JP3594811B2 - Liquid crystal panel, optical pickup and information reproducing device - Google Patents

Description

ここで、式（２）中のＷ_０はＷ（ｒ，φ）の瞳面上の平均値である。このＷｒｍｓは、波面収差の評価に用いられ、Ｗｒｍｓを小さくすれば波面収差の影響が少なく良好な再生を行うことができる。
【００８８】
ところで、式（２）から明らかなように、波面収差を補償するにはＷ（ｒ，φ）を小さくすればよい。そこで、ＤＶＤ５がそのラジアル方向に傾いたことにより発生したＷｔｌｔ（ｒ，φ）を補償するために、液晶パネル１０の透明電極１０ｃにおける各パターン電極に印加される駆動信号Ｓｄｖ１の電圧を制御して、あるパターン電極に対応する液晶１０ｇの領域の屈折率をΔｎだけ変化させたとすると、この屈折率の変化により当該パターン電極に対応する領域を通過する光ビームＢに対して光路差Δｎ×ｄを与えることができる。
【００８９】
そして、液晶１０ｇで与えられる光路差をＷｌｃ（ｒ，φ）とすると、液晶パネル１０を配置したときの対物レンズ４の瞳面における波面収差Ｗ（ｒ，φ）は以下に示す式（３）で表される。
【００９０】
【数３】
Ｗ（ｒ，φ）＝Ｗｔｌｔ（ｒ，φ）＋Ｗｌｃ（ｒ，φ） …（３）
この式（３）から明らかなように、ＤＶＤ５のチルト角に起因する波面収差Ｗ（ｒ，φ）を打ち消すには、
【数４】
Ｗ（ｒ，φ）＝Ｗｔｌｔ（ｒ，φ）＋Ｗｌｃ（ｒ，φ）＝０ …（４）
とすれば良い。すなわち、液晶１０ｇによりＤＶＤ５のチルト角に起困する波面収差Ｗｔｌｔ（ｒ，φ）に対して逆極性の波面収差、つまり、
【数５】
Ｗｌｃ（ｒ，φ）＝−Ｗｔｌｔ（ｒ，φ） …（５）
となる波面収差Ｗｌｃ（ｒ，φ）を光ビームＢに与えればよいことがわかる。
【００９１】
従って、透明電極１０ｃの中心を対物レンズ４の光軸が通ると場合に、液晶１０ｇによりＤＶＤ５のチルト角に起因する波面収差Ｗｔｌｔ（ｒ，φ）に対して逆極性の波面収差Ｗｌｃ（ｒ，φ）を与えるためには、図５で示されたＤＶＤ５のラジアル方向のチルト角に起因する波面収差分布に対応して液晶１０ｇを分割するようにパターン電極を設け、各パターン電極に対応する領域への印加電圧を、チルト角に起因する波面収差に対して逆極性の波面収差を与えるように制御すればよい。
【００９２】
ここで、図５は、当該ラジアル方向の光軸の傾斜に起因して対物レンズ４の瞳面上に発生する波面収差分布の状態を示すものである。
【００９３】
より具体的には、図５は、ＤＶＤ５の記録面がラジアル方向に＋１°傾いた場合の光スポットの最良像点における波面収差分布を、入射する光ビームＢの最大領域の範囲内において表した図であり、当該波面収差分布を、波面収差の値が−２５ｎｍ〜＋２５ｎｍの範囲を有する領域Ａを中心として５０ｎｍの範囲幅を有する領域Ａ乃至Ｋの境界線によって表している。そして、図５中のＸ２−Ｘ２は、ＤＶＤ５の傾く方向に対応した軸（すなわち、ラジアル方向）である。
【００９４】
なお、図６において、当該波面収差分布をＸ２−Ｘ２軸上における分布特性で表している。
【００９５】
また、波面収差の分布自体はチルト角の大きさによらず一定の分布をしており、チルト角の大きさにより変化するのは波面収差量である。この点について図６を用いて説明すると、図６に示す曲線のピーク値はチルト角が大きくなれば高くなり、チルト角が小さくなれば低くなる。
【００９６】
本実施形態では、上述のようにして算出された透明電極１０ｃの中心を対物レンズ４の光軸が通るとき当該対物レンズ４の瞳面上に発生する波面収差の分布に着目して、実施形態の透明電極１０ｃの分割形状を、図５の波面収差分布に対して上述した（ｉ）乃至（ｉｖ）の方法により上記位置ずれを加味した形状とし、パターン電極に対応する領域の液晶１０ｇにより、位置ずれがあるときに生じている波面収差Ｗｔｌｔ（ｒ，φ）を打ち消すように光ビームＢに位相差（すなわち、上記光路差Δｎ×ｄ）を与えて、位置ずれがあるときのチルト角に起因する波面収差Ｗｔｌｔ（ｒ，φ）の影響を再生に影響のない範囲まで減少させているのである。
【００９７】
すなわち、液晶１０ｇの各分割領域（透明電極１０ｃ内の各パターン電極に対応する分割領域）毎に電圧制御を行うことで液晶分子Ｍの向きを変化させ、各分割領域の屈折率を変えることにより光ビームＢに位相差を与えてＤＶＤ５の傾斜時に発生する波面収差Ｗｔｌｔ（ｒ，φ）を補償するのである。
【００９８】
以上説明したように、図３（ａ）に示す透明電極１０ｃ内の各パターン電極は、ＤＶＤ５の記録面がラジアル方向に＋１°傾いた場合の波面収差分布（図５参照）及び位置ずれにより生じる波面収差分布に基づいてその形状が設定されたものであり、透明電極１０ｃは、波面収差を５つの値で近似した場合に対応する五つのパターン電極を有している。
【００９９】
なお、パターン電極３２に対応する領域は波面収差の値が０となる領域を含む領域であり、パターン電極３１ｂに対応する液晶１０ｇの領域とパターン電極３０ｂに対応する液晶１０ｇの領域は対称的な形状であり、透過する光ビームＢに与える位相差の値は逆極性となっている。
【０１００】
更に、パターン電極３０ａに対応する液晶１０ｇの領域とパターン電極３１ａに対応する液晶１０ｇの領域は対称的な形状であり、透過する光ビームＢに与える位相差の値は逆極性となっている。
【０１０１】
なお、液晶１０ｇの分割数（すなわち、上記パターン電極の数）を更に多くして液晶１０ｇを細分化すれば、完全にＤＶＤ５のチルト角に起因する波面収差を打ち消すことができるが、そのために、例えば液晶１０ｇを碁盤目状に分割することにより分割数を多くすると、一の当該区分領域毎に駆動信号を制御して印加する必要があり、そのためには、透明電極１０ｃを各区分領域に分割して作成しなければならず、透明電極１０ｃの作成及び引き出し線等の配線を作成するが困難となる。
【０１０２】
そこで、本実施形態の液晶パネル１０においては、透明電極１０ｃの分割形状を、先に示した図３（ａ）のように波面収差分布に類似した分割形状にすることにより、容易に作成可能であり、且つ当該波面収差を効率的に補償することができるように構成している。
【０１０３】
また、上述した図３乃至図６による説明では、ＤＶＤ５のラジアル方向に生じた波面収差を補償する場合について説明したが、ＤＶＤ５のタンジェンシャル方向に生じた波面収差を補償する場合については、上記位置ずれを考慮する必要がないため、透明電極１０ｄの各パターン電極の形状を、透明電極１０ｃの中心を対物レンズ４の光軸が通るとき当該対物レンズ４の瞳面上に発生する波面収差の分布を透明電極１０ｃ上に投影した形状と略同一の形状（図４中破線で示される形状）を９０°回転させた形状とすれば、タンジェンシャル方向の光軸の傾斜に起因する波面収差を透明電極１０ｄを使用して補償する場合に対応する。
【０１０４】
従って、透明電極１０ｄにおける各パターン電極４０ａ、４０ｂ、４１ａ、４１ｂ及び４２の形状についても、タンジェンシャル方向に平行な対称軸を対象とした波面収差分布（図５におけるＸ２−Ｘ２軸をタンジェンシャル方向とした場合の波面収差分布）に類似した形状とされている。
【０１０５】
次に、各透明電極１０ｃ及び１０ｄに対する駆動信号Ｓｄｖ１及びＳｄｖ２の印加による液晶１０ｇの駆動について、図７及び図８を用いて説明する。
【０１０６】
なお、以下の説明は、ＤＶＤ５のタンジェンシャル方向に生じている波面収差のみを補償するための実施形態を説明するものであり、ＤＶＤ５のラジアル方向の光軸の傾斜に起因する波面収差については無補償としている。すなわち、ラジアル方向のチルト角が０度であり、タンジェンシャル方向のチルト角のみがディスク上に存在している場合についての実施形態である。
【０１０７】
なお、以後の実施形態では、透明電極１０ｃ（ラジアル方向の波面収差を補償するための電圧を印加するための電極）に印加される駆動信号Ｓｄｖ１を基準として説明を行う。
【０１０８】
更に、図７は各透明電極１０ｃ及び１０ｄを構成するパターン電極に印加される駆動信号Ｓｄｖ１及びＳｄｖ２の波形を示すものであり、図８はタンジェンシャル方向のチルト角が変化した場合の各パターン電極に対する駆動信号Ｓｄｖ１及びＳｄｖ２の変化を示すものである。
【０１０９】
図７に示すように、タンジェンシャル方向の光軸の傾斜に起因する波面収差のみを補償する場合には、透明電極１０ｃにおける各パターン電極には、液晶１０ｇに与える電位差の基準を示すものとして、夫々のパターン電極に同一の駆動信号Ｓｄｖ１が印加される。すなわち、パターン電極３０ａ、３０ｂ、３１ａ、３１ｂ及び３２の夫々に図７最上段乃至上から三段目に示す波形の駆動信号Ｓｄｖ１が印加されるのである。この駆動信号Ｓｄｖ１は、ラジアル方向のチルト角が０度のときに透明電極１０ｃに印加される駆動信号に相当する。
【０１１０】
なお、図７最上段乃至上から三段目に示す駆動信号Ｓｄｖ１は、それが印加されたとき、液晶パネル１０を透過する光ビームの全領域に対して同一である基準の位相差を与え、光ビームの波面を変化させない、すなわち、ガラス板を光ビームが通過するのと同じ効果を有する位相差を与える駆動信号Ｓｄｖ１である。更に、ラジアル方向及びタンジェンシャル方向のチルト角が共に０度であるときは、透明電極１０ｃには上記の駆動信号Ｓｄｖ１が夫々のパターン電極毎に印加され、一方、透明電極１０ｄの全てのパターン電極は接地される。
【０１１１】
これに対して、タンジェンシャル方向の光軸の傾斜に起因する波面収差を補償するための透明電極１０ｄには、図７上から四段目及び最下段に示す波形の駆動信号Ｓｄｖ２が印加される。
【０１１２】
ここで、図７上から四段目及び最下段に示す駆動信号Ｓｄｖ２は、透明電極１０ｄにおけるパターン電極４０ａ及び４０ｂに対応する液晶１０ｇの領域ではチルト角に起因する波面収差を補償するために光ビームＢに与える位相差を減少させる必要があり、パターン電極４１ａ及び４１ｂに対応する液晶１０ｇの領域ではチルト角に起因する波面収差を補償するために光ビームＢに与える位相差を増加させる必要があるようなチルト角がタンジェンシャル方向に発生している場合に印加される駆動信号Ｓｄｖ２である。
【０１１３】
このとき、パターン電極４１ａ及び４１ｂに対応する液晶１０ｇの領域では光ビームＢに与える位相差を上記基準の位相差より大きくする必要があり、当該領域の液晶１０ｇに印加される電位差を大きくする必要がある。よって、図７上から四段目に示すように、パターン電極４１ａ及び４１ｂに対しては、上記駆動信号Ｓｄｖ１とは逆相の駆動信号Ｓｄｖ２が印加される。
【０１１４】
これに対して、パターン電極４０ａ及び４０ｂの領域では、光ビームＢに与える位相差を上記基準の位相差より小さくする必要があり、この領域の液晶１０ｇに印加される電位差を小さくする必要がある。よって、図７最下段に示すように、パターン電極４０ａ及び４０ｂに対しては、上記駆動信号Ｓｄｖ１と同相の駆動信号Ｓｄｖ２が印加される。
【０１１５】
このように、パターン電極４１ａ及び４１ｂに対して駆動信号Ｓｄｖ１と逆相の駆動信号Ｓｄｖ２が印加されると共に、パターン電極４０ａ及び４０ｂに対して駆動信号Ｓｄｖ１と同相の駆動信号Ｓｄｖ２が印加されることにより、液晶１０ｇに対して、波面収差を補償するのに必要な位相差を光ビームＢに与えるために必要な電位差が生じさせられるのである。
【０１１６】
一方、パターン電極４１ａ及び４１ｂ並びに４０ａ及び４０ｂに与える駆動信号Ｓｄｖ２の電圧は、後述するように、チルト検出信号Ｓｐ２に基づいてＣＰＵ２１において算出された液晶１０ｇにより光ビームＢに与えるべき位相差に対応して設定される。
【０１１７】
具体的には、チルト角が大きくなれば波面収差の補償に必要な位相差が大きくなるため、液晶１０ｇに印加される電位差を大きくする必要があり、駆動信号Ｓｄｖ２の振幅が大きくなる。逆にチルト角が小さくなれば、波面収差の補償に必要な位相差が小さくなり、液晶１０ｇにかかる電位差は小さくてよいので、駆動信号Ｓｄｖ２の振幅は小さくなる。ここで、夫々の振幅の最大値と最小値の差が液晶１０ｇにかかる電位差となる。
【０１１８】
なお、パターン電極４２については常に接地されている。これは、パターン電極４２の領域におけるチルト角に起因する波面収差量が小さく、補償する必要がないからである。
【０１１９】
次に、タンジェンシャル方向のチルト角が変化した場合に、透明電極１０ｄの各パターン電極に印加される駆動信号Ｓｄｖ２がどのように変化するかについて図８を用いて説明する。
【０１２０】
なお、図８は、タンジェンシャル方向のチルト角が零の場合（光ビームＢの光軸とＤＶＤ５の情報記録面とのタンジェンシャル方向のなす角度が直角である理想的な場合）と、チルト角が正負いずれかの方向に変化した場合とについて、夫々、透明電極１０ｃ又は１０ｄに含まれる各パターン電極に印加される駆動信号Ｓｄｖ１及び駆動信号Ｓｄｖ２の波形の変化（図８最上段乃至上から３段目）と、実際に液晶１０ｇのパターン電極４０ａ、４０ｂ、４１ａ及び４１ｂに対応する領域に加えられる電位差の変化（すなわち、各パターン電極に対応する領域を通過した光ビームＢに与えられる位相差の大きさの変化。図８上から４段目乃至最下段）を示したものである。また、図８における太い両矢印は、チルト角の変化（右が正、左が負、中央がチルト角零）を示している。
【０１２１】
ここで、チルト角の正負の定義については、パターン電極４０ａ及び４０ｂに対応する光スポットＳＰ内の領域に負の波面収差が生じるチルト角を正とし、逆にパターン電極４０ａ及び４０ｂに対応する光スポットＳＰ内の領域に正の波面収差が生じるチルト角を負とする。
【０１２２】
まず、チルト角が零の場合を見てみると、この場合には、パターン電極４０ａ、４０ｂ、４１ａ及び４１ｂには、いずれも駆動信号Ｓｄｖ２は印加されない。この結果、液晶１０ｇに印加される電圧は駆動信号Ｓｄｖ１によるものだけとなり、よって、液晶１０ｇに加えられる電位差も当該駆動信号Ｓｄｖ１に起因するものだけとなって通過する光ビームＢには光スポットＳＰ内の全ての領域に上記基準の位相差が与えられ、光ビームＢの波面が変化されることなく液晶パネル１０を透過してＤＶＤ５に到達する。
【０１２３】
次に、ＤＶＤ５の情報記録面が傾くことにより、チルト角が正の方向に増加したとすると、これを検出したチルト検出信号Ｓｐ２に基づいて、図８中最上段及び上から二段目の右側に夫々示すような波形の駆動信号Ｓｄｖ２がパターン電極４０ａ及び４０ｂ並び４１ａ及び４１ｂに印加される。
【０１２４】
すなわち、この場合には、透明電極１０ｄのパターン電極４０ａ及び４０ｂに対応する液晶１０ｇの領域では、波面収差をタンジェンシャル方向のチルト角に起因する波面収差分布に基づいて補償するために、上記基準の位相差よりも大きい位相差を与える必要がある。つまり、パターン電極４０ａ及び４０ｂに対応する液晶１０ｇの領域には基準の位相差を発生させる電位差より大きい電位差を印加する必要がある。よって、パターン電極４０ａ及び４０ｂには、図８上から二段目の右側に示すように、対向している透明電極１０ｃに印加されている駆動信号Ｓｄｖ１に対して逆相の駆動信号Ｓｄｖ２が印加される。
【０１２５】
一方、透明電極１０ｄのパターン電極４１ａ及び４１ｂに対応する液晶１０ｇの領域では、波面収差をタンジェンシャル方向のチルト角に起因する波面収差分布に基いて補償するために、上記基準の位相差よりも小さい位相差を与える必要がある。つまり、パターン電極４１ａ及び４１ｂに対応する液晶１０ｇの領域には、基準の位相差を発生させる電位差より小さい電位差を印加する必要がある。そこで、パターン電極４１ａ及び４１ｂには、図８最上段の右側に示すように、対向している透明電極１０ｃに印加されている駆動信号Ｓdv1に対して同相の駆動信号Ｓdv2が印加される。
【０１２６】
そして、この時でも、透明電極１０ｃにおける各パターン電極には共通的に図８中上から三段目に示される波形の駆動信号Ｓｄｖ１が印加されているので、結果として、液晶１０ｇのパターン電極４１ａ及び４１ｂに対応する領域に加えられる電位差は図８中上から四段目の右側に示すような小さな振幅を有するものとなり、一方、液晶１０ｇのパターン電極４０ａ及び４０ｂに対応する領域に加えられる電位差は図８中上から最下段の右側に示すような大きな振幅を有するものとなる。
【０１２７】
従って、液晶１０ｇによりパターン電極４１ａ及び４１ｂに対応する領域を通過した光ビームＢに与えられる位相差は小さくなり、また、パターン電極４０ａ及び４０ｂに対応する領域を通過した光ビームＢに与えられる位相差は大きくなる。これにより、正の方向に生じているチルト角による波面収差を補償すべき位相差が光ビームＢに与えられることとなる。
【０１２８】
なお、チルト角が負の方向に生じている場合については、上述の同様の理論により、パターン電極４０ａ及び４０ｂには、図８上から二段目の左側に示すように、対向している透明電極１０ｃに印加されている駆動信号Ｓｄｖ１に対して同相の駆動信号Ｓｄｖ２が印加される。また、パターン電極４１ａ及び４１ｂには、図８最上段の左側に示すように、対向している透明電極１０ｃに印加されている駆動信号Ｓｄｖ１に対して逆相の駆動信号Ｓｄｖ２が印加される。
【０１２９】
このように、ＤＶＤ５のタンジェンシャル方向のチルト角を検出したチルト検出信号Ｓｐ２に基づいて透明電極１０ｄにおける各電極パターンに印加される駆動信号Ｓｄｖ２の波形が変化し、これにより、光ビームＢに対して与えられる位相差が液晶１０ｇの領域によって異なるので、当該チルト角に起因する波面収差を打ち消してこれを補償することができる。
【０１３０】
次に、実施形態の液晶パネル１０を用いて波面収差を補償した場合の上記残留波面収差の程度とラジアル方向の位置ずれの程度との関係について、図９を用いて説明する。
【０１３１】
なお、図９は、透明電極１０ｃの中心軸と対物レンズ４の光軸との間でラジアル方向の位置ずれがある場合において、当該位置ずれの大きさと液晶パネル１０による補償後の残留波面収差の量との関係を実験的に求め、透明電極１０ｃに含まれる各パターン電極の形状の設定に際して当該位置ずれがないとして設定した場合（図９中、■印で示す。）、当該位置ずれが０．３ｍｍあるとして設定した場合（図９中、●印で示す。）及び当該位置ずれが０．５ｍｍであるとして設定した場合（図９中、▲印で示す。）の夫々についてグラフ化したものである。
【０１３２】
図９から明らかなように、当該位置ずれが０．３ｍｍ存在するとして透明電極１０ｃ内の各パターン電極の形状を設定した場合には、当該各パターン電極の形状を、当該位置ずれがないとき当該対物レンズ４の瞳面上に発生する波面収差の分布を透明電極１０ｃ上に投影した形状と略同一の形状とした場合に比して、各中心軸間に位置ずれがないときに液晶パネル１０を動作させたときの残留波面収差の量は若干増加するものの、各中心軸間に通常起こり得る０．３ｍｍの位置ずれが発生しているときの当該残留波面収差の量は減少している。
【０１３３】
一方、当該位置ずれが０．５ｍｍ存在するとして透明電極１０ｃ内の各パターン電極の形状を設定した場合には、各中心軸間に０．５ｍｍの位置ずれが発生しているときの残留波面収差は減少するが、各中心軸間に位置ずれがないときに液晶パネル１０を動作させたときの残留波面収差の量及び各中心軸間に０．３ｍｍの位置ずれがあるときに液晶パネル１０を動作させたときの残留波面収差の量は共に増加してしまう。
【０１３４】
従って、位置ずれが０．３ｍｍしかないときに当該位置ずれが０．５ｍｍ存在するとして透明電極１０ｃ内の各パターン電極の形状を設定すると、全体としての平均的な残留波面収差は逆に増加してしまうこととなる。
【０１３５】
この結果から、透明電極１０ｃ内の各パターン電極の形状の設定において考慮すべきラジアル方向の位置ずれの量としては、予測される当該位置ずれの最大値を考慮すべき位置ずれ量の上限とすべきことが理解できる。
【０１３６】
以上説明したように、実施形態の液晶パネル１０によれば、透明電極１０ｃ内の各パターン電極の形状が、対物レンズ４の光軸と液晶パネル１０の中心軸（すなわち、透明電極１０ｃの中心軸）との間のラジアル方向の位置ずれが存在しているときに波面収差を補償する形状であり、且つ当該ラジアル方向に垂直な対称軸を中心として線対称の形状とされているので、予め位置ずれの発生が予測されている場合でも、当該位置ずれに起因する補償効果の劣化がなく、当該位置ずれ発生後の波面収差を効果的に補償することができる。
【０１３７】
また、位置ずれがＤＶＤ５におけるラジアル方向の位置ずれであるので、位置ずれが発生し易いラジアル方向について、当該位置ずれ発生後でも発生する波面収差を効果的に補償することができる。
【０１３８】
更に、各パターン電極の形状が、位置ずれがないとした場合の当該各パターン電極の形状に基づいて設定されているので、位置ずれがないに発生する波面をも実用上問題ない程度に補償することができる。
【０１３９】
更にまた、各パターン電極の形状が、対物レンズ４の瞳面上における波面収差の分布の形状に基づいて設定されているので、より効果的に当該波面収差を補償することができる。
【０１４０】
また、位置ずれが光ピックアップ１３の製造工程上における位置合わせ精度及びＤＶＤ５からの情報再生時におけるトラッキングサーボ制御時に発生する対物レンズ４の中心軸と液晶パネル１０の中心軸との相対的な位置ずれに基づいて予め設定されているので、実際の再生中において発生する位置ずれに対応して効果的に波面収差を補償することができる。
【０１４１】
更に、透明電極１０ｄがＤＶＤ５におけるタンジェンシャル方向に生じる波面収差分布に対応した形状を有する複数のパターン電極４０ａ、４０ｂ、４１ａ、４１ｂ及び４２により構成されていると共に、各パターン電極の領域にチルト角に起因する波面収差を補償するための位相差を発生させるための駆動信号が独立に印加されるので、各パターン電極の位置に応じて液晶１０ｇに加えられる電位差が異なることとなり、ＤＶＤ５のタンジェンシャル方向に生じる波面収差を効果的に補償することができる。
【０１４２】
更にまた、波面収差が補償された光ビームＢを用いてＤＶＤ５上の記録情報が再生されるので、正確に記録情報を再生することができる。
【０１４３】
（ＩＩ）変形形態
次に、本発明の変形形態について、図１０を用いて説明する。
【０１４４】
上述の実施形態においては、透明電極１０ｃ内の各パターン電極の形状を、透明電極１０ｃの中心軸と対物レンズ４の光軸との間の予測されるラジアル方向の位置ずれが０．３ｍｍであるとして設定したが、変形形態の液晶パネルにおいては、当該各パターン電極の形状が、当該予測される位置ずれを０．５ｍｍであるとして設定される。
【０１４５】
すなわち、実際の光ピックアップ１３の製造工程においては突発的に位置合わせ精度が極端に劣化する場合があり、更に、ＤＶＤ５からの情報の再生時においても例えばいわゆるトラックジャンプ時等においては、通常のトラッキングサーボ制御時に比して対物レンズ４のラジアル方向の移動量が更に大きくなる。
【０１４６】
従って、このような状況をも考慮すると、透明電極１０ｃ内の各パターン電極の形状設定においては、予測されるラジアル方向の位置ずれを０．５ｍｍとして設定した方がよい。
【０１４７】
すなわち、図１０に示すように、パターン電極３０ａ’、３０ｂ’、３１ａ’、３１ｂ’及び３２’の形状は、透明電極１０ｃ’の中心を対物レンズ４の光軸が通るとき当該対物レンズ４の瞳面上に発生する波面収差の分布を透明電極１０ｃ’上に投影した形状と略同一の形状（図１０中、破線で示す）に対して、透明電極１０ｃ’の中心軸の位置と対物レンズ４の光軸の位置とがラジアル方向に０．５ｍｍずれているとき（当該ずれているときに対物レンズ４を通過する光ビームＢの範囲を透明電極１０ｃ’に投影した範囲ＳＰ’を図１０中一点鎖線で示す。）に対物レンズ４の瞳面上に発生する波面収差の分布を透明電極１０ｃ’上に投影した形状を考慮すると共に、ラジアル方向に垂直な方向の軸を中心として線対称となるように設定される。
【０１４８】
なお、この形状の設定方法については、上記実施形態中（ｉ）乃至（ｉｖ）で示した方法において考慮すべき位置ずれを０．５ｍｍとした場合と同様である。
【０１４９】
そして、この手順によって形成された各パターン電極の形状は、図１０に示すように、位置ずれがないとしたときの各パターン電極の形状（図１０中破線で示す。）を実施形態の透明電極１０ｃに比して更にラジアル方向に夫々引き伸ばしたような形状となる。
【０１５０】
このように設定された各パターン電極を有する透明電極１０ｃ’によれば、実施形態の透明電極１０ｃの効果に加えて、ラジアル方向の上記位置ずれが極端に大きくなっても、波面収差の補償効果の劣化を低減することができる。
【０１５１】
なお、上述の実施形態及び変形形態では情報再生装置Ｓにおける液晶パネル１０に対して本発明を適用した場合について説明したが、これ以外に、本発明は、予め記録媒体に記録されているアドレス情報等を読み出しつつ当該記録媒体に情報を記録する情報記録装置において、記録用の光ビームの光軸と当該記録媒体の情報記録面との間の傾斜に起因して当該光ビームの照射範囲内に発生する波面収差を補償する液晶パネルに対して適用することも可能である。
【０１５２】
【発明の効果】
以上説明したように、請求項１に記載の発明によれば、各部分透明電極の形状が、集光手段の中心軸と当該液晶パネルの中心軸との間の光軸に垂直な面内の予め設定された位置ずれが存在しているときに波面収差を補償する形状であるので、予め位置ずれの発生が予測されている場合でも、当該位置ずれに起因する補償効果の劣化がなく、当該位置ずれ発生後の波面収差を効果的に補償することができる。
また、位置ずれの方向が予め特定できない場合でも、相互に反対方向に発生する少なくとも二通りの位置ずれに対応して当該位置ずれに起因する補償効果の劣化を防止し、当該位置ずれ発生後の波面収差を効果的に補償することができる。
さらに、位置ずれがディスク状記録媒体における半径方向の位置ずれであるので、位置ずれが発生し易い半径方向について、当該位置ずれ発生後でも、発生する波面収差を効果的に補償することができる。
【０１５４】
請求項２に記載の発明によれば、請求項１に記載の発明の効果に加えて、各部分透明電極の形状が、位置ずれがないとした場合の当該各部分透明電極の形状に基づいて設定されているので、位置ずれがない場合に発生する波面をも補償することができる。
【０１５５】
請求項３に記載の発明によれば、請求項１又は２に記載の発明の効果に加えて、各部分透明電極の形状が、集光手段の瞳面上における波面収差の分布に基づいて設定されているので、より効果的に当該波面収差を補償することができる。
【０１５７】
請求項４に記載の発明によれば、請求項１から３のいずれか一項に記載の発明の効果に加えて、位置ずれが液晶パネル及び集光手段を含む光ピックアップの製造工程上における位置合わせ精度及び記録媒体に対する情報の記録／再生時に発生する集光手段の中心軸と液晶パネルの中心軸との相対的な位置ずれに基づいて予め設定されているので、実際の記録／再生中において発生する位置ずれに対応して効果的に波面収差を補償することができる。
【０１６１】
請求項５に記載の発明によれば、請求項１から４のいずれか一項に記載の発明の効果に加えて、予め想定された液晶パネルの中心軸と集光手段の中心軸との間の位置ずれが実際に発生しても、当該位置ずれに起因する補償効果の劣化がなく、当該位置ずれ発生後の波面収差を効果的に補償することができることとなり、例えば、波面収差により記録媒体上の情報が誤検出されることを防止できる。
【０１６２】
請求項６に記載の発明によれば、請求項５に記載の発明の効果に加えて、液晶パネルの中心軸と集光手段の中心軸との間で位置ずれが発生しても波面収差を補償して良好に情報を再生することができる。
【図面の簡単な説明】
【図１】実施形態の情報再生装置の概要構成を示すブロック図である。
【図２】液晶パネルの構成を示す縦断面図であり、（ａ）は液晶分子が水平状態の液晶を示す縦断面図であり、（ｂ）は液晶分子が斜めの液晶を示す縦断面図であり、（ｃ）は液晶分子が垂直の液晶を示す縦断面図である。
【図３】実施形態の透明電極の構成を示す平面図であり、（ａ）はラジアル方向用の透明電極の構成を示す平面図であり、（ｂ）はタンジェンシャル方向用の透明電極の構成を示す平面図である。
【図４】実施形態における透明電極内の各パターン電極の形状を示す図である。
【図５】波面収差の分布を示す平面図である。
【図６】波面収差の大きさを示す図である。
【図７】実施形態の各パターン電極に印加される駆動信号の波形を示すタイミングチャートである。
【図８】実施形態における液晶に加えられる電位差を示す図である。
【図９】位置ずれの量と残留波面収差の量との関係を示す図である。
【図１０】変形形態における透明電極内の各パターン電極の形状を示す図である。
【符号の説明】
１…レーザダイオード
２…ハーフミラー
４…対物レンズ
５…ＤＶＤ
６…集光レンズ
７…受光器
１０…液晶パネル
１１…ラジアル方向チルトセンサ
１２…タンジェンシャル方向チルトセンサ
１３…光ピックアップ
１４…スピンドルモータ
２０…再生制御部
２１…ＣＰＵ
２２、２５…Ａ／Ｄ変換器
２３、２６…ＰＷＭ回路
２４、２７…増幅器
Ｓｒ…検出信号
Ｓｄ…再生信号
Ｓｄｖ１、Ｓｄｖ２…駆動信号
Ｓｐ１、Ｓｐ２…チルト検出信号
１０ａ、１０ｂ…ガラス基板
１０ｃ、１０ｃ’、１０ｄ…透明電極
１０ｅ、１０ｆ…配向膜
１０ｇ…液晶
３０ａ、３０ａ’、３０ｂ、３０ｂ’、３１ａ、３１ａ’、３１ｂ、３１ｂ’、３２、３２’、４０ａ、４０ｂ、４１ａ、４１ｂ、４２…パターン電極
ＳＰ、ＳＰ’…光スポット
Ｍ…液晶分子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an optical pickup in an information reproducing apparatus that irradiates a recording medium with a light beam such as a laser beam and reproduces the recording information on the recording medium, or records the recording information on the recording medium using the light beam. Wavefront aberration (mainly coma) generated in the irradiation range of the light beam on the information recording surface when the optical axis of the light beam is inclined with respect to the information recording surface of the recording medium in the optical pickup in the information recording apparatus. In the technical field of liquid crystal panels that optically compensate for
[0002]
[Prior art]
Conventionally, as a liquid crystal panel for compensating the wavefront aberration, a liquid crystal panel having a configuration in which electrodes are arranged on both surfaces of a liquid crystal layer is generally known.
[0003]
This liquid crystal panel changes the refractive index of a light beam passing through the liquid crystal by utilizing the fact that the orientation of liquid crystal molecules changes in accordance with the applied voltage in the liquid crystal, resulting from the inclination of the optical axis. This is to compensate for wavefront aberration.
[0004]
That is, by changing the voltage applied to each liquid crystal portion and changing the refractive index with respect to the light beam, the optical path length of the light beam is changed for each liquid crystal portion (that is, a different phase difference is provided for each portion). Thus, the optical path length to the information recording surface is changed to cancel the inclination of the optical axis.
[0005]
On the other hand, in the above-mentioned conventional liquid crystal panel, as a method for actually changing the optical path difference of the light beam for each liquid crystal portion, for example, a transparent electrode (typically, one of the liquid Are arranged on the surface or both surfaces.) By combining a plurality of partial transparent electrodes, and by changing the driving voltage applied to each of the partial transparent electrodes, each of the liquid crystal portions corresponding to each of the partial transparent electrodes is changed. There is a method of making the phase difference of the light beam different.
[0006]
At this time, in the conventional liquid crystal panel, the shape of the plurality of partial transparent electrodes in one transparent electrode depends on the central axis of the liquid crystal panel and the objective for condensing the light beam passing through the liquid crystal panel on the recording medium. In general, the determination is made on the assumption that the optical axis of the lens coincides, that is, on the assumption that the center of the pupil plane of the objective lens coincides with the center of the transparent electrode.
[0007]
Here, conventionally, when the liquid crystal panel and the objective lens are driven integrally, there is no problem because the center of the pupil plane of the objective lens and the center of the liquid crystal panel are not displaced. Due to the problem described above, the objective lens and the liquid crystal panel are often configured separately.
[0008]
In an optical pickup in which the objective lens and the liquid crystal panel are configured separately, when the center axis of the liquid crystal panel and the center axis of the objective lens are already displaced immediately after the manufacture due to a problem in the manufacturing process. There is.
[0009]
Also, when actually recording / reproducing information on / from the recording medium, for example, a so-called tracking servo control may be performed on the irradiation position of the light beam on the recording medium. The lens is moved by an actuator or the like in a direction perpendicular to the information tracks formed on the recording medium.
[0010]
Also in this case, the liquid crystal panel is generally fixed to the housing of the optical pickup. Therefore, also in this case, the positional deviation between the central axis of the liquid crystal panel and the central axis of the objective lens is inevitable. Will occur.
[0011]
[Problems to be solved by the invention]
However, even in the case where each of the above-described positional deviations occurs, since the shape of each partial transparent electrode itself is formed on the assumption that there is no such positional deviation, when the positional deviation actually occurs (rather, In the case where the displacement does not occur, it can be said that the wavefront aberration distribution to be compensated for the liquid crystal panel also changes, so that the wavefront aberration of the liquid crystal panel is not sufficiently compensated. There was a problem that there is.
[0012]
Therefore, the present invention has been made in view of the above problems, and a problem thereof is to effectively compensate for the wavefront aberration on the information recording surface even when it is predicted that a positional shift will occur. It is an object of the present invention to provide a liquid crystal panel capable of performing the above and an optical pickup and an information reproducing apparatus provided with the liquid crystal panel.
[0013]
[Means for Solving the Problems]
In order to solve the above problem, the invention according to claim 1 is arranged on an optical path of a light beam for recording / reproducing information, and the optical axis of the light beam and the information are recorded / reproduced. A liquid crystal panel for compensating a wavefront aberration generated on the information recording surface due to an inclination with respect to the information recording surface of a recording medium such as a DVD by giving a phase difference to the light beam. A transparent electrode for applying a voltage to the liquid crystal, having a transparent electrode composed of partial transparent electrodes such as a plurality of pattern electrodes having a shape corresponding to the distribution of the wavefront aberration to be compensated, The shape of the partially transparent electrode is in a plane perpendicular to the optical axis between a central axis of a focusing means such as an objective lens for focusing the light beam on the information recording surface and a central axis of the liquid crystal panel. Misalignment , It is shaped to compensate for the wavefront aberration generated when the position deviation of the axisymmetric shape about the vertical axis of symmetry in the direction of the positional deviation, and a predetermined size is presentThe recording medium is a disk-shaped recording medium, and the pattern shape of the transparent electrode is a shape obtained by extending the electrode pattern shape when there is no displacement in the radial direction..
[0014]
Therefore, even when the occurrence of the displacement is predicted in advance, the compensation effect due to the displacement does not deteriorate, and the wavefront aberration after the occurrence of the displacement can be effectively compensated.
Further, even when the direction of the positional deviation cannot be specified in advance, it is possible to prevent deterioration of the compensation effect caused by the positional deviation corresponding to at least two types of positional deviations occurring in opposite directions, and Wavefront aberration can be effectively compensated.
Further, in the radial direction in which the positional deviation is likely to occur, even after the positional deviation occurs, the generated wavefront aberration can be effectively compensated.
[0017]
Claims to solve the above problems2The invention described in claim1In the liquid crystal panel described in (1), the shape of each of the partial transparent electrodes is set based on the shape of each of the partial transparent electrodes when there is no displacement.
[0018]
Therefore, since the shape of the partial transparent electrode is set based on the shape when there is no displacement, the wavefront generated when there is no displacement can be compensated.
[0019]
Claims to solve the above problems3The invention described in claim 1 is claim 1Or 2Wherein the shape of each of the partial transparent electrodes is set based on a distribution of the wavefront aberration on a pupil plane of the light condensing unit.
[0020]
Therefore, since the shape of each partial transparent electrode is set based on the distribution of the wavefront aberration on the pupil plane corresponding to the wavefront aberration actually occurring within the irradiation range of the light beam, the wavefront aberration can be more effectively reduced. Can compensate.
[0023]
Claims to solve the above problems4The invention described in claim 13In the liquid crystal panel according to any one of the above, the misalignment is caused by a central axis of the liquid crystal panel and a central axis of the light focusing unit in a manufacturing process of the optical pickup including the liquid crystal panel and the light focusing unit. The alignment accuracy and the central axis of the light-collecting means generated by moving the light-collecting means in a plane perpendicular to the optical axis when recording / reproducing the information on / from the recording medium and the liquid crystal panel Is set in advance on the basis of the relative displacement with respect to the center axis of.
[0024]
Therefore, since the positional deviation for setting the shape of each partial transparent electrode is set in consideration of the positional accuracy in the manufacturing process of the optical pickup and the movement of the light condensing means during recording / reproducing of information, the actual deviation is set. The wavefront aberration can be effectively compensated for in response to the positional shift occurring during the recording / reproducing operation.
[0031]
Claims to solve the above problems5The invention described in claim 14And a light source such as a laser diode that emits the light beam, and a PWM circuit that applies the phase difference to the light beam by applying a voltage to each of the partially transparent electrodes. Voltage applying means, the light condensing means such as an objective lens for condensing the light beam that has passed through the liquid crystal panel on the recording medium, and the light condensing means is condensed by the light condensing means and reflected from the recording medium. And a light receiving means such as a light receiver for receiving the light beam and outputting a light receiving signal.
[0032]
Therefore, even if a positional deviation between the central axis of the liquid crystal panel and the central axis of the light condensing unit actually occurs in advance, the compensation effect due to the positional deviation does not deteriorate, and after the positional deviation occurs. Can be effectively compensated, and for example, it is possible to prevent the information on the recording medium from being erroneously detected due to the wavefront aberration.
[0033]
Claims to solve the above problems6The invention described in claim5And a reproducing unit such as a reproduction control unit that reproduces the information based on the light receiving signal when the information is recorded on the recording medium.
[0034]
Therefore, even if a positional shift occurs between the central axis of the liquid crystal panel and the central axis of the light condensing means, it is possible to compensate for the wavefront aberration and reproduce the information well.
[0035]
BEST MODE FOR CARRYING OUT THE INVENTION
(I)Embodiment
Next, a preferred embodiment of the present invention will be described with reference to the drawings.
[0036]
In the embodiment described below, a recording medium on which recording information is recorded is a DVD (an optical disk whose recording capacity is improved about seven times as compared with a conventional CD (Compact Disk)). When reading information, while compensating for the wavefront aberration generated due to a change in the angle between the DVD and the optical axis of the light beam (inclination caused by warpage of the DVD itself or vibration of the DVD due to external vibration or rotation). This is an embodiment in which the present invention is applied to an information reproducing apparatus to be read.
[0037]
First, the overall configuration of the information reproducing apparatus according to the embodiment will be described with reference to FIG.
[0038]
As shown in FIG. 1, the information reproducing apparatus S according to the embodiment includes a spindle motor 14 that rotates the DVD 5 at a predetermined rotation speed, a light beam B that irradiates the DVD 5 while compensating for generated wavefront aberration, and An optical pickup 13 that outputs a detection signal Sr corresponding to information recorded on the DVD 5 based on the detection signal Sr, and a liquid crystal panel described later included in the optical pickup 13 is driven to compensate for the wavefront aberration and to generate a detection signal Sr. It comprises a voltage application means for reproducing recorded information and outputting it as a reproduction signal Sd, and a reproduction control unit 20 as a reproduction means.
[0039]
The optical pickup 13 includes a laser diode 1 as a light source, a half mirror 2, an objective lens 4 as a light collecting means, a light collecting lens 6, a light receiver 7 as a light receiving means, and a liquid crystal according to the present invention. The panel 10 (fixed to the housing of the optical pickup 13) and a radial for detecting a radial tilt angle of a region on the DVD 5 to which the light beam B is irradiated (hereinafter referred to as a radial tilt angle). A directional tilt sensor 11 and a tangential tilt sensor 12 for detecting a tangential tilt angle of an area on the DVD 5 irradiated with the light beam B (hereinafter, referred to as a tangential tilt angle). ing.
[0040]
Here, the optical axis of the objective lens 4 and the central axis of the liquid crystal panel 10 should be originally parallel to each other and their positions should coincide with each other. Due to the lowering of the positioning accuracy above or the movement of the objective lens 4 in the radial direction (the horizontal direction in FIG. 1) when the so-called tracking servo control is performed on the objective lens 4, (Positional displacement in the radial direction) occurs. This displacement is generally considered to be at most about 0.3 mm.
[0041]
On the other hand, the reproduction control unit 20 includes a CPU 21, A / D converters 22 and 25, a PWM (Pulse Width Modulation; pulse width modulation) circuit 23 as a voltage application unit, a PWM circuit 26 as a voltage application unit, and an amplifier. 24 and 27.
[0042]
Next, the overall operation will be described.
[0043]
The DVD 5 is driven to rotate at a predetermined rotation speed by a spindle motor 14.
[0044]
At this time, the light beam B emitted from the laser diode 1 is partially reflected by the half mirror 2 and enters the liquid crystal panel 10. Then, the wavefront aberration is compensated when transmitting through the liquid crystal panel 10, and thereafter, the light is focused on the information recording surface of the DVD 5 by the objective lens 4.
[0045]
Next, the light beam B reflected on the information recording surface of the DVD 5 passes through the objective lens 4 and the liquid crystal panel 10 again, passes through the half mirror 2, and is collected on the light receiver 7 via the condenser lens 6. Is lighted. Then, the reflected light of the light beam B received by the light receiver 7 is converted into a detection signal Sr, which is an electric signal, by the light receiver 7 and supplied to the CPU 21. Thereafter, the CPU 21 performs a predetermined demodulation process or the like, and outputs the signal as a reproduction signal Sd corresponding to the recording information recorded on the DVD 5 to a reproduction circuit (not shown).
[0046]
In parallel with the above operation, the radial tilt angle of the DVD 5 is detected by the radial tilt sensor 11 and is output as a tilt detection signal Sp1 which is an analog signal. Then, the tilt detection signal Sp1 is supplied to the A / D converter22Are digitized and input to the CPU 21.
[0047]
On the other hand, the tangential tilt angle of the DVD 5 is detected by the tangential tilt sensor 12 and output as a tilt detection signal Sp2 which is an analog signal. The tilt detection signal Sp2 is supplied to the A / D converter25Are digitized and input to the CPU 21.
[0048]
Here, the radial tilt sensor 11 and the tangential tilt sensor 12 are optical sensors having the same structure, and have one light emitting unit and two light receiving units. The radial direction tilt sensor 11 is arranged to detect the radial tilt angle of the DVD 5, and the tangential direction tilt sensor 12 is arranged to detect the tangential tilt angle. It is.
[0049]
Next, based on the input tilt detection signal Sp1, the CPU 21 generates a drive signal Sdv1 having a waveform described later, performs PWM modulation in the PWM circuit 23, amplifies the signal in the amplifier 24, and amplifies the drive signal Sdv1 in the liquid crystal panel 10. Is output to the pattern electrode.
[0050]
At the same time, the CPU 21 generates a drive signal Sdv2 having a waveform described later based on the input tilt detection signal Sp2, performs PWM modulation in the PWM circuit 26, amplifies the drive signal Sdv2 in the amplifier 27, and outputs Output to the pattern electrode.
[0051]
More specifically, based on the tilt detection signal Sp1 or Sp2 output from the A / D converter 22 or 25, the CPU 21 operates in the radial direction or for each pattern electrode of the liquid crystal panel 10 described below. The amount of aberration compensation in the tangential direction (that is, the phase difference to be given to the light beam B passing through the liquid crystal panel 10 in order to cancel the wavefront aberration caused by the tilt angle in the radial or tangential direction) is calculated.
[0052]
At this time, the CPU 21 calculates the aberration compensation amount according to the value of the tilt detection signal Sp1 or Sp2 using the compensation amount data indicating the aberration compensation amount stored in a ROM (Read Only Memory) or the like (not shown) in advance. Then, the drive signal Sdv1 or Sdv2 indicating the aberration compensation amount is supplied to the PWM circuit 23 or 26.
[0053]
After that, the PWM signal 23 or 26 converts the pulse width of the drive signal Sdv1 or Sdv2. The drive signal Sdv1 or Sdv2 whose pulse width has been converted is amplified by the amplifier 24 or 27 at a predetermined amplification rate, and then output to each pattern electrode of the liquid crystal panel 10, respectively.
[0054]
Then, the liquid crystal panel 10 is driven in accordance with the drive signal Sdv1 or Sdv2 output to each pattern electrode to control the refractive index, thereby giving a phase difference to the light beam B passing through the liquid crystal panel 10. This compensates for wavefront aberration in the radial or tangential direction.
[0055]
Next, the configuration and operation of the liquid crystal panel 10 of the present invention will be described with reference to FIGS.
[0056]
As shown in a longitudinal sectional view of FIG. 2, the liquid crystal panel 10 of the embodiment has alignment films 10e and 10f for giving a predetermined molecular alignment to the liquid crystal 10g with a liquid crystal 10g containing the liquid crystal molecules M interposed therebetween. In addition, a transparent electrode 10c and a transparent electrode 10d made of ITO (Indium-tin Oxide) are formed outside the alignment films 10e and 10f. Further, glass substrates 10a and 10b as protective layers are formed on the outermost sides.
[0057]
In this configuration, each of the transparent electrodes 10c and 10d is divided into a pattern electrode as a partial transparent electrode corresponding to the distribution of the wavefront aberration, as described later, so that the transparent electrode 10c is inclined with respect to the optical axis in the radial direction. The transparent electrode 10d is an electrode for compensating the wavefront aberration caused by the inclination of the optical axis in the tangential direction.
[0058]
The liquid crystal 10g has a so-called birefringence effect in which the refractive index differs between the optical axis direction of the liquid crystal molecules M and the direction perpendicular thereto, as shown in FIG. 2A to 2C, the direction of the liquid crystal molecules M can be freely changed from the horizontal direction to the vertical direction, as shown in FIGS.
[0059]
At this time, the CPU 21 calculates a drive signal Sdv1 or Sdv2 to be applied to each of the transparent electrodes 10c and 10d based on the tilt detection signals Sp1 or Sp2, and outputs the drive signal Sdv1 or Sdv2 to the liquid crystal panel 10.
[0060]
Next, the configuration of each of the transparent electrodes 10c and 10d will be described with reference to FIG.
[0061]
First, as shown in FIG. 3A, the transparent electrode 10c includes five pattern electrodes 30a, 30b, which pass through the center of the transparent electrode 10c and are arranged line-symmetrically with respect to a symmetry axis perpendicular to the radial direction. It is divided into 31a, 31b and 32, and the respective pattern electrodes are insulated from each other.
[0062]
At this time, the reason why the shape of the transparent electrode 10c is line-symmetric is that the moving direction of the objective lens 4 is not one direction, and there are two types of radial directions of the DVD 5, namely, an inner circumferential direction and an outer circumferential direction. This is because the relative displacement of the objective lens 4 with respect to the liquid crystal panel 10 needs to be considered both inward and outward directions, so that the division pattern of the transparent electrode 10c is line-symmetric with respect to the center axis in the displacement direction. It becomes.
[0063]
Further, of these pattern electrodes, the pattern electrodes 30a and 30b are driven by the same drive signal Sdv1, and the pattern electrodes 31a and 31b are driven by the same drive signal Sdv1.
[0064]
The reason why the transparent electrode 10c is divided into the shape shown in FIG. 3A is that the shape of the pattern electrode (that is, the division of the region that is independently driven and controlled) is determined by the wavefront generated in the radial direction described later. This is because the shape is made in consideration of the influence of the radial displacement on the aberration distribution.
[0065]
As for the size of the entire transparent electrode 10c, the range of the light beam B passing through the objective lens 4 when the center of the transparent electrode 10c coincides with the position of the optical axis of the objective lens 4 is defined as the transparent electrode 10c. The range SP projected on 10c is sized to be the range shown in FIG.
[0066]
On the other hand, as shown in FIG. 3 (b), the transparent electrode 10d includes five pattern electrodes 40a, 40b, which pass through the center of the transparent electrode 10c and are arranged line-symmetrically about a symmetry axis perpendicular to the tangential direction. It is divided into 41a, 41b and 42, and the respective pattern electrodes are insulated from each other. Further, of these pattern electrodes, the pattern electrodes 40a and 40b are driven by the same drive signal Sdv2, and the pattern electrodes 41a and 41b are driven by the same drive signal Sdv2.
[0067]
The reason why the transparent electrode 10d is divided into the shape shown in FIG. 3B is different from the case of the transparent electrode 10c in that the shape of the pattern electrode is substantially the same as the distribution of wavefront aberration generated in the tangential direction described later. This is because the shape is as follows. At this time, since the size of the positional shift generated in the tangential direction is so small as to be negligible, the positional shift in the tangential direction is not considered when setting the shape of each pattern electrode.
[0068]
The size of the entire transparent electrode 10d is defined as the range of the light beam B passing through the objective lens 4 when the center of the transparent electrode 10d coincides with the position of the optical axis of the objective lens 4. The range SP projected on 10d has such a size that the range shown in FIG.
[0069]
Next, with reference to FIGS. 3 to 6, a description will be given of the burying of the wavefront aberration caused by the tilt angle of the DVD 5 by the liquid crystal panel 10 and the matters to be considered when setting the shape of each pattern electrode.
[0070]
The following description is mainly for a case where the wavefront aberration caused by the inclination of the optical axis in the radial direction is compensated (that is, the case where the drive signal Sdv1 is applied to the transparent electrode 10c to compensate the wavefront aberration). is there.
[0071]
First, the setting of the shapes of the pattern electrodes 30a, 30b, 31a, 31b, and 32 constituting the transparent electrode 10c will be described.
[0072]
The shapes of the pattern electrodes 30a, 30b, 31a, 31b, and 32 constituting the transparent electrode 10c are set in consideration of the influence of the radial displacement on the distribution of the wavefront aberration generated in the radial direction as described above. I have.
[0073]
That is, as shown in FIG. 4, the shape of the pattern electrodes 30a, 30b, 31a, 31b and 32 occurs on the pupil plane of the objective lens 4 when the optical axis of the objective lens 4 passes through the center of the transparent electrode 10c. A shape substantially the same as the shape in which the distribution of the wavefront aberration is projected on the transparent electrode 10c (the same shape as the shape obtained by rotating the shape of each pattern electrode in the transparent electrode 10d by 90 degrees as indicated by a broken line in FIG. 4). In contrast to the shape setting method, which will be described later, the position of the central axis of the transparent electrode 10c and the position of the optical axis of the objective lens 4 are 0.3 mm in the radial direction (this value is determined as described above. It is a value experimentally obtained in advance in consideration of the above alignment error and the maximum value of the amount of movement of the objective lens 4 during the tracking servo control. A range SP ′ obtained by projecting the range of the light beam B passing through the object lens 4 onto the transparent electrode 10c is indicated by a dashed line in FIG. 4). The distribution of the wavefront aberration generated on the pupil plane of the objective lens 4 is shown in FIG. The shape projected above is taken into consideration, and is set to be line-symmetric about an axis passing through the center of the transparent electrode 10c and perpendicular to the radial direction.
[0074]
Thereby, the shape of each pattern electrode included in the transparent electrode 10c is substantially the same as the shape of the distribution of the wavefront aberration generated on the pupil plane of the objective lens 4 when there is no displacement, projected on the transparent electrode 10c. The amount of residual wavefront aberration remaining after compensating the wavefront aberration by operating the liquid crystal panel 10 when there is no misalignment between the central axes slightly increases as compared with the case where It is possible to reduce the amount of the residual wavefront aberration when a possible displacement of 0.3 mm occurs.
[0075]
Next, a method of setting the shape of each pattern electrode constituting the transparent electrode 10c will be further described.
[0076]
The shape of each pattern electrode shown in FIG. 4 is set according to the following procedure.
[0077]
That is,
(I) A radial displacement between the position of the central axis of the transparent electrode 10c and the position of the optical axis of the objective lens 4 which is predicted in the operation of the information reproducing apparatus S is set. In the present embodiment, the predicted positional deviation is 0.3 mm.
[0078]
(Ii) Calculate the wavefront aberration that occurs on the pupil plane of the objective lens 4 when the displacement occurs.
[0079]
(Iii) Based on the shape of each pattern electrode when there is no displacement, the phase difference to be given to the light beam B by the transparent electrode 10c in order to reduce the wavefront aberration when the displacement is occurring. It is calculated for each part of the liquid crystal 10g.
[0080]
(Iv) The phase difference is given to each part of the liquid crystal 10g, and each electrode pattern in the transparent electrode 10c is symmetrical with respect to an axis of symmetry passing through the center of the transparent electrode 10c and perpendicular to the radial direction. Set the shape.
[0081]
As shown in FIG. 4, the shape of each pattern electrode formed by such a procedure is as shown in FIG. It has a shape like that.
[0082]
Next, in order to set the shape of each pattern electrode in the transparent electrode 10c by the method shown in (i) to (iv) described above, the shape of each pattern electrode when correcting the wavefront aberration when there is no displacement is described. (The shape shown by the broken line in FIG. 4 is substantially the same as the shape of the distribution of the wavefront aberration generated on the pupil plane of the objective lens 4 when there is no positional displacement, projected onto the transparent electrode 10c. ) Is set.
[0083]
First, let W (r, φ) be the wavefront aberration on the pupil plane of the objective lens 4. Here, (r, φ) is the polar coordinate of the pupil plane.
[0084]
When the DVD 5 is tilted with respect to the axis of the light beam B (that is, when the tilt angle is generated), the wavefront aberration (mainly coma aberration) is generated as described above, and the light beam is B cannot be squeezed. In this case, the wavefront aberration represented by the following equation (1) accounts for most of the wavefront aberration Wtlt (r, φ) generated due to the tilt angle.
[0085]
(Equation 1)
Wtlt (r, φ) ≒ ω₃₁× r³× cosφ + ω₁₁× r × cosφ (1)
Where ω₃₁And ω₁₁Is a constant given by the tilt angle of the DVD 5, the thickness of the substrate, the refractive index of the substrate, and the numerical aperture (NA) of the objective lens 4.₃₁Is coma, ω₁₁Represents aberration due to movement of the image point. The result of calculating the wavefront aberration distribution on the pupil plane using this formula corresponds to the wavefront aberration distribution (wavefront aberration distribution caused by the tilt angle in the radial direction) shown in FIG. 5 described later.
[0086]
Further, assuming that the standard deviation of the wavefront aberration W (r, φ) on the pupil plane is Wrms, the Wrms is represented by the following equation (2).
[0087]
(Equation 2)

Here, W in the equation (2)₀Is the average value of W (r, φ) on the pupil plane. This Wrms is used for evaluating the wavefront aberration. When Wrms is reduced, the influence of the wavefront aberration is small and good reproduction can be performed.
[0088]
By the way, as is apparent from equation (2), W (r, φ) may be reduced to compensate for the wavefront aberration. Therefore, in order to compensate for Wtlt (r, φ) generated by the DVD 5 tilting in the radial direction, the voltage of the drive signal Sdv1 applied to each pattern electrode in the transparent electrode 10c of the liquid crystal panel 10 is controlled. If the refractive index of the region of the liquid crystal 10g corresponding to a certain pattern electrode is changed by Δn, the change in the refractive index causes an optical path difference Δn × d for the light beam B passing through the region corresponding to the pattern electrode. Can be given.
[0089]
If the optical path difference given by the liquid crystal 10g is Wlc (r, φ), the wavefront aberration W (r, φ) on the pupil plane of the objective lens 4 when the liquid crystal panel 10 is arranged is expressed by the following equation (3). It is represented by
[0090]
(Equation 3)
W (r, φ) = Wtlt (r, φ) + Wlc (r, φ) (3)
As is apparent from the equation (3), to cancel the wavefront aberration W (r, φ) due to the tilt angle of the DVD 5,
(Equation 4)
W (r, φ) = Wtlt (r, φ) + Wlc (r, φ) = 0 (4)
It is good. That is, the wavefront aberration of the opposite polarity to the wavefront aberration Wtlt (r, φ) caused by the tilt angle of the DVD 5 due to the liquid crystal 10g, that is,
(Equation 5)
Wlc (r, φ) = − Wtlt (r, φ) (5)
It can be seen that the wavefront aberration Wlc (r, φ) that satisfies
[0091]
Accordingly, when the optical axis of the objective lens 4 passes through the center of the transparent electrode 10c, the wavefront aberration Wlc (r, r) of the opposite polarity to the wavefront aberration Wtlt (r, φ) caused by the tilt angle of the DVD 5 by the liquid crystal 10g. In order to provide φ), pattern electrodes are provided so as to divide the liquid crystal 10g in accordance with the wavefront aberration distribution caused by the tilt angle in the radial direction of the DVD 5 shown in FIG. It is sufficient to control the applied voltage to give a wavefront aberration of the opposite polarity to the wavefront aberration caused by the tilt angle.
[0092]
Here, FIG. 5 shows a state of a wavefront aberration distribution generated on the pupil plane of the objective lens 4 due to the inclination of the optical axis in the radial direction.
[0093]
More specifically, FIG. 5 shows the wavefront aberration distribution at the best image point of the light spot when the recording surface of the DVD 5 is tilted + 1 ° in the radial direction within the range of the maximum area of the incident light beam B. It is a figure, and the said wavefront aberration distribution is represented by the boundary line of the area | regions A to K which have a range width of 50 nm centering on the area | region A where the value of a wavefront aberration has the range of -25 nm-+25 nm. X2-X2 in FIG. 5 is an axis (that is, a radial direction) corresponding to the direction in which the DVD 5 tilts.
[0094]
In FIG. 6, the wavefront aberration distribution is represented by distribution characteristics on the X2-X2 axis.
[0095]
Further, the distribution of the wavefront aberration itself is constant regardless of the magnitude of the tilt angle, and the amount of the wavefront aberration that changes according to the magnitude of the tilt angle is obtained. This point will be described with reference to FIG. 6. The peak value of the curve shown in FIG. 6 increases as the tilt angle increases, and decreases as the tilt angle decreases.
[0096]
The present embodiment focuses on the distribution of wavefront aberration generated on the pupil plane of the objective lens 4 when the optical axis of the objective lens 4 passes through the center of the transparent electrode 10c calculated as described above. The shape of the divided transparent electrode 10c is a shape in which the above-described positional shift is added to the wavefront aberration distribution of FIG. 5 by the methods (i) to (iv) described above, and the liquid crystal 10g in the region corresponding to the pattern electrode is used. A phase difference (that is, the optical path difference Δn × d) is given to the light beam B so as to cancel the wavefront aberration Wtlt (r, φ) generated when there is a position shift, and the tilt angle when there is a position shift is The influence of the resulting wavefront aberration Wtlt (r, φ) is reduced to a range that does not affect reproduction.
[0097]
That is, by controlling the voltage for each divided region of the liquid crystal 10g (the divided region corresponding to each pattern electrode in the transparent electrode 10c), the direction of the liquid crystal molecules M is changed, and the refractive index of each divided region is changed. By giving a phase difference to the light beam B, the wavefront aberration Wtlt (r, φ) generated when the DVD 5 is tilted is compensated.
[0098]
As described above, each pattern electrode in the transparent electrode 10c shown in FIG. 3A is caused by the wavefront aberration distribution (see FIG. 5) and the displacement when the recording surface of the DVD 5 is inclined by + 1 ° in the radial direction. The shape is set based on the wavefront aberration distribution, and the transparent electrode 10c has five pattern electrodes corresponding to a case where the wavefront aberration is approximated by five values.
[0099]
The region corresponding to the pattern electrode 32 is a region including a region where the value of the wavefront aberration is 0, and the region of the liquid crystal 10g corresponding to the pattern electrode 31b and the region of the liquid crystal 10g corresponding to the pattern electrode 30b are symmetric. It has a shape, and the value of the phase difference given to the transmitted light beam B has the opposite polarity.
[0100]
Furthermore, the region of the liquid crystal 10g corresponding to the pattern electrode 30a and the region of the liquid crystal 10g corresponding to the pattern electrode 31a have symmetric shapes, and the phase difference value applied to the transmitted light beam B has the opposite polarity.
[0101]
If the number of divisions of the liquid crystal 10g (that is, the number of the pattern electrodes) is further increased to subdivide the liquid crystal 10g, the wavefront aberration caused by the tilt angle of the DVD 5 can be completely canceled. For example, if the number of divisions is increased by dividing the liquid crystal 10g in a grid pattern, it is necessary to control and apply a drive signal for each of the divided areas, and for that purpose, the transparent electrode 10c is divided into the divided areas. Therefore, it is difficult to create the transparent electrode 10c and create a wiring such as a lead line.
[0102]
Therefore, in the liquid crystal panel 10 of the present embodiment, the transparent electrode 10c can be easily formed by making the divided shape similar to the wavefront aberration distribution as shown in FIG. And the wavefront aberration can be efficiently compensated.
[0103]
In addition, in the above description with reference to FIGS. 3 to 6, the case where the wavefront aberration generated in the radial direction of the DVD 5 is compensated, but the case where the wavefront aberration generated in the tangential direction of the DVD 5 is compensated, is described above. Since there is no need to consider the shift, the shape of each pattern electrode of the transparent electrode 10d is determined by changing the distribution of the wavefront aberration generated on the pupil plane of the objective lens 4 when the optical axis of the objective lens 4 passes through the center of the transparent electrode 10c. Is substantially the same as the shape projected on the transparent electrode 10c (the shape indicated by the broken line in FIG. 4), and is rotated by 90 °, so that the wavefront aberration caused by the inclination of the optical axis in the tangential direction is transparent. This corresponds to a case where compensation is performed using the electrode 10d.
[0104]
Therefore, the shape of each of the pattern electrodes 40a, 40b, 41a, 41b, and 42 in the transparent electrode 10d also has a wavefront aberration distribution with respect to an axis of symmetry parallel to the tangential direction (the X2-X2 axis in FIG. (Wavefront aberration distribution in the case of と し た).
[0105]
Next, the driving of the liquid crystal 10g by applying the driving signals Sdv1 and Sdv2 to the transparent electrodes 10c and 10d will be described with reference to FIGS.
[0106]
In the following description, an embodiment for compensating only the wavefront aberration occurring in the tangential direction of the DVD 5 will be described, and the wavefront aberration caused by the inclination of the optical axis of the DVD 5 in the radial direction will not be described. Compensation. That is, this embodiment is directed to a case where the tilt angle in the radial direction is 0 degree and only the tilt angle in the tangential direction exists on the disc.
[0107]
In the following embodiments, the description will be made with reference to the drive signal Sdv1 applied to the transparent electrode 10c (electrode for applying a voltage for compensating the wavefront aberration in the radial direction).
[0108]
FIG. 7 shows the waveforms of the drive signals Sdv1 and Sdv2 applied to the pattern electrodes constituting the transparent electrodes 10c and 10d. FIG. 8 shows the pattern electrodes when the tilt angle in the tangential direction changes. 5 shows changes of the drive signals Sdv1 and Sdv2 with respect to the drive signals Sdv1 and Sdv2.
[0109]
As shown in FIG. 7, when only the wavefront aberration caused by the inclination of the optical axis in the tangential direction is compensated, each pattern electrode in the transparent electrode 10c indicates the reference of the potential difference applied to the liquid crystal 10g. The same drive signal Sdv1 is applied to each pattern electrode. That is, the drive signal Sdv1 having the waveform shown in the uppermost row of FIG. 7 to the third row from the top is applied to each of the pattern electrodes 30a, 30b, 31a, 31b, and 32. The drive signal Sdv1 corresponds to a drive signal applied to the transparent electrode 10c when the tilt angle in the radial direction is 0 degrees.
[0110]
The drive signal Sdv1 shown in the uppermost stage to the third stage from the top in FIG. 7 gives the same reference phase difference to the entire region of the light beam transmitted through the liquid crystal panel 10 when applied. The drive signal Sdv1 does not change the wavefront of the light beam, that is, provides a phase difference having the same effect as the light beam passing through the glass plate. Further, when the tilt angle in the radial direction and the tilt angle in the tangential direction are both 0 degrees, the drive signal Sdv1 is applied to the transparent electrode 10c for each pattern electrode. Is grounded.
[0111]
On the other hand, the drive signal Sdv2 having the waveforms shown in the fourth and bottom rows from the top in FIG. 7 is applied to the transparent electrode 10d for compensating the wavefront aberration caused by the inclination of the optical axis in the tangential direction. .
[0112]
Here, the drive signals Sdv2 shown in the fourth and bottom rows from the top in FIG. 7 are light signals for compensating the wavefront aberration caused by the tilt angle in the region of the liquid crystal 10g corresponding to the pattern electrodes 40a and 40b in the transparent electrode 10d. It is necessary to reduce the phase difference given to the beam B, and in the region of the liquid crystal 10g corresponding to the pattern electrodes 41a and 41b, it is necessary to increase the phase difference given to the light beam B in order to compensate for the wavefront aberration caused by the tilt angle. The drive signal Sdv2 is applied when a certain tilt angle occurs in the tangential direction.
[0113]
At this time, in the region of the liquid crystal 10g corresponding to the pattern electrodes 41a and 41b, the phase difference given to the light beam B needs to be larger than the reference phase difference, and the potential difference applied to the liquid crystal 10g in the region needs to be large. There is. Therefore, as shown in the fourth row from the top in FIG. 7, a drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 is applied to the pattern electrodes 41a and 41b.
[0114]
On the other hand, in the region of the pattern electrodes 40a and 40b, the phase difference given to the light beam B needs to be smaller than the reference phase difference, and the potential difference applied to the liquid crystal 10g in this region needs to be small. . Therefore, as shown at the bottom of FIG. 7, a drive signal Sdv2 having the same phase as the drive signal Sdv1 is applied to the pattern electrodes 40a and 40b.
[0115]
As described above, the drive signal Sdv2 having a phase opposite to the drive signal Sdv1 is applied to the pattern electrodes 41a and 41b, and the drive signal Sdv2 having the same phase as the drive signal Sdv1 is applied to the pattern electrodes 40a and 40b. As a result, a potential difference necessary for giving the light beam B a phase difference necessary for compensating the wavefront aberration is generated in the liquid crystal 10g.
[0116]
On the other hand, the voltage of the drive signal Sdv2 given to the pattern electrodes 41a and 41b and 40a and 40b corresponds to the phase difference to be given to the light beam B by the liquid crystal 10g calculated by the CPU 21 based on the tilt detection signal Sp2, as described later. Is set.
[0117]
Specifically, as the tilt angle increases, the phase difference required for compensating the wavefront aberration increases, so that it is necessary to increase the potential difference applied to the liquid crystal 10g, and the amplitude of the drive signal Sdv2 increases. Conversely, when the tilt angle is reduced, the phase difference required for compensating the wavefront aberration is reduced, and the potential difference applied to the liquid crystal 10g may be small, so that the amplitude of the drive signal Sdv2 is reduced. Here, the difference between the maximum value and the minimum value of each amplitude is the potential difference applied to the liquid crystal 10g.
[0118]
The pattern electrode 42 is always grounded. This is because the amount of wavefront aberration due to the tilt angle in the area of the pattern electrode 42 is small, and it is not necessary to compensate.
[0119]
Next, how the drive signal Sdv2 applied to each pattern electrode of the transparent electrode 10d changes when the tilt angle in the tangential direction changes will be described with reference to FIG.
[0120]
FIG. 8 shows a case where the tilt angle in the tangential direction is zero (an ideal case where the angle between the optical axis of the light beam B and the information recording surface of the DVD 5 in the tangential direction is a right angle) and a case where the tilt angle is Changes in either the positive or negative direction, changes in the waveforms of the drive signal Sdv1 and the drive signal Sdv2 applied to each pattern electrode included in the transparent electrode 10c or 10d, respectively (from the top of FIG. 8 to 3 from the top). And the change in the potential difference actually applied to the regions corresponding to the pattern electrodes 40a, 40b, 41a and 41b of the liquid crystal 10g (that is, the phase difference given to the light beam B passing through the region corresponding to each pattern electrode). 8 from the top to the bottom (from the top in FIG. 8). Further, thick double arrows in FIG. 8 indicate changes in the tilt angle (positive on the right, negative on the left, and zero on the center).
[0121]
Here, regarding the definition of the positive and negative of the tilt angle, the tilt angle at which a negative wavefront aberration occurs in the area within the light spot SP corresponding to the pattern electrodes 40a and 40b is defined as positive, and conversely, the light corresponding to the pattern electrodes 40a and 40b is defined as The tilt angle at which a positive wavefront aberration occurs in the area within the spot SP is assumed to be negative.
[0122]
First, looking at the case where the tilt angle is zero, in this case, the drive signal Sdv2 is not applied to any of the pattern electrodes 40a, 40b, 41a and 41b. As a result, the voltage applied to the liquid crystal 10g is only due to the drive signal Sdv1, and the potential difference applied to the liquid crystal 10g is also only due to the drive signal Sdv1. And the reference phase difference is given to all the regions, and the light beam B passes through the liquid crystal panel 10 and reaches the DVD 5 without being changed.
[0123]
Next, assuming that the information recording surface of the DVD 5 is tilted and the tilt angle is increased in the positive direction, based on the detected tilt detection signal Sp2, the uppermost stage in FIG. Are applied to the pattern electrodes 40a and 40b and the lines 41a and 41b.
[0124]
That is, in this case, in the area of the liquid crystal 10g corresponding to the pattern electrodes 40a and 40b of the transparent electrode 10d, the above-described reference is used in order to compensate the wavefront aberration based on the wavefront aberration distribution caused by the tilt angle in the tangential direction. It is necessary to give a phase difference larger than the phase difference of That is, it is necessary to apply a potential difference larger than a potential difference that generates a reference phase difference to the region of the liquid crystal 10g corresponding to the pattern electrodes 40a and 40b. Accordingly, as shown on the right side of the second row from the top in FIG. 8, a drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 applied to the opposing transparent electrode 10c is applied to the pattern electrodes 40a and 40b. Is done.
[0125]
On the other hand, in the region of the liquid crystal 10g corresponding to the pattern electrodes 41a and 41b of the transparent electrode 10d, the wavefront aberration is compensated based on the wavefront aberration distribution caused by the tilt angle in the tangential direction. It is necessary to give a small phase difference. That is, a potential difference smaller than the potential difference that generates the reference phase difference is applied to the region of the liquid crystal 10g corresponding to the pattern electrodes 41a and 41b.ApplicationThere is a need to. Therefore, the drive signal Sdv2 having the same phase as the drive signal Sdv1 applied to the opposing transparent electrode 10c is applied to the pattern electrodes 41a and 41b, as shown on the right side at the top of FIG.
[0126]
Also at this time, since the drive signal Sdv1 having the waveform shown in the third row from the top in FIG. 8 is commonly applied to each pattern electrode in the transparent electrode 10c, as a result, the pattern electrode 41a of the liquid crystal 10g is obtained. And the potential difference applied to the regions corresponding to 41b has a small amplitude as shown on the right side of the fourth row from the top in FIG. 8, while the potential difference applied to the regions corresponding to the pattern electrodes 40a and 40b of the liquid crystal 10g. Has a large amplitude as shown on the right side from the top to the bottom in FIG.
[0127]
Therefore, the phase difference given to the light beam B passing through the regions corresponding to the pattern electrodes 41a and 41b by the liquid crystal 10g becomes small, and the phase difference given to the light beam B passing through the regions corresponding to the pattern electrodes 40a and 40b. The phase difference increases. As a result, a phase difference for compensating the wavefront aberration due to the tilt angle generated in the positive direction is given to the light beam B.
[0128]
In the case where the tilt angle occurs in the negative direction, the transparent electrodes which are opposed to the pattern electrodes 40a and 40b as shown on the second left side from the top in FIG. A drive signal Sdv2 having the same phase as that of the drive signal Sdv1 applied to the electrode 10c is applied. In addition, as shown in the upper left portion of FIG. 8, a drive signal Sdv2 having a phase opposite to that of the drive signal Sdv1 applied to the opposing transparent electrode 10c is applied to the pattern electrodes 41a and 41b.
[0129]
As described above, the waveform of the drive signal Sdv2 applied to each electrode pattern on the transparent electrode 10d changes based on the tilt detection signal Sp2 that detects the tilt angle of the DVD 5 in the tangential direction. Since the phase difference given by the tilt angle differs depending on the region of the liquid crystal 10g, the wavefront aberration caused by the tilt angle can be canceled and compensated.
[0130]
Next, the relationship between the extent of the residual wavefront aberration and the extent of the radial displacement when the wavefront aberration is compensated for using the liquid crystal panel 10 of the embodiment will be described with reference to FIG.
[0131]
FIG. 9 shows the magnitude of the displacement and the residual wavefront aberration after compensation by the liquid crystal panel 10 when there is a displacement in the radial direction between the central axis of the transparent electrode 10c and the optical axis of the objective lens 4. The relationship with the amount is experimentally obtained, and when the shape of each pattern electrode included in the transparent electrode 10c is set such that there is no misalignment (indicated by a mark in FIG. 9), the misalignment is zero. . Are plotted as graphs for the case where it is set as 0.3 mm (indicated by a mark in FIG. 9) and the case where the positional deviation is set to be 0.5 mm (indicated by a mark in FIG. 9). It is.
[0132]
As is clear from FIG. 9, when the shape of each pattern electrode in the transparent electrode 10c is set assuming that the displacement is 0.3 mm, the shape of each pattern electrode is changed when there is no such displacement. Compared to the case where the distribution of the wavefront aberration generated on the pupil plane of the objective lens 4 is substantially the same as the shape projected on the transparent electrode 10c, the liquid crystal panel 10 Although the amount of residual wavefront aberration when the device is operated slightly increases, the amount of the residual wavefront aberration when a positional shift of 0.3 mm that can normally occur between the central axes occurs decreases.
[0133]
On the other hand, when the shape of each pattern electrode in the transparent electrode 10c is set on the assumption that the positional deviation is 0.5 mm, the residual wavefront aberration when the positional deviation of 0.5 mm occurs between the respective central axes. Is decreased, but the amount of residual wavefront aberration when the liquid crystal panel 10 is operated when there is no displacement between the central axes and the liquid crystal panel 10 is The amount of residual wavefront aberration when operating is both increased.
[0134]
Therefore, when the shape of each pattern electrode in the transparent electrode 10c is set assuming that the positional deviation is 0.5 mm when the positional deviation is only 0.3 mm, the average residual wavefront aberration as a whole increases conversely. Will be.
[0135]
From this result, as the amount of radial position shift to be considered in setting the shape of each pattern electrode in the transparent electrode 10c, the predicted maximum value of the position shift is set as the upper limit of the position shift amount to be considered. Understand what to do.
[0136]
As described above, according to the liquid crystal panel 10 of the embodiment, the shape of each pattern electrode in the transparent electrode 10c is determined by the optical axis of the objective lens 4 and the central axis of the liquid crystal panel 10 (that is, the central axis of the transparent electrode 10c). ), A shape that compensates for wavefront aberration when there is a radial misalignment, and has a shape that is line-symmetric about a symmetry axis that is perpendicular to the radial direction. Even when the occurrence of the displacement is predicted, there is no deterioration in the compensation effect due to the displacement, and the wavefront aberration after the occurrence of the displacement can be effectively compensated.
[0137]
In addition, since the displacement is a displacement in the radial direction of the DVD 5, in the radial direction in which the displacement is likely to occur, the wavefront aberration that occurs even after the occurrence of the displacement can be effectively compensated.
[0138]
Furthermore, since the shape of each pattern electrode is set based on the shape of each pattern electrode when there is no displacement, the wavefront generated without displacement is compensated to the extent that there is no practical problem. be able to.
[0139]
Furthermore, since the shape of each pattern electrode is set based on the shape of the distribution of the wavefront aberration on the pupil plane of the objective lens 4, the wavefront aberration can be more effectively compensated.
[0140]
Further, the positional deviation is caused by the positioning accuracy in the manufacturing process of the optical pickup 13 and the relative positional deviation between the central axis of the objective lens 4 and the central axis of the liquid crystal panel 10 caused by the tracking servo control at the time of reproducing the information from the DVD 5. , The wavefront aberration can be effectively compensated for in response to a position shift occurring during actual reproduction.
[0141]
Further, the transparent electrode 10d is composed of a plurality of pattern electrodes 40a, 40b, 41a, 41b and 42 having a shape corresponding to the wavefront aberration distribution generated in the tangential direction of the DVD 5, and the tilt angle is formed in the area of each pattern electrode. The drive signal for generating the phase difference for compensating the wavefront aberration caused by the above is independently applied, so that the potential difference applied to the liquid crystal 10g differs depending on the position of each pattern electrode, and the tangential of the DVD 5 Wavefront aberration occurring in the direction can be effectively compensated.
[0142]
Furthermore, since the recorded information on the DVD 5 is reproduced using the light beam B whose wavefront aberration has been compensated, the recorded information can be accurately reproduced.
[0143]
(II)Deformation form
Next, a modified embodiment of the present invention will be described with reference to FIG.
[0144]
In the above-described embodiment, the shape of each pattern electrode in the transparent electrode 10c is set such that the predicted positional deviation in the radial direction between the central axis of the transparent electrode 10c and the optical axis of the objective lens 4 is 0.3 mm. However, in the liquid crystal panel of the modified embodiment, the shape of each of the pattern electrodes is set such that the predicted positional deviation is 0.5 mm.
[0145]
That is, in the actual manufacturing process of the optical pickup 13, the positioning accuracy may suddenly be extremely deteriorated. Further, when reproducing information from the DVD 5, for example, at the time of a so-called track jump or the like, normal tracking is performed. The amount of movement of the objective lens 4 in the radial direction is further increased as compared with the servo control.
[0146]
Therefore, in consideration of such a situation, it is better to set the predicted positional deviation in the radial direction to 0.5 mm in setting the shape of each pattern electrode in the transparent electrode 10c.
[0147]
That is, as shown in FIG. 10, the shape of the pattern electrodes 30a ', 30b', 31a ', 31b', and 32 'is such that when the optical axis of the objective lens 4 passes through the center of the transparent electrode 10c', The distribution of the wavefront aberration generated on the pupil plane is substantially the same as the shape projected on the transparent electrode 10c '(shown by a broken line in FIG. 10). When the position of the optical axis 4 is shifted by 0.5 mm in the radial direction (the range SP ′ in which the range of the light beam B passing through the objective lens 4 is projected onto the transparent electrode 10c ′ when the position is shifted is shown in FIG. The shape of the distribution of the wavefront aberration generated on the pupil plane of the objective lens 4 projected on the transparent electrode 10c 'is taken into consideration, and the line is symmetric about the axis perpendicular to the radial direction. Set to It is.
[0148]
The method of setting this shape is the same as the method described in (i) to (iv) in the above-described embodiment when the positional deviation to be considered is 0.5 mm.
[0149]
As shown in FIG. 10, the shape of each pattern electrode formed by this procedure is the shape of each pattern electrode (shown by a broken line in FIG. 10) assuming that there is no displacement, as shown in FIG. The shape becomes more elongated in the radial direction as compared to 10c.
[0150]
According to the transparent electrode 10c ′ having each pattern electrode set as described above, in addition to the effect of the transparent electrode 10c of the embodiment, even if the positional deviation in the radial direction becomes extremely large, the effect of compensating the wavefront aberration is obtained. Degradation can be reduced.
[0151]
In the above-described embodiments and modified examples, the case where the present invention is applied to the liquid crystal panel 10 in the information reproducing apparatus S has been described. In an information recording apparatus that records information on the recording medium while reading the information and the like, the information is recorded within the irradiation range of the light beam due to the inclination between the optical axis of the recording light beam and the information recording surface of the recording medium. The present invention can also be applied to a liquid crystal panel that compensates for generated wavefront aberration.
[0152]
【The invention's effect】
As described above, according to the first aspect of the present invention, the shape of each partially transparent electrode is in a plane perpendicular to the optical axis between the central axis of the light collecting means and the central axis of the liquid crystal panel. Since there is a shape that compensates for wavefront aberration when there is a preset position shift, even if the occurrence of a position shift is predicted in advance, there is no deterioration in the compensation effect due to the position shift, and The wavefront aberration after the occurrence of the displacement can be effectively compensated.
Further, even when the direction of the positional deviation cannot be specified in advance, it is possible to prevent deterioration of the compensation effect caused by the positional deviation corresponding to at least two types of positional deviations occurring in opposite directions, and Wavefront aberration can be effectively compensated.
Further, since the positional deviation is a radial positional deviation in the disk-shaped recording medium, the generated wavefront aberration can be effectively compensated even in the radial direction where the positional deviation is likely to occur even after the positional deviation occurs.
[0154]
Claim2According to the invention described in (1), the claims1In addition to the effects of the invention described in the above, since the shape of each partial transparent electrode is set based on the shape of each partial transparent electrode when there is no displacement, it occurs when there is no displacement. The wavefront can also be compensated.
[0155]
Claim3According to the invention described in (1), claim 1Or 2In addition to the effects of the invention described in (1), since the shape of each partial transparent electrode is set based on the distribution of wavefront aberration on the pupil plane of the light condensing means, it is possible to more effectively compensate for the wavefront aberration. Can be.
[0157]
Claim4According to the invention described in (1), from claim 13In addition to the effects of the invention described in any one of the above, in addition to the positional deviation, the position shift occurs in the manufacturing process of the optical pickup including the liquid crystal panel and the light condensing means and the light condensing generated at the time of recording / reproducing information on the recording medium. Since it is set in advance based on the relative displacement between the center axis of the means and the center axis of the liquid crystal panel, the wavefront aberration is effectively compensated for in response to the displacement occurring during actual recording / reproduction. be able to.
[0161]
Claim5According to the invention described in (1), from claim 14In addition to the effect of the invention described in any one of the above, even if the positional deviation between the central axis of the liquid crystal panel and the central axis of the light condensing means that is assumed in advance actually occurs due to the positional deviation. Therefore, the wavefront aberration after the occurrence of the positional deviation can be effectively compensated, and, for example, erroneous detection of information on the recording medium due to the wavefront aberration can be prevented.
[0162]
Claim6According to the invention described in (1), the claims5In addition to the effects of the invention described in (1), even if a positional shift occurs between the central axis of the liquid crystal panel and the central axis of the light collecting means, it is possible to compensate for the wavefront aberration and to reproduce the information well.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an information reproducing apparatus according to an embodiment.
FIGS. 2A and 2B are vertical cross-sectional views illustrating a configuration of a liquid crystal panel. FIG. 2A is a vertical cross-sectional view illustrating a liquid crystal in which liquid crystal molecules are in a horizontal state, and FIG. (C) is a longitudinal sectional view showing a liquid crystal in which liquid crystal molecules are vertical.
3A and 3B are plan views illustrating a configuration of a transparent electrode according to an embodiment. FIG. 3A is a plan view illustrating a configuration of a transparent electrode for a radial direction, and FIG. 3B is a plan view of a configuration of a transparent electrode for a tangential direction. FIG.
FIG. 4 is a view showing the shape of each pattern electrode in a transparent electrode in the embodiment.
FIG. 5 is a plan view showing distribution of wavefront aberration.
FIG. 6 is a diagram illustrating the magnitude of wavefront aberration.
FIG. 7 is a timing chart showing a waveform of a drive signal applied to each pattern electrode of the embodiment.
FIG. 8 is a diagram showing a potential difference applied to a liquid crystal in the embodiment.
FIG. 9 is a diagram showing the relationship between the amount of displacement and the amount of residual wavefront aberration.
FIG. 10 is a view showing the shape of each pattern electrode in a transparent electrode according to a modified embodiment.
[Explanation of symbols]
1 ... Laser diode
2. Half mirror
4: Objective lens
5 ... DVD
6. Condensing lens
7 ... Receiver
10 LCD panel
11 ... radial direction tilt sensor
12 ... Tangential direction tilt sensor
13. Optical pickup
14 ... Spindle motor
20: playback control unit
21 ... CPU
22, 25 ... A / D converter
23, 26 ... PWM circuit
24, 27… Amplifier
Sr: detection signal
Sd: playback signal
Sdv1, Sdv2... Drive signal
Sp1, Sp2 ... Tilt detection signal
10a, 10b ... glass substrate
10c, 10c ', 10d ... transparent electrodes
10e, 10f: alignment film
10g ... liquid crystal
30a, 30a ', 30b, 30b', 31a, 31a ', 31b, 31b', 32, 32 ', 40a, 40b, 41a, 41b, 42 ... pattern electrodes
SP, SP '... light spot
M: liquid crystal molecules

Claims (6)

The information is arranged on an optical path of a light beam for recording / reproducing information, and the information is recorded due to an inclination between an optical axis of the light beam and an information recording surface of a recording medium on which the information is recorded / reproduced. In a liquid crystal panel for compensating a wavefront aberration generated on a recording surface by giving a phase difference to the light beam,
A transparent electrode for applying a voltage to the liquid crystal of the liquid crystal panel, having a transparent electrode composed of a plurality of partial transparent electrodes having a shape corresponding to the distribution of the wavefront aberration to be compensated,
The shape of each of the partial transparent electrodes is displaced in a plane perpendicular to the optical axis between a central axis of a condensing unit that condenses the light beam on the information recording surface and a central axis of the liquid crystal panel. A shape that is line-symmetric with respect to an axis of symmetry perpendicular to the direction of the displacement, and that compensates for the wavefront aberration that occurs when there is a displacement of a predetermined size. It is a,
The recording medium is a disk-shaped recording medium,
The liquid crystal panel according to claim 1 , wherein the pattern shape of the transparent electrode is a shape obtained by extending the electrode pattern shape in the radial direction when there is no displacement . The liquid crystal panel according to claim 1 ,
A liquid crystal panel, wherein the shape of each of the partial transparent electrodes is set based on the shape of each of the partial transparent electrodes when there is no displacement. In the liquid crystal panel according to claim 1 or 2,
A liquid crystal panel, wherein a shape of each of the partial transparent electrodes is set based on a distribution of the wavefront aberration on a pupil plane of the light collecting means. The liquid crystal panel according to any one of claims 1 to 3 ,
The misalignment is caused by the positional accuracy between the central axis of the liquid crystal panel and the central axis of the light condensing means in the manufacturing process of the optical pickup including the liquid crystal panel and the light condensing means, and the information with respect to the recording medium. When recording / reproducing the light, the relative position shift between the central axis of the light collecting means and the central axis of the liquid crystal panel caused by the movement of the light collecting means in a plane perpendicular to the optical axis. A liquid crystal panel, wherein the liquid crystal panel is set in advance. A liquid crystal panel according to any one of claims 1 to 4 ,
A light source for emitting the light beam;
By applying a voltage to each of the partially transparent electrodes, voltage applying means for giving the phase difference to the light beam,
The light condensing means for condensing the light beam passing through the liquid crystal panel on the recording medium,
Light receiving means for receiving the light beam reflected by the recording medium and outputting a light reception signal,
An optical pickup comprising: An optical pickup according to claim 5 ,
When the information is recorded on the recording medium, reproducing means for reproducing the information based on the light receiving signal,
An information reproducing apparatus comprising:

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