JP4258587B2

JP4258587B2 - Optical head device

Info

Publication number: JP4258587B2
Application number: JP14838599A
Authority: JP
Inventors: 陽輔藤野
Original assignee: Asahi Glass Co Ltd
Current assignee: AGC Inc
Priority date: 1999-05-27
Filing date: 1999-05-27
Publication date: 2009-04-30
Anticipated expiration: 2019-05-27
Also published as: JP2000339743A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＣＤ−Ｒ、ＣＤ−ＲＷ、ＤＶＤ−Ｒ、ＤＶＤ＋ＲＷなどの記録用光ディスクまたは光磁気ディスクなど、レーザ光の照射により光学的に情報記録が可能な光記録媒体に対して情報の書き込み、読み取り、または消去を行うための光ヘッド装置に関する。
【０００２】
【従来の技術】
ＣＤやＤＶＤなどの光ディスクまたは光磁気ディスクなどの光記録媒体に情報を書き込んだり、光記録媒体から情報を読み取ったりするために、レンズや回折素子などの光学素子、半導体レーザ、および受光素子などを備えた光ヘッド装置が用いられている。
【０００３】
従来の光ヘッド装置の一例として、特許第２７７６４８７号に記載されたものを図７および図８を用いて説明する。図７は従来の光ヘッド装置の基本構成を示す斜視図、図８は従来の光ヘッド装置に係るフォーカス誤差信号およびトラッキング誤差信号を得る構成を模式的に示す説明図である。
【０００４】
光ヘッド装置は、光源としての半導体レーザ１０１、半導体レーザ１０１の次段に配設され半導体レーザ１０１からの出射光と光記録媒体１０６での反射光をそれぞれ回折するための回折素子１０２，１０３、回折素子１０２，１０３の次段に配設されレーザ光を平行光線とするためのコリメートレンズ１０４、コリメートレンズ１０４の次段に配設されレーザ光を集光するための対物レンズ１０５、回折素子１０３からの回折光を受光する受光素子１０７を有している。
【０００５】
上記構成において、半導体レーザ１０１から出射されたレーザ光は、回折素子１０２で０次回折光と±１次回折光との３つに分割回折され、これらの３つの回折光が回折素子１０３とコリメートレンズ１０４とを通り、対物レンズ１０５によって光記録媒体１０６上へ集光される。すなわち、０次回折光を光記録媒体１０６の記録トラックのピット上へ集光させるとともに、上記２つの±１次回折光を、光記録媒体１０６に対してトラックと直交方向へわずかにずれ、トラック方向へより大きくずれた位置であり、かつ上記０次回折光に関して互いに対称な位置へ集光させる。
【０００６】
そして、光記録媒体１０６によって反射された反射光は、対物レンズ１０５、コリメートレンズ１０４を通り、回折素子１０３で回折され、その＋１次回折光が受光素子１０７の受光部へ導かれて光量が検出される。
【０００７】
回折素子１０３は、図８に示すように、光記録媒体１０６のトラック方向と垂直な分割線ＤＬによって領域１０３ａとこれに対向する部分に分割され、この対向する部分をさらにトラック方向と平行な分割線ＰＬによって領域１０３ｂと１０３ｃに分割されている。また、受光素子１０７は、複数領域に分割された６つの受光部１０７ａ，１０７ｂ，１０７ｃ，１０７ｄ，１０７ｅ，１０７ｆを有している。
【０００８】
合焦状態のときには、回折素子１０２による０次回折光、＋１次回折光、−１次回折光のそれぞれの反射戻り光が回折素子１０３の領域１０３ａによって回折された＋１次回折光を、受光素子１０７にそれぞれ回折限界近くまで絞られたスポットを形成するように集光させる。このとき、０次回折光の反射戻り光は受光素子１０７の受光部１０７ａと１０７ｂの分割線上に、＋１次回折光の反射戻り光は受光素子１０７の受光部１０７ｃに、−１次回折光の反射戻り光は受光素子１０７の受光部１０７ｄにそれぞれ集光される。
【０００９】
さらに、回折素子１０２による０次回折光の反射戻り光が回折素子１０３の領域１０３ｂによって回折された＋１次回折光を、受光素子１０７の受光部１０７ｅに、また、回折素子１０２による０次回折光の反射戻り光が回折素子１０３の領域１０３ｃによって回折された＋１次回折光を、受光素子１０７の受光部１０７ｆに、それぞれ回折限界近くまで絞られたスポットを形成するように集光させる。
【００１０】
受光素子１０７の受光部１０７ａ，１０７ｂ，１０７ｃ，１０７ｄ，１０７ｅ，１０７ｆの出力信号をそれぞれＳ_a，Ｓ_b，Ｓ_c，Ｓ_d，Ｓ_e，Ｓ_fとした場合、フォーカス誤差信号ＦＥＳは（Ｓ_a−Ｓ_b）、トラッキング誤差信号は３ビーム法（ＴＥＳ２）の場合は（Ｓ_c−Ｓ_d）、プッシュプル法（ＴＥＳ１）の場合は（Ｓ_e−Ｓ_f）によりそれぞれ得られる。また、記録情報信号であるピット信号（ＲＦ）は（Ｓ_a＋Ｓ_b＋Ｓ_e＋Ｓ_f）により得られる。
【００１１】
【発明が解決しようとする課題】
しかしながら、上記のような従来の光ヘッド装置には以下のような問題点があった。すなわち、光記録媒体からの反射戻り光は回折素子で回折されて受光素子上に回折限界近くまで絞られた光ビームとなって集光される。さらに光情報の記録時には、光記録媒体上において再生時の光強度の数倍以上の光出力が必要となるため、当然受光素子上での光強度も数倍以上となる。このように、受光素子において高強度の光ビームが集中した場合、一般的には空間電界効果により受光素子の周波数応答特性が著しく劣化するため、高倍速記録が困難であるという問題点があった。
【００１２】
本発明は、従来技術が有していた前述のような問題点を解決するものであり、記録時における受光素子への入射光強度を低く抑えて周波数応答特性の劣化を防止でき、高倍速記録が可能な光ヘッド装置を提供することを目的とする。
【００１３】
【課題を解決するための手段】
本発明は、レーザ光源からの光を光記録媒体に導き、前記光記録媒体からの反射光をホログラフィックビームスプリッタで回折させて受光素子により検出する、光情報の記録および再生を行う光ヘッド装置において、前記反射光は、前記ホログラフィックビームスプリッタで回折され、＋１次の回折光の光強度と−１次の回折光の光強度と、が異なるとともに、前記＋１次の回折光と前記−１次の回折光がそれぞれ異なる受光素子に入射し、前記それぞれの回折光が入射する前記それぞれの受光素子が、光情報の記録時と再生時とで切り替えて使用されることを特徴とする光ヘッド装置を提供する。
【００１４】
また、好ましくは、前記光情報の記録時に、前記＋１次の回折光と前記−１次の回折光のうち、小さい方の光強度となる回折光を検出する受光素子が使用され、
かつ、前記光情報の再生時に、前記＋１次の回折光と前記−１次の回折光のうち、大きい方の光強度となる回折光を検出する受光素子が使用されるように選択される上記の光ヘッド装置を提供する。
【００１５】
また、好ましくは、前記ホログラフィックビームスプリッタにおける回折格子の一つの断面形状のうち、一方が垂線で他方が斜線である鋸歯状または前記鋸歯状を階段状に近似した形状を有する上記の光ヘッド装置を提供する。
【００１６】
また、レーザ光源からの光を光記録媒体に導き、前記光記録媒体からの反射光を受光素子により検出する、光情報の記録および再生を行う光ヘッド装置において、前記光記録媒体からの反射光を回折させて異なる受光素子に入射させるとともに、＋１次の回折光の強度および−１次の回折光の強度が異なっている回折素子を有し、前記それぞれの回折光が入射する受光素子が、光情報の再生時と記録時とで切り替えて使用されることを特徴とする光ヘッド装置を提供する。
【００１７】
光記録媒体からの反射光をホログラフィックビームスプリッタで回折させて受光素子により検出する光ヘッド装置において、記録時と再生時とで異なる受光素子を使用し、好ましくはそれぞれ異なる受光素子に入射する＋１次および−１次の回折光の強度が異なるように、すなわち回折光の＋１次回折効率と−１次回折効率を非対称にすることにより、記録時における受光素子への入射光強度を低く抑えて周波数応答特性の劣化を防止できるようになり、高倍速記録に対応可能となる。
【００１８】
また、ホログラフィックビームスプリッタにおける回折格子の一つの断面形状が一方が垂線で他方が斜線である鋸歯状、あるいは階段状で前記鋸歯状に近似した形状を有するもの、すなわち回折格子をブレーズ化もしくは疑似ブレーズ化したものを用いることにより、回折格子の一つの大きさ（高さおよび深さ）を変化させることで回折光の＋１次回折効率と−１次回折効率との割合を任意に設定可能となる。
【００１９】
【発明の実施の形態】
以下、図面を参照して本発明の実施の形態を説明する。
図１ないし図６は本発明の光ヘッド装置の一実施形態に係り、図１は光ヘッド装置の基本構成を示す斜視図、図２は回折素子として用いられるホログラフィックビームスプリッタ周辺の構成を示す側面図、図３は受光素子の出力よりフォーカス誤差信号およびトラッキング誤差信号を得る構成を模式的に示す説明図、図４は疑似ブレーズ化したホログラフィックビームスプリッタの回折格子一周期当たりの段差形状を示す説明図、図５は図４のような構成の回折素子における格子高さに対する回折効率の計算例を示すグラフ、図６は受光素子の入射光強度に対する遮断周波数の測定例を示すグラフである。
【００２０】
本実施形態に係る光ヘッド装置は、ＣＤ−Ｒ、ＣＤ−ＲＷ、ＤＶＤ−Ｒ、ＤＶＤ＋ＲＷなどの記録用光ディスクまたは光磁気ディスクなど、レーザ光の照射により光学的に情報記録が可能な光記録媒体に対して情報の書き込みおよび読み取りなどを行う光学情報記録再生装置に用いられる。
【００２１】
図１に示すように、光ヘッド装置は、レーザ光源としての半導体レーザ１、半導体レーザ１の次段に配設され半導体レーザ１からの出射光を回折するための回折素子２、回折素子２の次段に配設され光記録媒体６からの反射光を回折するための回折素子３、回折素子３の次段に配設された半導体レーザ１の発振波長の１／４倍の位相差を有する１／４波長板９、１／４波長板９の次段に配設されレーザ光を平行光線とするためのコリメートレンズ４、コリメートレンズ４の次段に配設されレーザ光を集光するための対物レンズ５、回折素子３からの＋１次回折光を受光する受光素子７、回折素子３からの−１次回折光を受光する受光素子８を有している。また、回折素子２の近傍に配設された反射型ホログラフィック光学素子１０と、この反射型ホログラフィック光学素子１０からの＋１次回折光を受光する受光素子１１を有している。
【００２２】
半導体レーザ１は、例えば発振中心波長７８５ｎｍのものが用いられる。なお、図１において、半導体レーザ１は共振発光方向と光軸方向とが平行となるように配置した例を示しているが、共振発光方向と光軸方向とが垂直となるように配置し、反射プリズムなどにより出射光を反射させて折り返すような構成とすることもできる。
【００２３】
回折素子３は、図２に示すように、光記録媒体からの反射戻り光を回折させて＋１次回折光と−１次回折光を受光素子７，８へそれぞれ導くように、回折格子の一つの断面形状が一方が垂線で他方が斜線である鋸歯状のブレーズ化された回折格子により構成される。ここで、１は半導体レーザ、９は１／４波長板である。また、回折素子３は、ガラス、ポリオレフィンなどの無機または有機の基板の表面に凹凸を形成したものや、光学的に等方性の部材の凹凸と液晶などの光学的な異方性材料とを組合せたものや、高分子液晶などの異方性材料の凹凸と等方性の部材とを組み合わせたホログラムタイプのものなどでもよい。さらに、多段の階段状の格子で鋸歯状のブレーズ型の回折格子を近似した疑似ブレーズ型のものでもよい。
【００２４】
回折素子３の格子は、ドライエッチングまたはウェットエッチングや、射出成形や、プレスなどによって形成できる。これによって、半導体レーザ１からの出射光を透過するとともに光記録媒体６からの反射光を回折するようなビームスプリッタ機能を持たせることが可能である。回折素子３としては、往路透過率（往路０次回折効率）を高くすることができる点、および往復の光利用効率を大きくすることができる点を考慮し、往路では位相差（屈折率差）が小さく、復路で位相差（屈折率差）が大きくなる偏光型ホログラフィックビームスプリッタを用いるのがより好ましい。
【００２５】
ここで、回折素子３は、図１および図３に示すように、光記録媒体６のトラック方向と垂直な分割線ＤＬによって領域３ａとこれに対向する部分に分割され、この対向する部分をさらにトラック方向と平行な分割線ＰＬによって領域３ｂと３ｃに分割されている。
【００２６】
反射型ホログラフィック光学素子１０は、例えば回折素子２と同一面上に配置し、この面上に凹凸を形成した後、Ａｌなどにより反射ミラーを形成して構成される。なお、この反射型ホログラフィック光学素子１０においてもブレーズ化することにより＋１次の回折効率を上げることもできる。さらに、回折素子２，３、反射型ホログラフィック光学素子１０、および１／４波長板９は、積層することにより一素子化することが小型化の点で好ましい。
【００２７】
また、受光素子７は、複数領域に分割された６つの受光部７ａ，７ｂ，７ｃ，７ｄ，７ｅ，７ｆを有しており、同様に受光素子８は、複数領域に分割された６つの受光部８ａ，８ｂ，８ｃ，８ｄ，８ｅ，８ｆを有している。そして、これらの受光部７ａ〜７ｆ，８ａ〜８ｂの出力に基づいて、それぞれの受光素子ごとにフォーカス誤差信号、トラッキング誤差信号、および記録情報信号であるピット信号を生成する演算回路が設けられている。また、それぞれの受光素子７，８の出力に基づいて生成されたフォーカス誤差信号、トラッキング誤差信号、およびピット信号をいずれかに切り替える切替スイッチ１３ａ，１３ｂ，１３ｃが設けられている。なお、受光素子７，８，１１は、図示しない電流電圧変換アンプ、切替スイッチなどの回路と一体化して、ＩＣ化したものを使用することが好ましい。
【００２８】
次に、本実施形態の動作について具体的に説明する。往路においては、半導体レーザ１より出射したレーザ光を、回折素子２で０次回折光と±１次回折光との３つに分割回折させ、この３つの回折光を回折素子３、１／４波長板９、およびコリメートレンズ４を通して、対物レンズ５によって光記録媒体６上へ集光させる。すなわち、０次回折光を光記録媒体６の記録トラックのピット上へ集光させるとともに、上記２つの±１次回折光を、光記録媒体６に対してトラックと直交方向へわずかにずれ、トラック方向へより大きくずれた位置であり、かつ上記０次回折光に関して互いに対称な位置へ集光させる。
【００２９】
そして復路においては、光記録媒体６によって反射された反射光を、対物レンズ５、コリメートレンズ４、１／４波長板９を通して、回折素子３で回折させ、その＋１次回折光を受光素子７に、−１次回折光を受光素子８にそれぞれ導く。このときの光記録媒体６からの反射戻り光の偏光方向は、１／４波長板９により半導体レーザ１の出射光の偏光方向（Ｐ偏光）に対して９０度回転した偏光方向（Ｓ偏光）に変換されている。
【００３０】
合焦状態のときには、回折素子２による０次回折光、＋１次回折光、−１次回折光のそれぞれの反射戻り光が回折素子３の領域３ａによって回折された＋１次回折光を受光素子７に、−１次回折光を受光素子８にそれぞれ回折限界近くまで絞られたスポットを形成するように集光させる。このとき、０次回折光の反射戻り光に関する＋１次回折光は受光素子７の受光部７ａと７ｂの分割線上に、その−１次回折光は受光素子８の受光部８ａと８ｂの分割線上に、＋１次回折光の反射戻り光に関する＋１次回折光は受光素子７の受光部７ｃに、ぞの−１次回折光は受光素子８の受光部８ｃに、−１次回折光の反射戻り光に関する＋１次回折光は受光素子７の受光部７ｄに、その−１次回折光は受光素子８の受光部８ｄにそれぞれ集光される。
【００３１】
さらに、回折素子２による０次回折光の反射戻り光が回折素子３の領域３ｂによって回折された＋１次回折光を受光素子７の受光部７ｅに、その−１次回折光を受光素子８ｅに、また、回折素子２による０次回折光の反射戻り光が回折素子３の領域３ｃによって回折された＋１次回折光を受光素子７の受光部７ｆに、その−１次回折光を受光素子８ｆにそれぞれ回折限界近くまで絞られたスポットを形成するように集光させる。ここで、波長７８５ｎｍのレーザ光の場合において、集光スポット径は約１０μｍであった。
【００３２】
なお、再生時および記録時には、半導体レーザ１からの出射光のうち、実際に対物レンズ５に導かれない光の一部を、反射型ホログラフィック光学素子１０により受光素子１１上に反射集光させ、半導体レーザ１の光出力をモニタしている。具体的には、受光素子１１より出力されるモニタ信号を用いて、外部の駆動回路（自動出力制御（ＡＰＣ）回路など）により半導体レーザ１の光出力を制御している。また、再生時と記録時との動作切り替えについても、外部の制御回路などにより行っている。
【００３３】
次いで、フォーカス誤差信号およびトラッキング誤差信号の検出方法について図３を用いて説明する。光記録媒体に記録された情報の再生時には、切替スイッチ１３ａ，１３ｂ，１３ｃを作動させて受光素子７の出力を選択するように切り替え、受光部７ａ〜７ｆの出力信号に基づいてフォーカス誤差信号（ＦＥＳ）、トラッキング誤差信号（ＴＥＳ）、およびピット信号（ＲＦ）を得る。受光素子７の受光部７ａ，７ｂ，７ｃ，７ｄ，７ｅ，７ｆの出力信号をそれぞれＨ_a，Ｈ_b，Ｈ_c，Ｈ_d，Ｈ_e，Ｈ_fとした場合、フォーカス誤差信号（ＦＥＳ１）は（Ｈ_a−Ｈ_b）、トラッキング誤差信号は３ビーム法（ＴＥＳ２）の場合は（Ｈ_c−Ｈ_d）、プッシュプル法（ＴＥＳ１）の場合は（Ｈ_e−Ｈ_f）によりそれぞれ得られる。また、ピット信号（ＲＦ１）は（Ｈ_a＋Ｈ_b＋Ｈ_e＋Ｈ_f）により得られる。
【００３４】
なお、記録時と再生時とで受光素子７，８を切り替えるための信号は、装置本体の制御回路などより出力される外部切替信号を用い、その外部切替信号により切替スイッチ１３ａ，１３ｂ，１３ｃを作動させる。
【００３５】
また、光記録媒体６への情報の記録時には、切替スイッチ１３ａ，１３ｂ，１３ｃを作動させて受光素子８の出力を選択するように切り替え、受光部８ａ〜８ｆの出力信号に基づいてフォーカス誤差信号、トラッキング誤差信号、およびＲＦ信号を得る。受光素子８の受光部８ａ，８ｂ，８ｃ，８ｄ，８ｅ，８ｆの出力信号をそれぞれＬ_a，Ｌ_b，Ｌ_c，Ｌ_d，Ｌ_e，Ｌ_fとした場合、フォーカス誤差信号（ＦＥＳ２）は（Ｌ_a−Ｌ_b）、トラッキング誤差信号は３ビーム法（ＴＥＳ４）の場合は（Ｌ_c−Ｌ_d）、プッシュプル法（ＴＥＳ３）の場合は（Ｌ_e−Ｌ_f）によりそれぞれ得られる。また、ピット信号（ＲＦ２）は（Ｌ_a＋Ｌ_b＋Ｌ_e＋Ｌ_f）により得られる。
【００３６】
次に、回折素子３の構成および作用について詳細に説明する。回折素子の例を図４および図５に示す。図４は三段の階段状の格子を形成して疑似ブレーズ化した回折素子の一周期当たりの段差形状を、図５は図４の段差形状の回折素子における回折効率の計算結果をそれぞれ示したものである。本実施形態では、階段状の疑似ブレーズ化した回折素子を用いることによって、＋１次回折光と−１次回折光とで回折効率を非対称にする。
【００３７】
この例において、段差形状は、図４に示すように、回折格子の一周期あたりの規格化長さ（一周期の長さを１としたときの各段の長さ割合）を、一段目：４０％、二段目：４５％、三段目：１５％とし、一周期あたりの規格化高さ（一段目と三段目の高低差を１としたときの高さ割合）を、一段目：０％、二段目：２９％、三段目：７１％とした。また計算条件は、回折格子の一周期の長さ（ピッチ）を３．５μｍ、屈折率差（Δｎ）を０．１３、レーザ光の中心波長を７８５ｎｍとした。図５は、上記条件において、格子高さ（一段目と三段目の高低差）をパラメータとしたときの回折効率の計算結果である。この図５において、実線は−１次と＋１次との回折効率比、破線は＋１次の回折効率、二点破線は−１次の回折効率をそれぞれ百分率（％）で示している。
【００３８】
図５の計算結果から、格子高さを変えることによって±１次の回折効率比を任意に選べることがわかる。具体的には、格子高さを約２８００ｎｍにすることにより、＋１次の回折効率に対する−１次の回折効率の比を５１：１にした偏光型疑似ブレーズホログラフィックビームスプリッタが実現できる。
【００３９】
また、上記疑似ブレーズ格子の本例と矩形格子の比較例とのそれぞれにおける、回折効率および受光素子入射光強度の測定例を表１に示す。ここで、受光素子入射光強度は、光記録媒体の板面上での光強度を再生時は１ｍＷ、記録時は４９ｍＷとし、光記録媒体の反射率を７５％、回折素子２の０次回折効率を８０％、その他の光学素子の透過率を９５％とした場合の受光部７ａおよび７ｂと受光部８ａおよび８ｂへのそれぞれの入射光強度換算値である。
【００４０】
【表１】

【００４１】
さらに、受光部７ａとほぼ同等の受光面積を有するＳｉ−ＰＩＮフォトダイオードの入射光強度に対する遮断周波数特性の測定例を図６に示す。ここで、入射光の集光スポットは約１０μｍ、波長は７８０ｎｍとした。
【００４２】
表１および図６に示すように、回折素子３に矩形格子を用いるかあるいは記録時と再生時とで受光素子の切り替えを行わない場合、記録時には受光部８ａ，８ｂの分割線上の入射光強度は４．９ｍＷ程度となり、受光素子の遮断周波数は再生時と比べて１桁近く低くなる。この場合、受光素子の周波数応答特性が著しく劣化してしまうため、高倍速記録が困難である。
【００４３】
これに対して、本実施形態のようにブレーズ化または疑似ブレーズ化した回折素子３を用い、＋１次と−１次の回折効率を変えてそれぞれの回折光を異なる受光素子７，８に入射させ、再生時と記録時とで受光素子を切り替える場合は、受光部７ａ，７ｂおよび８ａ，８ｂにおける入射光強度は記録時、再生時共に約７０μＷとなる。したがって、受光素子の周波数応答特性の劣化を防止でき、十分高速応答可能であり、高倍速記録が可能となった。なお、ここで高い周波数応答特性を確保するために、回折素子の回折効率を下げることも考えられるが、この場合は再生時において受光素子への入射光強度が大きく減少して、十分なＳ／Ｎが得られない。
【００４４】
なお、本発明は、上述の実施形態にのみ限定されるものではなく、上述の実施形態ではフォーカス誤差検出方式としてフーコー法を用いた構成を例にとって説明したが、その他の方式、例えばＳＳＤ（スポットサイズディテクション法）などのフォーカス誤差検出方式による光ヘッド装置においても適用できる。
【００４５】
このように本実施形態では、ブレーズ化または疑似ブレーズ化した回折素子を用い、その＋１次と−１次の回折効率を変えて強度が異なる＋１次と−１次の回折光をそれぞれ異なる受光素子に入射させ、再生時と記録時とで受光素子を切り替えて使用することにより、記録時において使用する受光素子への入射光強度を低く抑えて、受光素子の周波数応答特性の劣化を回避することができ、高倍速記録に対応できる。
【００４６】
【発明の効果】
以上説明したように本発明によれば、光記録媒体からの反射光をホログラフィックビームスプリッタで回折させて受光素子により検出する光ヘッド装置において、記録時と再生時とで異なる受光素子を使用し、好ましくはそれぞれ異なる受光素子に入射する＋１次および−１次の回折光の強度が異なるようにすることにより、記録時における受光素子への入射光強度を低く抑えて周波数応答特性の劣化を防止することができ、高倍速記録が可能な光ヘッド装置を提供できる効果がある。
【図面の簡単な説明】
【図１】本発明の一実施形態に係る光ヘッド装置の基本構成を示す斜視図である。
【図２】本発明の一実施形態に係る回折素子として用いられるホログラフィックビームスプリッタ周辺の構成を示す側面図である。
【図３】本発明の一実施形態に係るフォーカス誤差信号およびトラッキング誤差信号を得る構成を模式的に示す説明図である。
【図４】本発明の一実施形態に係る三段の階段状に疑似ブレーズ化したホログラフィックビームスプリッタの回折格子一周期当たりの段差形状を示す説明図である。
【図５】図４のような構成の回折素子における格子高さに対する回折効率の計算例を示すグラフである。
【図６】受光素子の入射光強度に対する遮断周波数の測定例を示すグラフである。
【図７】従来の光ヘッド装置の一例を示す斜視図である。
【図８】従来の光ヘッド装置に係るフォーカス誤差信号およびトラッキング誤差信号を得る構成を模式的に示す説明図である。
【符号の説明】
１半導体レーザ
２，３回折素子
４コリメートレンズ
５対物レンズ
６光記録媒体
７，８，１１受光素子
７ａ〜７ｆ，８ａ〜８ｆ受光部
９１／４波長板
１０反射型ホログラフィック光学素子
１３ａ，１３ｂ，１３ｃ切替スイッチ[0001]
BACKGROUND OF THE INVENTION
The present invention writes information to an optical recording medium capable of optically recording information by irradiation with laser light, such as a recording optical disk such as CD-R, CD-RW, DVD-R, DVD + RW, or magneto-optical disk. The present invention relates to an optical head device for performing reading or erasing.
[0002]
[Prior art]
Optical elements such as lenses and diffractive elements, semiconductor lasers, and light-receiving elements are used to write information to and read information from optical recording media such as optical disks such as CDs and DVDs, or magneto-optical disks. An optical head device provided is used.
[0003]
As an example of a conventional optical head device, a device described in Japanese Patent No. 2767487 will be described with reference to FIGS. FIG. 7 is a perspective view showing a basic configuration of a conventional optical head device, and FIG. 8 is an explanatory diagram schematically showing a configuration for obtaining a focus error signal and a tracking error signal according to the conventional optical head device.
[0004]
The optical head device includes a semiconductor laser 101 as a light source,

diffractive elements

102, 103, which are disposed in the next stage of the semiconductor laser 101 and diffract light emitted from the semiconductor laser 101 and reflected light from the optical recording medium 106, respectively. A collimating lens 104 arranged at the next stage of the

diffractive elements

102 and 103 to make the laser beam parallel light, an objective lens 105 arranged at the next stage of the collimating lens 104 and condensing the laser light, and the diffractive element 103. The light receiving element 107 that receives the diffracted light from the light receiving element 107 is provided.
[0005]
In the above configuration, the laser light emitted from the semiconductor laser 101 is split and diffracted into three of zero-order diffracted light and ± first-order diffracted light by the diffraction element 102, and these three diffracted lights are diffracted by the diffraction element 103 and the collimating lens 104. Then, the light is condensed on the optical recording medium 106 by the objective lens 105. That is, the 0th-order diffracted light is condensed on the pits of the recording track of the optical recording medium 106, and the two ± 1st-order diffracted lights are slightly shifted in the direction perpendicular to the track with respect to the optical recording medium 106 in the track direction. The light beams are condensed at positions that are more greatly shifted and symmetrical with respect to the 0th-order diffracted light.
[0006]
The reflected light reflected by the optical recording medium 106 passes through the objective lens 105 and the collimating lens 104, is diffracted by the diffraction element 103, and the + 1st order diffracted light is guided to the light receiving portion of the light receiving element 107 to detect the amount of light. The
[0007]
As shown in FIG. 8, the diffraction element 103 is divided into a region 103a and a portion facing the region 103a by a dividing line DL perpendicular to the track direction of the optical recording medium 106, and the facing portion is further divided in parallel with the track direction. It is divided into regions 103b and 103c by a line PL. The light receiving element 107 has six light receiving

portions

107a, 107b, 107c, 107d, 107e, and 107f divided into a plurality of regions.
[0008]
In the in-focus state, the + 1st-order diffracted light obtained by diffracting the 0th-order diffracted light, the + 1st-order diffracted light, and the −1st-order diffracted light by the region 103a of the diffractive element 103 is diffracted by the light receiving element 107. The light is condensed so as to form a spot narrowed to the limit. At this time, the reflected return light of the 0th order diffracted light is on the dividing line of the light receiving portions 107a and 107b of the light receiving element 107, the reflected return light of the + 1st order diffracted light is reflected on the light receiving portion 107c of the light receiving element 107, and the reflected return light of the −1st order diffracted light. Are condensed on the light receiving portion 107d of the light receiving element 107, respectively.
[0009]
Further, the + 1st order diffracted light obtained by diffracting the reflected return light of the 0th order diffracted light by the diffraction element 102 by the region 103b of the diffractive element 103 is reflected on the light receiving portion 107e of the light receiving element 107, and the 0th order diffracted light is reflected back by the diffraction element 102. The + 1st order diffracted light diffracted by the region 103c of the diffractive element 103 is condensed on the light receiving portion 107f of the light receiving element 107 so as to form spots that are narrowed to near the diffraction limit.
[0010]
Receiving portion 107a of the light receiving

element

107, 107b, 107c, 107d, 107e, respectively the output signal of _{_{107f S a, S b, S}} c, S d, S e, when the S _f, the focus error signal FES is (S _a− S _b ), the tracking error signal is obtained by (S _c −S _d ) in the case of the three beam method (TES2), and (S _e −S _f ) in the case of the push pull method (TES1). A pit signal (RF) that is a recording information signal is obtained by (S _a + S _b + S _e + S _f ).
[0011]
[Problems to be solved by the invention]
However, the conventional optical head device as described above has the following problems. That is, the reflected return light from the optical recording medium is diffracted by the diffractive element and collected as a light beam focused on the light receiving element close to the diffraction limit. Further, when optical information is recorded, the light output on the optical recording medium is several times greater than the light intensity at the time of reproduction, and therefore the light intensity on the light receiving element naturally becomes several times or more. As described above, when a high-intensity light beam is concentrated in the light receiving element, generally, the frequency response characteristic of the light receiving element is significantly deteriorated due to the spatial electric field effect, which makes it difficult to perform high-speed recording. .
[0012]
The present invention solves the above-mentioned problems of the prior art, and can suppress the deterioration of frequency response characteristics by suppressing the incident light intensity to the light receiving element at the time of recording. An object of the present invention is to provide an optical head device capable of achieving the above.
[0013]
[Means for Solving the Problems]
The present invention guides light from the laser light source to the optical recording medium is detected by the light receiving element by diffracting the light reflected from the optical recording medium by a holographic beam splitter, the optical head device for recording and reproducing optical information The reflected light is diffracted by the holographic beam splitter, the light intensity of the + 1st order diffracted light and the light intensity of the −1st order diffracted light are different, and the + 1st order diffracted light and the −1st order diffracted light are different. An optical head characterized in that the next diffracted light is incident on different light receiving elements, and the respective light receiving elements on which the respective diffracted lights are incident are switched between recording and reproducing optical information. Providing equipment.
[0014]
Preferably, at the time of recording the optical information, a light receiving element that detects diffracted light having a smaller light intensity of the + 1st order diffracted light and the −1st order diffracted light is used.
And, during reproduction of the optical information, of said + 1-order diffracted light the -1-order diffracted light, Ru is selected as the light receiving element for detecting the diffracted light as the light intensity of the larger one is used above An optical head device is provided.
[0015]
Also, preferably, among the one cross-sectional shape of the diffraction grating in the holographic beam splitter, said optical one is having a serrated or shape approximating the previous SL serrated stepwise the other is shaded by perpendicular A head device is provided.
[0016]
Further, guide the light from the laser light source to the optical recording medium, it detects the light reflected from the optical recording medium by the light receiving element, an optical head device for recording and reproducing optical information, light reflected from the optical recording medium together to enter the different light receiving element diffracts, a plurality of diffraction elements are different intensities of + 1st order of the intensity of the diffracted light and the -1st-order diffracted light, the light receiving elements wherein each of the diffracted light incident, Provided is an optical head device that is used by switching between reproducing and recording optical information .
[0017]
In an optical head device that diffracts reflected light from an optical recording medium with a holographic beam splitter and detects it with a light receiving element , different light receiving elements are used for recording and reproduction, and preferably incident on different light receiving elements + 1 By making the + 1st order diffraction efficiency and the −1st order diffraction efficiency of the diffracted light asymmetric so that the intensities of the 1st order and −1st order diffracted light are different, the incident light intensity to the light receiving element during recording can be kept low. Deterioration of frequency response characteristics can be prevented, and high-speed recording can be supported.
[0018]
In addition, one of the diffraction gratings in the holographic beam splitter has a sawtooth shape in which one is a perpendicular line and the other is a slanted line, or a stepped shape approximate to the sawtooth shape, that is, the diffraction grating is blazed or pseudo-simulated. By using a blazed one, the ratio between the + 1st order diffraction efficiency and the −1st order diffraction efficiency of the diffracted light can be arbitrarily set by changing one size (height and depth) of the diffraction grating. Become.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
1 to 6 relate to one embodiment of an optical head device of the present invention, FIG. 1 is a perspective view showing a basic configuration of the optical head device, and FIG. 2 shows a configuration around a holographic beam splitter used as a diffraction element. FIG. 3 is a side view, FIG. 3 is an explanatory view schematically showing a configuration for obtaining a focus error signal and a tracking error signal from the output of the light receiving element, and FIG. 4 shows a step shape per one period of the diffraction grating of the holographic beam splitter that is pseudo-blazed. FIG. 5 is a graph showing a calculation example of the diffraction efficiency with respect to the grating height in the diffraction element configured as shown in FIG. 4, and FIG. 6 is a graph showing a measurement example of the cutoff frequency with respect to the incident light intensity of the light receiving element. .
[0020]
The optical head device according to this embodiment is an optical recording medium capable of optically recording information by laser light irradiation, such as a recording optical disk such as a CD-R, a CD-RW, a DVD-R, a DVD + RW, or a magneto-optical disk. Is used in an optical information recording / reproducing apparatus for writing and reading information on and off.
[0021]
As shown in FIG. 1, the optical head device includes a semiconductor laser 1 as a laser light source, a diffraction element 2 that is disposed in the next stage of the semiconductor laser 1, and diffracts light emitted from the semiconductor laser 1. A diffraction element 3 for diffracting reflected light from the optical recording medium 6 disposed in the next stage, and having a phase difference of 1/4 times the oscillation wavelength of the semiconductor laser 1 disposed in the next stage of the diffraction element 3 A quarter-wave plate 9, a collimating lens 4 disposed at the next stage of the quarter-wave plate 9 for collimating the laser light, and disposed at the next stage of the collimating lens 4 for condensing the laser light. Objective lens 5, light receiving element 7 for receiving + 1st order diffracted light from diffraction element 3, and light receiving element 8 for receiving −1st order diffracted light from diffraction element 3. In addition, it includes a reflective holographic optical element 10 disposed in the vicinity of the diffractive element 2 and a light receiving element 11 that receives + 1st order diffracted light from the reflective holographic optical element 10.
[0022]
As the semiconductor laser 1, for example, one having an oscillation center wavelength of 785 nm is used. 1 shows an example in which the semiconductor laser 1 is arranged so that the resonance light emission direction and the optical axis direction are parallel to each other, the semiconductor laser 1 is arranged so that the resonance light emission direction and the optical axis direction are perpendicular to each other. A configuration may also be adopted in which outgoing light is reflected by a reflecting prism or the like and folded.
[0023]
As shown in FIG. 2, the diffractive element 3 diffracts the reflected return light from the optical recording medium and guides the + 1st order diffracted light and the −1st order diffracted light to the light receiving elements 7 and 8, respectively. It is composed of a sawtooth blazed diffraction grating, one of which is perpendicular and the other is diagonal. Here, 1 is a semiconductor laser, and 9 is a quarter-wave plate. The diffractive element 3 is formed by forming irregularities on the surface of an inorganic or organic substrate such as glass or polyolefin, or irregularities of an optically isotropic member and an optically anisotropic material such as liquid crystal. A combination type or a hologram type combination of an uneven material of an anisotropic material such as a polymer liquid crystal and an isotropic member may be used. Furthermore, a pseudo blazed type in which a sawtooth blazed diffraction grating is approximated by a multistage stepped grating may be used.
[0024]
The grating of the diffractive element 3 can be formed by dry etching or wet etching, injection molding, pressing, or the like. As a result, it is possible to provide a beam splitter function that transmits the emitted light from the semiconductor laser 1 and diffracts the reflected light from the optical recording medium 6. The diffraction element 3 takes into account the point that it is possible to increase the forward transmittance (the zero-order diffraction efficiency of the forward route) and the point that it is possible to increase the light utilization efficiency of the round trip, the phase difference (refractive index difference) in the forward route. It is more preferable to use a polarization holographic beam splitter that has a small phase difference and a large phase difference (refractive index difference) on the return path.
[0025]
Here, as shown in FIGS. 1 and 3, the diffractive element 3 is divided into a region 3a and a portion facing it by a dividing line DL perpendicular to the track direction of the optical recording medium 6, and this facing portion is further divided. Divided into

regions

3b and 3c by a dividing line PL parallel to the track direction.
[0026]
The reflective holographic optical element 10 is configured, for example, by arranging on the same plane as the diffraction element 2 and forming irregularities on this plane, and then forming a reflective mirror with Al or the like. Note that the reflection-type holographic optical element 10 can also be blazed to increase the + 1st-order diffraction efficiency. Furthermore, it is preferable from the viewpoint of miniaturization that the

diffraction elements

2 and 3, the reflective holographic optical element 10, and the quarter-wave plate 9 are laminated to form one element.
[0027]
The light receiving element 7 has six

light receiving portions

7a, 7b, 7c, 7d, 7e, and 7f divided into a plurality of areas. Similarly, the light receiving element 8 has six light receiving parts divided into a plurality of areas. It has

parts

8a, 8b, 8c, 8d, 8e, 8f. An arithmetic circuit for generating a focus error signal, a tracking error signal, and a pit signal that is a recording information signal is provided for each light receiving element based on the outputs of the light receiving portions 7a to 7f and 8a to 8b. Yes. Further,

selector switches

13a, 13b, and 13c are provided for switching between a focus error signal, a tracking error signal, and a pit signal generated based on the outputs of the light receiving elements 7 and 8, respectively. The

light receiving elements

7, 8, and 11 are preferably integrated with circuits such as a current-voltage conversion amplifier and a changeover switch (not shown) to form an IC.
[0028]
Next, the operation of this embodiment will be specifically described. In the forward path, the laser light emitted from the semiconductor laser 1 is divided and diffracted into three of zero-order diffracted light and ± first-order diffracted light by the diffraction element 2, and these three diffracted lights are diffracted by the diffraction element 3 and the quarter wavelength plate. 9 and through the collimating lens 4, the light is condensed on the optical recording medium 6 by the objective lens 5. That is, the 0th-order diffracted light is condensed on the pits of the recording track of the optical recording medium 6 and the two ± 1st-order diffracted lights are slightly shifted from the optical recording medium 6 in the direction orthogonal to the track. The light beams are condensed at positions that are more greatly shifted and symmetrical with respect to the 0th-order diffracted light.
[0029]
In the return path, the reflected light reflected by the optical recording medium 6 is diffracted by the diffraction element 3 through the objective lens 5, the collimating lens 4, and the quarter wavelength plate 9, and the + 1st order diffracted light is transmitted to the light receiving element 7. The first-order diffracted light is guided to the light receiving element 8 respectively. The polarization direction of the reflected return light from the optical recording medium 6 at this time is a polarization direction (S-polarized light) rotated 90 degrees with respect to the polarization direction (P-polarized light) of the outgoing light of the semiconductor laser 1 by the quarter wavelength plate 9. Has been converted.
[0030]
In the in-focus state, the + 1st-order diffracted light obtained by diffracting the 0th-order diffracted light, the + 1st-order diffracted light, and the −1st-order diffracted light from the diffraction element 2 by the region 3a of the diffractive element 3 is applied to the light receiving element 7. The next diffracted light is condensed on the light receiving element 8 so as to form spots narrowed to near the diffraction limit. At this time, the + 1st order diffracted light relating to the reflected return light of the 0th order diffracted light is +1 on the dividing line of the light receiving portions 7a and 7b of the light receiving element 7, and the −1st order diffracted light is +1 on the dividing line of the light receiving portions 8a and 8b of the light receiving element 8. The + 1st order diffracted light related to the reflected return light of the 1st order diffracted light is received by the light receiving portion 7c of the light receiving element 7, the 1st order diffracted light is received by the light receiving portion 8c of the light receiving element 8, and the 1st order diffracted light related to the reflected return light of the -1st order diffracted light is received. The −1st order diffracted light is condensed on the light receiving portion 8 d of the light receiving element 8 on the light receiving portion 7 d of the element 7.
[0031]
Further, the + 1st order diffracted light obtained by diffracting the reflected return light of the 0th order diffracted light by the diffraction element 2 by the region 3b of the diffraction element 3 is transmitted to the light receiving portion 7e of the light receiving element 7, the −1st order diffracted light is transmitted to the light receiving element 8e, The + 1st order diffracted light obtained by diffracting the 0th-order diffracted light reflected by the diffraction element 2 by the region 3c of the diffractive element 3 is diffracted by the light receiving portion 7f of the light receiving element 7, and the −1st order diffracted light is received by the light receiving element 8f. The light is condensed so as to form a narrowed spot. Here, in the case of laser light having a wavelength of 785 nm, the focused spot diameter was about 10 μm.
[0032]
During reproduction and recording, a part of the light emitted from the semiconductor laser 1 that is not actually guided to the objective lens 5 is reflected and condensed on the light receiving element 11 by the reflective holographic optical element 10. The optical output of the semiconductor laser 1 is monitored. Specifically, the optical output of the semiconductor laser 1 is controlled by an external drive circuit (such as an automatic output control (APC) circuit) using the monitor signal output from the light receiving element 11. Further, the operation switching between reproduction and recording is also performed by an external control circuit or the like.
[0033]
Next, a method for detecting the focus error signal and the tracking error signal will be described with reference to FIG. When reproducing the information recorded on the optical recording medium, the

selector switches

13a, 13b and 13c are switched to select the output of the light receiving element 7, and a focus error signal (based on the output signals of the light receiving portions 7a to 7f is selected. FES), tracking error signal (TES), and pit signal (RF) are obtained. Receiving portion 7a of the

light receiving element

7, 7b, 7c, 7d, 7e, respectively H _a output signal of 7f, when a _{_{_{H b, H c, H d}}} , H e, H f, the focus error signal (FES1) is The tracking error signal is obtained by (H _a −H _b ), (H _c −H _d ) in the case of the three beam method (TES2), and (H _e −H _f ) in the case of the push pull method (TES1). The pit signal (RF1) is obtained by (H _a + H _b + H _e + H _f ).
[0034]
The signal for switching the light receiving elements 7 and 8 between recording and reproduction uses an external switching signal output from a control circuit or the like of the apparatus main body, and the

switches

13a, 13b, and 13c are switched by the external switching signal. Operate.
[0035]
Further, when information is recorded on the optical recording medium 6, the

selector switches

13a, 13b and 13c are switched to select the output of the light receiving element 8, and the focus error signal is based on the output signals of the light receiving portions 8a to 8f. Obtain a tracking error signal and an RF signal. Receiving portion 8a of the

photodetector

8, 8b, 8c, 8d, 8e, respectively L _a the output signal of 8f, when a _{_{_{L b, L c, L d}}} , L e, L f, the focus error signal (FES2) is (L _a −L _b ), the tracking error signal is obtained by (L _c −L _d ) in the case of the three beam method (TES4), and (L _e −L _f ) in the case of the push pull method (TES3). The pit signal (RF2) is obtained by (L _a + L _b + L _e + L _f ).
[0036]
Next, the configuration and operation of the diffraction element 3 will be described in detail. Examples of the diffraction element are shown in FIGS. FIG. 4 shows the step shape per period of the diffractive element formed into a pseudo-blazed structure by forming a three-step stepped grating, and FIG. 5 shows the calculation results of the diffraction efficiency in the step-shaped diffraction element of FIG. Is. In this embodiment, the diffraction efficiency is made asymmetric between the + 1st order diffracted light and the −1st order diffracted light by using a stair-like quasi-blazed diffraction element.
[0037]
In this example, as shown in FIG. 4, the step shape is the normalized length per one period of the diffraction grating (the ratio of the length of each stage when the length of one period is 1): 40%, second stage: 45%, third stage: 15%, standardized height per cycle (height ratio when the difference in height between the first and third stages is 1) : 0%, second stage: 29%, third stage: 71%. The calculation conditions were such that the length (pitch) of one period of the diffraction grating was 3.5 μm, the refractive index difference (Δn) was 0.13, and the center wavelength of the laser beam was 785 nm. FIG. 5 is a calculation result of diffraction efficiency when the grating height (difference in height between the first stage and the third stage) is used as a parameter under the above conditions. In FIG. 5, the solid line represents the -1st order and + 1st order diffraction efficiency ratio, the broken line represents the + 1st order diffraction efficiency, and the double dotted line represents the -1st order diffraction efficiency in percentage (%).
[0038]
From the calculation results of FIG. 5, it can be seen that the ± 1st-order diffraction efficiency ratio can be arbitrarily selected by changing the grating height. Specifically, by setting the grating height to about 2800 nm, a polarization type pseudo blazed holographic beam splitter in which the ratio of the −1st order diffraction efficiency to the + 1st order diffraction efficiency is 51: 1 can be realized.
[0039]
Table 1 shows measurement examples of diffraction efficiency and light receiving element incident light intensity in each of the present example of the pseudo-blazed grating and the comparative example of the rectangular grating. Here, the incident light intensity of the light receiving element is 1 mW during reproduction and 49 mW during recording, and the reflectance of the optical recording medium is 75%. This is a converted value of incident light intensity to the light receiving portions 7a and 7b and the light receiving portions 8a and 8b when the efficiency is 80% and the transmittance of other optical elements is 95%.
[0040]
[Table 1]

[0041]
Furthermore, FIG. 6 shows a measurement example of the cut-off frequency characteristics with respect to the incident light intensity of a Si-PIN photodiode having a light receiving area substantially equal to that of the light receiving portion 7a. Here, the condensing spot of incident light was about 10 μm, and the wavelength was 780 nm.
[0042]
As shown in Table 1 and FIG. 6, when a rectangular grating is used for the diffraction element 3 or when the light receiving element is not switched between recording and reproduction, the incident light intensity on the dividing line of the light receiving portions 8a and 8b is recorded. Is about 4.9 mW, and the cut-off frequency of the light receiving element is nearly one digit lower than that during reproduction. In this case, since the frequency response characteristics of the light receiving element are significantly deteriorated, high-speed recording is difficult.
[0043]
On the other hand, using the diffractive element 3 blazed or pseudo-blazed as in the present embodiment, the diffracted light of the + 1st order and the −1st order are changed and the diffracted light is made incident on different light receiving elements 7 and 8. When the light receiving element is switched between reproduction and recording, the incident light intensity at the

light receiving portions

7a, 7b and 8a, 8b is about 70 μW for both recording and reproduction. Therefore, it is possible to prevent the frequency response characteristics of the light receiving element from deteriorating, sufficiently respond at a high speed, and perform high-speed recording. Here, in order to ensure a high frequency response characteristic, the diffraction efficiency of the diffractive element may be lowered. However, in this case, the intensity of incident light on the light receiving element is greatly reduced during reproduction, and sufficient S / N cannot be obtained.
[0044]
Note that the present invention is not limited to the above-described embodiment. In the above-described embodiment, the configuration using the Foucault method as a focus error detection method has been described as an example. The present invention can also be applied to an optical head device using a focus error detection method such as a size detection method.
[0045]
As described above, in the present embodiment, a blazed or pseudo-blazed diffractive element is used, and + 1st order and −1st order diffracted lights having different intensities by changing their + 1st order and −1st order diffraction efficiencies are respectively received by different light receiving elements. By switching the light receiving element between playback and recording, the incident light intensity to the light receiving element used during recording can be kept low and deterioration of the frequency response characteristics of the light receiving element can be avoided. Can handle high-speed recording.
[0046]
【The invention's effect】
As described above, according to the present invention, in the optical head device that diffracts the reflected light from the optical recording medium by the holographic beam splitter and detects it by the light receiving element , different light receiving elements are used for recording and reproduction. Preferably, the intensity of the + 1st order and −1st order diffracted light incident on different light receiving elements is made different so that the intensity of incident light on the light receiving element during recording is kept low to prevent deterioration of frequency response characteristics. And an optical head device capable of high-speed recording can be provided.
[Brief description of the drawings]
FIG. 1 is a perspective view showing a basic configuration of an optical head device according to an embodiment of the present invention.
FIG. 2 is a side view showing a configuration around a holographic beam splitter used as a diffraction element according to an embodiment of the present invention.
FIG. 3 is an explanatory diagram schematically showing a configuration for obtaining a focus error signal and a tracking error signal according to an embodiment of the present invention.
FIG. 4 is an explanatory diagram showing a step shape per period of a diffraction grating of a holographic beam splitter pseudo-blazed in a three-step staircase shape according to an embodiment of the present invention.
5 is a graph showing a calculation example of diffraction efficiency with respect to the grating height in the diffraction element configured as shown in FIG.
FIG. 6 is a graph showing a measurement example of a cutoff frequency with respect to incident light intensity of a light receiving element.
FIG. 7 is a perspective view showing an example of a conventional optical head device.
FIG. 8 is an explanatory diagram schematically showing a configuration for obtaining a focus error signal and a tracking error signal according to a conventional optical head device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1

Semiconductor laser

2, 3 Diffraction element 4 Collimating lens 5 Objective lens 6

Optical recording medium

7, 8, 11 Light receiving element 7a-7f, 8a-8f Light receiving part 9 1/4 wavelength plate 10 Reflective holographic

optical element

13a, 13b , 13c selector switch

Claims

Directing light from a laser light source to the optical recording medium, diffract light reflected from the optical recording medium with the holographic beam splitter is detected by the light receiving element, an optical head device for recording and reproducing optical information,
The reflected light is diffracted by the holographic beam splitter, the light intensity of the + 1st order diffracted light is different from the light intensity of the −1st order diffracted light, and the + 1st order diffracted light and the −1st order diffracted light are different. Diffracted light is incident on different light receiving elements,
An optical head device characterized in that the respective light receiving elements on which the respective diffracted lights are incident are switched between recording and reproduction of optical information.

At the time of recording the optical information, a light receiving element that detects a diffracted light having a smaller light intensity among the + 1st order diffracted light and the −1st order diffracted light is used,
In addition, when the optical information is reproduced, a light receiving element that detects a diffracted light having a larger light intensity among the + 1st order diffracted light and the −1st order diffracted light is selected. Item 4. The optical head device according to Item 1.

Of one of the cross-sectional shape of the diffraction grating in the holographic beam splitter, one of claim 1 or 2 having a serrated or shape approximating the previous SL serrated stepwise the other is shaded by perpendicular Optical head device.

In an optical head device for recording and reproducing optical information, wherein light from a laser light source is guided to an optical recording medium, and reflected light from the optical recording medium is detected by a light receiving element.
Together to enter the different light receiving element by diffracting the light reflected from the optical recording medium has a diffraction element are different strength and -1 order of the intensity of the diffracted light of the + order diffracted light,
An optical head device characterized in that the light receiving elements on which the respective diffracted lights are incident are used by switching between reproducing and recording optical information .