JP2004020698A - Optical path deflecting device, optical path deflecting apparatus and image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical path deflecting device which can eliminate difference in the image point distance in the propagation direction of light caused by deflection of the optical path according to the polarizing direction and which prevents aberration due to the difference in the image point distance. <P>SOLUTION: The optical path deflecting device is equipped with a polarization direction switching means 2 installed in the entrance side of light to switch the polarization direction of the incident linearly polarized light, and an optical path deflecting means (birefringent medium) 3 to switch the propagation direction of light according to the polarization direction switched by the above polarization direction switching means 2. In this constitution, even when the image point distance differs between in the first and second propagation directions of the light caused by the deflection of the optical path by the optical path deflecting means 3 responding to the polarization direction, the image point distances are adjusted to be almost equal to each other by an image point distance compensation means 4 to eliminate the difference in the image point distance. This prevents aberration caused by the difference in the image point distance. <P>COPYRIGHT: (C)2004,JPO

Description

となる。
【００１８】
これは具体的には、図１１において受光部１０５で等しく結像させるためには、光源１０３の位置を▲３▼の場合（第２の進行方向）の方が▲２▼（第１の進行方向）に比べてΔＬだけ遠ざける必要があることを意味する。
【００１９】
逆に、光源１０３の位置及び受光部１０５の位置が固定の場合、受光部１０５の位置での収差Ｄｆは、結像レンズ１０４の像点距離差ΔＬと投射倍率Ｍとから、Ｄｆ＝Ｍ^２・ΔＬとなり、Ｍ＝５０／０．８５＝５８．８を仮定すると、
Ｄｆ（ｍｍ）＝４．４６０
となる。この収差は、一般的な結像レンズの焦点深度と比較して無視できない値であり、第１の光の進行方向と第２の光の進行方向とで焦点ボケが発生することを示している。
【００２０】
この結果、このような光路偏向デバイスを画像表示装置や撮像装置に利用する際には、各進行方向によって収差が発生し画像が劣化してしまう不具合があり、また、光スイッチに利用する際にはＳＮ比が劣化してしまうこととなる。
【００２１】
本発明は、偏光方向に応じた光路偏向に伴う光の進行方向における像点距離差をなくすことができ、像点距離差に起因する収差の発生を防止できる光路偏向デバイス、光路偏向装置及び画像表示装置を提供することを目的とする。
【００２２】
本発明は、上記目的を簡単な構造で実現する。
【００２３】
本発明は、上記目的を実現する上で、光学設計上も光路計算が複雑となることなく設計可能にする。
【００２４】
本発明は、上記目的を実現する上で、環境温度等の光偏向量の誤差要因による影響を排除して像点距離を常に一定に保てるようにする。
【００２５】
【課題を解決するための手段】
請求項１記載の発明の光路偏向デバイスは、光の入射側に配設されて入射する直線偏光の偏光方向を切換える偏光方向切換手段と、この偏光方向切換手段により切換えられた偏光方向に応じて光の進行方向を切換える光路偏向手段と、この光路偏向手段により切換えられた光の各進行方向における像点距離が略等しくなるよう調整する像点距離補償手段と、を備える。
【００２６】
従って、偏光方向に応じた光路偏向手段による光路偏向に伴う光の進行方向における像点距離に差があっても、像点距離補償手段によって像点距離が略等しくなるよう調整することで像点距離差がなくなり、像点距離差に起因する収差の発生が防止される。
【００２７】
請求項２記載の発明は、請求項１記載の光路偏向デバイスにおいて、前記光路偏向手段が、偏向用の複屈折性媒体である。
【００２８】
従って、請求項１記載の発明を実現する上で、光路偏向手段として一般的な複屈折性媒体を用いることができる。
【００２９】
請求項３記載の発明は、請求項１又は２記載の光路偏向デバイスにおいて、前記像点距離補償手段が、前記光の各光進行方向における像点距離差を短縮させる屈折率異方性を有する補償用の複屈折性媒体である。
【００３０】
従って、請求項１又は２記載の発明を実現する上で、像点距離補償手段として像点距離差を短縮させる屈折率異方性を有する複屈折性媒体を用いることで、簡単に実現可能となる。
【００３１】
請求項４記載の発明は、請求項３記載の光路偏向デバイスにおいて、前記補償用の複屈折性媒体は、一軸光学結晶による複屈折板であり、その光学結晶軸が入射光軸と略垂直に設定されている。
【００３２】
従って、請求項３記載の発明を実現する上で、補償用の複屈折性媒体として、一軸光学結晶による複屈折板を用い、その光学結晶軸を入射光軸と略垂直に設定することで、各々の進行方向に導かれる光に屈折、散乱等を発生させることなく像点距離差が短縮され、また、光学設計上も光路計算が複雑化することなく容易に設計可能となる。
【００３３】
請求項５記載の発明は、請求項３又は４記載の光路偏向デバイスにおいて、前記補償用の複屈折性媒体は、ＬｉＮｂＯ_３結晶であり、その光学結晶軸が前記偏光方向切換手段により切換えられる偏光方向のうちの一つと略一致するように設定されている。
【００３４】
従って、補償用の複屈折性媒体をＬｉＮｂＯ_３結晶製とし、その光学結晶軸を偏光方向切換手段により切換えられる偏光方向のうちの一つと略一致するように設定することで、良好な像点距離補償が可能となると同時に、ＬｉＮｂＯ_３結晶は光学結晶の中でも潮解性などなく安定で、さらにΔｎ（＝ｎｏ−ｎｅ）が適度な大きさを有しており、取扱いやすい。
【００３５】
請求項６記載の発明は、請求項５記載の光路偏向デバイスにおいて、前記補償用の複屈折性媒体の板厚は、当該複屈折性媒体がない場合の前記光路偏向手段による前記光の各進行方向において生ずる像点距離差ΔＬ及び入射光波長における各々の偏光方向の光に対する屈折率ｎｅ，ｎｏに対して、ΔＬ／（１／ｎｏ−１／ｎｅ）±３０（μｍ）の範囲内に設定されている。
【００３６】
従って、補償用の複屈折性媒体の板厚をΔＬ／（１／ｎｏ−１／ｎｅ）±３０（μｍ）の範囲内に設定することで、各進行方向に導かれる光の像点距離差は適切に短縮される。ちなみに、±３０（μｍ）を超える値に板厚を設定した場合、収差が十分解消されず良好な像が得られない。
【００３７】
請求項７記載の発明の光路偏向デバイスは、光の入射側に配設されて入射する直線偏光の偏光方向を切換える偏光方向切換手段と、この偏光方向切換手段により切換えられた偏光方向に応じて光の進行方向を切換える光路偏向手段と、を備え、前記光路偏向手段は、当該光路偏向手段により切換えられる光の各進行方向における像点距離が略等しくなるよう入射光の光軸に対して傾斜した傾斜面を有する。
【００３８】
従って、偏光方向に応じた光路偏向手段による光路偏向に伴う光の進行方向における像点距離に差があっても、像点距離が略等しくなるよう当該光路偏向手段を入射光の光軸に対して傾斜した傾斜面を有することで、像点距離差がなくなり、像点距離差に起因する収差の発生が防止される。特に、補償用の複屈折性媒体のような別部材を追加して備える必要がなく、例えば光路偏向手段の姿勢設定だけで簡単に実現可能となる。
【００３９】
請求項８記載の発明は、請求項７記載の光路偏向デバイスにおいて、入射光の光軸に対して傾斜した前記傾斜面を持つように前記光路偏向手段を傾斜させて保持する保持手段を備える。
【００４０】
従って、光路偏向手段の姿勢設定だけで簡単に請求項７記載の発明が実現可能となる。
【００４１】
請求項９記載の発明は、請求項７記載の光路偏向デバイスにおいて、前記光路偏向手段の入・出射両面を鋸歯構造に形成することにより入射光の光軸に対して傾斜した前記傾斜面を有する。
【００４２】
従って、偏光方向切換手段と当該光路偏向手段との設置時の位置調整を簡略化でき、さらに光路偏向手段を光軸に垂直に配置することができるため、大面積化した時に必要なスペースを比較的小さくすることもできる。
【００４３】
請求項１０記載の発明は、請求項７ないし９の何れか一記載の光路偏向デバイスにおいて、前記光路偏向手段が、ＬｉＮｂＯ_３による複屈折性媒体であり、入射光の光軸と当該複屈折性媒体の法線とのなす傾斜面の傾斜角ｉを、ｉ＝０の時にこの複屈折性媒体内で入射光が偏向する角度方向を正とした時、負方向に設定してなる。
【００４４】
従って、例えば画像表示装置において受光部上に良好に結像させるためには受光位置における結像レンズの焦点深度以内に各進行方向の像点距離の差を抑える必要があるが、入射光の光軸と複屈折性媒体の法線とのなす傾斜角ｉを負方向に設定することで、上記条件を満たすための関係を保つことができる。
【００４５】
請求項１１記載の発明は、請求項３ないし６の何れか一記載の光路偏向デバイスにおいて、前記補償用の複屈折性媒体を挟む位置に配設されて当該複屈折性媒体に対して電界を作用させるための少なくとも一対の電極を備える。
【００４６】
従って、像点距離は入射光の波長や環境変動によって変化してしまうが、補償用の複屈折性媒体を挟む位置に配設されて当該複屈折性媒体に対して電界を作用させるための少なくとも一対の電極を備えるので、これらの電極間に印加する電圧を適正に制御することで像点距離の変動を抑えることが可能となる。この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動を抑えることが可能となり、高精細なカラー画像表示に役立つ。
【００４７】
請求項１２記載の発明は、請求項８ないし１０の何れか一記載の光路偏向デバイスにおいて、前記複屈折性媒体を挟む位置に配設されて当該複屈折性媒体に対して電界を作用させるための少なくとも一対の電極を備える。
【００４８】
従って、像点距離は入射光の波長や環境変動によって変化してしまうが、傾斜配設された偏向用の複屈折性媒体を挟む位置に配設されて当該複屈折性媒体に対して電界を作用させるための少なくとも一対の電極を備えるので、これらの電極間に印加する電圧を適正に制御することで像点距離の変動を抑えることが可能となる。この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動を抑えることが可能となり、高精細なカラー画像表示に役立つ。
【００４９】
請求項１３記載の発明の光路偏向装置は、請求項１１又は１２記載の光路偏向デバイスと、前記電極に電圧を印加する電圧印加手段と、この光路偏向デバイスから出射される光の各進行方向における焦点位置を測定する焦点位置測定手段と、この焦点位置測定手段により測定された各進行方向での焦点位置の差に基づき前記電極に印加する前記電圧印加手段の印加電圧のフィードバック信号を生成するフィードバック信号生成手段と、を備える。
【００５０】
従って、像点距離は入射光の波長や環境変動によって変化してしまうが、光路偏向デバイスから出射される光の各進行方向における焦点位置を測定し、測定された各進行方向での焦点位置の差に基づき電極極に印加する印加電圧のフィードバック信号を生成することで、常に像点距離を一定に保つことが可能となる。この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動をなくすことが可能となり、高精細なカラー画像表示に役立つ。
【００５１】
請求項１４記載の発明の画像表示装置は、画像情報に従って光を制御可能な複数の画素を２次元的に配列した画像表示素子と、この画像表示素子を照明する照明装置と、前記画像表示素子に表示した画像パターンを観察するための光学装置と、画像フィールドを時間的に分割した複数のサブフィールドで形成する表示駆動手段と、前記画像表示素子の各画素からの出射光の光路を前記サブフィールド毎に偏向する請求項１ないし１２の何れか一記載の光路偏向デバイスを有する光路偏向装置又は請求項１３記載の光路偏向装置と、を備える。
【００５２】
従って、従来のピクセルシフト技術では投射光をスクリーンに結像させる時にシフト位置毎に像点距離が異なるために収差が発生し、同一面上に良好な結像が得られない問題があり、画像が劣化してしまう不具合があったが、本発明によれば、画像表示装置内に像点距離の差をなくす構成の請求項１ないし１２の何れか一記載の光路偏向デバイスを有する光路偏向装置又は請求項１３記載の光路偏向装置を備えているので、上記不具合を解消でき、焦点ボケによる画像劣化のない良好な表示が可能となる。
【００５３】
【発明の実施の形態】
本発明の第一の実施の形態を図１及び図２に基づいて説明する。図１は、本実施の形態の光路偏向デバイス１の原理的な構成例を示す側面図である。本実施の形態の光路偏向デバイス１は、概略的には、偏光方向切換手段２と光路偏向手段としての偏向用の複屈折性媒体３とを備えた図１０に示したような従来構成に加えて、その出射側（光進行方向の後段）に複屈折性媒体３により切換えられた光の各進行方向における像点距離が略等しくなるよう調整する像点距離補償手段４を配設させた構成とされている。
【００５４】
ここに、当該光路偏向デバイス１に入射する直線偏光の偏光方向を時間的に切換える偏光方向切換手段２としては、従来の場合と同様に、液晶層を用いて構成することができる。複屈折性媒体３は、例えば、ＬｉＮｂＯ_３よりなる複屈折板であり図１中に矢印で示す光学結晶方向は法線方向より４５°傾いている。
【００５５】
従来例で説明した通り、光シフト量６．６μｍを確保する場合、複屈折板３の板厚は１７２．２μｍが必要となり、その時の第１の光進行方向と第２の光進行方向との像点距離差ΔＬは１．２９μｍである。像点距離補償手段４は、この像点距離差ΔＬが例えば結像レンズ（図示せず）の焦点深度に比較して十分小さな値となるように補正するものである。
【００５６】
このような像点距離補償手段４としては、第１及び第２の進行方向における像点距離差ΔＬを短縮させる屈折率異方性を有する複屈折性媒体（補償用の複屈折性媒体）を好適に用いることが有効であり、その具体例として、複屈折性媒体３と同様に、ＬｉＮｂＯ_３を使用することが可能である。ただし、その光学結晶軸は、複屈折性媒体３で設定される光シフト量を変化させないよう、光軸と垂直な方向に設定するのが好ましい。ちなみに、この関係を保てない場合は像点距離補償手段４においても光シフトが発生することになり光学設計が複雑化する。
【００５７】
像点距離補償手段４用の複屈折性媒体としては、石英，ＫＤＰ（ＫＨ_２ＰＯ_４），ＤＫＤＰ（ＫＤ_２ＰＯ_４），ＬｉＮｂＯ_３，ＬｉＴａＯ_３などを用いることができるが、中でも、潮解性がなく安定して使用でき、さらにΔｎ（＝ｎｏ−ｎｅ）が適度な大きさのＬｉＮｂＯ_３が特に優れている。
【００５８】
ここではＬｉＮｂＯ_３を像点距離補償手段４に用いた場合の適切な厚みｄ_ｃｏｍｐについての例を示す。複屈折性媒体３から出射した２つの進行方向（第１の光進行方向、第２の光進行方向）の光は、偏光方向が互いに垂直であり、上記▲４▼に示す通り第２の光進行方向の光が進んでいる。そこで、第１の光の進行方向が常光に対応し、第２の光の進行方向が異常光に対応するように像点距離補償手段４を配置させる。
【００５９】
この時、各々の進行方向の場合の真空に対する像点移動距離は厚みをｄ_ｃｏｍｐとおけば、ｄ_ｃｏｍｐ　（１−１／ｎｏ）及びｄ_ｃｏｍｐ　（１−１／ｎｅ）で表される。従って、前述のΔＬ＝１．２９の像点移動距離差を解消するためには、
ｄ_ｃｏｍｐ　（１−１／ｎｏ）−ｄ_ｃｏｍｐ　（１−１／ｎｅ）＝ΔＬ＝１．２９
を満足する厚み、即ち、ｄ_ｃｏｍｐ＝７５．４（μｍ）に設定すればよい。
【００６０】
図２はＬｉＮｂＯ_３厚ｄ_ｃｏｍｐに対する収差を示すもので、結像レンズとして焦点深度±２ｍｍのものを採用した場合、像点距離補償手段４の厚みは、
４２＜ｄ_ｃｏｍｐ＜１０９
に設定することで良好な結像を得ることができる。
【００６１】
一般的に、ＬｉＮｂＯ_３を像点距離補償手段４に用いた場合、ｄ_ｃｏｍｐとしては、この像点距離補償手段４を設けない場合の像点距離差ΔＬ及び入射光波長におけるＬｉＮｂＯ_３の異常光、常光の屈折率ｎｅ，ｎｏによって定まる値、即ち、ｄ_ｃｏｍｐ＝ΔＬ／（１／ｎｅ−１／ｎｏ）（上記の場合、７５μｍ）に対して、±３０μｍの範囲内に設定することで良好な像点距離補償が可能となる。
【００６２】
本発明の第二の実施の形態を図３ないし図５に基づいて説明する。図３は、本実施の形態の光路偏向デバイス１１の原理的な構成例を示す側面図である。本実施の形態の光路偏向デバイス１１は、概略的には、偏光方向切換手段１２と光路偏向手段としての複屈折性媒体１３とを備える基本構成において、この複屈折性媒体１３により切換えられた光の各進行方向における像点距離が略等しくなるよう入射光の光軸に対して傾斜した傾斜面１４を持つように当該複屈折性媒体１３を傾斜させて保持する保持手段１５を備える構成とされている。
【００６３】
ここに、当該光路偏向デバイス１１に入射する直線偏光の偏光方向を時間的に切換える偏光方向切換手段１２としては、従来の場合と同様に、液晶層を用いて構成することができる。複屈折性媒体１３は、例えば、ＬｉＮｂＯ_３よりなる複屈折板であり図３中に矢印で示す光学結晶方向は法線方向より４５°傾いている。また、この複屈折性媒体１３は保持手段１５によって入射光の光軸に対して所定角度ｉだけ傾斜させた傾斜面１４を持つように設置されている。
【００６４】
以下、図４を参照して、複屈折性媒体１３が所定角度ｉだけ傾斜させた傾斜面１４を持つことで第１，第２の進行方向の光間の像点距離の差を補償させることが可能な点について説明する。図４（ａ），（ｂ）は複屈折性媒体（複屈折板）１３としてＬｉＮｂＯ_３を用いた時の光の進行方向を示すものであり、入射光１６，１７は複屈折板１３の法線方向から角度ｉだけ傾斜している（角度は時計回り方向を正にとるものとする）。図４（ａ）は入射光１６の偏光方向が図中に示す直交座標系においてＺ方向であり、図４（ｂ）は入射光１７の偏光方向がＹ方向である場合を示している。何れの場合も入射光１６，１７の偏光方向のみ異なり光学結晶及びその配置は同様である。光学結晶軸は前述の場合と同様にＬｉＮｂＯ_３を想定し、複屈折板１３の法線方向からΨ（＝４５°）だけ傾いたものが用いられ、厚みはｄ＝１７２．２μｍに設定される。このとき、図４（ａ）において光学結晶内での光進行方向の法線とのなす角ｒ′は、
ｔａｎｒ′＝−Ｂ／Ｃ＋ｓｉｎ（ｉ）＊｛（ＡＢ−Ｃ２）／（Ｂ−ｓｉｎ^２（ｉ））｝^１／２　……▲５▼
で示される（Ｍ．Ｆｒａｎｃｏｎ　ａｎｄ　Ｓ．Ｍａｌｌｉｃｋ：Ｐｏｌａｒｉｚａｔｉｏｎ　Ｉｎｔｅｒｆｅｒｏｍｅｔｅｒｓ，ＷＩＬＥＹ−ＩＮＴＥＲＳＣＩＥＮＣＥ，（１９７１）　ｐ．１４０）。ただし、
ａ＝１／ｎｅ＝１／２．２００＝０．４３７４
ｂ＝１／ｎｏ＝１／２．２８６＝０．４５４５
Ａ＝ｓｉｎ^２Ψ／ａ^２＋ｃｏｓ^２Ψ／ｂ^２　＝５．０３２９
Ｂ＝ｃｏｓ^２Ψ／ａ^２＋ｓｉｎ^２Ψ／ｂ^３　＝５．０３２９
Ｃ＝ｓｉｎΨ・ｃｏｓΨ・（１／ｂ^２−１／ａ^２）　＝−０．１９３
一方、図４（ｂ）において光学結晶内での光進行方向の法線とのなす角ｒは、
ｔａｎｒ＝ｂ＊ｓｉｎ（ｉ）／（１−ｂ^２ｓｉｎ^２（ｉ））^１／２　…………▲６▼
で表される。
【００６５】
これらの▲５▼▲６▼式から各々の偏光方向における入射角ｉに対する像点距離差、シフト量が求められる。
【００６６】
図５はその計算結果を示すものである。入射角０°の時には前述の通り、６．６μｍシフトし、収差はやはり前述の通り４．４６０ｍｍであり焦点ボケが発生する。この状態から光の入射角を変えることで像点距離差は変化し、−１７°において像点距離差が０となる。このとき、光シフト量は６．７６μｍであり初期値からの変化はほとんどない。即ち、ＬｉＮｂＯ_３を光軸から１７°傾斜させることで光シフト量を確保したまま像点距離差を解消し、第１の光進行方向及び第２の光進行方向における結像位置を一致させることが可能となる。
【００６７】
結像レンズとして焦点深度±２ｍｍのものを採用した場合、入射角（傾斜角）ｉは、
−２４＜ｉ＜−１０
に設定することで良好な結像を得ることができる。このように入射角ｉは負の方向、即ち、ｒ′を小さくする方向に傾けることで光路長差を補償することが可能となる。一般的に、ＬｉＮｂＯ_３を用いた場合、入射角（傾斜角）ｉとしては、光学シフト量等、用途によって定まる中心値（上記の場合、−１７°）に対して、±７°の範囲内に設定することで良好な像点距離補償が可能である。
【００６８】
本発明の第三の実施の形態を図６に基づいて説明する。本実施の形態の光路偏向デバイス１１では、第二の実施の形態における傾斜配設の複屈折性媒体１３に代えて、光路偏向手段としての複屈折性媒体２１の入・出射両面をＺ方向に複数に分割した形の鋸歯構造に加工することにより入射光の光軸に対して所定角度ｉだけ傾斜した傾斜面２２を持たせた構成としたものである。複屈折性媒体２１はＬｉＮｂＯ_３よりなる複屈折板であり光学結晶方向は図６中に矢印で示すように法線方向より４５°傾いている。複屈折性媒体２１の鋸歯構造は、例えば、グラジュエーションマスク等を用いたフォトリソグラフィ工程で形成することができる。
【００６９】
このような構造をとることで、偏光方向切換手段１２と複屈折板２１との設置時の位置調整を簡略化でき、さらに複屈折板２１を光軸に垂直に配置することができるため、大面積化した時に必要なスペースを比較的小さくすることができる。
【００７０】
本発明の第四の実施の形態を図７及び図８に基づいて説明する。本実施の形態は、例えば図１に示したような構成の光路偏向デバイス１を利用した光路偏向装置３１の構成例を示す。
【００７１】
本実施の形態の光路偏向装置３１では、光路偏向デバイス１が備える像点距離補償手段としての複屈折性媒体４の入・出射両面にこの複屈折性媒体４を挟むように配設されて複屈折性媒体４に電界を作用させるための一対の電極３２ａ，３２ｂが設けられ、これらの電極３２ａ，３２ｂ間に電圧を印加するために電圧印加手段としての電源３３が接続されている。
【００７２】
電極３２ａ，３２ｂ間に印加する電圧値は、入射光の波長や環境変動によって変化する像点距離差ΔＬを、複屈折性媒体４への電圧印加により電界を作用させることで所望の位置に制御するために印加される。入射光波長が変化する場合、前述の波長６３３ｍｍの屈折率（ｎｏ＝２．２８６，ｎｅ＝２．２００）から求められるΔＬ（＝１．２９）は前述の第一の実施の形態中の計算からＬｉＮｂＯ_３を７５．４μｍ厚に設定することで解消できた。この条件で、例えば波長３３９０ｎｍの光を入射させた場合、ＬｉＮｂＯ_３の３３９０ｎｍにおける屈折率（ｎｏ＝２．１４６，ｎｅ＝２．０８１）に対して電圧を印加することで、波長６３３ｎｍにおいて屈折率関係式（１／ｎｅ−１／ｎｏ）より求められる値、即ち、１／２．２０−１／２．２８６＝０．０１６６と同じ値が得られる電圧を求めればよい。
【００７３】
ＬｉＮｂＯ_３の場合、作用させる電界Ｅによる屈折率の変化Δｎｏ及びΔｎｅは波長３３９０ｎｍにおいて各々、
Δｎｏ＝−３．２１×１０^−１１Ｅ
Δｎｅ＝−１２６．２×１０^−１１Ｅ
で表され、ＬｉＮｂＯ_３の厚みとして前述のｄ_ｃｏｍｐ　＝７５．４（μｍ）を採用すると、電極３２ａ，３２ｂに印加する電圧Ｖに変換すると、
Δｎｏ＝−４．２８×１０^−７Ｖ
Δｎｅ＝−１．６８×１０^−６Ｖ
の値が得られる。
【００７４】
図８は波長３３９０ｎｍにおいて電圧Ｖを変化させた時の（１／ｎｅ−１／ｎｏ）の値の変化を示すものである。この図から分かるように、６３３ｎｍの時の値０．０１６６を得るのに６．９ｋＶの電圧を印加すればよいことになる。
【００７５】
具体的には、光路偏向装置３１としては、図７に示すように、光路偏向デバイス１から出射される光の各進行方向（第１，２の進行方向）における焦点位置を測定するための焦点距離測定手段３４と、この焦点距離測定手段３４により得られた各進行方向での焦点位置の差に基づき、電源３３で発生する印加電圧を制御するためのフィードバック信号を生成するフィードバック信号生成手段３５を付加して構成すればよい。なお、３６は焦点距離測定手段３４に光路偏向デバイス１から出射される光の一部を導くためのミラーである。
【００７６】
焦点距離測定手段３４は、通常、カメラのオートフォーカス機構に用いられている焦点距離測定手段を好適に用いることができ、例えばＣＣＤ（Ｃｈａｒｇｅ　Ｃｏｕｐｌｅｄ　Ｄｅｖｉｃｅ）アレイを利用することができる。動作としては、入射光としてある空間周波数を有する画像パターンを用意しこの光の一部或いは全部をＣＣＤアレイに入射させる。予めＣＣＤアレイにおいて、ある定められた焦点距離の時に得られる画像信号を基準信号としてフィードバック信号生成手段３５に記憶させておき、この値に最も近くなる画像信号が得られるように電源３３からの電圧を選べばよい。これによって、像点距離を常に一定に保つことが可能な光路偏向装置３１を構成することができ、環境温度等、光偏向量の誤差要因による影響を排除することができる。この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動をなくすことが可能となり、高精細なカラー画像表示が可能となる。
【００７７】
また基準信号を用いる代わりに、各進行方向における画像信号の差が最も少なくなるようにフィードバックしてもよく、これによって各進行方向における像点位置の差を低減させることが可能となる。
【００７８】
ミラー３６にはハーフミラーを用いて常時光の一部が焦点距離測定手段に導かれるようにしてもよいが、光利用効率を低下させないために、必要な時にのみ光路中に挿入され、それ以外は光路外に退避させるように設計するのが好ましい。
【００７９】
なお、本実施の形態では、像点距離補償手段としての複屈折性媒体４の両面に一対の電極３２ａ，３２ｂを設けて電圧を印加させるように構成したが、例えば、第二、第三の実施の形態のように像点距離補償手段を別個に要せず、光路偏向手段として設けられ傾斜面を有する複屈折性媒体１３，２１の場合にもその両面に一対の電極を設けて電圧印加可能に構成してもよい。
【００８０】
本発明の第五の実施の形態を図９に基づいて説明する。本実施の形態は、画像表示装置への適用例を示す。図９において、４１はＬＥＤランプを２次元アレイ状に配列した照明装置用の光源であり、この光源４１からスクリーン４２に向けて発せられる光の進行方向には拡散板４３、コンデンサレンズ４４、画像表示素子としての透過型液晶パネル４５、画像パターンを観察するための光学装置としての投射レンズ４６が順に配設されている。４７は光源４１に対する光源ドライブ部、４８は透過型液晶パネル４５に対する表示駆動手段としての液晶ドライブ部である。
【００８１】
ここに、透過型液晶パネル４５と投射レンズ４６との間の光路上にはピクセルシフト素子として機能する光路偏向装置４９が介在されている。この光路偏向装置４９は、前述した各実施の形態で説明したような光路偏向デバイス１又は１１等を有する構成、或いは、光路偏向装置３１からなるものであり、その光路偏向デバイスの有効領域は透過型液晶パネル７５に対応するように設定されている。この光路偏向装置４９には電圧印加回路及びこの電圧印加回路中のスイッチ等を開閉制御する機能を果たすドライブ制御部５０が接続されている。
【００８２】
光源ドライブ部４７で制御されて光源４１から放出された照明光は、拡散板４３により均一化された照明光となり、コンデンサレンズ４４により液晶ドライブ部４８で照明光源と同期して制御されて透過型液晶パネル４５をクリティカル照明する。この透過型液晶パネル４５で空間光変調された照明光は、画像光として光路偏向装置４９の有効領域に入射し、この光路偏向装置４９によって画像光が画素の配列方向に任意の距離だけシフトされる。この光は投射レンズ４６で拡大されスクリーン４２上に投射される。
【００８３】
シフト量は画素の配列方向に対して２倍の画像増倍を行うことから画素ピッチの１／２に設定される。シフト量に応じて液晶パネル４５を駆動する画像信号をシフト量分だけ補正することで、見掛け上高精細な画像を表示することができる。
【００８４】
ここに、従来の光路偏向デバイスでは投射光をスクリーンで結像させる時にシフト位置毎に像点距離が異なるために収差が発生し、同一面上に良好な結像が得られない問題があり、画像が劣化してしまう不具合があったが、本実施の形態では、光路偏向装置４９は前述の光路偏向デバイス１，１１等を有しているので、このような像点距離の差がなくなるように補償されるので、上記不具合を解消でき、焦点ボケによる画像劣化のない良好な表示が可能となる。
【００８５】
【発明の効果】
請求項１記載の発明によれば、光路偏向手段により切換えられた光の各進行方向における像点距離が略等しくなるよう調整する像点距離補償手段を備えるので、偏光方向に応じた光路偏向手段による光路偏向に伴う光の進行方向における像点距離に差があっても、像点距離補償手段によって像点距離が略等しくなるよう調整することで像点距離差をなくすことができ、像点距離差に起因する収差の発生を防止することができる。
【００８６】
請求項２記載の発明によれば、請求項１記載の発明を実現する上で、光路偏向手段として一般的な複屈折性媒体を用いることができる。
【００８７】
請求項３記載の発明によれば、請求項１又は２記載の発明を実現する上で、像点距離補償手段として像点距離差を短縮させる屈折率異方性を有する複屈折性媒体を用いることで、簡単に実現することができる。
【００８８】
請求項４記載の発明によれば、請求項３記載の発明を実現する上で、補償用の複屈折性媒体として、一軸光学結晶による複屈折板を用い、その光学結晶軸を入射光軸と略垂直に設定することで、各々の進行方向に導かれる光に屈折、散乱等を発生させることなく像点距離差を短縮させることができ、また、光学設計上も光路計算が複雑化することなく容易に設計することができる。
【００８９】
請求項５記載の発明によれば、請求項３又は４記載の光路偏向デバイスにおいて、補償用の複屈折性媒体をＬｉＮｂＯ_３結晶製とし、その光学結晶軸を偏光方向切換手段により切換えられる偏光方向のうちの一つと略一致するように設定したので、良好な像点距離補償が可能となると同時に、ＬｉＮｂＯ_３結晶は光学結晶の中でも潮解性などなく安定で、さらにΔｎ（＝ｎｏ−ｎｅ）が適度な大きさを有しており、取扱いやすいものとすることができる。
【００９０】
請求項６記載の発明によれば、請求項５記載の光路偏向デバイスにおいて、補償用の複屈折性媒体の板厚をΔＬ／（１／ｎｏ−１／ｎｅ）±３０（μｍ）の範囲内に設定したので、各進行方向に導かれる光の像点距離差を適切に短縮させることができる。
【００９１】
請求項７記載の発明の光路偏向デバイスによれば、偏光方向に応じた光路偏向手段による光路偏向に伴う光の進行方向における像点距離に差があっても、像点距離が略等しくなるよう当該光路偏向手段を入射光の光軸に対して傾斜させた傾斜面を有するので、像点距離差をなくすことができ、像点距離差に起因する収差の発生を防止することができ、特に、補償用の複屈折性媒体のような別部材を追加して備える必要がなく、例えば光路偏向手段の姿勢設定だけで簡単に実現することができる。
【００９２】
請求項８記載の発明によれば、光路偏向手段の姿勢設定だけで簡単に請求項７記載の発明を実現することができる。
【００９３】
請求項９記載の発明によれば、請求項７記載の光路偏向デバイスを実現する上で、偏光方向切換手段と当該光路偏向手段との設置時の位置調整を簡略化することができ、さらに光路偏向手段を光軸に垂直に配置することができるため、大面積化した時に必要なスペースを比較的小さくすることもできる。
【００９４】
請求項１０記載の発明によれば、請求項７ないし９の何れか一記載の光路偏向デバイスにおいて、例えば画像表示装置において受光部上に良好に結像させるためには受光位置における結像レンズの焦点深度以内に各進行方向の像点距離の差を抑える必要があるが、入射光の光軸と複屈折性媒体の法線とのなす傾斜角ｉを負方向に設定することで、上記条件を満たすための関係を保つことができる。
【００９５】
請求項１１記載の発明によれば、請求項３ないし６の何れか一記載の光路偏向デバイスにおいて、像点距離は入射光の波長や環境変動によって変化してしまうが、補償用の複屈折性媒体を挟む位置に配設されて当該複屈折性媒体に対して電界を作用させるための少なくとも一対の電極を備えるので、これらの電極間に印加する電圧を適正に制御することで像点距離の変動を抑えることができ、この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動を抑えることが可能となり、高精細なカラー画像表示に役立てることができる。
【００９６】
請求項１２記載の発明によれば、請求項８ないし１０の何れか一記載の光路偏向デバイスにおいて、像点距離は入射光の波長や環境変動によって変化してしまうが、傾斜配設された偏向用の複屈折性媒体を挟む位置に配設されて当該複屈折性媒体に対して電界を作用させるための少なくとも一対の電極を備えるので、これらの電極間に印加する電圧を適正に制御することで像点距離の変動を抑えることができ、この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動を抑えることが可能となり、高精細なカラー画像表示に役立てることができる。
【００９７】
請求項１３記載の発明の光路偏向装置によれば、像点距離は入射光の波長や環境変動によって変化してしまうが、光路偏向デバイスから出射される光の各進行方向における焦点位置を測定し、測定された各進行方向での焦点位置の差に基づき電極極に印加する印加電圧のフィードバック信号を生成することで、常に像点距離を一定に保つことができ、この結果、特に画像表示装置において投影光の波長を時間的に切換えるカラー化方式であるフィールドシーケンシャル法における色毎の像点距離の変動をなくすことが可能となり、高精細なカラー画像表示に役立てることができる。
【００９８】
請求項１４記載の発明の画像表示装置によれば、従来のピクセルシフト技術では投射光をスクリーンに結像させる時にシフト位置毎に像点距離が異なるために収差が発生し、同一面上に良好な結像が得られない問題があり、画像が劣化してしまう不具合があるが、本発明によれば、画像表示装置内に像点距離の差をなくす構成の請求項１ないし１２の何れか一記載の光路偏向デバイスを有する光路偏向装置又は請求項１３記載の光路偏向装置を備えているので、上記不具合を解消でき、焦点ボケによる画像劣化のない良好な表示を行わせることができる。
【図面の簡単な説明】
【図１】本発明の第一の実施の形態の光路偏向デバイスの原理的構成を示す側面図である。
【図２】その結晶の板厚とフォーカスとの関係を示す特性図である。
【図３】本発明の第二の実施の形態の光路偏向デバイスの原理的構成を示す側面図である。
【図４】傾斜面による像点距離補償の原理を説明するための模式図である。
【図５】入射角と光学長差、シフト量との関係を示す特性図である。
【図６】本発明の第三の実施の形態の光路偏向デバイスの原理的構成を示す側面図である。
【図７】本発明の第四の実施の形態の光路偏向装置の概略構成を示す側面図である。
【図８】その印加電圧と１／ｎｏ−１／ｎｅとの関係を示す特性図である。
【図９】本発明の第五の実施の形態の画像表示装置の概略構成を示す側面図である。
【図１０】従来の光路偏向デバイスの原理的構成を示す側面図である。
【図１１】その像点距離差に起因する収差によりボケが生ずる様子を示し、（ａ）は光学系の側面図、（ｂ）は受光部の正面図である。
【図１２】収差を計算するための説明図である。
【符号の説明】
１　　　光路偏向デバイス
２　　　偏光方向切換手段
３　　　光路偏向手段、複屈折性媒体
４　　　像点距離補償手段、補償用の複屈折性媒体
１１　　　光路偏向デバイス
１２　　　偏光方向切換手段
１３　　　光路偏向手段、複屈折性媒体
１４　　　傾斜面
１５　　　保持手段
２１　　　光路偏向手段、鋸歯構造の複屈折性媒体
２２　　　傾斜面
３１　　　光路偏向装置
３２ａ，３２ｂ　　　電極
３３　　　電圧印加手段
４１　　　照明装置
４５　　　画像表示素子
４６　　　光学装置
４８　　　表示駆動手段
４９　　　光路偏向装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical path deflecting device, an optical path deflecting device, and an image display device.
[0002]
[Prior art]
Conventionally, KH has been used as an optical element (optical path deflecting element) for changing the traveling direction (optical path) of light by an electric signal. ₂ PO ₄ (KDP), NH ₄ H ₂ P (ADP), LiNbO ₃ , LiTaO ₃ , GaAs, CdTe, etc., materials having a large primary electro-optic effect (Pockels effect), KTN, SrTiO ₃ , CS ₂ Device using a material having a large secondary electro-optic effect, such as glass, silica, TeO ₂ Acousto-optic devices using such materials are known (for example, edited by Shoji Aoki; "Optoelectronic Devices", Shokodo). Generally, an electro-optical device modulates an optical path or light intensity by changing a refractive index by applying a high voltage, and an acousto-optical device induces a light diffraction by applying an ultrasonic wave to induce a standing wave. Control. However, in order to obtain a sufficiently large light deflection amount by these methods, it is necessary to increase the image point distance, but the use of the material is limited due to the expensive material.
[0003]
On the other hand, an optical element using a liquid crystal material has also been proposed. As an example, there is a projection display device disclosed in Japanese Patent No. 2939826. This is because, in a projection display device that enlarges and projects an image displayed on a display element onto a screen by a projection optical system, at least an optical element that can turn the polarization direction of transmitted light in the optical path from the display element to the screen is provided. Means for shifting a projected image having at least one transparent element having one or more birefringence effects, and a projection area of each pixel of the display element which effectively reduces an aperture ratio of the display element Are projected discretely on the screen.
[0004]
[Problems to be solved by the invention]
In the example of the publication, a projection image having at least one optical element capable of rotating the polarization direction (polarization direction rotating means) and at least one transparent element having a birefringence effect (birefringent medium). The pixel shift is performed by the shift means (pixel shift means). However, in the conventional configuration, the traveling direction of light in the birefringent medium is straight (referred to as first light traveling direction) or refracted. , The light beam travels in one of the directions deflected by a predetermined angle (referred to as the second light traveling direction). However, when these lights are imaged on the light receiving unit, the image point distances in the respective traveling directions are different. There is a problem that an aberration is generated in the image and a good image cannot be obtained on the same surface.
[0005]
This point will be described in detail with reference to FIGS. FIG. 10 is a side view showing a basic configuration of a conventional optical path deflecting device 101 using a conventional birefringent medium 100 as an optical path deflecting unit. That is, a polarization direction switching means 102 capable of temporally switching the polarization direction of the incident linearly polarized light, and a multiplicity for switching the traveling direction of light from the polarization direction switching means 102 in accordance with the switched polarization direction. The device configuration includes the refractive medium 100.
[0006]
A liquid crystal material is used as the polarization direction switching means 102, and a ferroelectric liquid crystal is used particularly for an application requiring a high-speed response. Further, the refractive index difference Δn between the ordinary light and the extraordinary light satisfies the relationship of Δn · d = λ / 2 (λ is a predetermined wavelength of visible light) with the thickness d. Conventionally, as the birefringent medium 100, an optical crystal material having birefringence is used, and in particular, a uniaxial optical crystal is generally used. That is, KH ₂ PO ₄ (KDP), NH ₄ H ₂ P (ADP), LiNbO ₃ , LiTaO ₃ , GaAs, CdTe, etc., materials having a large primary electro-optic effect (Pockels effect), KTN, SrTiO ₃ , CS ₂ , Nitrobenzene, etc., materials with large secondary electro-optic effect, glass, silica, TeO ₂ Such materials are used.
[0007]
Hereinafter, the operation of the optical path deflecting device 101 using the conventional birefringent medium 100 will be described. The incident light is set in advance to linearly polarized light, and the polarization direction is determined from the relationship with the optical crystal axis direction of the birefringent medium 100. Specifically, assuming that the orthogonal coordinate system is as shown in FIG. 10, a uniaxial optical crystal material is used as the birefringent medium 100, and the optical crystal axis is (X, Y, Z) = (1, 0). , -1), the polarization direction (electric field vector direction) of the incident light is selected so as to exist on the XY plane or the XZ plane. Here, a case where the polarization direction of the incident light is in the XY plane will be described as an example. When passing through the polarization direction switching means 102, the incident light is temporally rotated (switched) by 0 ° or 90 ° in the polarization direction.
[0008]
First, at 0 °, that is, when the polarization direction is not rotated, the linearly polarized light enters the birefringent medium 100 while maintaining the polarization direction in the XY plane. Since the polarization direction (Y-axis direction) is perpendicular to the optical crystal axis, the light behaves as ordinary light and travels straight without being rotated. This light is emitted to a position in the traveling direction shown as “first light traveling direction” in FIG.
[0009]
On the other hand, when the polarization direction switching unit 102 receives a rotation of the polarization direction of 90 °, the linearly polarized light rotates the polarization direction to the XZ plane and enters the birefringent medium 100. The principle of 90 ° rotation will be described later. In this case, since the polarization direction (Z-axis direction) is not perpendicular to the optical crystal axis, the light behaves as extraordinary light, and travels by being rotated in a predetermined direction (in the figure, obliquely downward). This light is emitted to a position in the traveling direction shown as “second light traveling direction” in FIG.
[0010]
FIG. 11 is a schematic configuration diagram showing an example of an optical system configuration using such an optical path deflecting device 101, in which light emitted from a light source 103 is imaged on a light receiving unit 105 by a lens 104 via the optical path deflecting device 101. Is shown. A first light traveling direction by the optical path deflecting device 101 is shown by a dashed line in the figure, and a second light traveling direction is shown by a broken line in the figure.
[0011]
When the first and second light traveling directions are respectively as shown in the figure, the image formation state on the light receiving unit 105 is different from the first light traveling direction because the image point distances are different depending on the traveling directions. When the focal point is adjusted to the light receiving surface, the image in the second light traveling direction is blurred due to aberration as shown in FIG.
[0012]
Hereinafter, this aberration Df is calculated using a typical optical system. FIG. 12 shows LiNbO as a birefringent medium (birefringent plate) 100. ₃ 5 shows the traveling direction of light when using. The optical crystal axis used is inclined from the normal direction of the birefringent plate 100 by θ. In the drawing, the polarization direction of the incident light 106 is defined as the Z-axis direction. At this time, the incident light 106 is refracted in the birefringent plate 100,
γ = θ-tan ^-1 [(No / ne) ² tanθ] ……… ▲ 1 ▼
(See Tadashi Sueda, "Optical Electronics" Shokosha). Here, no is the ordinary light refractive index, ne is the extraordinary light refractive index, and the major axis of the refractive index ellipsoid is set in the polarization plane. First, the traveling direction (angle γ) of this light and the distance L passing through the birefringent plate 100 are determined. Assuming that the refractive index is that at a wavelength of 633 nm (no = 2.286, ne = 2.200) and the crystal axis θ is 45 °, in equation (1),
tan ^-1 [(No / ne) ² tan θ] = 42.80507
γ = 2.194925
It becomes. In order to temporarily obtain 6.6 μm as the optical path shift amount, the thickness d of the birefringent plate 100 is
d = 6.6 / tanγ = 172.2005
Is set.
[0013]
When the polarization direction is light in the Y-axis direction (ordinary light), light passing through the thickness d takes the first light traveling direction in FIG. 10, and the change in image point distance with respect to vacuum is
d (1-1 / no) = 93.9275... (2)
(Hayasui, "Optics of Optical Devices," Third Edition, p. 427, edited by Japan Opto-Mechatronics Association).
[0014]
On the other hand, when the polarization direction is extraordinary light, the light passing through the thickness d takes the second light traveling direction in FIG.
L = sqrt (6.6 * 6.6 + d * d) = 172.3269
It becomes.
[0015]
Hereinafter, the refractive index in the polarization direction in the cross section of the refractive index ellipsoid of the optical crystal cut by the incident light 106 will be obtained. The equation of the ellipse is obtained by newly taking the x and y axes in FIG. 12 in the short axis and long axis directions of the ellipsoid as shown in the figure.
(X / no) ² + (Y / ne) ² = 1
The point at which the line perpendicular to the optical axis passing through the center of the refractive index ellipsoid of the birefringent plate 100 (the line denoted by reference numeral 107 in FIG. 12) intersects the ellipsoid is the refractive index ne 'felt by this light. It is. That is, ne '= 2.238483.
[0016]
Therefore, the change in the image point distance of the incident light passing through the thickness d with respect to the vacuum is
d−L / ne ′ = 95.2167... (3)
It becomes.
[0017]
From the formulas (2) and (3), the image point distance difference between the traveling direction of the first light and the traveling direction of the second light is

It becomes.
[0018]
Specifically, in order to form an image equally in the light receiving unit 105 in FIG. 11, when the position of the light source 103 is (3) (second traveling direction), the position is (2) (first traveling direction). Direction), it is necessary to move away by ΔL.
[0019]
Conversely, when the position of the light source 103 and the position of the light receiving unit 105 are fixed, the aberration Df at the position of the light receiving unit 105 is given by Df = M from the image point distance difference ΔL of the imaging lens 104 and the projection magnification M. ² · ΔL, and assuming M = 50 / 0.85 = 58.8,
Df (mm) = 4.460
It becomes. This aberration is a value that cannot be ignored as compared with the depth of focus of a general imaging lens, and indicates that defocusing occurs in the traveling direction of the first light and the traveling direction of the second light. .
[0020]
As a result, when such an optical path deflecting device is used in an image display device or an image pickup device, there is a problem that aberration occurs in each traveling direction and an image is degraded. Means that the SN ratio is degraded.
[0021]
The present invention provides an optical path deflecting device, an optical path deflecting device, and an image that can eliminate an image point distance difference in a traveling direction of light due to an optical path deflection according to a polarization direction and can prevent an aberration caused by an image point distance difference. It is an object to provide a display device.
[0022]
The present invention achieves the above object with a simple structure.
[0023]
The present invention achieves the above-mentioned object, and makes it possible to design the optical design without complicating the optical path calculation.
[0024]
In order to achieve the above object, the present invention eliminates the influence of an error factor of the light deflection amount, such as the environmental temperature, so that the image point distance can always be kept constant.
[0025]
[Means for Solving the Problems]
The optical path deflecting device according to the first aspect of the present invention is arranged on the light incident side to switch the polarization direction of the linearly polarized light incident thereon, and according to the polarization direction switched by the polarization direction switching means. An optical path deflecting means for switching the traveling direction of the light, and an image point distance compensating means for adjusting the image point distance in each traveling direction of the light switched by the optical path deflecting means to be substantially equal.
[0026]
Therefore, even if there is a difference in the image point distance in the traveling direction of the light due to the optical path deflection by the optical path deflecting means according to the polarization direction, the image point distance is adjusted by the image point distance compensating means so as to be substantially equal. The difference in distance is eliminated, and the occurrence of aberration due to the difference in image point distance is prevented.
[0027]
According to a second aspect of the present invention, in the optical path deflecting device according to the first aspect, the optical path deflecting means is a birefringent medium for deflection.
[0028]
Accordingly, in realizing the first aspect of the present invention, a general birefringent medium can be used as the optical path deflecting means.
[0029]
According to a third aspect of the present invention, in the optical path deflecting device according to the first or second aspect, the image point distance compensating means has a refractive index anisotropy that reduces an image point distance difference in each light traveling direction of the light. This is a birefringent medium for compensation.
[0030]
Therefore, in realizing the first or second aspect of the present invention, it can be easily realized by using a birefringent medium having a refractive index anisotropy for reducing an image point distance difference as an image point distance compensating means. Become.
[0031]
According to a fourth aspect of the present invention, in the optical path deflecting device according to the third aspect, the birefringent medium for compensation is a birefringent plate made of a uniaxial optical crystal, and its optical crystal axis is substantially perpendicular to the incident optical axis. Is set.
[0032]
Therefore, in realizing the invention of claim 3, by using a birefringent plate made of a uniaxial optical crystal as a birefringent medium for compensation, and setting the optical crystal axis to be substantially perpendicular to the incident optical axis, The image point distance difference is reduced without causing refraction, scattering, and the like in the light guided in each traveling direction, and the optical design can be easily designed without complicating the optical path calculation.
[0033]
The invention according to claim 5 is the optical path deflecting device according to claim 3 or 4, wherein the birefringent medium for compensation is LiNbO 2. ₃ It is a crystal, and its optical crystal axis is set so as to substantially coincide with one of the polarization directions switched by the polarization direction switching means.
[0034]
Therefore, the birefringent medium for compensation is LiNbO ₃ By making the optical crystal axis substantially the same as one of the polarization directions switched by the polarization direction switching means, a good image point distance compensation becomes possible, and at the same time, LiNbO 3 ₃ The crystal is stable among optical crystals without deliquesce and the like, and Δn (= no-ne) has an appropriate size and is easy to handle.
[0035]
According to a sixth aspect of the present invention, in the optical path deflecting device according to the fifth aspect, the thickness of the birefringent medium for compensation is such that each light travels by the optical path deflecting unit when the birefringent medium is absent. The difference between the image point distance ΔL occurring in the direction and the refractive index ne, no for light in each polarization direction at the incident light wavelength is set within the range of ΔL / (1 / no-1 / ne) ± 30 (μm). Have been.
[0036]
Therefore, by setting the plate thickness of the birefringent medium for compensation within the range of ΔL / (1 / no-1 / ne) ± 30 (μm), the image point distance difference of the light guided in each traveling direction is set. Is appropriately shortened. By the way, when the plate thickness is set to a value exceeding ± 30 (μm), the aberration is not sufficiently eliminated and a good image cannot be obtained.
[0037]
According to a seventh aspect of the present invention, there is provided an optical path deflecting device which is disposed on the light incident side and switches the polarization direction of the linearly polarized light incident thereon, and in accordance with the polarization direction switched by the polarization direction switching means. Optical path deflecting means for switching the traveling direction of light, wherein the optical path deflecting means is inclined with respect to the optical axis of the incident light so that the image point distances in the traveling directions of the light switched by the optical path deflecting means are substantially equal. It has an inclined surface.
[0038]
Therefore, even if there is a difference in the image point distance in the traveling direction of the light due to the light path deflection by the light path deflecting means according to the polarization direction, the light path deflecting means is moved with respect to the optical axis of the incident light so that the image point distance becomes substantially equal. With the inclined surface inclined, the image point distance difference is eliminated, and the occurrence of aberration due to the image point distance difference is prevented. In particular, there is no need to additionally provide a separate member such as a birefringent medium for compensation, and it can be easily realized only by setting the posture of the optical path deflecting means.
[0039]
According to an eighth aspect of the present invention, in the optical path deflecting device according to the seventh aspect, there is provided a holding means for holding the optical path deflecting means in an inclined manner so as to have the inclined surface inclined with respect to the optical axis of the incident light.
[0040]
Therefore, the invention according to claim 7 can be easily realized only by setting the attitude of the optical path deflecting means.
[0041]
According to a ninth aspect of the present invention, in the optical path deflecting device according to the seventh aspect, the input and output surfaces of the optical path deflecting unit are formed in a saw-tooth structure, so that the inclined surface is inclined with respect to the optical axis of the incident light. .
[0042]
Therefore, the position adjustment at the time of installation of the polarization direction switching means and the optical path deflecting means can be simplified, and the optical path deflecting means can be arranged perpendicular to the optical axis. It can also be smaller.
[0043]
According to a tenth aspect of the present invention, in the optical path deflecting device according to any one of the seventh to ninth aspects, the optical path deflecting means is LiNbO. ₃ The incident light is deflected in the birefringent medium when the inclination angle i between the optical axis of the incident light and the normal line of the birefringent medium is i = 0 when i = 0. When the angle direction is positive, it is set to the negative direction.
[0044]
Therefore, for example, in order to form a good image on the light receiving unit in the image display device, it is necessary to suppress the difference between the image point distances in each traveling direction within the focal depth of the imaging lens at the light receiving position. By setting the inclination angle i between the axis and the normal line of the birefringent medium in the negative direction, the relationship for satisfying the above condition can be maintained.
[0045]
According to an eleventh aspect of the present invention, in the optical path deflecting device according to any one of the third to sixth aspects, the electric field deflecting device is disposed at a position sandwiching the compensating birefringent medium and applies an electric field to the birefringent medium. It has at least one pair of electrodes for operating.
[0046]
Therefore, although the image point distance changes depending on the wavelength of incident light and environmental fluctuations, at least for disposing the birefringent medium for compensation and applying an electric field to the birefringent medium. Since a pair of electrodes is provided, it is possible to suppress the fluctuation of the image point distance by appropriately controlling the voltage applied between these electrodes. As a result, it is possible to suppress a change in image point distance for each color in a field sequential method, which is a colorization method for temporally switching the wavelength of projection light in an image display device, which is useful for high-definition color image display.
[0047]
According to a twelfth aspect of the present invention, in the optical path deflecting device according to any one of the eighth to tenth aspects, the optical path deflecting device is disposed at a position sandwiching the birefringent medium and applies an electric field to the birefringent medium. At least a pair of electrodes.
[0048]
Therefore, the image point distance changes depending on the wavelength of the incident light and environmental fluctuations. However, the image point distance is disposed at a position sandwiching the deflecting birefringent medium that is inclined, and an electric field is applied to the birefringent medium. Since at least one pair of electrodes is provided for the operation, the fluctuation of the image point distance can be suppressed by appropriately controlling the voltage applied between these electrodes. As a result, it is possible to suppress a change in image point distance for each color in a field sequential method, which is a colorization method for temporally switching the wavelength of projection light in an image display device, which is useful for high-definition color image display.
[0049]
According to a thirteenth aspect of the present invention, there is provided an optical path deflecting device, wherein the optical path deflecting device according to the eleventh or twelfth aspect, a voltage applying means for applying a voltage to the electrode, and a light in each traveling direction of the light emitted from the optical path deflecting device. Focus position measuring means for measuring a focal position, and feedback for generating a feedback signal of an applied voltage of the voltage applying means to be applied to the electrode based on a difference between the focal positions in each traveling direction measured by the focal position measuring means. Signal generation means.
[0050]
Therefore, the image point distance changes due to the wavelength of the incident light and environmental fluctuations. However, the focal positions in the respective traveling directions of the light emitted from the optical path deflecting device are measured, and the focal positions in the measured traveling directions are measured. By generating a feedback signal of the applied voltage applied to the electrode pole based on the difference, it is possible to always keep the image point distance constant. As a result, in particular, it is possible to eliminate the fluctuation of the image point distance for each color in the field sequential method which is a colorization method for temporally switching the wavelength of the projection light in the image display device, which is useful for high-definition color image display.
[0051]
15. The image display device according to claim 14, wherein: an image display element in which a plurality of pixels capable of controlling light according to image information are two-dimensionally arranged; a lighting device for illuminating the image display element; and the image display element. An optical device for observing the image pattern displayed on the display device, display driving means for forming an image field by a plurality of time-divided subfields, and an optical path of light emitted from each pixel of the image display element. An optical path deflecting device having the optical path deflecting device according to any one of claims 1 to 12 or an optical path deflecting device according to claim 13 deflecting for each field.
[0052]
Therefore, in the conventional pixel shift technique, when the projection light is imaged on the screen, an aberration occurs because the image point distance is different for each shift position, and there is a problem that a good image cannot be obtained on the same plane. 13. The optical path deflecting device having the optical path deflecting device according to any one of claims 1 to 12, wherein the image display apparatus has a configuration in which a difference in image point distance is eliminated. Alternatively, since the optical path deflecting device according to the thirteenth aspect is provided, the above problem can be solved, and a favorable display without image deterioration due to defocus can be realized.
[0053]
BEST MODE FOR CARRYING OUT THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a side view showing an example of the principle configuration of an optical path deflecting device 1 according to the present embodiment. The optical path deflecting device 1 of the present embodiment is, in general, added to the conventional configuration as shown in FIG. 10 including a polarization direction switching means 2 and a deflecting birefringent medium 3 as an optical path deflecting means. Then, an image point distance compensating means 4 for adjusting the image point distances in the respective traveling directions of the light switched by the birefringent medium 3 to be substantially equal to each other is provided on the exit side (later stage of the light traveling direction). It has been.
[0054]
Here, the polarization direction switching means 2 for temporally switching the polarization direction of the linearly polarized light incident on the optical path deflecting device 1 can be configured using a liquid crystal layer as in the conventional case. The birefringent medium 3 is, for example, LiNbO ₃ The optical crystal direction indicated by the arrow in FIG. 1 is inclined by 45 ° from the normal direction.
[0055]
As described in the conventional example, when securing the light shift amount of 6.6 μm, the plate thickness of the birefringent plate 3 needs to be 172.2 μm, and the difference between the first light traveling direction and the second light traveling direction at that time. The image point distance difference ΔL is 1.29 μm. The image point distance compensating means 4 corrects the image point distance difference ΔL to a value sufficiently smaller than the focal depth of an imaging lens (not shown), for example.
[0056]
As such an image point distance compensating means 4, a birefringent medium having a birefringent medium having a refractive index anisotropy (a birefringent medium for compensation) for reducing the image point distance difference ΔL in the first and second traveling directions is used. It is effective to use it suitably, and as a specific example, like the birefringent medium 3, LiNbO ₃ It is possible to use However, the optical crystal axis is preferably set in a direction perpendicular to the optical axis so as not to change the light shift amount set in the birefringent medium 3. By the way, if this relationship cannot be maintained, a light shift will also occur in the image point distance compensating means 4 and the optical design will be complicated.
[0057]
As the birefringent medium for the image point distance compensating means 4, quartz, KDP (KH ₂ PO ₄ ), DKDP (KD ₂ PO ₄ ), LiNbO ₃ , LiTaO ₃ Among them, LiNbO having a moderate size without Δn (= no−ne) can be used. ₃ Is particularly excellent.
[0058]
Here, LiNbO ₃ Is appropriate when the image point distance compensating means 4 is used. _comp The following shows an example. The lights emitted from the birefringent medium 3 in the two traveling directions (first light traveling direction and second light traveling direction) have polarization directions perpendicular to each other, and as shown in the above (4), the second light The light in the traveling direction is traveling. Therefore, the image point distance compensating means 4 is arranged so that the traveling direction of the first light corresponds to the ordinary light and the traveling direction of the second light corresponds to the extraordinary light.
[0059]
At this time, the moving distance of the image point with respect to the vacuum in each traveling direction is represented by the thickness d. _comp If so, d _comp (1-1 / no) and d _comp It is represented by (1-1 / ne). Therefore, in order to eliminate the difference of the image point moving distance of ΔL = 1.29 described above,
d _comp (1-1 / no) -d _comp (1-1 / ne) = ΔL = 1.29
That is, d. _comp = 75.4 (μm).
[0060]
FIG. 2 shows LiNbO ₃ Thickness d _comp In the case where a lens having a focal depth of ± 2 mm is used as the imaging lens, the thickness of the image point distance compensating means 4 is
42 <d _comp <109
, Good image formation can be obtained.
[0061]
Generally, LiNbO ₃ Is used in the image point distance compensating means 4, d _comp In the case where the image point distance compensating means 4 is not provided, the image point distance difference ΔL and the LiNbO ₃ A value determined by the refractive indices ne and no of extraordinary light and ordinary light, ie, d _comp = ΔL / (1 / ne−1 / no) (in the above case, 75 μm), good image point distance compensation is possible by setting the range within ± 30 μm.
[0062]
A second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a side view showing an example of the principle configuration of the optical path deflecting device 11 of the present embodiment. The optical path deflecting device 11 of the present embodiment generally has a basic configuration including a polarization direction switching unit 12 and a birefringent medium 13 as an optical path deflecting unit. And holding means 15 for holding the birefringent medium 13 in an inclined manner so as to have an inclined surface 14 with respect to the optical axis of the incident light so that the image point distances in the respective traveling directions are substantially equal. ing.
[0063]
Here, the polarization direction switching means 12 for temporally switching the polarization direction of the linearly polarized light incident on the optical path deflecting device 11 can be configured using a liquid crystal layer as in the conventional case. The birefringent medium 13 is, for example, LiNbO ₃ The optical crystal direction indicated by the arrow in FIG. 3 is inclined by 45 ° from the normal direction. The birefringent medium 13 is provided so as to have an inclined surface 14 inclined by a predetermined angle i with respect to the optical axis of the incident light by the holding means 15.
[0064]
Hereinafter, referring to FIG. 4, the birefringent medium 13 has an inclined surface 14 inclined by a predetermined angle i to compensate for a difference in image point distance between the light in the first and second traveling directions. The points that can be performed will be described. FIGS. 4A and 4B show LiNbO 3 as a birefringent medium (birefringent plate) 13. ₃ The incident light 16 and 17 are inclined by an angle i from the normal direction of the birefringent plate 13 (the angle is positive in the clockwise direction). ). FIG. 4A shows the case where the polarization direction of the incident light 16 is the Z direction in the orthogonal coordinate system shown in the figure, and FIG. 4B shows the case where the polarization direction of the incident light 17 is the Y direction. In any case, only the polarization directions of the incident lights 16 and 17 are different, and the optical crystals and their arrangement are the same. The optical crystal axis is LiNbO as in the case described above. ₃ Is assumed, and the one that is inclined by Ψ (= 45 °) from the normal direction of the birefringent plate 13 is used, and the thickness is set to d = 172.2 μm. At this time, in FIG. 4A, an angle r 'formed between the light propagation direction and the normal in the optical crystal is:
tanr ′ = − B / C + sin (i) * ｛(AB−C2) / (B−sin ² (I))｝ ^1/2 …… ▲ 5 ▼
(M. Francon and S. Mallick: Polarization Interferometers, WILEY-INTERSCIENCE, (1971) p. 140). However,
a = 1 / ne = 1 / 2.200 = 0.4374
b = 1 / no = 1 / 2.286 = 0.4545
A = sin ² Ψ / a ² + Cos ² Ψ / b ² = 5.0329
B = cos ² Ψ / a ² + Sin ² Ψ / b ³ = 5.0329
C = sin {.cos}. (1 / b ² −1 / a ² ) = − 0.193
On the other hand, in FIG. 4B, the angle r between the light traveling direction and the normal in the optical crystal is:
tanr = b * sin (i) / (1-b ² sin ² (I)) ^1/2 ………… ▲ 6 ▼
Is represented by
[0065]
From these formulas (5) and (6), the image point distance difference and the shift amount with respect to the incident angle i in each polarization direction are obtained.
[0066]
FIG. 5 shows the calculation results. When the angle of incidence is 0 °, the image is shifted by 6.6 μm as described above, the aberration is also 4.460 mm as described above, and a defocus occurs. By changing the incident angle of light from this state, the image point distance difference changes, and the image point distance difference becomes 0 at -17 °. At this time, the light shift amount is 6.76 μm, and there is almost no change from the initial value. That is, LiNbO ₃ Is tilted by 17 degrees from the optical axis, the difference in image point distance is eliminated while the light shift amount is secured, and the imaging positions in the first light traveling direction and the second light traveling direction can be matched. .
[0067]
When a lens having a focal depth of ± 2 mm is used as the imaging lens, the incident angle (tilt angle) i is
−24 <i <−10
, Good image formation can be obtained. In this manner, the optical path length difference can be compensated by tilting the incident angle i in the negative direction, that is, in the direction in which r 'is reduced. Generally, LiNbO ₃ Is used, the incident angle (tilt angle) i is preferably set within a range of ± 7 ° with respect to a center value (-17 ° in the above case) determined by the application such as an optical shift amount. It is possible to compensate for the image point distance.
[0068]
A third embodiment of the present invention will be described with reference to FIG. In the optical path deflecting device 11 of the present embodiment, instead of the birefringent medium 13 of the second embodiment, the input and output surfaces of the birefringent medium 21 as the optical path deflecting means are arranged in the Z direction. It is configured to have an inclined surface 22 inclined by a predetermined angle i with respect to the optical axis of incident light by processing into a sawtooth structure of a plurality of divided shapes. The birefringent medium 21 is LiNbO ₃ The birefringent plate is made of a birefringent plate, and the direction of the optical crystal is inclined by 45 ° from the normal direction as shown by an arrow in FIG. The sawtooth structure of the birefringent medium 21 can be formed by, for example, a photolithography process using a gradient mask or the like.
[0069]
With such a structure, the position adjustment at the time of installing the polarization direction switching means 12 and the birefringent plate 21 can be simplified, and the birefringent plate 21 can be arranged perpendicular to the optical axis. The space required when the area is increased can be made relatively small.
[0070]
A fourth embodiment of the present invention will be described with reference to FIGS. This embodiment shows a configuration example of an optical path deflecting device 31 using the optical path deflecting device 1 having the configuration shown in FIG. 1, for example.
[0071]
In the optical path deflecting device 31 of the present embodiment, the birefringent medium 4 as the image point distance compensating means provided in the optical path deflecting device 1 is disposed on both the input and output surfaces of the birefringent medium 4 so as to sandwich the birefringent medium 4. A pair of electrodes 32a and 32b for applying an electric field to the refractive medium 4 are provided, and a power supply 33 as a voltage applying means is connected between the electrodes 32a and 32b to apply a voltage.
[0072]
The value of the voltage applied between the electrodes 32a and 32b is controlled to a desired position by applying an electric field to the birefringent medium 4 to control the image point distance difference ΔL that changes due to the wavelength of the incident light and environmental changes. To be applied. When the wavelength of the incident light changes, ΔL (= 1.29) obtained from the above-mentioned refractive index (no = 2.286, ne = 2.200) at the wavelength of 633 mm is calculated in the above-described first embodiment. From LiNbO ₃ Was set to a thickness of 75.4 μm. Under this condition, for example, when light having a wavelength of 3390 nm is incident, LiNbO ₃ By applying a voltage to the refractive index at 3390 nm (no = 2.146, ne = 2.081), the value obtained from the refractive index relational expression (1 / ne−1 / no) at a wavelength of 633 nm, that is, , 1 / 2.20-1 / 2.286 = 0.0166 may be obtained.
[0073]
LiNbO ₃ In the case of, the changes in the refractive index Δno and Δne due to the applied electric field E are respectively at a wavelength of 3390 nm,
Δno = −3.21 × 10 ^-11 E
Δne = -126.2 × 10 ^-11 E
And represented by LiNbO ₃ Of the above d _comp = 75.4 (μm), when converted into a voltage V applied to the electrodes 32a and 32b,
Δno = -4.28 × 10 ^-7 V
Δne = -1.68 × 10 ^-6 V
Is obtained.
[0074]
FIG. 8 shows a change in the value of (1 / ne-1 / no) when the voltage V is changed at a wavelength of 3390 nm. As can be seen from this figure, it is sufficient to apply a voltage of 6.9 kV to obtain a value of 0.0166 at 633 nm.
[0075]
Specifically, as shown in FIG. 7, the optical path deflecting device 31 has a focal point for measuring a focal position in each traveling direction (first and second traveling directions) of the light emitted from the optical path deflecting device 1. A distance measuring means 34 and a feedback signal generating means 35 for generating a feedback signal for controlling an applied voltage generated by the power supply 33 based on the difference between the focal positions in each traveling direction obtained by the focal distance measuring means 34 May be added. Reference numeral 36 denotes a mirror for guiding a part of the light emitted from the optical path deflecting device 1 to the focal length measuring means 34.
[0076]
As the focal length measuring unit 34, a focal length measuring unit normally used for an autofocus mechanism of a camera can be suitably used, and for example, a CCD (Charge Coupled Device) array can be used. In operation, an image pattern having a certain spatial frequency is prepared as incident light, and a part or all of this light is incident on the CCD array. In the CCD array, an image signal obtained at a predetermined focal length is stored in the feedback signal generating means 35 as a reference signal in advance, and the voltage from the power supply 33 is obtained so that an image signal closest to this value is obtained. You can choose As a result, the optical path deflecting device 31 capable of always keeping the image point distance constant can be configured, and the influence of an error factor of the light deflection amount such as the environmental temperature can be eliminated. As a result, it is possible to eliminate the fluctuation of the image point distance for each color in the field sequential method, which is a colorization method for temporally switching the wavelength of the projection light in the image display device, and it is possible to display a high-definition color image. Become.
[0077]
Instead of using the reference signal, feedback may be performed so that the difference between the image signals in each traveling direction is minimized, thereby making it possible to reduce the difference between the image point positions in each traveling direction.
[0078]
A part of the light may always be guided to the focal length measuring means by using a half mirror for the mirror 36, but it is inserted into the optical path only when necessary so as not to lower the light use efficiency. Is preferably designed to be retracted outside the optical path.
[0079]
In the present embodiment, a pair of electrodes 32a and 32b are provided on both surfaces of the birefringent medium 4 as the image point distance compensating means to apply a voltage. In the case of the birefringent media 13 and 21 which are provided as optical path deflecting means and have inclined surfaces, a pair of electrodes are provided on both surfaces of the birefringent media 13 and 21 without applying a separate image point distance compensating means as in the embodiment. You may comprise so that it is possible.
[0080]
A fifth embodiment of the present invention will be described with reference to FIG. This embodiment shows an example of application to an image display device. In FIG. 9, reference numeral 41 denotes a light source for a lighting device in which LED lamps are arranged in a two-dimensional array. In the traveling direction of light emitted from the light source 41 toward a screen 42, a diffusion plate 43, a condenser lens 44, an image A transmission type liquid crystal panel 45 as a display element and a projection lens 46 as an optical device for observing an image pattern are arranged in this order. Reference numeral 47 denotes a light source drive unit for the light source 41, and reference numeral 48 denotes a liquid crystal drive unit as display driving means for the transmission type liquid crystal panel 45.
[0081]
Here, an optical path deflector 49 functioning as a pixel shift element is interposed on the optical path between the transmission type liquid crystal panel 45 and the projection lens 46. The optical path deflecting device 49 has a configuration including the optical path deflecting device 1 or 11 as described in each of the above-described embodiments or the optical path deflecting device 31, and the effective area of the optical path deflecting device is transparent. It is set so as to correspond to the liquid crystal panel 75. The optical path deflecting device 49 is connected to a voltage application circuit and a drive control unit 50 that performs a function of opening and closing switches and the like in the voltage application circuit.
[0082]
Illumination light emitted from the light source 41 under the control of the light source drive unit 47 becomes illumination light uniformized by the diffusion plate 43, and is controlled by the condenser lens 44 in synchronization with the illumination light source by the liquid crystal drive unit 48, and is of a transmission type. The liquid crystal panel 45 is critically illuminated. The illumination light spatially modulated by the transmissive liquid crystal panel 45 enters the effective area of the optical path deflecting device 49 as image light, and the image light is shifted by an arbitrary distance in the pixel arrangement direction by the optical path deflecting device 49. You. This light is enlarged by the projection lens 46 and projected on the screen 42.
[0083]
The shift amount is set to の of the pixel pitch because image multiplication is performed twice in the pixel arrangement direction. By correcting the image signal for driving the liquid crystal panel 45 by the shift amount according to the shift amount, an apparently high-definition image can be displayed.
[0084]
Here, in the conventional optical path deflecting device, when projecting light is imaged on a screen, an aberration occurs because an image point distance is different for each shift position, and there is a problem that a good image cannot be obtained on the same surface. Although there was a problem that the image was degraded, in the present embodiment, since the optical path deflecting device 49 has the above-described optical path deflecting devices 1, 11 and the like, such a difference in image point distance is eliminated. Therefore, the above-mentioned problem can be solved, and good display without image deterioration due to defocus can be achieved.
[0085]
【The invention's effect】
According to the first aspect of the present invention, there is provided the image point distance compensating means for adjusting the image point distance in each traveling direction of the light switched by the optical path deflecting means to be substantially equal. Even if there is a difference in the image point distance in the light traveling direction due to the optical path deflection due to the light path deviation, the image point distance difference can be eliminated by adjusting the image point distance to be substantially equal by the image point distance compensating means. It is possible to prevent the occurrence of aberration caused by the distance difference.
[0086]
According to the second aspect of the present invention, a general birefringent medium can be used as the optical path deflecting means to realize the first aspect of the present invention.
[0087]
According to the third aspect of the present invention, in order to realize the first or second aspect of the present invention, a birefringent medium having a refractive index anisotropy for reducing an image point distance difference is used as an image point distance compensating means. Thus, it can be easily realized.
[0088]
According to the fourth aspect of the present invention, in order to realize the third aspect of the present invention, a birefringent plate made of a uniaxial optical crystal is used as a birefringent medium for compensation, and the optical crystal axis is set to the incident optical axis. By setting them substantially perpendicular, the difference in image point distance can be reduced without causing refraction and scattering of light guided in each traveling direction, and the optical path calculation becomes complicated in optical design. And can be easily designed.
[0089]
According to the fifth aspect of the present invention, in the optical path deflecting device of the third or fourth aspect, the birefringent medium for compensation is made of LiNbO. ₃ Since it is made of crystal and its optical crystal axis is set so as to be substantially coincident with one of the polarization directions switched by the polarization direction switching means, good image point distance compensation becomes possible and LiNbO ₃ The crystal is stable among optical crystals without deliquesce and the like, and Δn (= no-ne) has an appropriate size, so that the crystal can be easily handled.
[0090]
According to the sixth aspect of the present invention, in the optical path deflecting device according to the fifth aspect, the plate thickness of the birefringent medium for compensation is within a range of ΔL / (1 / no-1 / ne) ± 30 (μm). , The difference in image point distance of light guided in each traveling direction can be appropriately shortened.
[0091]
According to the optical path deflecting device of the present invention, even if there is a difference in the image point distance in the traveling direction of the light accompanying the optical path deflection by the optical path deflecting means according to the polarization direction, the image point distances become substantially equal. Since the optical path deflecting means has an inclined surface inclined with respect to the optical axis of the incident light, the difference in image point distance can be eliminated, and the occurrence of aberration due to the difference in image point distance can be prevented. It is not necessary to additionally provide another member such as a birefringent medium for compensation, and it can be easily realized only by setting the attitude of the optical path deflecting means.
[0092]
According to the invention of claim 8, the invention of claim 7 can be easily realized only by setting the attitude of the optical path deflecting means.
[0093]
According to the ninth aspect of the present invention, in realizing the optical path deflecting device according to the seventh aspect, it is possible to simplify the position adjustment at the time of installation of the polarization direction switching means and the optical path deflecting means. Since the deflecting means can be arranged perpendicular to the optical axis, the space required for a large area can be made relatively small.
[0094]
According to the tenth aspect of the present invention, in the optical path deflecting device according to any one of the seventh to ninth aspects, for example, in order to favorably form an image on the light receiving unit in an image display device, It is necessary to suppress the difference in the image point distance in each traveling direction within the depth of focus. However, by setting the inclination angle i between the optical axis of the incident light and the normal to the birefringent medium in the negative direction, the above condition is satisfied. Relationship can be maintained.
[0095]
According to the eleventh aspect of the present invention, in the optical path deflecting device according to any one of the third to sixth aspects, the image point distance varies depending on the wavelength of incident light and environmental fluctuation. Since at least one pair of electrodes is provided at a position sandwiching the medium and causes an electric field to act on the birefringent medium, the voltage applied between these electrodes is appropriately controlled to reduce the image point distance. As a result, it is possible to suppress the variation of the image point distance for each color in the field sequential method, which is a colorization method for temporally switching the wavelength of the projection light in the image display device. It can be used to display a simple color image.
[0096]
According to the twelfth aspect of the present invention, in the optical path deflecting device according to any one of the eighth to tenth aspects, the image point distance changes depending on the wavelength of incident light and environmental fluctuations. At least a pair of electrodes disposed at positions sandwiching the birefringent medium for applying an electric field to the birefringent medium, so that the voltage applied between these electrodes is appropriately controlled. In this way, it is possible to suppress the variation of the image point distance for each color in the field sequential method, which is a colorization method for temporally switching the wavelength of the projection light in the image display device. This makes it possible to display high-definition color images.
[0097]
According to the optical path deflecting device of the present invention, the image point distance varies depending on the wavelength of the incident light and environmental fluctuation, but the focal position in each traveling direction of the light emitted from the optical path deflecting device is measured. By generating a feedback signal of the applied voltage applied to the electrode pole based on the measured difference in the focal position in each traveling direction, the image point distance can always be kept constant, and as a result, especially, the image display device In this case, it is possible to eliminate the fluctuation of the image point distance for each color in the field sequential method, which is a color conversion method for temporally switching the wavelength of the projection light, which can be used for high-definition color image display.
[0098]
According to the image display apparatus of the present invention, when the conventional pixel shift technique forms an image of projection light on a screen, an aberration occurs because an image point distance is different for each shift position, so that aberration is generated on the same plane. Although there is a problem that a proper image cannot be obtained and there is a problem that an image is deteriorated, according to the present invention, there is provided a configuration for eliminating a difference in image point distance in an image display device. Since the optical path deflecting device having the optical path deflecting device according to the first aspect or the optical path deflecting apparatus according to the thirteenth aspect is provided, it is possible to solve the above-described problem and perform a favorable display without image deterioration due to defocus.
[Brief description of the drawings]
FIG. 1 is a side view showing a basic configuration of an optical path deflecting device according to a first embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the relationship between the thickness of the crystal and the focus.
FIG. 3 is a side view showing a basic configuration of an optical path deflecting device according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram for explaining the principle of image point distance compensation using an inclined surface.
FIG. 5 is a characteristic diagram showing a relationship between an incident angle, an optical length difference, and a shift amount.
FIG. 6 is a side view showing a basic configuration of an optical path deflecting device according to a third embodiment of the present invention.
FIG. 7 is a side view illustrating a schematic configuration of an optical path deflecting device according to a fourth embodiment of the present invention.
FIG. 8 is a characteristic diagram showing a relationship between the applied voltage and 1 / no-1 / ne.
FIG. 9 is a side view illustrating a schematic configuration of an image display device according to a fifth embodiment of the present invention.
FIG. 10 is a side view showing a basic configuration of a conventional optical path deflecting device.
FIGS. 11A and 11B show how blur occurs due to aberration caused by the difference in image point distance. FIG. 11A is a side view of an optical system, and FIG. 11B is a front view of a light receiving unit.
FIG. 12 is an explanatory diagram for calculating aberration.
[Explanation of symbols]
1 Optical path deflection device
2 Polarization direction switching means
3. Optical path deflecting means, birefringent medium
4. Image point distance compensation means, birefringent medium for compensation
11 Optical path deflection device
12 Polarization direction switching means
13. Optical path deflecting means, birefringent medium
14 Slope
15 Holding means
21 Optical path deflecting means, birefringent medium having sawtooth structure
22 slope
31 Optical path deflector
32a, 32b electrode
33 Voltage application means
41 Lighting device
45 Image display device
46 Optical device
48 display driving means
49 Optical path deflector

Claims (14)

Polarization direction switching means disposed on the light incident side to switch the polarization direction of incident linearly polarized light,
Optical path deflecting means for switching the traveling direction of light in accordance with the polarization direction switched by the polarization direction switching means;
Image point distance compensating means for adjusting the image point distance in each traveling direction of the light switched by the optical path deflecting means to be substantially equal;
An optical path deflecting device comprising: 2. An optical path deflecting device according to claim 1, wherein said optical path deflecting means is a birefringent medium for deflection. 3. The optical path deflecting device according to claim 1, wherein said image point distance compensating means is a compensating birefringent medium having a refractive index anisotropy for reducing an image point distance difference in each light traveling direction of said light. 4. The optical path deflecting device according to claim 3, wherein the birefringent medium for compensation is a birefringent plate made of a uniaxial optical crystal, and the optical crystal axis is set substantially perpendicular to an incident optical axis. 5. The compensation birefringent medium is a LiNbO ₃ crystal, and its optical crystal axis is set so as to substantially coincide with one of polarization directions switched by the polarization direction switching means. An optical path deflecting device according to claim 1. The thickness of the compensating birefringent medium is determined by the image point distance difference ΔL generated in each traveling direction of the light by the optical path deflecting unit when the birefringent medium is not present and the polarization direction of each polarization direction at the incident light wavelength. 6. The optical path deflecting device according to claim 5, wherein the refractive index for light ne, no is set within a range of [Delta] L / (1 / no-1 / ne) ± 30 ([mu] m). Polarization direction switching means disposed on the light incident side to switch the polarization direction of incident linearly polarized light,
Optical path deflecting means for switching the traveling direction of light in accordance with the polarization direction switched by the polarization direction switching means;
With
An optical path deflecting device, wherein the optical path deflecting means has an inclined surface inclined with respect to an optical axis of incident light such that image point distances in respective traveling directions of light switched by the optical path deflecting means are substantially equal. 8. The optical path deflecting device according to claim 7, further comprising holding means for holding the optical path deflecting means in an inclined manner so as to have the inclined surface inclined with respect to the optical axis of the incident light. 8. The optical path deflecting device according to claim 7, wherein the optical path deflecting means has the inclined surface inclined with respect to the optical axis of the incident light by forming both the input and output surfaces of the optical path deflecting means in a sawtooth structure. The optical path deflecting means is a birefringent medium made of LiNbO ₃ , and when the inclination angle i of the inclined surface between the optical axis of the incident light and the normal line of the birefringent medium is i = 0, this birefringence is obtained. The optical path deflecting device according to any one of claims 7 to 9, wherein when the angle direction in which the incident light is deflected in the recording medium is set to be positive, the direction is set to be negative. The optical path deflecting device according to any one of claims 3 to 6, further comprising at least a pair of electrodes disposed at positions sandwiching the birefringent medium for compensation and for applying an electric field to the birefringent medium. . The optical path deflecting device according to any one of claims 8 to 10, further comprising at least one pair of electrodes disposed at a position sandwiching the birefringent medium to apply an electric field to the birefringent medium. An optical path deflecting device according to claim 11 or 12,
Voltage applying means for applying a voltage to the electrode,
Focus position measuring means for measuring a focus position in each traveling direction of light emitted from the optical path deflecting device;
Feedback signal generating means for generating a feedback signal of an applied voltage of the voltage applying means applied to the electrode based on a difference between the focal positions in each traveling direction measured by the focal position measuring means,
An optical path deflecting device comprising: An image display element in which a plurality of pixels capable of controlling light according to image information are two-dimensionally arranged;
An illumination device for illuminating the image display element;
An optical device for observing an image pattern displayed on the image display element,
Display driving means for forming an image field by a plurality of time-divided subfields,
An optical path deflecting device having the optical path deflecting device according to any one of claims 1 to 12, or an optical path deflecting device according to claim 13, which deflects an optical path of light emitted from each pixel of the image display element for each of the subfields. ,
An image display device comprising:

Images