equal. The photodetector 7 detects the + 1st order diffracted light in the region 2b and the −1st order diffracted light in the region 2c of each of the sub beams A and B in order to generate a tracking error signal. For this reason, the + 1st order diffracted light in the regions 2b and the −1st order diffracted light in the regions 2c of the sub beams A and B can be used as tracking error signal detection light, and the sub push-pull signal of the DPP signal can be stably obtained. .
[0070]
Further, in the radial direction division diffraction grating 2 (first light dividing means), the light amounts or shapes of the + 1st order diffracted light in the region 2b and the -1st order diffracted light in the region 2c of the main beam M and the sub beams A and B are substantially equal. The light detector 7 is disposed at the position, and detects the + 1st order diffracted light in the region 2b and the −1st order diffracted light in the region 2c of each of the main beam M and the sub beams A and B in order to generate a tracking error signal. For this reason, the + 1st order diffracted light in the region 2b and the -1st order diffracted light in the region 2c of the main beam M and the sub beams A and B can be used as tracking error signal detection light, and the intensity ratio between the sub push-pull signal and the MPP signal can be increased. Since it can always be kept constant, the DPP signal can be obtained stably.
[0071]
Furthermore, the radial direction split diffraction grating 2 (first light splitting means) is radial because the efficiency of the 0th order diffracted light (transmitted light) is greater than the efficiency of ± 1st order diffracted light (first and second split light). The 0th-order diffracted light (transmitted light) of the direction-dividing diffraction grating 2 (first light splitting means) can be used for detecting a focus error signal (FES) and an information signal (RF) other than the tracking error signal.
[0072]
Further, since the radial direction division diffraction grating 2 (first light division means) is arranged closer to the optical recording medium than the tangential direction division diffraction grating 3 (second light division means), the radial direction division diffraction grating 2 ( The spot shape of the return light split by the first light splitting means) on the photodetector 7 is the return light photodetector 7 split by the tangential direction split diffraction grating 3 (second light splitting means). It becomes larger than the spot shape at. For this reason, the diffracted light that requires a large-area light-receiving portion due to the expansion or deformation of the spot on the photodetector 7 can be applied as tracking error signal light with a relatively slow response speed, and a high response speed is required. The RF signal light receiving unit can be made small, and the RF signal can be detected stably at high speed without causing any adverse effect on the tracking error signal detection.
[0073]
Further, the tangential direction split diffraction grating 3 (second light splitting means) converts the 0th-order diffracted light (transmitted light) transmitted through the radial direction split diffraction grating 2 (first light splitting means) into the tangential of the optical recording medium. Since the light is branched in the direction, the light that is not affected by the variation factor of the radial direction splitting diffraction grating 2 (first light splitting means) can be used by the tangential direction splitting diffraction grating 3 (second light splitting means). A stable signal can be obtained by the partial direction division diffraction grating 3 (second light dividing means).
[0074]
Further, since the radial direction split diffraction grating 2 (first light splitting means) is a diffraction grating, the radial direction split diffraction grating 2 (first light splitting means) can be configured by a simple manufacturing method and a three beam diffraction grating. 1 (light splitting means), tangential direction splitting diffraction grating 3 (second light splitting means), etc. are also provided with a design freedom that can be manufactured with a diffraction grating, and further, they can be formed on an integrated optical substrate. There are the above advantages.
[0075]
Furthermore, since the tangential direction split diffraction grating 3 (second light splitting means) is a diffraction grating, the tangential direction split diffraction grating 3 (second light splitting means) can be configured by a simple manufacturing method and three beams. The diffraction grating 1 (light splitting means), the radial direction splitting diffraction grating 2 (first light splitting means), etc. also give a design freedom that can be made with a diffraction grating, and they can be formed on an integrated optical substrate. There is a manufacturing advantage.
[0076]
Since the optical pickup device in the present embodiment includes the above-described optical integrated unit and an objective lens that condenses the light of the light source onto the optical recording medium, it is possible to generate a tracking error signal by a stable DPP method.
[0077]
Further, the radial-direction split diffraction grating 2 (first light splitting means) converts the return light of the main beam M and sub-beams A and B into 0th order diffracted light (transmitted light) and ± 1st order diffracted light (from transmitted light to an optical recording medium). Since the tracking error signal is generated on the basis of the output signal of the divided ± first-order diffracted light by the photodetector 7, the tracking error is generated. Independent light can be used for signal detection, and the degree of freedom in design for signal detection is improved.
[0078]
Further, the photodetector 7 detects the light of the ± first-order diffracted lights (first and second split lights) 4M and 5M obtained by splitting the main beam by the radial direction split diffraction grating 2 (first light splitting means). The first difference signal of the difference signal between the output signals S71 and S76 by the unit 7 and the ± first-order diffracted light obtained by dividing the sub beam A (first sub beam) by the radial direction division diffraction grating 2 (first light dividing means) (First and second split lights) The second difference signal of the difference signals of the output signals S70 and S75 from the photodetectors 7A and 5A and the sub-beam B (second sub-beam) are radially divided diffraction gratings. 2 (first light splitting means) ± first-order diffracted light (first and second split lights) 4B, 5B, the third difference of the difference signals of the output signals S72, S77 by the respective photodetectors 7B A signal is detected and the first Difference signal, a tracking error signal based on the second difference signal and the third difference signal is generated. For this reason, a tracking error signal based on the DPP method can be obtained stably.
[0079]
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0080]
【The invention's effect】
(1) According to the present invention, the light from the light source is branched into the main beam, the first sub-beam, and the second sub-beam and irradiated onto the optical recording medium. The return light from the optical recording medium is split at least in the radial direction of the optical recording medium by the first light splitting means, and is split at least in the tangential direction of the optical recording medium by the second light splitting means. Detected by the instrument. Since the first light splitting means and the second light splitting means are arranged at a predetermined distance, the first light splitting means and the second splitting means divide the return light separately. The shape of the return light to be divided can be easily set. As a result, even if the optical integrated unit varies due to the individual tolerance due to the dimensional tolerance and assembly tolerance of the component parts, a signal for generating a stable tracking error signal by the DPP method can be easily output. Can be made.
[0081]
(2) The first light splitting means splits the return light into transmitted light and first and second split lights that slightly deviate from the transmitted light in the radial direction of the optical recording medium. Therefore, the first and second split lights that slightly deviate from the transmitted light in the radial direction of the optical recording medium can be used as signal detection light. As a result, independent light can be used for signal detection, and the degree of design freedom for signal detection is improved.
[0082]
(3) Since the first light splitting means is arranged at a position where the amounts of the first and second split lights of the first and second sub beams are substantially equal, the sub push-pull signal of the DPP signal is stabilized. Can be obtained.
[0083]
(4) Since the first light splitting means is disposed at a position where the shapes of the first and second split lights of the first and second sub-beams are approximately equal to each other, the tracking error signal detection light is split by the split light. And a sub push-pull signal of the DPP signal can be stably obtained.
[0084]
(5) The first light splitting means is arranged at a position where the shapes of the first and second sub-beams and the first and second split lights of the main beam are approximately equal to each other. The intensity ratio of the push-pull signal (MPP) can be kept constant. For this reason, a DPP signal can be obtained stably.
[0085]
(6) Since the efficiency of the transmitted light is greater than the efficiency of the first and second split lights, the first light splitting means uses the transmitted light of the first light splitting means for signal detection other than the tracking error signal. Can be used.
[0086]
(7) Since the first light splitting means is arranged closer to the optical recording medium than the second light splitting means, the spot shape of the return light split by the first light splitting means at the photodetector is The return light divided by the second light dividing means becomes larger than the spot shape at the photodetector. For this reason, the light receiving unit of the photodetector for detecting the return light divided by the second light splitting unit is used as the light receiving unit of the photodetector for detecting the return light split by the first light splitting unit. It can be made smaller than the part. Since the detection speed increases as the size of the light receiving portion decreases, the return light divided by the first light splitting means can be applied as light for tracking error signal with a slow response speed, and the second light splitting means The divided return light can be applied to an RF signal that requires a high response speed. As a result, the RF signal can be detected stably at a high speed without adversely affecting the detection of the tracking error signal.
[0087]
(8) Since the second light splitting means branches the transmitted light that has passed through the first light splitting means in the tangential direction of the optical recording medium, the light that is not affected by the variation factors of the first light splitting means. Can be split by the second light splitting means. As a result, the split light split by the second light splitting means can be stably received by the photodetector.
[0088]
(9) Since the first light splitting means is a diffraction grating, it can be manufactured by a simple manufacturing method. Further, when the second light splitting means or the light branching means is a diffraction grating, it can be integrally formed with the optical substrate together with them.
[0089]
(10) Since the second light splitting means is a diffraction grating, it can be manufactured by a simple manufacturing method. Further, when the first light splitting means or the light branching means is a diffraction grating, it can be integrally formed with the optical substrate together with them.
[0090]
(11) According to another aspect of the present invention, an optical pickup device includes the above-described optical integrated unit and an objective lens that condenses light from a light source onto an optical recording medium. Therefore, it is possible to provide an optical pickup device that can generate a stable tracking error signal by the DPP method.
[0091]
(12) A tracking error signal is generated based on the output signals from the photodetectors of the first and second split lights divided in the radial direction by the first light splitting means. Independent light can be used for detection of the tracking error signal, and the degree of freedom in design related to signal detection is improved.
[0092]
(13) The photodetector includes a first difference signal of a difference signal of an output signal from each photodetector of the first and second divided lights obtained by dividing the main beam by the first light dividing means, The second difference signal of the difference signal of the output signal by the photodetector of each of the first and second divided lights obtained by dividing the first sub-beam by the first light dividing means, and the second sub-beam is the first light divided The third difference signal of the difference signal of the output signal by the photodetector of each of the first and second divided lights divided by the means is detected, and the first difference signal, the second difference signal, and the third difference are detected. A tracking error signal is generated based on the signal. For this reason, a tracking error signal based on the DPP method can be obtained stably.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an optical pickup device according to an embodiment of the present invention.
FIG. 2 is a plan view of a three-beam diffraction grating of the optical pickup device according to the present embodiment.
FIG. 3 is a plan view of a radial direction division diffraction grating of the optical pickup device according to the present embodiment.
FIG. 4 is a plan view of a tangential direction division diffraction grating 3 of the optical pickup device according to the present embodiment.
FIG. 5 is a diagram showing an arrangement of light on a photodetector of the optical pickup device according to the present embodiment.
FIG. 6 is a diagram showing an arrangement example of light on a radial direction division diffraction grating of the optical pickup device according to the present embodiment.
FIG. 7 is a diagram showing a schematic configuration of a conventional optical pickup device.
FIG. 8 is a diagram illustrating the element shapes of a hologram element and a light receiving element of a conventional optical pickup device, and regions where light diffracted by each region of the hologram element 109 is received by the light receiving element.
FIG. 9 is a diagram showing a beam shape on a hologram element of a conventional optical pickup device.
FIG. 10 is a diagram showing beam shapes obtained by diffracting the main beam M and sub beams A and B on the X′-X ′ line cross section in FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 3 beam diffraction grating, 2 radial direction division | segmentation diffracted photon, 3 tangential direction division | segmentation diffraction grating, 7 photodetector, 10 objective lens, 11 collimating lens, 12 optical disk, 13 1/4 wavelength plate, 14 compound prism, 15 optics Substrate, 16 package, 18 semiconductor laser.

Claims (13)

A light source for irradiating the optical recording medium with light;
Light branching means for branching the light of the light source into a main beam, a first sub-beam and a second sub-beam;
A photodetector for detecting return light from the optical recording medium;
First light splitting means for splitting the return light at least in the radial direction of the optical recording medium;
Second light splitting means for splitting the return light at least in the tangential direction of the optical recording medium;
The optical integrated unit, wherein the first light splitting unit and the second light splitting unit are arranged at a predetermined distance. 2. The light according to claim 1, wherein the first light splitting unit splits the return light into transmitted light and first and second split light slightly deviating from the transmitted light. 3. Integrated unit. The first light splitting means is arranged at a position where the light amounts of the first and second split lights of the first and second sub beams are approximately equal,
The optical integrated unit according to claim 2, wherein the photodetector detects the first and second divided lights to generate a tracking error signal. The first light splitting means is arranged at a position where the shapes of the first and second split lights of the first and second sub-beams are approximately equal,
The optical integrated unit according to claim 2, wherein the photodetector detects the first and second divided lights to generate a tracking error signal. The first light splitting means is arranged at a position where the shapes of the first and second sub-beams and the first split light of the main beam are approximately equal,
The optical integrated unit according to claim 2, wherein the photodetector detects the first and second split lights to generate a tracking error signal. The optical integrated unit according to claim 2, wherein the first light splitting unit has an efficiency of transmitted light larger than that of the first and second split lights. 2. The optical integrated unit according to claim 1, wherein the first light splitting unit is arranged closer to the optical recording medium than the second light splitting unit. 3. 3. The optical integrated unit according to claim 2, wherein the second light splitting unit branches the transmitted light transmitted through the first light splitting unit. The optical integrated unit according to claim 1, wherein the first light splitting unit is a diffraction grating. 2. The optical integrated unit according to claim 1, wherein the second light splitting means is a diffraction grating. An optical pickup device comprising: the optical integrated unit according to claim 1; and an objective lens that condenses light from the light source onto an optical recording medium. 12. A tracking error signal generating unit configured to generate a tracking error signal based on output signals from the photodetectors of the first and second split lights divided in the radial direction by the first light splitting unit. The optical pickup device described. The photodetector includes a first difference signal of a difference signal of an output signal from the photodetector of each of the first and second divided lights obtained by dividing the main beam by the first light dividing unit; A second difference signal of a difference signal of an output signal from the photodetector of each of the first and second divided lights obtained by dividing the first sub beam by the first light dividing means; and the second sub beam comprises: Detecting a third difference signal of a difference signal of an output signal by the photodetector of each of the first and second split lights divided by the first light splitting means;
13. The optical pickup device according to claim 12, wherein the tracking error signal generating unit generates a tracking error signal based on the first difference signal, the second difference signal, and the third difference signal.

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