JP4026248B2 - Optical disk device - Google Patents

Description

ここで、Ｗ３１は、レーザ光の波長λで規格化された３次のコマ収差係数であり、以下の式（２）で表すことができる。
【００２３】
【数２】

ここで、ＮＡは、対物レンズ２ｅの開口数、また、ｎ，ｔは、それぞれ光ディスク１の透明基板の屈折率と厚さで、θは光ディスク１のスキュー角である。
【００２４】
従って、ディスク基板によって発生するコマ収差による位相分布Ｗ（ｘ，ｙ）を補償するための位相分布−Ｗ（ｘ，ｙ）を、光ディスク１に入射する前の光ビームに対して持たせることにより、前述のコマ収差等の発生を抑制することが可能となる。
【００２５】
本発明の実施の形態では、凹面または凸面状の表面形状を有する透明部材によって液晶をはさみ込んだ液晶パネルに所定の電圧を印加して液晶の屈折率を変化させることにより、スキュー角に応じた所定の位相分布を光ビームに持たせるようにしている。
【００２６】
先ず、透明部材が平面形状を有する液晶パネルに対して電圧を印加した場合における光ビームの位相分布の変化について説明する。
図２は、透明部材の表面が平面形状を有する液晶パネルの断面を示す断面図である。この図に示すように、液晶パネル１０は、透明部材１０ａ，１０ｂ、透明電極１０ｃ，１０ｄ、配向膜１０ｅ，１０ｆ、および、液晶１０ｇによって構成されている。
【００２７】
透明部材１０ａ，１０ｂの片面には、例えば、ＩＴＯ（Indium Thin Oxide ）等が蒸着されて透明電極１０ｃ，１０ｄが形成されている。配向膜１０ｅ，１０ｆは、液晶の分子方向を特定するためのものである。液晶１０ｇは、例えば、ベンド型のネマティク液晶である。
【００２８】
このような液晶パネル１０の透明電極１０ｃ，１０ｄに対して電圧を印加すると、液晶１０ｇの方向に変化が生じ、結果として屈折率が変化する。例えば、前述のベンド型ネマティク液晶の場合は複屈折性を示し、配向方向の屈折率（ｎ_LC）が印加電圧に応じて変化するので、配向方向に沿った直線偏光の光ビームに対して、ｎ_LC×ｄ（ｄ：液晶の厚さ）の位相を与えることができる。
【００２９】
図３は、印加電圧と屈折率の変化Δｎ_LCとの関係を示す図である。この図に示すように、印加電圧が上昇してある所定の閾値を超えると屈折率変化が増大し始め、ある一定の電圧に到達すると停止する。一般に、屈折率の最大変化量は、０．１５〜０．２程度である。
【００３０】
なお、液晶に印加する電圧は、数ｋＨｚ程度の交流電圧であり、電圧値はその実効値を表しているものとする。
本発明では、液晶パネルの以上のような性質を利用し、光ビームに対して所望の位相分布（−Ｗ（ｘ，ｙ））を持たせることにより、コマ収差等の発生を防止する。
【００３１】
図４は、本実施の形態の補償光学系２ｄにおいて使用される液晶パネルの一例を示す図である。この図において、図４（Ａ）は、透明部材が凸面形状を有する液晶パネル２０である。この液晶パネル２０では、透明部材２０ａが凸面形状を有しており、その他の構成は、図２の場合と同様である。図５は、図４に示す透明部材２０ａの表面形状を示す図である。この図に示すように、透明部材２０ａは、中心からの距離の４乗に比例した曲面を有している。ここで、ｒは中心からの距離であり、ａは比例定数である。
【００３２】
図４（Ｂ）は、透明部材が凹面形状を有する液晶パネル３０である。この液晶パネル３０では、透明部材３０ｂが凹面形状を有しており、その他の構成は、図２の場合と同様である。この透明部材３０ｂも図４（Ａ）の場合と同様に、図５に示すような表面形状を有している。
【００３３】
これらの液晶パネル２０，３０を透過した光ビームに与えられる位相分布は、それぞれ、以下の式（３）および式（４）によって表すことができる。
【００３４】
【数３】

【００３５】
【数４】

ここで、ｎ_g は透明基板の屈折率である。これらの式から分かるように、液晶パネル２０，３０は、半径方向の距離の４乗および液晶と透明基板との屈折率の差に比例した位相分布を光ビームに対して与えることが可能となる。
【００３６】
ここで、光軸を中心とする（ｘ，ｙ）座標を考え、これら２つの液晶パネルを図６に示すように、光軸からｘ方向にそれぞれがずれＳを持つように並置する。このとき、各々の液晶パネルを透過する光ビームに与えられる位相分布は、以下の式（５）および式（６）によってそれぞれ表すことができる。
【００３７】
【数５】

【００３８】
【数６】

次に、これら２つの液晶パネル２０，３０の双方を透過する光ビームに与えられる位相分布Ｗ１２は、Ｗ１とＷ２の和によって与えられ、以下の式（７）によって表すことができる。
【００３９】
【数７】

ここで、右辺の｛｝内の第１項は、適当な係数を選べば、式（１）に示すｘ方向へ光ディスク１が傾いた場合に発生するコマ収差の式と等価である。また、第２項は、ｘに対して１次関数であるので、これら２つの液晶パネル２０，３０を透過した光は、ｘ方向への位置ずれ（光ディスク１上における光スポットのｘ方向への位置のずれ）を生ずることになる。しかし、このずれはトラッキングサーボまたはＰＬＬ（Phase Locked Loop ）回路等によって補正されるため、情報を読み書きする場合には障害とはならない。
【００４０】
従って、式（７）に示すＷ１２の係数を適宜設定することにより、式（２）に示す、光ディスク１のスキューによって発生するコマ収差を補正することが可能となる。
【００４１】
ここで、式（７）に含まれている係数は、透明部材の表面形状に係る定数ａと、液晶パネルのｘ方向へのずれＳと、液晶と透明部材の屈折率の差である。本実施の形態では、ずれＳを固定して、液晶の屈折率ｎ_LCを印加電圧によって制御することにより、Ｗ１２の値を適宜変化させて任意のコマ収差を補正する。
【００４２】
式（１）および式（７）から、光ディスク１のスキューによって発生するコマ収差をこれら２枚の液晶パネル２０，３０によって補正するための条件を求めると、以下の式（８）によって表すことができる。
【００４３】
【数８】

ここで、ｒ_obj は、対物レンズ２ｅの瞳半径であり、λは、光ビームの波長である。
【００４４】
以上の式（８）を満足するように、液晶への印加電圧を制御することにより、光ディスク１のスキューに起因するコマ収差の発生を補正することができる。
次に、以上の液晶パネル２０，３０の各係数の設定方法および駆動方法について説明する。
【００４５】
先ず、液晶パネル２０，３０の透明部材の屈折率と液晶の屈折率は、図７に示すように、液晶の屈折率の変化範囲内に透明部材の屈折率が収まるように設定する。即ち、ｎ＜ｎ_g ＜（ｎ＋０．２）の関係を満足するように、ｎおよびｎ_g を選択する。
【００４６】
光ディスク１にスキューが存在しない場合には、液晶パネル２０，３０による補正は不要であるので、その場合はｎ_LC＝ｎ_g となる電圧Ｖ０（図７参照）を液晶パネル２０，３０にそれぞれ印加する。
【００４７】
そして、スキューに対しては、液晶と透明部材との屈折率の差が式（８）の関係を満足するような電圧Ｖ１（図７参照）を算出して、液晶パネル２０，３０に対して印加する。
【００４８】
また、前述の場合とは逆方向のスキューに対しては、同じく式（８）の関係を満足するような電圧Ｖ２（図７参照）を算出して、液晶パネル２０，３０に対して印加する。
【００４９】
以上のような方法によれば、光ディスク１が有するスキューによって発生するコマ収差を補正することが可能となる。
次に、以上に説明した液晶パネル２０，３０を有する補償光学系２ｄの動作について説明する。なお、液晶パネル２０，３０は、図１に示す補償光学系２ｄに内蔵されており、光ディスク１が有するスキュー方向に沿って相互にずれＳを持たせて並置されているものとする。また、温度検知部２ｈは、液晶パネル２０または液晶パネル３０の何れかの液晶２０ｇまたは３０ｇの温度（またはその近傍の温度）を検出するものとする。
【００５０】
いま、図１に示す実施の形態において、光ディスク１が装着され、再生または記録が開始されたとすると、光ディスク１は、図示せぬスピンドルモータによって所定の角速度で回転されることになる。このとき、スキュー検出部４は、光ディスク１の光ビームが照射される付近のスキューを検出し、そのスキュー角を制御部３に通知する。
【００５１】
制御部３は、スキュー検出部４から通知されたスキュー角に対応する制御電圧Ｖｃを、図示せぬメモリのテーブル（スキュー角と制御電圧とが関連付けて格納されたテーブル）等から取得し、補償光学系２ｄに供給する。なお、このとき、制御部３は、温度検出部２ｈから供給される液晶の温度を参照し、制御電圧を適宜較正する。なお、この較正方法としては、液晶の温度と制御電圧の較正値とを関連付けて格納しているテーブル等を参照することによって行う。
【００５２】
その結果、図６に示す液晶パネル２０，３０には、Ｖｃが供給され、液晶がそれに応じて配向方向を変化させることにより屈折率が変化する。その結果、これらの液晶パネル２０，３０を透過した光ビームは、式（８）を満足する位相分布を有することになる。
【００５３】
このような位相分布を有する光ビームが光ディスク１の記録層に集光されると、光ディスク１がスキューを有している場合においてもコマ収差を発生せず、常に安定した光スポットが形成される。
【００５４】
この光スポットは、記録層の物理的な状態（例えば、記録層の凹凸）などに応じて反射され、対物レンズ２ｅ、補償光学系２ｄ、ビームスプリッタ２ｃ、および、レンズ２ｆを経由して光検出部２ｇに入射され、前述の記録層に記録されている情報に対応する電気信号に変換される。
【００５５】
その結果、光ディスク１がスキューを有する場合においても、コマ収差の発生を防止することができるので、記録層に記録されている情報を正確に再生することが可能となるとともに、記録層に対して情報を記録する場合においても、確実に情報を記録することが可能となる。
【００５６】
次に、補償光学系２ｄの第２の実施の形態について説明する。
図８は、補償光学系２ｄの第２の実施の形態の構成例を示す図である。第２の実施の形態では、凹面形状を有する２枚の液晶パネル３０が光軸に対して垂直な方向にずれＳを有するように並置されている。
【００５７】
前述した内容から推測されるように、液晶パネル２０は、負の特性を有する液晶パネル３０であるということができる。従って、同一の液晶パネルを２枚並置し、それぞれの液晶パネルに印加する電圧を個別に設定することでも、前述の場合と同様の効果を達成することが可能となる。
【００５８】
なお、図８に示す例では、凹面形状を有する液晶パネル３０が２枚並置されているが、凸面形状を有する液晶パネル２０を用いてもよいことはいうまでもない。
【００５９】
次に、以上の実施の形態の駆動方法について説明する。
図８に示す実施の形態では、図９に示すように、光ディスク１にスキューが存在しない場合には、液晶と透明部材の屈折率が等しくなる電圧Ｖ０を２枚の液晶パネル３０に対して印加する。
【００６０】
そして、スキューに対しては、液晶と透明部材の屈折率が式（８）に示す関係を満足する電圧Ｖ１（図９参照）を一方の液晶パネルに、また、Ｖ１が与える屈折率に対して同量異符号の屈折率差を与える電圧Ｖ２（図９参照）を他方の液晶パネルに対して印加するようにすればよい。
【００６１】
このような実施の形態によっても前述の場合と同様に、光ディスク１がスキューを有する場合でも、コマ収差の発生を防止することが可能となるので、光ディスク１に記録されている情報を正確に再生するとともに、光ディスク１に対して情報を確実に記録することが可能となる。
【００６２】
なお、このような実施の形態では、同一種類の液晶パネルを２枚使用することから、使用する部品の種類を減少させることが可能となるので、結果として装置のコストを削減することが可能となる。
【００６３】
次に、図１０を参照して、補償光学系２ｄの第３の実施の形態について説明する。
図１０は、補償光学系２ｄの第３の実施の形態の構成例を示す図である。この図では、凸面形状を有する透明部材４０ａと凹面形状を有する透明部材４０ｂとがずれＳを有して並置されており、その間に液晶４０ｃが封入されている。
【００６４】
この実施の形態は、図４に示す実施の形態において、２枚の液晶パネルによって実現している機能を１枚の液晶パネルに集約したものである。従って、この液晶パネルによって発生する位相分布は、式（７）で表すことができる。また、駆動方法も図４の場合と同様である。
【００６５】
以上の実施の形態によれば、図４に示す実施の形態と同様にコマ収差の発生を防止することができるだけでなく、図４の場合と比べて部品点数を減少させることが可能となるので、装置の製造コストを削減することができる。
【００６６】
次に、図１１を参照して、補償光学系２ｄの第４の実施の形態について説明する。
図１１は、補償光学系２ｄの第４の実施の形態の構成例を示す図である。この図では、凸面形状を有する透明部材と凹面形状を有する透明部材とが１つの部材５０ｃとして形成されており、その上下に透明部材５０ａ，５０ｂが配置されるとともに、それぞれの透明部材の間に液晶５０ｄ，５０ｅが封入されている。
【００６７】
この実施の形態では、図４の場合と比較して、透明部材が１枚削減されているだけであり、この液晶パネル５０によって発生する位相分布および駆動方法は、図４の場合と同様である。
【００６８】
以上の実施の形態によれば、図４に示す実施の形態と同様にコマ収差の発生を防止することができるだけでなく、図４の場合と比べて、僅少ではあるが、部品点数を減少させることが可能となるので、装置の製造コストを削減することができる。
【００６９】
次に、図１２を参照して、補償光学系２ｄの第５の実施の形態について説明する。
図１２は、補償光学系２ｄの第５の実施の形態の構成例を示す図である。この図では、凸面形状を有する透明部材６０ａと凹面形状を有する透明部材６０ｂとがずれＳを有して並置され、その間に透明部材６０ｃが配置されるとともにそれぞれの透明部材の間に液晶６０ｄ，６０ｅが封入されている。
【００７０】
この実施の形態は、基本的に図４と同様であり、この液晶パネル６０によって発生する位相分布は、図４の場合と同様であり、また、その駆動方法も図４の場合に準ずる。
【００７１】
以上の実施の形態によれば、図４に示す実施の形態と同様にコマ収差をの発生を防止することができるだけでなく、図４の場合と比べて、僅少ではあるが、部品点数を減少させることが可能となるので、装置の製造コストを削減することができる。
【００７２】
次に、図１３を参照して、補償光学系２ｄの第６の実施の形態について説明する。
図１３は、補償光学系２ｄの第６の実施の形態の構成例を示す図である。この図では、両面にずれＳを持たせて形成された凹面形状を有する透明部材７０ｃが、透明部材７０ａおよび７０ｂの間に配置されており、それぞれの間には液晶７０ｄ，７０ｅが封入されている。なお、透明部材７０ｃは、凹面形状の代わりに凸面形状を形成するようにしてもよい。
【００７３】
この実施の形態は、基本的には、図８に示す実施の形態と、図１１に示す実施の形態とを混合した方法であり、その駆動方法は、図８の場合と同様である。
以上の実施の形態によれば、図４に示す実施の形態と同様にコマ収差の発生を防止することができるだけでなく、図４の場合と比べて、僅少ではあるが、部品点数を減少させることが可能となるので、装置の製造コストを削減することができる。
【００７４】
次に、図１４を参照して、補償光学系２ｄの第７の実施の形態について説明する。
図１４は、補償光学系２ｄの第７の実施の形態の構成例を示す図である。この図では、凹面形状を有する透明部材８０ａ，８０ｂがずれＳを有するように配置されており、その間には両面が平面形状を有する透明部材８０ｃが配置されている。また、透明部材８０ａ〜８０ｃの間には、液晶８０ｄ，８０ｅが封入されている。なお、透明部材８０ａ，８０ｂは、凹面形状の代わりに凸面形状を形成するようにしてもよい。
【００７５】
この実施の形態は、基本的には、図８に示す実施の形態と、図１２に示す実施の形態とを、混合した方法であり、その駆動方法は、図８の場合と同様である。以上の実施の形態によれば、図４に示す実施の形態と同様にコマ収差の発生を防止することができるだけでなく、図４の場合と比べて、僅少ではあるが、部品点数を減少させることが可能となるので、装置の製造コストを削減することができる。
【００７６】
図１５は、補償光学系２ｄの第８の実施の形態の構成例を示す図である。この実施の形態では、図１０に示す場合と同様の液晶パネル９０，１００が並置されている。パネル９０は、凸面形状を有する透明部材９０ａと凹面形状を有する透明部材９０ｂとがずれＳを有して並置されており、その間には液晶９０ｃが封入されている。パネル１００も同様に、凸面形状を有する透明部材１００ａと凹面形状を有する透明部材１００ｂとがずれＳを有して並置されており、その間には液晶１００ｃが封入されている。なお、各液晶パネルのずれ方向は、それぞれ互い違いとなるように設定されている。
【００７７】
なお、以上の例では、図１０に示す場合と同様の液晶パネルを使用したが、第１〜第７の実施の形態に示す液晶パネルの何れを選択してもよい。
この実施の形態では、液晶パネル９０と液晶パネル１００によって光ビームに付与される位相分布は、等量異符号となるので、液晶パネル１００によって発生した位相分布は、液晶パネル９０によって相殺されることになる。従って、電圧を印加していない場合の位相分布は“０”となる。また、一方の液晶パネルを正方向用とし、他方を負方向用として、光ディスク１のスキューに応じてこれら液晶パネルの何れか一方に電圧を印加することにより、コマ収差の発生を防止することができる。
【００７８】
いま、電圧を印加した方の液晶パネルに封入されている液晶の屈折率をｎ_LC1 とし、印加電圧が０Ｖの場合の液晶の屈折率をｎ_LC0 とすると、これら２枚の液晶パネルを透過した光ビームの位相分布は、以下の式（９）によって表すことができる。
【００７９】
【数９】

この式から分かるように、液晶パネル９０，１００を透過した光ビームの位相分布からは、透明部材の透過率に係る項（ｎ_g ）が削除されていることから、透明部材と液晶の屈折率の設定を簡略化することができる。
【００８０】
図１６は、液晶パネル９０，１００の駆動方法を示す図である。この図に示すように、図１５に示す実施の形態では、＋方向のスキュー（例えば、図１の光ディスク１の表面が水平面から時計方向に傾くスキュー）に対しては、液晶パネル９０に対して電圧Ｖｓを印加することにより対応し、また、−方向のスキュー（光ディスク１の表面が水平面から反時計方向に傾くスキュー）に対しては、液晶パネル１００に対して電圧Ｖｓを印加することにより対応する。従って、スキューに応じた電圧を印加するようにすればよいことから、駆動方法を簡略化することができる。また、スキューが発生していない場合には、電圧を印加する必要がないことから消費電力を削減することも可能となる。
【００８１】
以上の実施の形態によれば、図４に示す実施の形態と同様にコマ収差の発生を防止することができるだけでなく、駆動方法を簡略化するとともに、消費電力を低減することが可能となる。また、液晶パネルと透明部材の屈折率の設定を行う必要がないことから、設計を簡略化することもできる。
【００８２】
【発明の効果】
以上説明したように本発明では、光源から射出された光ビームを対物レンズによって光ディスク上の所定の位置に集光し、光ディスクの記録層に対して情報を記録または再生する光ディスク装置において、光源と対物レンズの間にその中心を所定の距離だけずらして配置された凹面または凸面を有する２枚の透明部材と、凹面または凸面に当接するように設けられた液晶と、液晶に対して電圧を印加する透明電極と、から構成される補償光学系と、光ディスクのスキューを検出するスキュー検出部と、スキュー検出部によって検出されたスキューに応じて、補償光学系に対して所定の電圧を印加する電圧印加部とを有し、補償光学系は、対向面の一方が平面であり他方が凹面である１組の透明部材の間に液晶が封入されて形成された第１の液晶パネルと、対向面の一方が平面であり他方が凸面である１組の透明部材の間に液晶が封入されて形成された第２の液晶パネルとがその中心を所定の距離だけずらして配置されて構成されているようにしたので、光ディスクがスキューを有している場合においても、正確に情報を記録または再生することが可能となる。
【図面の簡単な説明】
【図１】本発明の実施の形態の構成例を示す図である。
【図２】一般的な液晶パネルの構成例を示す図である。
【図３】図２に示す液晶パネルの印加電圧と、屈折率変化との関係を示す図である。
【図４】図４（Ａ）は、図１に示す補償光学系に使用されている透明部材が凸面形状を有する液晶パネルの一例であり、図４（Ｂ）は、同じく透明部材が凹面形状を有する液晶パネルの一例である。
【図５】図４に示す凹面または凸面の形状を示す図である。
【図６】図１に示す補償光学系の第１の実施の形態の構成例である。
【図７】図６に示す液晶パネルに印加する電圧と屈折率との関係を示す図である。
【図８】図１に示す補償光学系の第２の実施の形態の構成例である。
【図９】図８に示す液晶パネルに印加する電圧と屈折率との関係を示す図である。
【図１０】図１に示す補償光学系の第３の実施の形態の構成例である。
【図１１】図１に示す補償光学系の第４の実施の形態の構成例である。
【図１２】図１に示す補償光学系の第５の実施の形態の構成例である。
【図１３】図１に示す補償光学系の第６の実施の形態の構成例である。
【図１４】図１に示す補償光学系の第７の実施の形態の構成例である。
【図１５】図１に示す補償光学系の第８の実施の形態の構成例である。
【図１６】図１５に示す補償光学系に印加する電圧とスキューとの関係を示す図である。
【図１７】従来におけるコマ収差の補正方法の一例を示す図である。
【符号の説明】
１……光ディスク，２……光ピックアップ部，２ａ……光源部，２ｂ……レンズ，２ｃ……ビームスプリッタ，２ｄ……補償光学系，２ｅ……対物レンズ，２ｆ……レンズ，２ｇ……光検出部，２ｈ……温度検出部，３……制御部，４……スキュー検出部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc apparatus, and more particularly to an optical disc apparatus that records light on or from a recording layer of an optical disc by focusing a light beam emitted from a light source at a predetermined position on the optical disc by an objective lens.
[0002]
[Prior art]
In recent years, the recording density of optical disks represented by CD (Compact Disk) and DVD (Digital Versatile Disk) has been increased.
[0003]
For example, in a DVD, data of 5 Gbytes (about 8 times that of a CD) can be recorded on a 12 cm disk that is the same as a CD.
As described above, in order to improve the recording density of the optical disc, the wavelength of the light beam applied to the optical disc in order to read / write data is shortened, and the numerical aperture of the objective lens for condensing the light beam on the optical disc It is necessary to increase NA (Numeric Apature).
[0004]
[Problems to be solved by the invention]
By the way, when the wavelength of the light beam is shortened or the numerical aperture NA is increased, if the optical disk has a skew, wavefront aberration (mainly coma aberration) occurs, and the accuracy of reading and writing information is improved. There was a case of decline.
[0005]
Therefore, conventionally, in order to solve such a problem, for example, as shown in FIG. 17, two transparent substrates having a concave surface and a convex surface are perpendicular to the optical axis and corrected. A method of correcting coma aberration by arranging a shift S in a direction parallel to a desired disk skew and controlling the shift S appropriately has been proposed.
[0006]
However, in such a method, an actuator for controlling the deviation S between the two transparent substrates is required, so that a mechanical operation part is generated, resulting in an increase in failure and a shortened life. There was a problem of fear.
[0007]
On the other hand, there has been proposed a method for correcting coma aberration by enclosing liquid crystal between two transparent substrates formed with a plurality of transparent electrodes and applying a voltage having a different phase to each transparent electrode. Yes.
[0008]
However, since the coma generated by the disk skew has a spatially continuous phase distribution, the coma having such characteristics cannot be completely corrected by the discrete phase distribution.
[0009]
The present invention has been made in view of the above points, and provides an optical disc apparatus capable of reliably compensating for a disc skew by adding a simple apparatus.
[0010]
[Means for Solving the Problems]
  In the present invention, in order to solve the above-mentioned problem, in an optical disc apparatus that focuses a light beam emitted from a light source at a predetermined position on an optical disc by an objective lens and records or reproduces information on a recording layer of the optical disc. Two transparent members having a concave surface or a convex surface arranged with a center shifted by a predetermined distance between the light source and the objective lens, a liquid crystal provided so as to contact the concave surface or the convex surface, A compensation optical system comprising a transparent electrode for applying a voltage to the liquid crystal, a skew detection unit for detecting the skew of the optical disc, and the compensation optical system according to the skew detected by the skew detection unit A voltage applying unit that applies a predetermined voltage to theThe adaptive optical system includes a first liquid crystal panel formed by enclosing a liquid crystal between a pair of transparent members in which one of the opposing surfaces is a flat surface and the other is a concave surface, and one of the opposing surfaces is a flat surface. And a second liquid crystal panel formed by enclosing a liquid crystal between a pair of transparent members, the other of which is a convex surface. The center of the second liquid crystal panel is shifted by a predetermined distance.An optical disc device is provided.
[0011]
  Here, the compensation optical system is provided between the light source and the objective lens so as to come into contact with the concave surface or the convex surface, and two transparent members having concave surfaces or convex surfaces arranged with the center shifted by a predetermined distance. The skew detection unit detects a skew of the optical disk. The skew detection unit includes a liquid crystal and a transparent electrode that applies a voltage to the liquid crystal. The voltage application unit applies a predetermined voltage to the adaptive optics system according to the skew detected by the skew detection unit.Further, the adaptive optics system includes a first liquid crystal panel formed by enclosing a liquid crystal between a pair of transparent members in which one of the opposing surfaces is a flat surface and the other is a concave surface, and one of the opposing surfaces is a flat surface. A second liquid crystal panel formed by enclosing a liquid crystal between a pair of transparent members having a convex surface on the other side is arranged with its center shifted by a predetermined distance.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration example of an embodiment of the present invention.
[0013]
In this figure, an optical disk 1 is, for example, a CD or a DVD, and records information by physically changing a recording layer arranged in a disk-shaped transparent substrate.
[0014]
The optical pickup unit 2 includes a light source unit 2a, a lens 2b, a beam splitter 2c, a compensation optical system 2d, an objective lens 2e, a lens 2f, a light detection unit 2g, and a temperature detection unit 2h. In accordance with the control 3, the optical beam 1 is irradiated with a light beam to read / write information.
[0015]
Here, the light source part 2a is comprised by the laser diode etc., for example, and inject | emits the coherent light of a single wavelength.
The lens 2b converts the light beam emitted from the light source unit 2a into parallel rays and enters the beam splitter 2c.
[0016]
The beam splitter 2c transmits the light emitted from the lens 2b so as to enter the compensation optical system 2d, and reflects the light beam reflected from the optical disc 1 in a substantially right angle direction so as to enter the lens 2f.
[0017]
As will be described later, the compensation optical system 2d compensates for coma aberration and the like caused by the skew of the optical disc 1.
The objective lens 2e focuses the light beam emitted from the adaptive optics system 2d on a predetermined area of the optical disc 1.
[0018]
The lens 2f condenses the light beam reflected by the optical disc 1 and whose traveling direction is changed by the beam splitter 2c on the detection surface of the light detection unit 2g.
The light detection unit 2g is configured by, for example, a photodiode, and converts the light collected by the lens 2f into a corresponding electric signal.
[0019]
The temperature detector 2h detects the temperature of the liquid crystal (details will be described later) of the adaptive optics 2d and notifies the controller 3 of the temperature.
The control unit 3 includes a microcomputer and controls the optical pickup unit 2 and each unit of the apparatus.
[0020]
The skew detection unit 4 is disposed in the vicinity of the objective lens 2e, detects the skew of the optical disc 1 in the vicinity of the light beam irradiation, and notifies the control unit 3 of the skew.
Next, coma aberration generated by the skew of the optical disk 1 will be described before the details of the adaptive optics system 2d.
[0021]
The light beam applied to the optical disc 1 through the objective lens 2e passes through the substrate of the optical disc 1 and is focused on the recording layer. At this time, if there is a skew in the optical disc 1, the light beam Spatial phase distribution, that is, wavefront aberration occurs. This wavefront aberration is dominated by the third-order coma aberration. When this coma aberration is expressed by coordinates (x, y) normalized by the pupil radius of the objective lens 2e, the following expression (1) is obtained.
[0022]
[Expression 1]

Here, W31 is a third-order coma aberration coefficient normalized by the wavelength λ of the laser light, and can be expressed by the following equation (2).
[0023]
[Expression 2]

Here, NA is the numerical aperture of the objective lens 2e, n and t are the refractive index and thickness of the transparent substrate of the optical disc 1, and θ is the skew angle of the optical disc 1, respectively.
[0024]
Therefore, by providing the light beam before entering the optical disk 1 with a phase distribution −W (x, y) for compensating for the phase distribution W (x, y) due to coma generated by the disk substrate. It is possible to suppress the occurrence of the above-mentioned coma aberration and the like.
[0025]
In the embodiment of the present invention, a predetermined voltage is applied to a liquid crystal panel in which liquid crystal is sandwiched by a transparent member having a concave surface or a convex surface shape to change the refractive index of the liquid crystal, thereby changing the liquid crystal panel according to the skew angle. The light beam has a predetermined phase distribution.
[0026]
First, a change in the phase distribution of a light beam when a voltage is applied to a liquid crystal panel having a transparent transparent member will be described.
FIG. 2 is a cross-sectional view showing a cross section of a liquid crystal panel in which the surface of the transparent member has a planar shape. As shown in this figure, the liquid crystal panel 10 includes transparent members 10a and 10b, transparent electrodes 10c and 10d, alignment films 10e and 10f, and a liquid crystal 10g.
[0027]
On one side of the transparent members 10a and 10b, for example, ITO (Indium Thin Oxide) or the like is deposited to form transparent electrodes 10c and 10d. The alignment films 10e and 10f are for specifying the molecular direction of the liquid crystal. The liquid crystal 10g is, for example, a bend type nematic liquid crystal.
[0028]
When a voltage is applied to the transparent electrodes 10c and 10d of the liquid crystal panel 10, a change occurs in the direction of the liquid crystal 10g, and as a result, the refractive index changes. For example, the above-described bend type nematic liquid crystal exhibits birefringence and has a refractive index (n_LC) Varies depending on the applied voltage, so that n is applied to the linearly polarized light beam along the alignment direction._LCA phase of xd (d: thickness of liquid crystal) can be given.
[0029]
FIG. 3 shows applied voltage and refractive index change Δn._LCIt is a figure which shows the relationship. As shown in this figure, when the applied voltage rises and exceeds a predetermined threshold, the refractive index change starts to increase, and stops when it reaches a certain voltage. In general, the maximum change in refractive index is about 0.15 to 0.2.
[0030]
The voltage applied to the liquid crystal is an alternating voltage of about several kHz, and the voltage value represents its effective value.
In the present invention, the above-described properties of the liquid crystal panel are utilized to give a desired phase distribution (−W (x, y)) to the light beam, thereby preventing the occurrence of coma and the like.
[0031]
FIG. 4 is a diagram showing an example of a liquid crystal panel used in the adaptive optics system 2d of the present embodiment. In this figure, FIG. 4A shows a liquid crystal panel 20 in which the transparent member has a convex shape. In the liquid crystal panel 20, the transparent member 20a has a convex shape, and other configurations are the same as those in FIG. FIG. 5 is a view showing the surface shape of the transparent member 20a shown in FIG. As shown in this figure, the transparent member 20a has a curved surface proportional to the fourth power of the distance from the center. Here, r is a distance from the center, and a is a proportionality constant.
[0032]
FIG. 4B shows a liquid crystal panel 30 in which the transparent member has a concave shape. In the liquid crystal panel 30, the transparent member 30b has a concave shape, and the other configuration is the same as that in the case of FIG. The transparent member 30b also has a surface shape as shown in FIG. 5 as in the case of FIG.
[0033]
The phase distribution given to the light beams transmitted through these liquid crystal panels 20 and 30 can be expressed by the following equations (3) and (4), respectively.
[0034]
[Equation 3]

[0035]
[Expression 4]

Where n_gIs the refractive index of the transparent substrate. As can be seen from these equations, the liquid crystal panels 20 and 30 can give the light beam a phase distribution proportional to the fourth power of the distance in the radial direction and the difference in refractive index between the liquid crystal and the transparent substrate. .
[0036]
Here, considering the (x, y) coordinates centered on the optical axis, these two liquid crystal panels are juxtaposed so as to have a deviation S in the x direction from the optical axis, as shown in FIG. At this time, the phase distribution given to the light beam transmitted through each liquid crystal panel can be expressed by the following equations (5) and (6), respectively.
[0037]
[Equation 5]

[0038]
[Formula 6]

Next, the phase distribution W12 given to the light beam passing through both of these two liquid crystal panels 20 and 30 is given by the sum of W1 and W2, and can be expressed by the following equation (7).
[0039]
[Expression 7]

Here, the first term in {} on the right side is equivalent to the equation of coma aberration that occurs when the optical disc 1 is tilted in the x direction shown in Equation (1) if an appropriate coefficient is selected. Further, since the second term is a linear function with respect to x, the light transmitted through these two liquid crystal panels 20 and 30 is displaced in the x direction (the light spot on the optical disc 1 in the x direction). Misalignment). However, since this deviation is corrected by a tracking servo or a PLL (Phase Locked Loop) circuit, it does not become an obstacle when reading and writing information.
[0040]
Therefore, by appropriately setting the coefficient of W12 shown in Expression (7), it is possible to correct the coma aberration generated by the skew of the optical disc 1 shown in Expression (2).
[0041]
Here, the coefficient included in Expression (7) is a constant a relating to the surface shape of the transparent member, a deviation S in the x direction of the liquid crystal panel, and a difference in refractive index between the liquid crystal and the transparent member. In this embodiment, the deviation S is fixed, and the refractive index n of the liquid crystal_LCIs controlled by the applied voltage, thereby arbitrarily changing the value of W12 to correct any coma.
[0042]
From the equations (1) and (7), when the condition for correcting the coma aberration caused by the skew of the optical disk 1 by these two liquid crystal panels 20 and 30 is obtained, it can be expressed by the following equation (8). it can.
[0043]
[Equation 8]

Where r_objIs the pupil radius of the objective lens 2e, and λ is the wavelength of the light beam.
[0044]
By controlling the voltage applied to the liquid crystal so as to satisfy the above formula (8), the occurrence of coma aberration due to the skew of the optical disc 1 can be corrected.
Next, a method for setting and driving each coefficient of the liquid crystal panels 20 and 30 will be described.
[0045]
First, as shown in FIG. 7, the refractive index of the transparent member of the liquid crystal panels 20 and 30 and the refractive index of the liquid crystal are set so that the refractive index of the transparent member falls within the change range of the refractive index of the liquid crystal. That is, n <n_g<N and n so as to satisfy the relationship of (n + 0.2)_gSelect.
[0046]
When there is no skew in the optical disc 1, correction by the liquid crystal panels 20 and 30 is unnecessary, and in this case, n_LC= N_gA voltage V0 (see FIG. 7) is applied to the liquid crystal panels 20 and 30, respectively.
[0047]
For the skew, a voltage V1 (see FIG. 7) is calculated such that the difference in refractive index between the liquid crystal and the transparent member satisfies the relationship of the equation (8), and the liquid crystal panels 20 and 30 are compared. Apply.
[0048]
Further, for the skew in the direction opposite to that described above, a voltage V2 (see FIG. 7) that similarly satisfies the relationship of Expression (8) is calculated and applied to the liquid crystal panels 20 and 30. .
[0049]
According to the method as described above, it is possible to correct coma generated by the skew of the optical disc 1.
Next, the operation of the adaptive optics system 2d having the liquid crystal panels 20 and 30 described above will be described. The liquid crystal panels 20 and 30 are incorporated in the adaptive optics system 2d shown in FIG. 1, and are arranged side by side with a deviation S along the skew direction of the optical disc 1. The temperature detection unit 2h detects the temperature of the liquid crystal 20g or 30g of the liquid crystal panel 20 or the liquid crystal panel 30 (or a temperature in the vicinity thereof).
[0050]
Now, in the embodiment shown in FIG. 1, if the optical disc 1 is mounted and reproduction or recording is started, the optical disc 1 is rotated at a predetermined angular velocity by a spindle motor (not shown). At this time, the skew detection unit 4 detects a skew in the vicinity of the optical beam 1 irradiated with the light beam, and notifies the control unit 3 of the skew angle.
[0051]
The control unit 3 acquires a control voltage Vc corresponding to the skew angle notified from the skew detection unit 4 from a memory table (a table in which the skew angle and the control voltage are associated with each other) (not shown) and the like. This is supplied to the optical system 2d. At this time, the control unit 3 refers to the temperature of the liquid crystal supplied from the temperature detection unit 2h and appropriately calibrates the control voltage. This calibration method is performed by referring to a table or the like that stores the temperature of the liquid crystal and the calibration value of the control voltage in association with each other.
[0052]
As a result, Vc is supplied to the liquid crystal panels 20 and 30 shown in FIG. 6, and the refractive index changes as the liquid crystal changes the orientation direction accordingly. As a result, the light beams transmitted through these liquid crystal panels 20 and 30 have a phase distribution that satisfies the equation (8).
[0053]
When the light beam having such a phase distribution is condensed on the recording layer of the optical disc 1, even when the optical disc 1 has a skew, no coma is generated and a stable light spot is always formed. .
[0054]
This light spot is reflected according to the physical state of the recording layer (for example, unevenness of the recording layer), and is detected through the objective lens 2e, the compensation optical system 2d, the beam splitter 2c, and the lens 2f. The light enters the portion 2g and is converted into an electric signal corresponding to the information recorded on the recording layer.
[0055]
As a result, even when the optical disc 1 has a skew, the occurrence of coma aberration can be prevented, so that information recorded on the recording layer can be accurately reproduced and the recording layer can be reproduced. Even when information is recorded, it is possible to reliably record the information.
[0056]
Next, a second embodiment of the adaptive optics system 2d will be described.
FIG. 8 is a diagram illustrating a configuration example of the second embodiment of the adaptive optics system 2d. In the second embodiment, two liquid crystal panels 30 having a concave shape are juxtaposed so as to have a deviation S in a direction perpendicular to the optical axis.
[0057]
As can be inferred from the contents described above, it can be said that the liquid crystal panel 20 is a liquid crystal panel 30 having negative characteristics. Therefore, it is possible to achieve the same effect as described above by arranging two identical liquid crystal panels side by side and individually setting the voltage applied to each liquid crystal panel.
[0058]
In the example shown in FIG. 8, two liquid crystal panels 30 having a concave shape are juxtaposed, but it goes without saying that the liquid crystal panel 20 having a convex shape may be used.
[0059]
Next, the driving method of the above embodiment will be described.
In the embodiment shown in FIG. 8, as shown in FIG. 9, when there is no skew in the optical disk 1, the voltage V <b> 0 at which the refractive indexes of the liquid crystal and the transparent member are equal is applied to the two liquid crystal panels 30. To do.
[0060]
With respect to the skew, the voltage V1 (see FIG. 9) in which the refractive index of the liquid crystal and the transparent member satisfies the relationship shown in the equation (8) is applied to one liquid crystal panel, and the refractive index given by V1. What is necessary is just to apply the voltage V2 (refer FIG. 9) which gives the refractive index difference of the same amount different sign with respect to the other liquid crystal panel.
[0061]
Even in such an embodiment, as in the case described above, even when the optical disc 1 has a skew, it is possible to prevent the occurrence of coma aberration, so that information recorded on the optical disc 1 can be accurately reproduced. In addition, information can be reliably recorded on the optical disc 1.
[0062]
In such an embodiment, since two liquid crystal panels of the same type are used, it is possible to reduce the types of parts to be used, and as a result, the cost of the apparatus can be reduced. Become.
[0063]
Next, a third embodiment of the adaptive optics system 2d will be described with reference to FIG.
FIG. 10 is a diagram illustrating a configuration example of the third embodiment of the adaptive optical system 2d. In this figure, a transparent member 40a having a convex shape and a transparent member 40b having a concave shape are juxtaposed with a shift S, and a liquid crystal 40c is sealed therebetween.
[0064]
In this embodiment, the functions realized by two liquid crystal panels in the embodiment shown in FIG. 4 are integrated into one liquid crystal panel. Therefore, the phase distribution generated by this liquid crystal panel can be expressed by the following equation (7). Further, the driving method is the same as in FIG.
[0065]
According to the above embodiment, it is possible not only to prevent the occurrence of coma aberration as in the embodiment shown in FIG. 4, but also to reduce the number of parts compared to the case of FIG. The manufacturing cost of the apparatus can be reduced.
[0066]
Next, a fourth embodiment of the adaptive optics system 2d will be described with reference to FIG.
FIG. 11 is a diagram illustrating a configuration example of the fourth embodiment of the adaptive optics system 2d. In this figure, a transparent member having a convex shape and a transparent member having a concave shape are formed as one member 50c, and transparent members 50a and 50b are disposed above and below the transparent member 50c, and between the transparent members. Liquid crystals 50d and 50e are enclosed.
[0067]
In this embodiment, as compared with the case of FIG. 4, only one transparent member is reduced, and the phase distribution generated by the liquid crystal panel 50 and the driving method are the same as in FIG. .
[0068]
According to the above embodiment, not only the occurrence of coma aberration can be prevented in the same way as the embodiment shown in FIG. 4, but also the number of parts is reduced compared with the case of FIG. Therefore, the manufacturing cost of the device can be reduced.
[0069]
Next, a fifth embodiment of the adaptive optics system 2d will be described with reference to FIG.
FIG. 12 is a diagram illustrating a configuration example of the fifth embodiment of the adaptive optical system 2d. In this figure, a transparent member 60a having a convex shape and a transparent member 60b having a concave shape are juxtaposed with a shift S, and a transparent member 60c is disposed between them, and a liquid crystal 60d, 60e is enclosed.
[0070]
This embodiment is basically the same as that of FIG. 4, the phase distribution generated by the liquid crystal panel 60 is the same as that of FIG. 4, and the driving method is also the same as that of FIG.
[0071]
According to the above embodiment, not only can the coma aberration be prevented as in the embodiment shown in FIG. 4, but also the number of parts is reduced compared with the case of FIG. Therefore, the manufacturing cost of the device can be reduced.
[0072]
Next, a sixth embodiment of the adaptive optics system 2d will be described with reference to FIG.
FIG. 13 is a diagram illustrating a configuration example of the sixth embodiment of the adaptive optical system 2d. In this figure, a transparent member 70c having a concave shape formed with a deviation S on both surfaces is disposed between the transparent members 70a and 70b, and liquid crystals 70d and 70e are sealed between the transparent members 70a and 70b. Yes. In addition, you may make it the transparent member 70c form a convex surface shape instead of a concave surface shape.
[0073]
This embodiment is basically a method in which the embodiment shown in FIG. 8 and the embodiment shown in FIG. 11 are mixed, and the driving method is the same as in the case of FIG.
According to the above embodiment, not only can the occurrence of coma aberration be prevented as in the embodiment shown in FIG. 4, but also the number of components is reduced compared with the case of FIG. Therefore, the manufacturing cost of the device can be reduced.
[0074]
Next, a seventh embodiment of the adaptive optics system 2d will be described with reference to FIG.
FIG. 14 is a diagram illustrating a configuration example of the seventh embodiment of the adaptive optics system 2d. In this figure, the transparent members 80a and 80b having a concave shape are disposed so as to have a deviation S, and a transparent member 80c having a planar shape on both surfaces is disposed therebetween. Liquid crystals 80d and 80e are sealed between the transparent members 80a to 80c. The transparent members 80a and 80b may form a convex shape instead of the concave shape.
[0075]
This embodiment is basically a method in which the embodiment shown in FIG. 8 and the embodiment shown in FIG. 12 are mixed, and the driving method is the same as in the case of FIG. According to the above embodiment, not only can the occurrence of coma aberration be prevented as in the embodiment shown in FIG. 4, but also the number of components is reduced compared with the case of FIG. Therefore, the manufacturing cost of the device can be reduced.
[0076]
FIG. 15 is a diagram illustrating a configuration example of the eighth embodiment of the adaptive optical system 2d. In this embodiment, the same liquid crystal panels 90 and 100 as those shown in FIG. 10 are juxtaposed. In the panel 90, a transparent member 90a having a convex surface shape and a transparent member 90b having a concave surface shape are juxtaposed with a deviation S, and a liquid crystal 90c is sealed therebetween. Similarly, in the panel 100, the transparent member 100a having a convex shape and the transparent member 100b having a concave shape are arranged side by side with a deviation S, and a liquid crystal 100c is sealed therebetween. In addition, the displacement directions of the liquid crystal panels are set to be alternate.
[0077]
In the above example, the same liquid crystal panel as that shown in FIG. 10 is used, but any of the liquid crystal panels shown in the first to seventh embodiments may be selected.
In this embodiment, the phase distribution given to the light beam by the liquid crystal panel 90 and the liquid crystal panel 100 has an equal amount of different signs, so that the phase distribution generated by the liquid crystal panel 100 is canceled by the liquid crystal panel 90. become. Therefore, the phase distribution when no voltage is applied is “0”. Further, the coma aberration can be prevented from occurring by applying a voltage to one of the liquid crystal panels according to the skew of the optical disc 1 with one liquid crystal panel for the positive direction and the other for the negative direction. it can.
[0078]
The refractive index of the liquid crystal sealed in the liquid crystal panel to which the voltage is applied is n_LC1And the refractive index of the liquid crystal when the applied voltage is 0 V is n_LC0Then, the phase distribution of the light beam transmitted through these two liquid crystal panels can be expressed by the following equation (9).
[0079]
[Equation 9]

As can be seen from this equation, the term (n) relating to the transmittance of the transparent member is obtained from the phase distribution of the light beams transmitted through the liquid crystal panels 90 and 100._g) Is deleted, the setting of the refractive index of the transparent member and the liquid crystal can be simplified.
[0080]
FIG. 16 is a diagram illustrating a method for driving the liquid crystal panels 90 and 100. As shown in this figure, in the embodiment shown in FIG. 15, the skew in the + direction (for example, the skew in which the surface of the optical disc 1 in FIG. 1 is tilted clockwise from the horizontal plane) is relative to the liquid crystal panel 90. A voltage Vs is applied, and a negative skew (a skew in which the surface of the optical disk 1 is tilted counterclockwise from the horizontal plane) is applied by applying the voltage Vs to the liquid crystal panel 100. To do. Therefore, it is only necessary to apply a voltage corresponding to the skew, so that the driving method can be simplified. Further, when there is no skew, it is not necessary to apply a voltage, so that power consumption can be reduced.
[0081]
According to the above embodiment, it is possible not only to prevent the occurrence of coma aberration as in the embodiment shown in FIG. 4, but also to simplify the driving method and reduce the power consumption. . Further, since it is not necessary to set the refractive indexes of the liquid crystal panel and the transparent member, the design can be simplified.
[0082]
【The invention's effect】
  As described above, in the present invention, a light beam emitted from a light source is condensed at a predetermined position on the optical disk by an objective lens, and information is recorded on or reproduced from a recording layer of the optical disk. Two transparent members having a concave surface or a convex surface, the center of which is shifted by a predetermined distance between the objective lenses, a liquid crystal provided in contact with the concave surface or the convex surface, and applying a voltage to the liquid crystal A compensation optical system comprising a transparent electrode, a skew detection unit for detecting the skew of the optical disc, and a voltage for applying a predetermined voltage to the compensation optical system according to the skew detected by the skew detection unit With application sectionThe adaptive optical system includes a first liquid crystal panel formed by enclosing liquid crystal between a pair of transparent members in which one of the opposing surfaces is a flat surface and the other is a concave surface, and one of the opposing surfaces is a flat surface. A second liquid crystal panel formed by enclosing liquid crystal between a pair of transparent members having a convex surface on the other side is arranged with its center shifted by a predetermined distance.Thus, even when the optical disc has a skew, information can be accurately recorded or reproduced.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of an embodiment of the present invention.
FIG. 2 is a diagram illustrating a configuration example of a general liquid crystal panel.
3 is a diagram showing a relationship between an applied voltage of the liquid crystal panel shown in FIG. 2 and a change in refractive index.
4A is an example of a liquid crystal panel in which the transparent member used in the adaptive optics system shown in FIG. 1 has a convex shape, and FIG. 4B shows the same case where the transparent member has a concave shape. It is an example of the liquid crystal panel which has.
5 is a diagram showing a concave surface or a shape of a convex surface shown in FIG. 4. FIG.
FIG. 6 is a configuration example of the first embodiment of the adaptive optics system shown in FIG. 1;
7 is a diagram showing a relationship between a voltage applied to the liquid crystal panel shown in FIG. 6 and a refractive index.
8 is a configuration example of a second embodiment of the adaptive optics system shown in FIG. 1;
9 is a diagram showing a relationship between a voltage applied to the liquid crystal panel shown in FIG. 8 and a refractive index.
10 is a configuration example of a third embodiment of the adaptive optics system shown in FIG. 1; FIG.
FIG. 11 is a configuration example of the fourth embodiment of the adaptive optics system shown in FIG. 1;
12 is a configuration example of a fifth embodiment of the adaptive optics system shown in FIG. 1; FIG.
13 is a configuration example of a sixth embodiment of the adaptive optics system shown in FIG.
FIG. 14 is a configuration example of a seventh embodiment of the adaptive optics system shown in FIG. 1;
FIG. 15 is a configuration example of an eighth embodiment of the adaptive optics system shown in FIG. 1;
16 is a diagram showing a relationship between a voltage applied to the adaptive optics system shown in FIG. 15 and a skew.
FIG. 17 is a diagram illustrating an example of a conventional coma aberration correction method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Optical disk, 2 ... Optical pick-up part, 2a ... Light source part, 2b ... Lens, 2c ... Beam splitter, 2d ... Compensation optical system, 2e ... Objective lens, 2f ... Lens, 2g ... Light detection unit, 2h ... Temperature detection unit, 3 ... Control unit, 4 ... Skew detection unit

Claims (9)

In an optical disc apparatus that focuses a light beam emitted from a light source at a predetermined position on an optical disc by an objective lens and records or reproduces information on a recording layer of the optical disc.
Two transparent members having a concave surface or a convex surface disposed with a center shifted by a predetermined distance between the light source and the objective lens, a liquid crystal provided so as to contact the concave surface or the convex surface, and the liquid crystal An adaptive optics system comprising a transparent electrode for applying a voltage to
A skew detector for detecting skew of the optical disc;
A voltage application unit that applies a predetermined voltage to the adaptive optics system according to the skew detected by the skew detection unit;
I have a,
The compensation optical system includes a first liquid crystal panel formed by enclosing a liquid crystal between a pair of transparent members, one of the opposing surfaces being a flat surface and the other being a concave surface, and one of the opposing surfaces being a flat surface. optical disc and the other is characterized that you have formed by arranging a is a set of the second liquid crystal panel in which liquid crystal is formed is sealed between the transparent member is shifted its center by a predetermined distance convex apparatus.   2. The optical disk apparatus according to claim 1, wherein the voltage application unit applies the same voltage to the transparent electrodes formed on the opposing surfaces of the first and second liquid crystal panels.   3. The optical disk device according to claim 2, wherein one transparent member of the first liquid crystal panel and one transparent member of the second liquid crystal panel are formed of one transparent member.   In an optical disc apparatus that focuses a light beam emitted from a light source at a predetermined position on an optical disc by an objective lens and records or reproduces information on a recording layer of the optical disc.
  Two transparent members having a concave surface or a convex surface disposed with a center shifted by a predetermined distance between the light source and the objective lens, a liquid crystal provided so as to contact the concave surface or the convex surface, and the liquid crystal An adaptive optics system comprising a transparent electrode for applying a voltage to
  A skew detector for detecting skew of the optical disc;
  A voltage application unit that applies a predetermined voltage to the adaptive optics system according to the skew detected by the skew detection unit;
  Have
  The compensation optical system includes a first liquid crystal panel formed by enclosing liquid crystal between a pair of transparent members, one of the opposing surfaces being a flat surface and the other being a concave surface or a convex surface, and one of the opposing surfaces being a flat surface. And a second liquid crystal panel formed by enclosing a liquid crystal between a pair of transparent members having the same shape as the first liquid crystal panel, and the center thereof being shifted by a predetermined distance. An optical disc apparatus characterized by being configured. Before SL voltage application unit, each optical disc apparatus according to claim 4, wherein applying different respective voltages to the transparent electrodes formed on the opposing surfaces of the first and second liquid crystal panels.   6. The optical disc apparatus according to claim 5, wherein one transparent member of the first liquid crystal panel and one transparent member of the second liquid crystal panel are constituted by one transparent member. In an optical disc apparatus that focuses a light beam emitted from a light source at a predetermined position on an optical disc by an objective lens and records or reproduces information on a recording layer of the optical disc.
Two transparent members having a concave surface or a convex surface disposed with a center shifted by a predetermined distance between the light source and the objective lens, a liquid crystal provided so as to contact the concave surface or the convex surface, and the liquid crystal An adaptive optics system comprising a transparent electrode for applying a voltage to
A skew detector for detecting skew of the optical disc;
Depending on the skew detected by the skew detecting unit, and a voltage applying unit for applying a Jo Tokoro voltage to the compensation optical system,
Have
The adaptive optics system includes a liquid crystal panel in which a pair of transparent members, one of which is a concave surface and the other is a convex surface, are arranged with their centers shifted from each other by a predetermined distance, and liquid crystal is sealed therebetween. optical disc device you characterized in that it is configured. In an optical disc apparatus that focuses a light beam emitted from a light source at a predetermined position on an optical disc by an objective lens and records or reproduces information on a recording layer of the optical disc.
Two transparent members having a concave surface or a convex surface disposed with a center shifted by a predetermined distance between the light source and the objective lens, a liquid crystal provided so as to contact the concave surface or the convex surface, and the liquid crystal An adaptive optics system comprising a transparent electrode for applying a voltage to
A skew detector for detecting skew of the optical disc;
A voltage application unit that applies a predetermined voltage to the adaptive optics system according to the skew detected by the skew detection unit;
A second adaptive optics system ;
Has, the voltage applying unit, the adaptive optics system and a voltage is selectively optical disc apparatus you and applying a to the second adaptive optics. A temperature detector for detecting the temperature of the liquid crystal or the vicinity thereof;
The optical disk apparatus according to any one of claims 1 to 8, further comprising a calibration unit for calibrating the detected temperature voltage by the voltage applying unit applies by the temperature detecting unit.

Images