JP3669531B2

JP3669531B2 - Optical pickup and magneto-optical signal recording / reproducing apparatus

Info

Publication number: JP3669531B2
Application number: JP18135196A
Authority: JP
Inventors: 紀彰西; 公博斉藤; 秀一松本; 真人服部; 忠司森本; 充紀植田; 毅久保; 憲雅松尾; 和由堀江; 由利子佐藤; 邦宣篠
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 1995-06-23
Filing date: 1996-06-22
Publication date: 2005-07-06
Anticipated expiration: 2016-06-22
Also published as: JPH0969245A

Description

【０００１】
【目次】
以下の順序で本発明を説明する。
発明の属する技術分野
従来の技術
発明が解決しようとする課題
課題を解決するための手段
発明の実施の形態
（１）光ピツクアツプ
（１−１）複屈折
（１−２）偏光分離素子（Ｙ方向分離型）
（１−３）偏光分離素子（Ｘ方向分離型）
（２）光磁気信号記録再生装置
（３）他の実施例
発明の効果
【０００２】
【発明の属する技術分野】
本発明は光ピツクアツプに関し、特に光磁気デイスク装置に適用して好適なものである。
【０００３】
【従来の技術】
従来、光磁気デイスク装置に用いられる光ピツクアツプ１は、図１５に示すように、光源としてのレーザダイオード２から射出されたレーザ光をグレーテイング素子３、ビームスプリツタ４、コリメータレンズ５及び対物レンズ６を順次通つて光磁気デイスク１１上に集光し、その反射光を対物レンズ６、コリメータレンズ５、ビームスプリツタ４、ウオーラストンプリズム７及びマルチレンズ８を順次通つてフオトデイテクタ９上に結像するような構成のものが用いられている。
【０００４】
【発明が解決しようとする課題】
ところが、この構成の光ピツクアツプ１は複数の光学部品を個別に組み合わせるような構成になつているため、装置全体としての小型化が難しく、また信頼性の向上が難しいという問題があつた。
そこで光磁気デイスク再生装置の場合にも、コンパクトデイスク再生装置に用いられている図１６に示す光ピツクアツプ２０のように、小型かつ信頼性の高い光ピツクアツプの実現が望まれている。
【０００５】
光ピツクアツプ２０は光ピツクアツプモジユール２１を有し、光ピツクアツプモジユール２１の筺体２２内に、光源として設けられているレーザダイオードＬＤから射出されたレーザ光を断面台形形状のガラスプリズム２３の斜面の表面に付着された半透明膜２４によつて反射し、透明蓋板２５、反射ミラー２６及び２７、並びに対物レンズ２８を順次通して光デイスク２９に照射し、その反射光を対物レンズ２８、反射ミラー２７、２６を順次通して戻り光として半透明膜２４に導く。
【０００６】
ガラスプリズム２３は、レーザダイオードＬＤと共に半導体基板３０上に設けられ、半透明膜２４を通つた戻り光をガラスプリズム２３内に導入して、ガラスプリズム２３の底面と半導体基板３０との間に付着された半透明膜３１とガラスプリズム２３の上面に付着された全反射膜３２と、底面の半透明膜３１との間を折り返すように反射させる。
かくしてガラスプリズム２３内に導入された戻り光は、レーザダイオードＬＤに対して共役の位置にある全反射膜３２を挟む前後位置において、半導体基板３０に設けられた２つのフオトデイテクタＰＤ１及びＰＤ２に透過され、これによりフオトデイテクタＰＤ１及びＰＤ２から情報検出信号が出力される。
【０００７】
この構成の光ピツクアツプモジユール２１は全体として無偏光光学系を形成しているため光磁気信号の再生には用いることができないが、同じような構成で光磁気デイスク用の光ピツクアツプを構成することができれば、現在用いられている光ピツクアツプに比して一段と小型化を実現することができると考えられる。
【０００８】
本発明は以上の点を考慮してなされたもので、従来に比して小型かつ信頼性の高い光ピツクアツプ及び光磁気信号記録再生装置を実現しようとするものである。
【０００９】
【課題を解決するための手段】
かかる課題を解決するため本発明においては、 (a)１軸性結晶の光学軸が反射面の法線に垂直な面内に設定されており、又は (b)１軸性結晶の光学軸が、当該１軸性結晶への主光線の入射面の法線と、反射面の法線とに平行な面内に設定されており、又は (c)２軸性結晶の屈折率方位のうち中間の屈折率との差が大きい方の屈折率に対応する方位が、反射面の法線に垂直な面内に設定されており、又は (d)２軸性結晶の屈折率方位のうち中間の屈折率との差が大きい方の屈折率に対応する方位が、２軸性結晶への主光線の法線と、反射面の法線とに平行な面内に設定されている、ような条件を特定する。
かくして本願発明によれば、偏光分離素子を１軸性結晶又は２軸性結晶を材料する複屈折性材料単体によって形成すると共に、反射面に対する結晶の設定条件を、入射及び反射において変化が生じないように設定したことにより、高い精度で２つの分離スポツトを形成できる。
【００１０】
【発明の実施の形態】
以下図面について、本発明の一実施例を詳述する。
【００１１】
（１）光ピツクアツプ
（１−１）複屈折
本発明に係る光ピツクアツプは偏光分離素子として複屈折性材料単体（その性質を表す屈折率楕円体の軸方位を違えて貼り合わせるなどを一切行わない）を用いており、しかもその素子内において入射光を少なくとも１回以上反射させることを特徴とする。
【００１２】
因に通常は素子内に入射された光線を内部で反射させることなく透過させて偏光を分離している。この実施例の場合には、図１に示すように、電界密度ベクトルＤの違いによつて界面における屈折方向が異なること（すなわち波面法線ｋの方向が異なること）が重要項目となる。この結果入射光線は常光線（ｏ-ray）と、異常光線（ｅ-ray without walk-off ）とに分離される。図１は１軸性結晶ＹＶＯ₄（λ＝ 780〔nm〕において、ｎe ＝2.1893及びｎo ＝1.9734）に対して空気中から収束光が入射する場合を示し、ｏ-rayはスネルの法則に従う光線を表し、ｅ-rayはスネルの法則に従わない光線を表す。
【００１３】
これに対して、この実施例の場合には、素子内で入射された光線を１回以上反射させることを特徴とし、複屈折が重要項目となる。この複屈折とは結晶内部において波面法線ベクトルｋが同じ光線でも電界密度ベクトルＤの振動方向が異なると、光線（光のエネルギーの進む方向）ベクトルＳ（＝光波の電界ベクトルＥ×光波の磁界ベクトルＨ）が異なる現象をいう。以下、複屈折について説明する。
【００１４】
複屈折結晶内を進む光線に対する屈折率は、図２に示すように、屈折率楕円体をその光線の波面方向ベクトルｋに垂直でかつ原点を通る平面で切つたときにできる楕円の２つの軸の長さ、すなわちベクトルＤ１及びＤ２によつて表すことができ、その際における軸の方向が屈折率に対応する電界密度ベクトルＤの方位となる。因に図２におけるベクトルＤ1 及びＤ2 に対しておよそ４５〔°〕になるように偏光を入射すれば偏光分離後における２成分の差によつて光磁気信号を得ることができる。
【００１５】
簡単に言えば、この屈折率の違いが図１における波面法線ベクトルｋの違い（常光線（ｏ-ray）と異常光線（ｅ-ray without walk-off ）の違い）である。ただし厳密には、波面法線ベクトルｋの違いによつて屈折率は変化するので屈折率変化を考慮する必要がある。
このように屈折率の違いによつて生じる波面法線ベクトルｋは、波面法線ベクトルｋがスネルの法則に従うことを用いて屈折率と固有偏光ベクトルＤとの組によつて決定することができる。
【００１６】
因に、偏光を分離するだけなら波面法線ベクトルｋの違いだけで十分であるが、分離した光線がどのように進むかを正確に把握しようとすると、波面法線ベクトルｋと光線ベクトルＳとがずれること（すなわちWalk-off）を考慮しなくてはならない。
この光線ベクトルＳを次式で計算する。まず複屈折率材料内における電界ベクトルＥがＤ＝εＥを満し、Ｄ及びεが既知（屈折率楕円体が既知であるので、ｎ²＝ε／ε₀より、εも既知）であることを用いて電界ベクトルＥをε^-1Ｄとして求める。
【００１７】
さらに図３に示すように、磁界ベクトルＨ及び磁束密度ベクトルＢにはＨ//Ｂ//ｋ×Ｄが成り立ち、磁界ベクトルＨの方向も分かるので光線ベクトルＳの方向は先に求めた電界ベクトルＥからＳ＝Ｅ×Ｈで求める。
この式は反射の際にも成り立つ。複屈折結晶は光線波面ベクトルｋと固有ベクトルＤとによつて屈折率が異なることに基づいて上記の場合と同様に、界面で一般的には、２方向に分離する。
これらのことを考慮して、光線追跡した場合が、図１のｅ-ray(with walk-off）である。因に図１は結晶内において反射を伴わない場合の図である。
【００１８】
（１−２）偏光分離素子（Ｙ方向分離型）
続いて本発明に係る偏光分離素子の構成を説明する。図４（Ａ）に示すように、戻り光を２回反射させることにより３回通過させる偏光分離素子４１として、１軸性結晶をその光学軸を反射面の法線に垂直な面内に設定する。このときＰ偏光とＳ偏光は図４（Ｂ）においてスポツト群「ｏｏｏ」及び「ｅｅｅ」によつて示すようにｙ軸方向に分離される。
【００１９】
この偏光分離素子の場合、反射の前後においてＰ偏光及びＳ偏光に位相差及び反射率差が生じないように結晶の光学特性を抑圧している。このようにすると、固有偏光ベクトルＤとＳ偏光及びＰ偏光の関係は反射の前後において保存され、しかも固有屈折率についても反射の前後で一致する。従つて反射界面におけるスポツト群「ｏｏｏ」及び「ｅｅｅ」以外の光線の分離は発生せず、互いに離れた２つのフオトデイテクタ上にそれぞれ２つのスポツト群「ｏｏｏ」及び「ｅｅｅ」のみが完全に分離して集光される。
【００２０】
因に図４（Ｂ）において、スポツト群「ｏｏｏ」は、入射光が１回目−２回目−３回目に通過したとき、すべての通過時に常光線「ｏ」として移動が生じなかつたことを表す。
これに対して、スポツト群「ｅｅｅ」は、入射光が１回目−２回目−３回目に通過したとき、１回目にはｙ方向にベクトルｅ１だけ異常光線「ｅ」として移動し、その後２回目及び３回目の通過時には異常光線「ｅ」としてベクトルｅ２及びｅ３だけｘ方向に移動したことを表す。
【００２１】
因に反射の前後において、仮に位相差及び反射率差が生じてスポツトが分離したとしても、順次分離するスポツト光はその後の反射を経て多少は拡がるが最終的にはスポツト群を維持する。このように考えられる８つのスポツト群のうちはつきりと分れた２つのスポツト群から差動出力を求めれば光磁気信号を得ることができる。
【００２２】
前述の偏光分離素子は結晶が１軸性結晶の場合であるが、結晶が２軸性結晶である場合には、結晶の屈折率方位のうち中間の屈折率との差がより大きい方の屈折率に対応する方位を反射面の法線に垂直な面内に設定すれば良い。この場合も結晶内において入射光線を少なくとも１回以上反射させるようにする。因にこの例の場合には、３つの屈折率のうち屈折率の近い２つをｎｏ、残る１つをｎｅと考えれば、対応が付け易い。
【００２３】
さらにこの構成において、結晶の３つの屈折率方位のうち中間の屈折率に対応する方位を反射面の法線に平行な方位に設定するようにすれば、見かけ上ｎｏ、ｎｅの差が大きくなり（光線の分離角を大きくでき）、実使用に近い偏光分離素子を得ることができる。
これら２軸性結晶の場合にも、１軸性結晶の場合と同様の効果が得られ、これにより結晶材料の選択幅が広く、設計の自由度が大きい偏光分離素子を得ることができる。
【００２４】
（１−３）偏光分離素子（Ｘ方向分離型）
この偏光分離素子４１は、図５（Ａ）に示すように、１軸性結晶の光学軸を、結晶に入射する主光線の入射面の法線と反射面の法線に平行な面内に設定する。このときＰ偏光とＳ偏光は、図５（Ｂ）に示すように、２つのスポツト「ｏｅｏ」及び「ｅｏｅ」としてｘ軸方向に分離される。
【００２５】
図５（Ｂ）において、スポツト「ｅｏｅ」は、位置「ｏｏｏ」に入射した戻り光が１回目−２回目−３回目に偏光分離素子４１を通過したとき、１回目には異常光線「ｅ」としてｘ方向にベクトルｅ１だけ移動し、２回目には常光線「ｏ」として移動せず、３回目には異常光線「ｅ」としてベクトルｅ３だけ移動することを表している。
【００２６】
これに対してスポツト「ｏｅｏ」は、１回目には常光線「ｏ」として移動せず、２回目には異常光線「ｅ」としてベクトルｅ２だけ移動し、３回目には常光線として移動しないことを表している。
この結果、２つのスポツト「ｅｏｅ」及び「ｏｅｏ」はｘ方向にはつきり分離した位置に生ずることになる。
【００２７】
このように同じ１軸性結晶を用いても光軸の配置を換えるだけで偏光の分離方向を換えることができることにより、光学系（サーボエラーの検出法、ＰＤ分割法など）に設計の幅を持たせることができる。
なお偏光分離素子に２軸性結晶を用いる場合には、結晶の屈折率方位のうち中間の屈折率との差がより大きい方の屈折率に対応する方位を、結晶に入射される主光線の入射面の法線と反射面の法線とに平行な面内に設定すれば良い。このようにしても上述と同様の効果を得ることができる。
【００２８】
さらにこの構成において、結晶の３つの屈折率方位のうち中間の屈折率に対応する方位が結晶に入射する主光線の入射面及び反射面の法線に共に平行になるように結晶の屈折率の方位を設定するようにすれば、見かけ上ｎｏ、ｎｅの差が大きくなり（光線の分離角を大きくでき）、実使用に近い偏光分離素子を得ることができる。
これら２軸性結晶の場合にも、１軸性結晶の場合と同様の効果が得られ、これにより結晶材料の選択幅が広く、設計の自由度が大きい偏光分離素子を得ることができる。
【００２９】
なおこのように上述の偏光分離素子において複屈折性材料単体を用いたことにより製造時における光学軸の貼り合わせ精度を気にせずに済む分、高い精度の偏光分離素子を実現することができる。
また複屈折性材料単体で偏光分離素子を形成したことにより、経時変化の影響も受けない偏光分離素子を実現できる。
【００３０】
（２）光磁気信号記録再生装置
図６に前項の偏光分離素子を用いた光ピツクアツプを示す。また図７に光ピツクアツプを用いた光磁気信号記録再生装置の光学系を示し、図８に光磁気信号記録再生装置５１の構成を示す。
図６に示すように、光ピツクアツプ４１はフオトデイテクタＰＤ１、ＰＤ２及びＰＤ３を集積した半導体基板４２上にレーザダイオードＬＤ及び偏光分離素子４３等を搭載してなる。
【００３１】
この実施例に示す偏光分離素子４３は前項までに説明した複屈折結晶でなり、結晶内で光線を２回反射させる。ここで偏光分離素子４３は断面ほぼ台形形状に加工されており、レーザダイオードＬＤと向き合う斜面に形成された偏光ビームスプリツタ膜４４によつてレーザ光を反射し、光磁気デイスクの記録面を照射するようになされている。因に偏光ビームスプリツタ膜４４には透過率が例えばＴｓ＝30〔％〕及びＴｐ＝65〔％〕のものを用いる。
【００３２】
光磁気デイスクの記録面で反射されたレーザ光の戻り光は偏光ビームスプリツタ膜４４を介して偏光分離素子４３の結晶内に導かれ、その一部が偏光分離素子４３の底面から半透過膜４５を介してフオトデイテクタＰＤ１に出力される。
一方、偏光分離素子４３の底面で反射されたレーザ光は、偏光分離素子４３の上面に設けられた高反射膜４６で再び反射された後、偏光分離素子４３の底面下にあるフオトデイテクタＰＤ２及びＰＤ３に集光される。
【００３３】
これらフオトデイテクタＰＤ１〜ＰＤ３から出力された電気信号は、図８に示すように、Ｉ／Ｖ増幅回路５３を介して電流電圧変換され、マトリクス増幅回路５４に与えられる。
マトリクス増幅回路５４はフオトデイテクタＰＤ２及びＰＤ３から得られる出力信号の差分を光磁気信号Ｓ３として出力し、フオトデイテクタＰＤ１〜ＰＤ３から得られる出力信号のいずれか１つの和をピツト信号Ｓ４として出力する。
【００３４】
またマトリクス増幅回路５４はフオトデイテクタＰＤ１の出力信号とフオトデイテクタＰＤ２及びＰＤ３のうち少なくとも１つの出力信号とからフオーカスエラー信号Ｓ２を演算して出力し、フオトデイテクタＰＤ１〜ＰＤ３のうち少なくとも１つからトラツキングエラー信号Ｓ１を演算して出力する。
復調復号回路５５は入力された光磁気信号Ｓ３及びピツト信号Ｓ４に基づいて光磁気デイスク５０に記録されている情報を再生し、後段の処理回路に出力する。ここで、偏光分離素子４３としてＬＮ（LiNbO₃、１軸性結晶）又はＫＴＰ（KTiOPO₄、２軸性結晶）を用い得る。
【００３５】
以上の構成によれば、受光素子が形成された半導体基板４２上に前項までの条件を満たす偏光分離素子４３及び発光素子を配置して光ピツクアツプモジユール４１を形成したことにより、光磁気信号検出用の光ピツクアツプを小型かつ軽量化することができる。このように光ピツクアツプモジユール４１を構成したことにより、調整工数の低減と信頼性の向上を達成することができる。またこのような小型の光ピツクアツプを用いるようにしたことにより従来に比して小型の光磁気信号記録再生装置を実現することができる。
【００３６】
かくするにつき、フオトデイテクタＰＤ１〜ＰＤ３の少なくとも１つの和信号を求めることにより、記録媒体として光デイスクを用いた場合にも、ピツトＲＦ信号を得ることができる。従つて、光磁気用光ピツクアツプ及びレーザカプラ製造設備を光デイスク用にも共用することができる。
【００３７】
図５の光ピツクアツプモジユール４１を実現できる結晶として、図１０に示すようなＬＮ（LiNbO₃）や、図１１に示すようなＫＴＰ（KTiOPO₄）や、図１２に示すようなＹＶＯ₄を適用でき、いずれもスポツト群間に実用上十分な大きさの分離が得られた。
図１３及び図１４において、４４はビームスプリツタ膜、４５は半透過膜、４６は高反射膜、４７は反射防止膜を示す。
【００３８】
（３）他の実施例
なお上述の実施例においては、偏光分離素子に入射された光線を結晶素子内で２回反射させる場合について述べたが、反射回数はこれに限らず、３回以上であつても良い。反射する回数を増やせば、よりスポツトの分離を大きくでき、製造トレランスを改善することができる。またこの場合には偏光分離素子をより薄型化することができ、しかも充分なスポツト分離を実現できる。図９に結晶内での反射回数が４回の偏光分離素子を示す。
【００３９】
また上述の実施例においては、光ピツクアツプとして光磁気デイスク用のものについて述べたが、本発明はこれに限らず、書換可能なコンパクトデイスク（ＭＯ−ＣＤ）や光テープ等の光記録媒体から情報を読み出すのに用いる光ピツクアツプにも適用し得る。
【００４０】
同様に上述の実施例においては、光ピツクアツプの応用装置として光磁気デイスク再生装置について述べたが、本発明はこれに限らず、光テープ記録装置等の光装置に適用し得る。
【００４１】
さらに、図６の光ピツクアツプモジユール４１は、偏光分離素子４３の結晶中を入射光を受ける斜面を広く開いておくように構成したが、このようにすると、図１３に示すようにレーザダイオードからの直接光が迷光としてフオトデイテクタＰＤ１〜ＰＤ３に照射されるおそれがある。
この迷光を防止する構成として、図１４に示すように、入射用斜面４３Ａの底面近傍に垂直面４３Ｂを形成する。このようにすれば、迷光は垂直面４３Ｂによつて入射できないように遮蔽されると共に、たとえ底面に入射しても全反射条件によつて全反射することにより、少なくともフオトデイテクタへの入力を防止できる。
【００４２】
さらに図６の光ピツクアツプモジユール４１において、斜面上に形成されたビームスプリツタ膜４４をＲ_S＞Ｒ_Pのような条件を満足するような膜を形成する。このようにすれば、光磁気信号のエンハンスが実現されかつノイズに対する比率を向上させることができる。
【００４３】
上述のように本発明によれば、偏光分離素子を１軸性結晶又は２軸性結晶を材料とする複屈折性材料単体によつて形成すると共に、反射面に対する結晶の設定条件を、入射及び反射において変化が生じないように設定したことにより、高い精度で２つの分離スポツトを形成できる。
【図面の簡単な説明】
【図１】複屈折の説明に供する略線的断面図である。
【図２】光線が入射される側から見た固有偏光方向を示す略線図である。
【図３】波面法線方向と光線のエネルギーが進行する方向との関係を示す略線図である。
【図４】図４（Ａ）及び（Ｂ）は偏光分離素子内で反射された後、最終的に分離された光線のスポツト群を示す略線図である。
【図５】図５（Ａ）及び（Ｂ）は偏光分離素子内で反射された後、最終的に分離された光線のスポツト群を示す略線図である。
【図６】図６（Ａ）及び（Ｂ）は光ピツクアツプモジユールの構成を示す略線的側断面図及び横断面図である。
【図７】光磁気信号記録再生装置における光ピツクアツプの取り付け位置を示す略線的側面図である。
【図８】本発明に係る光磁気信号記録再生装置の構成を示すブロツク図である。
【図９】結晶内で光線を４回反射させる偏光分離素子の説明に供する略線図である。
【図１０】図１０（Ａ）及び（Ｂ）はＬＮ結晶を用いた場合の光ピツクアツプモジユールを示す略線的側断面図及び横断面図である。
【図１１】図１１（Ａ）及び（Ｂ）はＫＴＰ結晶を用いた場合の光ピツクアツプモジユールを示す略線的側断面図及び横断面図である。
【図１２】図１２（Ａ）及び（Ｂ）はＹＶＯ₄結晶を用いた場合の光ピツクアツプモジユールを示す略線的側断面図及び横断面図である。
【図１３】迷光についての説明に供する側断面図である。
【図１４】迷光の問題を解決した実施例を示す側断面図である。
【図１５】従来の光磁気信号の再生用に用いられる光ピツクアツプを示す略線的側面図である。
【図１６】図１６（Ａ）及び（Ｂ）はコンパクトデイスクの再生用に用いられる光ピツクアツプを示す略線的側断面図である。
【符号の説明】
４１……光ピツクアツプモジユール、４２……半導体基板、４３……偏光分離素子、４４……偏光ビームスプリツタ、４５……半透過膜、５１……光磁気信号再生装置、５２……光磁気デイスク、５３……Ｉ／Ｖ増幅回路、５４……マトリクス増幅回路、５５……復調復号回路。[0001]
【table of contents】
The present invention will be described in the following order.
DETAILED DESCRIPTION OF THE INVENTION Means for Solving the Problems to be Solved by the Conventional Invention (1) Optical pickup (1-1) Birefringence (1-2) Polarization separating element (Y direction) Separate type)
(1-3) Polarization separation element (X direction separation type)
(2) Magneto-optical signal recording / reproducing apparatus (3) Effects of other embodiments of the invention
BACKGROUND OF THE INVENTION
The present invention relates to an optical pickup, and is particularly suitable for application to a magneto-optical disk apparatus.
[0003]
[Prior art]
Conventionally, as shown in FIG. 15, an optical pickup 1 used in a magneto-optical disk apparatus converts laser light emitted from a laser diode 2 as a light source into a grating element 3, a beam splitter 4, a collimator lens 5, and an objective lens. 6 is sequentially collected on the magneto-optical disk 11, and the reflected light is passed through the objective lens 6, the collimator lens 5, the beam splitter 4, the Wollaston prism 7 and the multi-lens 8 in order to be connected to the photodetector 9. The thing of the structure which is imaged is used.
[0004]
[Problems to be solved by the invention]
However, the optical pickup 1 having this configuration has a configuration in which a plurality of optical components are individually combined. Therefore, there is a problem that it is difficult to reduce the size of the entire apparatus and to improve reliability.
Therefore, in the case of a magneto-optical disk reproducing apparatus, it is desired to realize a small and highly reliable optical pickup like the optical pickup 20 shown in FIG. 16 used in a compact disk reproducing apparatus.
[0005]
The optical pick-up 20 has an optical pick-up module 21, and laser light emitted from a laser diode LD provided as a light source in a housing 22 of the optical pick-up module 21 is formed on a slope of a trapezoidal glass prism 23. The light is reflected by the translucent film 24 attached to the surface, and sequentially passes through the transparent cover plate 25, the reflection mirrors 26 and 27, and the objective lens 28 to irradiate the optical disk 29, and the reflected light is reflected on the objective lens 28 and the reflection. The light passes through the mirrors 27 and 26 sequentially and is guided to the translucent film 24 as return light.
[0006]
The glass prism 23 is provided on the semiconductor substrate 30 together with the laser diode LD, introduces return light that has passed through the semitransparent film 24 into the glass prism 23, and adheres between the bottom surface of the glass prism 23 and the semiconductor substrate 30. The reflected light is reflected so as to be folded back between the translucent film 31 and the total reflection film 32 attached to the upper surface of the glass prism 23 and the semitransparent film 31 on the bottom surface.
Thus, the return light introduced into the glass prism 23 is transmitted to the two photodetectors PD1 and PD2 provided on the semiconductor substrate 30 at the front and rear positions sandwiching the total reflection film 32 that is conjugate to the laser diode LD. Thus, information detection signals are output from the photodetectors PD1 and PD2.
[0007]
Since the optical pickup module 21 having this configuration forms a non-polarization optical system as a whole, it cannot be used for reproducing a magneto-optical signal. However, an optical pickup for a magneto-optical disk is configured with the same configuration. If possible, it is considered that further downsizing can be realized as compared with the optical pickup currently used.
[0008]
The present invention has been made in view of the above points, and aims to realize an optical pickup and a magneto-optical signal recording / reproducing apparatus that are smaller and more reliable than those of the prior art.
[0009]
[Means for Solving the Problems]
In order to solve such problems, in the present invention, (a) the optical axis of the uniaxial crystal is set in a plane perpendicular to the normal line of the reflecting surface, or (b) the optical axis of the uniaxial crystal is Is set in a plane parallel to the normal of the incident surface of the principal ray to the uniaxial crystal and the normal of the reflective surface, or (c) the middle of the refractive index orientation of the biaxial crystal The orientation corresponding to the refractive index with the larger difference from the refractive index of is set in the plane perpendicular to the normal of the reflecting surface, or (d) the middle of the refractive index orientation of the biaxial crystal A condition in which the orientation corresponding to the refractive index having the larger difference from the refractive index is set in a plane parallel to the principal ray normal to the biaxial crystal and the normal to the reflecting surface Is identified.
Thus, according to the present invention, the polarization separating element is formed of a single birefringent material made of a uniaxial crystal or a biaxial crystal, and the setting condition of the crystal with respect to the reflecting surface does not change in incidence and reflection. With this setting, two separation spots can be formed with high accuracy.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[0011]
(1) Optical pickup (1-1) Birefringence The optical pickup according to the present invention does not perform any pasting as a polarization separating element, with a birefringent material alone (with different refractive index ellipsoids representing the properties of different axes and bonding). And the incident light is reflected at least once in the element.
[0012]
For this reason, the polarized light is usually separated by transmitting the light incident on the element without reflecting it inside. In the case of this embodiment, as shown in FIG. 1, it is an important item that the refraction direction at the interface varies depending on the difference in the electric field density vector D (that is, the direction of the wavefront normal line k varies). As a result, incident light is separated into ordinary light (o-ray) and extraordinary light (e-ray without walk-off). FIG. 1 shows a case in which convergent light is incident from the air on a uniaxial crystal YVO ₄ (ne = 2.1893 and no = 1.9734 at λ = 780 [nm]), and o-ray is a light beam according to Snell's law. E-ray represents a ray that does not follow Snell's law.
[0013]
On the other hand, in the case of this embodiment, the light ray incident in the element is reflected one or more times, and birefringence is an important item. This birefringence means that if the oscillation direction of the electric field density vector D is different even if the wavefront normal vector k is the same inside the crystal, the light ray (direction in which the light energy travels) vector S (= the electric field vector E of the light wave × the magnetic field of the light wave). A phenomenon in which the vector H) is different. Hereinafter, birefringence will be described.
[0014]
As shown in FIG. 2, the refractive index for a light beam traveling in a birefringent crystal has two axes of an ellipse formed when the refractive index ellipsoid is cut by a plane perpendicular to the wavefront direction vector k of the light beam and passing through the origin. , That is, the direction of the axis at that time is the direction of the electric field density vector D corresponding to the refractive index. Incidentally, if the polarized light is incident so as to be approximately 45 [°] with respect to the vectors D1 and D2 in FIG. 2, a magneto-optical signal can be obtained by the difference between the two components after polarization separation.
[0015]
In short, this difference in refractive index is the difference in wavefront normal vector k in FIG. 1 (difference between ordinary ray (o-ray) and extraordinary ray (e-ray without walk-off)). However, strictly speaking, since the refractive index changes depending on the difference of the wavefront normal vector k, it is necessary to consider the refractive index change.
Thus, the wavefront normal vector k generated by the difference in refractive index can be determined by the combination of the refractive index and the intrinsic polarization vector D using the fact that the wavefront normal vector k follows Snell's law. .
[0016]
For this reason, if only the polarized light is separated, the difference in the wavefront normal vector k is sufficient. However, in order to accurately grasp how the separated light beam travels, the wavefront normal vector k and the light vector S It is necessary to take into account the fact that it is off (ie Walk-off).
This ray vector S is calculated by the following equation. First, the electric field vector E in the birefringent material satisfies D = εE, and D and ε are known (since the refractive index ellipsoid is known, ε is also known from n ² = ε / ε ₀ ). Is used to determine the electric field vector E as ε ⁻¹ D.
[0017]
Further, as shown in FIG. 3, the magnetic field vector H and the magnetic flux density vector B have H // B // k × D, and the direction of the magnetic field vector H is also known. From E, S = E × H.
This formula also holds for reflection. The birefringent crystal is generally separated in two directions at the interface, as described above, based on the fact that the refractive index differs depending on the ray wavefront vector k and the eigenvector D.
Considering these things, the case of ray tracing is the e-ray (with walk-off) in FIG. Incidentally, FIG. 1 is a diagram in the case where no reflection occurs in the crystal.
[0018]
(1-2) Polarization separation element (Y direction separation type)
Next, the configuration of the polarization separation element according to the present invention will be described. As shown in FIG. 4A, the uniaxial crystal is set in a plane perpendicular to the normal line of the reflecting surface as a polarization separation element 41 that passes the reflected light twice by reflecting it twice. To do. At this time, the P-polarized light and the S-polarized light are separated in the y-axis direction as indicated by the spot groups “ooo” and “eeee” in FIG.
[0019]
In the case of this polarization separation element, the optical characteristics of the crystal are suppressed so that there is no phase difference and reflectance difference between the P-polarized light and the S-polarized light before and after reflection. In this way, the relationship between the intrinsic polarization vector D and the S and P polarizations is preserved before and after the reflection, and the intrinsic refractive index also agrees before and after the reflection. Therefore, no separation of rays other than the spot groups “ooo” and “eeee” occurs at the reflection interface, and only two spot groups “ooo” and “eeee” are completely separated on the two photodetectors separated from each other. And condensed.
[0020]
In FIG. 4B, the spot group “ooo” indicates that when incident light passes through the first, second, and third times, no movement occurs as an ordinary ray “o” at all passages. .
On the other hand, the spot group “eeee” moves as the extraordinary ray “e” by the vector e1 in the y direction for the first time when the incident light passes the first time, the second time, and the third time, and then the second time. In the third pass, it indicates that the vector e2 and e3 have moved in the x direction as an extraordinary ray “e”.
[0021]
Incidentally, even if the phase difference and the reflectance difference are generated before and after the reflection and the spots are separated, the spot light to be sequentially separated spreads a little after the subsequent reflection, but finally the spot group is maintained. A magneto-optical signal can be obtained if a differential output is obtained from two spot groups that are clearly divided among the eight spot groups considered in this way.
[0022]
The polarization separation element described above is a case where the crystal is a uniaxial crystal. However, when the crystal is a biaxial crystal, the refraction having the larger difference from the intermediate refractive index in the refractive index orientation of the crystal is larger. The direction corresponding to the rate may be set in a plane perpendicular to the normal line of the reflecting surface. In this case as well, incident light is reflected at least once in the crystal. In the case of this example, if two of the three refractive indexes that are close to the refractive index are considered as no, and the remaining one as ne, it is easy to cope with them.
[0023]
Furthermore, in this configuration, if the azimuth corresponding to the intermediate refractive index among the three refractive index azimuths of the crystal is set to an azimuth parallel to the normal line of the reflecting surface, the difference between no and ne will increase. (The separation angle of light can be increased), and a polarization separation element close to actual use can be obtained.
In the case of these biaxial crystals, the same effect as in the case of the uniaxial crystals can be obtained, whereby a polarization separation element having a wide selection range of crystal materials and a large degree of design freedom can be obtained.
[0024]
(1-3) Polarization separation element (X direction separation type)
As shown in FIG. 5A, the polarization separation element 41 has an optical axis of a uniaxial crystal in a plane parallel to the normal line of the principal ray incident on the crystal and the normal line of the reflection surface. Set. At this time, the P-polarized light and the S-polarized light are separated in the x-axis direction as two spots “oeo” and “eoe” as shown in FIG.
[0025]
In FIG. 5B, the spot “eoe” indicates that when the return light incident on the position “ooo” passes through the polarization separation element 41 for the first time, the second time, and the third time, the extraordinary ray “e” appears for the first time. Represents that the vector e1 moves in the x direction, and the second time does not move as the ordinary ray “o”, and the third time as the extraordinary ray “e” moves by the vector e3.
[0026]
On the other hand, the spot “oeo” does not move as an ordinary ray “o” at the first time, moves only by the vector e2 as an extraordinary ray “e” at the second time, and does not move as an ordinary ray at the third time. Represents.
As a result, the two spots “eoe” and “oeo” occur in positions separated in the x direction.
[0027]
In this way, even if the same uniaxial crystal is used, the polarization separation direction can be changed by simply changing the arrangement of the optical axes, so that the design range of the optical system (servo error detection method, PD division method, etc.) You can have it.
When a biaxial crystal is used for the polarization separation element, the orientation corresponding to the refractive index having a larger difference from the intermediate refractive index among the refractive index orientations of the crystal is set to the principal ray incident on the crystal. What is necessary is just to set in the surface parallel to the normal line of an entrance plane, and the normal line of a reflective surface. Even if it does in this way, the same effect as the above-mentioned can be acquired.
[0028]
Furthermore, in this configuration, the refractive index of the crystal is such that the orientation corresponding to the intermediate refractive index among the three refractive index orientations of the crystal is parallel to the normal of the principal ray incident surface and the reflective surface incident on the crystal. If the azimuth is set, the difference between no and ne is increased apparently (the light beam separation angle can be increased), and a polarization separation element close to actual use can be obtained.
In the case of these biaxial crystals, the same effect as in the case of the uniaxial crystals can be obtained, whereby a polarization separation element having a wide selection range of crystal materials and a large degree of design freedom can be obtained.
[0029]
In this way, by using a single birefringent material in the above-described polarization separation element, it is possible to realize a polarization separation element with high accuracy as long as it is not necessary to worry about the bonding accuracy of the optical axis at the time of manufacture.
In addition, since the polarization separation element is formed of a single birefringent material, a polarization separation element that is not affected by changes over time can be realized.
[0030]
(2) Magneto-optical signal recording / reproducing apparatus FIG. 6 shows an optical pickup using the polarization separation element described in the previous section. FIG. 7 shows an optical system of a magneto-optical signal recording / reproducing apparatus using an optical pickup, and FIG.
As shown in FIG. 6, the optical pickup 41 has a laser diode LD, a polarization separation element 43, and the like mounted on a semiconductor substrate 42 on which photodetectors PD1, PD2, and PD3 are integrated.
[0031]
The polarization separation element 43 shown in this embodiment is the birefringent crystal described in the previous section, and reflects the light beam twice in the crystal. Here, the polarization separation element 43 is processed to have a substantially trapezoidal cross section, and the laser beam is reflected by the polarization beam splitter film 44 formed on the inclined surface facing the laser diode LD, and the recording surface of the magneto-optical disk is irradiated. It is made to do. Incidentally, a polarizing beam splitter film 44 having a transmittance of, for example, Ts = 30 [%] and Tp = 65 [%] is used.
[0032]
The return light of the laser beam reflected by the recording surface of the magneto-optical disk is guided into the crystal of the polarization separation element 43 through the polarization beam splitter film 44, and a part of the return light is transmitted from the bottom surface of the polarization separation element 43 to the semi-transmissive film. And output to the photo detector PD1.
On the other hand, the laser light reflected by the bottom surface of the polarization separation element 43 is reflected again by the high reflection film 46 provided on the top surface of the polarization separation element 43 and then the photodetectors PD2 and PD3 below the bottom surface of the polarization separation element 43. It is focused on.
[0033]
The electrical signals output from these photodetectors PD1 to PD3 are converted into currents and voltages via an I / V amplifier circuit 53 as shown in FIG.
The matrix amplifier circuit 54 outputs the difference between the output signals obtained from the photodetectors PD2 and PD3 as a magneto-optical signal S3, and outputs the sum of any one of the output signals obtained from the photodetectors PD1 to PD3 as a pit signal S4.
[0034]
The matrix amplifier circuit 54 calculates and outputs a focus error signal S2 from the output signal of the photodetector PD1 and at least one of the photodetectors PD2 and PD3, and outputs a tracking error from at least one of the photodetectors PD1 to PD3. The signal S1 is calculated and output.
The demodulation / decoding circuit 55 reproduces the information recorded on the magneto-optical disk 50 based on the inputted magneto-optical signal S3 and the pit signal S4, and outputs it to the processing circuit at the subsequent stage. Here, LN (LiNbO ₃ , uniaxial crystal) or KTP (KTiOPO ₄ , biaxial crystal) can be used as the polarization separation element 43.
[0035]
According to the above configuration, the optical pickup module 41 is formed by arranging the polarization separation element 43 and the light emitting element satisfying the conditions described above on the semiconductor substrate 42 on which the light receiving element is formed, thereby detecting the magneto-optical signal. The optical pickup for use can be reduced in size and weight. By configuring the optical pickup module 41 in this way, it is possible to reduce the adjustment man-hours and improve the reliability. Further, by using such a small optical pickup, it is possible to realize a magneto-optical signal recording / reproducing apparatus that is smaller than the conventional one.
[0036]
Accordingly, by obtaining at least one sum signal of the photodetectors PD1 to PD3, a pit RF signal can be obtained even when an optical disk is used as a recording medium. Therefore, the magneto-optical optical pickup and the laser coupler manufacturing facility can be shared for the optical disk.
[0037]
As a crystal capable of realizing the optical pickup module 41 of FIG. 5, LN (LiNbO ₃ ) as shown in FIG. 10, KTP (KTiOPO ₄ ) as shown in FIG. 11, or YVO ₄ as shown in FIG. 12 is applied. In any case, a practically sufficient separation between the spot groups was obtained.
13 and 14, reference numeral 44 denotes a beam splitter film, 45 denotes a semi-transmissive film, 46 denotes a highly reflective film, and 47 denotes an antireflection film.
[0038]
(3) Other Embodiments In the above-described embodiments, the case where the light beam incident on the polarization separation element is reflected twice in the crystal element has been described. May be hot. Increasing the number of reflections can increase spot separation and improve manufacturing tolerances. In this case, the polarization separation element can be made thinner, and sufficient spot separation can be realized. FIG. 9 shows a polarization beam splitting element having four reflections in the crystal.
[0039]
In the above-described embodiment, the optical pickup is for a magneto-optical disk. However, the present invention is not limited to this, and information is recorded from an optical recording medium such as a rewritable compact disk (MO-CD) or optical tape. The present invention can also be applied to an optical pickup used for reading out.
[0040]
Similarly, in the above-described embodiments, the magneto-optical disk reproducing apparatus has been described as an optical pickup application apparatus, but the present invention is not limited to this, and can be applied to an optical apparatus such as an optical tape recording apparatus.
[0041]
Further, the optical pickup module 41 of FIG. 6 is configured so that the inclined surface for receiving incident light is wide open in the crystal of the polarization splitting element 43. In this case, however, as shown in FIG. The direct light may be irradiated to the photodetectors PD1 to PD3 as stray light.
As a configuration for preventing this stray light, a vertical surface 43B is formed in the vicinity of the bottom surface of the incident slope 43A as shown in FIG. In this way, stray light is blocked by the vertical surface 43B so that it cannot be incident, and even if it is incident on the bottom surface, it is totally reflected by the total reflection condition, so that at least input to the photodetector can be prevented. .
[0042]
Further, in the optical pickup module 41 of FIG. 6, a beam splitter film 44 formed on the inclined surface is formed so as to satisfy a condition such as R _S > R _P. In this way, enhancement of the magneto-optical signal can be realized and the ratio to noise can be improved.
[0043]
As described above, according to the present invention, the polarization separating element is formed of a single birefringent material made of a uniaxial crystal or a biaxial crystal, and the setting conditions of the crystal with respect to the reflecting surface are set to be incident and By setting so that no change occurs in the reflection, two separation spots can be formed with high accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view for explaining birefringence.
FIG. 2 is a schematic diagram showing an intrinsic polarization direction viewed from the side on which light is incident.
FIG. 3 is a schematic diagram showing a relationship between a wavefront normal direction and a direction in which light energy travels.
FIGS. 4A and 4B are schematic diagrams showing spot groups of rays finally separated after being reflected in the polarization separation element. FIGS.
FIGS. 5A and 5B are schematic diagrams showing spot groups of rays finally separated after being reflected in the polarization separation element.
FIGS. 6A and 6B are a schematic cross-sectional side view and a horizontal cross-sectional view showing the configuration of an optical pickup module, respectively.
FIG. 7 is a schematic side view showing the mounting position of the optical pickup in the magneto-optical signal recording / reproducing apparatus.
FIG. 8 is a block diagram showing a configuration of a magneto-optical signal recording / reproducing apparatus according to the present invention.
FIG. 9 is a schematic diagram for explaining a polarization separation element that reflects a light beam four times in a crystal.
FIGS. 10A and 10B are a schematic side sectional view and a transverse sectional view showing an optical pickup module when an LN crystal is used.
FIGS. 11A and 11B are a schematic side sectional view and a transverse sectional view showing an optical pickup module when a KTP crystal is used.
FIGS. 12A and 12B are a schematic side sectional view and a transverse sectional view showing an optical pickup module when a YVO ₄ crystal is used.
FIG. 13 is a side sectional view for explaining stray light.
FIG. 14 is a side sectional view showing an embodiment in which the problem of stray light is solved.
FIG. 15 is a schematic side view showing an optical pickup used for reproducing a conventional magneto-optical signal.
FIGS. 16A and 16B are schematic cross-sectional side views showing an optical pickup used for reproducing a compact disk. FIGS.
[Explanation of symbols]
41... Optical pick-up module, 42... Semiconductor substrate, 43... Polarization separating element, 44... Polarized beam splitter, 45. Disc, 53... I / V amplification circuit, 54... Matrix amplification circuit, 55.

Claims

A semiconductor substrate on which a light receiving element group is formed;
A light emitting element mounted on the semiconductor substrate and emitting a light beam to a magneto-optical signal recording medium;
A birefringent material made of a uniaxial crystal is used as a material, and the return light of the light beam reflected on the magneto-optical signal recording medium is incident and separated, and the separated return light is separated at the crystal interface. A polarization separation element that is guided to the light receiving element group by being reflected by the reflecting surface, and the optical axis of the uniaxial crystal is set in a plane perpendicular to the normal line of the reflecting surface. Light pick-up characterized by

A semiconductor substrate on which a light receiving element group is formed;
A light emitting element mounted on the semiconductor substrate and emitting a light beam to a magneto-optical signal recording medium;
A birefringent material made of a uniaxial crystal is used as a material, and the return light of the light beam reflected on the magneto-optical signal recording medium is incident and separated, and the separated return light is separated at the crystal interface. A polarization separation element that is guided by the reflecting surface to the light receiving element group, and the optical axis of the uniaxial crystal is normal to the incident surface of the principal ray on the uniaxial crystal; An optical pickup characterized by being set in a plane parallel to the normal line of the reflecting surface.

A semiconductor substrate on which a light receiving element group is formed;
A light emitting element mounted on the semiconductor substrate and emitting a light beam to a magneto-optical signal recording medium;
The birefringent material is made of a biaxial crystal as a material, and the return light of the light beam reflected by the magneto-optical signal recording medium is incident and separated, and the separated return light is separated at the crystal interface. A polarization separating element that is guided to the light receiving element group by being reflected by the reflecting surface, and has an orientation with respect to the refractive index having a larger difference from the intermediate refractive index among the orientations of the refractive indices of the biaxial crystals. Is set in a plane perpendicular to the normal line of the reflecting surface.

A semiconductor substrate on which a light receiving element group is formed;
A light emitting element mounted on the semiconductor substrate and emitting a light beam to a magneto-optical signal recording medium;
The birefringent material is made of a biaxial crystal as a material, and the return light of the light beam reflected by the magneto-optical signal recording medium is incident and separated, and the separated return light is separated at the crystal interface. A polarized light separating element that is guided to the light receiving element group by being reflected by a reflecting surface, and corresponds to a refractive index having a larger difference from an intermediate refractive index among refractive index orientations of the biaxial crystal. An optical pick-up characterized in that the orientation to be set is set in a plane parallel to the normal line of the principal ray to the biaxial crystal and the normal line of the reflection surface.

4. The light according to claim 3, wherein an orientation corresponding to an intermediate refractive index among the three refractive index orientations of the biaxial crystal is set to an orientation parallel to a normal line of the reflecting surface. Pickup.

Of the three refractive index orientations of the biaxial crystal, the orientation corresponding to the intermediate refractive index is parallel to the incident surface of the principal ray on the biaxial crystal and the reflecting surface. The optical pickup according to claim 4, wherein the refractive index orientation of the axial crystal is defined.

A semiconductor substrate on which a group of light receiving elements is formed, a light emitting element mounted on the semiconductor substrate and emitting a light beam to a magneto-optical signal recording medium, and a birefringent material alone made of a uniaxial crystal, Polarized light guided to the light receiving element group by entering and separating the return light of the light beam reflected by the magneto-optical signal recording medium and reflecting the separated return light by a reflection surface formed by a crystal interface. An optical pickup having a separation element ;
A signal processing circuit for reproducing a magneto-optical signal based on an output from the light receiving element group of the optical pickup , and an optical axis of the uniaxial crystal is set in a plane perpendicular to a normal line of the reflecting surface A magneto-optical signal reproducing apparatus characterized by the above.

A semiconductor substrate on which a group of light receiving elements is formed, a light emitting element mounted on the semiconductor substrate and emitting a light beam to a magneto-optical signal recording medium, and a birefringent material alone made of a uniaxial crystal, Polarized light guided to the light receiving element group by entering and separating the return light of the light beam reflected by the magneto-optical signal recording medium and reflecting the separated return light by a reflection surface formed by a crystal interface. An optical pickup having a separation element;
A signal processing circuit for reproducing a magneto-optical signal based on an output from the light receiving element group of the optical pickup;
And the optical axis of the uniaxial crystal is set in a plane parallel to the normal of the incident surface of the principal ray to the uniaxial crystal and the normal of the reflecting surface.
A magneto-optical signal reproducing apparatus.

A semiconductor substrate on which a group of light receiving elements is formed, a light emitting element mounted on the semiconductor substrate and emitting light to a magneto-optical signal recording medium, and a birefringent material made of a biaxial crystal as a material, and Polarized light guided to the light receiving element group by entering and separating the return light of the light beam reflected by the magneto-optical signal recording medium and reflecting the separated return light by a reflection surface formed by a crystal interface. An optical pickup having a separation element;
A signal processing circuit for reproducing a magneto-optical signal based on an output from the light receiving element group of the optical pickup;
The orientation with respect to the refractive index having the larger difference from the intermediate refractive index among the orientations of the refractive indexes of the biaxial crystal is set in a plane perpendicular to the normal line of the reflecting surface.
A magneto-optical signal reproducing apparatus.

A semiconductor substrate on which a group of light receiving elements is formed, a light emitting element mounted on the semiconductor substrate and emitting light to a magneto-optical signal recording medium, and a birefringent material made of a biaxial crystal as a material, and Polarized light guided to the light receiving element group by entering and separating the return light of the light beam reflected by the magneto-optical signal recording medium and reflecting the separated return light by a reflection surface formed by a crystal interface. An optical pickup having a separation element;
A signal processing circuit for reproducing a magneto-optical signal based on an output from the light receiving element group of the optical pickup;
The orientation corresponding to the refractive index having the larger difference from the intermediate refractive index among the refractive index orientations of the biaxial crystal is the normal of the principal ray to the biaxial crystal and the reflection Set in a plane parallel to the surface normal
A magneto-optical signal reproducing apparatus.