JP2004252058A

JP2004252058A - Polarized light splitter, and projection type display device using the same

Info

Publication number: JP2004252058A
Application number: JP2003041097A
Authority: JP
Inventors: Yoshihiro Masumoto; 吉弘枡本
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2003-02-19
Filing date: 2003-02-19
Publication date: 2004-09-09
Anticipated expiration: 2023-02-19
Also published as: JP3915712B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high contrast image capable of realizing an excellent resolution performance without causing an astigmatic difference and high in contrast without any twist in the polarization plane caused by incident angle dependence and skewed rays. <P>SOLUTION: The polarized light splitter is composed of a polarized light splitting base material, and two adjacent prism members with the base material in between. The base material has a wire grid structure periodically forming metal threads at minute intervals of wavelength units. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は、主に投写型表示装置に用いる偏光分離素子と、当該偏光分離素子と反射型の空間光変調素子を用いて構成される投写型表示装置に関する。
【０００２】
【従来の技術】
光の電気振動（或いは、これと直交する磁気振動）について、振動方向がランダムな状態である自然光に対し、特定状態に振動が偏った光を偏光を呼ぶ。液晶パネルの表示原理は偏光を利用しており、この用途には、ヨウ素や有機染料などを含ませた高分子のフィルムを特定方向に延伸し、一定方向の直線偏光の光だけを通過させ、これと直交する偏光の光を吸収するフィルム型の偏光板が広く実用化されている。
【０００３】
同様の偏光機能素子として、プリズム型の偏光分離素子がある。これは、図１０に示す様に、２つの三角プリズム９０１、９０２を貼り合わせて立方体形状にしたもので、例えば、片側のプリズム９０１の接合面には、偏光分離多層膜９０３を、蒸着やスパッタリング工法により形成する。これは、例えば、自然光９０４を入射させ、偏光分離多層膜９０３を通過するＰ偏光９０５と、多層膜９０３を反射するＳ偏光９０６に分離する。或いは、この反対に、９０５の方向からＰ偏光を入射させ、９０６の方向からＳ偏光を入射させ、これらを合成させて、９０４の方向に出射させる事ができる。
【０００４】
尚、Ｐ偏光とは、入射光の光軸と、偏光分離多層膜９０３の法線９０７を含む平面を定義し、電界の振動面がこの平面と平行である偏光成分を示す。また、Ｓ偏光とは、電界の振動面がこの平面と直交する偏光成分を示す。一般に、三角プリズム９０１と９０２は、頂角４５度−９０度−４５度の直角三角形を底面とする三角柱とし、これらを接合させて、立方体形状にしている。この場合、プリズムの入出射界面は光軸に直交し、ダイクロイック多層膜９０３への入射角は、光軸に沿った光線について４５度となる。
【０００５】
また、ワイヤーグリッドは、これまで主に赤外分光など比較的波長の長い光について、偏光を分離する素子として実用化されている。これは、波長オーダーの微小な金属格子構造を用いたもので、電界の振動方向がグリッド細線の長手方向と直交する偏光成分を透過させ、電界の振動方向がグリッド細線の長手方向と一致する偏光成分を反射させる。この原理に基づく偏光素子は、例えば米国特許第２，２２４，２１４に開示されている。
【０００６】
近年、微細加工技術の進歩により、可視波長（４００〜７００ｎｍ）オーダの微小ピッチのワイヤーグリッド構造が提案されている（例えば、米国特許第６，１２２，１０３など）。これは、例えば図１１に示す構造である。透明基材９１０の片面に、アルミニウムの薄膜を形成し、これをパターンエッチングすることで、可視の波長オーダの微小グリッド構造９１１を構成する。この時、微小グリッドの細線方向９１２について、偏波面（電界の振動方向）がこれに直交する光は透過し、偏波面が平行な光は反射する。
【０００７】
また、液晶パネルなどの空間光変調素子を、放電ランプの強力な光で照明し、その光学像を投写レンズを用いてスクリーン上に拡大投影する投写型表示装置は、迫力ある大画面の映像を容易に提供する手段として広く使われている。このうち、反射型液晶パネルを使う従来構成の一例を図１２に示す。これは、超高圧水銀灯などのランプ９２１、発光体９２２の放射する光を集めて照明光束を形成する凹面鏡９２３、照明光から不要な赤外光や紫外光を除去するＵＶ−ＩＲカットフィルタ９２４、偏光分離素子９２５、三原色の光に分解合成を行うプリズム合成体９２６、三原色のＲＧＢに対応した３枚の反射型液晶パネル９２７、９２８、９２９、投写レンズ９３０、などから構成される。
【０００８】
３枚の反射型液晶パネルには、ＲＧＢの原色光学像が偏光状態の変化として形成される。すなわち、紙面に沿った偏光の光をＰ偏光、紙面に直交する偏光の光をＳ偏光と表現し、各々の液晶パネルは、偏光分離素子９２５で反射されたＳ偏光成分の光で照明される。黒表示は、照明光のＳ偏光成分がそのまま保持されて反射され、Ｓ偏光として偏光分離素子９２５に再入射した光は、投写レンズ９３０に到達せず、黒表示となる。白表示は、照明光のＳ偏光成分が偏波面の回転作用を受け、Ｐ偏光として偏光分離素子に再入射する。Ｐ偏光は、偏光分離素子９２５を直進し、投写レンズに到達して白表示となる。これら２つの偏光状態の中間的な偏波面の回転により、偏光分離素子９２５を通過して投写レンズ９３０に入射できる光の強度が変調され、中間階調を表現できる。
【０００９】
プリズム合成体９２６は、３つのプリズム９３１、９３２、９３３を組み合わせた所謂フィリップスタイプの色分離合成プリズムである。これは、プリズム９３１と９３２の間に微小エアギャップを設け、プリズム９３１のプリズム９３２と接する界面には、色選択反射のダイクロイック多層膜が形成される。同じく、プリズム９３２と９３３の接合面には、いずれかのプリズム界面に色選択ダイクロイック多層膜が形成される。これら２つのダイクロイック多層膜の波長選択特性を適切に選び、３枚の液晶パネルへ入出射する光をＲＧＢの三原色光に対応させる事ができる。
【００１０】
偏光分離素子９２５は、例えば、図１０に示した誘電体多層膜による偏光分離プリズムが利用される。或いは、図１１に示したワイヤーグリッド型の偏光分離板を利用できる。同様の投写型表示装置として、米国特許第６，２３４，６３４号公報、特開２００２−３７２７４９号公報に開示される。
【００１１】
【特許文献１】
米国特許第２，２２４，２１４号公報
【特許文献２】
米国特許第６，１２２，１０３号公報
【特許文献３】
米国特許第６，２３４，６３４号公報
【特許文献４】
特開２００２−３７２７４９号公報
【特許文献５】
特開平２−２５００２６号公報
【特許文献６】
米国特許第５，９８６，８１５号公報
【００１２】
【発明が解決しようとする課題】
図１０に示す誘電体多層膜を用いたプリズム型の偏光分離素子の課題を述べる。１個のプリズムで波長がおよそ４３０〜６５０ｎｍの可視帯域の光について、良好な偏光分離特性を実現する事が難しい。すなわち、作用する波長について広帯域化が難しく、短波長側や長波長側で、偏光分離特性が低下し、良好なＳ偏光反射、良好なＰ偏光透過が得らなくなるという課題がある。また、誘電体多層膜の偏光分離特性は、入射角依存が大きいという課題がある。図１０に図示したような光軸に沿った理想的な直進光線について良好な特性が得られても、これと角度を成して進行する光線、投写レンズで集光できる円錐状のＦナンバ規定の光線群について、傾斜角の大きい光は、良好な偏光分離特性が得られにくいという課題がある。
【００１３】
光軸と角度を成して進行する、所謂、スキュー光線は、幾何構成上の捻れ作用により、所望のＰ偏光、Ｓ偏光状態を得られないという課題がある。例えば、図１２に示す投写型表示装置を構成し、図１０に示す偏光分離素子を用いた場合を想定する。この場合、液晶パネルにとって、必要な入射光についてのＳ偏光の規定、出射光のＰ偏光の規定は、液晶パネルの法線方向に取った光軸と、偏光分離素子９２５に入出射する光軸を含む平面を基準に決まる、つまり、紙面に完全に平行な偏波面の光をＰ偏光と呼び、紙面に直交して上記各光軸を含む平面について、偏波面がこの平面方向の光をＳ偏光と呼ぶ。
【００１４】
これに対し、誘電体多層膜９２５Ａの入出射状態で規定される偏光分離機能でのＰ偏光、Ｓ偏光の偏波面方位は、スキュー光線について捻れた座標空間を持ち、この捻れ成分の要因により、スキュー光線の場合は、液晶パネルが良好なコントラストで表示変調を行うのに必要な上記各偏波面の光線が完全に得られないという課題がある。つまり、スキュー光線について、この光線の誘電体多層膜９２５Ａ前後の進行ベクトルと、誘電体多層膜の法線方向を含む平面を規定する。図示した光軸について、この定義される平面と、紙面に沿った方向は完全に一致するが、スキュー光線については、捻れた平面が定義される。この捻れた平面に沿った偏波面の光が、誘電体多層膜で透過分離されるＰ偏光成分であり、捻れた平面に直交し、進行ベクトルを含む平面に沿った偏波面の光が反射分離されるＳ偏光成分となる。従って、図１０に示すプリズム型の偏光分離素子は、スキュー光線を含む円錐状の拡がりを持ったＦナンバ光線群について、作用を受ける液晶パネルから見て、統一的な１つの直線で規定されるＰ偏光、Ｓ偏光の作用効果を持たない、各光線の捻れ方位の影響により、良好な直線偏光が得られにくく、投写型表示装置を構成した場合に、コントラストの低下、表示むら、色むらなどを招くので問題がある。
【００１５】
この課題に対し、液晶パネルの入射側にλ／４板などの位相差板を挿入することで、表示品位、コントラストが改善できる事が提案されている（特開平２−２５００２６、米国特許第５，９８６，８１５）。但し、この提案は、上記捻れにより発生する光線の偏波面の乱れを補償するように位相差板を挿入するものであり、補償の効果度合いによっては、コントラストや画質の改善が不十分である。また、コストと量産性の面で実用的な位相差板は、ポリビニルアルコールやポリカーボネートの透明樹脂フィルムを、一定方向に延伸させて位相差を形成し、これを所定のリターダンス（屈折率異方性）が得られるように積層させたものが一般的である。
【００１６】
この樹脂フィルムを投写型表示装置に用いると、紫外線に対する耐光性の問題で、長期使用時に特性が劣化する、透明度が低下する、焦げる、と言った信頼性の課題がある。また、使用温度条件が厳しく、多くの風量を送る冷却機能が必要、冷却すると埃が付着し画質欠陥を生じる、照射光量をあまり大きくできない、と言った課題がある。
【００１７】
また、プリズム型の偏光分離素子は、これを構成する光学硝材とその温度条件に依って、その内部歪みが複屈折作用を持ち、偏光制御された所定の偏光状態が、部分的に乱されるという課題がある。これは、投写型表示装置に用いた際に、コントラストの部分むらや、色むらとなるので大きな問題がある。この為、プリズム内の熱歪みが大きくならないように、使用できる光量条件に制約を生じる。或いは、光弾性定数の極めて小さい特殊な材料を使う必要があり、これはコストと量産性の面で問題を生じる。また、光弾性定数の小さい硝材は、多くの鉛を含む場合があり、商品に採用した後、廃棄物の環境保護の面で、有害物質となり得るので問題がある。
【００１８】
これに対し、図１１に示すワイヤーグリッド型の偏光分離素子は、多くの優位点を持つ。例えば、入射角依存が相対的に小さく、円錐光線群に対して比較的良好な偏光分離機能を提供できる。また、作用して反射、あるいは透過させる光線について、その偏波面は、ワイヤーグリッドの細線方向に沿ったＳ偏光と、これと直交するＰ偏光成分に規定される。つまり、捻れて進行するスキュー光線についても、そのＳ偏光とＰ偏光は、光軸に沿って進行する主光線と同様の定義、考え方を採用できる。その結果、投写型表示装置を構成した場合に、コントラストや表示低下を改善できる。
【００１９】
一方、図１１に示す偏光分離素子を用いて、図１２に示すものと同様の投写型表示装置を構成した場合、新たに以下の課題がある。ワイヤーグリッド型の偏光分離素子は、単体では偏光分離の消光比があまり大きく取れない。従って、そのままではコントラスト性能の高い表示装置を構成できない。
【００２０】
また、コントラストを有利に得るには、図１２の構成のまま、偏光分離素子９２５の位置に、４５度入射となるようにワイヤーグリッド型偏光板を置くことが望ましい。すなわち、照明光をＳ偏光反射で利用し、液晶パネルに導く。液晶パネルからは、白表示：Ｐ偏光、黒表示：Ｓ偏光の出射光を受け、Ｐ偏光の光を透過させて投写レンズに導くとよい。このような構成を取った場合、液晶パネル〜投写レンズの結像系の光路に、所定厚みを有するガラス基材を４５度に傾けて配置することになる。この場合、紙面に沿った方向に拡がる光線群と、紙面に直交する方向に拡がる光線群で、４５度傾斜のガラス基材による屈折作用が異なり、スクリーン上で非点隔差を生じるという問題がある。これは、結像点の解像度を低下させ、画像の鮮鋭度を低下させるので問題がある。
【００２１】
更に、図１２に示す投写型表示装置は、プリズム合成体９２６の構成が複雑で、作りにくい、必要な精度を出しにくいという課題がある。特に、プリズム９３１と９３２の間に微小間隔のエアギャップを精度良く形成する必要があり、これが課題となる。エアギャップは、間隔が小さすぎると干渉縞や、面精度の管理が難しく、間隔が大きすぎると収差を発生させて画像の乱れを生じる。また、間隔が平行に維持できない場合も、結像性能を低下させるので問題がある。
【００２２】
また、この投写型表示装置は、投写レンズのバックフォーカスが長く、レンズの後ろ玉径が大きくなる、広角化が難しい、投写レンズのコストが高くなる、という課題がある。投写レンズの後ろ玉から結像面である液晶パネルまでの間に、偏光分離素子９２５と、色分離合成用のプリズム合成体９２６を配置する光路長が必要であり、また、表示むらを考えれば、液晶パネルを照明する光と、液晶パネルから投写レンズに進行する光は、全てテレセントリック（主光線を光軸と平行にさせる）とする必要がある。投写レンズに進行する光を収束光とできないので、より一層、レンズ後ろ玉が大きく、広角化、これに伴う収差補正が難しい。
【００２３】
【課題を解決するための手段】
上記問題点を解決するために本発明の偏光分離素子は、入射する光を透過するＰ偏光と反射されるＳ偏光に分離する偏光分離基材と、当該基材を挟み込んで隣接する２つのプリズム部材とからなり、前記基材は波長単位の微小な金属格子構造を配列してなるワイヤーグリッド型の偏光分離基材とするとよい。
【００２４】
更に、偏光分離基材を直進するＰ偏光の光軸について、偏光分離素子の入射側プリズム界面と出射側プリズム界面の各々を、当該光軸に略直交させ、当該光軸に回転非対称で挿入される偏光分離基材の屈折作用による非点隔差を低減させるとなお良い。
【００２５】
また、当該プリズムの１つは、平坦な光学界面領域と、光学界面領域の周囲に設けられたリブ領域からなり、リブ領域の突起頂部にて偏光分離基材のマイクログリッドを形成した基板面の周囲と接合され、光学界面領域と、マイクログリッド形成面が、所定の微小距離を介して略平行に保持されるとなおよい。
【００２６】
或いは、当該プリズムの１つは、所定の微小厚さを有するスペーサ部材を介して偏光分離基材のマイクログリッドを形成した基板面の周囲と接合され、プリズムの光学界面領域と、マイクログリッド形成面が、所定の微小距離を介して略平行に保持されるとなおよい。
【００２７】
上記問題点を解決するために本発明の他の偏光分離素子は、入射する光を透過するＰ偏光と反射されるＳ偏光に分離するものであって、当該素子は２つのプリズム部材を接合してなり、プリズム部材の少なくとも１つの接合面に、微小な金属格子構造を配列してなるワイヤーグリッド型の偏光分離層を形成するとよい。
【００２８】
更に、プリズムの接合面に金属細線を埋め込む彫り込みグリッド、あるいは、金属細線を形成する積層グリッドのいずれかを形成するに当たり、その加工方向を接合面の法線方向ではなく、当該接合面に入射させる光線の光軸方向から加工するとなお良い。
【００２９】
また、２つのプリズムの接合面には、いずれも周期Ｐのワイヤーグリッド構造を形成し、これを、互いに位相がＰ／２ずつずれるように接合させて、周期１／Ｐのワイヤーグリッド構造とするとなお良い。
【００３０】
上記問題点を解決するために本発明の投写型表示装置は、光源と、光源の放射する光を集めて照明光を形成する集光照明手段と、偏光分離素子と、偏光の変化を利用して光学像を形成する反射型の空間光変調素子と、投写レンズ、から構成され、偏光分離素子は、入射する光を透過するＰ偏光と反射されるＳ偏光に分離する偏光分離基材と、当該基材を挟み込んで隣接する２つのプリズム部材とからなり、偏光分離基材は波長単位の微小な金属格子構造を配列して成るなるワイヤーグリッド型とし、偏光分離素子は、空間光変調素子を照明する光の光路と、空間光変調素子で変調された出射光が投写レンズに到る光路に配置されて照明光と出射光の光路弁別を行うと共に、出射光の偏光に応じて投写レンズに到る有効光束の制御を行って投写画像を形成するとよい。
【００３１】
上記問題点を解決するために本発明の他の投写型表示装置は、光源と、光源の放射する光を集めて照明光を形成する集光照明手段と、偏光分離素子と、偏光の変化を利用して光学像を形成する反射型の空間光変調素子と、投写レンズ、から構成され、偏光分離素子は、少なくとも２つのプリズム部材を接合してなり、プリズム部材の少なくとも１つの接合面に、波長単位の微小な金属格子構造を配列してなるワイヤーグリッド型の偏光分離層を形成し、偏光分離素子は、空間光変調素子を照明する光の光路と、空間光変調素子で変調された出射光が投写レンズに到る光路に配置されて照明光と出射光の光路弁別を行うと共に、出射光の偏光に応じて投写レンズに到る有効光束の制御を行って投写画像を形成するとなお良い。
【００３２】
【発明の実施の形態】
（偏光分離素子の実施の形態１）
図１は、本発明の偏光分離素子について、構成の一例を示す。１１は偏光分離基材である、ガラス基板の片面に微小なワイヤーグリッド構造を形成した偏光分離板であり、微小金属細線の凹凸構造を可視の波長帯域レベルのピッチで構成し、可視の自然光に対し、Ｐ偏光を透過、Ｓ偏光を反射させる機能を有する。尚、図１のグリッド構造は、構成を模式的に示す為に表現したものであり、実際の外観、スケールとは一致しない。１２、１３は、プリズム部材である三角柱プリズムであり、偏光分離板１１を挟み込んで一体化され、全体として立方体のプリズム構造としている。
【００３３】
本構成に依れば、矢印１４から入射した自然光は、偏光分離板１１の作用により、Ｓ偏光は反射されて矢印１５方向に出射し、Ｐ偏光は透過して矢印１６方向に進行する。ここで、Ｐ偏光とは、入射光線の光軸と偏光分離板１１の法線方向を含む平面を定義し、この平面に沿って電界が振動する光をＰ偏光、この平面と直交する方向に電界が振動する光をＳ偏光としている。ワイヤーグリッドの微小細線方向（矢印１７方向）について言えば、矢印１７と電界の振動が平行な成分をＳ偏光と呼び、これは反射されて１５方向に進行する。矢印１７と電界の振動が直交する光をＰ偏光と呼び、これは透過して１６方向に進行する。
【００３４】
微小なワイヤーグリッド構造のピッチと格子高さを適切に選択すれば、この偏光分離素子は、プロジェクタなどで必要な可視帯域について、良好な偏光分離特性を得ることができる。
【００３５】
構成上、偏光分離板１１のワイヤーグリッドを形成しない裏面界面と、三角プリズム１２の隣接する界面は、屈折率整合させた透光性接着剤で接合し、不要な界面損失を減らすと良い。また、ワイヤーグリッドの形成面と、三角プリズム１３の隣接界面は、微小な空気間隔を介してお互いを保持する一体構造とすれば良い。三角プリズム１２、１３と、偏光分離素子１１の必要な光学界面には、反射防止膜を形成し、不要反射を低減させると良い。
【００３６】
図１に示す本発明の偏光分離素子は、これを透過する光を結像系に用いても、偏光分離板１１の基材による屈折で非点隔差を発生しない利点がある。この為に、偏光分離板１１の基材屈折率と、三角プリズム１２、１３の硝材屈折率は、互いに近い大きさとするとなお良い。所定厚みのガラス平板基材を４５度傾けて光路に挿入する場合と比較して、三角プリズムに入出射する光学界面が、光軸とおよそ直交して配置されるので、上記問題を解決できる。４５度に傾斜した三角プリズムの界面と偏光分離素子１１のワイヤーグリッド面の境界は、非点隔差の要因となる非回転対称の屈折作用を持つが、この作用長が非常に短いので、従来構成で問題となるようなレベルの非点隔差は発生させない。
【００３７】
図１に示す構成は、４５度−９０度−４５度の三角柱からなるプリズム部材を２個用いた立方体形状の実例を示したが、他のプリズム構成であっても構わない。２個のプリズム部材で挟持したワイヤーグリッドの偏光分離板を使い、特性と用途に適した入射角の構成とすればよい。この際、組み合わせたプリズム構成において、光軸に対し、入射界面と出射界面をおよそ直交させれば、光学界面はおよそ光軸に対して回転対称となるので、非点隔差を発生させず、結像系に用いても、良好な性能を実現できる。
【００３８】
図２は、図１に示した偏光分離素子の他の構成の一例である。偏光分離板２１は同様のワイヤーグリッドを形成したガラス基材であり、これを、２つの台形プリズム２２、２３で挟み込んで保持している。こうすれば、光線の偏光分離板２１への入射角を４５度より大きくできる。この場合、矢印２４から入射する光線の光軸、反射されて矢印２５から出射するＳ偏光の光軸、透過して矢印２９から出射するＰ偏光の光軸について、必要ないずれかの光学界面２７、２８、２９を、各光軸に直交させるとよい。図示していない他の光軸と他の界面についても、同様である。液晶パネルなどの表示素子から投写レンズに到る結像系に挿入される光軸について、その界面を当該光軸に直交する構成とすればよい。
【００３９】
上記発明に依れば、ワイヤーグリッド偏光板の長所を活かし、非点隔差を発生させない応用が可能であるので、大きな効果を得ることができる。つまり、可視の広い波長帯域について良好な特性を持ち、入射角依存が小さく、スキュー光線での偏波面の捻れを発生させない、主として投写型表示装置に適した偏光分離素子を実現できる。
【００４０】
（偏光分離素子の実施の形態２）
図１に示した本発明の偏光分離素子の実施の形態１は、図３に示す様な構成にするとなお好ましい。ワイヤーグリッド構造４４を形成した偏光分離基材であるガラス基材４１は、斜線ハッチングで図示した周囲の領域４５を介して、三角プリズム４２と接合させる。プリズム部材である三角プリズム４２は、ガラス基材４１と接合する面について、ワイヤーグリッド構造４４と微小エアギャップを介して接する様に、凹部平坦面４６を構成しておく。これは、接合面を微小な深さだけ掘り下げ、その平坦面を光学的に問題のないレベルまで、研磨などで良好な面精度に仕上げたものである。
【００４１】
ガラス基材４１の裏面は、もう１つのプリズム部材である三角プリズム４３と接合させる。判りやすくするために図３では、２つの三角プリズムを分離して記載しているが、これらを、ワイヤーグリッド構造４４を介して接合し、実施の形態１と同様の作用効果を得る偏光分離素子を実現できる。これは、偏光分離板４１と、三角プリズム４２を、精度良く、簡便に固着して保持できる構造である。
【００４２】
（偏光分離素子の実施の形態３）
図４は、上記実施の形態２について、より好ましい他の実施の形態を示す。ワイヤーグリッドを構成したガラス基材４１は、所定ギャップを構成する極薄のスペーサ部材５１を介して、プリズム部材である三角プリズム５２と接合する。図４は、判りやすくするために３つの部材を分離して記載したが、これらを一体化する事で、より構成しやすい本発明の偏光分離素子を構成できる。
【００４３】
（偏光分離素子の実施の形態４）
図５は、上記実施の形態１と同様の作用と効果を得る偏光分離素子について、より簡便で好ましい構成の一例を述べる。プリズム部材である三角プリズム６１と６２は、互いに接合されて立方体を構成し、上述と同様のプリズム型偏光分離素子を構成する。三角プリズム６１の接合面には、偏光分離基材に相当する、良好な偏光分離機能を有するワイヤーグリッド構造６３を、直接そのガラス界面上に構成することで、部品点数と光学界面を削減でき、より簡便で量産性の高い偏光分離素子を構成できる。
【００４４】
例えば、このようなワイヤーグリッド構造は、以下のプロセスで形成できる。まず、所謂、写真露光技術により、ガラス界面上に微小グリッド構造のパターン形成を行う。これは、感光性樹脂層をコートし、微小グリッドのマスクパターンを露光転写し、エッチングすべき領域と、加工せずに保護すべき領域（レジスト層）を形成する。パターン形成後、イオンエッチングを行い、ガラス界面のワイヤーグリッド形成領域を、所定構造で所定深さまで、彫り込み加工する。この後、アルミなどの誘電体材料を、蒸着、スパッタ、塗布工程などで、彫り込み領域に充填させ、不要部分の誘電体材料をレジスト層を一緒に除去すると良い。
【００４５】
この場合、４５度−９０度−４５度の三角プリズム６１の界面６４について、図６に模式的に示すような形状でワイヤーグリッド構造を形成するとなお良い。すなわち、イオンエッチングで彫り込み加工をする場合に、矢印６５の方向から彫り込むのではなく、偏光分離素子として用いる場合に光軸方向となる矢印６６の方向から彫り込み加工をすると良い。こうすると、界面６７に直交する光軸６８に沿って進行する光線について、形成されるワイヤーグリッド構造は、より好ましい格子形状として作用する。これは、界面６９についてこれと直交する光軸７０に沿って進行する光線についても同様である。
【００４６】
例えば、図６に示すワイヤーグリッドを形成した三角プリズムを２個作成し、このワイヤーグリッド面を、互いに１／２の周期間隔を補うようにずらして精度良く接着すれば、より好ましい偏光分離素子を構成できる。このように構成した偏光分離素子７５の断面模式図を、図７に示す。三角プリズム７６、７７は、周期Ｐでワイヤーグリッド構造７８、７９が構成された同一のものであり、これを、ワイヤーグリッド構造が互いにＰ／２ずつ位相がずれるようにして、接合している。こうすれば、１個あたりのプリズムに形成するワイヤーグリッド構造は、可視波長レベルの２倍の周期であっても、これを互いに１／２周期でずらせば、所望とする可視波長レベルのワイヤーグリッド構造を構成でき、より性能が良く、加工しやすい素子を得ることができる。
【００４７】
（投写型表示装置の実施の形態１）
図８は本発明の投写型表示装置について、好ましい実施の形態の一例を示す。投写型表示装置は、光源を構成する超高圧水銀灯１０１、放物面鏡１０２と、ＵＶ−ＩＲカットフィルタ１０４、色分離合成プリズム１０５、反射型の空間光変調素子である青用の反射型液晶パネル１０６、緑用の反射型液晶パネル１０７、赤用の反射型液晶パネル１０８、投写レンズ１０９、本発明の偏光分離素子１１０、などから構成される。
【００４８】
超高圧水銀灯１０１は、外部から供給される駆動電源によりアーク放電を形成し、発光体１０３を発生させる。このランプは、高い発光効率で可視全域にバランスの良い発光スペクトルを有するので投写型表示装置に用いる上で最適なランプの１つである。発光体１０３の放射する光は、放物面鏡１０２により集光され、以降の液晶パネルを照明する照明光を形成する。照明光から有害な紫外線と赤外線を取り除く目的で、ＵＶ−ＩＲカットフィルタ１０４を用いる。
【００４９】
一般に、光源の放射する光を集めて照明光を形成する集光照明手段として、明るさの均一性の高い照明を実現するために、インテグレータと呼ばれる照明用の光学素子が用いられる場合が多い。これは、１組のレンズアレイを組み合わせたものや、ガラスロッドの内部で多重反射を繰り返し明るさの均一性を改善するものである。また、透過型や反射型の偏光を利用する液晶パネルを照明する場合、偏光変換光学系と呼ばれるものが用いられ、光源の直後で直線偏光に近い光を形成し、光損失を改善する方式がある。これは、光源の放射する自然光を、偏波面の直交する２つの偏光（Ｐ偏光、Ｓ偏光）に分離し、片側の偏波面を９０度回転させて互いの偏波面を揃えた後に、これらの光束の光路合成を行う方式である。但し、本発明の投写型表示装置の構成と作用効果を説明する上で、上記インテグレータや偏光変換光学系は関係せず、各実施例はこれらを割愛して説明する。
【００５０】
色分離合成プリズム１０５は、所謂、フィリップス型のプリズム合成体であり、最初の三角プリズム１１１の所定界面に、青反射のダイクロイック多層膜を形成している。これにより、照明光の青成分だけが反射され、対応する青表示の液晶パネル１０６を照明し、かつ、当該液晶パネルにて変調されて出射した光を投写レンズ１０９の方向に導く。また、次の三角プリズム１０５Ａと最初の三角プリズム１０５Ｂの接合面には、微小なエアギャップが形成され、別の所定界面に形成された赤反射ダイクロイック多層膜によって反射された赤成分の光を、更に全反射させて、対応する赤表示の液晶パネル１０８に導く。更に、これらのプリズムとダイクロイック多層膜を直進した緑成分の光は、対応する緑表示の液晶パネル１０７を照明し、反射変調されて出射する緑の光は、折り返して、投写レンズ１０９に進行する。
【００５１】
偏光分離素子１１０は、上述した本発明の偏光分離素子の各実施例について、いずれの構成を採用しても良い。例えば、ワイヤーグリッドの偏光分離層１１２を、２つの三角プリズム１１３、１１４を用いて狭持した立方体プリズム型の構成を図示している。
【００５２】
偏光分離素子１１０に入射した光は、そのＳ偏光成分のみを反射し、液晶パネル１０６、１０７、１０８を照明する光を形成する。各々の液晶パネルでは、外部から供給される駆動信号に応じた光学像が形成され、黒表示部分はＳ偏光で入射した光をＳ偏光のまま折り返し、白表示部分はＳ偏光で入射した光をＰ偏光の状態まで偏波面を回転させて折り返す。中間の階調は、偏波面の回転が９０度以下であり、Ｐ偏光成分として取り出される光量に応じた明るさとなる。変調されて液晶パネルから出射した光は、Ｐ偏光成分は、偏光分離素子１１０を直進し、投写レンズに入射して白表示となる。Ｓ偏光成分は、偏光分離層１１２で反射されて光源側に戻る。従って、黒表示となる。
【００５３】
以上述べた構成は、反射型液晶パネルを用いた投写型表示装置として、一般的であるが、本発明の偏光分離素子の構成が新しく、この作用効果により、より優れた投写型表示装置を構成できる。
【００５４】
例えば、図１に示した偏光分離素子を用いた場合、平板型のワイヤーグリッド偏光子を用いるので、この利点を発揮できる。つまり、入射角依存が小さく、スキュー光線に対する偏波面の捻れを発生しないので、コントラストと色むらの均一性が優れた画像を提供できる。また、平板型の偏光子であっても、前後を三角プリズムで挟み込み、全体として立方体の構造をとるので、斜めに挿入したガラス基材の屈折による非点隔差により、投写画像の解像度が劣化することを抑制できる。
【００５５】
尚、４５度に斜め挿入した平板型のワイヤーグリッド偏光子を単独で用いた場合であっても、その反射経路を結像系に利用すれば、非点隔差の問題は発生しない。但し、この場合、図８と光学レイアウトを変更し、Ｐ偏光を照明光側に利用し、Ｓ偏光を変調された光の出射側に利用する必要がある。しかし、これは、以下の点で表示コントラストが不利になり、白黒のメリハリのついた投写画像を提供できないという、別の新たな問題を生じる。その理由を以下に述べる。
【００５６】
一般に、偏光分離素子は、透過させるＰ偏光の弁別比に比較し、反射させるＳ偏光の弁別比を高くできる特徴がある。これは、誘電体多層膜を利用した場合であっても、ワイヤーグリッドを利用した場合であっても、同様である。従って、反射されるＳ偏光を結像系に利用するように偏光分離素子を配置すると、黒表示として液晶パネルから出射した不要なＰ偏光成分が、大部分について偏光分離層を透過して除去されるものの、僅かな成分がＳ偏光と同様に反射されて投写レンズ側に進行し、これが黒浮き表示を生じてコントラストの低下を招く。これに対し、図８に表示したように、透過するＰ偏光を結像系に利用する構成は、コントラストを高くする上で有利である。つまり、液晶パネルから黒表示成分として出射する不要なＳ偏光成分の光を、より高い効率で反射し、光源側に戻して投写レンズに到達しないようにできる。結果として、黒浮きを抑制できる。以上の観点から、ワイヤーグリッドを利用した平板型の偏光分離素子を用いた場合、ガラス基材の屈折による非点隔差の問題は重大であり、これを改善できる本発明の偏光分離素子の構成は大きな価値がある。
【００５７】
図５に示した偏光分離素子を用いた場合、作用効果は、上述と同様であり、ワイヤグリッド構造を内蔵したプリズム型の偏光分離素子をより簡便に構成できるので利点がある。
【００５８】
（投写型表示装置の実施の形態２）
図９は、図８で述べた実施の形態１に対し、更に好ましい本発明の投写型表示装置の構成の一例を示す。上述した本発明の偏光分離素子を用いると共に、図８と同じ番号で指示したものは、同じ構成である。この実施例では、偏光分離素子１１０の照明光入射側に、プリ偏光板１２１を配置し、投写レンズ１０９側に、不要光を除去する為の偏光板１２２を配置している。偏光板１２１は、偏光分離素子１１０に対し、必要なＳ偏光成分だけを通過させ、偏光板１２２は、偏光分離素子１１０に対し、必要なＰ偏光成分だけを通過させる。本構成は、追加して配置して２枚の偏光板の作用により、よりコントラストが高く、黒浮きの少ない投写型表示装置を構成できる。
【００５９】
【発明の効果】
以上述べたように本発明の偏光分離素子と、これを用いた投写型表示装置は、非点隔差を発生させず優れた解像度性能を実現できる、入射角依存やスキュー光線による偏波面の捻れが無くコントラストの高い画像を提供できる、など、多くの優れた効果を得ることができる。
【図面の簡単な説明】
【図１】本発明の偏光分離素子の一例を示す略構成図
【図２】本発明の偏光分離素子の他の構成例を示す断面模式図
【図３】本発明の偏光分離素子の他の一例を示す略構成図
【図４】本発明の偏光分離素子の他の一例を示す略構成図
【図５】本発明の偏光分離素子の他の一例を示す略構成図
【図６】本発明の偏光分離素子を作成する際の加工方向を示す略線図
【図７】本発明の偏光分離素子の他の構成例を示す断面模式図
【図８】本発明の投写型表示装置の一例を示す略構成図
【図９】本発明の投写型表示装置の他の一例を示す略構成図
【図１０】従来の偏光分離素子の一例を示す略構成図
【図１１】従来の偏光分離素子の他の一例を示す略構成図
【図１２】従来の投写型表示装置の一例を示す略構成図
【符号の説明】
１１、２１偏光分離板
１２、１３、４２、４３、５２、６１、６２、７６、７７三角プリズム
２２、２３台形プリズム
４１ガラス基材
４４、６３、７８、７９ワイヤーグリッド構造
５１スペーサ部材
１０１超高圧水銀灯
１０２放物面鏡
１０３発光体
１０４ＵＶ−ＩＲカットフィルタ
１０５色分離合成プリズム
１０６、１０７、１０８反射型液晶パネル
１０９投写レンズ
１１０偏光分離素子
１２１プリ偏光板
１２２偏光板[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polarization separation element mainly used for a projection display apparatus, and a projection display apparatus including the polarization separation element and a reflective spatial light modulation element.
[0002]
[Prior art]
Regarding electric vibration of light (or magnetic vibration orthogonal to the light), light whose vibration is biased to a specific state is called polarization with respect to natural light whose vibration direction is random. The display principle of liquid crystal panels uses polarized light.For this purpose, a polymer film containing iodine, organic dye, etc. is stretched in a specific direction, allowing only linearly polarized light in a certain direction to pass. Film-type polarizing plates that absorb light of a polarization orthogonal to this have been widely put to practical use.
[0003]
As a similar polarization function element, there is a prism type polarization separation element. As shown in FIG. 10, two triangular prisms 901 and 902 are bonded together to form a cubic shape. For example, a polarization separation multilayer film 903 is formed on the joining surface of one prism 901 by vapor deposition or sputtering. It is formed by a construction method. For example, the natural light 904 is incident, and is separated into a P-polarized light 905 passing through the polarization split multilayer film 903 and an S-polarized light 906 reflecting the multilayer film 903. Alternatively, conversely, P-polarized light can be incident from the direction 905, S-polarized light can be incident from the direction 906, and these can be combined and emitted in the direction 904.
[0004]
The P-polarized light defines a plane including the optical axis of the incident light and the normal 907 of the polarized light separating multilayer film 903, and indicates a polarized light component whose vibration plane of the electric field is parallel to this plane. The S-polarized light indicates a polarized light component whose vibration plane of the electric field is orthogonal to this plane. In general, the triangular prisms 901 and 902 are triangular prisms having a right-angled triangle with a vertical angle of 45 ° -90 ° -45 ° as a bottom surface, and these are joined to form a cubic shape. In this case, the entrance / exit interface of the prism is orthogonal to the optical axis, and the angle of incidence on the dichroic multilayer film 903 is 45 degrees for light rays along the optical axis.
[0005]
The wire grid has been put to practical use as an element for separating polarized light mainly for light having a relatively long wavelength such as infrared spectroscopy. This uses a minute metal grating structure of the order of the wavelength, and transmits polarized light components in which the direction of vibration of the electric field is perpendicular to the longitudinal direction of the fine grid lines, and the polarized light whose vibration direction matches the longitudinal direction of the fine grid lines. Reflect components. A polarizing element based on this principle is disclosed, for example, in U.S. Pat. No. 2,224,214.
[0006]
In recent years, with the progress of fine processing technology, a fine pitch wire grid structure on the order of visible wavelength (400 to 700 nm) has been proposed (for example, US Pat. No. 6,122,103). This is, for example, the structure shown in FIG. By forming an aluminum thin film on one surface of the transparent base material 910 and pattern-etching the thin film, a micro grid structure 911 on the order of visible wavelengths is formed. At this time, in the fine line direction 912 of the minute grid, light whose polarization plane (the vibration direction of the electric field) is orthogonal to this is transmitted, and light whose polarization plane is parallel is reflected.
[0007]
In addition, a projection display device that illuminates a spatial light modulation element such as a liquid crystal panel with the strong light of a discharge lamp and enlarges and projects the optical image on a screen using a projection lens is a powerful large-screen image. It is widely used as a means to easily provide. FIG. 12 shows an example of a conventional configuration using a reflective liquid crystal panel. This includes a lamp 921 such as an ultra-high pressure mercury lamp, a concave mirror 923 that collects light emitted from the light emitter 922 to form an illumination light beam, a UV-IR cut filter 924 that removes unnecessary infrared light and ultraviolet light from the illumination light, It comprises a polarization splitting element 925, a prism composite 926 for decomposing and combining light of three primary colors, three reflective liquid crystal panels 927, 928, 929 corresponding to RGB of the three primary colors, a projection lens 930, and the like.
[0008]
On the three reflective liquid crystal panels, RGB primary color optical images are formed as changes in the polarization state. That is, the polarized light along the plane of the paper is expressed as P-polarized light, and the polarized light perpendicular to the plane of the paper is expressed as S-polarized light, and each liquid crystal panel is illuminated with the light of the S-polarized component reflected by the polarization separation element 925. . In the black display, the S-polarized light component of the illumination light is reflected as it is, and the light re-entering the polarization splitting element 925 as S-polarized light does not reach the projection lens 930 and is displayed in black. In the white display, the S-polarized component of the illumination light is rotated by the rotation of the plane of polarization, and re-enters the polarization splitting element as P-polarized light. The P-polarized light travels straight through the polarization beam splitter 925, reaches the projection lens, and displays white. The rotation of the polarization plane intermediate between these two polarization states modulates the intensity of light that can pass through the polarization separation element 925 and enter the projection lens 930, thereby expressing an intermediate gradation.
[0009]
The prism composite 926 is a so-called Philips type color separation / combination prism in which three prisms 931, 932, and 933 are combined. This is because a small air gap is provided between the prisms 931 and 932, and a dichroic multilayer film for color selective reflection is formed on the interface of the prism 931 in contact with the prism 932. Similarly, on the joint surface between the prisms 932 and 933, a color selection dichroic multilayer film is formed at one of the prism interfaces. By appropriately selecting the wavelength selection characteristics of these two dichroic multilayer films, the light entering and exiting the three liquid crystal panels can be made to correspond to the three primary colors of RGB.
[0010]
As the polarization separation element 925, for example, a polarization separation prism using a dielectric multilayer film illustrated in FIG. 10 is used. Alternatively, a wire grid type polarization separation plate shown in FIG. 11 can be used. Similar projection display devices are disclosed in U.S. Patent No. 6,234,634 and JP-A-2002-372749.
[0011]
[Patent Document 1]
U.S. Pat. No. 2,224,214
[Patent Document 2]
US Patent No. 6,122,103
[Patent Document 3]
US Patent No. 6,234,634
[Patent Document 4]
JP-A-2002-372749
[Patent Document 5]
JP-A-2-250026
[Patent Document 6]
U.S. Pat. No. 5,986,815
[0012]
[Problems to be solved by the invention]
The problem of the prism type polarization separation element using the dielectric multilayer film shown in FIG. 10 will be described. It is difficult to realize good polarization separation characteristics for light in the visible band having a wavelength of about 430 to 650 nm with one prism. That is, there is a problem that it is difficult to broaden the wavelength at which the wavelength acts, and that the polarization separation characteristics are reduced on the short wavelength side and the long wavelength side, so that good S-polarized light reflection and good P-polarized light transmission cannot be obtained. Further, there is a problem that the polarization separation characteristics of the dielectric multilayer film largely depend on the incident angle. Even if good characteristics are obtained for an ideal straight light beam along the optical axis as shown in FIG. 10, a light beam traveling at an angle to this light, and a conical F-number rule that can be collected by the projection lens The light ray group having the large inclination angle has a problem that it is difficult to obtain good polarization separation characteristics.
[0013]
A so-called skew ray that travels at an angle to the optical axis has a problem that a desired P-polarized light and S-polarized light state cannot be obtained due to a geometrical twisting action. For example, it is assumed that the projection display device shown in FIG. 12 is configured and the polarization separation element shown in FIG. 10 is used. In this case, for the liquid crystal panel, the definition of the S-polarized light for the necessary incident light and the definition of the P-polarized light for the outgoing light are based on the optical axis taken in the normal direction of the liquid crystal panel and the optical axis entering and exiting the polarization separation element 925. That is, light having a plane of polarization completely parallel to the plane of the paper is referred to as P-polarized light. For a plane perpendicular to the plane of the paper and including each of the above optical axes, the plane of polarization defines light in this plane direction as S-polarized light. Called polarized light.
[0014]
On the other hand, the polarization plane directions of the P-polarized light and the S-polarized light in the polarization splitting function defined by the input / output state of the dielectric multilayer film 925A have a coordinate space twisted with respect to the skew ray, and due to the twist component, In the case of a skew ray, there is a problem that a ray of each of the above-mentioned polarization planes necessary for the liquid crystal panel to perform display modulation with good contrast cannot be obtained completely. That is, for the skew ray, a plane including the traveling vector of the ray before and after the dielectric multilayer 925A and the normal direction of the dielectric multilayer is defined. For the illustrated optical axis, the plane defined is completely coincident with the direction along the plane of the paper, but for skew rays, a twisted plane is defined. The light on the plane of polarization along this twisted plane is the P-polarized light component transmitted through and separated by the dielectric multilayer film. The light on the plane of polarization along the plane perpendicular to the plane of twist and containing the traveling vector is reflected and separated. S component. Therefore, the prism-type polarization splitting element shown in FIG. 10 is defined by a single unified straight line when viewed from the liquid crystal panel that is affected by the F-number ray group having a conical spread including the skew ray. P-polarized light and S-polarized light do not have the effect, and it is difficult to obtain good linearly polarized light due to the influence of the twist direction of each light beam. When a projection display device is configured, the contrast is reduced, the display is uneven, and the color is uneven. There is a problem.
[0015]
To solve this problem, it has been proposed that a display quality and contrast can be improved by inserting a retardation plate such as a λ / 4 plate on the incident side of the liquid crystal panel (Japanese Patent Application Laid-Open No. H2-250026, US Pat. , 986,815). However, in this proposal, a phase difference plate is inserted so as to compensate for the disturbance of the polarization plane of the light beam caused by the twist, and the contrast and the image quality are insufficiently improved depending on the degree of the effect of the compensation. A retardation plate that is practical in terms of cost and mass productivity is formed by stretching a transparent resin film of polyvinyl alcohol or polycarbonate in a certain direction to form a retardation, and applying a predetermined retardance (refractive index anisotropy). Are generally laminated so as to obtain the above-mentioned properties.
[0016]
When this resin film is used in a projection display device, there is a problem of reliability such as deterioration of characteristics over a long period of use, deterioration of transparency, and burning due to the problem of light resistance to ultraviolet rays. In addition, there is a problem that the use temperature condition is severe, a cooling function for sending a large amount of air is required, dust adheres when cooling, and image quality defects occur, and the irradiation light amount cannot be too large.
[0017]
In addition, the prism type polarization splitting element has a birefringent internal strain depending on the optical glass material constituting the element and its temperature condition, and a predetermined polarization state controlled by polarization is partially disturbed. There is a problem that. This is a major problem because it causes uneven contrast and uneven color when used in a projection display device. For this reason, there are restrictions on the amount of light that can be used so that thermal distortion in the prism does not increase. Alternatively, it is necessary to use a special material having a very small photoelastic constant, which causes problems in cost and mass productivity. Further, a glass material having a small photoelastic constant may contain a large amount of lead, and there is a problem in that it can be a harmful substance in terms of environmental protection of waste after adoption in commercial products.
[0018]
On the other hand, the wire grid type polarization splitting element shown in FIG. 11 has many advantages. For example, the incidence angle dependence is relatively small, and a relatively good polarization splitting function can be provided for a group of cone rays. In addition, the polarization plane of a light ray that acts to reflect or transmit is defined by an S-polarized light along a thin line direction of a wire grid and a P-polarized light component orthogonal thereto. In other words, with respect to the skew light beam that travels in a twisted manner, the S-polarized light and the P-polarized light can adopt the same definition and concept as the principal light beam that travels along the optical axis. As a result, when a projection display device is configured, it is possible to improve contrast and display degradation.
[0019]
On the other hand, when a projection display device similar to that shown in FIG. 12 is configured using the polarization splitting element shown in FIG. 11, there is a new problem as follows. The wire grid type polarization splitting element alone cannot provide a very large extinction ratio for polarization splitting. Therefore, a display device having high contrast performance cannot be constituted as it is.
[0020]
Further, in order to obtain a favorable contrast, it is desirable to place a wire grid type polarizing plate at the position of the polarization splitting element 925 so as to be incident at 45 degrees with the configuration of FIG. That is, the illumination light is used for S-polarized light reflection and is guided to the liquid crystal panel. It is preferable that the liquid crystal panel receives emitted light of white display: P-polarized light and black display: S-polarized light, transmits the P-polarized light, and guides the light to the projection lens. In such a configuration, a glass substrate having a predetermined thickness is arranged at an angle of 45 degrees in the optical path of the image forming system from the liquid crystal panel to the projection lens. In this case, there is a problem that a refraction effect of a 45-degree tilted glass substrate is different between a light ray group that spreads in a direction along the paper surface and a light ray group that spreads in a direction perpendicular to the paper surface, resulting in an astigmatic difference on a screen. . This is problematic because it reduces the resolution of the imaging point and reduces the sharpness of the image.
[0021]
Further, the projection display device shown in FIG. 12 has a problem that the configuration of the prism composite 926 is complicated, difficult to produce, and difficult to obtain necessary accuracy. In particular, it is necessary to precisely form an air gap with a minute interval between the prisms 931 and 932, which is a problem. If the gap is too small, it is difficult to control the interference fringes and the surface accuracy. If the gap is too large, aberrations are generated to cause image disturbance. Also, when the intervals cannot be maintained in parallel, there is a problem because the imaging performance is reduced.
[0022]
Further, this projection type display device has problems that the back focus of the projection lens is long, the diameter of the rear lens of the lens is large, it is difficult to widen the angle, and the cost of the projection lens is high. An optical path length for disposing the polarization separation element 925 and the prism composite 926 for color separation / combination is required between the rear lens of the projection lens and the liquid crystal panel which is the image plane. All of the light illuminating the liquid crystal panel and the light traveling from the liquid crystal panel to the projection lens need to be telecentric (to make the principal ray parallel to the optical axis). Since the light that travels to the projection lens cannot be converged light, the rear lens of the lens is even larger, and it is difficult to widen the angle and to correct aberrations associated therewith.
[0023]
[Means for Solving the Problems]
In order to solve the above problems, a polarization separation element of the present invention comprises: a polarization separation substrate that separates incident light into P polarized light that transmits and S polarized light that is reflected; and two prisms that sandwich the substrate and are adjacent to each other. It is preferable that the substrate is a wire grid type polarization separation substrate in which a minute metal lattice structure in wavelength units is arranged.
[0024]
Further, with respect to the optical axis of the P-polarized light that goes straight through the polarization separation substrate, each of the entrance-side prism interface and the exit-side prism interface of the polarization separation element is inserted substantially rotationally asymmetrically to the optical axis. More preferably, the astigmatic difference due to the refraction of the polarized light separating substrate is reduced.
[0025]
One of the prisms includes a flat optical interface region and a rib region provided around the optical interface region. It is more preferable that the optical interface region and the microgrid forming surface are joined to the surroundings and that the microgrid forming surface is held substantially in parallel with a predetermined minute distance.
[0026]
Alternatively, one of the prisms is bonded to the periphery of the substrate surface on which the microgrid of the polarization separation substrate is formed via a spacer member having a predetermined minute thickness, and the optical interface region of the prism and the microgrid formation surface Are preferably maintained substantially parallel via a predetermined minute distance.
[0027]
In order to solve the above problem, another polarization separation element of the present invention separates incident light into P-polarized light that is transmitted and S-polarized light that is reflected, and the element is formed by joining two prism members. It is preferable to form a wire grid type polarization separation layer in which a minute metal grid structure is arranged on at least one joining surface of the prism member.
[0028]
Furthermore, in forming either the engraved grid that embeds the fine metal wires on the bonding surface of the prism or the laminated grid that forms the fine metal wires, the processing direction is incident on the bonding surface instead of the normal direction of the bonding surface. It is even better to work from the optical axis direction of the light beam.
[0029]
In addition, a wire grid structure having a period P is formed on the joint surface of the two prisms, and these are joined so that their phases are shifted from each other by P / 2 to form a wire grid structure having a period 1 / P. Still better.
[0030]
In order to solve the above problems, the projection display device of the present invention utilizes a light source, a condensing illumination unit that collects light emitted by the light source to form illumination light, a polarization separation element, and a change in polarization. A reflection-type spatial light modulation element that forms an optical image, and a projection lens, wherein the polarization separation element is a polarization separation substrate that separates incident light into P polarized light that transmits and S polarized light that is reflected, The substrate comprises two prism members adjacent to each other with the substrate interposed therebetween. The polarization separation substrate is a wire grid type formed by arranging minute metal grating structures in wavelength units. The polarization separation element is a spatial light modulation element. The optical path of the light to be illuminated and the output light modulated by the spatial light modulator are arranged in the optical path to the projection lens to discriminate the optical path between the illumination light and the output light, and to the projection lens according to the polarization of the output light. Controlling the effective luminous flux and projecting It is preferable to form an image.
[0031]
In order to solve the above problems, another projection display device according to the present invention includes a light source, a condensing illumination unit that collects light emitted from the light source to form illumination light, a polarization separation element, and a polarization change element. A reflection-type spatial light modulation element that forms an optical image by utilizing, and a projection lens, wherein the polarization separation element is formed by joining at least two prism members, and on at least one joining surface of the prism members, A wire grid type polarization separation layer is formed by arranging minute metal grating structures in wavelength units. The polarization separation element is composed of an optical path for illuminating the spatial light modulation element and an output light modulated by the spatial light modulation element. It is more preferable to form the projection image by arranging the emitted light in the optical path reaching the projection lens to discriminate the optical path between the illumination light and the emitted light, and controlling the effective light flux reaching the projection lens according to the polarization of the emitted light. .
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1 of polarization separation element)
FIG. 1 shows an example of the configuration of the polarization beam splitter of the present invention. Numeral 11 is a polarization separation plate having a fine wire grid structure formed on one side of a glass substrate, which is a polarization separation base material. On the other hand, it has a function of transmitting P-polarized light and reflecting S-polarized light. It should be noted that the grid structure shown in FIG. 1 is shown to schematically show the configuration, and does not match the actual appearance and scale. Reference numerals 12 and 13 denote triangular prisms, which are prism members, which are integrated with the polarization separation plate 11 interposed therebetween, and have a cubic prism structure as a whole.
[0033]
According to this configuration, the natural light incident from the arrow 14 is reflected by the action of the polarization splitter 11 and is emitted in the direction of the arrow 15 while the P-polarized light is transmitted and proceeds in the direction of the arrow 16. Here, the P-polarized light defines a plane including the optical axis of the incident light beam and the normal direction of the polarization separation plate 11, and the light whose electric field oscillates along this plane is the P-polarized light in the direction orthogonal to this plane. The light whose electric field oscillates is S-polarized light. In the direction of the fine line of the wire grid (direction of arrow 17), a component in which the vibration of the electric field is parallel to the arrow 17 is called S-polarized light, which is reflected and travels in 15 directions. Light in which the vibration of the electric field is perpendicular to the arrow 17 is called P-polarized light, which transmits and travels in 16 directions.
[0034]
By properly selecting the pitch and the grating height of the fine wire grid structure, this polarization separation element can obtain good polarization separation characteristics in a visible band required for a projector or the like.
[0035]
Due to the configuration, the interface between the back surface of the polarization separation plate 11 where the wire grid is not formed and the adjacent interface of the triangular prism 12 may be joined with a translucent adhesive whose refractive index has been matched to reduce unnecessary interface loss. In addition, the surface on which the wire grid is formed and the adjacent interface between the triangular prisms 13 may have an integral structure that holds each other via a minute air gap. It is preferable to form an antireflection film on a necessary optical interface between the triangular prisms 12 and 13 and the polarization separation element 11 to reduce unnecessary reflection.
[0036]
The polarizing beam splitter of the present invention shown in FIG. 1 has an advantage that astigmatism does not occur due to refraction by the base material of the polarizing beam splitter 11 even when light transmitted therethrough is used for an imaging system. For this reason, it is more preferable that the refractive index of the base material of the polarization separating plate 11 and the refractive index of the glass material of the triangular prisms 12 and 13 are close to each other. The above-mentioned problem can be solved because the optical interface for entering and exiting the triangular prism is arranged substantially perpendicular to the optical axis, as compared with the case where a glass plate base material having a predetermined thickness is inserted into the optical path at an angle of 45 degrees. The boundary between the interface of the triangular prism inclined at 45 degrees and the boundary of the wire grid surface of the polarization splitting element 11 has a non-rotationally symmetric refraction which causes astigmatism. In this case, a level of astigmatism, which is problematic in the above, is not generated.
[0037]
Although the configuration shown in FIG. 1 shows an example of a cubic shape using two prism members each formed of a 45-90-45-degree triangular prism, other prism configurations may be used. A polarization splitting plate of a wire grid sandwiched between two prism members may be used, and the configuration may be such that the incident angle is suitable for the characteristics and application. At this time, in the combined prism configuration, if the entrance interface and the exit interface are approximately perpendicular to the optical axis, the optical interface is approximately rotationally symmetric with respect to the optical axis. Good performance can be achieved even when used in an image system.
[0038]
FIG. 2 is an example of another configuration of the polarization beam splitter shown in FIG. The polarized light separating plate 21 is a glass substrate on which a similar wire grid is formed, and is held between two trapezoidal prisms 22 and 23. By doing so, the angle of incidence of the light beam on the polarization separation plate 21 can be made larger than 45 degrees. In this case, any one of the necessary optical interfaces 27 is required for the optical axis of the light beam entering from the arrow 24, the optical axis of the S-polarized light reflected and emitted from the arrow 25, and the optical axis of the P-polarized light transmitted and emitted from the arrow 29. , 28, 29 may be orthogonal to each optical axis. The same applies to other optical axes and other interfaces not shown. Regarding an optical axis inserted into an imaging system from a display element such as a liquid crystal panel to a projection lens, its interface may be configured to be orthogonal to the optical axis.
[0039]
According to the above-mentioned invention, it is possible to make use of the advantages of the wire grid polarizer and to apply it without causing astigmatism, so that a great effect can be obtained. In other words, it is possible to realize a polarization splitting element which has good characteristics in a wide visible wavelength band, has small incident angle dependence, and does not generate a twist of a polarization plane due to a skew ray, and is mainly suitable for a projection display device.
[0040]
(Embodiment 2 of polarization separation element)
The first embodiment of the polarization beam splitter of the present invention shown in FIG. 1 is more preferably configured as shown in FIG. The glass substrate 41, which is a polarization separation substrate on which the wire grid structure 44 is formed, is joined to the triangular prism 42 via a peripheral region 45 shown by oblique hatching. The triangular prism 42, which is a prism member, has a flat concave surface 46 so that the surface to be bonded to the glass substrate 41 is in contact with the wire grid structure 44 via a minute air gap. In this method, a bonding surface is dug down by a minute depth, and a flat surface thereof is finished to an optically satisfactory level by polishing or the like with good surface accuracy.
[0041]
The back surface of the glass substrate 41 is joined to a triangular prism 43 which is another prism member. In FIG. 3, two triangular prisms are separately illustrated for easy understanding, but these are joined via a wire grid structure 44 to obtain a polarization splitting element having the same operation and effect as in the first embodiment. Can be realized. This is a structure in which the polarization separation plate 41 and the triangular prism 42 can be fixed and held accurately and simply.
[0042]
(Embodiment 3 of polarization splitting element)
FIG. 4 shows another preferred embodiment of the second embodiment. The glass substrate 41 forming the wire grid is joined to a triangular prism 52 as a prism member via an extremely thin spacer member 51 forming a predetermined gap. FIG. 4 shows three members separated for easy understanding, but by integrating them, a polarization separating element of the present invention which is easier to configure can be configured.
[0043]
(Embodiment 4 of polarization separation element)
FIG. 5 illustrates an example of a simpler and preferable configuration of a polarization beam splitter that obtains the same operation and effect as in the first embodiment. The triangular prisms 61 and 62, which are prism members, are joined together to form a cube, and constitute a prism-type polarization splitting element similar to that described above. On the bonding surface of the triangular prism 61, a wire grid structure 63 having a good polarization separation function, which is equivalent to a polarization separation substrate, is directly formed on the glass interface, so that the number of parts and the optical interface can be reduced. A more simple and highly mass-produced polarization separation element can be configured.
[0044]
For example, such a wire grid structure can be formed by the following process. First, a pattern of a fine grid structure is formed on a glass interface by a so-called photographic exposure technique. In this method, a photosensitive resin layer is coated, a mask pattern of a fine grid is exposed and transferred, and an area to be etched and an area to be protected without processing (resist layer) are formed. After pattern formation, ion etching is performed, and a wire grid forming region at the glass interface is carved to a predetermined depth with a predetermined structure. Thereafter, a dielectric material such as aluminum is preferably filled in the engraved region by vapor deposition, sputtering, coating or the like, and unnecessary portions of the dielectric material are removed together with the resist layer.
[0045]
In this case, it is more preferable to form the wire grid structure in the shape schematically shown in FIG. 6 for the interface 64 of the triangular prism 61 of 45-90-45 degrees. That is, when performing engraving by ion etching, it is preferable to perform engraving not from the direction of arrow 65 but from the direction of arrow 66 that is the optical axis direction when used as a polarization separation element. In this way, for a light ray traveling along the optical axis 68 orthogonal to the interface 67, the formed wire grid structure acts as a more preferable lattice shape. This is the same for the light beam traveling along the optical axis 70 orthogonal to the interface 69.
[0046]
For example, two more triangular prisms each having a wire grid as shown in FIG. 6 are formed, and the wire grid surfaces are shifted with respect to each other so as to compensate for a half period interval, and are bonded with high accuracy. Can be configured. FIG. 7 is a schematic cross-sectional view of the polarization separation element 75 configured as described above. The triangular prisms 76 and 77 are the same in which wire grid structures 78 and 79 are configured with a period P, and are joined such that the wire grid structures are out of phase with each other by P / 2. In this case, even if the wire grid structure formed on one prism has a period twice as long as the visible wavelength level, if the two lines are shifted from each other by 周期 period, the wire grid structure at the desired visible wavelength level can be obtained. A structure can be formed, and an element with better performance and easy processing can be obtained.
[0047]
(First Embodiment of Projection Display Device)
FIG. 8 shows an example of a preferred embodiment of the projection display device of the present invention. The projection type display device includes an ultra-high pressure mercury lamp 101, a parabolic mirror 102, a UV-IR cut filter 104, a color separation / combination prism 105, and a reflective liquid crystal for blue, which is a reflective spatial light modulator, constituting a light source. It comprises a panel 106, a reflective liquid crystal panel 107 for green, a reflective liquid crystal panel 108 for red, a projection lens 109, the polarization splitting element 110 of the present invention, and the like.
[0048]
The ultra-high pressure mercury lamp 101 forms an arc discharge by a driving power supply supplied from the outside, and generates a luminous body 103. This lamp is one of the most suitable lamps for use in a projection display device because it has a high luminous efficiency and a well-balanced emission spectrum over the entire visible range. The light emitted from the light emitter 103 is collected by the parabolic mirror 102 to form illumination light for illuminating the liquid crystal panel thereafter. A UV-IR cut filter 104 is used to remove harmful ultraviolet rays and infrared rays from the illumination light.
[0049]
In general, an optical element for illumination called an integrator is often used as a converging illumination unit that collects light emitted from a light source to form illumination light in order to realize illumination with high uniformity of brightness. This is to improve brightness uniformity by combining multiple lens arrays or repeating multiple reflections inside a glass rod. In addition, when illuminating a liquid crystal panel using transmission or reflection type polarized light, a method called a polarization conversion optical system is used. Immediately after the light source, a method that forms light close to linearly polarized light to improve light loss is used. is there. This is because natural light emitted from a light source is separated into two polarized lights (P-polarized light and S-polarized light) having orthogonal polarization planes, and the polarization planes on one side are rotated by 90 degrees to align the respective polarization planes. This is a method for performing optical path synthesis of light beams. However, in describing the configuration and the operation and effect of the projection display apparatus of the present invention, the integrator and the polarization conversion optical system are not related, and each embodiment will be described without these.
[0050]
The color separation / combination prism 105 is a so-called Philips type prism combination, and forms a blue-reflective dichroic multilayer film on a predetermined interface of the first triangular prism 111. As a result, only the blue component of the illumination light is reflected, illuminates the corresponding blue display liquid crystal panel 106, and guides the light modulated and emitted by the liquid crystal panel toward the projection lens 109. Further, a small air gap is formed on the joint surface between the next triangular prism 105A and the first triangular prism 105B, and the red component light reflected by the red reflection dichroic multilayer film formed at another predetermined interface is Further, the light is totally reflected and guided to the corresponding liquid crystal panel 108 for displaying red. Further, the green component light that has traveled straight through these prisms and the dichroic multilayer film illuminates the corresponding green display liquid crystal panel 107, and the green light that is reflected and modulated and emitted returns to the projection lens 109. .
[0051]
The polarization beam splitting element 110 may employ any of the above-described embodiments of the polarization beam splitting element of the present invention. For example, a cubic prism type configuration in which a polarization splitting layer 112 of a wire grid is sandwiched between two triangular prisms 113 and 114 is illustrated.
[0052]
The light incident on the polarization separation element 110 reflects only the S-polarized light component and forms light for illuminating the liquid crystal panels 106, 107, and 108. In each liquid crystal panel, an optical image corresponding to a drive signal supplied from the outside is formed, and the black display portion folds the light incident as S-polarized light as S-polarized light, and the white display portion reflects the light incident as S-polarized light. The plane of polarization is rotated and turned back to the state of P polarization. The intermediate gradation has a rotation of the polarization plane of 90 degrees or less, and has a brightness corresponding to the amount of light extracted as a P-polarized component. The P-polarized light component of the modulated light emitted from the liquid crystal panel travels straight through the polarization separation element 110, enters the projection lens, and becomes white. The S-polarized light component is reflected by the polarization separation layer 112 and returns to the light source side. Therefore, black display is performed.
[0053]
The configuration described above is generally used as a projection type display device using a reflection type liquid crystal panel. However, the configuration of the polarization splitting element of the present invention is new, and a more excellent projection type display device is constituted by this operation and effect. it can.
[0054]
For example, when the polarization separation element shown in FIG. 1 is used, this advantage can be exerted because a flat-plate wire grid polarizer is used. That is, since the dependency on the incident angle is small and the polarization plane is not twisted with respect to the skew ray, an image having excellent uniformity of contrast and color unevenness can be provided. Further, even in the case of a flat polarizer, since the front and rear are sandwiched by a triangular prism and the overall structure is cubic, the resolution of the projected image is degraded due to the astigmatic difference due to the refraction of the glass substrate inserted obliquely. Can be suppressed.
[0055]
Incidentally, even when a flat-plate wire grid polarizer obliquely inserted at 45 degrees is used alone, the problem of astigmatism does not occur if its reflection path is used for an imaging system. In this case, however, it is necessary to change the optical layout as shown in FIG. 8 so that P-polarized light is used on the illumination light side and S-polarized light is used on the emission side of the modulated light. However, this creates another new problem in that the display contrast is disadvantageous in the following points, and a projected image with black and white sharpness cannot be provided. The reason is described below.
[0056]
In general, a polarization splitting element has a feature that the discrimination ratio of S-polarized light to be reflected can be higher than the discrimination ratio of P-polarized light to be transmitted. This is the same regardless of whether a dielectric multilayer film is used or a wire grid is used. Therefore, when the polarization splitting element is arranged so that the reflected S-polarized light is used for the imaging system, unnecessary P-polarized light components emitted from the liquid crystal panel as a black display are mostly removed through the polarization splitting layer. However, a small component is reflected in the same manner as the S-polarized light and travels to the projection lens side, which causes a floating black display to lower the contrast. On the other hand, as shown in FIG. 8, a configuration in which transmitted P-polarized light is used for an imaging system is advantageous in increasing the contrast. In other words, unnecessary S-polarized light emitted from the liquid crystal panel as a black display component can be reflected with higher efficiency, returned to the light source side, and prevented from reaching the projection lens. As a result, black floating can be suppressed. In view of the above, when a flat-plate polarization separation element using a wire grid is used, the problem of astigmatism due to the refraction of the glass substrate is significant, and the configuration of the polarization separation element of the present invention that can improve this is as follows. Great value.
[0057]
When the polarization separation element shown in FIG. 5 is used, the operation and effect are the same as those described above, and there is an advantage that a prism-type polarization separation element having a built-in wire grid structure can be more easily configured.
[0058]
(Embodiment 2 of a projection type display device)
FIG. 9 shows an example of the configuration of the projection display apparatus of the present invention, which is more preferable than Embodiment 1 described in FIG. Components using the polarization splitting element of the present invention described above and denoted by the same reference numerals as those in FIG. In this embodiment, a pre-polarizing plate 121 is disposed on the illumination light incident side of the polarization separating element 110, and a polarizing plate 122 for removing unnecessary light is disposed on the projection lens 109 side. The polarizing plate 121 allows only the necessary S-polarized light component to pass through the polarized light separating element 110, and the polarizing plate 122 allows only the necessary P-polarized light component to pass through the polarized light separating element 110. According to this configuration, a projection display device having higher contrast and less floating of black can be configured by the additional arrangement of the two polarizing plates.
[0059]
【The invention's effect】
As described above, the polarization separation element of the present invention and the projection display device using the same can realize excellent resolution performance without generating astigmatism, and have a polarization plane twist due to incident angle dependence and skew rays. Many excellent effects can be obtained, for example, an image with no contrast and high contrast can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an example of a polarization beam splitter of the present invention.
FIG. 2 is a schematic cross-sectional view showing another configuration example of the polarization beam splitter of the present invention.
FIG. 3 is a schematic configuration diagram showing another example of the polarization beam splitter of the present invention.
FIG. 4 is a schematic configuration diagram showing another example of the polarization beam splitter of the present invention.
FIG. 5 is a schematic configuration diagram showing another example of the polarization beam splitter of the present invention.
FIG. 6 is a schematic diagram showing a processing direction when producing the polarization beam splitter of the present invention.
FIG. 7 is a schematic cross-sectional view showing another configuration example of the polarization beam splitter of the present invention.
FIG. 8 is a schematic configuration diagram showing an example of a projection display device of the present invention.
FIG. 9 is a schematic configuration diagram showing another example of the projection display device of the present invention.
FIG. 10 is a schematic configuration diagram showing an example of a conventional polarization separation element.
FIG. 11 is a schematic configuration diagram showing another example of a conventional polarization splitting element.
FIG. 12 is a schematic configuration diagram showing an example of a conventional projection display device.
[Explanation of symbols]
11,21 Polarized light separator
12, 13, 42, 43, 52, 61, 62, 76, 77 Triangular prism
22, 23 trapezoidal prism
41 Glass substrate
44, 63, 78, 79 Wire grid structure
51 Spacer member
101 Ultra-high pressure mercury lamp
102 Parabolic mirror
103 luminous body
104 UV-IR cut filter
105 color separation / combination prism
106, 107, 108 reflective liquid crystal panel
109 Projection lens
110 polarization splitter
121 pre-polarizing plate
122 Polarizing plate

Claims

A polarized light separating element comprising a polarized light separating substrate that separates incident light into P-polarized light that transmits and S-polarized light that is reflected, and two prism members adjacent to each other with the substrate interposed therebetween. A polarization splitting element characterized in that it is a wire grid type polarization splitting substrate in which a minute metal grid structure is arranged.

With respect to the optical axis of the P-polarized light that goes straight through the polarization separation substrate, each of the entrance-side prism interface and the exit-side prism interface of the polarization separation element is inserted substantially orthogonally to the optical axis and rotationally asymmetrically inserted into the optical axis. 2. The polarization separation element according to claim 1, wherein an astigmatic difference due to a refraction action of the polarization separation substrate is reduced.

One of the prisms includes a flat optical interface region and a rib region provided around the optical interface region. The polarization separation element according to claim 1, wherein the polarization separation element is joined to a periphery, and the optical interface region and the microgrid forming surface are held substantially in parallel via a predetermined minute distance.

One of the prisms is bonded to the periphery of the substrate surface on which the microgrid of the polarization separation substrate is formed via a spacer member having a predetermined minute thickness, and the optical interface region of the prism and the microgrid forming surface 2. The polarization separation element according to claim 1, wherein the polarization separation element is held substantially parallel via a predetermined minute distance.

A polarized light separating element that separates incident light into P-polarized light that transmits and S-polarized light that is reflected, wherein the polarized light separating element is formed by joining two prism members, and at least one joining surface of the prism members has A polarized light separating element comprising a wire grid type polarized light separating layer formed by arranging fine metal lattice structures.

In forming either the engraved grid that embeds the fine metal wires in the prism bonding surface, or the laminated grid that forms the fine metal wires, the processing direction is not the normal direction of the bonding surface, but the light beam that is incident on the bonding surface. 6. The polarization separation element according to claim 5, wherein the polarization separation element is processed from an optical axis direction.

On the joining surface of the two prisms, a wire grid structure with a period P is formed, and these are joined so that the phases are shifted from each other by P / 2 to form a wire grid structure with a P / 2 period. The polarization separation element according to claim 5, wherein:

A light source, a condensing illumination unit that collects light emitted from the light source to form illumination light, a polarization separation element, a reflective spatial light modulation element that forms an optical image by using a change in polarization, and a projection. The polarization splitting element is composed of a polarization splitting substrate that splits incident light into P-polarized light that transmits incident light and S-polarized light that is reflected, and two prism members that sandwich the substrate and are adjacent to each other. A polarization separation element, wherein the substrate is a wire grid type polarization separation substrate formed by arranging minute metal lattice structures in wavelength units, and the polarization separation element is a light that illuminates the spatial light modulation element. And the emitted light modulated by the spatial light modulator is arranged on the optical path reaching the projection lens to perform optical path discrimination between the illumination light and the emitted light, and the projection lens according to the polarization of the emitted light. Control of the effective light flux Projection display device characterized by forming a have the projected image.

A light source, a condensing illumination unit that collects light emitted from the light source to form illumination light, a polarization separation element, a reflective spatial light modulation element that forms an optical image by using a change in polarization, and a projection. Wherein the polarization splitting element is formed by bonding at least two prism members, and at least one bonding surface of the prism members is arranged in a wire grid type by arranging a minute metal grating structure in wavelength units. The polarization splitting layer is formed, and the polarization splitting element is disposed on an optical path of light for illuminating the spatial light modulation element, and an emission path modulated by the spatial light modulation element to reach the projection lens. A projection display device, which performs optical path discrimination between the illumination light and the emitted light and controls an effective light flux reaching a projection lens according to the polarization of the emitted light to form a projected image.