JP3828740B2 - Optical detector, optical pickup, and optical information reproducing apparatus using the same - Google Patents

Description

【００５１】
式（１）によると、ＣＤ−Ｒディスクでのスポット間隔Ｔｐ３１を０．８０μｍに設定した場合のＤＶＤ−ＲＡＭディスク上でのスポット間隔Ｔｐ２２は、０．６７μｍとなる。これは、ＤＶＤ−ＲＡＭディスクにおけるトラックピッチの半値０．７４μｍに対して約１０％程度のズレ位置であり、後述するサーボ信号検出方式を用いることにより問題なくＤＶＤ−ＲＡＭディスクからサーボ信号を検出することが可能となっている。また、逆にＤＶＤ−ＲＡＭディスク上でのスポット間隔Ｔｐ２２を０．７４μｍに設定した場合においては、ＣＤ−Ｒディスクでのスポット間隔Ｔｐ３１は、０．８９μｍとなる。これは、ＣＤ−Ｒディスクにおけるトラックピッチ０．８μｍに対して約１０％程度のズレ位置であり、後述するサーボ信号検出方式を用いることにより問題なくＣＤ−Ｒディスクからサーボ信号を検出することが可能であり、スポット間隔の設定基準となる光ディスクは任意に選択可能である。
【００５２】
尚、図２にて示した光検出器９は後述するように所定の波長のレーザ光に対して、田の字型に４つの受光面からなる受光領域を少なくとも１つ備えている構成である。光ディスク１または光ディスク１０を反射した０次光及び±１次回折光の光ビームは、各受光領域のほぼ中心すなわち受光領域内の縦、横の分割線が十字に交わっている点と光ビームの強度中心がほぼ一致する位置に集光される。このとき各光ビームは光路に対して傾斜して配置されているハーフミラー４を透過するときに所定の非点収差が与えられているために、後ほど説明するように田の字型の受光領域から非点収差方式によりフォーカスエラー信号を検出するようになっている。同様に、４つの受光面からなる出力信号を用いることにより、プッシュプル方式またはディファレンシャルフェイズディテクション方式によるトラッキングエラー信号が検出可能である。
【００５３】
次に、光ディスク１上の光スポットの強度分布について、図６を用いて説明する。本実施例においては、図４にて示したように光ディスク１に照射されるスポット１００及び１０１、１０２のディスク半径方向に関する照射位置間隔は、ＤＶＤ−ＤＡＭディスクの案内溝ピッチの略半分に一致するように設定されている。すなわち、例えば図６に示すＤＶＤ−ＲＡＭディスク上の３つの光スポット１００、１０１、１０２の配置は、図中の（ｂ）に示すように０次光の光スポット１００がディスクの案内溝間２０３の真上に位置している場合は、＋１次回折光の光スポット１０１と−１次回折光の光スポット１０２はそれぞれ隣接する案内溝２０２の真上に位置している。そして案内溝２０２に対して光スポット照射位置が相対的にずれていくような場合でも、光スポット１００、１０１、１０２の間には、図６（ａ）または（ｃ）に示すような位置関係が常に保たれる。一方、光ディスクによる反射光ビームは、案内溝２０２による回折の影響を受けて、光スポットの照射位置とディスクの案内溝の相対的な位置変化に応じて周期的に変化する特有の強度分布パターンを有することになる。そして、０次光の光スポット１００の反射光ビームと、＋１次回折光による光スポット１０１及び−１次回折光による光スポット１０２の反射光ビームでその強度分布を比較すると、図６（ａ）及び（ｃ）に示すように完全に左右が反転したような変化を示している。
【００５４】
ところで、これら反射光ビームから非点収差方式によるフォーカスエラー信号を検出すると、検出したフォーカスエラー信号に大きな外乱が発生しやすくなるという問題がある。これは先ほど述べた案内溝２０２での回折の影響による反射光ビームの強度分布パターンの周期的変化と、それによって生じるプッシュプル信号のもれ込み外乱が主要因となっているものである。従って、図７（ａ）及び（ｂ）に示すように光スポット１００の反射光束から得られたフォーカスエラー信号と光スポット１０１及び光スポット１０２の反射光束から得られたフォーカスエラー信号を比較すると、フォーカスエラー信号の波形自体はほぼ同一であるのに対して、信号内に発生する外乱成分はその位相がほぼ完全に反転している。
【００５５】
そこで光スポット１００の反射光束から得られたフォーカスエラー信号と、光スポット１０１または光スポット１０２の反射光束から得られたフォーカスエラー信号もしくはその両者の和信号を加算処理すると、図７（ｃ）に示すようにフォーカスエラー自体は倍加される一方で外乱成分がほぼ完全にキャンセルされた良好なフォーカスエラー信号を得ることができる。
【００５６】
上記に示したような現象は、プッシュプル方式によるトラッキングエラー信号検出についても同様に当てはまる。つまり、一般にプッシュプル方式によるトラッキングエラー信号を検出する際、対物レンズがトラッキング方向に変位するとそれに伴って光検出器９の受光面に照射される光スポットも変位してしまい、図８（ａ）及び（ｂ）に示すように検出されたトラッキングエラー信号には大きなオフセットが発生する。このオフセットは図８（ａ）及び（ｂ）のように光スポット１００の反射光ビームから検出したトラッキング信号にも光スポット１０１及び光スポット１０２の反射光ビームから検出したトラッキングエラー信号にも同じ向きにほぼ同程度だけ発生する。一方、トラッキングエラー信号自体は上記のフォーカスエラー信号の説明で述べた理由と全く同じ理由で、光スポット１００の反射光ビームから検出された信号の位相と、光スポット１０１及び１０２の反射光ビームから検出された信号の位相がほぼ完全に反転している。このことから、各光スポットのディスク反射光から検出されたトラッキングエラー信号を減算処理することにより、オフセット成分だけをキャンセルし、図８（ｃ）に示したようなオフセットが大幅に低減された良好なトラッキングエラー信号を得ることができる。
【００５７】
本発明による実施例においては、以上のような原理を利用して良好なフォーカスエラー信号およびトラッキングエラー信号を検出するものである。
【００５８】
図９は本発明による光検出器および信号処理回路に関する第１の実施例を示した平面図及びブロック図である。光検出器９のパッケージ２０には、図のように各分割受光面が記号ａ、ｂ、ｃ、ｄで表されている田の字型に４分割された受光領域２１０が配置され、その両隣に受光領域２１０と同様に分割受光面が記号ｅ、ｆ、ｇ、ｈで表されている４分割受光領域２１１、及び記号ｉ、ｊ、ｋ、ｌで表されている４分割受光領域２１２が配置されている。さらに、分割受光面が記号ｍ、ｎ、ｏ、ｐで表されている４分割受光領域４１０、分割受光面が記号ｑ、ｒで表されている２分割受光領域４１１、分割受光面が記号ｓ、ｔで表されている２分割受光領域４１２が配置されている。そして受光領域２１０上には、ディスク上光スポット１００のディスク反射光が集光され検出光スポット１１０を形成している。同様に受光領域２１１上にはディスク上光スポット１０１のディスク反射光が、受光領域２１２上にはディスク上光スポット１０２のディスク反射光がそれぞれ集光され、検出光スポット１１１および１１２を形成している。
【００５９】
また、受光領域４１０上には、ディスク上光スポット３００のディスク反射光が集光され検出光スポット３１０を形成している。同様に受光領域４１１上にはディスク上光スポット１０１のディスク反射光が、受光領域４１２上にはディスク上光スポット１０２のディスク反射光がそれぞれ集光され、検出光スポット３１１および３１２を形成している。
【００６０】
ここで、本発明の第１の実施例においては、同一筐体内の微小距離ｄだけ離れた２つの異なる波長のレーザ光源（２波長マルチレーザ）と１つの回折格子及び１つの光検出器から光学系を構成している。そのため、受光領域２００、２０１、２０２からなる受光領域列と受光領域４１０、４１１、４１２からなる受光領域列は、光学系の結像系に対応して異なる位置に配置されることとなる。更に、各レーザ光の±１次回折光に対応する受光領域２０１、２０２、４１１、４１２に関しては、波長の大きなレーザ光源に対応した受光領域４１１、４１２間の間隔が回折格子３での光ビームの回折角度にほぼ比例して大きな配置となっている。
【００６１】
受光面ａ、ｂ、ｃ、ｄの各々で光電変換されて検出された各検出電流は、光検出器９のパッケージ２０に設けられた電流−電圧変換増幅器４０、４１、４２、４３によって電圧に変換され、それぞれ光検出器９の出力端子に送られる。同様に受光面ｅ、ｆ、ｇ、ｈ、ｉ、ｊ、ｋ、ｌ、ｍ、ｎ、ｏ、ｐ、ｑ、ｒ、ｓ、ｔの出力線は電流−電圧変換増幅器４４、４５、４６、４７、４８、４９、５０、５１、８０、８１、８２、８３、８４、８５、８６、８７に接続されている。（以下、説明を簡単にするため、これら電圧変換された検出信号については、その検出信号が検出された受光面と同一の記号を付する。）結局、光検出器９の２０本の出力端子には、それぞれ ａ、ｂ、ｃ、ｄ、ｅ、ｆ、ｇ、ｈ、ｉ、ｊ、ｋ、ｌ、ｍ、ｎ、ｏ、ｐ、ｑ、ｒ、ｓ、ｔが出力されることになる。
【００６２】
次に演算回路について説明する。光検出器９の出力端子から出力される２０本の検出信号のうち、出力信号ａ、ｂ、ｃ、ｄからは、加算器５２、５３、減算器５４によって信号（ａ＋ｃ）−（ｂ＋ｄ）が出力され、加算器５５、５６、減算器５７によって信号（ａ＋ｄ）−（ｂ＋ｃ）が出力される。ここで、信号（ａ＋ｃ）−（ｂ＋ｃ）は、いわゆる非点収差方式によって検出されるディスク上光スポット１００のフォーカスエラー信号に相当する。また（ａ＋ｄ）、（ｂ＋ｃ）は、検出光スポット１１０をディスクのトラッキング方向（半径方向）に２分割した場合の各々の領域における検出光量に相当し、この２個の信号の差信号（ａ＋ｄ）−（ｂ＋ｃ）はいわゆるプッシュプル方式によって検出されるディスク上光スポット１００のトラッキングエラー信号に相当する。
【００６３】
さらに、出力信号ａ、ｂ、ｃ、ｄには位相差検出回路７７が接続されており、この回路によっていわゆる位相差検出方式（ディファレンシャル・フェイズ・ディテクション方式）によるディスク上光スポット１００のトラッキングエラー信号も検出されるようになっている。尚、この位相差検出方式については、既に公知の技術なので詳細な説明はここでは省略する。
【００６４】
また、加算器７６により出力信号ａ、ｂ、ｃ、ｄの和信号ＤＶＤ−ＲＦを生成することにより、光ディスクに記録されている情報信号を所定の信号再生回路により再生可能となっている。尚、本実施例では示されていないが、前記加算器７６を光検出器９のパッケージ２０内に格納し、光検出器９の信号出力端子に和信号（ａ＋ｂ＋ｃ＋ｄ）の出力端子を追加する構成も可能である。
【００６５】
さらに、出力信号ｅ、ｆ、ｇ、ｈからは、加算器５８、５９、減算器６０によって信号（ｅ＋ｇ）−（ｆ＋ｈ）が出力され、加算器６１、６２、減算器６３によって信号（ｅ＋ｈ）−（ｆ＋ｇ）が出力されている。同様に出力信号ｉ、ｊ、ｋ、ｌからは、加算器６４、６５、減算器６６によって信号（ｉ＋ｋ）−（ｊ＋ｌ）が出力され、また加算器６７、６８、減算器６９によって信号（ｉ＋ｌ）−（ｊ＋ｋ）が出力されている。
【００６６】
信号（ｅ＋ｇ）−（ｆ＋ｈ）及び（ｉ＋ｋ）−（ｊ＋ｌ）は加算器７０によって信号（ｅ＋ｇ＋ｉ＋ｋ）−（ｆ＋ｈ＋ｊ＋ｌ）として出力されており、更に増幅器７１によって所定の増幅率Ｋ１で増幅されている。この増幅器７１の増幅率Ｋ１は信号（ｅ＋ｇ＋ｉ＋ｋ）−（ｆ＋ｈ＋ｊ＋ｌ）が信号（ａ＋ｃ）−（ｂ＋ｄ）とほぼ同一の信号振幅になるように定められている。なお、この信号（ｅ＋ｇ＋ｉ＋ｋ）−（ｆ＋ｈ＋ｊ＋ｌ）は、いわゆる非点収差方式によって検出されたディスク上光スポット１０１および１０２のフォーカスエラー信号の和信号に相当するものである。
【００６７】
一方、（ｅ＋ｈ）−（ｆ＋ｇ）及び（ｉ＋ｌ）−（ｊ＋ｋ）は、加算器７３によって信号（ｅ＋ｈ＋ｉ＋ｌ）−（ｆ＋ｇ＋ｊ＋ｋ）が出力され、さらに増幅器７４によって所定の増幅率Ｋ２で増幅されている。この増幅器７４の増幅率Ｋ２は信号（ｅ＋ｈ＋ｉ＋ｌ）−（ｆ＋ｇ＋ｊ＋ｋ）が信号（ａ＋ｄ）−（ｂ＋ｃ）とほぼ同一の信号振幅になるように定められている。尚、この信号（ｅ＋ｈ＋ｉ＋ｌ）−（ｆ＋ｇ＋ｊ＋ｋ）は、検出光スポット１１１と１１２をディスクのトラッキング方向（半径方向）に２分割した場合の各々の領域における総検出光量の差に相当し、いわゆるプッシュプル方式によって検出されるディスク上スポット１０１および１０２のトラッキングエラー信号の和に相当するものである。減算器７５から出力される信号は、
｛（ａ＋ｄ)−(ｂ＋ｃ）｝−Ｋ２・｛（ｅ＋ｈ＋ｉ＋ｌ)−(ｆ＋ｇ＋ｊ＋ｋ）｝となる。この信号は、受光領域２００から得られたディスク上スポット１００のトラッキングエラー信号から、受光領域２０１および２０２から得られたディスク上スポット１０１および１０２のトラッキングエラー信号を減算した信号に相当するものである。
【００６８】
ところで、この信号処理回路のフォーカスエラー信号出力端子とトラッキングエラー信号出力端子にはそれぞれ切り替えスイッチ７８および７９が設けられている。これは、以下のように光ディスクの種類に応じて、アクチュエータ７の制御に用いられるフォーカスエラー信号とトラッキングエラー信号を適宜切り替えるために設けられているものである。すなわち、例えばＤＶＤ−ＲＡＭディスクのようにディスクの記録面に連続した案内溝が設けられている光ディスクを再生する場合は、図９に示すようにまず切り替えスイッチ７８を切り替え、減算器５４から出力された信号（ａ＋ｃ）−（ｂ＋ｄ）と増幅器７１から出力された信号Ｋ１・｛（ｅ＋ｉ＋ｇ＋ｋ）−（ｈ＋ｌ＋ｆ＋ｊ）｝を加算器７２により加算処理した信号
｛（ａ＋ｃ)−(ｂ＋ｄ）｝＋Ｋ１・｛（ｅ＋ｉ＋ｇ＋ｋ)−(ｈ＋ｌ＋ｆ＋ｊ）｝をフォーカスエラー信号として出力する。この信号は前記したように非点収差方式による光ディスク上の光スポット１００のフォーカスエラー信号と、光スポット１０１と１０２のフォーカスエラー信号の和信号振幅を合わせて足しあわせた信号に相当する。したがってこの信号は、前記したように案内溝での回折によるフォーカスエラー信号のもれ込み外乱を大幅に解消した良好なフォーカスエラー信号となっている。
【００６９】
次にトラッキングエラー信号については、切り替えスイッチ７９を切り替え、信号
｛（ａ＋ｄ)−(ｂ＋ｃ）｝−Ｋ２・｛（ｅ＋ｈ＋ｉ＋ｌ)−(ｆ＋ｇ＋ｊ＋ｋ）｝を出力させる。これは前記したように受光領域２１０から得られたディスク上スポット１００のトラッキングエラー信号から、受光領域２１１および２１２から得られたディスク上スポット１０１および１０２のトラッキングエラー信号の和信号を減算した信号に相当し、この方式はディファレンシャル・プッシュプル方式といわれている。したがって、この信号はプッシュプル方式で検出されたにも係わらず対物レンズ変位に伴うオフセットが大幅に解消された良好なトラッキングエラー信号になっている。
【００７０】
一方、出力信号ｍ、ｎ、ｏ、ｐからは、加算器８８、８９、減算器９０によって信号（ｍ＋ｏ）−（ｎ＋ｐ）が出力され、加算器９１、９２、減算器９３によって信号（ｍ＋ｐ）−（ｎ＋ｏ）が出力される。ここで、信号（ｍ＋ｏ）−（ｎ＋ｐ）は、いわゆる非点収差方式によって検出されるディスク上光スポット３００のフォーカスエラー信号に相当する。また（ｍ＋ｐ）、（ｎ＋ｏ）は、検出光スポット３１０をディスクのトラッキング方向（半径方向）に２分割した場合の各々の領域における検出光量に相当し、この２個の信号の差信号（ｍ＋ｐ）−（ｎ＋ｏ）はいわゆるプッシュプル方式によって検出されるディスク上光スポット３００のトラッキングエラー信号に相当する。
【００７１】
また、加算器９９により出力信号ｍ、ｎ、ｏ、ｐの和信号ＣＤ−ＲＦを生成することにより、光ディスクに記録されている情報信号を所定の信号再生回路により再生可能となっている。尚、本実施例では示されていないが、前記加算器９９を光検出器９のパッケージ２０内に格納し、光検出器９の信号出力端子に和信号（ｍ＋ｎ＋ｏ＋ｐ）の出力端子を追加する構成も可能である。
【００７２】
さらに、出力信号ｑ、ｒ、ｓ、ｔからは、減算器９４からプッシュプル方式によって検出されるトラッキングエラー信号（ｑ−ｒ）、減算器９５からプッシュプル方式によって検出されるトラッキングエラー信号（ｓ−ｔ）が出力されており、加算器９６によって信号（ｑ＋ｓ）−（ｒ＋ｔ）が出力され、更に増幅器９７によって所定の増幅率Ｋ３で増幅されている。この増幅器９７の増幅率Ｋ３は信号（ｑ＋ｓ）−（ｒ＋ｔ）が信号（ｍ＋ｐ）−（ｎ＋ｏ）とほぼ同一の信号振幅になるように定められている。ここで、信号（ｑ＋ｓ）−（ｒ＋ｔ）は、検出光スポット３１１と３１２をディスクのトラッキング方向（半径方向）に２分割した場合の各々の領域における総検出光量の差に相当し、いわゆるプッシュプル方式によって検出されるディスク上スポット３０１および３０２のトラッキングエラー信号の和に相当するものである。減算器９８から出力される信号は、
｛（ｍ＋ｐ）−（ｎ＋ｏ）｝−Ｋ３・｛（ｑ＋ｓ）−（ｒ＋ｔ）｝
となる。この信号は、受光領域４１０から得られたディスク上スポット１００のトラッキングエラー信号から、受光領域４１１および４１２から得られたディスク上スポット１０１および１０２のトラッキングエラー信号を減算した信号に相当するものであり、この方式はディファレンシャル・プッシュプル方式といわれている。したがって、この信号はプッシュプル方式で検出されたにも係わらず対物レンズ変位に伴うオフセットが大幅に解消された良好なトラッキングエラー信号になっている。
【００７３】
尚、ＤＶＤ−ＲＯＭディスクように記録信号に応じた位相ピットがディスク上に設けられている再生専用ディスクを再生する場合は、フォーカスエラー信号として通常の非点収差方式による信号を用いても外乱の影響はない。またトラッキングエラー信号として位相差検出回路７７から出力された位相差検出方式によるトラッキングエラー信号を用いることができる。そこで切り替えスイッチ７８および７９を切り替え、フォーカスエラー信号として（ａ＋ｃ）−（ｂ＋ｄ）を、トラッキングエラー信号としては位差検出回路７７から出力されたトラッキングエラー信号を出力させるようにすれば、再生専用ディスクに適した所望のエラー信号を得ることができる。また、ＣＤ−ＲＯＭディスクに関しても、非点収差方式及びディファレンシャル・プッシュプル方式を用いることにより良好な信号再生が可能である。
【００７４】
ここで、光検出面上での検出光スポットの位置調整に関して説明する。図１０はＤＶＤでの光検出器上の光スポット、図１１はＣＤでの光検出器上の光スポットを示している。図１０において、ＤＶＤの検出光スポット１１０、１１１、１１２はそれぞれ受光領域２１０、２１１、２１２の所定の位置に照射されている。また、図１１においては、ＣＤの検出光スポット３１０、３１１、３１２はそれぞれ受光領域４１０、４１１、４１２の所定の位置に照射されている。本発明の第１の実施例においては、ＤＶＤの光軸を基準にして集光光学系の光軸の設定及び調整を行っている構成である。そのため、ＣＤにおける検出光スポットは、ＤＶＤでの光軸を中心にレーザ光源の間隔に略比例した位置に配置されることとなる。図１２は、ＤＶＤ光軸が調整されている状態でのＣＤでの検出光スポットを示している。ＣＤの０次の検出光スポット３１０はＤＶＤでの０次の光スポット１１０が配置される位置を中心とした円周上に配置され、ＣＤの±１次の検出光スポット３１１、３１２は０次の検出光スポットを中心として回折した位置に照射される。半導体レーザ２を光軸中心に回転することにより、ＣＤの０次検出光スポット３１０は図１２の矢印方向に回転するために、ＣＤでの検出光スポット位置の調整を可能としている。
【００７５】
次に、本発明による第２の実施例を、図１３を用いて説明する。図中に使用している同一記号は、今までの説明で用いられているものと共通である。先の図９の構成と異なる点は、パッケージ２１内の受光領域の構成である。図１３においては、ＣＤ−Ｒディスクを再生する場合に用いる±１次回折光用の受光領域を、ＤＶＤ−ＲＡＭを再生する場合に用いる±１次回折光用の受光領域と兼用した構成となっている。すなわち、ＣＤ−Ｒの再生あるいは記録を行う場合には、受光領域２１３、２１４の受光面ｅ、ｆ、ｉ、ｊを用いることにより、先の第１の実施例にて説明したのと同様にフォーカスエラー信号やトラッキングエラー信号を検出することが可能である。このような構成とすることにより、受光面より出力する信号線の本数を４本低減することが可能となり、実際の光検出器を容易かつ安価なものとすることが可能である。尚、ＤＶＤ−ＲＡＭディスクの再生時においても、受光面の面積を拡大した部分には光ディスクからの光は戻らないために、第１の実施例と同様の効果が得られるのは言うまでもない。
【００７６】
次に、本発明による光検出器および信号処理回路に関する第３の実施例を、図１４を用いて説明する。図中に使用している同一記号は、今までの説明で用いられているものと共通である。先の図９の構成と異なる点は、パッケージ２２内の受光領域の構成である。図１４においては、ＤＶＤ−ＲＡＭディスクを再生する場合に用いる±１次回折光用の受光領域を削除した構成となっている。そのため、非点収差方式によるフォーカスエラー信号にもれ込み外乱の影響が残るため、ＤＶＤ−ＲＡＭディスクの再生は困難である。ＣＤ−Ｒディスク再生する場合においては、ディファレンシャルプッシュプル方式によるトラッキングエラー信号の生成が可能であり、さらに、回折格子をＣＤ−Ｒ専用として用いることが可能となるため、ＣＤ側での±１次回折光の光ディスク２上での位置調整が回折格子の回転を用いることにより容易な構成となっている。
【００７７】
次に、本発明による光検出器および信号処理回路に関する第４の実施例を、図１５及び図１６を用いて説明する。図中に使用している同一記号は、今までの説明で用いられているものと共通である。図１５は、ＣＤ−ＲＯＭディスク上での光スポットの配置を示している。記録ピット４００はトラック方向に配置されており、Ｔｐ３（１．６μｍ）の間隔で形成されている。光ディスク１０上の光スポットは、０次光及び±１次回折光の３つのスポットとなっており、＋１次回折光のスポット３０１及び−１次回折光のスポット３０２は、０次光のスポット３００からＴｐ３の４分の１に相当するＴｐ３２（０．４μｍ）の間隔を隔てた位置に配置されている。図１６は、光検出器および信号処理回路に関する平面図及びブロック図である。先の図１４の構成と異なる点は、パッケージ２３内の受光領域の構成である。図１６においては、ＣＤ側検出系の±１次回折光を受光する受光領域を各１つの受光面４１３、４１４で構成している。受光面４１３、４１４からの出力は、電流−電圧変換増幅器８４、８６から出力され減算器９４を用いることにより、±１次回折光の差信号として出力されている。その結果、図１５で示した光ディスク１０上のスポット配置と組合せることにより、３ビーム方式によるトラッキングエラー信号の検出が可能である。
【００７８】
次に、本発明による光検出器および信号処理回路に関する第５の実施例を、図１７及び図１８を用いて説明する。図中に使用している同一記号は、今までの説明で用いられているものと共通である。図１７は、第５の実施例における光学系構成を示したものであり、図２に示した第１の実施例と異なる点は、２つの異なる波長のレーザ光源を同一の筐体内に配置した半導体レーザ１７（２波長マルチレーザ）においては、それぞれのレーザ光源から出射されるレーザ光の偏光方向が互いに略垂直となるように配置されている点と、２つの偏光回折格子１８、１９が光路中に配置されている点である。この偏光回折格子１８及び１９の互いの偏光による回折方向は垂直に配置されており、さらにそれら偏光による回折方向は対応するレーザ光源の偏光方向と一致するように配置されている。そのため、各偏光回折格子の格子溝及び角度は自由に設定することが可能である。図１８は、光検出器および信号処理回路に関する平面図及びブロック図である。先の図１４の構成と異なる点は、パッケージ２４内の受光領域の構成である。図１８においては、ＣＤ側検出系の±１次回折光を受光する受光領域を図１６と同様に各１つの受光面４１３、４１４で構成している。受光面４１３、４１４からの出力は、電流−電圧変換増幅器８４、８６から出力され減算器９４を用いることにより、±１次回折光の差信号として出力されている。先に説明したように、偏光回折格子１８、１９は互いに独立して設計することが可能であるために、例えばＤＶＤ−ＲＡＭの光ディスク１と例えばＣＤ−ＲＯＭの光ディスク１０に対して、独立にディスク上のスポット配置が可能である。そのため、ＤＶＤ側では図４に示したスポット配置を選択することが可能であり、ＤＶＤ−ＲＯＭやＤＶＤ−ＲＡＭディスクの再生に必要フォーカスエラー信号やトラッキングエラー信号を検出することが可能であると同時に、ＣＤ側では図１５に示したスポット配置を選択することが可能であり、３ビーム方式によるトラッキングエラー信号の検出が可能である。
【００７９】
次に本発明による検出光スポットの調整方法に関する第６の実施例を図１９から図２２を用いて説明する。図中に使用している同一記号は、今までの説明で用いられているものと共通である。図１９は、第６の実施例における光ピックアップの構成図を示したものであり、図２に示した第１の実施例と異なる点は、集光光学系のハーフミラーと光検出器９の間の光路中にダイクロ回折格子３０が配置されている点である。このダイクロ回折格子３０はＣＤの光ビームのみ回折させるような特性をもつものであり、ＣＤ再生時の光ディスク１０からの反射光のみを回折させている。そのため、ＤＶＤにおける検出器９上での検出光スポットの照射状態は図１０に示したものと同様になる。一方、ＣＤにおいてはダイクロ回折格子３０による光ビームの回折により、図２０に示すような検出光スポットの照射状態となる。図２０において、検出光スポット３１５、３１６、３１７はダイクロ回折格子３０での０次光検出スポット、検出光スポット３１８ａ、３１９ａ、３２０ａはダイクロ回折格子３０での＋１次光検出スポット、検出光スポット３１８ｂ、３１９ｂ、３２０ｂはダイクロ回折格子３０での−１次光検出スポットを示している。第６の実施例においては、ダイクロ回折格子３０での＋１次回折光である光検出スポット３１８ａ、３１９ａ、３２０ａを受光領域４１０、４１１、４１２に照射する構成である。そのため、図２１に示すように光検出スポット３１８ａ、３１９ａ、３２０ａは、ダイクロ回折格子３０を光軸に沿って前後に動かすことにより０次の検出光スポットに対して接近あるいは離間させることが可能であり、図２２に示すようにダイクロ回折格子３０を回転することにより０次の検出光スポット３１５を中心に回転することが可能である。
【００８０】
そのため、ダイクロ回折格子３０の位置及び回転調整によりＣＤの検出光スポットの照射位置調整が可能である。その結果、ＣＤの検出光スポットの照射位置を受光領域の受光範囲内とすることが出来ることとなる。
【００８１】
また、図２１に示すように光検出スポット３１８ａ、３１９ａ、３２０ａが、ダイクロ回折格子３０を光軸に沿って前後に動かすことにより０次の検出光スポットに対して接近あるいは離間させることが可能であることから、検出器９における受光領域の位置を所望な配置にすることも可能となる。即ち、ダイクロ回折格子３０の位置を調整することで、検出器９における受光領域配置の設計自由度を大きくすることが可能となる。この例を図１０、図２０、図２１を用いて示す。図２０においては、ＤＶＤの検出光スポットが照射されるのが、受光領域２１０、２１１、２１２であり(図１０参照)、ＣＤの検出光スポットが照射されるのが、受光領域４１０、４１１、４１２である。ここで、ダイクロ回折格子３０の位置を調整するとＣＤの検出光スポット３１８ａ、３１９ａ、３２０ａの照射位置を受光領域４１０、４１１、４１２上とすることが出来ることが図２１に示されている。更に、図２１において、ダイクロ回折格子３０の位置を調整することで、ＣＤの検出光スポット３１８ａ、３１９ａ、３２０ａの照射位置を受光領域２１０、２１１、２１２上にすることが出来る。
【００８２】
例えば、まずＤＶＤの検出に使用する反射光(ダイクロ回折格子３０における０次光の光ビーム)を検出器９上での検出光スポットの照射状態が図１０に示されるような、受光領域での受光出来る範囲内における所定の位置に検出光スポットが照射されるようにする。
【００８３】
ここで、上記にて説明している所定の位置とは、該所定の位置に検出光スポットが照射された場合に、検出光スポットが検出され、検出に基づいて出力される出力信号が、その後の信号処理等に使用可能であるような出力信号を出力可能である受光領域における照射位置のことである。
【００８４】
即ち、図１０に示される検出器９上での検出光スポットの照射状態においては、検出光スポットが検出され、検出に基づいて出力される信号出力が、その後の信号処理等に使用可能であるような受光領域における照射位置となるように検出器９などの位置を決めたものである。一方、この時、製造バラツキなどから、ＣＤの検出に使用する反射光（ダイクロ回折格子３０における＋１次光、もしくは−１次光の光ビーム）は、上記ＤＶＤについて説明したような受光領域での受光出来る範囲内における所定の位置に検出光スポットが照射されるとは限らない。従って、上記のＤＶＤの検出に使用する反射光を基準として、検出器９の位置を決めた場合には、ＣＤの検出に使用する反射光に関しては、受光領域での受光出来る受光範囲内における所定の位置に検出光スポットが照射されるとは限らない。
【００８５】
ここで、ＣＤの検出に使用する反射光は、ダイクロ回折格子３０における回折光であるから、前記ダイクロ回折格子３０を光軸に沿って前後に動かすか、光軸周りに回転させることにより、ＣＤの検出に使用する反射光の照射位置をＤＶＤの受光領域に対して接近あるいは離間させることが可能である。従って、前記ダイクロ回折格子３０を光軸に沿って前後に動かすか、光軸周りに回転させることにより、ＣＤの検出に用いる反射光の照射位置を受光領域での受光出来る範囲内における所定の位置となるように調整することが可能となる。この調整においては、ＤＶＤの検出に用いる反射光はダイクロ回折格子３０における０次光であるので、受光領域での受光出来る範囲内における所定の位置に照射されるように保たれる。
【００８６】
なお、上記において、ダイクロ回折格子３０は、ＤＶＤの光ビームは回折させず、ＣＤの光ビームのみを回折させるとしていたが、これに限定されるものではない。
【００８７】
すなわち、本実施例のようにＤＶＤの検出に使用する反射光は、ダイクロ回折格子３０における０次光を用い、ＣＤの検出に使用する反射光は、ダイクロ回折格子３０における＋１次光もしくは−１次光を用いる場合において、ダイクロ回折格子３０はＤＶＤ及びＣＤの光ビームを共に回折させる機能を有しても一向に構わない。
【００８８】
次に、前記ダイクロ回折格子３０を光軸に沿って前後に動かすか、光軸周りに回転させることにより、ＣＤもしくは、ＤＶＤの検出に用いる反射光の照射位置を受光領域での受光出来る範囲内における所定の位置となるように調整することを示す実施例を以下に説明する。
【００８９】
なお、以下に示す第７乃至第９実施例においては、上述の式（１）の関係を用いることで、１つの３スポット用回折格子によって、ＣＤ系及びＤＶＤ系ディスク共にＤＰＰ信号を検出できる様な光ビームを生成している。
【００９０】
図２３は本発明の第７の実施例である光ピックアップ装置の概略構成図である。レーザ光源７００１は互いに発振波長の異なる（発振波長６５０ｎｍ帯と７８０ｎｍ帯）２つの半導体レーザチップを同一のパッケージ内に設けた２波長マルチレーザ光源である。
【００９１】
例えばＤＶＤ−ＲＯＭの様な高密度光ディスクを再生する場合は、波長６５０ｎｍ帯の光ビームを２波長マルチレーザ光源７００１から出射させる。この光ビームは３スポット用の回折格子７００９を通過し、光軸に対して４５°の角度を成して配置されているハーフミラー７００３で反射され、立ち上げミラー７００４を経てコリメータレンズ７００５によって平行光束に変換されて対物レンズ７００６に到達する。この対物レンズ７００６はアクチュエータ７００７にて保持されており、光ディスク７００８上に光ビームを集光させて光スポットを形成する。光ディスク７００８を反射した光ビームは往路と同じ光路を逆にたどって対物レンズ７００６、コリメータレンズ７００５、立ち上げミラー７００４を経てハーフミラー７００３に入射する。そしてハーフミラー７００３を透過した光ビームはホログラム素子７０１０に達する。ホログラム素子７０１０は、後述するように波長７８０ｎｍ帯の光ビームに対して+１次回折光ビームまたは−１次回折光ビームを分離発生させ、これら回折光ビームのどちらか一方を光検出器７００２内の所定の受光領域に集光させる機能を持つよう格子溝パターンが設計されている素子であるが、当然、波長６５０ｎｍ帯の光ビームが入射しても０次光ビームおよび±１次回折光ビームが生じる。しかしながら本実施例では、このうちホログラム素子７０１０をまっすぐ透過した０次光ビームだけが検出レンズ７０１１を経て光検出器７００２内の所定の受光領域に入射する様に設計されている。なお検出レンズ７０１１はシリンドリカルレンズと凹レンズを組み合わせたレンズであり、前記０次光ビームを光検出器７００２内の所定の受光領域に集光させる機能とハーフミラー７００３によって該０次光ビーム内に付加されたコマ収差並びに図２３のｙ方向とｘ方向に関する非点収差をキャンセルし、なおかつｘｙ平面内においてｙ軸方向に対して４５°傾いた方向に所定量の非点収差を発生させる機能を有している。
【００９２】
次にＣＤ−ＲＯＭの様な従来の光ディスクを再生する場合は、２波長マルチレーザ光源７００１から波長７８０ｎｍ帯の光ビームを出射する。この光ビームは上記と同様に３スポット用の回折格子７００９を通過し０次回折光と±１次回折光に回折分離するが、その際各々の光ビームは例えば光ディスク７００８上において４分の１トラックピッチずつディスク半径方向にずれて光スポットを形成するように回折分離する。回折格子７００９を通過した光ビームは光軸に対して４５°の角度を成して配置されているハーフミラー７００３で反射され、立ち上げミラー７００４を経てコリメータレンズ７００５によって平行光束に変換され対物レンズ７００６に到達する。対物レンズ７００６はアクチュエータ７００７にて保持されており、前述したようにＤＶＤディスク上に波長６５０ｎｍ帯の光ビームを集光する機能と共に、ＣＤ−ＲＯＭの様な光ディスク７００８上に波長７８０ｎｍ帯の光ビームを集光させて光スポットを形成する機能を同時に有する。
【００９３】
光ディスク７００８を反射した光ビームは往路と同じ光路を逆にたどって対物レンズ７００６、コリメータレンズ７００５、立ち上げミラー７００４を経てハーフミラー７００３に入射し、このハーフミラー７００３を透過した後、ホログラム素子７０１０に達する。このホログラム素子７０１０は所定の格子溝パターンを備えており、入射した波長７８０ｎｍ帯の光ビームを所定の回折効率で回折分離し±１次回折光ビームを発生させるが、この際ハーフミラー７００３及び検出レンズ７０１１を透過することによって前記＋１次回折光ビームまたは−１次回折光ビーム内に生じる非点収差およびコマ収差をキャンセルし、この回折光ビームを、検出レンズ７０１１を経て光検出器７００２内の波長６５０ｎｍ帯の光ビームが到達する所定の受光領域とは異なる位置にある所定の受光領域にほぼ収差なく集光させる機能を持つ。
【００９４】
上記の図２１で、ダイクロ回折格子３０を光軸に沿って前後に動かすことにより、光検出スポット３１８ａ、３１９ａ、３２０ａが、０次の検出光スポットに対して接近あるいは離間させることが可能であることは既に説明した。
【００９５】
従って、図２３においても、ホログラム素子７０１０を光軸に沿って前後に動かすことにより、波長７８０ｎｍ帯の光ビームが到達する光検出器７００２内の位置を変えることが可能となる。このことを用いることで、図２３において、光検出器７００２でのＣＤの検出光スポットの照射位置調整をすることが出来る。また、ホログラム素子７０１０の位置を調整することで、光検出器７００２における受光領域配置の設計自由度を大きくすることが可能となる。例えば、光ディスクから反射した波長７８０ｎｍ帯の光ビームが到達する光検出器７００２内の受光領域と波長６５０ｎｍ帯の光ビームが到達する光検出器７００２内の受光領域とを同じ直線状に配置することも可能となる。
【００９６】
もしくは、光ディスクから反射した波長６５０ｎｍ帯の光ビーム波長、及び７８０ｎｍ帯の光ビームの両者を、光検出器７００２内の同一の受光領域に集光させることが出来るものである。即ち、波長６５０ｎｍ帯の光ビーム波長、及び７８０ｎｍ帯の光ビームの両者に対して、受光領域の共用化を可能とするものである。
【００９７】
まず本実施例において３スポット用回折格子７００９は例えば上記した様に、ＤＶＤ−ＲＯＭやＤＶＤ−ＲＡＭの様な光ディスク７００８上において、図 ２４Ａ 及びＢに示すようにディスク半径方向におけるスポット間隔δが０．６７μｍ程度となる様に、波長６５０ｎｍ帯の入射光ビームを回折分離し０次光ビーム７１０２ａ、＋１次光及び−１次光ビーム７１０２ｂ、７１０２ｃを発生させ、かつＣＤ−ＲＯＭ並びにＣＤ−Ｒの様な光ディスク７００８上において図２４Ｃに示すように、ディスク半径方向におけるスポット間隔δ'が０．８μｍ程度となる様に波長７８０ｎｍ帯の入射光ビームを回折分離し０次光ビーム７１０３ａ、＋１次光及び−１次光ビーム７１０３ｂ、７１０３ｃを発生させる格子溝パターンの回折格子となっている。またホログラム素子７０１０のホログラムパターンは、ホログラム素子７０１０により回折分離した波長６５０ｎｍ帯の光ビームの０次光と、ホログラム素子７０１０により回折分離した波長７８０ｎｍ帯の光ビームの＋１次回折光または−１次回折光を光検出器７００２内の所定の受光領域に導く機能を有すれば等間隔直線状の格子溝パターンであっても良い。もちろんホログラム素子７０１０の格子溝パターンが所定の不等間隔曲線状のパターンであっても一向に構わない。適当な不等間隔曲線状格子溝パターンを備えた格子を用いると、この格子で回折され光検出器７００２内に導かれる＋１次または−１次回折光ビームに所定の波面収差を付加することが出来るので、該＋１次または−１次回折光ビームに含まれる不要な収差成分並びに該＋１次または−１次回折光ビームの焦点位置を補正し、良好な検出光スポットを光検出器に照射させることが出来る。
【００９８】
次に本実施例における光検出器７００２内の受光領域の受光面パターンについて図２５を用いて説明する。図２５に示した様に受光領域の受光面パターンは、田の字型に４分割された３個の受光面と２分割された２個の合計１６個の独立した受光面が直線状に配置された構成となっている。そしてＤＶＤ系ディスク再生時は、図 ２４Ａ及びＢにおける光ディスク上のスポット７１０２ａ、７１０２ｂ、７１０２ｃのディスク反射光が図２５Ａに示した様にそれぞれの受光領域に入射し光スポット７１１２ａ、７１１２ｂ、７１１２ｃを形成し、ＣＤ系ディスク再生時は図２４Ｃにおける光ディスク上のスポット７１０３ａ、７１０３ｂ、７１０３ｃのディスク反射光が図２５Ｂに示した様にそれぞれの受光領域に入射し光スポット７１１３ａ、７１１３ｂ、７１１３ｃを形成する。ここで３スポット用回折格子７００９において生じる回折分離光のうち、０次光ビームを検出する受光領域としては図２５に示す様にＤＶＤ系ディスク再生時およびＣＤ系ディスク再生時ともに受光領域７０２０ａを用いている。しかしながら３スポット用回折格子７００９で生じる回折分離光のうち、+１次光ビームまたは-１次光ビームを検出する受光領域はＤＶＤ系ディスク再生時とＣＤ系ディスク再生時で、それぞれ異なった受光領域を用いている。これは、回折格子による光ビームの回折角は先に述べたようにほぼ波長に比例するため、３スポット用回折格子７００９によって回折分離した波長７８０ｎｍ帯の０次光ビームと±１次光ビームの光検出器７００２面上におけるスポット間隔が、波長６５０ｎｍ帯の光ビームのスポット間隔に比べ約１.２（＝７８０÷６５０）倍広がるためである。よって光検出器７００２面上におけるスポット間隔はＤＶＤ系ディスク再生時とＣＤ系ディスク再生時とで異なるものの、ＤＶＤ系およびＣＤ系共にディファレンシャルプッシュプル方式を適用出来るように、それぞれ異なった受光領域を用いて光ビームを検出している。
【００９９】
この様な光検出器によるフォーカス誤差信号及びトラッキング誤差信号の検出方式は、既に述べたため詳細な説明は省略するが、図２６に示すような演算回路によってフォーカス誤差信号を非点収差方式にて検出し、トラッキング誤差信号を位相差検出方式（ＤＰＤ方式）にて検出する。ここで図中の符号７０４０、７０４１、７０４２、７０４３、７０４４、７０４５、７０４６、７０４７は電流-電圧変換増幅器を、符号７０４８、７０４９、７０５０、７０５１，７０５２，７０５３、７０５４、７０５５、７０５６、７０５７、７０５８、７０５９、７０６３、７０６４は加算器を、符号７０７０、７０７１，７０７２、７０７３は減算器を、符号７０９０、７０９１は切り替えスイッチを、符号７０８０は位相差検出回路を、また符号７０６０は増幅率Ｋ３、符号７０６１及び７０６２は増幅率Ｋ４の増幅器をそれぞれ表している。なおこれ以降、図中における同一符号は今までの説明で用いられているものと共通とする。
【０１００】
ＤＶＤ−ＲＡＭディスクを再生する場合は、図２７に示すような演算回路に切り替え、フォーカス誤差信号を差動非点収差方式（詳細は特願平１１−１７１８４４号で開示しているので詳細は省略。）にて検出し、トラッキング誤差信号をディファレンシャルプッシュプル方式（ＤＰＰ方式）にて検出する。
【０１０１】
さらにＣＤ−ＲＯＭ、ＣＤ−ＲなどのＣＤ系ディスクを再生する場合は、図１７に示す様な演算回路に切り替え、フォーカス誤差信号を非点収差方式、トラッキング誤差信号をディファレンシャルプッシュプル方式（ＤＰＰ方式）にて検出する。
【０１０２】
なお本実施例における光検出器７００２内の受光領域の受光面パターンは、図２５に示した様に１６分割のものを用いたが、当然本発明における受光領域の受光面パターンとしてはこの様な構成に限定されるものではなく、少なくともＤＶＤ系ディスク再生時とＣＤ系ディスク再生時でそれぞれの光ビームが同一の光検出器に入射して、各種サーボ信号や情報信号を検出できる受光領域の受光面パターンであれば他のどのような受光領域の受光面パターンを本発明に適用しても良い。以下、光検出器７００２の受光領域の受光面パターンを変更した実施例について説明する。
【０１０３】
本発明の第８の実施例は、第７の実施例における光ピックアップ装置と同じ構成であるが、受光領域の受光面パターンを図２９に示すように、田の字型に４分割された１個の受光面と５分割された２個の合計１４個の独立した受光面を直線状に配置した構成に置き換えたものである。この様な受光領域の受光面パターンにすると、３スポット用回折格子７００９で生じる回折分離光のうち、+１次光ビームまたは-１次光ビームを検出する際、ＤＶＤ系ディスク再生時とＣＤ系ディスク再生時とで同じ受光領域を用いることが出来、受光面数の削減が可能となる。
【０１０４】
この様な光検出器によるフォーカス誤差信号及びトラッキング誤差信号の検出方式に関しては、第７の実施例に述べたものと同じ検出方式を用いることが出来るので詳細な説明は省略するが、ＤＶＤ−ＲＯＭディスクを再生する場合は、図３０に示すような演算回路を用いてフォーカス誤差信号を非点収差方式にて検出し、トラッキング誤差信号を位相差検出方式（ＤＰＤ方式）にて検出する。
【０１０５】
またＤＶＤ−ＲＡＭディスクを再生する場合は、図３１に示すような演算回路に切り替え、フォーカス誤差信号を差動非点収差方式にて検出し、トラッキング誤差信号をディファレンシャルプッシュプル方式（ＤＰＰ方式）にて検出する。
【０１０６】
さらにＣＤ−ＲＯＭ、ＣＤ−ＲなどのＣＤ系ディスクを再生する場合は、図３２に示す様な演算回路に切り替え、フォーカス誤差信号を非点収差方式、トラッキング誤差信号をディファレンシャルプッシュプル方式（ＤＰＰ方式）にて検出する。
【０１０７】
続いて第７の実施例における受光領域の受光面パターンを変更した別の実施例について以下、説明する。
【０１０８】
本発明の第９の実施例は第７の実施例における光ピックアップ装置と同じ構成であるが、受光領域の受光面パターンを図３３のように田の字型に４分割された１個の受光面と２分割された２個の合計８個の独立した受光面を直線状に配置した構成に置き換えたものである。この様な構成にすると、より受光面数の削減が可能となる。この様な光検出器によるフォーカス誤差信号及びトラッキング誤差信号の検出方式も第７の実施例に述べたものと同じ検出方式を用いることが出来るので詳細な説明は省略するが、ＤＶＤ−ＲＯＭディスクを再生する場合は、図３４に示すような演算回路を用いてフォーカス誤差信号を非点収差方式にて検出し、トラッキング誤差信号を位相差検出方式（ＤＰＤ方式）にて検出する。ここで図中の符号７０６５は増幅率Ｋ３の増幅器を、符号７０７４は減算器を、また符号７０９２は切り替えスイッチを表している。
【０１０９】
ＣＤ−ＲＯＭ、ＣＤ−ＲなどのＣＤ系ディスクを再生する場合は、図３５に示す様な演算回路に切り替え、フォーカス誤差信号を非点収差方式、トラッキング誤差信号をディファレンシャルプッシュプル方式（ＤＰＰ方式）にて検出する。
【０１１０】
さらに受光領域の受光面パターンを簡略化した別の実施例について以下、説明する。
【０１１１】
本発明の第１０の実施例は第７の実施例における光ピックアップ装置と同じ構成であるが、受光領域の受光面パターンを図３６のように田の字型に４分割された１個の受光面とその両端にそれぞれ受光面を配置した合計６個の独立した受光面を直線状に配置した構成に置き換えたものである。
【０１１２】
ここで図中の７１２２ａ、７１２２ｂ、７１２２ｃはＤＶＤ系ディスク再生時において、３スポット用回折格子７００９によって回折分離した３本の光ビームが光ディスク７００８を反射し、光検出器７００２内の受光領域上に集光した様子を表しており、７１２３ａ、７１２３ｂ、７１２３ｃはＣＤ系ディスク再生時において３スポット用回折格子７００９によって回折分離した３本の光ビームが光ディスク７００８を反射し、光検出器７００２内の受光領域上に集光した様子を表している。また３スポット用回折格子７００９はＣＤ−ＲＯＭ並びにＣＤ−Ｒの様な光ディスク７００８上において、ディスク半径方向におけるスポット間隔が情報トラックのトラックピッチの４分の１である０．４μｍ程度となる様に前記第２の半導体レーザ光源を出射した波長７８０ｎｍ帯の光ビームを回折分離させる機能を有するものとする。この様な光ピックアップ装置によるフォーカス誤差信号及びトラッキング誤差信号の検出方式としては、ＤＶＤ−ＲＯＭディスクを再生する場合は、図３７に示すような演算回路を用いてフォーカス誤差信号を非点収差方式にて検出し、トラッキング誤差信号を位相差検出方式（ＤＰＤ方式）にて検出する。なお図中の符号７０９３は切り替えスイッチを表している。またＣＤ−ＲＯＭ、ＣＤ−ＲなどのＣＤ系ディスクを再生する場合は、図３８に示す様な演算回路に切り替え、フォーカス誤差信号を非点収差方式、トラッキング誤差信号を３スポット方式にて検出する。
【０１１３】
ここで第９及び第１０の実施例においては、波長６５０ｎｍ帯の光ビームは必ずしも３スポット用回折格子７００９において回折分離する必要は無い。よって３スポット用回折格子７００９の溝深さを制御することにより波長６５０ｎｍ帯の光ビームの回折光効率をほぼ０％としても良い。
【０１１４】
また、第７及至第１０の実施例におけるホログラム素子７０１０を光軸方向に移動及び光軸周りに回転することによって、ホログラム素子７０１０を素通りする０次光の光検出器７００２内における集光位置を変えることなく、ホログラム素子７０１０で回折分離される＋１次回折光（または−１次回折光）の光検出器７００２内における集光位置を変位させることが出来る。そのためホログラム素子７０１０によって、フォーカス誤差信号及びトラッキング誤差信号が正しく出力されるよう光検出器７００２内の受光領域と、この受光領域に入射する光スポットとの相対位置を調整することが出来る。
【０１１５】
また前記に示したように、ホログラム素子７０１０に刻んだ格子を鋸歯状化して信号検出に必要な回折光の回折効率を選択的に向上させることにより、信号検出に用いる光束に関し高い光利用効率を得る事が出来、また信号検出に用いない不要な光が迷光成分になって受光領域に飛び込み信号検出のＳ／Ｎ比を低下させる可能性を極力減らす事が出来る。なお、これまでの実施例で述べたホログラム素子７０１０に刻んだ格子を鋸歯状化する際は、図３９に示す様に格子の側壁に傾きをつけても、また格子を階段状にしても一向に構わない。また、ホログラム素子７０１０の回折効率に波長または偏光依存性を持たせることにより、信号光の光利用効率をさらに改善することができる。
【０１１６】
ここで、回折効率に波長依存性をもたせた回折格子について、説明する。
【０１１７】
一般に、矩形状の格子溝断面を持つ回折格子の場合、図４０に示したように回折格子３０の格子溝幅をｗ、格子周期をｐ、格子溝深さをｈと定義すると、０次光７１０１ａの光強度Ｉ０、＋１次光７１０１ｂ（−１次光７１０１ｃ）の光強度Ｉ１はｗ、ｐ、ｈに大きく依存し、入射光の光強度を１とした場合、式(２)の様に表わせる。
【０１１８】
【数２】

【０１１９】
ただしｎは回折格子が刻まれている透明部材７０３０の屈折率、λは回折格子に入射した光ビームの波長である。よって、式(２)より、６５０ｎｍ帯の入射光に関してはより多くの０次回折光を生じさせるために、次の式(３)
【０１２０】
【数３】

【０１２１】
を満たし、なおかつ７８０ｎｍ帯の入射光に関してはより多くの1次回折光を生じさせるために、次の式(４)
【０１２２】
【数４】

【０１２３】
を同時に満たす様な格子溝深さにすれば良い。
【０１２４】
例えば （ｎ−１）ｈ = １９５０［ｎｍ］となるように格子溝深さを設定すると、（ｎ−１）ｈ＝３ ・６５０＝２．５・７８０ となり、式(３)と式(４)を同時に満たすため、光の利用効率を改善する事が出来る。
【０１２５】
ところで、このような波長依存性もしくは波長選択性を有するホログラム素子は、前述したような格子溝深さのコントロールによって実現される素子に限定されるものではない。７８０ｎｍ帯の光に対しては±1次回折光の回折効率が充分高く、６５０ｎｍ帯の光に対しては０次光の効率が充分高くなるような素子であれば、どのような原理に基づく素子であっても一向に構わない。
【０１２６】
ここで、本発明の第１１の実施例として、回折効率に偏光依存性を持たせた偏光性素子を用いて信号検出光の光利用効率を改善させた例について図を用いて説明する。図４１は本発明の第１１の実施例としての光ピックアップ装置の概略構成図である。なお図２３に示した本発明の第７の実施例と同じ部品には、同じ番号を付している。本実施例は上記の第７実施例と異なり、ホログラム素子７０１０の代わりに偏光依存性ホログラム７０１２を用い、かつ偏光変換素子７０１３と組み合わせることにより、偏光を利用して光の利用効率を改善している。
【０１２７】
ここで偏光変換素子７０１３としては、６５０ｎｍ帯の光ビームに対して５λ／４ 板として機能する波長板を用いている。また偏光依存性ホログラム７０１２は例えばＳ偏光を有する光束のみ所定の回折効率で回折させ、それに垂直な偏光方向であるＰ偏光を有する光束は回折せずにそのまま透過させるよう機能する。
【０１２８】
例えばＤＶＤ−ＲＯＭの様な高密度光ディスクを再生する場合は、波長６５０ｎｍ帯のS偏光の光ビームを２波長マルチレーザ光源７００１から出射させる。この光ビームは３スポット用の回折格子７００９を通過して、光軸に対して４５°の角度を成して配置されているダイクロハーフミラー７００３に入射する。ダイクロハーフミラー７００３において反射した光ビームは、立ち上げミラー７００４を経て偏光変換素子７０１３に入射する。
【０１２９】
ここで偏光変換素子７０１３は６５０ｎｍ帯の光ビームに対しては ５λ／４ 板として働くため、S偏光で入射してきた光ビームは偏光変換素子７０１３を通過後円偏光の光ビームとなりコリメータレンズ７００５によって平行光束に変換され対物レンズ７００６に到達する。対物レンズ７００６はアクチュエータ７００７にて保持されており、例えばＤＶＤ−ＲＯＭの様な光ディスク７００８上に光ビームを集光させて光スポットを形成する事が出来る。光ディスク７００８を反射した光ビームは往路を逆にたどって対物レンズ７００６、コリメータレンズ７００５を経て偏光変換素子７０１３に入射し、円偏光で入射してきた光ビームは偏光変換素子７０１３を通過後P偏光の光ビームとなって、立ち上げミラー７００４を経てダイクロハーフミラー７００３を透過して、偏光依存性ホログラム７０１２に入射する。偏光依存性ホログラム７０１２は、P偏光の光ビームに対しては回折機能は作用せず、単なる透明部材となるため、偏光依存性ホログラム７０１２に入射したP偏光の光ビームは回折されず、そのまま素通りして検出レンズ７０１１を経て光検出器７００２内の所定の受光領域に到達する。
【０１３０】
次にＣＤ−ＲＯＭの様な従来の光ディスクを再生する場合は、２波長マルチレーザ光源７００１から波長７８０ｎｍ帯のＳ偏光の光ビームを出射する。２波長マルチレーザ１を出射した光ビームは３スポット用の回折格子７００９を通過し、光軸に対して４５°の角度を成して配置されているダイクロハーフミラー７００３に入射する。ダイクロハーフミラー７００３において反射した光ビームは立ち上げミラー７００４を経て偏光変換素子７０１３に入射する。ここで偏光変換素子７０１３は前述したように６５０ｎｍ帯の光ビームに対しては ５λ／４ 板として機能する素子であるため、波長７８０ｎｍ帯の光に対してはほぼλ板として働く。そのため波長７８０ｎｍ帯の光は偏光変換素子７０１３を通過後もS偏光のままでコリメータレンズ７００５によって平行光束に変換され対物レンズ７００６に到達する。対物レンズ７００６はアクチュエータ７００７にて保持されており、前述したようにＤＶＤディスク上に光ビームを集光する機能とＣＤ−ＲＯＭの様な光ディスク７００８上に光ビームを集光させて光スポットを形成する機能を同時に有する。光ディスク７００８を反射した光ビームは往路を逆にたどって対物レンズ７００６、コリメータレンズ７００５を経て偏光変換素子７０１３に入射し、偏光変換素子７０１３を通過後もS偏光の光ビームのままで、立ち上げミラー７００４を経てダイクロハーフミラー７００３を透過して、偏光依存性ホログラム７０１２に入射する。偏光依存性ホログラム７０１２はS偏光の光ビームに対しては回折させる機能を持っているため、偏光依存性ホログラム７０１２において光ビームは所定の回折効率で回折され、検出レンズ７０１１を経て光検出器７００２内の、波長６５０ｎｍ帯の光ビームが到達する所定の受光領域とは異なる位置にある所定の受光領域に到達する。このような構成にすると、ＤＶＤ再生時、ＣＤ再生時いずれの場合においても信号検出に必要な光束だけを効率よく光検出器に導くことができ、光利用効率を大幅に改善させるとともに、不要な迷光成分を除去することができる。
【０１３１】
なお光検出器７００２の受光領域での光スポットと受光面との位置関係及び光ディスク再生時における情報信号、フォーカス誤差信号，トラッキング誤差信号の検出方法は、上記第７の実施例と同じである。
【０１３２】
また、偏光依存性ホログラム７０１２を光軸方向に移動並びに光軸まわりに回転する事によって、上記第７の実施例と同様に光検出器７００２において光検出される６５０ｎｍ帯の光ビーム７１１３ａ、７１１３ｂ、７１１３ｃの焦点位置や受光面上の位置を変えずに、光検出器７００２において光検出される７８０ｎｍ帯の光ビーム７１１２ａ、７１１２ｂ、７１１２ｃの焦点位置や受光面上の位置を独立して変える事が出来るため、６５０ｎｍ帯光ビームと７８０ｎｍ帯光ビームに対するディテクタ調整やフォーカス誤差信号オフセット調整を独立に行う事が可能である。
【０１３３】
さらにダイクロハーフミラー７００３に対して、６５０ｎｍの光に関してはＳ偏光がほぼ全反射、Ｐ偏光がほぼ１００％透過し、７８０ｎｍの光に関してはＳ偏光が反射・透過共に約５０％となるような機能を持たせば、より光の利用効率を改善できる。
【０１３４】
ところで、今まで述べた実施例においてホログラム素子７０１０の配置位置はハーフミラー７００３と検出レンズ７０１１の間としていたが、これに限定されるものではなく検出レンズ７０１１と光検出器７００２の間の光路中であっても良い。また今まで述べた実施例では、ホログラム素子７０１０は波長６５０ｎｍ帯の光ビームの０次光と波長７８０ｎｍ帯の光ビームの＋１次回折光または−１次回折光の光ビームを光検出器７００２内の所定の位置に導く機能を有するものとしていたが、当然これに限定されるものではなく、例えば全く逆に波長６５０ｎｍ帯の光ビームの＋１次回折光または−１次回折光と波長７８０ｎｍ帯の光ビームの０次光を光検出器７００２内の所定の位置に導く機能を有する回折格子であっても一向に構わない。
【０１３５】
図４２に本発明の光ピックアップを搭載した光ディスク装置の概略ブロック図を示す。光ピックアップ５０８は、例えば図９で示したようなパッケージ２０、図２４、図４１に示すピックアップ装置を搭載しており、ここで検出された各種検出信号は、信号処理回路内のサーボ信号生成回路５０４及び情報信号再生回路５０５に送られる。サーボ信号生成回路５０４では、これら検出信号から各光ディスクに適したフォーカスエラー信号やトラッキングエラー信号が生成され、これをもとにアクチュエータ駆動回路５０３を経て光ピックアップ５０８内の対物レンズアクチュエータを駆動し、対物レンズの位置制御を行う。また、情報信号再生回路５０５では前記検出信号から光ディスク１に記録された情報信号が再生される。尚、前記サーボ信号生成回路５０４及び情報信号再生回路５０５で得られた信号の一部はコントロール回路５００に送られる。コントロール回路５００は、これら各種信号を用いてそのとき再生しようとしている光ディスク１の種類を判別し、判別結果に応じてＤＶＤ用レーザ点灯回路５０７もしくはＣＤ用レーザ点灯回路５０６のいずれかを駆動させ、さらにこれまで述べてきたように各光ディスクの種類に応じたサーボ信号検出方式を選択するようにサーボ信号生成回路５０４の回路構成を切り替える機能を有する。尚、このコントロール回路５００にはアクセス制御回路５０２とスピンドルモータ駆動回路５０１が接続されており、それぞれ光ピックアップ５０８のアクセス方向位置制御や光ディスク１のスピンドルモータ５０９の回転制御が行われる。
【０１３６】
以上述べたように本発明の実施例によれば、２つの異なる波長のレーザ光源を同一の筐体内に配置した半導体レーザと、少なくとも一つの回折格子、及び１つの光検出器を用いた光ピックアップの光学系構成で、ＤＶＤ−ＲＯＭ、ＤＶＤ−ＲＡＭやＣＤ−ＲＯＭなどの異なる基板厚さや異なる溝構造からなる各種光ディスクの再生あるいは記録に必要なフォーカスエラー信号及びトラッキングエラー信号を得ることが可能である。さらに、２つのレーザ波長の比と光ディスクのトラックピッチの比が略等しい場合には、１つの回折格子で光学系が実現できると同時に、この回折格子やハーフミラーなどの光学部品に関しては波長特性や偏光特性を必要としないために、従来と比較して簡素で低価格な光学系を実現することができる。
【0137】
また、光ピックアップ装置の光源に２波長マルチレーザを用い、光検出系において一方又は両方の波長の光ビームに対して戻り光を回折させることによって、光検出器の受光領域を２波長に対して共用化を可能とする。これにより、１系統の光検出系で複数種類の光ディスクの情報の再生を行う事により光学部品数を低減し、光ピックアップ装置のさらなる小型化、簡略化、低価格化を実現できる。また、２波長マルチレーザを用い、回折格子やハーフミラーを共用化、あるいは光検出器の受光領域を共用化することで、さらなる光学部品数の低減を図ることができる。
【発明の効果】
本発明によれば、小型化、簡略化、低価格化を実現できる光検出器、光ピックアップ、光学的情報再生装置の提供が可能になる。
【図面の簡単な説明】
【図１】従来の光ピックアップの構成図である。
【図２】本発明の第１の実施形態における光ピックアップの構成図である。
【図３】本発明の第１の実施形態における光ディスク上のスポット配置を示しており、ＤＶＤ−ＲＯＭディスクの場合の図である。
【図４】本発明の第１の実施形態における光ディスク上のスポット配置を示しており、ＤＶＤ−ＲＡＭディスクの場合の図である。
【図５】本発明の第１の実施形態における光ディスク上のスポット配置を示しており、ＣＤ−Ｒディスクの場合の図である。
【図６】光ディスク上の光スポットの強度分布について説明した図である。
【図７】フォーカスエラー信号への外乱を示す図である。
【図８】プッシュプル方式によるトラッキングエラー信号を示す図である。
【図９】本発明の第１の実施形態による光検出器および信号処理回路の平面図及びブロック図である。
【図１０】ＤＶＤでの検出光スポットの照射状態を示す図である。
【図１１】ＣＤでの検出光スポットの照射状態を示す図である。
【図１２】ＤＶＤのみ調整された状態でのＣＤの検出光スポットの照射状態を示す図である。
【図１３】本発明の第２の実施形態による光検出器および信号処理回路の平面図及びブロック図である。
【図１４】本発明の第３の実施形態による光検出器および信号処理回路の平面図及びブロック図である。
【図１５】本発明の第４の実施形態における光ディスク上のスポット配置を示しており、ＣＤ−ＲＯＭディスクの場合の図である。
【図１６】本発明の第４の実施形態による光検出器および信号処理回路の平面図及びブロック図である。
【図１７】本発明の第５の実施形態における光ピックアップの構成図である。
【図１８】本発明の第５の実施形態による光検出器および信号処理回路の平面図及びブロック図である。
【図１９】本発明の第６の実施形態における光ピックアップの構成図である。
【図２０】本発明の第６の実施形態におけるＣＤでの検出光スポットの照射状態を示す図である。
【図２１】本発明の第６の実施形態におけるＣＤでの検出光スポットの平行移動を示す図である。
【図２２】本発明の第６の実施形態におけるＣＤでの検出光スポットの回転移動を示す図である。
【図２３】本発明の第７の実施形態を示した光ピックアップ装置の概略構成図。
【図２４】光ディスク上における光スポット位置
(ａ)ＤＶＤ−ＲＯＭディスク上光スポット位置
(ｂ)ＤＶＤ−ＲＡＭディスク上光スポット位置
(ｃ)ＣＤ−ＲＯＭ、ＣＤ−Ｒディスク上光スポット位置
【図２５】第７の実施形態における光検出器の受光領域の受光面パターン図
(ａ)ＤＶＤ再生時
(ｂ)ＣＤ再生時
【図２６】第７の実施形態においてＤＶＤ−ＲＯＭ再生時に用いる信号処理回路の概略図
【図２７】第７の実施形態においてＤＶＤ−ＲＡＭ再生時に用いる信号処理回路の概略図
【図２８】第７の実施形態においてＣＤ−ＲＯＭ，ＣＤ−Ｒ再生時に用いる信号処理回路の概略図
【図２９】第８の実施形態における光検出器の受光領域の受光面パターン図
(ａ)ＤＶＤ再生時
(ｂ)ＣＤ再生時
【図３０】第８の実施形態においてＤＶＤ−ＲＯＭ再生時に用いる信号処理回路の概略図
【図３１】第８の実施形態においてＤＶＤ−ＲＡＭ再生時に用いる信号処理回路の概略図
【図３２】第８の実施形態においてＣＤ−ＲＯＭ，ＣＤ−Ｒ再生時に用いる信号処理回路の概略図
【図３３】第９の実施形態における光検出器の受光領域の受光面パターン図
(ａ)ＤＶＤ再生時
(ｂ)ＣＤ再生時
【図３４】第９の実施形態においてＤＶＤ−ＲＯＭ再生時に用いる信号処理回路の概略図
【図３５】第９の実施形態においてＣＤ−ＲＯＭ，ＣＤ−Ｒ再生時に用いる信号処理回路の概略図
【図３６】第１０の実施形態における光検出器の受光領域の受光面パターン図
(ａ)ＤＶＤ再生時
(ｂ)ＣＤ再生時
【図３７】第１０の実施形態においてＤＶＤ−ＲＯＭ再生時に用いる信号処理回路の概略図
【図３８】第１０の実施形態においてＣＤ−ＲＯＭ，ＣＤ−Ｒ再生時に用いる信号処理回路の概略図
【図３９】回折格子の鋸歯状化を示した図
(ａ)格子の側面に傾きを持たせた概略図
(ｂ)階段状に格子を刻んだ概略図
【図４０】矩形状の格子溝断面を持つ回折格子による光の回折を示した概略図。
【図４１】本発明の第１１の実施形態を示した光ピックアップ装置の概略構成図。
【図４２】本発明による光ピックアップを搭載した光ディスク装置の概略ブロック図である。
【符号の説明】
１、１０……光ディスク、 ２、１１、１５、１７……半導体レーザ、３、１６、３０……回折格子、 ４……ハーフミラー、 ５……コリメートレンズ、 ６……対物レンズ、 ７……アクチュエータ、 ８……駆動コイル、 ９、１４……光検出器、 １２……ダイクロプリズム、 １８、１９……偏光回折格子、２０、２１、２２、２３、２４……パッケージ、 ３０……ダイクロ回折格子、 ２００……マーク、 ２０１……ピット、 １００、１０１、１０２、３００、３０１、３０２、３０３、３０４……ディスク上光スポット、 １１０、１１１、１１２、３１０、３１１、３１２、３１３、３１４、３１５、 ３１６、３１７、３１８、３１９、３２０……検出光スポット、 ２００……記録ピット、 ２０１、４００……記録マーク、 ２０２、４０１……案内溝、 ２０３、４０２……案内溝間、 ２１０、２１１、２１２、２１３、２１４、４１０、４１１、４１２……受光領域、 ５００……コントロール回路、 ５０１……スピンドルモータ駆動回路、 ５０２……アクセス制御回路、 ５０３……アクチュエータ駆動回路、 ５０４……サーボ信号生成回路、 ５０５……情報信号再生回路、 ５０６……ＣＤ用レーザ点灯回路、 ５０７……ＤＶＤ用レーザ点灯回路、 ５０８……光ピックアップ、 ５０９……スピンドルモータ、 ７００１……レーザ光源、 ７００２……光検出器、 ７００３……ハーフミラー、 ７００４……立ち上げミラー、 ７００５……コリメータレンズ、 ７００６……対物レンズ、 ７００７……アクチュエータ、 ７００８……光ディスク、 ７００９……３スポット用の回折格子、 ７０１０……ホログラム素子、 ７０１１……検出レンズ、 ７０１２……偏光依存性ホログラム、 ７０１３……偏光変換素子。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a photodetector, an optical pickup used for reproducing an information signal recorded on an optical information recording medium (hereinafter referred to as an optical disc), and an optical information reproducing apparatus (hereinafter referred to as an optical disc device) using the same. ).
[0002]
[Prior art]
An optical disc device is an information recording / reproducing device characterized by non-contact, large capacity, high-speed access, and low-cost media. Utilizing these features, it can be used as a digital audio signal recording / reproducing device or as an external storage device of a computer. Has been.
[0003]
Currently, there are various types of optical discs depending on the substrate thickness and the corresponding wavelength. For example, the optimum wavelength of the laser beam for recording or reproduction with respect to a disk substrate thickness of 1.2 mm such as CD or CD-R is 780 nm band, whereas recently standardized DVD-ROM or DVD-RAM, etc. The disk substrate thickness is 0.6 mm and the corresponding wavelength is in the 650 nm band. There has also been proposed an optical disc apparatus using a laser beam having a further shorter wavelength. Based on these circumstances, for example, an optical pickup for DVD that has begun to spread in recent years has two different wavelengths of 780 nm band and 650 nm band in consideration of compatibility with CD optical disks that have already been widely spread. The one with a semiconductor laser is the mainstream.
[0004]
On the other hand, along with the expansion of the use of these optical discs, downsizing and cost reduction of optical disc apparatuses are being promoted, and in order to achieve this, technology for downsizing and simplifying optical pickups is indispensable. In order to reduce the size and simplification of the optical pickup, it is effective to reduce the number of parts constituting the optical system or use a low-cost part. In particular, when considering the correspondence to multiple types of optical discs, an optical system corresponding to each optical disc is required. However, the simplification of the optical system or the reduction in the number of components by sharing optical components can Effective for downsizing and cost reduction. As an example, in Japanese Patent Application Laid-Open Nos. 8-55363 and 9-54977, in order to enable reproduction of a plurality of types of optical discs, the laser beams of two semiconductor lasers are combined on an intermediate optical path. A technique that enables reproduction of information by an objective lens is disclosed.
[0005]
[Problems to be solved by the invention]
As described above, an optical pickup equipped with two semiconductor lasers has an optical system configuration in which a condensing optical system portion such as an objective lens and a collimating lens is shared in order to reduce the size and cost of the optical pickup itself. There are many things that exist. An example of such a conventional optical system configuration is shown in FIGS.
[0006]
In FIG. 1A, for example, a light beam emitted from a semiconductor laser 11 oscillating at a wavelength of 650 nm reaches the dichroic half prism 12. The dichroic half prism 12 is an optical element in which two prisms are bonded, and a reflecting film that reflects about 50% and transmits about 50% of laser light with a wavelength of 650 nm and transmits about 100% of laser light with a wavelength of 780 nm. Is formed. The light beam emitted from the semiconductor laser 11 is reflected by the reflecting film of the dichroic half prism 12 arranged at an angle of 45 ° with respect to the optical axis, and then converted into a parallel light beam by the collimator lens 5. The objective lens 6 is reached. The objective lens 6 is integrally held by the actuator 7, and by energizing the drive coil 8, for example, a light beam can be focused on the information recording surface of the optical disc 1 such as a DVD-ROM to form a light spot. Is possible. The light beam reflected from the optical disk 1 follows the same optical path as the outward light, passes through the objective lens 6 and the collimating lens 5, and reaches the dichroic half prism 12. About 50% of the return light amount passes through the dichroic half prism 12 and then reaches the dichroic half mirror 13. Here, the dichroic half mirror 13 is an optical element that transmits about 100% of 650 nm wavelength laser light and transmits about 50% of 780 nm wavelength laser light and reflects about 50%.
[0007]
For this reason, the light beam that has reached the dichroic half mirror 13 passes through the dichroic half mirror 13 and is collected at a predetermined position of the photodetector 14.
[0008]
On the other hand, in FIG. 1B, for example, a light beam emitted from the semiconductor laser 15 oscillating at a wavelength of 780 nm passes through the diffraction grating 16 for generating three beams and then has an angle of about 45 ° with respect to the optical axis. It is configured to reach the dichroic half mirror 13 that is arranged. As described above, the dichroic half mirror 13 has a characteristic of reflecting about 50% of the laser light having a wavelength of 780 nm, and the dichroic half prism 12 has a characteristic of transmitting about 100% of the laser light having a wavelength of 780 nm. The light beam emitted from the semiconductor laser 15 is reflected by the dichroic half mirror 13, passes through the dichroic half prism 12, is converted into a parallel light beam by the collimator lens 5, and reaches the objective lens 6. The objective lens 6 is a lens capable of condensing the light beam emitted from the semiconductor laser 15 on the information recording surface on the optical disk 10 even on the optical disk 10 such as a CD-ROM. A light spot is formed on the surface. The light beam reflected from the optical disk 10 travels in the same optical path as that of the outward light, passes through the objective lens 6, the collimating lens 5, and the dichroic half prism 12, and reaches the dichroic half mirror 13.
[0009]
As described above, since the dichroic half mirror 13 is an optical element that transmits about 780 nm wavelength laser light by about 50%, the light beam that has reached the dichroic half mirror 13 passes through the dichroic half mirror 13 and then the photodetector 14. The light is condensed at a predetermined position.
[0010]
In the configuration of the conventional optical system shown in FIG. 1, the condensing optical system portion from the dichroic half prism 12 through the collimating lens 5 to the objective lens 6 is shared, and the number of parts is reduced. There is a need for wavelength-selective optical elements such as dichroic half prisms and dichroic half mirrors, which have wavelength selectivity for two different wavelengths, and two different wavelength semiconductor lasers. Optical elements and semiconductor lasers are still expensive parts when viewed from the components of the optical pickup, which hinders further cost reduction of the optical pickup.
[0011]
In view of the above situation, the problem to be solved by the present invention is that an optical pickup for recording or reproducing information on a plurality of different types of optical discs and an optical disc apparatus using the same are compared with the conventional optical system configuration. In addition to realizing a simple configuration, a low-cost optical system configuration is realized by using inexpensive optical elements and as few semiconductor lasers as possible.
[0012]
[Means for Solving the Problems]
  Above issuesIs solved by the invention described in the claims. For example, the light receiving region that receives one light beam out of the light beams emitted from the first laser light source and reflected by the first optical information recording medium is divided into at least three light beams. A first light-receiving region divided into four light-receiving surfaces, and a light beam emitted from the second laser light source and branched into at least three light beams and reflected by the second optical information recording medium Of the light receiving region that receives one light beam, the second light receiving region divided into four light receiving surfaces, and the light beam reflected by the first optical information recording medium, the 1 A light receiving region for receiving two light beams other than one light beam, each of which is divided into four light receiving surfaces, and the second optical information recording medium. Of the reflected light beam, other than the one light beam A light receiving region for receiving two light beams, each of which includes a fifth light receiving region and a sixth light receiving region each divided into four light receiving surfaces, each of the first and second light receiving regions, A focus error signal by an astigmatism method and a signal that can generate a tracking error signal by a push-pull method and a differential phase detection method are output, and the third and fourth light receiving regions each have a tracking error by a push-pull method. A signal that can generate a signal is output, and each of the fifth and sixth light receiving regions outputs a signal that can generate a focus error signal by an astigmatism method and a signal that can generate a tracking error signal by a push-pull method. Is solved.
[0013]
  Also,First and second laser light sources, a light branching element for branching the light beams emitted from the first and second laser light sources into three light beams, respectively, and the light beams as optical information recording media This is solved by an optical pickup having a condensing optical system for irradiating and the above-described photodetector.
[0014]
  In addition, the optical pickup that detects a signal from an optical information recording medium, a servo signal generation circuit that generates a servo signal from a signal detected by the optical pickup, and the signal detected by the optical pickup, A control circuit that determines the type of the optical information recording medium and selects a servo signal detection method of the servo signal generation circuit, and an actuator drive that controls the position of the objective lens actuator of the optical pickup based on the selected servo signal And an optical information reproducing device having a circuit.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
The configuration and operation of the optical pickup as the first embodiment of the present invention will be described below with reference to the drawings.
[0041]
In FIG. 2A, a semiconductor laser 2 is a laser light source that oscillates at a wavelength of 650 nm, for example, and a laser light source that oscillates at a wavelength of 780 nm, for example (two-wavelength multilaser). The two laser light sources are arranged at a predetermined interval d. FIG. 2A shows a state in which the 650 nm laser light source in the semiconductor laser 2 is turned on. The light beam emitted from the 650 nm laser light source passes through the diffraction grating 3 and reaches the half mirror 4. Here, the light beam that has passed through the diffraction grating 3 is at least three light beams: zero-order light that is directly transmitted by the diffraction grooves formed on the grating and ± first-order diffracted light that travels separately from the zero-order light at a predetermined diffraction angle. This is a beam configuration. The half mirror 4 is disposed at an angle of 45 ° with respect to the optical axis of the light beam. The reflection film formed on the surface of the half mirror 4 reflects about 50% of 650 nm wavelength laser light and about 50%. It is an optical element to transmit. The light beam is reflected by the reflection film of the half mirror 4 disposed at an angle of 45 ° with respect to the optical axis, and then converted into a parallel light beam by the collimator lens 5 and reaches the objective lens 6. Here, the objective lens 6 corresponds to laser light having a wavelength of 650 nm and a wavelength of 780 nm, and can be focused on optical disks having different substrate thicknesses. The objective lens 6 is integrally held by an actuator 7, and a light beam is applied to the information recording surface of the optical disk 1 having a substrate thickness of 0.6 mm, such as a DVD-ROM or DVD-RAM, by energizing the drive coil 8. It is possible to form three light spots of 0th order light and ± 1st order diffracted light. The light beam reflected from the optical disk 1 follows the same optical path as the outward light, passes through the objective lens 6 and the collimating lens 5 and reaches the half mirror 4, and about 50% of the return light quantity of the light beam is half mirror 4. After being transmitted, the light is condensed at a predetermined position of the photodetector 9.
[0042]
FIG. 2B shows a state in which the 780 nm laser light source in the semiconductor laser 2 is lit. A light beam emitted from a 650 nm laser light source and a 780 nm laser light source arranged at a predetermined distance d passes through the diffraction grating 3 and reaches the half mirror 4. Here, the light beam transmitted through the diffraction grating 3 is at least three light beams of 0th order light and ± 1st order diffracted light diffracted by the diffraction grooves formed on the grating. The half mirror 4 is arranged so as to form an angle of 45 ° with respect to the optical axis of the light beam. At the same time, the reflecting film formed on the surface reflects about 50% of the laser light having a wavelength of 780 nm. An optical element that transmits about 50%.
[0043]
The light beam is reflected by the reflection film of the half mirror 4 disposed at an angle of 45 ° with respect to the optical axis, and then converted into a parallel light beam by the collimator lens 5 and reaches the objective lens 6. The objective lens 6 is integrally held by an actuator 7, and when a drive coil 8 is energized, a light beam is applied onto an information recording surface of an optical disc 10 having a substrate thickness of 1.2 mm such as a CD-ROM or CD-R. It is possible to form three spots of 0th order light and ± 1st order diffracted light.
[0044]
The light beam reflected from the optical disk 10 follows the same optical path as the outward light, passes through the objective lens 6 and the collimating lens 5 and reaches the half mirror 4, and about 50% of the return light quantity of the light beam is half mirror 4. After being transmitted, the light is condensed at a predetermined position of the photodetector 9.
[0045]
3 to 5 show the spot arrangement on the optical disk in the first embodiment of the present invention. FIG. 3 shows the spot arrangement on the DVD-ROM disk, and FIG. 4 shows the spot on the DVD-RAM disk. Arrangement, FIG. 5 shows a spot arrangement on a CD-R disc.
[0046]
In FIG. 3, the recording pits 200 on the DVD-ROM disc are arranged in the track direction of the optical disc at an interval of a track pitch Tp1 (0.74 μm). As described with reference to FIG. 2, the light spot on the optical disk is made up of three spots of zero-order light and ± first-order light by the diffraction grating 3, and a spot 100 of zero-order light, a spot 101 of + 1st-order diffracted light, As shown in FIG. 3, the spots 102 of the −1st order diffracted light are arranged on the optical disc 1 at an interval Tp11 corresponding to the track pitch Tp1.
[0047]
In FIG. 4, on the DVD-RAM disc, guide grooves 202 are alternately formed with guide groove intervals 203 at intervals of a track pitch Tp2 (1.48 μm). The recording marks 201 are arranged in the track direction of the optical disc at an interval Tp21 (0.74 μm) corresponding to half of Tp2. The light beam is diffracted by the diffraction grating 3 in the same manner as in FIG. 3, and becomes three spots of zero-order light and ± first-order diffracted light on the optical disk. The spot 100 of the 0th order light, the spot 101 of the + 1st order diffracted light, and the spot 102 of the −1st order diffracted light are placed on the optical disc 1 at an interval Tp22 (= Tp11) corresponding to substantially half of the track pitch Tp2, as shown in FIG. Has been placed.
[0048]
In FIG. 5, guide grooves 401 are alternately formed on the CD-R disc with guide groove intervals 402 at intervals of a track pitch Tp3 (1.6 μm). The recording mark 400 is arranged in the track direction on the guide groove 401 of the optical disc at Tp3. The light spots on the optical disk 10 are the three spots of 0th-order light and ± 1st-order diffracted light as in FIGS. 3 and 4, and these 0th-order light spot 100 and + 1st-order diffracted light spots 101 and −1. The spots 102 of the next diffracted light are arranged on the optical disc 10 at intervals of Tp31 corresponding to approximately half of Tp3.
[0049]
Here, since the diffraction angle in the same diffraction grating by the laser beams having different wavelengths has a relation that it is substantially proportional to the wavelength under the condition that the diffraction angle is small, the three spots on the optical disk in the first embodiment are not related. The interval is almost proportional to the wavelength. Further, since the direction of the spot row on the optical disk, that is, the diffraction direction of the light beam is the same regardless of the wavelength, the distance between the spots on the optical disk in the disk radial direction is substantially proportional to the wavelength. That is, the following relationship holds between the two wavelengths λ1 (= 650 nm) and λ2 (= 780 nm) and the spot intervals Tp22 and Tp31 on the optical disc.
[0050]
[Expression 1]

[0051]
According to equation (1), the spot interval Tp22 on the DVD-RAM disk when the spot interval Tp31 on the CD-R disc is set to 0.80 μm is 0.67 μm. This is a shift position of about 10% with respect to the half value of 0.74 μm of the track pitch in the DVD-RAM disk, and the servo signal is detected from the DVD-RAM disk without any problem by using a servo signal detection method described later. It is possible. Conversely, when the spot interval Tp22 on the DVD-RAM disc is set to 0.74 μm, the spot interval Tp31 on the CD-R disc is 0.89 μm. This is a deviation position of about 10% with respect to a track pitch of 0.8 μm on the CD-R disc, and a servo signal can be detected from the CD-R disc without any problem by using a servo signal detection method described later. It is possible to select an optical disc as a reference for setting the spot interval.
[0052]
The photodetector 9 shown in FIG. 2 has a configuration in which at least one light receiving area consisting of four light receiving surfaces is formed in a square shape with respect to laser light having a predetermined wavelength, as will be described later. . The light beams of the 0th order light and the ± 1st order diffracted light reflected from the optical disc 1 or the optical disc 10 are substantially the center of each light receiving region, that is, the point where the vertical and horizontal dividing lines in the light receiving region cross each other and the intensity of the light beam. The light is collected at a position where the centers substantially coincide. At this time, since each light beam is given a predetermined astigmatism when passing through the half mirror 4 disposed to be inclined with respect to the optical path, a square-shaped light-receiving region as will be described later. Thus, a focus error signal is detected by an astigmatism method. Similarly, the tracking error signal by the push-pull method or the differential phase detection method can be detected by using the output signal composed of four light receiving surfaces.
[0053]
Next, the intensity distribution of the light spot on the optical disc 1 will be described with reference to FIG. In this embodiment, as shown in FIG. 4, the irradiation position interval in the disk radial direction of the spots 100, 101, and 102 irradiated to the optical disk 1 coincides with substantially half of the guide groove pitch of the DVD-DAM disk. Is set to That is, for example, the arrangement of the three light spots 100, 101, 102 on the DVD-RAM disk shown in FIG. 6 is such that the zero-order light spot 100 is located between the guide grooves 203 of the disk as shown in FIG. , The light spot 101 of the + 1st order diffracted light and the light spot 102 of the −1st order diffracted light are respectively located directly above the adjacent guide grooves 202. Even in the case where the light spot irradiation position is shifted relative to the guide groove 202, the positional relationship between the light spots 100, 101, 102 is as shown in FIG. Is always kept. On the other hand, the reflected light beam from the optical disk is affected by diffraction by the guide groove 202, and has a unique intensity distribution pattern that periodically changes according to the relative position change of the irradiation position of the light spot and the guide groove of the disk. Will have. The intensity distributions of the reflected light beam of the 0th-order light spot 100 and the reflected light beam of the light spot 101 by the + 1st order diffracted light and the reflected light beam of the light spot 102 by the −1st order diffracted light are compared. As shown in c), the change is such that the left and right are completely reversed.
[0054]
By the way, when a focus error signal by the astigmatism method is detected from these reflected light beams, there is a problem that a large disturbance is likely to occur in the detected focus error signal. This is mainly due to the periodic change in the intensity distribution pattern of the reflected light beam due to the diffraction effect in the guide groove 202 described above, and the push-pull signal leakage disturbance caused thereby. Therefore, as shown in FIGS. 7A and 7B, when the focus error signal obtained from the reflected light flux of the light spot 100 and the focus error signal obtained from the reflected light flux of the light spot 101 and the light spot 102 are compared, While the waveform of the focus error signal itself is substantially the same, the phase of the disturbance component generated in the signal is almost completely inverted.
[0055]
Therefore, when the focus error signal obtained from the reflected light beam of the light spot 100 and the focus error signal obtained from the reflected light beam of the light spot 101 or the light spot 102 or a sum signal of both are added, FIG. As shown, the focus error itself is doubled, while a good focus error signal in which the disturbance component is almost completely canceled can be obtained.
[0056]
The phenomenon as described above is similarly applied to tracking error signal detection by the push-pull method. That is, in general, when detecting a tracking error signal by the push-pull method, when the objective lens is displaced in the tracking direction, the light spot irradiated on the light receiving surface of the photodetector 9 is also displaced accordingly, and FIG. And as shown in (b), a large offset occurs in the detected tracking error signal. This offset is the same for the tracking signal detected from the reflected light beam of the light spot 100 and the tracking error signal detected from the reflected light beam of the light spot 101 and the light spot 102 as shown in FIGS. Occurs only to the same extent. On the other hand, the tracking error signal itself is based on the phase of the signal detected from the reflected light beam of the light spot 100 and the reflected light beams of the light spots 101 and 102 for the same reason as described in the explanation of the focus error signal. The phase of the detected signal is almost completely inverted. Therefore, by subtracting the tracking error signal detected from the disk reflected light of each light spot, only the offset component is canceled, and the offset as shown in FIG. 8C is greatly reduced. A tracking error signal can be obtained.
[0057]
In the embodiment according to the present invention, a good focus error signal and tracking error signal are detected by utilizing the principle as described above.
[0058]
FIG. 9 is a plan view and a block diagram showing a first embodiment relating to a photodetector and a signal processing circuit according to the present invention. The package 20 of the photodetector 9 is provided with a light receiving area 210 in which each divided light receiving surface is divided into four square shapes represented by symbols a, b, c, and d as shown in the figure. Similarly to the light receiving region 210, a divided light receiving surface 211 is represented by symbols e, f, g, and h, and a four divided light receiving region 212 is represented by symbols i, j, k, and l. Has been placed. Further, the divided light receiving surface is represented by four divided light receiving regions 410 represented by symbols m, n, o, and p, the divided light receiving surface is represented by symbols q, r, and the divided light receiving surface is represented by symbols s. , T, a two-divided light receiving region 412 is arranged. Then, on the light receiving area 210, the disk reflected light of the on-disk light spot 100 is condensed to form a detection light spot 110. Similarly, the disk reflected light of the on-disk light spot 101 is collected on the light receiving area 211 and the reflected light of the on-disk light spot 102 is collected on the light receiving area 212 to form detection light spots 111 and 112, respectively. Yes.
[0059]
In addition, on the light receiving area 410, the disk reflected light of the on-disk light spot 300 is condensed to form a detection light spot 310. Similarly, the disk reflected light of the on-disk light spot 101 is collected on the light receiving area 411 and the reflected light of the on-disk light spot 102 is collected on the light receiving area 412 to form detection light spots 311 and 312. Yes.
[0060]
Here, in the first embodiment of the present invention, two different wavelength laser light sources (two-wavelength multi-lasers) separated by a minute distance d in the same housing, one diffraction grating, and one photodetector are used for optically. The system is configured. For this reason, the light receiving area sequence including the light receiving areas 200, 201, and 202 and the light receiving area sequence including the light receiving areas 410, 411, and 412 are arranged at different positions corresponding to the imaging system of the optical system. Further, with respect to the light receiving regions 201, 202, 411, 412 corresponding to the ± 1st order diffracted light of each laser beam, the interval between the light receiving regions 411, 412 corresponding to the laser light source having a large wavelength is the light beam in the diffraction grating 3. The arrangement is almost proportional to the diffraction angle.
[0061]
Each detection current detected by photoelectric conversion on each of the light receiving surfaces a, b, c, d is converted into a voltage by current-voltage conversion amplifiers 40, 41, 42, 43 provided in the package 20 of the photodetector 9. Each is converted and sent to the output terminal of the photodetector 9. Similarly, the light receiving surfaces e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, and t output lines are current-voltage conversion amplifiers 44, 45, 46, 47, 48, 49, 50, 51, 80, 81, 82, 83, 84, 85, 86, 87. (Hereinafter, for the sake of simplicity, these voltage-converted detection signals are given the same symbols as the light receiving surface on which the detection signals are detected.) After all, the 20 output terminals of the photodetector 9 Are output as a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, respectively. .
[0062]
Next, the arithmetic circuit will be described. Of the 20 detection signals output from the output terminal of the photodetector 9, signals (a + c) − (b + d) are output from the output signals a, b, c, and d by the adders 52 and 53 and the subtractor 54. The signal (a + d) − (b + c) is output by the adders 55 and 56 and the subtractor 57. Here, the signal (a + c) − (b + c) corresponds to a focus error signal of the on-disk light spot 100 detected by a so-called astigmatism method. Further, (a + d) and (b + c) correspond to the detected light quantity in each region when the detection light spot 110 is divided into two in the tracking direction (radial direction) of the disk, and the difference signal (a + d) between these two signals. -(B + c) corresponds to the tracking error signal of the light spot 100 on the disc detected by the so-called push-pull method.
[0063]
Further, a phase difference detection circuit 77 is connected to the output signals a, b, c, and d, and this circuit enables tracking error of the optical spot 100 on the disc by a so-called phase difference detection method (differential phase detection method). A signal is also detected. Since this phase difference detection method is a known technique, a detailed description thereof will be omitted here.
[0064]
Further, by generating the sum signal DVD-RF of the output signals a, b, c, and d by the adder 76, the information signal recorded on the optical disc can be reproduced by a predetermined signal reproduction circuit. Although not shown in the present embodiment, the adder 76 is stored in the package 20 of the photodetector 9, and the output terminal of the sum signal (a + b + c + d) is added to the signal output terminal of the photodetector 9. Is also possible.
[0065]
Further, from the output signals e, f, g, and h, signals (e + g) − (f + h) are output by the adders 58 and 59 and the subtractor 60, and the signals (e + h) are output by the adders 61 and 62 and the subtractor 63. -(F + g) is output. Similarly, from the output signals i, j, k, and l, signals (i + k) − (j + l) are output by the adders 64 and 65 and the subtractor 66, and signals (i + l) are output by the adders 67 and 68 and the subtractor 69. ) − (J + k) is output.
[0066]
The signals (e + g) − (f + h) and (i + k) − (j + l) are output as a signal (e + g + i + k) − (f + h + j + l) by the adder 70 and further amplified by the amplifier 71 at a predetermined amplification factor K1. The amplification factor K1 of the amplifier 71 is determined so that the signal (e + g + i + k) − (f + h + j + l) has substantially the same signal amplitude as the signal (a + c) − (b + d). This signal (e + g + i + k)-(f + h + j + l) corresponds to the sum signal of the focus error signals of the on-disk light spots 101 and 102 detected by the so-called astigmatism method.
[0067]
On the other hand, (e + h)-(f + g) and (i + l)-(j + k) are output by the adder 73 as a signal (e + h + i + l)-(f + g + j + k) and further amplified by the amplifier 74 at a predetermined amplification factor K2. The amplification factor K2 of the amplifier 74 is determined so that the signal (e + h + i + l) − (f + g + j + k) has substantially the same signal amplitude as the signal (a + d) − (b + c). This signal (e + h + i + l)-(f + g + j + k) corresponds to the difference between the total detected light amounts in the respective areas when the detection light spots 111 and 112 are divided into two in the disk tracking direction (radial direction). This corresponds to the sum of the tracking error signals of the spots 101 and 102 on the disc detected by the method. The signal output from the subtractor 75 is
{(A + d) − (b + c)} − K2 · {(e + h + i + l) − (f + g + j + k)}. This signal corresponds to a signal obtained by subtracting the tracking error signals of the spots 101 and 102 on the disk obtained from the light receiving areas 201 and 202 from the tracking error signal of the spot 100 on the disk obtained from the light receiving area 200. .
[0068]
By the way, selector switches 78 and 79 are provided at the focus error signal output terminal and the tracking error signal output terminal of the signal processing circuit, respectively. This is provided for appropriately switching between a focus error signal and a tracking error signal used for controlling the actuator 7 according to the type of the optical disk as described below. That is, for example, when reproducing an optical disk having a continuous guide groove on the recording surface of the disk, such as a DVD-RAM disk, first, the changeover switch 78 is switched as shown in FIG. Signal (a + c) − (b + d) and the signal K1 · {(e + i + g + k) − (h + 1 + f + j)} output from the amplifier 71 are added by the adder 72
{(A + c) − (b + d)} + K1 · {(e + i + g + k) − (h + 1 + f + j)} is output as a focus error signal. As described above, this signal corresponds to a signal obtained by adding together the sum signal amplitudes of the focus error signal of the light spot 100 on the optical disc by the astigmatism method and the focus error signals of the light spots 101 and 102. Therefore, as described above, this signal is a good focus error signal in which the leakage error of the focus error signal due to diffraction in the guide groove is largely eliminated.
[0069]
Next, for the tracking error signal, the changeover switch 79 is switched to
{(A + d) − (b + c)} − K2 · {(e + h + i + l) − (f + g + j + k)} is output. This is obtained by subtracting the sum signal of the tracking error signals of the spots 101 and 102 on the disk obtained from the light receiving areas 211 and 212 from the tracking error signal of the spot 100 on the disk obtained from the light receiving area 210 as described above. Correspondingly, this method is called a differential push-pull method. Therefore, although this signal is detected by the push-pull method, it is a good tracking error signal in which the offset due to the displacement of the objective lens is greatly eliminated.
[0070]
On the other hand, signals (m + o) − (n + p) are output from the output signals m, n, o, and p by the adders 88 and 89 and the subtracter 90, and the signal (m + p) is output by the adders 91 and 92 and the subtractor 93. -(N + o) is output. Here, the signal (m + o) − (n + p) corresponds to a focus error signal of the on-disk light spot 300 detected by a so-called astigmatism method. Further, (m + p) and (n + o) correspond to the detected light quantity in each region when the detection light spot 310 is divided into two in the tracking direction (radial direction) of the disk, and the difference signal (m + p) between these two signals. -(N + o) corresponds to the tracking error signal of the light spot 300 on the disc detected by the so-called push-pull method.
[0071]
Further, by generating the sum signal CD-RF of the output signals m, n, o, and p by the adder 99, the information signal recorded on the optical disc can be reproduced by a predetermined signal reproduction circuit. Although not shown in the present embodiment, the adder 99 is stored in the package 20 of the photodetector 9, and the output terminal of the sum signal (m + n + o + p) is added to the signal output terminal of the photodetector 9. Is also possible.
[0072]
Further, from the output signals q, r, s, t, a tracking error signal (q-r) detected from the subtractor 94 by the push-pull method, and a tracking error signal (s) detected from the subtractor 95 by the push-pull method. -T) is output, the signal (q + s)-(r + t) is output by the adder 96, and further amplified by the amplifier 97 at a predetermined amplification factor K3. The amplification factor K3 of the amplifier 97 is determined so that the signal (q + s)-(r + t) has substantially the same signal amplitude as the signal (m + p)-(n + o). Here, the signal (q + s) − (r + t) corresponds to the difference in the total detected light amount in each region when the detection light spots 311 and 312 are divided into two in the tracking direction (radial direction) of the disk. This corresponds to the sum of the tracking error signals of the spots 301 and 302 on the disc detected by the method. The signal output from the subtractor 98 is
{(M + p)-(n + o)}-K3. {(Q + s)-(r + t)}
It becomes. This signal corresponds to a signal obtained by subtracting the tracking error signals of the spots 101 and 102 on the disk obtained from the light receiving areas 411 and 412 from the tracking error signal of the spot 100 on the disk obtained from the light receiving area 410. This method is called a differential push-pull method. Therefore, although this signal is detected by the push-pull method, it is a good tracking error signal in which the offset due to the displacement of the objective lens is greatly eliminated.
[0073]
When playing back a read-only disc such as a DVD-ROM disc in which phase pits corresponding to the recording signal are provided on the disc, even if a signal by the normal astigmatism method is used as the focus error signal, the disturbance is not disturbed. There is no effect. Further, a tracking error signal based on the phase difference detection method output from the phase difference detection circuit 77 can be used as the tracking error signal. Therefore, if the change-over switches 78 and 79 are switched so that (a + c)-(b + d) is output as the focus error signal and the tracking error signal output from the position difference detection circuit 77 is output as the tracking error signal, the read-only disc A desired error signal suitable for the above can be obtained. Also, with respect to a CD-ROM disc, good signal reproduction is possible by using an astigmatism method and a differential push-pull method.
[0074]
Here, the position adjustment of the detection light spot on the light detection surface will be described. FIG. 10 shows a light spot on the photodetector for DVD, and FIG. 11 shows a light spot on the photodetector for CD. In FIG. 10, detection light spots 110, 111, and 112 of the DVD are irradiated to predetermined positions in the light receiving areas 210, 211, and 212, respectively. In FIG. 11, CD detection light spots 310, 311, and 312 are irradiated to predetermined positions of the light receiving areas 410, 411, and 412, respectively. In the first embodiment of the present invention, the optical axis of the condensing optical system is set and adjusted based on the optical axis of the DVD. Therefore, the detection light spot on the CD is arranged at a position substantially proportional to the interval between the laser light sources with the optical axis of the DVD as the center. FIG. 12 shows a detection light spot on a CD with the DVD optical axis adjusted. The zero-order detection light spots 310 of the CD are arranged on the circumference centered on the position where the zero-order light spot 110 is arranged on the DVD, and the ± first-order detection light spots 311 and 312 of the CD are zero-order. Irradiated to the position diffracted around the detection light spot. By rotating the semiconductor laser 2 about the optical axis, the zero-order detection light spot 310 of the CD rotates in the direction of the arrow in FIG. 12, and thus the detection light spot position on the CD can be adjusted.
[0075]
Next, a second embodiment according to the present invention will be described with reference to FIG. The same symbols used in the drawings are the same as those used in the above description. The difference from the configuration of FIG. 9 is the configuration of the light receiving region in the package 21. In FIG. 13, the light receiving area for ± 1st order diffracted light used when reproducing a CD-R disc is also used as the light receiving area for ± 1st order diffracted light used when reproducing a DVD-RAM. . That is, when reproducing or recording a CD-R, by using the light receiving surfaces e, f, i, j of the light receiving areas 213, 214, the same as described in the first embodiment. It is possible to detect a focus error signal and a tracking error signal. With such a configuration, the number of signal lines output from the light receiving surface can be reduced by four, and an actual photodetector can be easily and inexpensively made. Even when a DVD-RAM disc is played back, the light from the optical disc does not return to the portion where the area of the light receiving surface is enlarged, so it goes without saying that the same effect as in the first embodiment can be obtained.
[0076]
Next, a third embodiment relating to the photodetector and the signal processing circuit according to the present invention will be described with reference to FIG. The same symbols used in the drawings are the same as those used in the above description. The difference from the configuration of FIG. 9 is the configuration of the light receiving region in the package 22. In FIG. 14, the light receiving area for ± first-order diffracted light used for reproducing a DVD-RAM disk is deleted. For this reason, the influence of the disturbance remains in the focus error signal by the astigmatism method, and it is difficult to reproduce the DVD-RAM disc. When playing back a CD-R disc, it is possible to generate a tracking error signal by the differential push-pull method, and furthermore, it is possible to use a diffraction grating exclusively for the CD-R. The position of the folded light on the optical disk 2 can be easily adjusted by using the rotation of the diffraction grating.
[0077]
Next, a fourth embodiment relating to the photodetector and the signal processing circuit according to the present invention will be described with reference to FIGS. The same symbols used in the drawings are the same as those used in the above description. FIG. 15 shows the arrangement of light spots on the CD-ROM disc. The recording pits 400 are arranged in the track direction and are formed at intervals of Tp3 (1.6 μm). The light spots on the optical disk 10 are three spots of 0th order light and ± 1st order diffracted light, and the spot 301 of + 1st order diffracted light and the spot 302 of −1st order diffracted light are from the spot 300 of 0th order light to Tp3. It arrange | positions in the position which left | separated the space | interval of Tp32 (0.4 micrometer) equivalent to 1/4. FIG. 16 is a plan view and a block diagram regarding a photodetector and a signal processing circuit. The difference from the configuration of FIG. 14 is the configuration of the light receiving region in the package 23. In FIG. 16, a light receiving area for receiving ± first-order diffracted light of the CD side detection system is constituted by one light receiving surface 413, 414, respectively. Outputs from the light receiving surfaces 413 and 414 are output from the current-voltage conversion amplifiers 84 and 86 and output as a difference signal of ± first-order diffracted light by using the subtractor 94. As a result, by combining with the spot arrangement on the optical disk 10 shown in FIG. 15, it is possible to detect the tracking error signal by the three-beam method.
[0078]
Next, a fifth embodiment relating to the photodetector and the signal processing circuit according to the present invention will be described with reference to FIGS. The same symbols used in the drawings are the same as those used in the above description. FIG. 17 shows the configuration of the optical system in the fifth embodiment. The difference from the first embodiment shown in FIG. 2 is that two laser light sources having different wavelengths are arranged in the same casing. In the semiconductor laser 17 (two-wavelength multi-laser), the points where the polarization directions of the laser beams emitted from the respective laser light sources are substantially perpendicular to each other, and the two polarization diffraction gratings 18 and 19 are optical paths. It is a point arranged inside. The diffraction directions of the polarization diffraction gratings 18 and 19 due to the polarization of each other are arranged vertically, and the diffraction directions of the polarizations are arranged so as to coincide with the polarization directions of the corresponding laser light sources. Therefore, the grating groove and angle of each polarization diffraction grating can be set freely. FIG. 18 is a plan view and a block diagram relating to a photodetector and a signal processing circuit. The difference from the configuration of FIG. 14 is the configuration of the light receiving region in the package 24. In FIG. 18, the light receiving region for receiving the ± first-order diffracted light of the CD side detection system is constituted by one light receiving surface 413, 414 as in FIG. Outputs from the light receiving surfaces 413 and 414 are output from the current-voltage conversion amplifiers 84 and 86 and output as a difference signal of ± first-order diffracted light by using the subtractor 94. As described above, since the polarization diffraction gratings 18 and 19 can be designed independently of each other, for example, the discs are independent of the DVD-RAM optical disc 1 and the CD-ROM optical disc 10, for example. An upper spot arrangement is possible. Therefore, it is possible to select the spot arrangement shown in FIG. 4 on the DVD side, and it is possible to detect a focus error signal and a tracking error signal necessary for reproducing a DVD-ROM or DVD-RAM disc. On the CD side, the spot arrangement shown in FIG. 15 can be selected, and the tracking error signal can be detected by the three-beam method.
[0079]
Next, a sixth embodiment relating to the detection light spot adjusting method according to the present invention will be described with reference to FIGS. The same symbols used in the drawings are the same as those used in the above description. FIG. 19 shows a configuration diagram of the optical pickup in the sixth embodiment. The difference from the first embodiment shown in FIG. 2 is that the half mirror of the condensing optical system and the photodetector 9 are different. The dichroic diffraction grating 30 is disposed in the optical path between them. The dichroic diffraction grating 30 has such a characteristic that only the light beam of the CD is diffracted, and diffracts only the reflected light from the optical disk 10 during CD reproduction. Therefore, the irradiation state of the detection light spot on the detector 9 in the DVD is the same as that shown in FIG. On the other hand, in the CD, the light beam is diffracted by the dichroic diffraction grating 30 and the detection light spot is irradiated as shown in FIG. In FIG. 20, detection light spots 315, 316, and 317 are zero-order light detection spots on the dichroic diffraction grating 30, and detection light spots 318a, 319a, and 320a are + 1st-order light detection spots and detection light spots 318b on the dichroic diffraction grating 30. Reference numerals 319b and 320b denote -1st order light detection spots on the dichroic diffraction grating 30. In the sixth embodiment, the light detection areas 410, 411, and 412 are irradiated with the light detection spots 318a, 319a, and 320a that are + 1st order diffracted light from the dichroic diffraction grating 30. Therefore, as shown in FIG. 21, the light detection spots 318a, 319a, and 320a can be moved closer to or away from the zero-order detection light spot by moving the dichroic diffraction grating 30 back and forth along the optical axis. Yes, it is possible to rotate around the zero-order detection light spot 315 by rotating the dichroic diffraction grating 30 as shown in FIG.
[0080]
Therefore, the irradiation position of the CD detection light spot can be adjusted by adjusting the position and rotation of the dichroic diffraction grating 30. As a result, the irradiation position of the CD detection light spot can be within the light receiving range of the light receiving region.
[0081]
Further, as shown in FIG. 21, the light detection spots 318a, 319a, and 320a can be moved closer to or away from the zero-order detection light spot by moving the dichroic diffraction grating 30 back and forth along the optical axis. For this reason, the position of the light receiving region in the detector 9 can be set to a desired arrangement. That is, by adjusting the position of the dichroic diffraction grating 30, it is possible to increase the degree of freedom in designing the arrangement of the light receiving regions in the detector 9. This example is shown using FIG. 10, FIG. 20, and FIG. In FIG. 20, the light detection areas 210, 211, and 212 are irradiated with the detection light spot of the DVD (see FIG. 10), and the light detection areas 410, 411, and 212 are irradiated with the detection light spot of the CD. 412. Here, FIG. 21 shows that by adjusting the position of the dichroic diffraction grating 30, the irradiation positions of the CD detection light spots 318 a, 319 a, and 320 a can be on the light receiving areas 410, 411, and 412. Furthermore, in FIG. 21, by adjusting the position of the dichroic diffraction grating 30, the irradiation positions of the CD detection light spots 318a, 319a, and 320a can be placed on the light receiving areas 210, 211, and 212.
[0082]
For example, first, the reflected light used for DVD detection (the zero-order light beam in the dichroic diffraction grating 30) is irradiated with a detection light spot on the detector 9, as shown in FIG. A detection light spot is irradiated to a predetermined position within a range where light can be received.
[0083]
Here, the predetermined position described above means that when the detection light spot is irradiated to the predetermined position, the detection light spot is detected, and the output signal output based on the detection is It is an irradiation position in the light receiving region where an output signal that can be used for signal processing or the like can be output.
[0084]
That is, in the irradiation state of the detection light spot on the detector 9 shown in FIG. 10, the detection light spot is detected, and the signal output output based on the detection can be used for subsequent signal processing and the like. The position of the detector 9 and the like is determined so as to be the irradiation position in such a light receiving region. On the other hand, at this time, the reflected light (+ 1st order light or -1st order light beam in the dichroic diffraction grating 30) used for CD detection is caused in the light receiving region as described for the DVD due to manufacturing variation. The detection light spot is not always applied to a predetermined position within the range where light can be received. Therefore, when the position of the detector 9 is determined with reference to the reflected light used for the DVD detection, the reflected light used for the CD detection is predetermined within the light receiving range where light can be received in the light receiving area. The detection light spot is not always irradiated to the position.
[0085]
Here, since the reflected light used for detecting the CD is diffracted light in the dichroic diffraction grating 30, the dichroic diffraction grating 30 is moved back and forth along the optical axis or rotated around the optical axis. It is possible to make the irradiation position of the reflected light used for detecting the light approach or move away from the light receiving area of the DVD. Accordingly, by moving the dichroic diffraction grating 30 back and forth along the optical axis or rotating it around the optical axis, the irradiation position of the reflected light used for CD detection is a predetermined position within the range where light can be received in the light receiving area. It becomes possible to adjust so that. In this adjustment, the reflected light used for detecting the DVD is 0th-order light in the dichroic diffraction grating 30, so that the reflected light is irradiated so as to irradiate a predetermined position within the light receiving area.
[0086]
In the above description, the dichroic diffraction grating 30 does not diffract the DVD light beam but diffracts only the CD light beam. However, the present invention is not limited to this.
[0087]
That is, as in the present embodiment, the reflected light used for DVD detection uses the 0th order light in the dichroic diffraction grating 30, and the reflected light used for CD detection uses the + 1st order light or −1 in the dichroic diffraction grating 30. In the case of using the next light, the dichroic diffraction grating 30 may have a function of diffracting both the DVD and CD light beams.
[0088]
Next, by moving the dichroic diffraction grating 30 back and forth along the optical axis, or by rotating the dichroic diffraction grating 30 around the optical axis, the irradiation position of the reflected light used for detecting the CD or DVD is within the range where light can be received in the light receiving region. In the following, an embodiment showing the adjustment to be a predetermined position in will be described.
[0089]
In the seventh to ninth embodiments shown below, the DPP signal can be detected on both the CD and DVD discs by using one three-spot diffraction grating by using the relationship of the above formula (1). A simple light beam.
[0090]
FIG. 23 is a schematic configuration diagram of an optical pickup device according to a seventh embodiment of the present invention. A laser light source 7001 is a two-wavelength multi-laser light source in which two semiconductor laser chips having different oscillation wavelengths (oscillation wavelengths of 650 nm band and 780 nm band) are provided in the same package.
[0091]
For example, when reproducing a high-density optical disk such as a DVD-ROM, a light beam having a wavelength of 650 nm is emitted from a two-wavelength multi-laser light source 7001. This light beam passes through a diffraction grating 7009 for three spots, is reflected by a half mirror 7003 arranged at an angle of 45 ° with respect to the optical axis, and is parallel by a collimator lens 7005 via a rising mirror 7004. It is converted into a light beam and reaches the objective lens 7006. The objective lens 7006 is held by an actuator 7007, and a light beam is condensed on the optical disc 7008 to form a light spot. The light beam reflected from the optical disc 7008 follows the same optical path as the forward path, and enters the half mirror 7003 through the objective lens 7006, the collimator lens 7005, and the rising mirror 7004. The light beam that has passed through the half mirror 7003 reaches the hologram element 7010. The hologram element 7010 separates and generates a + 1st order diffracted light beam or a −1st order diffracted light beam with respect to a light beam having a wavelength of 780 nm band, as will be described later, and either one of these diffracted light beams is predetermined in the photodetector 7002. The grating groove pattern is designed so as to have a function of condensing in the light receiving region, but naturally, a 0th-order light beam and a ± 1st-order diffracted light beam are generated even when a light beam having a wavelength of 650 nm is incident. However, in this embodiment, it is designed such that only the 0th-order light beam that has been transmitted straight through the hologram element 7010 is incident on a predetermined light receiving region in the photodetector 7002 through the detection lens 7011. The detection lens 7011 is a lens in which a cylindrical lens and a concave lens are combined. The detection lens 7011 is added to the zero-order light beam by a function of condensing the zero-order light beam in a predetermined light receiving region in the photodetector 7002 and a half mirror 7003. 23 has a function of canceling the coma and the astigmatism in the y direction and the x direction in FIG. 23 and generating a predetermined amount of astigmatism in a direction inclined by 45 ° with respect to the y axis direction in the xy plane. is doing.
[0092]
Next, when reproducing a conventional optical disk such as a CD-ROM, a two-wavelength multi-laser light source 7001 emits a light beam having a wavelength of 780 nm. As described above, this light beam passes through the diffraction grating 7009 for three spots and is diffracted and separated into 0th order diffracted light and ± 1st order diffracted light. At this time, each light beam is, for example, a quarter track pitch on the optical disc 7008. Diffraction separation is performed so that a light spot is formed by shifting in the radial direction of the disk. The light beam that has passed through the diffraction grating 7009 is reflected by a half mirror 7003 disposed at an angle of 45 ° with respect to the optical axis, passes through a rising mirror 7004, is converted into a parallel light beam by a collimator lens 7005, and is an objective lens. 7006 is reached. The objective lens 7006 is held by an actuator 7007. As described above, the objective lens 7006 has a function of condensing a light beam having a wavelength of 650 nm on a DVD disk and a light beam having a wavelength of 780 nm on an optical disk 7008 such as a CD-ROM. At the same time to form a light spot by condensing the light.
[0093]
The light beam reflected from the optical disk 7008 follows the same optical path as the forward path, enters the half mirror 7003 through the objective lens 7006, the collimator lens 7005, and the rising mirror 7004. After passing through the half mirror 7003, the hologram element 7010 is transmitted. To reach. The hologram element 7010 has a predetermined grating groove pattern, and diffracts and separates an incident light beam having a wavelength of 780 nm band with a predetermined diffraction efficiency to generate a ± first-order diffracted light beam. Astigmatism and coma generated in the + 1st order diffracted light beam or -1st order diffracted light beam by passing through 7011 are canceled, and this diffracted light beam passes through the detection lens 7011 and has a wavelength of 650 nm in the photodetector 7002. It has a function of condensing light to a predetermined light receiving area at a position different from the predetermined light receiving area to which the light beam reaches almost without aberration.
[0094]
In FIG. 21, by moving the dichroic diffraction grating 30 back and forth along the optical axis, the light detection spots 318a, 319a, and 320a can approach or separate from the zeroth-order detection light spot. I have already explained that.
[0095]
Therefore, also in FIG. 23, by moving the hologram element 7010 back and forth along the optical axis, it is possible to change the position in the photodetector 7002 where the light beam having the wavelength of 780 nm reaches. By using this fact, in FIG. 23, it is possible to adjust the irradiation position of the CD detection light spot in the photodetector 7002. In addition, by adjusting the position of the hologram element 7010, it is possible to increase the degree of freedom in designing the arrangement of the light receiving regions in the photodetector 7002. For example, the light receiving region in the photodetector 7002 where the light beam having a wavelength of 780 nm reflected from the optical disk arrives and the light receiving region in the photodetector 7002 where the light beam having a wavelength of 650 nm reach are arranged in the same straight line. Is also possible.
[0096]
Alternatively, both the light beam wavelength of 650 nm band reflected from the optical disc and the light beam of 780 nm band can be condensed on the same light receiving region in the photodetector 7002. That is, the light receiving region can be shared for both the light beam wavelength in the 650 nm band and the light beam in the 780 nm band.
[0097]
First, in the present embodiment, the three-spot diffraction grating 7009 has a spot interval δ of 0 in the radial direction of the disc as shown in FIGS. 24A and 24B on an optical disc 7008 such as a DVD-ROM or DVD-RAM as described above. The incident light beam having a wavelength of 650 nm is diffracted and separated so as to be about .67 μm to generate the 0th order light beam 7102a, the + 1st order light, and the −1st order light beams 7102b, 7102c, and the CD-ROM and CD-R On such an optical disc 7008, as shown in FIG. 24C, the incident light beam having a wavelength of 780 nm is diffracted and separated so that the spot interval δ ′ in the disc radial direction is about 0.8 μm, and the 0th-order light beam 7103a and + 1st-order light And −1st order light beams 7103b and 7103c for generating a grating groove pattern diffraction grating. . The hologram pattern of the hologram element 7010 includes a zero-order light of a 650 nm wavelength light beam diffracted and separated by the hologram element 7010 and a + 1st order diffracted light or a −1st order diffracted light of a 780 nm wavelength light beam diffracted and separated by the hologram element 7010. As long as it has a function of guiding the light to a predetermined light receiving region in the light detector 7002, it may be an equidistant linear lattice groove pattern. Needless to say, even if the grating groove pattern of the hologram element 7010 is a predetermined unevenly curved pattern, it does not matter. When a grating having an appropriate unevenly spaced curved grating groove pattern is used, a predetermined wavefront aberration can be added to the + 1st order or −1st order diffracted light beam diffracted by this grating and guided into the photodetector 7002. Therefore, an unnecessary aberration component included in the + 1st order or -1st order diffracted light beam and the focal position of the + 1st order or -1st order diffracted light beam can be corrected, and a good detection light spot can be irradiated to the photodetector. .
[0098]
Next, the light receiving surface pattern of the light receiving region in the photodetector 7002 in this embodiment will be described with reference to FIG. As shown in FIG. 25, the light-receiving surface pattern of the light-receiving area is arranged in a straight line with three light-receiving surfaces divided into four in a square shape and two divided into a total of 16 independent light-receiving surfaces. It has been configured. When reproducing a DVD-based disc, the reflected light from the spots 7102a, 7102b and 7102c on the optical disc in FIGS. 24A and 24B is incident on the respective light receiving areas as shown in FIG. 25A to form light spots 7112a, 7112b and 7112c. At the time of reproduction of the CD-type disc, the disc reflected light of the spots 7103a, 7103b, and 7103c on the optical disc in FIG. 24C is incident on the respective light receiving areas as shown in FIG. 25B to form light spots 7113a, 7113b, and 7113c. Here, of the diffracted and separated light generated in the three-spot diffraction grating 7009, the light receiving area 7020a is used as the light receiving area for detecting the 0th-order light beam both when reproducing the DVD disk and when reproducing the CD disk as shown in FIG. ing. However, among the diffracted and separated lights generated by the three-spot diffraction grating 7009, the light receiving areas for detecting the + first-order light beam or the -1st-order light beam are different light receiving areas when reproducing a DVD disc and when reproducing a CD disc. Is used. This is because the diffraction angle of the light beam by the diffraction grating is substantially proportional to the wavelength as described above, and therefore, the zero-order light beam and the ± first-order light beam in the 780 nm wavelength band separated by the three-spot diffraction grating 7009 are separated. This is because the spot interval on the surface of the photodetector 7002 is increased by about 1.2 (= 780 ÷ 650) times compared to the spot interval of the light beam having a wavelength of 650 nm. Therefore, although the spot interval on the surface of the photodetector 7002 is different between the DVD disk reproduction and the CD disk reproduction, different light receiving areas are used so that the differential push-pull method can be applied to both the DVD system and the CD system. The light beam is detected.
[0099]
Since the detection method of the focus error signal and the tracking error signal by such a photodetector has already been described, detailed description thereof is omitted, but the focus error signal is detected by the astigmatism method by an arithmetic circuit as shown in FIG. The tracking error signal is detected by a phase difference detection method (DPD method). Here, reference numerals 7040, 7041, 7042, 7043, 7044, 7045, 7046, 7047 in the figure denote current-voltage conversion amplifiers, and reference numerals 7048, 7049, 7050, 7051, 7052, 7053, 7054, 7055, 7056, 7057, 7058, 7059, 7063, and 7064 are adders, 7070, 7071, 7072, and 7073 are subtractors, 7090 and 7091 are changeover switches, 7080 is a phase difference detection circuit, and 7060 is an amplification factor K3. Reference numerals 7061 and 7062 respectively denote amplifiers having an amplification factor K4. Hereinafter, the same reference numerals in the drawings are common to those used in the above description.
[0100]
When reproducing a DVD-RAM disc, the operation circuit is switched to that shown in FIG. 27, and the focus error signal is disclosed in the differential astigmatism method (details are omitted as disclosed in Japanese Patent Application No. 11-171844). The tracking error signal is detected by a differential push-pull method (DPP method).
[0101]
Further, when reproducing CD-type discs such as CD-ROM and CD-R, the arithmetic circuit as shown in FIG. 17 is switched, the focus error signal is astigmatism, and the tracking error signal is differential push-pull (DPP). ) To detect.
[0102]
In this embodiment, the light receiving surface pattern of the light receiving region in the photodetector 7002 is divided into 16 parts as shown in FIG. 25, but naturally the light receiving surface pattern of the light receiving region in the present invention is such as this. It is not limited to the structure, and at least when receiving a DVD disc and when playing a CD disc, each light beam is incident on the same photodetector to detect various servo signals and information signals. As long as it is a surface pattern, any other light receiving area light receiving surface pattern may be applied to the present invention. Hereinafter, an embodiment in which the light receiving surface pattern of the light receiving region of the photodetector 7002 is changed will be described.
[0103]
The eighth embodiment of the present invention has the same configuration as the optical pickup device in the seventh embodiment, but the light receiving surface pattern of the light receiving area is divided into four in a square shape as shown in FIG. This is a configuration in which a total of 14 independent light receiving surfaces, which are divided into 5 light receiving surfaces and 2 divided into 5, are replaced with a linear arrangement. With such a light receiving surface pattern of the light receiving area, when detecting the + first order light beam or the −first order light beam among the diffraction separated light generated by the three-spot diffraction grating 7009, the DVD system disc reproduction and the CD system are detected. The same light receiving area can be used during disk reproduction, and the number of light receiving surfaces can be reduced.
[0104]
Regarding the detection method of the focus error signal and the tracking error signal by such a photodetector, the same detection method as that described in the seventh embodiment can be used, so that detailed explanation is omitted, but the DVD-ROM is omitted. When reproducing a disc, a focus error signal is detected by an astigmatism method using an arithmetic circuit as shown in FIG. 30, and a tracking error signal is detected by a phase difference detection method (DPD method).
[0105]
When reproducing a DVD-RAM disc, the operation circuit is switched to the arithmetic circuit as shown in FIG. 31, the focus error signal is detected by the differential astigmatism method, and the tracking error signal is changed to the differential push-pull method (DPP method). To detect.
[0106]
Further, when reproducing a CD-type disc such as a CD-ROM or CD-R, the operation circuit is switched to the arithmetic circuit as shown in FIG. 32, the focus error signal is the astigmatism method, and the tracking error signal is the differential push-pull method (DPP method). ) To detect.
[0107]
Next, another embodiment in which the light receiving surface pattern of the light receiving area in the seventh embodiment is changed will be described below.
[0108]
The ninth embodiment of the present invention has the same configuration as that of the optical pickup device in the seventh embodiment. However, the light receiving surface pattern of the light receiving area is divided into four squares as shown in FIG. A total of eight independent light receiving surfaces divided into two divided into two are replaced with a configuration in which the surfaces are arranged in a straight line. With such a configuration, the number of light receiving surfaces can be further reduced. The detection method of the focus error signal and the tracking error signal by such a photodetector can be the same detection method as that described in the seventh embodiment, so detailed description is omitted, but a DVD-ROM disc is used. When reproducing, a focus error signal is detected by an astigmatism method using an arithmetic circuit as shown in FIG. 34, and a tracking error signal is detected by a phase difference detection method (DPD method). Here, reference numeral 7065 in the figure denotes an amplifier having an amplification factor K3, reference numeral 7074 denotes a subtractor, and reference numeral 7092 denotes a changeover switch.
[0109]
When reproducing a CD-type disc such as a CD-ROM or CD-R, the operation circuit is switched to the arithmetic circuit as shown in FIG. 35, the focus error signal is the astigmatism method, and the tracking error signal is the differential push-pull method (DPP method). To detect.
[0110]
Further, another embodiment in which the light receiving surface pattern of the light receiving area is simplified will be described below.
[0111]
The tenth embodiment of the present invention has the same configuration as that of the optical pickup device in the seventh embodiment, but one light receiving surface in which the light receiving surface pattern of the light receiving area is divided into four in a square shape as shown in FIG. A total of six independent light receiving surfaces in which light receiving surfaces are respectively arranged on the surface and both ends thereof are replaced with a linear arrangement.
[0112]
Here, 7122a, 7122b, and 7122c in the figure indicate that three light beams diffracted and separated by the three-spot diffraction grating 7009 reflect the optical disk 7008 during the reproduction of the DVD disk, and are reflected on the light receiving region in the photodetector 7002. 7123a, 7123b, and 7123c reflect the three light beams diffracted and separated by the three-spot diffraction grating 7009 when the CD disk is reproduced, and the light received in the photodetector 7002 is reflected. It shows a state of focusing on the area. Further, the three-spot diffraction grating 7009 has a spot spacing in the radial direction of the disc on the optical disc 7008 such as a CD-ROM or CD-R of about 0.4 μm, which is a quarter of the track pitch of the information track. It has a function of diffracting and separating a light beam having a wavelength of 780 nm emitted from the second semiconductor laser light source. As a detection method of the focus error signal and the tracking error signal by such an optical pickup device, when reproducing a DVD-ROM disc, an arithmetic circuit as shown in FIG. 37 is used to convert the focus error signal into an astigmatism method. The tracking error signal is detected by a phase difference detection method (DPD method). Reference numeral 7093 in the drawing represents a changeover switch. When reproducing a CD-type disc such as a CD-ROM or CD-R, the arithmetic circuit as shown in FIG. 38 is switched to detect the focus error signal by the astigmatism method and the tracking error signal by the three-spot method. .
[0113]
Here, in the ninth and tenth embodiments, the light beam having a wavelength of 650 nm is not necessarily diffracted and separated by the three-spot diffraction grating 7009. Therefore, by controlling the groove depth of the three-spot diffraction grating 7009, the diffracted light efficiency of the light beam having a wavelength of 650 nm may be set to approximately 0%.
[0114]
Further, by moving the hologram element 7010 in the seventh to tenth embodiments in the optical axis direction and rotating around the optical axis, the condensing position of the zero-order light passing through the hologram element 7010 in the photodetector 7002 is determined. Without changing, the condensing position in the photodetector 7002 of the + 1st order diffracted light (or −1st order diffracted light) diffracted and separated by the hologram element 7010 can be displaced. Therefore, the hologram element 7010 can adjust the relative position between the light receiving region in the photodetector 7002 and the light spot incident on the light receiving region so that the focus error signal and the tracking error signal are correctly output.
[0115]
In addition, as described above, the grating engraved in the hologram element 7010 is sawtoothed to selectively improve the diffraction efficiency of the diffracted light necessary for signal detection, thereby increasing the light utilization efficiency for the light flux used for signal detection. Further, the possibility that unnecessary light not used for signal detection becomes a stray light component and jumps into the light receiving region to reduce the S / N ratio of signal detection can be reduced as much as possible. Note that when the grating engraved on the hologram element 7010 described in the above embodiments is sawtoothed, the grating sidewalls may be inclined as shown in FIG. 39, or the grating may be stepped. I do not care. Further, by making the diffraction efficiency of the hologram element 7010 dependent on the wavelength or polarization, the light utilization efficiency of the signal light can be further improved.
[0116]
Here, a diffraction grating in which the diffraction efficiency has wavelength dependency will be described.
[0117]
In general, in the case of a diffraction grating having a rectangular grating groove cross section, if the grating groove width of the diffraction grating 30 is defined as w, the grating period is defined as p, and the grating groove depth is defined as h as shown in FIG. The light intensity I0 of 7101a and the light intensity I1 of the + 1st order light 7101b (-1st order light 7101c) greatly depend on w, p, and h. When the light intensity of the incident light is 1, the following formula (2) I can express.
[0118]
[Expression 2]

[0119]
However, n is the refractive index of the transparent member 7030 engraved with the diffraction grating, and λ is the wavelength of the light beam incident on the diffraction grating. Therefore, from the equation (2), in order to generate more zero-order diffracted light with respect to incident light in the 650 nm band, the following equation (3)
[0120]
[Equation 3]

[0121]
In order to generate more first-order diffracted light with respect to incident light in the 780 nm band, the following equation (4)
[0122]
[Expression 4]

[0123]
It is sufficient to make the grating groove depth satisfying the above.
[0124]
For example, when the grating groove depth is set so that (n−1) h = 1950 [nm], (n−1) h = 3 · 650 = 2.5 · 780 is obtained, and Expressions (3) and (4) ) At the same time, the light utilization efficiency can be improved.
[0125]
By the way, the hologram element having such wavelength dependency or wavelength selectivity is not limited to an element realized by controlling the grating groove depth as described above. An element based on any principle as long as the diffraction efficiency of ± 1st order diffracted light is sufficiently high for light of 780 nm band and the efficiency of 0th order light is sufficiently high for light of 650 nm band But it does n’t matter.
[0126]
Here, as an eleventh embodiment of the present invention, an example in which the light use efficiency of the signal detection light is improved by using a polarizing element in which the diffraction efficiency has polarization dependency will be described with reference to the drawings. FIG. 41 is a schematic configuration diagram of an optical pickup device as an eleventh embodiment of the present invention. The same parts as those in the seventh embodiment of the present invention shown in FIG. Unlike the seventh embodiment described above, this embodiment uses a polarization-dependent hologram 7012 instead of the hologram element 7010 and is combined with the polarization conversion element 7013 to improve the light use efficiency by using polarized light. Yes.
[0127]
Here, as the polarization conversion element 7013, a wave plate that functions as a 5λ / 4 plate for a 650 nm band light beam is used. For example, the polarization-dependent hologram 7012 functions to diffract only a light beam having S-polarized light with a predetermined diffraction efficiency, and to transmit a light beam having P-polarized light having a polarization direction perpendicular thereto without being diffracted.
[0128]
For example, when reproducing a high-density optical disk such as a DVD-ROM, an S-polarized light beam having a wavelength of 650 nm is emitted from a two-wavelength multi-laser light source 7001. This light beam passes through a three-spot diffraction grating 7009 and enters a dichroic half mirror 7003 arranged at an angle of 45 ° with respect to the optical axis. The light beam reflected by the dichroic half mirror 7003 enters the polarization conversion element 7013 through the rising mirror 7004.
[0129]
Here, since the polarization conversion element 7013 functions as a 5λ / 4 plate for a light beam in the 650 nm band, the light beam incident as S-polarized light becomes a circularly polarized light beam after passing through the polarization conversion element 7013, and is collimated by the collimator lens 7005. It is converted into a parallel light beam and reaches the objective lens 7006. The objective lens 7006 is held by an actuator 7007, and a light spot can be formed by condensing a light beam on an optical disk 7008 such as a DVD-ROM. The light beam reflected from the optical disk 7008 travels in the reverse direction and enters the polarization conversion element 7013 through the objective lens 7006 and the collimator lens 7005. The light beam incident as circularly polarized light passes through the polarization conversion element 7013 and then becomes P-polarized light. It becomes a light beam, passes through the rising mirror 7004, passes through the dichroic half mirror 7003, and enters the polarization-dependent hologram 7012. The polarization-dependent hologram 7012 does not have a diffraction function for a P-polarized light beam and is merely a transparent member. Therefore, the P-polarized light beam incident on the polarization-dependent hologram 7012 is not diffracted and passes through as it is. Then, the light reaches a predetermined light receiving region in the photodetector 7002 through the detection lens 7011.
[0130]
Next, when reproducing a conventional optical disk such as a CD-ROM, an S-polarized light beam having a wavelength of 780 nm is emitted from a two-wavelength multi-laser light source 7001. The light beam emitted from the two-wavelength multi-laser 1 passes through a three-spot diffraction grating 7009 and enters a dichroic half mirror 7003 arranged at an angle of 45 ° with respect to the optical axis. The light beam reflected by the dichroic half mirror 7003 enters the polarization conversion element 7013 through the rising mirror 7004. Here, since the polarization conversion element 7013 is an element that functions as a 5λ / 4 plate with respect to a light beam in the 650 nm band as described above, it substantially functions as a λ plate with respect to light in the wavelength of 780 nm band. Therefore, the light in the wavelength band of 780 nm is converted into a parallel light beam by the collimator lens 7005 while being S-polarized after passing through the polarization conversion element 7013, and reaches the objective lens 7006. The objective lens 7006 is held by an actuator 7007. As described above, a light spot is formed by condensing a light beam on an optical disk 7008 such as a CD-ROM and a function of condensing a light beam on a DVD disk. At the same time. The light beam reflected from the optical disk 7008 travels in the reverse direction and enters the polarization conversion element 7013 through the objective lens 7006 and the collimator lens 7005. After passing through the polarization conversion element 7013, it remains as an S-polarized light beam. The light passes through the mirror 7004, passes through the dichroic half mirror 7003, and enters the polarization-dependent hologram 7012. Since the polarization-dependent hologram 7012 has a function of diffracting an S-polarized light beam, the light beam is diffracted at a predetermined diffraction efficiency in the polarization-dependent hologram 7012, passes through a detection lens 7011, and is a photodetector 7002. Of these, a predetermined light receiving region at a position different from the predetermined light receiving region to which the light beam having a wavelength of 650 nm reaches is reached. With such a configuration, it is possible to efficiently guide only the light beam necessary for signal detection to the photodetector in both cases of DVD reproduction and CD reproduction, greatly improving light utilization efficiency and unnecessary. The stray light component can be removed.
[0131]
Note that the positional relationship between the light spot and the light receiving surface in the light receiving region of the photodetector 7002 and the method for detecting the information signal, focus error signal, and tracking error signal during optical disc reproduction are the same as in the seventh embodiment.
[0132]
Further, by moving the polarization-dependent hologram 7012 in the direction of the optical axis and rotating around the optical axis, light beams 7113a, 7113b in the 650 nm band that are detected by the photodetector 7002 as in the seventh embodiment, Without changing the focal position of the 7113c and the position on the light receiving surface, the focal positions of the 780 nm band light beams 7112a, 7112b and 7112c detected by the photodetector 7002 can be changed independently. Therefore, the detector adjustment and the focus error signal offset adjustment for the 650 nm band light beam and the 780 nm band light beam can be performed independently.
[0133]
Furthermore, with respect to the dichroic half mirror 7003, S-polarized light is almost totally reflected and P-polarized light is almost 100% transmitted for 650 nm light, and S-polarized light is reflected and transmitted about 50% for 780 nm light. If it has, the utilization efficiency of light can be improved.
[0134]
By the way, although the arrangement position of the hologram element 7010 is between the half mirror 7003 and the detection lens 7011 in the embodiments described so far, it is not limited to this, and is in the optical path between the detection lens 7011 and the photodetector 7002. It may be. Further, in the embodiment described so far, the hologram element 7010 is configured to transmit the 0th-order light of the light beam having the wavelength of 650 nm and the light beam of the first-order diffracted light of the light beam having the wavelength of 780 nm in the photodetector 7002. However, the present invention is not limited to this. For example, the + 1st order diffracted light or the −1st order diffracted light of the light beam having the wavelength of 650 nm and the 0 light beam of the wavelength of 780 nm are completely reversed. Even a diffraction grating having a function of guiding the next light to a predetermined position in the photodetector 7002 may be used.
[0135]
FIG. 42 shows a schematic block diagram of an optical disc apparatus equipped with the optical pickup of the present invention. The optical pickup 508 includes, for example, the package 20 shown in FIG. 9 and the pickup device shown in FIGS. 24 and 41. Various detection signals detected here are servo signal generation circuits in the signal processing circuit. 504 and the information signal reproduction circuit 505. The servo signal generation circuit 504 generates a focus error signal and a tracking error signal suitable for each optical disk from these detection signals, and drives the objective lens actuator in the optical pickup 508 via the actuator drive circuit 503 based on this, Controls the position of the objective lens. The information signal reproduction circuit 505 reproduces the information signal recorded on the optical disc 1 from the detection signal. Part of the signals obtained by the servo signal generation circuit 504 and the information signal reproduction circuit 505 are sent to the control circuit 500. The control circuit 500 uses these various signals to determine the type of the optical disk 1 that is to be reproduced at that time, and drives either the DVD laser lighting circuit 507 or the CD laser lighting circuit 506 according to the determination result, Further, as described above, the servo signal generation circuit 504 has a function of switching the circuit configuration so as to select the servo signal detection method corresponding to the type of each optical disk. An access control circuit 502 and a spindle motor drive circuit 501 are connected to the control circuit 500, and the access direction position control of the optical pickup 508 and the rotation control of the spindle motor 509 of the optical disc 1 are performed.
[0136]
Less thanAs described above, according to the embodiment of the present invention, an optical pickup using a semiconductor laser in which laser light sources having two different wavelengths are arranged in the same housing, at least one diffraction grating, and one photodetector. With this optical system configuration, it is possible to obtain focus error signals and tracking error signals necessary for reproduction or recording of various optical discs having different substrate thicknesses and different groove structures such as DVD-ROM, DVD-RAM and CD-ROM. is there. Furthermore, when the ratio of the two laser wavelengths and the ratio of the track pitch of the optical disk are substantially equal, an optical system can be realized with one diffraction grating, and at the same time, with respect to optical components such as the diffraction grating and the half mirror, wavelength characteristics and Since polarization characteristics are not required, an optical system that is simpler and less expensive than the conventional one can be realized.
[0137]
  In addition, a two-wavelength multilaser is used as the light source of the optical pickup device, and the return light is diffracted with respect to the light beam of one or both wavelengths in the light detection system, so that the light receiving region of the light detector is made to have two wavelengths. Allows sharing. As a result, the number of optical components can be reduced by reproducing information from a plurality of types of optical discs using a single light detection system, and further downsizing, simplification, and cost reduction of the optical pickup device can be realized.Further, the number of optical components can be further reduced by using a two-wavelength multilaser and by sharing a diffraction grating and a half mirror, or by sharing a light receiving region of a photodetector.
【The invention's effect】
  The present inventionAccording to the present invention, it is possible to provide a photodetector, an optical pickup, and an optical information reproducing device that can realize miniaturization, simplification, and cost reduction.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a conventional optical pickup.
FIG. 2 is a configuration diagram of an optical pickup according to the first embodiment of the present invention.
FIG. 3 shows a spot arrangement on an optical disc in the first embodiment of the present invention, and is a diagram in the case of a DVD-ROM disc.
FIG. 4 shows a spot arrangement on the optical disc in the first embodiment of the present invention, and is a diagram in the case of a DVD-RAM disc.
FIG. 5 shows a spot arrangement on the optical disc in the first embodiment of the present invention, and is a diagram in the case of a CD-R disc.
FIG. 6 is a diagram illustrating the intensity distribution of a light spot on an optical disc.
FIG. 7 is a diagram illustrating a disturbance to a focus error signal.
FIG. 8 is a diagram showing a tracking error signal by a push-pull method.
FIG. 9 is a plan view and a block diagram of a photodetector and a signal processing circuit according to the first embodiment of the present invention.
FIG. 10 is a diagram showing an irradiation state of a detection light spot on a DVD.
FIG. 11 is a diagram showing an irradiation state of a detection light spot on a CD.
FIG. 12 is a diagram illustrating an irradiation state of a detection light spot of a CD in a state where only a DVD is adjusted.
FIG. 13 is a plan view and a block diagram of a photodetector and a signal processing circuit according to a second embodiment of the present invention.
FIG. 14 is a plan view and a block diagram of a photodetector and a signal processing circuit according to a third embodiment of the present invention.
FIG. 15 shows a spot arrangement on an optical disc in a fourth embodiment of the present invention, and is a diagram in the case of a CD-ROM disc.
FIG. 16 is a plan view and a block diagram of a photodetector and a signal processing circuit according to a fourth embodiment of the present invention.
FIG. 17 is a configuration diagram of an optical pickup according to a fifth embodiment of the present invention.
FIG. 18 is a plan view and a block diagram of a photodetector and a signal processing circuit according to a fifth embodiment of the present invention.
FIG. 19 is a configuration diagram of an optical pickup according to a sixth embodiment of the present invention.
FIG. 20 is a diagram illustrating an irradiation state of a detection light spot on a CD according to a sixth embodiment of the present invention.
FIG. 21 is a diagram illustrating parallel movement of a detection light spot on a CD according to a sixth embodiment of the present invention.
FIG. 22 is a diagram showing rotational movement of a detection light spot on a CD according to a sixth embodiment of the present invention.
FIG. 23 is a schematic configuration diagram of an optical pickup device showing a seventh embodiment of the present invention.
FIG. 24 shows the light spot position on the optical disc.
(a) Light spot position on DVD-ROM disc
(b) Light spot position on DVD-RAM disc
(c) Light spot position on CD-ROM, CD-R disc
FIG. 25 is a light-receiving surface pattern diagram of the light-receiving region of the photodetector in the seventh embodiment.
(a) During DVD playback
(b) During CD playback
FIG. 26 is a schematic diagram of a signal processing circuit used during DVD-ROM playback in the seventh embodiment.
FIG. 27 is a schematic diagram of a signal processing circuit used for DVD-RAM playback in the seventh embodiment.
FIG. 28 is a schematic diagram of a signal processing circuit used for CD-ROM and CD-R playback in the seventh embodiment.
FIG. 29 is a light-receiving surface pattern diagram of the light-receiving region of the photodetector in the eighth embodiment.
(a) During DVD playback
(b) During CD playback
FIG. 30 is a schematic diagram of a signal processing circuit used for DVD-ROM playback in the eighth embodiment.
FIG. 31 is a schematic diagram of a signal processing circuit used for DVD-RAM playback in the eighth embodiment.
FIG. 32 is a schematic diagram of a signal processing circuit used for CD-ROM and CD-R playback in the eighth embodiment.
FIG. 33 is a light-receiving surface pattern diagram of the light-receiving region of the photodetector in the ninth embodiment.
(a) During DVD playback
(b) During CD playback
FIG. 34 is a schematic diagram of a signal processing circuit used for DVD-ROM playback in the ninth embodiment.
FIG. 35 is a schematic diagram of a signal processing circuit used for CD-ROM and CD-R playback in the ninth embodiment.
FIG. 36 is a light-receiving surface pattern diagram of the light-receiving region of the photodetector in the tenth embodiment.
(a) During DVD playback
(b) During CD playback
FIG. 37 is a schematic diagram of a signal processing circuit used for DVD-ROM playback in the tenth embodiment.
FIG. 38 is a schematic diagram of a signal processing circuit used for CD-ROM and CD-R playback in the tenth embodiment.
FIG. 39 is a diagram showing sawtoothing of a diffraction grating
(a) Schematic with the grid side tilted
(b) Schematic diagram with a grid of steps
FIG. 40 is a schematic diagram showing light diffraction by a diffraction grating having a rectangular grating groove cross section.
FIG. 41 is a schematic configuration diagram of an optical pickup device showing an eleventh embodiment of the present invention.
FIG. 42 is a schematic block diagram of an optical disc apparatus equipped with an optical pickup according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1,10 ... Optical disk, 2, 11, 15, 17 ... Semiconductor laser, 3, 16, 30 ... Diffraction grating, 4 ... Half mirror, 5 ... Collimating lens, 6 ... Objective lens, 7 ... Actuator, 8 ... Drive coil, 9, 14 ... Photo detector, 12 ... Dichro prism, 18, 19 ... Polarized diffraction grating, 20, 21, 22, 23, 24 ... Package, 30 ... Dichro diffraction Lattice, 200 ... Mark, 201 ... Pit, 100, 101, 102, 300, 301, 302, 303, 304 ... Light spot on disk, 110, 111, 112, 310, 311, 312, 313, 314, 315, 316, 317, 318, 319, 320 ... detection light spot, 200 ... recording pit, 201,400 ... recording mark, 202, 401... Guide groove, 203, 402... Between guide grooves, 210, 211, 212, 213, 214, 410, 411, 412 ... light receiving area, 500... Control circuit, 501. 502 ...... Access control circuit 503 ...... Actuator drive circuit 504 ...... Servo signal generation circuit 505 ...... Information signal reproduction circuit 506 ...... Laser lighting circuit for CD 507 ...... Laser lighting circuit for DVD 508 …… Optical Pickup, 509 …… Spindle Motor, 7001 …… Laser Light Source, 7002 …… Photodetector, 7003 …… Half Mirror, 7004 …… Rising Mirror, 7005 …… Collimator Lens, 7006 …… Objective Lens, 7007 …… Actuator, 7008 …… Optical disc 7009 ...... third diffraction grating for spot, 7010 ...... hologram element, 7011 ...... detection lens, 7012 ...... polarization dependent hologram 7013 ...... polarization conversion element.

Claims (14)

A light receiving region for receiving one light beam out of the light beams emitted from the first laser light source and reflected by the first optical information recording medium. A first light receiving region divided into two light receiving surfaces;
A light receiving region for receiving one light beam out of the light beams emitted from the second laser light source and reflected by the second optical information recording medium. A second light receiving region divided into two light receiving surfaces;
A light receiving region for receiving two light beams other than the one light beam among the light beams reflected by the first optical information recording medium, each divided into four light receiving surfaces. Third and fourth light receiving regions;
A light receiving area for receiving two light beams other than the one light beam among the light beams reflected by the second optical information recording medium, each divided into four light receiving surfaces. A fifth light receiving region and a sixth light receiving region,
Each of the first and second light receiving regions outputs a signal that can generate a focus error signal by an astigmatism method and a tracking error signal by a push-pull method and a differential phase detection method,
Each of the third and fourth light receiving regions outputs a signal capable of generating a tracking error signal by a push-pull method,
Each of the fifth and sixth light receiving regions outputs a signal that can generate a focus error signal by an astigmatism method and a signal that can generate a tracking error signal by a push-pull method. The photodetector of claim 1.
The distance between the center of the first light receiving area and the center of the third or fourth light receiving area is different from the distance between the center of the second light receiving area and the center of the fifth or sixth light receiving area. A photodetector. The photodetector of claim 1.
The light receiving region divided into four parts is divided by a first dividing line and a second dividing line that intersect each other. The photodetector of claim 1.
The first, second, third, fourth, fifth, and sixth light receiving regions are divided into four light receiving surfaces having a square shape. The photodetector of claim 1.
Each of the third and fourth light receiving regions outputs a signal that can generate a focus signal by an astigmatism method and a signal that can generate a tracking error signal by a push-pull method. The photodetector according to claim 3 or 4,
Each of the first and second light receiving regions is an astigmatism method based on a difference in received light amount between a set of two light receiving surfaces at diagonal positions and a set of two light receiving surfaces at other diagonal positions. A signal that can generate a focus error signal due to, and a signal that can generate a tracking error signal by a push-pull method from the difference in the amount of light received between the pair of two adjacent light receiving surfaces and the other two adjacent light receiving surfaces And a signal that can generate a tracking error signal by a differential phase detection method using four light receiving surfaces. The photodetector according to claim 3 or 4,
Each of the third and fourth light receiving regions is an astigmatism method based on a difference in received light amount between a set of two light receiving surfaces at diagonal positions and a set of two light receiving surfaces at other diagonal positions. A signal that can generate a focus error signal due to, and a signal that can generate a tracking error signal by a push-pull method from the difference in the amount of light received between the pair of two adjacent light receiving surfaces and the other two adjacent light receiving surfaces A photodetector. The photodetector according to claim 3 or 4,
Each of the fifth and sixth light receiving regions is an astigmatism method based on a difference in received light amount between a set of two light receiving surfaces at diagonal positions and a set of two light receiving surfaces at other diagonal positions. A signal that can generate a focus error signal by, and a signal that can generate a tracking error signal by the push-pull method from the difference in the amount of light received between the pair of two adjacent light receiving surfaces and the other two adjacent light receiving surfaces A photodetector. First and second laser light sources;
A light branching element for branching the light beams emitted from the first and second laser light sources into three light beams,
A condensing optical system that irradiates the optical information recording medium with the light beam;
An optical pickup comprising: the photodetector according to claim 1. A first and a second laser light source, wherein the ratio of the wavelength of the emitted light beam is substantially equal to the ratio of the track pitches of the first and second optical information recording media;
A light branching element that branches any of the light beams emitted from the first and second laser light sources into three light beams;
A condensing optical system that irradiates the optical information recording medium with the light beam;
An optical pickup comprising: the photodetector according to claim 1. The optical pickup according to claim 9 or 10,
The wavelength of the light beam emitted from the first laser light source is smaller than the wavelength of the light beam emitted from the second laser light source;
An optical pickup characterized in that an interval between the first light receiving region and the third or fourth light receiving region is smaller than an interval between the second light receiving region and the fifth or sixth light receiving region. . A first laser light source;
A second laser light source that emits a light beam in a direction substantially parallel to the light beam emitted from the first laser light source;
A half mirror that reflects or transmits the light beam emitted from the first laser light source and reflects or transmits the light beam emitted from the first laser light source;
An objective lens that focuses the light beam reflected by the half mirror onto an optical information recording medium;
An optical pickup comprising: the photodetector according to claim 1. The optical pickup according to any one of claims 9 to 12, wherein a signal is detected from the optical information recording medium;
A servo signal generation circuit that generates a servo signal from the signal detected by the optical pickup;
A control circuit for determining a type of the optical information recording medium based on a signal detected by the optical pickup and selecting a servo signal detection method of the servo signal generation circuit;
An optical information reproducing apparatus comprising: an actuator drive circuit that controls a position of an objective lens actuator of the optical pickup based on the selected servo signal. An optical pickup according to any one of claims 9 to 12, which detects a signal from an optical information recording medium;
A servo signal generation circuit that generates a focus error signal or a tracking error signal from a signal detected by the optical pickup; and
An actuator drive circuit for controlling the position of the objective lens actuator of the optical pickup from the focus error signal or the tracking error signal;
An access control circuit for performing access control of the optical pickup;
A spindle motor driving circuit for rotating the optical information recording medium, and an optical information reproducing apparatus.

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