JP4505979B2 - Optical head, light emitting / receiving element, and optical recording medium recording / reproducing apparatus - Google Patents

Description

簡単のため、ランドとグルーブの形状はともに等幅の矩形であるものとした。図６〜図１１は、Ｘ軸にラジアル方向を、Ｙ軸にタンジェンシャル方向を、Ｚ軸に戻り光の強度をそれぞれとっている。
図６は、スポットがランド上に位置しラジアル方向の合焦位置が光軸方向に−０．３５μｍシフトした状態を示す。
図７は、スポットがランド上に位置しラジアル方向の合焦位置が光軸方向でグルーブの位置に一致した状態を示す。
図８は、スポットがランド上に位置しラジアル方向の合焦位置が光軸方向に＋０．３５μｍシフトした状態を示す。
図９は、スポットがグルーブ上に位置しラジアル方向の合焦位置が光軸方向に−０．３５μｍシフトした状態を示す。
図１０は、スポットがグルーブ上に位置しラジアル方向の合焦位置が光軸方向でランドの位置に一致した状態を示す。
図１１は、スポットがグルーブ上に位置しラジアル方向の合焦位置が光軸方向に＋０．３５μｍシフトした状態を示す。
【００２１】
なお、ランドグルーブ記録においては、ランドおよびグルーブの双方に記録するため、通常のランド−ランド間又は、グルーブ−グルーブ間を意味するトラック周期で考えると、スポット径に対するトラック周期が大きいため、図１２に示すように、ディスクにおける回折光の対物レンズ瞳上における重なり方が大きく異なってくる。
図１２（Ａ）、（Ｂ）に示されているように、従来のランド記録を用いたディスク再生では、通常０次光と±１次光の全てが重なることはない。これに対して、図１２（Ｃ）、（Ｄ）に示されているように、ランドグルーブ記録を用いた場合には、０次光と±１次光が重なる。図６〜図１１において、スポット内で強度が突出している部分は、０次光と±１次光の全てが重なっている領域である。
図６〜図１１、図１２から明らかなように、スポットのラジアル方向についての光軸方向の合焦位置がずれていない状態（図７、図１０）では、スポットがランド上にあるかグルーブ上にあるかでスポット内の強度分布が変わらないのに対して、スポットのラジアル方向についての光軸方向の合焦位置がずれた状態（図６、図８、図９、図１１）では、スポット内の強度分布に差異が生じている。しかも、スポットがランド上にあるかグルーブ上にあるかで、スポット内の強度分布の傾向が逆転している。つまり、図６と図１１が同一であり、図８と図１１が同一の傾向となっている。
【００２２】
前述したように、前記各副ビームは光回折素子６５の作用によってラジアル方向についてデフォーカスされているが、タンジェンシャル方向についてはデフォーカスされておらずスポット形状が絞られた状態となっている。
図１３は、光検出素子７４の受光部７４Ａ、７４Ｂ、７４Ｃ上における、強度分布の変化の様子を模式的に示した説明図であり、図１３（Ａ）は主スポットがグルーブ上に位置した状態を示す説明図、図１３（Ｂ）は主スポットがランド上に位置した状態を示す説明図、図１３（Ｃ）は主スポットがグルーブ上に位置した状態を示す説明図、図１３（Ｄ）はラジアル方向の位置に対するトラッキングエラー信号ＴＥとランドグルーブ判別信号ＣＴＳを示す説明図である。
図１３（Ａ）、（Ｂ）、（Ｃ）に示されているように、各受光部７４Ａ、７４Ｃのうち、中央部（中央の分割領域ｒ、ｔ）の強度が大きくなる場合と、周辺部（周辺の分割領域ｈ、ｉ、ｌ、ｍ）の強度が大きくなる場合との間で変化するため、ランド・グルーブ上での強度分布の変化による、各受光部７４Ａ、７４Ｃからの出力の変化を用いて、トラック判別信号ＣＴＳを、演算式（式（４））によって得ることが可能となる。トラッキングエラー信号ＴＥは演算式（式（２））によって得られる。
なお、主スポットと２つの副スポットの光ディスクの記録面上における位置関係は、主スポットがグルーブ上のときに副スポットはランド上（図１３（Ｄ）の場合）に位置するか、主スポットがグルーブ上のときに副スポットはグルーブ上に位置するかのどちらかとなるように設定することが望ましく、どちらに設定するかによって、トラック判別信号ＣＴＳの正負が反転することになる。
【００２３】
前記光回折素子６５による光ビームのラジアル方向についての光軸方向の合焦位置のシフトは、例えば、図１４（Ａ）のように、同一の曲線パターンをタンジェンシャル方向に繰り返し配置した光回折素子６５を用いることによって実現可能である。
このように同一の曲線パターンをタンジェンシャル方向に繰り返し配置した光回折素子６５は、タンジェンシャル方向にはパワーを持たないため、タンジェンシャル方向の、どの位置を透過した光ビームに対しても、回折光に付加される収差量は同等になり、安定した特性が得られる。
２つの副スポットでは、回折する方向が異なるため、図１４（Ｂ）に示すように、透過する位置がずれてしまうが、同一パターンの繰り返しなので、位置による特性変化は発生しない。
このようにして、トラック判別信号ＣＴＳを生成することによって、ランド幅とグルーブ幅が略等しい、ランドグルーブ記録方式においても、従来使用されてきたトラッキング制御方法が使用可能となる。もちろん、ランドおよびグルーブの何れか一方に記録する方式であっても適用可能である。
【００２４】
次に、本発明の特徴であるフォーカス制御のキャリブレーションについて説明する。
既に説明したように、フォーカス制御はフォーカスエラー信号ＦＥの検出に基づいて光ヘッドの対物レンズを光軸方向に移動させるサーボ制御を行なうことによって行なわれる。
このフォーカス制御はフォーカスエラーが0になるように、つまりフォーカスエラー信号ＦＥが所定の制御目標値となる電圧値（以下フォーカスバイアスという）に一致するように制御される。前記フォーカスバイアスは周囲環境や経時変化によって光学部品や受発光素子の特性が影響を受けるなどして変化する。
先に述べたように、記録密度が高くなるにしたがってフォーカス制御の精度を上げる必要があり、前記フォーカスバイアスの変動の許容量も少なくなる。このため、前記フォーカスバイアスを常に最適となるように制御する必要がある。
第１の実施の形態では、前記２つの副スポットに基づいて検出されるトラッキングエラー信号生成用のプッシュプル信号に基づいてフォーカス制御のキャリブレーション、すなわち前記フォーカスバイアスのキャリブレーションを行なうようにしている。
すなわち、第１の実施の形態では、トラッキングエラー信号ＴＥを検出するために形成された２つの副スポットは、ラジアル方向について光軸方向の合焦位置が異なっている。つまり、２つの副スポットは、ラジアル方向についてはデフォーカスしているため、対物レンズ７０が光軸方向に移動することによって非対称な挙動を示す。このため、光検出素子７４の分割領域７４Ａ、７４Ｃから出力される検出信号も非対称的に変化する。
図１５は、対物レンズ７０のデフォーカス量（主スポットのデフォーカス量）と、式（３）に示されたトラッキングエラー信号ＴＥ＝（ｊ−ｋ）Ｋ（（ｈ−ｉ）＋（ｌ−ｍ））のうち、プッシュプル信号ＳＰＰ１＝（ｈ−ｉ）、ＳＰＰ２＝（ｌ−ｍ）の振幅との関係を示す特性図であり、前記デフォーカス量を横軸に、プッシュプル信号の振幅を縦軸にとっている。
なお、前記プッシュプル信号ＳＰＰ１、ＳＰＰ２は特許請求の範囲の第１、第２プッシュプル信号に相当し、前記信号値ｈ、ｉは特許請求の範囲の第１、第２信号に相当し、信号値ｌ、ｍは特許請求の範囲の第３、第４信号に相当している。
【００２５】
図１５に示されているように、主スポットのデフォーカス量に対するプッシュプル信号ＳＰＰ１、ＳＰＰ２の振幅は、互いに傾きが逆となる特性を有している。したがって、プッシュプル信号ＳＰＰ１、ＳＰＰ２の振幅の値に基づいて前記デフォーカス量に対応する値を求めることができる。つまり、プッシュプル信号ＳＰＰ１、ＳＰＰ２によってデフォーカス検出用信号が構成される。
副スポットのプッシュプル信号ＳＰＰ１、ＳＰＰ２の振幅をそれぞれＳＰＰ１Ａ、ＳＰＰ２Ａと表記すると、フォーカスキャリブレーション関数はたとえば以下に示す式（５）で生成することができる。
Ｙ＝（ＳＰＰ１Ａ−ＳＰＰ２Ａ）／（ＳＰＰ１Ａ＋ＳＰＰ２Ａ） （５）
図１６は、副スポットのラジアル方向のデフォーカス量を±０．３５μｍとした場合における前記キャリブレーション関数の計算例である。横軸Ｘはデフォーカス量、縦軸Ｙはデフォーカス量に対応するキャリブレーション値（以下関数値という）である。
図１６に示されているように、±０．１５umの領域でほぼ直線的な挙動を示している。これにより、前記フォーカスキャリブレーション関数の関数値から、デフォーカス量を逆算することが可能である。
例えば、図１に示したサーボ制御回路１０９で行なわれるフォーカス制御によって前記フォーカスバイアスが０となるように制御された状態において、前記フォーカスキャリブレーション関数の関数値に対応するデフォーカスを求め、該デフォーカスを補正する量に見合うよう前記フォーカスバイアスを補正することフォーカス制御を補正して最適フォーカス位置を維持することができる。
【００２６】
図１７は、上述したように関数値に基づいてフォーカスエラー信号の補正を行なう部分の構成を示すブロック図である。
図１７に示されているように、プッシュプル信号生成部１２１は、プリアンプ１２０から出力される検出信号ｈ、ｉ、ｌ、ｍを入力して、前記プッシュプル信号の振幅ＳＰＰ１Ａ，ＳＰＰ２Ａを生成するように構成されている。
補正部１２２は、前記プッシュプル信号生成部１２１から入力される前記プッシュプル信号の振幅ＳＰＰ１Ａ，ＳＰＰ２Ａから前記キャリブレーション関数を前記式（５）に基づいて求めるとともに、このキャリブレーション関数を記憶するように構成されている。
フォーカスサーボ制御部１０９Ａは、サーボ制御回路１０９内でプリアンプ１２０から入力されるフォーカスエラー信号ＦＥに基づいてフォーカスサーボ制御を行なうものであり、前記補正部１２１から入力される前記キャリブレーション関数の関数値に基づいて前記フォーカスバイアスをシフトするように構成されている。
次に、動作について説明する。
予め、環境変化や経時変化がない状態における、前記キャリブレーション関数の関数値を基準の関数値として前記補正部１２２に記憶しておく。
その後、例えば所定の時間毎に、または周囲の温度によって、電源投入時、ディスク交換時、等のタイミングで、前記関数値がどうなっているかを検出し、その検出した前記関数値が予め記憶されていた前記基準の関数値に一致するように、フォーカスサーボ制御回路１０９Ａにおいてフォーカスバイアスをずらすことで補正が行われる。
【００２７】
上記の構成の他に、前記補正部１２２に、前記フォーカスキャリブレーション関数の関数値と、その関数値に対応した前記フォーカスバイアスをシフトすべきシフト量との関係をメモリーしておいて、その関係に基づいてフォーカスサーボ制御回路１０９Ａによってフォーカスバイアスをシフトするように構成してもよい。
また、フォーカスキャリブレーション関数の関数値と、前記フォーカスバイアスのシフト量との関係を記憶しておく際には、図１６のような曲線としてメモリーしておいてもよいし、構成を簡単にするため、前記フォーカスキャリブレーション関数の関数値と、前記フォーカスバイアスのシフト量との関係を直線としてメモリーしておいてもよい。
また、上記の例においては、副スポットのプッシュプル信号の振幅を用いるため、キャリブレーション関数の値は、トラッキングサーボがオンの状態（トラッキングサーボがかかっている状態）では、適切な値を得ることができない。
しかし、アドレス信号やクロック信号の目的で前記光記録媒体のトラックが高い周波数でウォブリングしているような場合には、前記プッシュプル信号に含まれるウォブリング成分の振幅、すなわちトラッキングサーボに無関係な信号の振幅を用いることによって、トラッキングサーボがオンの状態でもキャリブレーション関数の値を得ることができる。
また、前記キャリブレーション関数は一例に過ぎず、（５）式以外の式で示されるものであってもよい。
上述した構成によれば、環境の変化や経時変化によって最適なフォーカス位置からのずれが生じても、フォーカスバイアスを最適になるように補正することによって、対物レンズのフォーカス制御をより高精度に行なうことができる。
換言すれば、周囲環境や経時変化によって光学部品や受発光素子の特性が影響を受けるなどしてフォーカス制御に狂いが生じても、フォーカス制御を適宜補正することでより精度の高いフォーカス制御を維持することができる。また、上記のことから前記受発光素子に対する製造精度の要求を緩和することができるとともに、経時変化による特性劣化を抑制することもできる。
【００２８】
次に、本発明の受発光素子について説明する。
図１８は、本発明の受発光素子を用いた光ヘッドの好適な実施の形態の一例（第２の実施の形態）の構成図である。
図１８において、光ヘッド５は、光源と光検出素子と光学部品を複合、集積化した受発光素子１３０と、この受発光素子１３０から出射された光ビームを最適な状態で光ディスク１上に集光するための他の部品とからなる。前記他の部品は、１／４波長板６８、対物レンズ７０、液晶素子７７、コリメーター８１、アナモミラー８２、色収差補正レンズ８３を含む。
前記１／４波長板６８、対物レンズ７０は図２で説明したものと同じ機能を有するものである。前記コリメーター８１は、光ビームを平行光または収束光に変換するものである。前記アナモミラー８２は、光ビームのビーム成形を行なうものであり、前記アナモルフィックプリズム６３と同様の作用を奏するものである。
前記液晶素子７７は高いＮＡを有する光学系において光ディスク１の基板厚の誤差などにより発生する球面収差を補正するものである。
前記色収差補正レンズ８３は例えば短波長の光源が使用された場合に発生する色収差を補正するものである。
【００２９】
図１９は受発光素子と受光素子の構成を示す説明図であり、図１９（Ａ）は受発光素子を側面からみた構成図、図１９（Ｂ）は光検出素子の一部を示す平面図、図１９（Ｃ）は光検出素子の他の部分を示す平面図である。
図１９（Ａ）を参照して受発光素子１３０の構成について説明する。
前記受発光素子１３０は、光源１３１、ミラープリズム１３２、基板１３３、半波長板１３４、複合レンズ１３５、複合プリズム１３６、光検出素子１３７などを備えて構成されている。
前記受発光素子１３０は、前記基板１３３に対して前記ミラープリズム１３２、半波長板１３４、複合レンズ１３５、複合プリズム１３６、光検出素子１３７などが一体的に設けられている。
前記複合レンズ１３５は、光回折素子１３５ａ、カップリングレンズ１３５ｂ、シリンドリカルレンズ１３５ｃ、ホログラム素子１３５ｄ、凹レンズ１３５ｅ、分割型ホログラム素子１３５ｇを有して構成されている。
前記複合プリズム１３６は、偏光ビームスプリッタ膜１３６ａ、ハ−フミラー１３６ｂを有して構成されている。
図１９（Ｂ）、（Ｃ）に示されているように前記光検出素子１３７は、トラッキングエラー信号とランドグルーブ判別信号を得るための３つの受光部１３７Ａ、１３７Ｂ、１３７Ｃ、フォーカスエラー信号を得るための２つの受光部１３７Ｄ、１３７Ｅ、ＲＦ信号を得るための受光部１３７Ｆ、ＤＰＰ信号を得るための４つの受光部１３７Ｇ、１３７Ｈ、１３７Ｉ、１３７Ｊから構成されている。４つの受光部１３７Ｇ、１３７Ｈ、１３７Ｉ、１３７Ｊは、矩形の四隅の位置に設けられて受光部１３７Ｇ、１３７Ｊが対角線上に位置し、受光部１３７Ｈ、１３７Ｉが対角線上に位置するように構成されている。
【００３０】
次に、図１８、図１９を参照して受発光素子１３０の光路を説明する。
前記光源１３１を出射した光ビームは、前記ミラープリズム１３２によって光路を折り曲げられ、前記基板１３３上のアパ−チャを通過し、前記半波長板１３４によって偏光方向を回転され、前記複合レンズ１３５に入射する。
前記光ビームは、複合レンズ１３５上の、前記光回折素子１３５ａによって、トラッキングエラー検出およびランドグルーブ判別に用いられる３ビームに分離され、前記複合レンズ１３５上のカップリングレンズ１３５ｂによって、複合プリズム１３６とコリメーター８１に入射するＮＡを小さく変換され、複合プリズム１３６の偏光ビームスプリッタ膜１３６ａ（Ｐ偏光は透過、Ｓ偏光は反射となされている）をＰ偏光として透過し、前記コリメーター８１へと向かう。
前記光ディスク１から反射されて戻ってきた光ビームは再びコリメーター８１によって、収束光に変換された後、前記複合プリズム１３６の偏光ビームスプリッタ膜１３６ａをＳ偏光として反射し、ハ−フミラー１３６ｂによって、一部は反射、一部は透過光に分離される。
前記ハ−ブミラー１３６ｂで反射された光は、前記複合レンズ１３５上のシリンドリカルレンズ１３５ｃによって、光ディスク１上のトラック方向を横断する方向（ラジアル方向）についてのみ光軸方向の合焦位置がシフトされる。すなわち、ラジアル方向にビーム形状が引き伸ばされる。
そして、前記光ビームは、前記複合レンズ１３５上のホログラム素子１３５ｄによって、フォーカスエラー信ＦＥをスポットサイズ法によって検出するために、タンジェンシャル方向についてのみ光軸方向の合焦位置をシフトされた±１次光と、ＲＦ信号検出およびトラッキングエラー信号ＴＥ検出、ランドグルーブ判別信号ＣＴＳ検出を行うための０次光とに分離され、光検出素子１３７の受光部１３７Ａ〜１３７Ｅによって受光される。各受光部１３７Ａ〜１３７Ｅの構成は第１の実施の形態で説明した図３と同様であるため説明は省略する。
一方、前記ハ−フミラー１３６ｂを透過した光ビームは、前記全反射面１３６ｅによって全反射され、前記複合レンズ１３５上の凹レンズ１３５ｅによって、光軸方向の合焦位置が調整され、分割型ホログラム素子１３５ｇによって、ＲＦ信号を検出するための０次光と、ＤＰＤ信号を検出するための±１次光とに分離され、前記光検出素子１３７の受光部１３７Ｆ〜１３７Ｊに集光される。
【００３１】
図２０は、分割型ホログラム素子１３５ｇと受光部１３７Ｆ〜１３７Ｊの構成を示す構成図である。
分割型ホログラム素子１３５ｇは、全体として矩形状に構成され縦横が２等分された４つの矩形の分割領域Ａ、Ｂ、Ｃ、Ｄに分割されている。分割領域Ａ、Ｃが対角線上に位置し、分割領域Ｂ、Ｄが対角線上に位置するように設けられている。
前記光検出素子１３７の各受光部１３７Ｇ〜１３７Ｊと前記分割型ホログラム素子１３５の各分割領域Ａ〜Ｄとはそれぞれ対応する位置関係となるように設けられている。
そして、前記分割型ホログラム素子１３５ｇは、それに入射された前記光ビームを、各分割領域Ａ〜Ｄによって前記受光部１３７Ｆに照射される０次光と、前記受光部１３７Ｇ〜１３７Ｊに入射される４つの−１次光および４つの＋１次光とに分離するように構成されている。
前記分割領域Ａに入射された前記光ビームは、前記受光部１３７Ｇに−１次光が照射され受光部１３７Ｊに＋１次光が照射されるように分離される。
前記分割領域Ｂに入射された前記光ビームは、前記受光部１３７Ｈに−１次光が照射され受光部１３７Ｉに＋１次光が照射されるように分離される。
前記分割領域Ｃに入射された前記光ビームは、前記受光部１３７Ｇに−１次光が照射され受光部１３７Ｊに＋１次光が照射されるように分離される。
前記分割領域Ｄに入射された前記光ビームは、前記受光部１３７Ｈに−１次光が照射され受光部１３７Ｉに＋１次光が照射されるように分離される。
したがって、前記受光部１３７Ｇ、１３７Ｊからは分割領域Ａ、Ｃに相当する出力信号ＡＣが得られる。前記受光部１３７Ｈ、１３７Ｉからは分割領域Ｂ、Ｄに相当する出力信号ＢＤが得られる。したがって、各出力信号から周知のＤＰＤ信号を生成することができる。
なお、受光部１３７Ｆからは光ビームの０次光に相当するＲＦ信号が得られる。
このようにして、前記光検出素子１３７で受光された光によって生成される各出力信号をもとに、フォーカスエラー信号ＦＥ、トラッキングエラー信号ＴＥ、ランドグルーブ判別信号ＣＴＳ等のサーボ信号と、ＲＦ信号が生成され、情報の再生およびディスク上の光スポットの制御が行われる。光検出素子上におけるスポットと受光部との関係を図１７下部に示している。
各種信号は例えば、次の式によって検出される。
ＦＥ＝（ａ＋ｃ−ｂ−ｎ−ｏ）−（ｄ＋ｆ−ｅ−ｐ−ｑ） （６）
ＴＥ＝（ｊ−ｋ）−Ｋ＊｛（ｈ−ｉ）＋（ｌ−ｍ）｝ （７）
（ただしＫは係数、＊は乗算を示す記号）
ＣＴＳ＝｛（ｈ＋ｉ）−ｒ｝−｛（ｌ＋ｍ）−ｔ｝ （８）
ＲＦ信号＝出力信号ＲＦ
ＤＰＤ信号＝ 出力信号ＡＣと出力信号ＢＤの位相差信号
これにより、ＲＦ信号が、単独の受光部１３７Ｆから生成可能となり、ＲＦ信号の低ノイズ化、広帯域化が可能となるとともに、４つの受光部１３７Ｇ〜１３７ＪによってＤＰＤ信号を検出することができる。
【００３２】
そして、第１の実施の形態の図１７の説明した場合と同様に、トラッキングエラー信号ＴＥを生成するためのプッシュプル信号ＳＰＰ１、ＳＰＰ２の振幅ＳＰＰ１Ａ、ＳＰＰ２Ａを用いて前記式（５）でキャリブレーション値Ｙを求めることでフォーカスバイアスをキャリブレーションすることができる。各部の動作については第１の実施の形態と同様であるため説明を省略する。
このような第２の実施の形態においても第１の実施の形態と同様の効果を奏することはもちろんである。
【００３３】
なお、第１、第２の実施の形態では、前記光源として、単一の発光点を有する半導体レーザーを用いた場合を例にとって説明したが、本発明はこれに限定されるものではない。
すなわち、前記光源が２つ以上の発光点を有し、１つの発光点が前記主スポットを形成し、他の発光点が前記２つの副スポットを形成するように構成されているものを使用することもできる。この場合、前記他の発光点から出射される２つ副ビームによって形成される２つの副スポットは、ラジアル方向についての光軸方向の合焦位置が主ビームの合焦位置に対してそれぞれ一方は対物レンズに近い方にずれ、他方は対物レンズから遠い方にずれるように構成されることになる。
また、第１、第２の実施の形態では、２つの副スポットを２つ用いて前記キャリブレーション関数の関数値を演算することでデフォーカス量を求める例について説明したが、本発明はこれに限定されるものではない。
例えば、前記副スポットのうちの１つを主スポットで代用し前記キャリブレーション関数を演算してもよい。また、主スポットと２つの副スポットから得られる検出信号を全てを用いて前記キャリブレーション関数を演算するように構成してもよい。
【００３４】
また、上述した各実施の形態では、前記光ヘッドおよび受発光素子は、前記プリアンプやサーボ制御回路と別体に構成された例を示したが、前記光ヘッドおよび受発光素子に前記プリアンプやサーボ制御回路の構成要素の一部が組み込まれて構成されていてもよいことはもちろんである。
【００３５】
【発明の効果】
以上説明したように本発明の光ヘッドによれば、前記光検出手段によって生成された前記デフォーカス検出用信号は、該デフォーカス検出用信号を演算することによって前記主スポットの合焦位置と前記情報記録面とのずれ量であるデフォーカス量に対応する値が算出可能な信号として構成されている。
したがって、前記デフォーカス量に対応する値に基づいて対物レンズのフォーカス制御を補正することにより、対物レンズのフォーカス制御をより高精度に行なうことができる。また、周囲環境や経時変化によって光学部品や受発光素子の特性が影響を受けるなどしてフォーカス制御に狂いが生じても、フォーカス制御を適宜補正することでより精度の高いフォーカス制御を維持することができる。また、前記光ヘッドに対する製造精度の要求を緩和することができるとともに、経時変化による特性劣化を抑制することもできる。
また、本発明の受発光素子によれば、前記光検出手段によって生成された前記デフォーカス検出用信号は、該デフォーカス検出用信号を演算することによって前記主スポットの合焦位置と前記情報記録面とのずれ量であるデフォーカス量に対応する値が算出可能な信号として構成されている。
したがって、前記デフォーカス量に対応する値に基づいて対物レンズのフォーカス制御を補正することにより、対物レンズのフォーカス制御をより高精度に行なうことができる。また、周囲環境や経時変化によって光学部品や受発光素子の特性が影響を受けるなどしてフォーカス制御に狂いが生じても、フォーカス制御を適宜補正することでより精度の高いフォーカス制御を維持することができる。また、前記受発光素子に対する製造精度の要求を緩和することができるとともに、経時変化による特性劣化を抑制することもできる。
【図面の簡単な説明】
【図１】第１の実施の形態に係る光ヘッドを組み込んだ光記録媒体記録再生装置の概略構成を示すブロック図である。
【図２】第１の実施の形態における光ヘッドの構成図であり、図２（Ａ）は平面図、図２（Ｂ）は側面図である。
【図３】光検出素子上におけるスポットと受光部との関係を示す平面図である。
【図４】図４はホログラム素子７２の動作説明図であり、図４（Ａ）はタンジェンシャル方向からホログラム素子７２とシリンドリカルレンズ７２と光検出素子７４を見た状態を示す説明図、図４（Ｂ）は、ラジアル方向からシリンドリカルレンズ７２と光検出素子７４を見た状態を示す説明図である。
【図５】光検出素子の平面図である。
【図６】ＤＶＲディスク再生時のディスク回折光の対物レンズ瞳上における強度分布および位相分布を計算した結果を表す特性線図である。
【図７】ＤＶＲディスク再生時のディスク回折光の対物レンズ瞳上における強度分布および位相分布を計算した結果を表す特性線図である。
【図８】ＤＶＲディスク再生時のディスク回折光の対物レンズ瞳上における強度分布および位相分布を計算した結果を表す特性線図である。
【図９】ＤＶＲディスク再生時のディスク回折光の対物レンズ瞳上における強度分布および位相分布を計算した結果を表す特性線図である。
【図１０】ＤＶＲディスク再生時のディスク回折光の対物レンズ瞳上における強度分布および位相分布を計算した結果を表す特性線図である。
【図１１】ＤＶＲディスク再生時のディスク回折光の対物レンズ瞳上における強度分布および位相分布を計算した結果を表す特性線図である。
【図１２】図１２（Ａ）は従来のランド記録を用いたディスク再生時における０次光と±１次光の説明図、図１２（Ｂ）は対物レンズ瞳上における０次光と±１次光の関係を示す説明図、図１２（Ｃ）はランドグルーブ記録を用いたディスク再生時における０次光と±１次光の説明図、図１２（Ｄ）はランドグルーブ記録を用いたディスク再生時における対物レンズ瞳上における０次光と±１次光の関係を示す説明図である。
【図１３】 光検出素子の各受光部上における、強度分布の変化の様子を模式的に示した説明図であり、図１３（Ａ）は主スポットがグルーブ上に位置した状態を示す説明図、図１３（Ｂ）は主スポットがランド上に位置した状態を示す説明図、図１３（Ｃ）は主スポットがグルーブ上に位置した状態を示す説明図、図１３（Ｄ）はラジアル方向の位置に対するトラッキングエラー信号ＴＥとランドグルーブ判別信号ＣＴＳを示す説明図である。
【図１４】図１４（Ａ）は同一曲線パターンをタンジェンシャル方向に繰り返し配置した光回折素子の説明図、図１４（Ｂ）はスポットの位置関係の説明図である。
【図１５】対物レンズのデフォーカス量と、トラッキングエラー信号ＴＥのプッシュプル信号の振幅との関係を示す特性図である。
【図１６】プッシュプル信号ＳＰＰ１、ＳＰＰ２を用いたキャリブレーション関数の一例を示す特性線図図である。
【図１７】第１の実施の形態に係る光ヘッドを組み込んだ光記録媒体記録再生装置のうち、前記キャリブレーション値Ｙに基づいてフォーカスエラー信号の補正を行なう部分の構成を示すブロック図である。
【図１８】本発明の受発光素子を用いた光ヘッドの好適な実施の形態の一例（第２の実施の形態）の構成図である。
【図１９】受発光素子と受光素子の構成を示す説明図であり、図１９（Ａ）は受発光素子を側面からみた構成図、図１９（Ｂ）は光検出素子の一部を示す平面図、図１９（Ｃ）は光検出素子の他の部分を示す平面図である。
【図２０】分割型ホログラム素子と各受光部の構成を示す構成図である。
【符号の説明】
１……光ディスク、２……光ヘッド、６１……半導体レーザ、６５……光回折素子、７０……対物レンズ、７４……光検出素子、１３０……受発光素子。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light receiving and emitting element and an optical head for writing and reading information signals to and from the optical recording medium, and information on an optical recording medium such as an optical disk configured by including such a light receiving and emitting element or optical head. The present invention relates to an optical recording medium recording / reproducing apparatus for recording and reproducing signals.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there are optical recording medium recording / reproducing apparatuses for recording / reproducing information signals on / from an optical recording medium such as an optical disk. In such an optical recording medium recording / reproducing apparatus, an information signal is written to and read from the optical recording medium by an optical head (optical pickup apparatus).
The optical head collects and irradiates a light beam output from a light source on the information recording surface of the optical disk by an objective lens, writes an information signal on the information recording surface, and irradiates the information recording surface with light. The reflected light of the beam is detected, and the information signal recorded on the information recording surface is read. The optical head is provided with a light emitting / receiving element having a detector for detecting the reflected light, either integrally or separately.
The objective lens needs to converge the light beam in accordance with the size of the pit written or read on the information recording surface.
Therefore, the smaller the pits, that is, the higher the recording density of the optical disc, the more the objective lens must converge the light beam. Therefore, the numerical aperture of the objective lens is higher, and the wavelength of the light beam output from the light source needs to be shorter.
Here, when the wavelength of the light beam output from the light source is λ and the numerical aperture of the objective lens is NA, the focal depth Df of the objective lens is expressed by the following equation.
Df≈λ / (NA)²
For example, in a CD (compact disc), if λ = 780 nm and NA = 0.45, the depth of focus is Df = 3.9 μm.
In the case of DVD, if λ = 650 nm and NA = 0.60, the depth of focus is Df = 1.8 μm.
As can be seen from the above formula, the higher the recording density of the optical disc, the smaller the depth of focus, and thus the tighter the tolerance of in-focus position with respect to the recording surface of the objective lens. In the future, due to the high recording density of optical discs, higher NA and shorter wavelengths will progress. For example, when λ = 405 nm and NA = 0.85, the depth of focus becomes Df = 0.56 μm.
[0003]
[Problems to be solved by the invention]
Therefore, if the accuracy of the focus control of the objective lens is the same as the current situation, the higher the recording density of the optical disc, the more strict the manufacturing accuracy for the optical head and the light emitting / receiving element, and the deterioration of characteristics due to changes over time. There is concern about becoming larger.
The present invention has been made in view of such a situation, and an object of the present invention is to provide an optical head, a light emitting / receiving element, and an optical recording medium recording / reproducing apparatus capable of performing focus control of an objective lens with high accuracy. Is to provide.
[0004]
  An optical head according to the present invention includes a light source that emits a light beam, and converges and irradiates the light beam toward an information recording surface of the optical recording medium, and receives a reflected light beam reflected from the optical recording medium. An objective lens that emits light and light detection means that receives the reflected light beam, and a main spot is formed on the information recording surface by the light beam emitted from the light source.2Configured to form two secondary spots,The main spot is for recording and / or reproducing information on the information recording surface,The formation of the main spot and the sub-spot is performed in the radial direction across the track of the optical recording medium.TwoIn such a way that the focusing positions in the optical axis direction of the light beams forming the sub-spots are different from each other,In addition, one focusing position of the two sub-spots is closer to the objective lens than the focusing position of the main spot, and the other focusing position of the two sub-spots is the focusing position of the main spot. It is configured to be farther from the objective lens than the focal position.,The light detecting means includes a first light receiving unit and a second light receiving unit configured to receive the two sub-spots, respectively, and the first light receiving unit is divided into at least two in the radial direction. 1 and a second divided area, and the second light receiving unit has a third and a fourth divided area divided into at least two in the radial direction, and a detection signal detected in the first to fourth divided areas Are the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4, respectively, the first push-pull signal SPP1 is determined by the difference signal (S1-S2) between the first signal and the second signal. The second push-pull signal SPP2 is formed by the difference signal (S3-S4) between the third signal and the fourth signal, and the tracking error signal is generated using the first and second push-pull signals SPP1 and SPP2. Sought before The first, the second push-pull signal SPP1, SPP2 contains signal components sinusoidal having an amplitude, the defocus detection signal is constituted by the first, second push-pull signal SPP1, SPP2And a signal corresponding to a defocus amount, which is a deviation amount between the focus position of the main spot and the information recording surface, by calculating the defocus detection signal. To do.
  In addition, the light receiving and emitting element of the present invention includes a light source that emits a light beam, and converges and irradiates the light beam toward an information recording surface of the optical recording medium, and a reflected light beam reflected from the optical recording medium. An objective lens that emits light by being incident thereon, and a reflected light beam reflected from the optical recording medium by irradiating the light beam through the objective lens toward the information recording surface of the optical recording medium. A light detecting means for receiving light via the light source, and a main spot on the information recording surface by the light beam emitted from the light source.2Configured to form two secondary spots,The main spot is for recording and / or reproducing information on the information recording surface, and the formation of the main spot and the sub-spot includes the main spot in a radial direction across the track of the optical recording medium. The focus position in the optical axis direction of the light beam forming the two sub-spots is different from each other, and one focus position of the two sub-spots is closer to the objective lens than the focus position of the main spot. It is configured to be close and the other in-focus position of the two sub-spots is farther from the objective lens than the in-focus position of the main spot.,The light detecting means includes a first light receiving unit and a second light receiving unit configured to receive the two sub-spots, respectively, and the first light receiving unit is divided into at least two in the radial direction. 1 and a second divided area, and the second light receiving unit has a third and a fourth divided area divided into at least two in the radial direction, and a detection signal detected in the first to fourth divided areas Are the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4, respectively, the first push-pull signal SPP1 is determined by the difference signal (S1-S2) between the first signal and the second signal. The second push-pull signal SPP2 is formed by the difference signal (S3-S4) between the third signal and the fourth signal, and the tracking error signal is generated using the first and second push-pull signals SPP1 and SPP2. Sought before The first, the second push-pull signal SPP1, SPP2 contains signal components sinusoidal having an amplitude, the defocus detection signal is constituted by the first, second push-pull signal SPP1, SPP2And a signal corresponding to a defocus amount, which is a deviation amount between the focus position of the main spot and the information recording surface, by calculating the defocus detection signal. To do.
  Also, the optical recording medium recording / reproducing apparatus of the present invention comprises a driving means for rotationally driving the optical recording medium, a light beam applied to the rotating optical recording medium, and reflection from the information recording surface of the optical recording medium. In an optical recording medium recording / reproducing apparatus having an optical head for detecting a light beam and a signal processing circuit for generating a reproduction signal based on a detection signal from the optical head, the optical head includes a light source, an objective lens, A light detection means, wherein the light source is configured to emit the light beam, and the objective lens converges and irradiates the light beam toward an information recording surface of the optical recording medium, and the optical recording medium The reflected light beam reflected from the light beam is incident and emitted, and the light detection means is configured to receive the reflected light beam and output the detection signal, and is emitted from the light source. The main spot on the information recording surface by the light beam and2Configured to form two secondary spots,The main spot is for recording and / or reproducing information on the information recording surface, and the formation of the main spot and the sub-spot includes the main spot in a radial direction across the track of the optical recording medium. The focus position in the optical axis direction of the light beam forming the two sub-spots is different from each other, and one focus position of the two sub-spots is closer to the objective lens than the focus position of the main spot. It is configured to be close and the other in-focus position of the two sub-spots is farther from the objective lens than the in-focus position of the main spot.,The light detecting means includes a first light receiving unit and a second light receiving unit configured to receive the two sub-spots, respectively, and the first light receiving unit is divided into at least two in the radial direction. 1 and a second divided area, and the second light receiving unit has a third and a fourth divided area divided into at least two in the radial direction, and a detection signal detected in the first to fourth divided areas Are the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4, respectively, the first push-pull signal SPP1 is determined by the difference signal (S1-S2) between the first signal and the second signal. The second push-pull signal SPP2 is formed by the difference signal (S3-S4) between the third signal and the fourth signal, and the tracking error signal is generated using the first and second push-pull signals SPP1 and SPP2. Sought before The first, the second push-pull signal SPP1, SPP2 contains signal components sinusoidal having an amplitude, the defocus detection signal is constituted by the first, second push-pull signal SPP1, SPP2The detection signal is configured as a signal that can calculate a value corresponding to a defocus amount that is a shift amount between the focus position of the main spot and the information recording surface by calculating the defocus detection signal. It is characterized by that.
  Also, the optical recording medium recording / reproducing apparatus of the present invention comprises a driving means for rotationally driving the optical recording medium, a light beam applied to the rotating optical recording medium, and reflection from the information recording surface of the optical recording medium. In an optical recording medium recording / reproducing apparatus having an optical head that detects a light beam and a signal processing circuit that generates a reproduction signal based on a detection signal from the optical head, the optical head includes an objective lens, a light source, and light A light receiving and emitting element provided with a detecting means, the light source is configured to emit the light beam, and the objective lens converges and irradiates the light beam toward an information recording surface of an optical recording medium. The reflected light beam reflected from the optical recording medium is incident and emitted, and the light detection means is configured to receive the reflected light beam and output the detection signal. It is a main spot on the information recording surface by the light beam emitted from the light source2Configured to form two secondary spots,The main spot is for recording and / or reproducing information on the information recording surface, and the formation of the main spot and the sub-spot includes the main spot in a radial direction across the track of the optical recording medium. The focus position in the optical axis direction of the light beam forming the two sub-spots is different from each other, and one focus position of the two sub-spots is closer to the objective lens than the focus position of the main spot. It is configured to be close and the other in-focus position of the two sub-spots is farther from the objective lens than the in-focus position of the main spot.,The light detecting means includes a first light receiving unit and a second light receiving unit configured to receive the two sub-spots, respectively, and the first light receiving unit is divided into at least two in the radial direction. 1 and a second divided area, and the second light receiving unit has a third and a fourth divided area divided into at least two in the radial direction, and a detection signal detected in the first to fourth divided areas Are the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4, respectively, the first push-pull signal SPP1 is determined by the difference signal (S1-S2) between the first signal and the second signal. The second push-pull signal SPP2 is formed by the difference signal (S3-S4) between the third signal and the fourth signal, and the tracking error signal is generated using the first and second push-pull signals SPP1 and SPP2. Sought before The first, the second push-pull signal SPP1, SPP2 contains signal components sinusoidal having an amplitude, the defocus detection signal from said first, second push-pull signal SPP1, SPP2The detection signal is a signal that can calculate a value corresponding to a defocus amount that is a shift amount between the focus position of the main spot and the information recording surface by calculating the defocus detection signal. It is characterized by being configured.
[0005]
According to the optical head of the present invention, the sub-spot is detected by the light detection means to generate a sinusoidal defocus detection signal having an amplitude, and the defocus detection signal is the defocus detection signal. Is calculated as a signal capable of calculating a value corresponding to a defocus amount, which is a shift amount between the focus position of the main spot and the information recording surface. Therefore, it is possible to correct the focus control of the objective lens based on the value corresponding to the defocus amount.
According to the light emitting / receiving element of the present invention, the sub spot is detected by the light detection means to generate a sinusoidal defocus detection signal having an amplitude, and the defocus detection signal is the defocus detection signal. By calculating the signal, it is configured as a signal capable of calculating a value corresponding to a defocus amount which is a shift amount between the focus position of the main spot and the information recording surface. Therefore, it is possible to correct the focus control of the objective lens based on the value corresponding to the defocus amount.
According to the optical recording medium recording / reproducing apparatus of the present invention, the sub spot is detected by the light detection means, and a sinusoidal defocus detection signal having an amplitude is generated, and the defocus detection signal is By calculating a focus detection signal, a signal corresponding to a defocus amount that is a shift amount between the focus position of the main spot and the information recording surface can be calculated. Therefore, it is possible to correct the focus control of the objective lens based on the value corresponding to the defocus amount.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.
The embodiment described below is a preferred specific example of the present invention, and thus technically preferable various kinds of limitations are given. However, the scope of the present invention is not limited to the following description. As long as there is no description which limits, it is not restricted to these aspects.
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of an optical recording medium recording / reproducing apparatus incorporating an optical head according to the first embodiment of the present invention.
In FIG. 1, a disk device 101 includes a spindle motor 103 as a driving unit that rotationally drives an optical disk 1 (optical recording medium), an optical head 104, and a feed motor 105 as a driving unit for the optical head 104. .
Here, the spindle motor 103 is driven and controlled by a system controller 107 and a servo control circuit 109 (corresponding to a servo circuit in claims), and is rotated at a predetermined rotational speed.
As the optical disc 1, a Pit disc dedicated to reproduction may be used, but “CD-R / RW”, “DVD-R”, “DVD-RAM”, “DVD-R / RW”, “DVD + RW”, etc. It is more effective to use “DVR-BLUE” which is a high density optical disk using a short wavelength light source.
The signal modulation / demodulation unit and the ECC block 108 perform signal modulation, demodulation, and addition of ECC (error correction code). The optical head 104 irradiates the information recording surface (signal recording surface) of the rotating optical disc 1 with light according to the signal modulation and the instruction of the ECC block 108. Recording is performed by such light irradiation. The optical head 104 detects a light beam as will be described later based on the reflected light beam from the information recording surface of the optical disc 1 and supplies a signal corresponding to each light beam to the preamble unit 20.
The preamplifier unit 120 is configured to generate a focus error signal, a tracking error signal, an RF signal, and the like based on a signal corresponding to each light beam. Depending on the type of recording medium to be reproduced, the servo control circuit 109, the signal modulation & ECC block 108, etc. perform predetermined processing such as demodulation and error correction processing based on these signals.
Thus, the demodulated recording signal is sent to the external computer 115 or the like via the interface 111 if it is for data storage of a computer, for example. Thereby, an external computer or the like can receive a signal recorded on the optical disc 1 as a reproduction signal.
For audio / visual use, the digital / analog conversion is performed by the D / A conversion unit of the D / A and A / D converter 112 and is supplied to the audio / visual processing unit 113 where audio / video signal processing is performed. And transmitted to an external imaging / projection device via the audio / visual signal input / output unit 114.
The optical head 104 is connected to a feed motor 105 for moving to a predetermined recording track on the optical disc 1, for example. The servo control circuit 109 controls the spindle motor 103, the feed motor 105, and the focusing direction and the tracking direction of the biaxial actuator that holds the objective lens of the optical head 104.
A configuration for correcting the focus servo in the servo control circuit 109 is provided. This configuration will be described in detail later with reference to FIG.
[0007]
2A and 2B are configuration diagrams of the optical head in the first embodiment. FIG. 2A is a plan view and FIG. 2B is a side view.
In this embodiment, an example of an optical head that performs “beam shaping” using an anamorphic prism is shown.
Optical recording medium recording / reproducing apparatus, in particular, recording / reproducing type optical recording medium recording such as “CD-R / RW”, “DVD-R”, “DVD-RAM”, “DVD-R / RW”, “DVD + RW”, “DVR-BLUE”, etc. In the case of a reproducing apparatus, the recording characteristics change depending on the shape of the spot condensed on the disc.
Usually, a semiconductor laser is often used as a light source for this type of system. In the case of a semiconductor laser, the divergence angle of the emitted beam is structurally parallel to the bonding surface (θ // direction). The full width at half maximum is about 10 degrees, and the full width at half maximum is about 20 to 30 degrees in the direction perpendicular to the joint surface (θ⊥ direction) (this difference in divergence angle θ⊥ / θ // is called the aspect ratio). Using a morphic prism or the like, the magnification of the outgoing light beam with respect to the incident light beam is changed (ie, compressed or expanded) in a specific direction of the light beam cross section, and then emitted (“beam shaping”), and the light intensity distribution depends on the direction. It is used so that non-uniformity does not occur so much.
[0008]
The configuration of the optical head 2 according to the first embodiment will be described with reference to FIG.
The optical head 2 includes a semiconductor laser 61 as a light source, an outward collimator lens 62, an anamorphic prism 63, a half-wave plate 64, a light diffraction element 65 (spot forming means), a polarization beam splitter prism 66, a light detection element 67, A quarter wavelength plate 68, a rising mirror 69, an objective lens 70, a return path collimator lens 71, a hologram element 72, a cylindrical lens 73, a light detection element 74, and the like are provided.
The semiconductor laser 61 constitutes a light source and is configured to emit a light beam.
The forward collimator lens 62 is for making the light beam emitted from the semiconductor laser 61 into parallel light.
The anamorphic prism 63 corrects the light beam from the forward collimator lens 62. That is, it is configured to correct the non-uniformity of the light intensity distribution in the light beam by enlarging the cross section of the light beam in the direction corresponding to the θ // direction of the light beam. As the anamorphic prism 63, a straight type anamorphic prism devised by the present applicant in Japanese Patent Application No. P2000-123723 can be used.
The half-wave plate 64 rotates the polarization direction of the light beam incident from the anamorphic prism 63.
[0009]
The light diffraction element 65 generates three light beams, that is, a main beam and two light beams incident from the half-wave plate 64 in order to generate a tracking error signal and a land groove discrimination signal (CTS signal), which will be described later. It is comprised so that it may isolate | separate into a sub beam.
The main beam and two sub-beams are irradiated on the light detection element 74 to form a main spot and two sub-spots, but the light diffraction element 65 includes the main spot and two sub-spots. The optical disc 1 has a function of changing (defocusing) the focusing position in the radial direction (direction orthogonal to the track) in the optical axis direction.
In this example, the optical diffraction element 65 is configured such that the focal positions of the main spot and the two sub-spots in the tangential direction (direction parallel to the track) of the optical disc 1 are the same in the optical axis direction. However, in the present invention, the in-focus position in the tangential direction (direction parallel to the track) of the optical disc 1 is not particularly limited, and for example, it is shifted by the same amount as the radial direction. It doesn't matter.
In the present specification, the in-focus position refers to the position of the focal point (convergence point) where the light beam with respect to the objective lens 70 is in focus (convergent).
That is, when the main spot is focused on the recording surface of the optical disc 1 in the radial direction, the light diffraction element 65 has one of the two sub-spots closer to the light source than the recording surface. Focusing is performed, and the other is configured to focus at a position farther from the recording surface.
[0010]
The polarization beam splitter prism 66 includes a polarization beam splitter surface 66a and a total reflection surface 66b. The polarization beam splitter surface 66a is configured to transmit P-polarized light and reflect S-polarized light in the incident light beam. The total reflection surface 66b is configured to reflect the light beam regardless of the polarization direction.
The quarter-wave plate 68 is configured so that the P-polarized light beam transmitted through the polarization beam splitter surface 66a of the polarization beam splitter prism 66 is circularly polarized.
The raising mirror 69 is provided between the quarter-wave plate 68 and the objective lens 70, and is configured to bend the optical path of the light beam by 90 degrees.
The objective lens 70 is configured to condense the incident light beam on the information recording surface of the optical disc 1 and convert the light beam reflected and returned from the optical disc 1 into parallel light.
The return path collimator lens 71 is configured to receive the return path light beam reflected by the total reflection surface 66b and convert it into convergent light.
[0011]
The hologram element 72 is configured to separate the incident light beam into ± first order light and zero order light. The ± first-order light is for detecting a focus error signal by the spot size method. The zero-order light is used for RF signal detection and tracking error signal detection. The configuration of the hologram element 72 will be described later.
The cylindrical lens 73 is configured such that each light beam emitted from the hologram element 72 is defocused only in the radial direction, and the shape of the light beam is extended in the radial direction.
The light detection element 74 is configured to receive each light beam emitted from the cylindrical lens 73 and output a detection signal.
[0012]
A schematic operation of the optical head 2 configured as described above will be described.
The light beam emitted from the semiconductor laser 61 passes through the forward collimator lens 62, the anamorphic prism 63, and the half-wave plate 64 and enters the diffraction grating 65.
The light beam incident on the diffraction grating 65 is separated into the main beam and two sub beams, and is transmitted as a P-polarized light through the polarization beam splitter surface 66a of the polarization beam splitter prism 66. It becomes circularly polarized light and enters the objective lens 70. The light beam is condensed on the information recording surface of the optical disc 1 by the objective lens 70, and signal recording / reproduction is performed. The light beam reflected and returned from the optical disk 1 is converted again into parallel light by the objective lens 70, the optical path is converted by 90 degrees by the rising mirror 69, and is incident on the quarter-wave plate 68.
The light beam is converted in the direction of polarization by 90 degrees with respect to the forward path by the quarter-wave plate 68 and reflected as S-polarized light by the deflecting beam splitter surface 66a of the polarizing beam splitter prism 66, and then the total reflection surface 66b. And totally incident on the return-path collimator lens 71.
The light is converted into convergent light by the return path collimator lens 71 and then incident on the hologram element 72.
The light beam is separated into ± first-order light and zero-order light by the hologram element 72 and received by the light detection element 74. Based on the received optical signal, servo signals such as a focus error signal, a tracking error signal, and a land / groove discrimination signal, and an RF signal are generated, and information is reproduced and a light spot on the disk is controlled.
[0013]
FIG. 3 is a plan view showing the relationship between the spot on the photodetecting element and the light receiving portion.
The light diffraction element 65, the hologram element 72, and the light detection element 74 will be described in detail with reference to FIG.
As shown in FIG. 3, the light detection element 74 has three light receiving portions 74A, 74B, and 74C for obtaining a tracking error signal TE, a land groove discrimination signal CTS, and an RF signal, and a focus error signal. It comprises two light receiving parts 74D and 74E.
The three light receiving portions 74A, 74B, and 74C are provided at equal intervals in a straight line in the tangential direction, and the light receiving portion 74B that receives the main spot in the center sandwiches the light receiving portion 74B in the tangential direction. A light receiving portion 74A (corresponding to the first light receiving portion in the claims) and a light receiving portion 74C (corresponding to the second light receiving portion in the claims) that receive the two sub-spots are positioned.
Each of the light receiving portions 74A, 74B, and 74C has a divided region that is divided into three in the radial direction. That is, the light receiving portion 74A includes two divided areas h and i (corresponding to the first and second divided areas in the claims) sandwiching the divided area r located at the center in the radial direction. Similarly, the light receiving unit 74B has divided regions j and k with the divided region s interposed therebetween, and the light receiving unit 74C has divided regions l and m with the divided region t interposed therebetween (third and fourth divided regions of the claims). Equivalent).
In the first embodiment, the tracking error signal is detected based on the radial light intensity distribution of the main spot and the two sub-spots on each of the light receiving portions 74A, 74B, and 74C. That is, the tracking error signal is detected by the differential push-pull method.
[0014]
Further, the land / groove discrimination signal is detected based on the radial light intensity distribution of the two sub-spots on the light receiving portions 74A and 74C. This will be described later.
Further, the RF signal is detected based on the light amount of the main spot on the light receiving unit 74B.
[0015]
The two light receiving portions 74D and 74E are linearly provided in the radial direction across the light receiving portion 74B, and are arranged at equal intervals with the light receiving portion 74B.
Each of the light receiving portions 74D and 74E has a divided area divided into five in the tangential direction. That is, the light receiving unit 74D includes a divided region b positioned in the center in the tangential direction, two divided regions a and c sandwiching the divided region b, and two divided regions n and o positioned outside the divided region b. Similarly, the light receiving unit 74E includes a divided region e positioned at the center in the tangential direction, two divided regions f and d sandwiching the divided region e, and two divided regions q and p positioned outside the divided region e.
In the first embodiment, the focus error signal has a dimension in a tangential direction of a spot made of ± primary light formed by separating the main spot on each of the light receiving portions 74D and 74E by the hologram element 72. Detected on the basis. That is, the focus error signal is detected by the spot size method.
[0016]
For example, the detection signals detected by the light receiving units 74A to 74E are subjected to current-voltage conversion by an amplifier (not shown) formed on the semiconductor substrate of the light detection element 74 of the optical head 2, and then an arithmetic circuit (not shown) or A focus error signal FE, a tracking error signal TE, a track discrimination signal CTS, and an RF signal are calculated as follows by an arithmetic circuit outside the light detection element connected to each of the divided regions.
The signal values output from the respective divided areas a, b, c, d, e, f, h, i, j, k, l, m, r, s, and t are respectively a, b, c, d, and e. , F, h, i, j, k, l, m, r, s, t, the calculation formula of the focus error signal FE by the spot size method, the calculation formula of the tracking error signal TE by the differential push-pull method, The calculation formula of the RF signal and the track discrimination signal CTS are, for example, as shown below. Since the following formulas (1), (2), and (3) are based on the well-known spot size method, differential push-pull method, and well-known principles, the explanation is omitted, and the formula (4) is described later. To do.
FE = (a + c−b−n−o) − (d + f−e−p−q) (1)
TE = (j−k) −K * {(h−i) + (1−m)} (2)
(Where K is a coefficient, * is a multiplication symbol)
RF = j + k + s (3)
CTS = {(h + i) -r}-{(l + m) -t} (4)
[0017]
Next, the light diffraction element 65 will be described.
The main beam and the two sub-beams are separated by the action of the light diffraction element 65, and a main spot and two sub-spots are formed by irradiating the light detection element 74.
The optical diffractive element 65 has an effect of making the focal position of the main spot and the two sub-spots different in the optical axis direction (defocusing) in the radial direction of the optical disc 1 (direction orthogonal to the track). Have.
When the main spot is focused on the recording surface of the optical disc 1 in the radial direction, the light diffraction element 65 is aligned at a position closer to the objective lens than the recording surface. The other is configured to be focused at a position farther from the objective lens than the recording surface. Therefore, when the distance between the objective lens and the recording surface varies, the change in the intensity distribution of the spots on the light detection element 74 of the two sub-spots exhibits an asymmetric behavior. For this reason, the amplitudes of the push-pull signals SPP1 = (hi) and SPP2 = (lm) output from the light detection element 74 that has received the two sub-spots exhibit opposite behaviors. That is, when the amplitude of one push-pull signal increases, the amplitude of the other push-pull signal decreases.
[0018]
Next, the hologram element 72 will be described.
FIG. 4 is an explanatory view of the operation of the hologram element 72. 4A shows a state in which the hologram element 72, the cylindrical lens 72, and the light detection element 74 are viewed from the tangential direction, and FIG. 4B shows the state in which the cylindrical lens 72 and the light detection element 74 are viewed from the radial direction. FIG. 5 is a plan view of the light detection element 74.
4A and 4B are diagrams of a configuration in which a hologram element 72 is provided between the cylindrical lens 73 and the light detection element 74, unlike FIG. 2, the cylindrical lens 73 and the hologram element are illustrated. Since the operation is the same even if the position of 72 is switched, description will be made with reference to FIG.
As shown in FIGS. 4 and 5, the hologram element 72 converts the light beam (main beam and two sub beams) reflected from the recording surface of the optical disc 1 into zero-order light and ± first-order light. It is comprised so that it may isolate | separate. And only in the direction (tangential direction) in which the spot size is detected, the focus positions in the optical axis direction of ± primary light are defocused so as to be different from each other. For this reason, the focusing position in the optical axis direction is kept substantially equal in the radial direction of the three spots of zero-order light and ± first-order light.
On the other hand, the cylindrical lens 73 shifts the focusing position in the optical axis direction of the light beam (main beam and two sub beams) reflected from the recording surface of the optical disc 1 in the radial direction (stretches the beam shape in the radial direction). ) Is designed to defocus. For this reason, the focusing position in the optical axis direction is kept substantially the same in the tangential direction.
By extending the shape of the light beam in the radial direction by the cylindrical lens 73, it becomes possible to further increase the spot diameter in the direction in which push-pull detection is performed (radial direction). The characteristic deterioration due to the positional deviation caused by the environmental change of the spot with respect to the part is also alleviated.
Further, since the hologram element 72 forms a spot of ± first-order light by shifting the focusing position of the light beam in the optical axis direction only in the tangential direction, the light beam of ± first-order light acts on the cylindrical lens 73. Thus, the radial dimension of the ± primary light spot is maintained even if the spot is stretched in the radial direction, and the shape asymmetry does not occur between the ± primary light spots in the radial direction.
[0019]
Next, the detection principle of the track discrimination signal CTS will be described.
Next, the principle of signal detection in the track discrimination signal detection method according to the present invention will be described.
The optical diffractive element 65 forms two sub beams whose focal positions in the optical axis direction are different from each other in the radial direction with respect to the main beam, the main beam is focused on the recording surface of the optical disc 1, and the signal When the recording / reproduction is performed, the two sub beams are configured such that the focal position in the optical axis direction is deviated (defocused) in the radial direction.
In that state, when the main spot and the two sub-spots by the main beam and the two sub-beams traverse the track on the recording surface of the optical disc in the radial direction, the intensity distribution is equal in the land / groove at the main spot. In the sub-spot, track discrimination is performed using the fact that a large difference occurs in the intensity distribution in the spot in the land / groove due to a change in the interference state of the wavefront due to the shift of the focusing position in the optical axis direction in the radial direction.
[0020]
As an example, FIG. 6 to FIG. 11 show characteristic diagrams showing the results of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of the DVR disc.
As calculation conditions,

For simplicity, both the land and the groove are assumed to be rectangular with the same width. 6 to 11, the radial direction is taken on the X axis, the tangential direction is taken on the Y axis, and the intensity of the return light is taken on the Z axis.
FIG. 6 shows a state where the spot is located on the land and the in-focus position in the radial direction is shifted by −0.35 μm in the optical axis direction.
FIG. 7 shows a state in which the spot is located on the land and the in-focus position in the radial direction coincides with the groove position in the optical axis direction.
FIG. 8 shows a state where the spot is located on the land and the in-focus position in the radial direction is shifted by +0.35 μm in the optical axis direction.
FIG. 9 shows a state where the spot is located on the groove and the focus position in the radial direction is shifted by −0.35 μm in the optical axis direction.
FIG. 10 shows a state where the spot is located on the groove and the in-focus position in the radial direction coincides with the land position in the optical axis direction.
FIG. 11 shows a state where the spot is located on the groove and the focus position in the radial direction is shifted by +0.35 μm in the optical axis direction.
[0021]
In land / groove recording, since recording is performed on both the land and the groove, the track period relative to the spot diameter is large when considering the normal track-to-land or land-to-groove track period. As shown in FIG. 5, the way in which the diffracted light on the disc overlaps on the objective lens pupil is greatly different.
As shown in FIGS. 12A and 12B, in the disk reproduction using the conventional land recording, the normal 0th order light and the ± 1st order light do not always overlap. On the other hand, as shown in FIGS. 12C and 12D, when land groove recording is used, the 0th order light and the ± 1st order light overlap. 6 to 11, the portion where the intensity protrudes in the spot is a region where all of the 0th order light and the ± 1st order light overlap.
As apparent from FIGS. 6 to 11 and 12, in the state where the focal position in the optical axis direction in the radial direction of the spot is not shifted (FIGS. 7 and 10), the spot is on the land or on the groove. In the state in which the intensity distribution in the spot does not change depending on whether the focal position in the optical axis direction with respect to the radial direction of the spot is shifted (FIGS. 6, 8, 9, and 11). There is a difference in the intensity distribution. Moreover, the tendency of the intensity distribution in the spot is reversed depending on whether the spot is on the land or on the groove. That is, FIG. 6 and FIG. 11 are the same, and FIG. 8 and FIG. 11 have the same tendency.
[0022]
As described above, each of the sub beams is defocused in the radial direction by the action of the optical diffraction element 65, but is not defocused in the tangential direction and the spot shape is narrowed.
FIG. 13 is an explanatory diagram schematically showing how the intensity distribution changes on the light receiving portions 74A, 74B, and 74C of the light detecting element 74, and FIG. 13A shows that the main spot is located on the groove. FIG. 13B is an explanatory diagram showing a state where the main spot is located on the land, FIG. 13C is an explanatory diagram showing a state where the main spot is located on the groove, and FIG. ) Is an explanatory diagram showing a tracking error signal TE and a land groove discrimination signal CTS with respect to a position in the radial direction.
As shown in FIGS. 13 (A), (B), and (C), when the intensity of the central portion (central divided regions r and t) of the light receiving portions 74A and 74C increases, The output of each light receiving unit 74A, 74C due to a change in the intensity distribution on the land / groove, since the intensity of the area (peripheral divided areas h, i, l, m) changes. Using the change, the track discrimination signal CTS can be obtained by an arithmetic expression (Expression (4)). The tracking error signal TE is obtained by an arithmetic expression (Expression (2)).
Note that the positional relationship between the main spot and the two sub-spots on the recording surface of the optical disc is such that when the main spot is on the groove, the sub-spot is positioned on the land (in the case of FIG. 13D) or the main spot is It is desirable to set the sub-spot so that it is located on the groove when on the groove, and the sign of the track discrimination signal CTS is inverted depending on which one is set.
[0023]
The shift of the focusing position in the optical axis direction with respect to the radial direction of the light beam by the light diffractive element 65 is, for example, an optical diffractive element in which the same curve pattern is repeatedly arranged in the tangential direction as shown in FIG. This can be realized by using 65.
Since the optical diffraction element 65 in which the same curved pattern is repeatedly arranged in the tangential direction does not have power in the tangential direction, it can diffract a light beam transmitted through any position in the tangential direction. The amount of aberration added to the light becomes equal, and stable characteristics can be obtained.
Since the two sub-spots have different diffraction directions, the transmission position is shifted as shown in FIG. 14B. However, since the same pattern is repeated, the characteristic change due to the position does not occur.
By generating the track discrimination signal CTS in this manner, the conventionally used tracking control method can be used even in the land / groove recording method in which the land width and the groove width are substantially equal. Of course, the present invention can be applied to a system in which recording is performed on either a land or a groove.
[0024]
Next, focus control calibration, which is a feature of the present invention, will be described.
As already described, focus control is performed by performing servo control for moving the objective lens of the optical head in the optical axis direction based on detection of the focus error signal FE.
This focus control is performed so that the focus error becomes 0, that is, the focus error signal FE coincides with a voltage value (hereinafter referred to as a focus bias) that is a predetermined control target value. The focus bias changes due to the influence of the characteristics of the optical component and the light emitting / receiving element depending on the surrounding environment and changes with time.
As described above, it is necessary to increase the accuracy of focus control as the recording density increases, and the allowable amount of variation in the focus bias decreases. For this reason, it is necessary to control the focus bias so as to be always optimum.
In the first embodiment, focus control calibration, that is, calibration of the focus bias is performed based on a push-pull signal for generating a tracking error signal detected based on the two sub-spots. .
That is, in the first embodiment, the two sub-spots formed for detecting the tracking error signal TE have different focal positions in the optical axis direction in the radial direction. That is, since the two sub-spots are defocused in the radial direction, the objective lens 70 exhibits an asymmetric behavior as it moves in the optical axis direction. For this reason, the detection signals output from the divided regions 74A and 74C of the light detection element 74 also change asymmetrically.
FIG. 15 shows the defocus amount of the objective lens 70 (defocus amount of the main spot) and the tracking error signal TE = (j−k) K ((hi) + (l −) − expressed by the equation (3). m)) is a characteristic diagram showing the relationship between the amplitudes of push-pull signals SPP1 = (hi) and SPP2 = (lm), and the amplitude of the push-pull signal with the defocus amount on the horizontal axis. Is on the vertical axis.
The push-pull signals SPP1 and SPP2 correspond to the first and second push-pull signals in the claims, and the signal values h and i correspond to the first and second signals in the claims. Values l and m correspond to the third and fourth signals in the claims.
[0025]
As shown in FIG. 15, the amplitudes of the push-pull signals SPP1 and SPP2 with respect to the defocus amount of the main spot have characteristics that the inclinations are opposite to each other. Therefore, a value corresponding to the defocus amount can be obtained based on the amplitude values of the push-pull signals SPP1 and SPP2. That is, the push-pull signals SPP1 and SPP2 constitute a defocus detection signal.
When the amplitudes of the sub-spot push-pull signals SPP1 and SPP2 are expressed as SPP1A and SPP2A, respectively, the focus calibration function can be generated by the following equation (5), for example.
Y = (SPP1A-SPP2A) / (SPP1A + SPP2A) (5)
FIG. 16 is a calculation example of the calibration function when the defocus amount in the radial direction of the sub spot is ± 0.35 μm. The horizontal axis X is a defocus amount, and the vertical axis Y is a calibration value (hereinafter referred to as a function value) corresponding to the defocus amount.
As shown in FIG. 16, a substantially linear behavior is shown in the region of ± 0.15 μm. Thereby, the defocus amount can be calculated backward from the function value of the focus calibration function.
For example, in a state where the focus bias is controlled to 0 by the focus control performed by the servo control circuit 109 shown in FIG. 1, defocus corresponding to the function value of the focus calibration function is obtained, and the defocus is performed. Correcting the focus bias to match the amount of focus correction can correct the focus control and maintain the optimum focus position.
[0026]
FIG. 17 is a block diagram showing the configuration of the portion that corrects the focus error signal based on the function value as described above.
As shown in FIG. 17, the push-pull signal generation unit 121 receives the detection signals h, i, l, and m output from the preamplifier 120, and generates the amplitudes SPP1A and SPP2A of the push-pull signal. It is configured as follows.
The correction unit 122 obtains the calibration function from the amplitudes SPP1A and SPP2A of the push-pull signal input from the push-pull signal generation unit 121 based on the equation (5), and stores the calibration function. It is configured.
The focus servo control unit 109A performs focus servo control based on the focus error signal FE input from the preamplifier 120 in the servo control circuit 109, and the function value of the calibration function input from the correction unit 121. The focus bias is shifted based on the above.
Next, the operation will be described.
The function value of the calibration function in a state where there is no environmental change or change with time is stored in the correction unit 122 in advance as a reference function value.
After that, for example, the function value is detected at a predetermined time or depending on the ambient temperature at the time of power-on, disk replacement, etc., and the detected function value is stored in advance. Correction is performed by shifting the focus bias in the focus servo control circuit 109A so as to match the reference function value.
[0027]
In addition to the above configuration, the correction unit 122 stores in memory the relationship between the function value of the focus calibration function and the shift amount to shift the focus bias corresponding to the function value. Based on the above, the focus bias may be shifted by the focus servo control circuit 109A.
Further, when the relationship between the function value of the focus calibration function and the shift amount of the focus bias is stored, it may be stored as a curve as shown in FIG. 16 or the configuration is simplified. Therefore, the relationship between the function value of the focus calibration function and the shift amount of the focus bias may be stored as a straight line.
In the above example, since the amplitude of the push-pull signal of the secondary spot is used, the calibration function value should be an appropriate value when the tracking servo is on (the tracking servo is on). I can't.
However, when the track of the optical recording medium is wobbling at a high frequency for the purpose of an address signal or a clock signal, the amplitude of the wobbling component included in the push-pull signal, that is, a signal irrelevant to the tracking servo. By using the amplitude, the value of the calibration function can be obtained even when the tracking servo is on.
The calibration function is only an example, and may be expressed by an expression other than the expression (5).
According to the configuration described above, the focus control of the objective lens can be performed with higher accuracy by correcting the focus bias so that the focus bias is optimized even when a deviation from the optimum focus position occurs due to environmental changes or changes with time. be able to.
In other words, even if the focus control is distorted due to the influence of the surrounding environment and changes in the optical components and the characteristics of the light emitting and receiving elements, the focus control can be corrected appropriately to maintain more accurate focus control. can do. In addition, from the above, it is possible to relax the demand for manufacturing accuracy for the light emitting / receiving element, and it is also possible to suppress deterioration of characteristics due to changes over time.
[0028]
Next, the light emitting / receiving element of the present invention will be described.
FIG. 18 is a configuration diagram of an example (second embodiment) of a preferred embodiment of an optical head using the light emitting and receiving element of the present invention.
In FIG. 18, an optical head 5 is a light receiving / emitting element 130 in which a light source, a light detecting element, and an optical component are combined and integrated, and a light beam emitted from the light receiving / emitting element 130 is collected on the optical disc 1 in an optimal state. It consists of other parts for light. The other components include a quarter-wave plate 68, an objective lens 70, a liquid crystal element 77, a collimator 81, an anamorphic mirror 82, and a chromatic aberration correction lens 83.
The quarter-wave plate 68 and the objective lens 70 have the same functions as those described with reference to FIG. The collimator 81 converts a light beam into parallel light or convergent light. The anamorphic mirror 82 performs beam shaping of a light beam, and has the same effect as the anamorphic prism 63.
The liquid crystal element 77 corrects spherical aberration caused by an error in the substrate thickness of the optical disk 1 in an optical system having a high NA.
The chromatic aberration correcting lens 83 corrects chromatic aberration generated when, for example, a short wavelength light source is used.
[0029]
19A and 19B are explanatory views showing the configuration of the light receiving / emitting element and the light receiving element, FIG. 19A is a configuration view of the light receiving / emitting element viewed from the side, and FIG. 19B is a plan view showing a part of the light detecting element. FIG. 19C is a plan view showing another part of the photodetecting element.
A structure of the light receiving and emitting element 130 will be described with reference to FIG.
The light emitting / receiving element 130 includes a light source 131, a mirror prism 132, a substrate 133, a half-wave plate 134, a composite lens 135, a composite prism 136, a light detection element 137, and the like.
The light emitting / receiving element 130 is integrally provided with the mirror prism 132, the half-wave plate 134, the composite lens 135, the composite prism 136, the light detection element 137, and the like on the substrate 133.
The compound lens 135 includes a light diffraction element 135a, a coupling lens 135b, a cylindrical lens 135c, a hologram element 135d, a concave lens 135e, and a split hologram element 135g.
The composite prism 136 includes a polarizing beam splitter film 136a and a half mirror 136b.
As shown in FIGS. 19B and 19C, the light detection element 137 obtains three light receiving portions 137A, 137B, and 137C for obtaining a tracking error signal and a land groove discrimination signal, and a focus error signal. It comprises two light receiving portions 137D and 137E for receiving, a light receiving portion 137F for obtaining an RF signal, and four light receiving portions 137G, 137H, 137I and 137J for obtaining a DPP signal. The four light receiving parts 137G, 137H, 137I, and 137J are provided at the positions of the four corners of the rectangle so that the light receiving parts 137G and 137J are located on the diagonal line, and the light receiving parts 137H and 137I are located on the diagonal line. Yes.
[0030]
Next, the optical path of the light emitting / receiving element 130 will be described with reference to FIGS.
The light beam emitted from the light source 131 is bent in the optical path by the mirror prism 132, passes through the aperture on the substrate 133, is rotated in the polarization direction by the half-wave plate 134, and enters the compound lens 135. To do.
The light beam is separated into three beams used for tracking error detection and land / groove discrimination by the light diffraction element 135a on the compound lens 135, and by the coupling lens 135b on the compound lens 135, The NA incident on the collimator 81 is converted to a small value, and the polarization beam splitter film 136a of the composite prism 136 (P-polarized light is transmitted and S-polarized light is reflected) is transmitted as P-polarized light and travels toward the collimator 81. .
The light beam reflected and returned from the optical disk 1 is again converted into convergent light by the collimator 81, and then the polarization beam splitter film 136a of the composite prism 136 is reflected as S-polarized light, and the half mirror 136b Some are reflected and some are separated into transmitted light.
The light reflected by the herb mirror 136b is shifted in focus in the optical axis direction only in the direction (radial direction) crossing the track direction on the optical disk 1 by the cylindrical lens 135c on the compound lens 135. . That is, the beam shape is stretched in the radial direction.
The light beam is shifted ± 1 in the optical axis direction only in the tangential direction in order to detect the focus error signal FE by the spot size method by the hologram element 135d on the compound lens 135. The secondary light is separated into zero-order light for performing RF signal detection, tracking error signal TE detection, and land / groove discrimination signal CTS detection, and is received by the light receiving portions 137A to 137E of the light detection element 137. The configuration of each of the light receiving units 137A to 137E is the same as that of FIG. 3 described in the first embodiment, and thus the description thereof is omitted.
On the other hand, the light beam transmitted through the half mirror 136b is totally reflected by the total reflection surface 136e, the in-focus position in the optical axis direction is adjusted by the concave lens 135e on the compound lens 135, and the divided hologram element 135g. Thus, the zero-order light for detecting the RF signal and the ± first-order light for detecting the DPD signal are separated and condensed on the light receiving portions 137F to 137J of the light detection element 137.
[0031]
FIG. 20 is a configuration diagram showing the configuration of the split hologram element 135g and the light receiving portions 137F to 137J.
The divided hologram element 135g is divided into four rectangular divided areas A, B, C, and D that are formed in a rectangular shape as a whole and are divided into two equal parts. The divided areas A and C are provided on a diagonal line, and the divided areas B and D are provided on a diagonal line.
The light receiving portions 137G to 137J of the light detection element 137 and the divided regions A to D of the split hologram element 135 are provided to have a corresponding positional relationship.
The split hologram element 135g is incident on the light beam incident on the light receiving unit 137F by the divided regions A to D and the light receiving units 137G to 137J. It is configured to be separated into one −1st order light and four + 1st order lights.
The light beam incident on the divided area A is separated such that the light receiving unit 137G is irradiated with −1st order light and the light receiving unit 137J is irradiated with + 1st order light.
The light beam incident on the divided region B is separated such that the light receiving unit 137H is irradiated with −1st order light and the light receiving unit 137I is irradiated with + 1st order light.
The light beam incident on the divided region C is separated such that the light receiving unit 137G is irradiated with −1st order light and the light receiving unit 137J is irradiated with + 1st order light.
The light beam incident on the divided region D is separated such that the light receiving portion 137H is irradiated with −1st order light and the light receiving portion 137I is irradiated with + 1st order light.
Therefore, output signals AC corresponding to the divided areas A and C are obtained from the light receiving portions 137G and 137J. Output signals BD corresponding to the divided regions B and D are obtained from the light receiving portions 137H and 137I. Therefore, a known DPD signal can be generated from each output signal.
Note that an RF signal corresponding to the 0th-order light of the light beam is obtained from the light receiving unit 137F.
In this way, servo signals such as a focus error signal FE, a tracking error signal TE, and a land groove discrimination signal CTS, and an RF signal are generated based on output signals generated by the light received by the light detection element 137. Is generated and information reproduction and light spot control on the disc are performed. The relationship between the spot on the light detection element and the light receiving portion is shown in the lower part of FIG.
Various signals are detected by the following equations, for example.
FE = (a + c−b−n−o) − (d + f−e−p−q) (6)
TE = (j−k) −K * {(h−i) + (1−m)} (7)
(Where K is a coefficient and * is a symbol indicating multiplication)
CTS = {(h + i) -r}-{(l + m) -t} (8)
RF signal = output signal RF
DPD signal = phase difference signal between output signal AC and output signal BD
Thereby, the RF signal can be generated from the single light receiving unit 137F, the RF signal can be reduced in noise and widened, and the DPD signal can be detected by the four light receiving units 137G to 137J.
[0032]
Then, similarly to the case described with reference to FIG. 17 of the first embodiment, calibration is performed by the above equation (5) using the push-pull signals SPP1 and SPP2 amplitudes SPP1A and SPP2A for generating the tracking error signal TE. The focus bias can be calibrated by obtaining the value Y. Since the operation of each part is the same as that of the first embodiment, description thereof is omitted.
Of course, in the second embodiment, the same effects as in the first embodiment can be obtained.
[0033]
In the first and second embodiments, the case where a semiconductor laser having a single light emitting point is used as the light source has been described as an example. However, the present invention is not limited to this.
That is, the light source has two or more light emitting points, one light emitting point forms the main spot, and the other light emitting point forms the two sub spots. You can also In this case, the two sub-spots formed by the two sub-beams emitted from the other light emitting points have one in-focus position in the optical axis direction in the radial direction with respect to the focus position of the main beam. It is configured so that it is shifted closer to the objective lens and the other is shifted further away from the objective lens.
In the first and second embodiments, the example in which the defocus amount is obtained by calculating the function value of the calibration function using two two sub-spots has been described. It is not limited.
For example, the calibration function may be calculated by substituting one of the sub-spots with a main spot. Further, the calibration function may be calculated using all detection signals obtained from the main spot and the two sub-spots.
[0034]
In each of the above-described embodiments, the optical head and the light emitting / receiving element are configured separately from the preamplifier and the servo control circuit. However, the optical amplifier and the light emitting / receiving element include the preamplifier and the servo. Of course, a part of the components of the control circuit may be incorporated.
[0035]
【The invention's effect】
As described above, according to the optical head of the present invention, the defocus detection signal generated by the light detection means calculates the defocus detection signal and the focus position of the main spot. A signal corresponding to a defocus amount that is a deviation amount from the information recording surface is configured as a signal that can be calculated.
Therefore, the focus control of the objective lens can be performed with higher accuracy by correcting the focus control of the objective lens based on the value corresponding to the defocus amount. In addition, even if the focus control is distorted due to the influence of the surrounding environment or changes in the optical components or the characteristics of the light emitting and receiving elements, the focus control can be corrected appropriately to maintain more accurate focus control. Can do. In addition, it is possible to alleviate the demand for manufacturing accuracy for the optical head, and it is also possible to suppress deterioration of characteristics due to changes over time.
Further, according to the light receiving and emitting element of the present invention, the defocus detection signal generated by the light detection means calculates the defocus detection signal and the focus position of the main spot and the information recording A signal corresponding to a defocus amount that is a deviation amount from the surface is configured as a signal that can be calculated.
Therefore, the focus control of the objective lens can be performed with higher accuracy by correcting the focus control of the objective lens based on the value corresponding to the defocus amount. In addition, even if the focus control is distorted due to the influence of the surrounding environment or changes in the optical components or the characteristics of the light emitting and receiving elements, the focus control can be corrected appropriately to maintain more accurate focus control. Can do. In addition, it is possible to alleviate the demand for manufacturing accuracy for the light emitting / receiving element, and it is also possible to suppress deterioration of characteristics due to changes over time.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of an optical recording medium recording / reproducing apparatus incorporating an optical head according to a first embodiment.
2A and 2B are configuration diagrams of an optical head according to the first embodiment, in which FIG. 2A is a plan view and FIG. 2B is a side view.
FIG. 3 is a plan view showing a relationship between a spot on a light detection element and a light receiving unit.
4 is an operation explanatory view of the hologram element 72. FIG. 4A is an explanatory view showing a state in which the hologram element 72, the cylindrical lens 72, and the light detection element 74 are viewed from the tangential direction. (B) is explanatory drawing which shows the state which looked at the cylindrical lens 72 and the photon detection element 74 from the radial direction.
FIG. 5 is a plan view of a light detection element.
FIG. 6 is a characteristic diagram showing the result of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of the DVR disc.
FIG. 7 is a characteristic diagram showing the result of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of a DVR disc.
FIG. 8 is a characteristic diagram showing the result of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of the DVR disc.
FIG. 9 is a characteristic diagram showing the result of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of the DVR disc.
FIG. 10 is a characteristic diagram showing the result of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of the DVR disc.
FIG. 11 is a characteristic diagram showing the result of calculating the intensity distribution and phase distribution of the disc diffracted light on the objective lens pupil during reproduction of a DVR disc.
12A is an explanatory diagram of zero-order light and ± 1st-order light during disk reproduction using conventional land recording, and FIG. 12B is a diagram illustrating 0th-order light and ± 1 on the objective lens pupil. FIG. 12C is an explanatory diagram showing the relationship of the next light, FIG. 12C is an explanatory diagram of 0th order light and ± 1st order light at the time of disc reproduction using land groove recording, and FIG. 12D is a disc using land groove recording. It is explanatory drawing which shows the relationship between the 0th-order light and the ± 1st-order light on the objective-lens pupil at the time of reproduction | regeneration.
FIG. 13 is an explanatory view schematically showing how the intensity distribution changes on each light receiving portion of the light detection element, and FIG. 13 (A) is an explanatory view showing a state where the main spot is located on the groove. FIG. 13B is an explanatory view showing a state where the main spot is located on the land, FIG. 13C is an explanatory view showing a state where the main spot is located on the groove, and FIG. 13D is a view in the radial direction. It is explanatory drawing which shows the tracking error signal TE with respect to a position, and the land groove discrimination | determination signal CTS.
14A is an explanatory diagram of an optical diffraction element in which the same curve pattern is repeatedly arranged in the tangential direction, and FIG. 14B is an explanatory diagram of the positional relationship of spots.
FIG. 15 is a characteristic diagram showing the relationship between the defocus amount of the objective lens and the amplitude of the push-pull signal of the tracking error signal TE.
FIG. 16 is a characteristic diagram showing an example of a calibration function using push-pull signals SPP1 and SPP2.
FIG. 17 is a block diagram showing a configuration of a portion that corrects a focus error signal based on the calibration value Y in the optical recording medium recording / reproducing apparatus incorporating the optical head according to the first embodiment. .
FIG. 18 is a configuration diagram of an example (second embodiment) of a preferred embodiment of an optical head using the light emitting and receiving element of the present invention.
19A and 19B are explanatory diagrams showing the configuration of the light emitting / receiving element and the light receiving element, in which FIG. 19A is a structural view of the light receiving / emitting element viewed from the side, and FIG. 19B is a plan view showing a part of the light detecting element; FIG. 19C is a plan view showing another part of the photodetecting element.
FIG. 20 is a configuration diagram showing a configuration of a split hologram element and each light receiving unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical disk, 2 ... Optical head, 61 ... Semiconductor laser, 65 ... Optical diffraction element, 70 ... Objective lens, 74 ... Photodetection element, 130 ... Light receiving / emitting element.

Claims (30)

A light source that emits a light beam; and an objective lens that converges and irradiates the light beam toward an information recording surface of the optical recording medium, and that makes a reflected light beam reflected from the optical recording medium incident and emitted; wherein a light detecting means for receiving reflected light beam, the main spot and two sub-spots on the information recording surface by the light beam emitted from the light source is configured to be formed, said main spot For recording and / or reproducing information on the information recording surface, the formation of the main spot and the sub-spot includes the main spot and two sub-spots in a radial direction across the track of the optical recording medium. as the focus position of the optical axis of the light beams forming different each other, and one of the focus position of the two sub-spots of the main spot Than focus position becomes the position closer to the objective lens, and the other focus position of the two sub-spots are configured so as to be farther from the objective lens than the focus position of the main spot, the light The detection means includes a first light receiving unit and a second light receiving unit configured to receive the two sub-spots, respectively, and the first light receiving unit is divided into at least two in the radial direction. The second light receiving unit has third and fourth divided regions divided into at least two in the radial direction, and the detection signals detected in the first to fourth divided regions are respectively provided. When the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4 are used, the first push-pull signal SPP1 is formed by the difference signal (S1-S2) between the first signal and the second signal. , The third signal and the fourth signal The second push-pull signal SPP2 is formed by the difference signal (S3-S4), and the tracking error signal is obtained using the first and second push-pull signals SPP1, SPP2, and the first and second push-pull signals SPP1 and SPP2 include sinusoidal signal components having amplitude, and the defocus detection signal is composed of the first and second push-pull signals SPP1 and SPP2 , and by calculating the defocus detection signal, the main value corresponding to the defocus amount which is the amount of deviation of focus and the position and the information recording surface of the spot Ru is configured as a calculation possible signal, the optical head. Wherein the light source has two or more light emitting points, one light emitting points forms the main spot, the optical head according to claim 1, wherein the other light-emitting points are arranged to form the two sub-spots . Wherein the light source has only one light emitting point, the main spot and two single optical head according to claim 1, wherein the spot forming means provided we are formed from the light beam emitted by-spot from the light emitting point. The spot forming means, the light source and the optical head 請 Motomeko 3 wherein that consists by optical diffraction element provided between the objective lens. Said first signal component of the sinusoidal with the amplitude in the second push-pull signal SPP1, SPP is 請 Motomeko 1 wherein Ru der based on wobbling component of the tracks formed on the optical recording medium Light head. The amplitude of the first push-pull signal SPP1 SPP1A, the amplitude of the second push-pull signal SPP2 is taken as SPP2A, a value corresponding to the defocus amount, Ru indicated by (SPP1A-SPP2A) / (SPP1A + SPP2A) 請 Motomeko 1 light head described. The information recording surface lands and grooves are formed, the optical recording medium wherein lands and 請 Motomeko 1 optical head according that is configured to at least one of recording or reproducing information of the groove is performed. A light source that emits a light beam; and an objective lens that converges and irradiates the light beam toward an information recording surface of the optical recording medium, and that makes a reflected light beam reflected from the optical recording medium incident and emitted; Light detecting means for receiving, via the objective lens, a reflected light beam reflected from the optical recording medium by irradiating the light beam through the objective lens toward the information recording surface of the optical recording medium. A main spot and two sub-spots are formed on the information recording surface by the light beam emitted from the light source, and the main spot records and / or reproduces information on the information recording surface. The formation of the main spot and the sub-spot is performed in the radial direction across the track of the optical recording medium with respect to the main spot and the two sub-spots. The focusing position in the optical axis direction of the light beam forming the pot is different from each other, and one focusing position of the two sub-spots is closer to the objective lens than the focusing position of the main spot. And the other in-focus position of the two sub-spots is configured to be farther from the objective lens than the in-focus position of the main spot, and the light detection means A first light receiving portion configured to receive light; and a second light receiving portion. The first light receiving portion includes first and second divided regions that are divided into at least two portions in a radial direction. The light receiving unit has third and fourth divided regions divided into at least two in the radial direction, and the detection signals detected in the first to fourth divided regions are the first signal S1, the second signal S2, and the second signal, respectively. 3 signal S3, 4th signal S The first push-pull signal SPP1 is formed by the difference signal (S1-S2) between the first signal and the second signal, and the difference signal (S3-S4) between the third signal and the fourth signal. 2 push-pull signals SPP2 are formed, and tracking error signals are obtained using the first and second push-pull signals SPP1 and SPP2, and the first and second push-pull signals SPP1 and SPP2 have a sine wave shape having an amplitude. The defocus detection signal is composed of the first and second push-pull signals SPP1 and SPP2 , and the defocus detection signal is calculated to calculate the focus position of the main spot and the information. values corresponding to the defocus amount which is the amount of deviation between recording surface Ru is configured as a calculation possible signal, receiving the light-emitting element. The light source has two or more light emitting points, and one light emitting point forms the main spot, and the other light emitting point forms the two sub spots. Item 9. The light emitting and receiving element according to item 8 . The said light source has only one light emission point, The spot formation means which forms the said main spot and two subspots from one light beam radiate | emitted from the said light emission point is provided. 9. The light emitting / receiving element according to 8 . 11. The light emitting / receiving element according to claim 10 , wherein the spot forming unit includes an optical diffraction element provided between the light source and the objective lens. The sinusoidal signal component having the amplitude included in the first and second push-pull signals SPP1, SPP is based on a wobbling component of a track formed on the optical recording medium. Item 9. The light emitting and receiving element according to item 8 . When the amplitude of the first push-pull signal SPP1 is SPP1A and the amplitude of the second push-pull signal SPP2 is SPP2A, the value corresponding to the defocus amount is represented by (SPP1A−SPP2A) / (SPP1A + SPP2A). The light emitting / receiving element according to claim 8 . The information recording surface lands and grooves are formed, the optical recording medium wherein lands and grooves of the at least one recording or reproducing information optical element of 請 Motomeko 8, wherein that is configured to be performed. A driving means for rotationally driving the optical recording medium, an optical head for irradiating the rotating optical recording medium with a light beam and detecting a reflected light beam from the information recording surface of the optical recording medium, and the optical head In the optical recording medium recording / reproducing apparatus having a signal processing circuit that generates a reproduction signal based on the detection signal, the optical head includes a light source, an objective lens, and light detection means, and the light source includes the light beam. The objective lens converges and irradiates the light beam toward the information recording surface of the optical recording medium, and makes the reflected light beam reflected from the optical recording medium incident and output. The light detection means is configured to receive the reflected light beam and output the detection signal, and the information recording surface is formed by the light beam emitted from the light source. The main spot and two sub-spots is configured to be formed on said main spot is for performing recording and / or reproducing of information for the information recording surface, the formation of the sub-spot and the main spot Is different from each other in the focal position in the optical axis direction of the light beam forming the main spot and the two sub-spots in the radial direction across the track of the optical recording medium, and one of the two sub-spots. The in-focus position is closer to the objective lens than the in-focus position of the main spot, and the other in-focus position of the two sub-spots is a position farther from the objective lens than the in-focus position of the main spot. is configured such that, the light detecting means comprises a first light receiving portion and the second light receiving portion to which the two sub-spots are configured so as to receive respectively, before The first light receiving unit includes first and second divided regions divided into at least two in the radial direction, and the second light receiving unit includes third and fourth divided regions divided into at least two in the radial direction. And when the detection signals detected in the first to fourth divided regions are the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4, respectively, the first signal and the second signal The first push-pull signal SPP1 is formed by the difference signal (S1-S2), the second push-pull signal SPP2 is formed by the difference signal (S3-S4) between the third signal and the fourth signal, and the tracking error signal is The first and second push-pull signals SPP1 and SPP2 are used, and the first and second push-pull signals SPP1 and SPP2 include a sinusoidal signal component having an amplitude, and a defocus detection signal. Is composed of the first and second push-pull signals SPP1 and SPP2 , and the detection signal is calculated by calculating the defocus detection signal and the amount of deviation between the focus position of the main spot and the information recording surface. optical recording medium recording and reproducing apparatus a value corresponding to a certain amount of defocus is configured as a calculation possible signal. Wherein the light source has two or more light emitting points, one light emitting points forms the main spot, the other light emitting points according 請 Motomeko 15 that is configured to form the two sub-spots Optical recording medium recording / reproducing apparatus. Wherein the light source has only one light emitting point, the main spot and two one light according 請 Motomeko 15 spot forming means that are provided for forming a light beam emitted by-spot from the light emitting point Recording medium recording / reproducing apparatus. The spot forming means, the light source and the optical recording medium recording and reproducing apparatus 請 Motomeko 17 wherein that consists by optical diffraction element provided between the objective lens. Said first signal component of the sinusoidal with the amplitude in the second push-pull signal SPP1, SPP is 請 Motomeko 15 wherein Ru der based on wobbling component of the tracks formed on the optical recording medium Optical recording medium recording / reproducing apparatus. When the amplitude of the first push-pull signal SPP1 is SPP1A and the amplitude of the second push-pull signal SPP2 is SPP2A, the value corresponding to the defocus amount is represented by (SPP1A−SPP2A) / (SPP1A + SPP2A). The optical recording medium recording / reproducing apparatus according to claim 15 . The lands and grooves are formed on the information recording surface, the optical recording medium is an optical recording medium recording according 請 Motomeko 15 that is configured to record or reproduce at least one information of the land and groove is made Playback device. The objective lens is provided so as to be movable at least in the optical axis direction of the objective lens, and the optical recording medium recording / reproducing apparatus includes a servo circuit that moves the objective lens based on a detection signal from the optical head, The servo circuit is configured so that the optical axis of the objective lens matches the information recording surface based on a value corresponding to the defocus amount calculated based on the defocus detection signal. 16. The optical recording medium recording / reproducing apparatus according to claim 15 , wherein the optical recording medium recording / reproducing apparatus is configured to perform direction movement control. A driving means for rotationally driving the optical recording medium, an optical head for irradiating the rotating optical recording medium with a light beam and detecting a reflected light beam from the information recording surface of the optical recording medium, and the optical head In an optical recording medium recording / reproducing apparatus having a signal processing circuit for generating a reproduction signal based on the detection signal, the optical head includes an objective lens, and a light emitting / receiving element provided with a light source and light detection means. The light source is configured to emit the light beam, and the objective lens converges and irradiates the light beam toward an information recording surface of the optical recording medium, and also reflects reflected light from the optical recording medium. The light detection means is configured to be incident and output, and the light detection unit is configured to receive the reflected light beam and output the detection signal, and the light beam emitted from the light source Thus the information main spot and two sub-spots on the recording surface is configured to be formed, the main spot is for performing recording and / or reproducing of information for the information recording surface, said main spot And the sub-spots are formed so that the focal positions in the optical axis direction of the light beam forming the main spot and the two sub-spots are different from each other in the radial direction across the track of the optical recording medium, and The in-focus position of one of the two sub-spots is closer to the objective lens than the in-focus position of the main spot, and the in-focus position of the other sub-spot is more than the in-focus position of the main spot. wherein is configured to be distant from the objective lens, said light detecting means includes a first light receiving portion in which the two sub-spots is configured to receive, respectively Two light receiving portions, the first light receiving portion has first and second divided regions divided into at least two portions in the radial direction, and the second light receiving portion is divided into at least two portions in the radial direction. When the detection signals detected in the first to fourth divided areas are the first signal S1, the second signal S2, the third signal S3, and the fourth signal S4, respectively, having the third and fourth divided areas. A first push-pull signal SPP1 is formed by the difference signal (S1-S2) between the first signal and the second signal, and a second push-pull signal SPP2 is formed by the difference signal (S3-S4) between the third signal and the fourth signal. The tracking error signal is obtained using the first and second push-pull signals SPP1 and SPP2, and the first and second push-pull signals SPP1 and SPP2 include a sinusoidal signal component having an amplitude. And The defocus detection signal is composed of the first and second push-pull signals SPP1 and SPP2 , and the detection signal is calculated by calculating the defocus detection signal and the focus position of the main spot and the information recording surface. optical recording medium recording and reproducing apparatus values corresponding to the defocus amount Ru is configured as capable of calculating signal which is the amount of deviation between. The light source has two or more light emitting points, and one light emitting point forms the main spot, and the other light emitting point forms the two sub spots. optical recording medium recording and reproducing apparatus of claim 2 3, wherein. The said light source has only one light emission point, The spot formation means which forms the said main spot and two sub-spots from one light beam radiate | emitted from the said light emission point is provided. 2 3 the optical recording medium recording and reproducing apparatus according. The spot forming means includes optical recording medium recording and reproducing apparatus according to claim 2 5, wherein be constituted by optical diffraction element provided between the light source and the objective lens. Said first signal component of the sinusoidal with the amplitude in the second push-pull signal SPP1, SPP is 請 Motomeko 23 wherein Ru der based on wobbling component of the tracks formed on the optical recording medium Optical recording medium recording / reproducing apparatus. The amplitude of the first push-pull signal SPP1 SPP1A, the amplitude of the second push-pull signal SPP2 is taken as SPP2A, a value corresponding to the defocus amount, Ru indicated by (SPP1A-SPP2A) / (SPP1A + SPP2A) optical recording medium recording and reproducing apparatus 請 Motomeko 23 wherein. Wherein the information recording surface land and groove is formed, the optical recording medium wherein lands and the optical recording medium recording the 請 Motomeko 23 described that is configured so that the recording or reproducing at least one information of the groove is performed Playback device. The objective lens is provided so as to be movable at least in the optical axis direction of the objective lens, and the optical recording medium recording / reproducing apparatus includes a servo circuit that moves the objective lens based on a detection signal from the optical head, The servo circuit is configured so that the optical axis of the objective lens matches the information recording surface based on a value corresponding to the defocus amount calculated based on the defocus detection signal. optical recording medium recording and reproducing apparatus 請 Motomeko 23 described that is configured to perform the movement control of the direction.

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