JP4520099B2 - Optical element, light deflection element, and image display device - Google Patents

Description

また、電界方向を反転させた時、液晶分子８は図３においてＸ軸を中心とした線対称の配置（第２の配向状態）を取り、偏光方向がＺ軸方向である直線偏光の進行方向は、図３（ａ）中のｂ´に示す通りとなる。
【００６３】
従って、この直線偏光に対して液晶層５に作用させる電界方向を制御することで、ｂとｂ´との２位置、即ち、２Ｓ分の光偏向が可能となる。
【００６４】
液晶層５の材料の代表的物性値（ｎｏ＝１．６，ｎｅ＝１．８）に対して得られる光偏向量について，光偏向量Ｓを計算した結果を図４に示す。図４に明らかなように、θ＝４５°付近が最も光偏向量が大きい。仮に、液晶分子８のチルト角θが２２．５°のとき、２Ｓ＝５（μｍ）の偏向量を得るためには、ここに示される通り、液晶の厚みを３２μｍ厚に設定すれば良い。また、ホメオトロピック配向強誘電液晶において、約７００Ｖ／ｃｍの電界に対して，０．１ｍｓの応答速度が報告されており（Ozaki他、J.J.Appl.Physics、Vol.３０、No.9B、pp2366-2368（1991）を参照）、サブｍｓオーダの十分高速な応答速度が得られる。
【００６５】
また、キラルスメクチックＣ相よりなる液晶においては、チルト角θは温度Ｔにより変化し、相転移点をＴｃとすると、θ∝（Ｔ−Ｔｃ）^βなる関係がある。βは材料により異なるが、０．５程度の値をとる。この特性を利用した温度制御で光偏向量を制御することも可能である。
【００６６】
例えば、仮にチルト角θとして上記の２２．５°を設定し、これに対応する温度をＴ_{θ＝２２．５°}とすれば、Ｔ＞Ｔ_{θ＝２２．５°}では，θ≦２２．５°であり、Ｔ≦Ｔ_{θ＝２２．５°}ではθ＞２２．５°であるため、温度によりチルト角θを制御でき、これによって光偏向量を制御できることとなる。また、位置制御に関しては、電界による微調を同様に行うことができ、温度、電界あるいはその両者の組合せにより適切な光偏向を達成できる。
【００６７】
以上は、電界強度がＥｓ以上で螺旋構造が解けてチルト角θが光学軸の傾斜角に等しい場合について説明したが、電界強度がＥｓ以下の場合には、上記θを液晶分子８の方向を平均化した光学軸の傾斜角として扱えば良い。
【００６８】
図５は、電界発生用の印加電圧とそれにともなう光偏向量の変化を示すグラフである。印加電圧は一般的には矩形波状である。図１及び図２の光偏向素子１の構成において、この電圧印加により液晶層５の内部に所定方向（±Ｙ方向）の電界が発生する。電圧の切替え直後に液晶分子８の回転が発生し、液晶物性や発生電界により決まる時間（光偏向方向切替時間）後、光偏向量が一定となる。この偏向方向は電圧値を保持する間は変化しない（光偏向方向保持時間）
次に、本光偏向素子１のさらに詳細な構成や、その作用効果について説明する。
【００６９】
図６は、本発明の光学素子におけるライン電極周辺の断面構造を説明する為の模式図である。図６において、基板２上の隣接するライン電極６間には、透明充填材３が充填されている。また、液晶層５と基板２上のライン電極６との間には誘電体層４が設けられている。なお、液晶層５と対向する側の基板２、ライン電極６等は図示を省略している。
【００７０】
透明基板２としては、ガラス、プラスチック等の透明材料を用いることができる。ライン電極６の詳細については後述するが、図７には、ライン電極６の電極幅Ｗやライン電極間距離Ｄを図示している。
【００７１】
透明充填材３の材料としては、光硬化又は熱硬化型樹脂が利用可能である。これらはプレポリマー状態で基板上にスピンコート、ディッピング、バーコートなどの塗布法や、スクリーン印刷、グラビア印刷、フレキソ印刷等の印刷法で形成可能である。
【００７２】
誘電体層４の機能は、液晶層５に印加する電界の局所的な変動を抑制することであるが、光学的には、内部吸収、界面反射、回折等極力発生しないよう構成するのが望ましい。
【００７３】
以上のような構成の光偏向素子１において、誘電体層４の層厚に対して発生電界がどのように変化するかについて本出願人が検討したところ、誘電体層４の厚みを増加させるにしたがって、液晶層５に印加される電界が減少する傾向が認められた。電界効率の低下は電源負荷を招き、さらに印加電圧の上昇にともなって発熱、電磁ノイズ発生の原因ともなりうる。これらに鑑みた場合、65％以上の電界発生効率が好ましい。
【００７４】
誘電体の厚みをｔ_de、比誘電率をε_deとしたとき、
ｔ_de・ε_de≦１２００（μｍ）
である時に、光偏向素子１のライン電極６群による電界を、効率的に液晶層５に印加させることができることが確認された。
【００７５】
例えば、誘電体層として比誘電率８のガラスを用いた場合、誘電体層４の厚みは１５０μｍ以下が望ましい。より望ましくは３０μｍ以下にすることで、後の実施例に示す通り、効率向上が図れて有用である。
【００７６】
光偏向素子１を、ガラスを用いた透明な一対の基板２と、基板２間に充填されたホメオトロピック配向をなすキラルスメクチックＣ相よりなる液晶層５と、少なくとも一方の基板２上の光路を含む領域に配置された複数本のライン電極６と、基板２上の隣接するライン電極６間に充填された透明充填材３と、を備え、ライン電極６の隣接する各ライン電極６に対して段階的に異なる電圧値を設定することで光を偏向させるにおいては、大面積化したときに大電圧が必要となるため、効率的に低電圧で所定電界を得られる本構成は、電源への負荷、周辺電子部品への電磁ノイズ等を低減する上できわめて有用である。
【００７７】
ライン電極群をなす各ライン電極６の配列ピッチＤについては、
D≦２・ｔ_de
とすることが望ましい。
【００７８】
例えば、ｔ_de＝３０μｍである場合、Ｄとしては３０μｍ以下に設定する。
【００７９】
特に、透明な一対の基板２と、基板２間に充填されたホメオトロピック配向をなすキラルスメクチックＣ相よりなる液晶層５と、少なくとも一方の基板２上の光路を含む領域に配置された複数本のライン電極６と、基板２上の隣接するライン電極６間に充填された透明充填材３と、を備え、ライン電極群の隣接する各ライン電極６に対して段階的に異なる電圧値を設定することで光を偏向させる光偏向素子１においては、一旦、配向不良が発生した場合、強誘電性液晶である為、ネマチック液晶と異なりそれを除去することはきわめて難しい。
【００８０】
これは、ネマチック液晶の粘性がきわめて低く液晶分子が界面規制力に沿って分子を再配向させやすいのに比較して、強誘電性液晶は、粘性が高くドメインを形成しやすい為、一旦配向不良が発生した場合、再配向させるのが困難な為である。本例の構成においては、電界の局所的な変動が抑制でき配向不良を防ぐことが可能となり信頼性を向上させることができる。
【００８１】
また、ライン電極群をなす各ライン電極６の幅Ｗと配列ピッチＤとの間に、
Ｗ＞０．１・Ｄ
の関係を持たせることで、液晶層５に印加する電界の局所的な変動を抑制しながら、効率的に電界を印加することができる。
【００８２】
例えば、配列ピッチＤを３０μｍとした時、ライン電極６の幅は１５μｍ以下、より望ましくは１２μｍ以下とするのがよい。ただし、ライン電極６として酸化インジウム・スズ等の透明酸化物材料を用いる場合は、現状、市販流通している技術ではライン幅１０μｍ前後が一般的であるため、下限は、これらのパターン形成技術に制約される。
【００８３】
また、ライン電極６として透明材料を用いることで、光利用効率を高め信号品質を向上させることができる。この場合、透明なライン電極６としては、酸化スズ（ＳｎＯ₂）、酸化インジウム（Ｉｎ₂Ｏ₃）、酸化インジウム・スズ（ＩＴＯ）、酸化亜鉛（ＺｎＯ）、酸化亜鉛・アンチモン（ＺｎＯ・Ｓｂ２０５）、酸化スズ・アンチモン（ＡＴＯ）などを用いることができる。
【００８４】
これらを形成する場合、ライン電極６の形状の開口マスクを重ねた状態で、スパッタリング法、蒸着法、イオンプレーティング法などの方法で直接基板２上に所定形状の膜を成長させる方法や、塗布法、浸漬法、ゾルゲル法などで基板全面に成膜させた後、所定のマスキングを施した上で、塩酸系エッチャントなどによりウェットエッチングさせ、あるいはドライエッチングする方法がある。
【００８５】
中でも酸化亜鉛・アンチモン及び酸化スズ・アンチモンよりなるライン電極６の材料は、透明性に優れ、表面抵抗値も液晶に印加する電界を発生する上で問題のない値に制御でき、さらに、屈折率も従来多く使用されていた酸化インジウム・スズ（屈折率１．８〜２．０）に比較して小さく制御できる為、透明充填材との屈折率差を低くでき有用である。
【００８６】
誘電体層４としては、透明で電気的に絶縁性を有し、耐候性が高く、しかも複屈折性の小さいものが望ましく、無機透明材料であればガラス、有機材料であればポリカーボネート、アクリルなどを好適に用いることができる。
【００８７】
無機透明材料は、熱、光に対する耐性に優れる為、長期信頼性に優れた素子を構成することができ有用である。特に、ガラス材は複屈折がなく、変形が少ないことから好ましい。
【００８８】
有機透明材料を用いた場合、転写成形、射出成形による製造方法をとることで、量産性に優れた素子を提供することができる。
【００８９】
図８は、光偏向素子１を用いた画像表示装置の概要を示す概念図である。図８において、符号１１は、照明用の光源であり、白色あるいは任意の色の光を高速にＯＮ、ＯＦＦできるものであるならば、いかなる種類や型の光源であっても利用することができる。たとえば、ＬＥＤランプやレーザ光源、あるいは、白色のランプ光源などを２次元アレイ状に配列して、かかる光源に対して高速動作するシャッタを組合せたものなどを照明用の光源として用いることができる。
【００９０】
符号１２は、光源から出た光を均一に画像表示素子１３に照射させるための照明装置であり、拡散板１２ａ、コンデンサレンズ１２ｂなどから構成される。
【００９１】
符号１３は、照明装置１２から入射した均一の照明光を、画像フィールドを時間的に更に細分割した複数個の画像サブフィールドごとに、画像情報に基づいて空間光変調して、画像光として出射する画像表示素子である。画像表示素子１３としては、透過型液晶ライトバルブ、反射型液晶ライトバルブ、ＤＭＤ素子などを用いることができる。
【００９２】
符号１４は、前記画像サブフィールドごとに、画像表示素子１３から出射される画像光の光路を偏向して、偏向画像光として出射する光偏向素子である。該光偏向素子１４により、画像サブフィールドごとの光路の偏向量に応じて、スクリーン１６上に投射される画像表示位置がずらされる状態となる画像パターンを表示させることが可能となり、画像表示素子３の実際の画素数を見かけ上増倍した画素数として、画像表示させることができる。
【００９３】
符号１５は、画像表示素子１３に表示された画像パターンを観察するための光学部材であり、符号５は投射レンズ、符号６はスクリーンである。さらに、符号１７は光源１１を駆動するための光源駆動手段であり、符号１８は画像表示素子１３を駆動するための表示駆動回路であり、符号１９は光偏向素子１を駆動するための光偏向駆動回路である。また、符号２０は、光源駆動回路１７、表示駆動回路１８、光偏向駆動回路１９などを含め画像表示装置の全体を制御するための画像表示制御回路である。
【００９４】
次に、図８に示す画像表示装置の基本的な動作について説明する。光源駆動回路１７で制御されて光源１１から放射された光は、拡散板１２ａにより均一化された照明光となり、コンデンサレンズ１２ｂにより、光源駆動回路１７と同期して動作する表示駆動回路１８により制御されている画像表示素子１３をクリティカルに照明する。ここでは、画像表示素子１３の例として、透過型液晶パネル、すなわち、透過型液晶ライトバルブを用いている。透過型液晶ライトバルブからなる画像表示素子１３により空間光変調された照明光は、画像光として光偏向素子１に入射され、光偏向素子１から出射された出射光は、偏向画像光として、投射レンズ１５で拡大された後、スクリーン１６に投射される。すなわち、透過型液晶ライトバルブからなる画像表示素子１３の画像光の出射側に配置されている光偏向素子１によって、画像光は、光偏向駆動回路１９からの駆動信号に応じて、画素の配列方向に任意の距離だけシフト（偏向）された偏向画像光として出射されて、投射レンズ１５を介して、スクリーン１６上に投射される。
【００９５】
なお、図８においては、透過型液晶ライトバルブからなる画像表示素子１３の直後に、光偏向素子１を配置しているが、光偏向素子１の配置位置はかかる場合に限定されるものではなく、スクリーン１６の直前などに配置することとしても良い。ただし、スクリーン１６付近に配置する場合、光偏向素子１を形成する光偏向素子の大きさや、更には、光偏向素子を形成する透明電極の配設ピッチなどを、光偏向素子１の配置位置における画面サイズや画素サイズに応じて設定することが必要になる。
【００９６】
しかし、いかなる配置位置に光偏向素子１４を配置する場合であっても、前記偏向画像光の光路のシフト（偏向）量は、画素ピッチの整数分の１であることが望ましい。すなわち、画素の配列方向に対して２倍の画素増倍を行なう場合は、偏向画像光の光路のシフト量は、画素ピッチの１／２とし、配列方向に対して３倍の画素増倍を行なう場合は、画素ピッチの１／３とすることが望ましい。また、光偏向素子４の構成によって、偏向画像光の光路のシフト量が画素ピッチよりも大きくなる場合には、光路のシフト量を画素ピッチの（整数倍＋整数分の１）の距離に設定してもよい。
【００９７】
この光偏向素子１を画素配列方向の縦横２次元に用いることにより、例えば２倍の画像増倍を行なう光偏向素子を２枚用いることにより、見かけ上の画素４倍の効果が得られ、使用した透過型液晶ライトバルブの解像度以上の高精細な画像を表示することができる。また、光偏向素子１の構成によってシフト量が大きくなる場合には、シフト量を画素ピッチの（整数倍＋整数分の１）の距離に設定しても良い。いずれの場合も、画素のシフト位置に対応したサブフィールドの画像信号で透過型液晶ライトバルブである画像表示素子１３を駆動する。
【００９８】
なお、図８では、単板の透過型液晶ライトバルブと単色ＬＥＤランプを用いた単色の画像表示装置を示したが、３原色の光源１１と、照明装置１２と、３枚の画像表示素子１３とを用いて、３原色の画像を混合してフルカラー画像を表示させることもできる。また、単板の画像表示素子１３を時間順次に三原色光で照明するフィールドシーケンシャル方式でもフルカラー画像を表示することができる。この場合、三色の光源１１からの光路をクロスプリズムで混合して照明しても良いし、白色ランプ光源１１と回転カラーフィルターの組合せで、時間順次の三原色光を生成してもよい。
【００９９】
【実施例】
本発明の一実施例について説明する。
【０１００】
［実施例１］
電界計算を以下の通り実施した。
【０１０１】
すなわち、前述の光偏向素子１の一実施例である図９に示す構成の光偏向素子１について（以下の各実施例において、図９に示す構成の光偏向素子１を条件を変えて用いている）、発生する電界を計算した。計算の目的は誘電体層４の厚みを変化させることで、液晶層５に印加される横方向の電界がどのように変化するかを求め、効果的に機能する条件を得ることである。
【０１０２】
電極６は、上下の基板２のそれぞれに１００μｍピッチで設け、互いに位置補間する配置とした。ここでの計算は、ライン電極６に印加する電圧が段階的に変化するようにしており、これにしたがって横方向に電界が発生する。
各計算に用いた値を表１に示す。
【０１０３】
【表１】

【０１０４】
液晶層５の層中央部における電界の分布を計算した結果を図１０に示す。ただし、ここでの計算は電界印加直後の分布であり，液晶分子の動作による電界の緩和は反映されていない。計算の結果、誘電体層４の厚みが厚くなるにしたがって液晶層５に印加される横方向電界は小さくなることが判明した。
【０１０５】
このことから、誘電体層の厚みｔ_de、比誘電率ε_deにおいて、
ｔ_de・ε_de≦１２００（μｍ）
であるときに、電界発生効率として６５％以上を確保が確保され、素子のライン電極６による電界を、効率的に液晶層５に印加させることが可能であることが確認できた。
【０１０６】
［実施例２］
表2に示す条件で電界を計算した。計算の目的はライン電極６の配列ピッチＤを変化させることで、液晶層５に印加される横方向の電界がどのように変化するかを求め、効果的に機能する条件を得ることである。
【０１０７】
誘電体層４は上下の基板２の内面側にそれぞれ３０μｍ厚で設けた。ここでの計算は、ライン電極６に印加する電圧が段階的に変化するようにしており、これにしたがって横方向に電界が発生する。
【０１０８】
【表２】

【０１０９】
計算結果を図１１に示す。図１１は、横軸にライン電極６と著高する方向の位置、縦軸に電界強度を示している。液晶層５のライン電極ピッチが４０μｍよりも広くなると電極ピッチに応じた周期的な電界変動が発生する。図中５０μｍまでは許容できるレベルであるが、それ以上大きなライン電極ピッチでは液晶層５の配向不良が発生することが別の実験から確認された。他の誘電体層４の厚みについても同様の計算を実施したところ、各ライン電極６の配列ピッチＤと誘電体層４の厚みｔ_deとの間の関係が、
Ｄ≦２・t_de
である場合に、均一な電界が得られることが判明した。
【０１１０】
［実施例３］
表３に示す条件にて電界を計算した。計算の目的はライン電極の電極幅Ｗを変化させることで、液晶層５に印加される横方向の電界がどのように変化するかを求め、効果的に機能する条件を得ることである。
【０１１１】
誘電体層４は上下の基板２の内面側にそれぞれ１５０μｍ厚で設け、ライン電極ピッチを１００μｍに設定した。ここでの計算は、ライン電極に印加する電圧が段階的に変化するようにしており、これにしたがって横方向に電界が発生する。
【０１１２】
【表３】

【０１１３】
計算結果を図１２に示す。ライン電極幅Ｗが広いほど電界強度が高くなる。これを１０μｍよりも広くとることで、１００Ｖ／ｍｍ印加の電極環電位差に対して７０％の効率で電界が発生していることがわかった。ここではライン電極ピッチＤが１００μｍの場合について例を示しているが、ＷとＤの関係として、
Ｗ＞０．１・Ｄ
であるときに効率的な電界発生がなされることが判明した。
【０１１４】
［実施例４］
大きさ３０ｍｍ×４０ｍｍ、厚さ３ｍｍのガラスの基板２の中央領域表面に０．１ｍｍピッチ、０．０１ｍｍ幅、０．２μｍ厚の酸化インジウム・スズ（ＩＴＯ）よりなる１００本の透明ライン電極６を高周波マグネトロンスパッタリング法により形成した。電極６のピッチと幅は、フォトリソ工程によりあらかじめレジスト材料でライン電極６の形成部以外をカバリングし、成膜後、レジストをリフトオフすることで所定値を得た。その後、レジストを洗浄除去した後、市販のＵＶ硬化樹脂を基板上に滴下し、１ｍｍ厚の誘電体（硼珪酸ガラス）をその上から重ね、加圧した状態で紫外線露光し、樹脂を硬化させた。これを複合基板とし、硼珪酸ガラスの表面側を研磨し１５０μｍとした。この複合基板に対して干渉計を用いて表面平滑性を測定したところ、測定エリア１０ｍｍ×１０ｍｍの範囲で波面収差６３．３ｎｍ（ｒｍｓ）以下の平坦性が得られた。
【０１１５】
この誘電体表面に、ＩＰＡ（イソプロピルアルコール）に溶解したポリアミック酸を塗布し、焼結させることで、ポリイミドよりなる垂直配向膜を形成した。これを基板２とし、同条件で作製した２枚の基板２を、ＩＴＯを半ピッチずらした状態で重ね、空セルを形成した。なお両基板２のギャップを調整する為のスペーサは基板２の端部に配置し、この部分を接着剤で固定した。基板２を約９０度に加熱した状態で、二枚の基板２間に強誘電性液晶（チッソ製ＣＳ１０２９）を毛管法にて注入して液晶層５とした。冷却後の液晶層５は透明であり、コノスコープ像観察から基板２に垂直に配向していることが確認できた.
この液晶セルを図８に示す画像表示装置に組み込み、表示画像を形成したところ、スクリーン１６上にて高精細の画像が得られた。
【０１１６】
［比較例］
前述の実施例の比較例として、実施例４の構成において、１ｍｍ厚の硼珪酸ガラスに代えて、１５０μｍ厚の硼珪酸ガラスを用意し、これを基板２に貼り合せた後、実施例1と同様に干渉計によって表面性を測定したところ、波面収差は７０．９ｎｍであった。これによって無機透明材料を貼り合せ後、研磨する工程にてより、平坦性を確保できることがわかった。
【０１１７】
【発明の効果】
請求項１に記載の発明は、より低い電圧で液晶を駆動させることが可能となり、低電圧化が図られ、もって、効率的な電界の発生を実現できる。
【０１１８】
又、電極の配置に基づく局所的な変化を抑えて、液晶の配向不良を防ぐことができる。
【０１１９】
請求項２に記載の発明は、請求項１に記載の発明において、効率的に、低電圧で所定電界を得ることができ、電源への負荷、周辺電子部品への電磁ノイズ等を低減する上できわめて有用である。
【０１２０】
請求項３に記載の発明は、請求項１又は２に記載の発明において、電極として光吸収率の高い材料を用いた場合、光利用効率が低下するばかりでなく、発熱により光学素子としての特性を変動させてしまい、また、反射率の高い材料を用いた場合、光源側光学素子と多重反射を発生させる可能性がありノイズ要因となるが、本発明によればこれらの不具合を抑制できる。
【０１２１】
請求項４に記載の発明は、光偏向装置の低電圧化が図り、効率的な電界の発生を実現できる。
【図面の簡単な説明】
【図１】本発明の一実施の形態である光偏向素子の全体構成の説明図である。
【図２】光偏向素子の液晶分子配向状態を模式的に示した説明図である。
【図３】光偏向素子の液晶分子配向状態を模式的に示した説明図である。
【図４】光偏向素子の液晶配向角と光軸シフト量との関係を示すグラフである。
【図５】光偏向素子の電圧と光偏向量の時間変化を示すグラフである。
【図６】光学素子におけるライン電極周辺の断面構造を説明する為の模式図である。
【図７】ライン電極の電極幅やライン電極間距離を説明する説明図である。
【図８】本発明の一実施の形態である画像表示装置を説明する概念図である。
【図９】本発明の一実施例である光偏向素子の縦断面図である。
【図１０】液晶層の層中央部における電界の分布を計算した結果を示すグラフである。
【図１１】ライン電極ピッチと電界変動との関係を示すグラフである。
【図１２】ライン電極幅と電界強度との関係を示すグラフである。
【符号の説明】
１ 光学素子、光偏向素子
２ 基板
４ 誘電体層
５ 液晶層
６ 電極
１３ 画像表示素子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical element using liquid crystal, an optical deflecting element, and an image display apparatus including the optical deflecting element.
[0002]
[Prior art]
Various proposals have heretofore been made for optical elements that are light deflection elements using liquid crystal materials (see Patent Documents 1 to 3).
[0003]
Various proposals have been made regarding pixel shift elements (see Patent Documents 4 to 7).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 6-18940
[Patent Document 2]
JP-A-9-133904
[Patent Document 3]
JP-A-10-221703
[Patent Document 4]
Japanese Patent No. 2939826
[Patent Document 5]
JP-A-5-313116
[Patent Document 6]
JP-A-6-324320
[Patent Document 7]
JP-A-10-133135
[0005]
[Problems to be solved by the invention]
Regarding the technology relating to the optical deflection element, first, in Patent Document 1, a light beam shifter made of an artificial birefringent plate is proposed for the purpose of reducing the light loss of the optical space switch. In detail, a light beam shifter in which two wedge-shaped transparent substrates are arranged in opposite directions, a liquid crystal layer is sandwiched between the transparent substrates, and the light beam shifter is connected to the rear surface of a matrix type deflection control element. A beam shifter has been proposed. At the same time, two wedge-shaped transparent substrates are arranged in opposite directions, matrix drive is possible between the transparent substrates, and a light beam shifter sandwiching a liquid crystal layer that shifts the incident light beam by a half cell is provided. There has been proposed a light beam shifter in which multiple stages are shifted by half a cell.
[0006]
Patent Document 2 proposes an optical deflection switch that can obtain a large deflection, has high deflection efficiency, and can arbitrarily set a deflection angle and a deflection distance. Specifically, two transparent substrates are arranged opposite to each other at a predetermined interval, a vertical alignment process is performed on the opposed surfaces, and a smectic A phase ferroelectric liquid crystal is sealed between the transparent substrates. The liquid crystal element includes a driving device that is vertically aligned with respect to the electrode pair, the electrode pair is arranged so that an AC electric field can be applied in parallel with the smectic layer, and the AC electric field is applied to the electrode pair. In other words, the refraction angle and the direction of displacement of the polarized light incident on the liquid crystal layer can be changed by the birefringence due to the inclination of the liquid crystal molecules by using the electroclinic effect of the smectic A phase ferroelectric liquid crystal.
[0007]
In the technique of Patent Document 1, since nematic liquid crystal is used as the liquid crystal material, it is difficult to increase the response speed to sub-milliseconds, and it cannot be used for applications that require high-speed switching. Further, in the technique of Patent Document 2, switching by an electroclinic effect using a smectic A-phase ferroelectric liquid crystal is proposed, but the electroclinic effect is highly temperature dependent and a stable shift cannot be expected.
[0008]
Therefore, in Patent Document 3, a first window having an optically transparent common electrode, a second window having a large number of transparent conductive electrodes in an electrically bundled parallel stripe shape, a first window, and a second window. An optical element comprising a liquid crystal molecular layer provided in the middle of the window, wherein the optical device is positioned such that the optical beam is incident on the first window and reflected or transmitted by the second window, and further includes a control signal Is applied to the outer electrode of each cell individually to generate a linear information voltage gradient along the junction electrode and through the cell region, thereby causing a linear or non-linear portion of the electro-optical properties of the LC. An apparatus for wavefront modulating an optical beam is proposed, which is configured to cause a local change in refractive index in a liquid crystal layer. Also, according to claim 4, by addressing the active area with a voltage from within the linear portion of the LC electro-optical properties of the CL layer at a predetermined tilt angle between 0 and 3 degrees, the transmission area is reflected from the transmitted or reflected optical wavefront. A device is proposed which is used to deflect an optical beam by generating a phase characteristic with a blaze effect.
[0009]
According to the technique of Patent Document 3, nematic liquid crystal is also used as the liquid crystal, and therefore, as in Patent Document 1, it is not suitable for applications that require high-speed response. Further, in Patent Document 3, a transparent conductive electrode having a parallel stripe shape is described. However, in this structure, there is a possibility that a local variation of the electric field described as the subject of the present invention occurs. It is difficult to obtain a uniform amount of light deflection.
[0010]
Next, regarding the technology related to the pixel shift element, first, in Patent Document 4, in a projection display device that enlarges and projects an image displayed on a display element onto a screen by a projection optical system, an optical path from the display element to the screen is disclosed. Means for shifting a projected image having at least one optical element capable of rotating the polarization direction of transmitted light and at least one transparent element having a birefringence effect, and an aperture ratio of the display element And a means for discretely projecting the projection area of each pixel of the display element on the screen is disclosed.
[0011]
In Patent Document 4, at least one optical element (referred to as an optical rotatory element) capable of rotating the polarization direction and at least one transparent element (referred to as a birefringent element) having a birefringence effect are included. The pixel shift is performed by the projection image shift means (pixel shift means). However, as a problem, since the optical rotation element and the birefringence element are used in combination, the light amount loss is large, and the pixel shift amount depends on the light wavelength. Fluctuation and resolution is likely to decrease, optical noise such as ghost due to leaked light is likely to occur at positions outside the pixel shift where images are not originally formed due to mismatch of optical characteristics between the optical rotation element and birefringence element, The cost for this is mentioned. In particular, the KH as described above for the birefringent element.₂PO₄(KDP), NH₄H₂PO₄(ADP), LiNbO₃, LiTaO₃This is remarkable when a material having a large primary electro-optic effect (Pockels effect) such as, GaAs, CdTe, or the like is used.
[0012]
In the projector disclosed in Patent Document 5, the image to be originally displayed stored in the image storage circuit is sampled in a checkered pattern in the pixel selection circuit by the control circuit and sequentially displayed on the spatial light modulator. Further, the control circuit controls the panel rocking mechanism in response to this display to move the adjacent pixel pitch distance of the spatial light modulator by an integer, thereby allowing the image to be originally displayed to be displayed in time. It is reproduced by a typical synthesis. As a result, an image can be displayed with a resolution that is an integral multiple of the pixels of the spatial light modulator, and a projector can be constructed at low cost by using a spatial light modulator with coarse pixels and a simple optical system.
[0013]
However, Patent Document 5 describes a pixel shift method in which the image display element itself is swung at a high speed by a distance smaller than the pixel pitch. In this method, the optical system is fixed, and various aberrations are thus eliminated. Although the occurrence is small, since the image display element itself needs to be translated accurately and at high speed, the accuracy and durability of the movable part is required, and vibration and sound become a problem.
[0014]
Furthermore, according to the technique disclosed in Patent Document 6, the display image is arranged in the vertical direction and the horizontal direction in order to improve the resolution of the display image apparently without increasing the number of pixels of the image display device such as an LCD. Each of the plurality of pixels emits light according to the display pixel pattern, and an optical member that changes the optical path for each field is disposed between the image display device on which the image is displayed and the observer or the screen. In addition, for each field, a display pixel pattern whose display position is shifted in accordance with the change of the optical path is displayed on the image display device. Here, the optical path is changed by causing the portions having different refractive indexes to appear alternately in the optical path between the image display device and the observer or the screen for each field of the image information. It is.
[0015]
In the technique of Patent Document 6, a combination mechanism of an electro-optic element and a birefringent material, a lens shift mechanism, a vari-angle prism, a rotating mirror, a rotating glass, and the like are described as means for changing the optical path. In addition to the method of combining birefringent elements, a method of switching optical paths by displacing (translating, tilting) optical elements such as lenses, reflectors, and birefringent plates by means of voice coils, piezoelectric elements, etc. has been proposed. In this method, the configuration is complicated to drive the optical element, and the cost is increased.
[0016]
Further, according to the technique of Patent Document 7, a light beam deflecting device that can eliminate the need for a rotating machine element, can achieve a reduction in overall size, high accuracy and high resolution, and is hardly affected by external vibration is proposed. Has been. Specifically, a translucent piezoelectric element disposed on the traveling path of the light beam, a transparent electrode provided on the surface of the piezoelectric element, a light beam incident surface A and a light beam emitting surface B of the piezoelectric element. Voltage applying means for applying a voltage to the piezoelectric element through the electrode in order to change the optical path length between and the electrode to deflect the optical axis of the light beam.
[0017]
In this technique, a method has been proposed in which a light-transmitting piezoelectric element is sandwiched between transparent electrodes and the thickness is changed by applying a voltage to shift the optical path, but a relatively large transparent piezoelectric element is required, There are the same problems as in the case of Patent Document 6 described above, such as an increase in apparatus cost.
[0018]
When the above-mentioned problems of the prior art are arranged, the problem with the conventional pixel shift element is that
1. High cost due to the complicated structure, large equipment, loss of light, optical noise such as ghost, or reduced resolution
2. Positional accuracy, durability, vibration and sound problems, especially in configurations with moving parts
3. Response speed in nematic liquid crystal
It is.
[0019]
Therefore, in order to solve these problems, the applicant of the present application has applied a plurality of electrode line groups arranged substantially parallel to a desired optical path shift direction in a region including an optical path on a substrate for applying an electric field. (See Japanese Patent Application No. 2001-287907).
[0020]
However, for example, in such an optical deflection element, the detailed structure and physical properties of electrodes and dielectrics effective for solving the above-described problems have not been known.
[0021]
An object of the present invention is to enable liquid crystal to be driven at a lower voltage for an optical element and an optical deflection element using liquid crystal, and to realize efficient generation of an electric field by lowering the voltage. .
[0022]
[Means for Solving the Problems]
  According to the first aspect of the present invention, a pair of transparent substrates and a space between the substrates are filledIncludes liquid crystals consisting of chiral smectic C phase with homeotropic alignmentA liquid crystal layer, a plurality of electrodes provided on at least one of the pair of substrates at intervals in the plate width direction of the substrate, and a relative dielectric constant provided between the liquid crystal layer and the electrodes A dielectric layer of 8;Voltage applying means for deflecting light by applying voltages of different sizes stepwise between adjacent electrodes with respect to each electrode;The dielectric layer has a thickness t_deAnd when
38 ≦ t_de≦ 150 (μm)
And each electrode of the plurality of electrodes has an arrangement pitch D,
D ≦ 2 · t_de
It is an optical element.
[0023]
Therefore, if the dielectric layer having the thickness and relative dielectric constant of the present invention is used, the liquid crystal can be driven at a lower voltage, the voltage can be lowered, and the generation of an efficient electric field can be realized. I was able to verify.
[0025]
  orThe variation of the electric field direction and the size corresponding to the arrangement pitch occurs, the liquid crystal alignment direction becomes non-uniform, the distribution of the optical element transmittance or the amount of light deflection, etc. occurs, and good characteristics cannot be obtained. It was possible to prevent this, and it was verified that a local change based on the arrangement of the electrodes can be suppressed and liquid crystal alignment failure can be prevented.
[0026]
  Claim2The invention described in claim1In the optical element described in the above, when each electrode has a width W and an arrangement pitch D,
W> 0.1 · D
It is.
[0027]
Therefore, in an element that needs to be applied with different voltage values stepwise, it is necessary to apply a large voltage when the element has a large area. A predetermined electric field can be obtained with a voltage, which is extremely useful for reducing a load on a power source, electromagnetic noise to peripheral electronic components, and the like.
[0028]
  Claim3The invention described in claim 1Or 2In each of the optical elements described above, each of the electrodes is formed of a transparent material.
[0029]
Therefore, when a material having a high light absorption rate is used as an electrode, not only the light utilization efficiency is lowered, but also the characteristics as an optical element are changed due to heat generation, and when a material having a high reflectance is used, Although it may cause multiple reflections with the light source side optical element and becomes a noise factor, according to the present invention, these problems can be suppressed.
[0038]
  Claim4The image display device according to the present invention includes: an image display element that spatially modulates illumination light based on image information and outputs the image light as image light for each of a plurality of image subfields obtained by further subdividing the image field in time; In synchronization with the element, the optical path of the image light incident from each pixel of the image display element driven for each image subfield is deflected to increase the apparent number of pixels of the image display element for display. Claims1~3An optical display device comprising the light deflection element according to any one of the above.
[0039]
Therefore, the voltage of the optical deflecting device can be lowered, and the generation of an efficient electric field can be realized.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
[Definition]
Hereinafter, main terms used in the present specification will be described.
[0041]
(1) Optical deflection element
“Optical deflection element” means that the optical path of light is deflected by an electric signal from the outside, that is, the outgoing light is shifted in parallel to the incident light, rotated at a certain angle, or both Means an optical element capable of switching the optical path. In this description, the magnitude of the shift is referred to as “shift amount” with respect to the light deflection due to the parallel shift, and the rotation amount is referred to as “rotation angle” with respect to the light deflection due to rotation. “Optical deflection device” means a device that includes such an optical deflection element and deflects the optical path of light.
[0042]
(2) Light deflection switching time
The light deflection direction switching time is the time required for switching the optical path and is the time corresponding to the liquid crystal switching time.
[0043]
(3) Subfield
Usually, in an image display device such as a liquid crystal projector, images are sequentially rewritten and displayed at a certain cycle. The image per sheet is called a field. In the present invention, as described above, the optical path shift is performed in a time division manner so that the pixels are doubled and displayed. An image that is time division and displayed is called a subfield. Therefore, for example, when the number of divisions is 2, that is, when the optical path shift is switched at two positions, an image of one field is formed by two subfields.
[0044]
At the time of subfield switching, it is the time for shifting the optical path, and at the time of displaying the subfield, it is the time for completing the optical path shift and displaying one subfield.
[0045]
(4) Pixel shift element
“Pixel shift element” is an image display element in which a plurality of pixels that can control light according to image information is two-dimensionally arranged, a light source that illuminates the image display element, and an image pattern displayed on the image display element. An optical member for observing, and a light deflecting means for deflecting an optical path between the image display element and the optical member for each of a plurality of subfields obtained by dividing the image field in time, and the light deflecting means for each subfield. This means an optical deflecting means in an image display device that displays an image pattern in which the display position is shifted in accordance with the deflection of the optical path, thereby increasing the apparent number of pixels of the image display element. Therefore, basically, it can be said that the optical deflection element and the optical deflection device defined above can be applied as the optical deflection means.
[0046]
[Embodiment of the Invention]
An embodiment of the present invention will be described.
[0047]
First, the basic configuration and operation of the optical deflection element 1 according to the present embodiment will be described with reference to FIGS.
[0048]
FIG. 1 is an explanatory diagram of the overall configuration of the optical deflection element 1. The optical deflection element 1 of FIG. 1 implements the optical element and the optical deflection element of the present invention. First, a pair of transparent substrates 2 are provided so as to face each other. In order to satisfactorily align the liquid crystal layer 5, it is desirable to form an alignment film (not shown in FIG. 1) on the inner surface of at least one of the substrates 2. A liquid crystal layer 5 made of a ferroelectric liquid crystal made of a chiral smectic C phase is filled between the alignment film and the other substrate 2.
[0049]
A plurality of line electrodes 6 for applying an electric field to the liquid crystal layer 5 corresponding to the target light deflection direction are arranged on the liquid crystal panel having the pair of substrates 2 and the liquid crystal layer 5, and the power source 7 is connected. The line electrode 6 is an electrode on a line provided on at least one of the pair of substrates 2 so as to be arranged at a predetermined interval (described later) in the plate width direction of the substrate 2. Each line electrode 6 is provided outside the optical path and is connected to each resistance end of a plurality of resistors 7a arranged in series. A potential gradient is generated between adjacent transparent electrodes 6, and an electric field is applied. It is configured as follows. That is, the voltage application means is realized by deflecting light by applying voltages of different magnitudes between the line electrodes 6 by the power source 7 and the resistor 7a.
[0050]
Next, the liquid crystal layer 5 will be described. First, a “smectic liquid crystal” is a liquid crystal molecule formed by arranging the major axis direction of liquid crystal molecules in a layered manner. With regard to such a liquid crystal, a liquid crystal in which the normal direction of the layer (layer normal direction) and the major axis direction of the liquid crystal molecules coincide with each other is referred to as “smectic A phase”, and a liquid crystal that does not coincide with the normal direction is referred to as “ It is called “chiral smectic C phase”.
[0051]
A ferroelectric liquid crystal composed of a chiral smectic C phase generally has a so-called spiral structure in which the liquid crystal molecule direction is spirally rotated for each layer in the state where an external electric field does not work. The chiral smectic C phase antiferroelectric liquid crystal is The liquid crystal molecules face each other in the opposite direction. Since the liquid crystal composed of these chiral smectic C phases has an asymmetric carbon in the molecular structure and is spontaneously polarized by this, the liquid crystal molecules are rearranged in a direction determined by the spontaneous polarization Ps and the external electric field E. The optical properties are controlled. In the following description, the light deflection element 1 will be described by taking a ferroelectric liquid crystal as an example of the liquid crystal layer 5. However, the present invention is not limited to this, and the liquid crystal layer 5 is also used in the case of an antiferroelectric liquid crystal. Can do.
[0052]
The structure of a ferroelectric liquid crystal composed of a chiral smectic C phase is composed of a main chain, a spacer, a skeleton, a bonding part, a chiral part, and the like. As the main chain structure, polyacrylate, polymethacrylate, polysiloxane, polyoxyethylene and the like can be used. The spacer is for linking a skeleton, a bonding part, and a chiral part responsible for molecular rotation to the main chain, and a methylene chain having an appropriate length is selected. In addition, a —COO— bond or the like is selected as a bond portion that bonds the chiral portion and a rigid skeleton such as a biphenyl structure.
[0053]
In the optical deflecting element 1 of the present embodiment, the ferroelectric liquid crystal layer 5 made of a chiral smectic C phase has a rotational axis of molecular helical rotation perpendicular to the surface of the substrate 2 by an alignment film, so-called homeotropic alignment is achieved. Eggplant. As an alignment method for such homeotropic alignment, a well-known technique can be applied. That is, (1) shear stress method, (2) magnetic field orientation method, (3) temperature gradient method, (4) SiO oblique deposition method, (5) photo-alignment method, etc. Takezoe, Fukuda, "Structures and properties of ferroelectric liquid crystals," Corona, p. 235).
[0054]
In the present optical deflection element 1, the chiral smectic C phase has an extremely high speed response as compared with the nematic liquid crystal, and switching in sub ms is possible. In addition, the liquid crystal molecule direction is uniquely determined with respect to the electric field direction, and the director direction is fixed above a certain electric field strength. Therefore, the smectic A phase utilizing the electroclinic effect that takes the director angle proportional to the electric field strength is used. Compared to the liquid crystal, the director direction is easily controlled and easy to handle.
[0055]
In addition, the liquid crystal layer 5 made of a chiral smectic C phase having homeotopic orientation is more effective in the operation of the liquid crystal molecules than in the case of taking the homogeneous orientation (the state in which the liquid crystal molecules are oriented parallel to the substrate surface). Therefore, it is easy to control the light deflection direction by adjusting the direction of the external electric field, and has the advantage that the required electric field is low. Further, when the liquid crystal molecules are homogeneously aligned, the liquid crystal molecules strongly depend not only on the direction of the electric field but also on the substrate surface, so that more positional accuracy is required for the installation of the optical deflection element. Conversely, in the case of homeotopic orientation as in the present embodiment, the setting margin of the optical deflection element 1 increases with respect to optical deflection. In making use of these features, it is not necessary that the spiral axis be strictly oriented perpendicular to the substrate surface, and it may be tilted to some extent. For example, even if a part of the side surface forming the spiral structure is perpendicular to the substrate 2 and the spiral axis itself is tilted from the normal direction of the substrate, the liquid crystal molecules are not affected by the regulation force from the substrate 2. It only needs to be able to face one direction.
[0056]
Next, the basic operation principle of the present optical deflection element 1 will be described with reference to FIGS. FIG. 2 schematically shows the alignment state of the liquid crystal molecules with respect to the configuration shown in FIG. In FIG. 2, the line electrode 6 is provided on a substrate (not shown) on both sides of the optical deflecting element 1, and the line electrode 6 may be formed only on the one-side substrate, but the liquid crystal layer 5 is efficiently laterally disposed. In order to apply the electric field in the direction, it is desirable to form it on both sides.
[0057]
In addition, the incident light with respect to the light deflecting element 1 is linearly polarized light, and the polarization direction thereof is the vertical direction as shown by the arrows in FIG. 2 (hereinafter, the polarization direction is similarly incident by the vertical and horizontal arrows). The line electrodes 6 are arranged so as to be opposite to each other so that the electric field direction is orthogonal to the polarization direction thereof, and different voltage values are set stepwise for each adjacent line electrode of the line electrode group. In addition, it is preferable to provide an electromagnetic shield so that the leakage electric field from the electrode 6 does not adversely affect the peripheral devices of the optical deflection element 1. The liquid crystal molecules 8 can take the orientation direction in a spiral shape as described above depending on the applied electric field direction, and FIG. 2 shows the possible orientation states in a cone shape.
[0058]
FIG. 3 shows an XZ cross section in the liquid crystal layer 5 when the XYZ orthogonal coordinate system is shown in FIG. As shown in FIG. 3, if the liquid crystal molecule 8 has a sufficiently large electric field, it takes either the first alignment state or the second alignment state (see FIG. 3B) depending on the electric field direction. Distributed. θ is the tilt angle of the liquid crystal molecules 8 from the liquid crystal rotation axis, and is simply referred to as “tilt angle” hereinafter. Assuming that the spontaneous polarization Ps of the liquid crystal layer 5 is positive and an electric field E is applied in the positive direction of the Y axis (upward on the paper surface), the liquid crystal molecules 8 have a liquid crystal rotation axis substantially in the direction perpendicular to the substrate. It coincides with the first orientation direction shown in b).
[0059]
When the refractive index in the major axis direction of the liquid crystal layer 5 is ne and the refractive index in the minor axis direction is no, linearly polarized light having a polarization direction in the Y-axis direction is selected as incident light, and the incident light advances in the X-axis positive direction. At this time, the light travels straight in the liquid crystal layer 5 as ordinary light upon receiving the refractive index no, and proceeds in the direction a in FIG. That is, no light deflection is received.
[0060]
On the other hand, when linearly polarized light whose polarization direction is the Z-axis direction is incident, the refractive index in the incident direction is obtained from both the direction of the liquid crystal molecules and the refractive indexes no and ne. More specifically, it is obtained from the relationship with the direction of light passing through the center of the ellipsoid in a refractive index ellipsoid having refractive indexes no and ne as principal axes, but details are omitted here. The light is deflected corresponding to the refractive indexes no and ne and the direction of the liquid crystal molecules 8 (tilt angle θ), and is shifted in the direction shown by b (in the case of the first alignment state) in FIG.
[0061]
Now, when the thickness (gap) of the liquid crystal layer 5 is d, the shift amount S is expressed by the following formula 1 (see, for example, “Crystal Optics” Applied Physics Society, Optical Society, p198).
[0062]

Further, when the electric field direction is reversed, the liquid crystal molecules 8 take a line-symmetrical arrangement (second alignment state) about the X axis in FIG. 3 and the traveling direction of linearly polarized light whose polarization direction is the Z axis direction. Is as shown by b 'in FIG.
[0063]
Therefore, by controlling the direction of the electric field applied to the liquid crystal layer 5 with respect to this linearly polarized light, it is possible to deflect light at two positions b and b ′, that is, 2S.
[0064]
FIG. 4 shows the result of calculating the light deflection amount S for the light deflection amount obtained with respect to the representative physical property values (no = 1.6, ne = 1.8) of the material of the liquid crystal layer 5. As is apparent from FIG. 4, the amount of light deflection is the largest in the vicinity of θ = 45 °. If the tilt angle θ of the liquid crystal molecules 8 is 22.5 °, in order to obtain a deflection amount of 2S = 5 (μm), the thickness of the liquid crystal may be set to 32 μm as shown here. In addition, a response speed of 0.1 ms has been reported for homeotropically oriented ferroelectric liquid crystals with respect to an electric field of about 700 V / cm (Ozaki et al., JJAppl. Physics, Vol. 30, No. 9B, pp2366- 2368 (1991)), a sufficiently high response speed on the order of sub ms is obtained.
[0065]
In a liquid crystal composed of a chiral smectic C phase, the tilt angle θ varies with temperature T, and θ∝ (T−Tc) where Tc is the phase transition point.^βThere is a relationship. β varies depending on the material, but takes a value of about 0.5. It is also possible to control the amount of light deflection by temperature control utilizing this characteristic.
[0066]
For example, suppose that 22.5 ° is set as the tilt angle θ, and the temperature corresponding to this is set to T_{θ = 22.5 °}Then, T> T_{θ = 22.5 °}Then, θ ≦ 22.5 °, and T ≦ T_{θ = 22.5 °}Since θ> 22.5 °, the tilt angle θ can be controlled by temperature, and the amount of light deflection can be controlled by this. As for position control, fine adjustment by an electric field can be performed in the same manner, and appropriate light deflection can be achieved by temperature, electric field, or a combination of both.
[0067]
In the above, the case where the electric field strength is Es or higher and the spiral structure is dissolved and the tilt angle θ is equal to the tilt angle of the optical axis has been described. However, when the electric field strength is equal to or lower than Es, θ is the direction of the liquid crystal molecules 8. What is necessary is just to treat it as the averaged inclination angle of the optical axis.
[0068]
FIG. 5 is a graph showing an applied voltage for generating an electric field and a change in the amount of light deflection accompanying therewith. The applied voltage is generally rectangular. In the configuration of the optical deflection element 1 shown in FIGS. 1 and 2, an electric field in a predetermined direction (± Y direction) is generated inside the liquid crystal layer 5 by applying the voltage. Immediately after the voltage is switched, the liquid crystal molecules 8 are rotated, and the amount of light deflection becomes constant after a time determined by the properties of the liquid crystal and the generated electric field (light deflection direction switching time). This deflection direction does not change while holding the voltage value (light deflection direction holding time).
Next, a more detailed configuration of the present optical deflection element 1 and its operation and effect will be described.
[0069]
FIG. 6 is a schematic view for explaining a cross-sectional structure around the line electrode in the optical element of the present invention. In FIG. 6, a transparent filler 3 is filled between adjacent line electrodes 6 on the substrate 2. A dielectric layer 4 is provided between the liquid crystal layer 5 and the line electrode 6 on the substrate 2. Note that the substrate 2, the line electrode 6 and the like on the side facing the liquid crystal layer 5 are not shown.
[0070]
As the transparent substrate 2, a transparent material such as glass or plastic can be used. Although details of the line electrode 6 will be described later, FIG. 7 illustrates an electrode width W of the line electrode 6 and a distance D between the line electrodes.
[0071]
As the material of the transparent filler 3, a photo-curing or thermosetting resin can be used. These can be formed on the substrate in a prepolymer state by a coating method such as spin coating, dipping or bar coating, or a printing method such as screen printing, gravure printing or flexographic printing.
[0072]
The function of the dielectric layer 4 is to suppress local fluctuations of the electric field applied to the liquid crystal layer 5, but it is optically preferable that the dielectric layer 4 is configured so as not to generate as much as possible such as internal absorption, interface reflection, and diffraction. .
[0073]
In the optical deflection element 1 having the above-described configuration, the present applicant examined how the generated electric field changes with respect to the layer thickness of the dielectric layer 4. As a result, the thickness of the dielectric layer 4 was increased. Therefore, the tendency for the electric field applied to the liquid crystal layer 5 to decrease was recognized. A decrease in electric field efficiency causes a power load, and may cause heat generation and electromagnetic noise as the applied voltage increases. In view of these, an electric field generation efficiency of 65% or more is preferable.
[0074]
The thickness of the dielectric is t_de, Relative dielectric constant ε_deWhen
t_de・ Ε_de≦ 1200 (μm)
At that time, it was confirmed that the electric field generated by the group of line electrodes 6 of the optical deflection element 1 can be efficiently applied to the liquid crystal layer 5.
[0075]
For example, when glass having a relative dielectric constant of 8 is used as the dielectric layer, the thickness of the dielectric layer 4 is desirably 150 μm or less. More desirably, when the thickness is 30 μm or less, as shown in a later example, the efficiency can be improved, which is useful.
[0076]
The light deflection element 1 includes a pair of transparent substrates 2 made of glass, a liquid crystal layer 5 made of a chiral smectic C phase filled between the substrates 2 and having a homeotropic alignment, and an optical path on at least one of the substrates 2. A plurality of line electrodes 6 arranged in a region to be included, and a transparent filler 3 filled between adjacent line electrodes 6 on the substrate 2. In deflecting light by setting different voltage values in stages, a large voltage is required when the area is increased, so this configuration that can efficiently obtain a predetermined electric field with a low voltage is It is extremely useful for reducing electromagnetic noise to the load and peripheral electronic components.
[0077]
Regarding the arrangement pitch D of each line electrode 6 forming the line electrode group,
D ≦ 2 ・ t_de
Is desirable.
[0078]
For example, t_de= 30 μm, D is set to 30 μm or less.
[0079]
In particular, a pair of transparent substrates 2, a liquid crystal layer 5 made of a chiral smectic C phase having a homeotropic alignment filled between the substrates 2, and a plurality of liquid crystals arranged in a region including an optical path on at least one substrate 2. Line electrodes 6 and a transparent filler 3 filled between adjacent line electrodes 6 on the substrate 2, and different voltage values are set stepwise for each adjacent line electrode 6 of the line electrode group. Thus, in the light deflecting element 1 that deflects light, once alignment failure occurs, it is a ferroelectric liquid crystal, and therefore it is extremely difficult to remove it, unlike a nematic liquid crystal.
[0080]
This is because the viscosity of a nematic liquid crystal is extremely low and the liquid crystal molecules are easy to re-align molecules along the interface regulating force. This is because it is difficult to re-orientate. In the configuration of this example, local fluctuations in the electric field can be suppressed and alignment defects can be prevented, and reliability can be improved.
[0081]
Further, between the width W and the array pitch D of each line electrode 6 forming the line electrode group,
W> 0.1 · D
Thus, the electric field can be efficiently applied while suppressing local fluctuation of the electric field applied to the liquid crystal layer 5.
[0082]
For example, when the arrangement pitch D is 30 μm, the width of the line electrode 6 is preferably 15 μm or less, more preferably 12 μm or less. However, when a transparent oxide material such as indium / tin oxide is used as the line electrode 6, the line width around 10 μm is generally used in the currently marketed technology, so the lower limit is limited to these pattern forming technologies. Be constrained.
[0083]
Further, by using a transparent material for the line electrode 6, it is possible to increase the light utilization efficiency and improve the signal quality. In this case, as the transparent line electrode 6, tin oxide (SnO₂), Indium oxide (In₂O_Three), Indium oxide / tin oxide (ITO), zinc oxide (ZnO), zinc oxide / antimony (ZnO / Sb205), tin oxide / antimony (ATO), or the like can be used.
[0084]
In the case of forming these, a method of growing a film of a predetermined shape directly on the substrate 2 by a method such as sputtering, vapor deposition, ion plating, etc., with an opening mask in the shape of the line electrode 6 overlaid, There is a method in which a film is formed on the entire surface of the substrate by a method, a dipping method, a sol-gel method, etc., and then subjected to a predetermined masking, followed by wet etching with a hydrochloric acid-based etchant or dry etching.
[0085]
Above all, the material of the line electrode 6 made of zinc oxide / antimony and tin oxide / antimony is excellent in transparency, and the surface resistance value can be controlled to a value that does not cause a problem in generating an electric field applied to the liquid crystal. In contrast, indium tin oxide (refractive index: 1.8 to 2.0), which has been widely used in the past, can be controlled to be small, so that the difference in refractive index from the transparent filler can be reduced.
[0086]
The dielectric layer 4 is preferably transparent, electrically insulative, high in weather resistance, and low in birefringence. For inorganic transparent materials, glass, for organic materials, polycarbonate, acrylic, etc. Can be suitably used.
[0087]
Since the inorganic transparent material is excellent in resistance to heat and light, it can form an element having excellent long-term reliability and is useful. In particular, a glass material is preferable because it has no birefringence and is less deformed.
[0088]
When an organic transparent material is used, an element excellent in mass productivity can be provided by employing a manufacturing method by transfer molding or injection molding.
[0089]
FIG. 8 is a conceptual diagram showing an outline of an image display device using the light deflection element 1. In FIG. 8, reference numeral 11 denotes a light source for illumination, and any type or type of light source can be used as long as it can quickly turn on and off white or any color light. . For example, an LED lamp, a laser light source, a white lamp light source, or the like arranged in a two-dimensional array and combined with a shutter that operates at high speed with respect to the light source can be used as a light source for illumination.
[0090]
Reference numeral 12 denotes an illumination device for uniformly irradiating the image display element 13 with light emitted from the light source, and includes a diffusion plate 12a, a condenser lens 12b, and the like.
[0091]
Reference numeral 13 designates uniform illumination light incident from the illuminating device 12 and spatially modulates it based on image information for each of a plurality of image subfields obtained by further subdividing the image field in time, and emits the image light as image light. This is an image display element. As the image display element 13, a transmissive liquid crystal light valve, a reflective liquid crystal light valve, a DMD element, or the like can be used.
[0092]
Reference numeral 14 denotes an optical deflecting element that deflects the optical path of the image light emitted from the image display element 13 for each image subfield and emits the deflected image light. The light deflection element 14 can display an image pattern in which the image display position projected on the screen 16 is shifted in accordance with the deflection amount of the optical path for each image subfield. The actual number of pixels can be displayed as the number of pixels that is apparently multiplied.
[0093]
Reference numeral 15 denotes an optical member for observing an image pattern displayed on the image display element 13, reference numeral 5 denotes a projection lens, and reference numeral 6 denotes a screen. Further, reference numeral 17 denotes a light source driving means for driving the light source 11, reference numeral 18 denotes a display driving circuit for driving the image display element 13, and reference numeral 19 denotes an optical deflection for driving the optical deflection element 1. It is a drive circuit. Reference numeral 20 denotes an image display control circuit for controlling the entire image display apparatus including the light source drive circuit 17, the display drive circuit 18, the light deflection drive circuit 19, and the like.
[0094]
Next, the basic operation of the image display apparatus shown in FIG. 8 will be described. The light emitted from the light source 11 under the control of the light source driving circuit 17 becomes illumination light made uniform by the diffusion plate 12a, and is controlled by the display driving circuit 18 operating in synchronization with the light source driving circuit 17 by the condenser lens 12b. The image display element 13 is illuminated critically. Here, as an example of the image display element 13, a transmissive liquid crystal panel, that is, a transmissive liquid crystal light valve is used. Illumination light spatially modulated by the image display element 13 composed of a transmissive liquid crystal light valve is incident on the light deflection element 1 as image light, and the emitted light emitted from the light deflection element 1 is projected as deflection image light. After being magnified by the lens 15, it is projected onto the screen 16. That is, image light is arranged in accordance with a drive signal from the light deflection drive circuit 19 by the light deflection element 1 arranged on the image light output side of the image display element 13 formed of a transmissive liquid crystal light valve. The light is emitted as deflected image light shifted (deflected) by an arbitrary distance in the direction, and is projected onto the screen 16 through the projection lens 15.
[0095]
In FIG. 8, the light deflection element 1 is disposed immediately after the image display element 13 formed of a transmissive liquid crystal light valve. However, the position of the light deflection element 1 is not limited to this case. It may be arranged immediately before the screen 16 or the like. However, when it is arranged near the screen 16, the size of the light deflection element forming the light deflection element 1, the arrangement pitch of the transparent electrodes forming the light deflection element, and the like are determined at the position where the light deflection element 1 is arranged. It is necessary to set according to the screen size and pixel size.
[0096]
However, it is desirable that the amount of shift (deflection) of the optical path of the deflected image light is 1 / integer of the pixel pitch, regardless of the arrangement position of the light deflection element 14. That is, when the pixel multiplication is performed twice in the pixel arrangement direction, the shift amount of the optical path of the deflected image light is ½ of the pixel pitch, and the pixel multiplication is three times in the arrangement direction. When performing, it is desirable to set to 1/3 of the pixel pitch. Further, when the shift amount of the optical path of the deflected image light is larger than the pixel pitch due to the configuration of the light deflection element 4, the shift amount of the optical path is set to a distance of (integer multiple + 1 / integer) of the pixel pitch. May be.
[0097]
By using this optical deflecting element 1 in two dimensions vertically and horizontally in the pixel arrangement direction, for example, by using two optical deflecting elements that perform double image multiplication, an apparent fourfold effect can be obtained and used. High-definition images exceeding the resolution of the transmissive liquid crystal light valve can be displayed. Further, when the shift amount becomes large depending on the configuration of the optical deflection element 1, the shift amount may be set to a distance of (integer multiple + 1 / integer) of the pixel pitch. In either case, the image display element 13 which is a transmissive liquid crystal light valve is driven by an image signal in a subfield corresponding to the pixel shift position.
[0098]
In FIG. 8, a single-color image display device using a single-plate transmissive liquid crystal light valve and a single-color LED lamp is shown, but the three primary color light sources 11, the illumination device 12, and the three image display elements 13 are shown. And a full color image can be displayed by mixing three primary color images. A full-color image can also be displayed by a field sequential method in which the single-panel image display element 13 is illuminated with the three primary colors in time sequence. In this case, the light paths from the three color light sources 11 may be mixed and illuminated by a cross prism, or time-sequential three primary color lights may be generated by a combination of the white lamp light source 11 and a rotating color filter.
[0099]
【Example】
An embodiment of the present invention will be described.
[0100]
[Example 1]
The electric field calculation was performed as follows.
[0101]
That is, with respect to the optical deflection element 1 having the configuration shown in FIG. 9 which is an embodiment of the optical deflection element 1 described above (in the following embodiments, the optical deflection element 1 having the configuration shown in FIG. 9 is used under different conditions). Calculated the electric field generated. The purpose of the calculation is to determine how the lateral electric field applied to the liquid crystal layer 5 changes by changing the thickness of the dielectric layer 4, and to obtain conditions that function effectively.
[0102]
The electrodes 6 were provided on each of the upper and lower substrates 2 at a pitch of 100 μm and arranged to interpolate with respect to each other. In this calculation, the voltage applied to the line electrode 6 is changed stepwise, and an electric field is generated in the lateral direction accordingly.
The values used for each calculation are shown in Table 1.
[0103]
[Table 1]

[0104]
FIG. 10 shows the result of calculating the electric field distribution at the center of the liquid crystal layer 5. However, the calculation here is a distribution immediately after the application of the electric field, and does not reflect the relaxation of the electric field due to the operation of the liquid crystal molecules. As a result of the calculation, it was found that the lateral electric field applied to the liquid crystal layer 5 decreases as the thickness of the dielectric layer 4 increases.
[0105]
From this, the thickness t of the dielectric layer_de, Relative permittivity ε_deIn
t_de・ Ε_de≦ 1200 (μm)
As a result, it was confirmed that the electric field generation efficiency of 65% or more was ensured, and the electric field generated by the line electrode 6 of the device could be efficiently applied to the liquid crystal layer 5.
[0106]
[Example 2]
The electric field was calculated under the conditions shown in Table 2. The purpose of the calculation is to determine how the lateral electric field applied to the liquid crystal layer 5 changes by changing the arrangement pitch D of the line electrodes 6, and to obtain conditions that function effectively.
[0107]
The dielectric layers 4 were provided on the inner surfaces of the upper and lower substrates 2 with a thickness of 30 μm. In this calculation, the voltage applied to the line electrode 6 is changed stepwise, and an electric field is generated in the lateral direction accordingly.
[0108]
[Table 2]

[0109]
The calculation results are shown in FIG. In FIG. 11, the horizontal axis indicates the position in the direction of the line electrode 6 and the vertical axis indicates the electric field strength. When the line electrode pitch of the liquid crystal layer 5 is larger than 40 μm, periodic electric field fluctuations corresponding to the electrode pitch occur. In the figure, it is an acceptable level up to 50 μm, but it was confirmed from another experiment that an alignment defect of the liquid crystal layer 5 occurs at a line electrode pitch larger than that. When the same calculation was performed for the thicknesses of the other dielectric layers 4, the arrangement pitch D of the line electrodes 6 and the thickness t of the dielectric layers 4 were also calculated._deThe relationship between
D ≦ 2 ・ t_de
It was found that a uniform electric field can be obtained.
[0110]
[Example 3]
The electric field was calculated under the conditions shown in Table 3. The purpose of the calculation is to determine how the lateral electric field applied to the liquid crystal layer 5 changes by changing the electrode width W of the line electrode, and to obtain conditions that function effectively.
[0111]
The dielectric layers 4 were provided on the inner surfaces of the upper and lower substrates 2 with a thickness of 150 μm, and the line electrode pitch was set to 100 μm. In this calculation, the voltage applied to the line electrode is changed stepwise, and an electric field is generated in the lateral direction accordingly.
[0112]
[Table 3]

[0113]
The calculation results are shown in FIG. The wider the line electrode width W, the higher the electric field strength. It was found that by taking this wider than 10 μm, an electric field was generated with an efficiency of 70% with respect to the electrode ring potential difference applied with 100 V / mm. Here, an example is shown for the case where the line electrode pitch D is 100 μm, but as the relationship between W and D,
W> 0.1 · D
It has been found that efficient electric field generation occurs.
[0114]
[Example 4]
100 transparent line electrodes 6 made of indium tin oxide (ITO) having a pitch of 0.1 mm, a width of 0.01 mm, and a thickness of 0.2 μm on the surface of the central region of a glass substrate 2 having a size of 30 mm × 40 mm and a thickness of 3 mm. Was formed by a high frequency magnetron sputtering method. The pitch and width of the electrodes 6 were obtained in advance by covering the portions other than the portions where the line electrodes 6 were formed with a resist material by a photolithography process, and lifting off the resist after film formation. Then, after washing and removing the resist, a commercially available UV curable resin is dropped on the substrate, a 1 mm thick dielectric (borosilicate glass) is stacked on top of it, and exposed to UV light in a pressurized state to cure the resin. It was. This was used as a composite substrate, and the surface side of the borosilicate glass was polished to 150 μm. When the surface smoothness of the composite substrate was measured using an interferometer, a flatness with a wavefront aberration of 63.3 nm (rms) or less was obtained in a measurement area of 10 mm × 10 mm.
[0115]
The dielectric surface was coated with polyamic acid dissolved in IPA (isopropyl alcohol) and sintered to form a vertical alignment film made of polyimide. This was used as a substrate 2, and two substrates 2 produced under the same conditions were stacked with ITO being shifted by a half pitch to form empty cells. In addition, the spacer for adjusting the gap of both the board | substrates 2 was arrange | positioned at the edge part of the board | substrate 2, and this part was fixed with the adhesive agent. In a state where the substrate 2 is heated to about 90 degrees, a ferroelectric liquid crystal (CS1029 manufactured by Chisso) is injected between the two substrates 2 by a capillary method to form a liquid crystal layer 5. The liquid crystal layer 5 after cooling was transparent, and it was confirmed that it was aligned perpendicular to the substrate 2 from conoscopic image observation.
When this liquid crystal cell was incorporated in the image display device shown in FIG. 8 and a display image was formed, a high-definition image was obtained on the screen 16.
[0116]
[Comparative example]
As a comparative example of the above-described example, in the configuration of Example 4, instead of 1 mm-thick borosilicate glass, 150 μm-thick borosilicate glass was prepared and bonded to the substrate 2. Similarly, when the surface property was measured with an interferometer, the wavefront aberration was 70.9 nm. As a result, it was found that flatness can be ensured in the step of polishing after bonding the inorganic transparent material.
[0117]
【The invention's effect】
  Claim1According to the invention described in (1), the liquid crystal can be driven at a lower voltage, the voltage can be reduced, and an efficient electric field can be generated.
[0118]
  orThe local change based on the electrode arrangement can be suppressed to prevent the alignment failure of the liquid crystal.
[0119]
  Claim2The invention described in claim1In the invention described in (1), a predetermined electric field can be efficiently obtained at a low voltage, which is extremely useful for reducing a load on a power source, electromagnetic noise to peripheral electronic components, and the like.
[0120]
  Claim3The invention described in claim1 or 2In the invention described in the above, when a material having a high light absorptance is used as the electrode, not only the light utilization efficiency is lowered, but also the characteristics as an optical element are fluctuated by heat generation, and a material having a high reflectance is used. When used, it may cause multiple reflections with the light source side optical element, which causes noise, but according to the present invention, these problems can be suppressed.
[0121]
  Claim4In the invention described in (1), the voltage of the optical deflecting device can be lowered, and the generation of an efficient electric field can be realized.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an overall configuration of an optical deflection element according to an embodiment of the present invention.
FIG. 2 is an explanatory view schematically showing a liquid crystal molecule alignment state of the light deflection element.
FIG. 3 is an explanatory view schematically showing a liquid crystal molecule alignment state of the light deflection element.
FIG. 4 is a graph showing a relationship between a liquid crystal alignment angle of an optical deflection element and an optical axis shift amount.
FIG. 5 is a graph showing temporal changes in the voltage of the light deflection element and the amount of light deflection.
FIG. 6 is a schematic diagram for explaining a cross-sectional structure around a line electrode in an optical element.
FIG. 7 is an explanatory diagram for explaining an electrode width of a line electrode and a distance between line electrodes.
FIG. 8 is a conceptual diagram illustrating an image display apparatus according to an embodiment of the present invention.
FIG. 9 is a longitudinal sectional view of an optical deflection element that is one embodiment of the present invention.
FIG. 10 is a graph showing the result of calculating the electric field distribution at the center of the liquid crystal layer.
FIG. 11 is a graph showing the relationship between line electrode pitch and electric field fluctuation.
FIG. 12 is a graph showing the relationship between line electrode width and electric field strength.
[Explanation of symbols]
1 Optical elements, light deflection elements
2 Substrate
4 Dielectric layer
5 Liquid crystal layer
6 electrodes
13 Image display element

Claims (4)

A pair of transparent substrates;
A liquid crystal layer containing a liquid crystal composed of a chiral smectic C phase having a homeotropic alignment filled between the substrates;
A plurality of electrodes provided on at least one of the pair of substrates in a row in the plate width direction of the substrate; and
A dielectric layer having a relative dielectric constant of 8 provided between the liquid crystal layer and the electrode;
Voltage application means for deflecting light by applying voltages of different sizes stepwise between adjacent electrodes with respect to each electrode, and
The dielectric layer, when the thickness as t _{de,
38 ≦ t de ≦ 150 (μm} )
And
Each electrode of the plurality of electrodes, when the arrangement pitch is D,
D ≦ 2 · t _de
An optical deflection element. Each electrode has a width W and an arrangement pitch D,
W> 0.1 · D
The optical deflection element according to claim 1 , wherein Wherein each electrode is formed of a transparent material, the light deflecting element according to claim 1 or 2. An image display element that spatially modulates illumination light based on image information and emits it as image light for each of a plurality of image subfields obtained by further subdividing the image field in time;
In synchronization with this image display element, the apparent number of pixels of the image display element is multiplied by deflecting the optical path of image light incident from each pixel of the image display element driven for each image subfield. an image display device comprising an optical deflection element, the according to one of any claims 1 to 3, and the display.

Images