JP4064666B2 - Projection device - Google Patents

Description

【００３５】
若干付言すると、透過型のライトバルブを用いるときは一般に、照明光を分離する偏光ビームスプリッタと、光を合成する偏光ビームスプリッタが別体に成るが、このような場合は、別体の偏光ビームスプリッタとして、特性が互いに同じもの、即ち「透過率：Ｔｓおよび透過率：Ｔｐ」が互いに同じであるものが用いられる。このような場合、上の説明における「第１の波長選択性リターダへ入射される白色照明光の偏光状態」は、光の分離を行う偏光ビームスプリッタに対する偏光状態を意味する。
【００３６】
反射型のライトバルブを用いるときは、光の分離と合成を同一の偏光ビームスプリッタで行うことができるので、この場合の、透過率：Ｔｓ、Ｔｐや、照明白色光の偏光状態は、この偏光ビームスプリッタについて一義的に定まる。
【００３７】
以下に、この発明の原理と、前述の波長選択性リターダにおける「分光特性シフト効果」につき説明する。
【００３８】
図１（ａ）は、偏光ビームスプリッタと波長選択性リターダを用いた投影装置の１例を説明図的に略示している。図中、符号１０は第１の波長選択性リターダ、符号１２は偏光ビームスプリッタを示す。また、符号１４はダイクロイックプリズム、符号１６、１８、２０は反射型のライトバルブ、符号２２は第２の波長選択性リターダ、符号２４は偏光子をそれぞれ示している。
【００３９】
説明の具体性のため、波長選択性リターダ１０、２４は「赤色帯域の偏光（以下、赤色帯域光と称する）を９０度変換する」機能を持つものとする。
【００４０】
直線偏光状態の白色照明光Ｌ１（説明の具体性のため、偏光ビームスプリッタ１２に対してＰ偏光状態とする）を第１の波長選択性リターダ１０に入射させると、波長選択性リターダ１０を通過した光は、波長選択性リターダ１０の分光特性により、赤色帯域光：Ａが偏光変換により「偏光方向が９０度旋回」して偏光ビームスプリッタ１２に対してＳ偏光となり、他の波長帯域光（青色・緑色帯域光）：ＮＡは偏光変換されず、当初のＰ偏光状態のまま偏光ビームスプリッタ１２に入射する。
【００４１】
波長選択性リターダ１０を透過後、赤色帯域光：ＡはＳ偏光に偏光変換されているので、偏光ビームスプリッタ１２の偏光分離膜１２Ａにより反射され、第１のライトバルブ１６への照明光となる。青色・緑色帯域光：ＮＡはＰ偏光状態を保っているので、偏光ビームスプリッタ１２の偏光分離膜１２Ａを透過してダイクロイックプリズム１４に入射する。
【００４２】
ダイクロイックプリズム１４は「色分離素子」であって、ダイクロイック膜１４Ａにより青色・緑色帯域光：ＮＡを青色帯域光：Ｂと緑色帯域光Ｃとに分離する。分離された青色帯域光：Ｂは第２のライトバルブ１８への照明光となり、緑色帯域光：Ｃは第３のライトバルブ２０への照明光となる。
【００４３】
第１〜第３のライトバルブ１６、１８、２０に「各液晶画素の電圧印加を画像信号に従って制御」して画像を表示すると、電圧の印加された画素では照明光の偏光方向が変化する。即ち、各照明光：Ａ、Ｂ、Ｃは「上記画像に従い（偏光方向の変化として）変調」されて反射され、入射光路を逆進する。
【００４４】
ライトバルブ１６から偏光ビームスプリッタ１２に戻った光は、ライトバルブ１６により「偏光ビームスプリッタ１２に対してＰ偏光状態に変換」された光成分が偏光ビームスプリッタ１２を透過して赤色映像光：ＬＡとなる。ライトバルブ１８による反射光（青色映像光：ＬＢ）はダイクロイックプリズム１４で反射され、ダイクロイックプリズム１４を透過する（ライトバルブ２０からの）反射光（緑色映像光：ＬＣ）と合成され、偏光ビームスプリッタ１２に入射する。
【００４５】
偏光ビームスプリッタ１２は、ダイクロイックプリズム１４側から入射してくる光のうち、ライトバルブによりＳ偏光状態に変換された光成分を反射する。反射された光は緑色映像光：ＬＢ、青色映像光：ＬＣであり、ライトバルブ１６による赤色映像光：ＬＡと合成されて合成光：ＬＴとなる。
【００４６】
合成光：ＬＴは第２の波長選択性リターダ２２を透過するが、このとき、赤色映像光：ＬＡの偏光状態がＰ偏光状態からＳ偏光状態へ偏光変換され、他の映像光：ＬＢ、ＬＣの偏光状態と揃うことに成る。偏光状態の揃った合成光ＬＴは、偏光子２４を透過し、このとき、ノイズ光として混入しているＰ偏光成分が除去される。
【００４７】
偏光子２４を透過した光Ｌ２は、「結像光学系」である投射レンズ２６に入射し、投射レンズ２６の作用により、図示されないスクリーン上に投影され「拡大カラー画像」として結像する。
【００４８】
図１（ｂ）は、波長選択性リターダ１０における上記分光特性を模式化して示している。即ち、図１（ｂ）の縦軸は変換効率（波長選択性リターダ１０を透過した所定偏光方向の光の分光強度）を示し、横軸は波長を示す。
【００４９】
白色照明光Ｌ１をＰ偏光状態としたとき、実線で示す部分はＰ偏光状態をＳ偏光状態に変換する変換効率（前述のＦ(λ)に対応する）であり、図示のように白色照明光Ｌ１のうち赤色帯域光は偏光方向を９０度旋回されてＳ偏光となる。破線の部分は波長選択性リターダ１０を透過したＰ偏光の強度を表し、前述の｛１−Ｆ(λ)｝に相当する。
【００５０】
入射白色光Ｌ１の偏光状態をＳ偏光にすると、波長選択性リターダ１０を透過した後の光強度分布は、図１（ｂ）においてＳ偏光について破線のようになり、Ｐ偏光について実線のようになる。
【００５１】
図１（ｂ）に符号「ξ」で示す波長領域（緑色帯域と赤色帯域の境界部）では「波長が大きくなるに連れて変換効率（実線）が単調に増大」する。即ち、この波長領域：ξでは「当初のＰ偏光状態の光と、偏光変換されたＳ偏光状態の光とが混在」している。波長領域：ξを「偏光方向を９０度旋回させる中間帯域」と呼ぶ。また、この中間領域において破線と実線の交叉する点：ＣＰを「クロスポイント」と呼ぶ。
【００５２】
現実の波長選択性リターダには、偏光変換した透過光の分光特性に「Ｐ偏光、Ｓ偏光が混在する中間帯域」が必ず存在する。中間帯域：ξを考えると、中間帯域：ξ内の光の一部は「緑色帯域光」として偏光ビームスプリッタ１２を透過し、一部は「赤色帯域光」として偏光ビームスプリッタ１２により反射される。
【００５３】
このように、中間帯域の存在は、偏光変換による「波長に従った色分割」を曖昧にするので、中間帯域の存在がコントラストを低下させる原因となる。
【００５４】
一方において、偏光ビームスプリッタ１２におけるＳ偏光の透過率をＴｓ、Ｐ偏光の透過率をＴｐとすると「種々の入射角の光線に対して、Ｓ偏光の透過率：Ｔｓが０％、Ｐ偏光の透過率：Ｔｐが１００％である偏光ビームスプリッタ」の実現は、設計的にも製造面においても困難であり、偏光ビームスプリッタは一般に、照明光の入射角：０〜十数度の範囲で用いられるので、Ｔｐ、Ｔｓの何れかを優先して特性が良好になるように設計が行われており、例えばＴｓを小さくすることを優先する場合であると０〜十数度の入射角範囲で、Ｔｐを数十％以上、Ｔｓを数％以下に設定するのが一般である。
【００５５】
図１（ａ）に示すような投影装置では、波長選択性リターダ１０、２２における中間帯域の存在と、偏光ビームスプリッタ１２におけるＴｐ、Ｔｓの不完全さとが作用して「フレア光」が発生し、投影画像におけるコントラストを低下させる原因となる。
【００５６】
以下、コントラストの低下を説明する。偏光ビームスプリッタ１２で反射される光（赤色帯域光）と、偏光ビームスプリッタ１２を透過する光（緑色・青色帯域光）を個別的に考える。白色照明光Ｌ１は図の如く、偏光ビームスプリッタ１２に対してＰ偏光であるとする。
【００５７】
第１の波長選択性リターダ１０を透過した後の光強度の、Ｓ偏光成分：Ａｓ、Ｐ偏光成分：Ａｐは、波長選択性リターダ１０への入射照明光Ｌ１がＰ偏光なので、入射照明光Ｌ１の分光強度分布：Ｗに対し、Ｓ偏光成分はクロス透過率（図１（ｂ）の実線部分）：Ｔ１Ｎ、Ｐ偏光成分はパラレル透過率（図１（ｂ）の破線部分）：Ｔ１Ｐをかけて、それぞれ、以下のようになる。
Ａｓ＝Ｗ・Ｔ１Ｎ Ａｐ＝Ｗ・Ｔ１Ｐ 。
【００５８】
すると、偏光ビームスプリッタ１２により反射される光量のＳ偏光成分：Ｂｓ、Ｐ偏光成分：Ｂｐは、上記透過率：Ｔｓ、Ｔｐを用いて、
Ｂｓ＝Ａｓ（１−Ｔｓ）＝Ｗ・Ｔ１Ｎ（１−Ｔｓ）
Ｂｐ＝Ａｐ（１−Ｔｐ）＝Ｗ・Ｔ１Ｐ（１−Ｔｐ）
となり、これらの成分光が赤色用のライトバルブ１６に対する照明光となる。
【００５９】
表示画像が「真黒」となるべき「暗出力時」におけるフレア光を考察する。
赤色用のライトバルブ１６は「暗出力時」には変調されず、照明光がそのままの偏光方向を保って１００％反射されるものとすると、上記成分：Ｂｓ、Ｂｐがそのまま偏光ビームスプリッタ１２に戻る。
【００６０】
暗出力時におけるフレア光としては、この場合、偏光ビームスプリッタ１２を透過して投射レンズ２６側へ向う分のみを考えればよい。すると、ライトバルブ１６から偏光ビームスプリッタ１２に戻り、これを透過するＳ偏光成分：Ｃｓ、Ｐ偏光成分：Ｃｐは、
Ｃｓ＝Ｂｓ・Ｔｓ＝Ｗ・Ｔ１Ｎ（１−Ｔｓ）Ｔｓ
Ｃｐ＝Ｂｐ・Ｔｐ＝Ｗ・Ｔ１Ｐ（１−Ｔｐ）Ｔｐ
となり、これらが第２の波長選択性リターダ２２に入射する。
【００６１】
この入射光（ライトバルブ１６からの光）のうち、第２の波長選択性リターダ２２を通過するＳ偏光成分：Ｄｓ、Ｐ偏光成分：Ｄｐは、波長選択性リターダ２２のクロス透過率：Ｔ２Ｎ、パラレル透過率：Ｔ２Ｐを上記Ｃｓ、Ｃｐにかけてそれぞれ、以下のようになる。
【００６２】

これらの光成分は偏光子２４に入射する。
【００６３】
偏光子２４は「明表示光を透過させる」ようにするために、この場合はＳ偏光のみを透過する素子であるから、上記透過光成分のうち、Ｐ偏光成分：Ｄｐはカットされ、Ｓ偏光成分：Ｄｓのみが投射レンズへと向かう。暗出力時を考えているから、このＳ偏光成分：Ｄｓがフレア光の成分になる。
【００６４】
次に、偏光ビームスプリッタ１２を透過した光（緑色帯域光、青色帯域光）について同様の考察を行うと、まず、偏光ビームスプリッタ１２を透過したＳ偏光成分：Ｂｓ’、Ｐ偏光成分：Ｂｐ’は、以下の如くになる。
【００６５】
Ｂｓ’＝Ａｓ・Ｔｓ＝Ｗ・Ｔ１Ｎ・Ｔｓ
Ｂｐ’＝Ａｐ・Ｔｐ＝Ｗ・Ｔ１Ｐ・Ｔｐ
これらの成分光はダイクロイックプリズム１４で２色に分離され、青色、緑色用のライトバルブ１８、２０に対する照明光となる。これら照明光は暗出力時には、ライトバルブ１８、２０それぞれにおいて、入射時の偏光方向を保ったまま反射される。暗出力時においてフレア光となるのは、偏光ビームスプリッタ１２に戻って反射される成分のみを考慮すればよい。
【００６６】
偏光ビームスプリッタ１２により反射されるＳ偏光成分：Ｃｓ’、Ｐ偏光成分：Ｃｐ’は、ライトバルブ１８、２０での反射率を１００％として、それぞれ、
Ｃｓ’＝Ｂｓ’（１−Ｔｓ）＝Ｗ・Ｔ１Ｎ・Ｔｓ（１−Ｔｓ）
Ｃｐ’＝Ｂｐ’（１−Ｔｐ）＝Ｗ・Ｔ１Ｐ・Ｔｐ（１−Ｔｐ）
となる。
【００６７】
これらの成分：Ｃｓ’，Ｃｐ’光が、第２の波長選択性リターダ２２に入射し、第２の波長選択性リターダ２２を透過すると、透過光のＳ偏光成分：Ｄｓ’、Ｐ偏光成分：Ｄｐ’は、それぞれ、

これらの成分光のうち、Ｐ偏光成分：Ｄｐ’は偏光子２４でカットされるから、投射レンズ２６へ向うフレア成分は、Ｓ偏光成分：Ｄｓ’のみである。
【００６８】
従って、暗出力時において、第１の波長選択性リターダ１０に入射する白色照明光：Ｌ１のうちでフレア光となるのは、前述のＳ偏光成分：Ｄｓと、直上で算出したＳ偏光成分：Ｄｓ’の和：

となる。
【００６９】
この（１）式の右辺括弧内における「Ｔ１Ｎ・Ｔ２Ｐ」、「Ｔ１Ｐ・Ｔ２Ｎ」を考えると、前述の通り、Ｔ１Ｎは波長選択性リターダ１０におけるクロス透過率（図１（ｂ）の実線部分）であり、Ｔ１Ｐはパラレル透過率（図１（ｂ）の破線部分）である。
【００７０】
そこで仮に、第１、第２の波長選択性リターダ１０、２２が同一の分光特性を持ち、この分光特性が図１（ｂ）に示す如きものであるとすると、上記積：Ｔ１Ｎ・Ｔ２Ｐは、図１（ｃ）に示すように、波長選択性リターダ２２におけるＰ偏光成分の透過率（破線）と波長選択性リターダ１０におけるＳ偏光成分の透過率（実線）との積になり、同図に斜線を施した部分の面積に等しくなる。
【００７１】
一方、積：Ｔ１Ｐ・Ｔ２Ｎは、図１（ｄ）に示すように、波長選択性リターダ１０におけるＰ偏光成分の透過率（実線）と波長選択性リターダ２２におけるＳ偏光成分の透過率（破線）との積になり、同図に斜線を施した部分の面積に等しくなる。
【００７２】
この場合、波長選択性リターダ１０、２２が同一の分光特性を持つことから、積：Ｔ１Ｎ・Ｔ２Ｐ、Ｔ１Ｐ・Ｔ２Ｎは互いに等しくなる。
【００７３】
しかしながら、波長選択性リターダ２２の分光特性を図１（ｂ）に示す如きものとし、波長選択性リターダ１０の分光特性を、図１（ｂ）におけるクロスポイントＣＰが同図の左側（短波長側）へシフトしたようなものであったとすると、積：Ｔ１Ｎ・Ｔ２Ｐは、図１（ｅ）に示すように、波長選択性リターダ２２におけるＰ偏光成分の透過率（破線）と波長選択性リターダ１０におけるＳ偏光成分の透過率（実線）との積になり、同図に斜線を施した部分の面積に等しくなる。この面積は、図１（ｃ）に示す「斜線部」の面積よりも大きい。
【００７４】
一方、積：Ｔ１Ｐ・Ｔ２Ｎは、図１（ｆ）に示すように、波長選択性リターダ１０におけるＰ偏光成分の透過率（実線）と波長選択性リターダ２２におけるＳ偏光成分の透過率（破線）との積になり、図の場合には０となる。
【００７５】
一方において、（１）式における積：Ｔ１Ｎ・Ｔ２Ｐ、Ｔ１Ｐ・Ｔ２Ｎに乗ぜられる係数：Ｔｓ（１−Ｔｓ）、Ｔｐ（１−Ｔｐ）は、偏光ビームスプリッタ１２の偏光分離膜１２Ａの特性により定まる。
【００７６】
偏光ビームスプリッタ１２の特性として、Ｓ偏光の反射率を高く（即ち、Ｓ偏光の透過率を低く）し、Ｐ偏光の透過率を数十％として、透過光の消光比を確保する特性（Ｔｓ＜１−Ｔｐを満たすような特性）のものを想定し、例えば、Ｔｓ＝０．０１、Ｔｐ＝０．８の場合を考えて見る。そうすると、
Ｔｓ（１−Ｔｓ）＝０．００９９
Ｔｐ（１−Ｔｐ）＝０．１６
となり、Ｔｓ（１−Ｔｓ）はＴｐ（１−Ｔｐ）の６％程度に過ぎない。
【００７７】
そうすると、暗出力時におけるフレア光の強度を与える（１）式の右辺において、括弧内は「０．００９９・Ｔ１Ｎ・Ｔ２Ｐ＋０．１６・Ｔ１Ｐ・Ｔ２Ｎ）」となるので、Ｔ１Ｎ・Ｔ２Ｐはある程度大きくても、Ｔｓ（１−Ｔｓ）の値が０．００９９と小さいので影響は小さい。
【００７８】
一方、Ｔ１Ｐ・Ｔ２Ｎの方は、その係数であるＴｐ（１−Ｔｐ）の値が０．１６と大きいため、Ｔ１Ｐ・Ｔ２Ｎの値が大きいと、フレア光に対する影響が大きくなる。
【００７９】
この場合、上に例として説明したように「波長選択性リターダ２２の分光特性が図１（ｂ）に示す如きものであり、波長選択性リターダ１０の分光特性が図１（ｂ）におけるクロスポイントＣＰを同図の左側（短波長側）へシフトさせたようなものであって、積：Ｔ１Ｎ・Ｔ２Ｐ、Ｔ１Ｐ・Ｔ２Ｎが、図１（ｅ）、（ｆ）に示す如きものであるとすると、積：Ｔ１Ｐ・Ｔ２Ｎは０となるから、（１）式右辺の括弧内は「０．００９９・Ｔ１Ｎ・Ｔ２Ｐ」となり、積：Ｔ１Ｎ・Ｔ２Ｐはある程度大きいが、係数が０．００９９と小さいので、全体としては小さな値となり、フレア光の強度を有効に小さくすることができる。
【００８０】
図１（ｃ）、（ｄ）の場合には、Ｔ１Ｎ・Ｔ２Ｐ＝Ｔ１Ｐ・Ｔ２Ｎであるから、（１）式の右辺の大きさは「２Ｗ｛０．１６９９Ｔ１Ｎ・Ｔ２Ｐ｝」となる。図１（ｅ）、（ｆ）の場合において、Ｔ１Ｎ・Ｔ２Ｐの大きさが、仮に、図１（ｃ）におけるＴ１Ｎ・Ｔ２Ｐの２倍の大きさであったとしても、（１）式の右辺の大きさは、０．０１９８Ｔ１Ｎ・Ｔ２Ｐとなり、図１（ｃ）、（ｄ）の場合の１２％に過ぎない。
【００８１】
即ち、偏光反射ビームスプリッタ１２が特性「Ｔｓ＜１−Ｔｐ」を満足する場合において、白色照明光Ｌ１を偏光ビームスプリッタ１２に対しＰ偏光で入射させる場合には、第２の波長選択性リターダ２２の分光特性に対し、第１の波長選択性リターダ１０の分光特性として「第２の波長選択性リターダ２の分光特性を短波長側へシフトさせたもの」を用いれば、フレア光の強度を有効に軽減できることになる。
【００８２】
上には、白色照明光Ｌ１を偏光ビームスプリッタ１２に対してＰ偏光の状態で入射させた場合を説明した。図１（ａ）の構成において、白色照明光Ｌ１を偏光ビームスプリッタ１２に対してＳ偏光で入射させた場合を考えると、上記と同様の考察により（計算過程は上記の場合と同様なので省略する）、上記の（１）式に対応するフレア光の式は次のようになる。
【００８３】

となる。
【００８４】
この値は、白色照明光をＰ偏光で入射させた場合の（１）式において、積：Ｔ１Ｎ・Ｔ２Ｐ、Ｔ１Ｐ・Ｔ２Ｎに掛かる係数：Ｔｐ（１−Ｔｐ）、Ｔｓ（１−Ｔｓ）を入れ替えたものとなっている。
【００８５】
この場合、偏光ビームスプリッタの特性として上記と同様、Ｔｓ＜（１−Ｔｐ）の場合を考えると、係数の大小関係はＴｐ（１−Ｔｐ）＜＜Ｔｓ（１−Ｔｓ）であるから、Ｔｓ（１−Ｔｓ）を係数とする積：Ｔ１Ｐ・Ｔ２Ｎを小さくするようにすればよく、これを実現するには、第２の波長選択性リターダ２２の分光特性として「第１の波長選択性リターダ１０の分光特性を短波長側へシフトさせたもの」を用いることにより、（２）式の値を小さくしてフレア光の強度を有効に低減化できる。
【００８６】
上には、偏光ビームスプリッタ１２の特性が「Ｔｓ＜（１−Ｔｐ）」である場合を説明したが、上記特性の大小関係が逆の場合、即ち「Ｔｓ＞（１−Ｔｐ）」である場合には、上記と逆になる。即ちこの場合、偏光ビームスプリッタ１２へ白色照明光をＰ偏光で入射させるときには、第２の波長選択性リターダ２２の分光特性として「第１の波長選択性リターダ１０の分光特性を短波長側へシルトさせたもの」を用いることによりフレア光の強度を有効に低減化でき、白色照明光をＳ偏光で入射させるときは、第１の波長選択性リターダ１０の分光特性として「第２の波長選択性リターダ２２の分光特性を短波長側へシフトさせたもの」を用いることによりフレア光の強度を有効に低減化できる。
【００８７】
図１（ａ）に示す如き装置構成において、波長選択性リターダ１０、２２の分光特性として「青色帯域の偏光を９０度変換」する場合を考えて見ると、この場合には、フレア光の強度を有効に軽減させるには、以下のようにすれば良い。
【００８８】
即ち、偏光ビームスプリッタ１２の特性が「Ｔｓ＞（１−Ｔｐ）」である場合、白色照明光をＰ偏光で入射させる場合には、第１の波長選択性リターダ１０の分光特性として「第２の波長選択性リターダ２２の分光特性を短波長側へシフトさせたもの」を用いることによりフレア光の強度を有効に低減化でき、白色照明光をＳ偏光で入射させる場合には、第２の波長選択性リターダ２２の分光特性として「第１の波長選択性リターダ１０の分光特性を短波長側へシフトさせた」ものを用いることによりフレア光の強度を有効に低減化できる。
【００８９】
また、偏光ビームスプリッタ１２の特性が「Ｔｓ＜（１−Ｔｐ）」である場合、白色照明光をＰ偏光で入射させる場合には、第２の波長選択性リターダ２２の分光特性として「第１の波長選択性リターダ１０の分光特性を短波長側へスライドさせたもの」を用いることによりフレア光の強度を有効に低減化でき、白色照明光をＳ偏光で入射させる場合には、第１の波長選択性リターダ１０の分光特性として「第２の波長選択性リターダ２２の分光特性を短波長側へシフトさせたもの」を用いることによりフレア光の強度を有効に低減化できる。
【００９０】
このように、図１（ａ）の如き構成の投影装置において、偏光ビームスプリッタの特性と白色照明光の偏光状態がＰ偏光かＳ偏光かに応じて、第１及び第２の波長選択性リターダの分光特性を相互に「波長シフト」した関係とすることにより、「暗出力時におけるフレア光強度を有効に軽減してコントラストを向上させる」ことができることを説明した。
【００９１】
従って、このような原理を適用するには、第１及び第２の波長選択性リターダとして、互いに「波長スライド同一」の分光特性を持つものを組合せればよいことになるが、この発明においては、第１、第２の波長選択性リターダとして、分光特性が同一のものあるいは波長スライド同一なものを組合せ、且つ、一方若しくは双方の波長選択性リターダを「光束光路に対して傾ける」ことにより生じる「分光特性シフト効果」を利用してコントラストの向上を図るのである。
【００９２】
分光特性シフト効果は「光束光路に対して波長選択性リターダを傾けると、このリターダの持つ分光特性が、その形状（波長を横軸に、変換効率を横軸にとって示した形状）を保ったまま、短波長側へシフトする」現象である。
【００９３】
具体的な１例として、図２（ａ）に、緑色帯域の偏光を９０度偏光させる分光特性をもった波長選択性リターダを光束光路に対して傾けたときの分光特性２−１（傾け角：０）、２−１（傾け角：２０度）、２−３（傾け角：３０度）を示している。傾け角の増大に伴ない、分光特性が形状同一性を保ちつつ短波長側へシフトする様子がわかる。
【００９４】
図２（ｂ）は、図２（ａ）に示す波長選択性リターダに対する傾け角（光束光路の入射角度）と「分光特性のシフト量（波長シフト量）」との関係を示している。
分光特性シフト効果は、特定の波長選択性リターダに特有の現象ではなく、波長選択性リターダ一般に対する一般的な現象である。分光特性シフト効果による分光特性のシフト量は、波長選択性リターダの設計に依存する。
【００９５】
上に説明した「フレア光の軽減によるコントラストの向上」を実現する上において、第１、第２の波長選択性リターダの分光特性を互いに波長方向にスライドさせることが必要であり、図１（ａ）の如き構成で、これを実現しようとすると、波長選択性リターダ相互の「分光特性のシフト量」を設計上定め、このようなシフト量で分光特性が互いにシフトした１対の波長選択性リターダを作成する必要がある。
【００９６】
これに対し「分光特性シフト効果」を利用すると、予め作成した同一の分光特性を持つ１対の波長選択性リターダを組合せ、一方若しくは双方のリターダを光束光路に対して傾け、傾け角を調整することにより、容易に、フレア光強度を最小にできるような状態を実現することができる。
【００９７】
また、互いに「波長スライド同一」である１対の波長選択性リターダを組み合わせると、分光特性シフト効果を利用することにより、より広い波長領域で波長選択性リターダ間の分光特性のシフト量調整を容易に行うことができる。
【００９８】
１対の波長選択性リターダは上記のように、双方を光束光路に対して傾けることもできるが、傾け角の調整の面倒を考えると、一方の波長選択性リターダのみを傾けるのが好ましい。その場合、投射レンズに近い側の第２の波長選択性リターダを傾けると、結像光束に非点収差が発生するので「第２の波長選択性リターダと同一光路長（光学的厚さ）を有する平行平板を逆に傾斜させることで非点収差をキャンセルさせる」等、非点収差の影響を加味した装置設計が必要であり、投射レンズのバックフォーカスを大きくなったりすることを考慮すると、入射側に用いられる第１の波長選択性リターダを傾ける方が好ましい（請求項１０）。
【００９９】
このように、第１の波長選択性リターダを傾ける場合、波長選択性リターダが「赤色帯域の偏光を９０度変換する素子」のときは、偏光ビームスプリッタにおけるＰ偏光及びＳ偏光の透過率：Ｔｐ及びＴｓが、条件：Ｔｓ＜１−Ｔｐを満足する場合には、偏光ビームスプリッタに対してＰ偏光の白色照明光を入射させればよく（請求項４）、偏光ビームスプリッタにおけるＰ偏光及びＳ偏光の透過率：Ｔｐ及びＴｓが、条件：Ｔｓ＞１−Ｔｐを満足する場合には、偏光ビームスプリッタに対してＳ偏光の白色照明光を入射させればよい（請求項５）。
【０１００】
また、波長選択性リターダが「青色帯域の偏光を９０度変換する素子」である場合であれば、偏光ビームスプリッタにおけるＰ偏光及びＳ偏光の透過率：Ｔｐ及びＴｓが、条件：Ｔｓ＞１−Ｔｐを満足する場合には、Ｐ偏光の白色照明光を入射させ、偏光ビームスプリッタにおけるＰ偏光及びＳ偏光の透過率：Ｔｐ及びＴｓが、条件：Ｔｓ＜１−Ｔｐを満足する場合には、偏光ビームスプリッタに対してＳ偏光の白色照明光を入射させるようにすれば、第１の波長選択性リターダを傾けることにより（請求項７、請求項８）、コントラストの向上を図ることができる。
【０１０１】
次ぎに、この発明の他の課題である「投影画像の明るさの向上」につき説明する。上に暗出力時におけるフレア光の強度を説明したが、同様の考察を明出力について行うと、以下のようになる。
【０１０２】
先の説明と同様、図１（ａ）の装置構成を例に取ると、Ｐ偏光照明（白色照明光を偏光ビームスプリッタ１２に対してＰ偏光状態で入射させる）の場合の偏光ビームスプリッタ１２による反射光の、Ｓ偏光成分：Ｂｓ、Ｐ偏光成分：Ｂｐはそれぞれ、
Ｂｓ=Ａｓ（１−Ｔｓ）＝Ｗ・Ｔ１Ｎ（１−Ｔｓ）
Ｂｐ=Ａｐ（１−Ｔｐ）＝Ｗ・Ｔ１Ｐ（１−Ｔｐ）
となり、明出力では、ライトバルブ１６により偏光方向を変えられて反射されるので、ライトバルブ１６による反射光の、Ｓ偏光成分：ＲＢｓ、Ｐ偏光成分：ＲＢｐは、上記ＢｓとＢｐを入れ替え、ライトバルブ１６の変換効率：ηを乗じたもの、即ち、
ＲＢｐ＝Ｂｓ・η ＲＢｓ＝Ｂｐ・η
となる。
【０１０３】
明出力では、偏光ビームスプリッタ１６を通過する分だけを考えればよく、Ｓ偏光成分：ＲＢｓには透過率Ｔｓ、Ｐ偏光成分：ＲＢｐにはＴｓを乗じて、
Ｃｓ＝ＲＢｓ・Ｔｓ＝Ｂｐ・η・Ｔｓ＝Ｗ・Ｔ１Ｐ（１−Ｔｐ）Ｔｓ・η
Ｃｐ＝ＲＢｐ・Ｔｐ＝Ｂｓ・η・Ｔｐ＝Ｗ・Ｔ１Ｎ（１−Ｔｓ）Ｔｐ・η
の光が偏光ビームスプリッタ１２を透過して、第２の波長選択性リターダ２２に入射する。
【０１０４】
第２の波長選択性リターダ２２を通過するＳ偏光成分：Ｄｓ、Ｐ偏光成分：Ｄｐはそれぞれ、

となり、偏光子２４に入射するが、偏光子２４は明出力光を透過させるように、この場合はＳ偏光のみを透過させる素子であるから、上記成分：Ｄｐはカットされて、成分：Ｄｓのみが投射レンズ２６へ向かう。
【０１０５】
偏光ビームスプリッタ１２を透過した光成分：ＮＡ（緑色・青色帯域光）について同様の考察を行うと、
Ｂｓ’=Ａｓ・Ｔｓ＝Ｗ・Ｔ１Ｎ・Ｔｓ
Ｂｐ’=Ａｐ・Ｔｐ＝Ｗ・Ｔ１Ｐ・Ｔｐ
の光がダイクロイックプリズム１４へとむかい、ダイクロイックプリズム１４で２色に分離され、ライトバルブ１８、２０に対する照明光になる。これらライトバルブ１８、２０で偏光方向を変換されて反射される光のうち、投射レンズ２６へ向う成分は、偏光ビームスプリッタ１２で反射される成分であり、偏光ビームスプリッタ１２による反射成分は、Ｐ偏光成分、Ｓ偏光成分につき、
Ｃｓ’＝Ｂｐ’（１−Ｔｓ）η＝Ｗ・Ｔ１Ｐ・Ｔｐ（１−Ｔｓ）η
Ｃｐ’＝Ｂｓ’（１−Ｔｐ）η＝Ｗ・Ｔ１Ｎ・Ｔｓ（１−Ｔｐ）η
となる。
【０１０６】
これらの光が第２の波長選択性リターダ２２に入射するが、第２の波長選択性リターダ２２を通過するＳ偏光成分：Ｄｓ’、Ｐ偏光成分：Ｄｐ’は、

となる。
【０１０７】
これらのうち偏光子２４によりＰ偏光成分：Ｄｐ’がカットされ、Ｓ偏光成分：Ｄｓ’が投射レンズ２６へ向かう。
【０１０８】
従って、投射レンズ２６へ向う全光量は、

となり、明出力光の光量は、偏光ビームスプリッタ１２の特性（Ｔｓ、Ｔｐ）と、第１、第２の波長選択性リターダ１０、２２の分光特性をそれぞれ乗じたものに依存している。
【０１０９】
（３）式は、右辺括弧内における（Ｔ１Ｐ・Ｔ２Ｐ＋Ｔ１Ｎ・Ｔ２Ｎ）が最大となるとき最大となるが、このことは、明出力光が「第１および第２の波長選択性リターダの分光特性が同一」であるときに最大となることを意味している。
【０１１０】
Ｓ偏光入射について、上記と同様の考察を行うと、（３）式に対応するものとして、

が得られるが、この（４）式は（３）式と同じである。
【０１１１】
即ち、投影画像の明るさは照明光の偏光方向には左右されず、第１、第２の波長選択性リターダ１０、２２が同一の偏光特性を持つときに最大となる。
【０１１２】
投影画像の表示が行われる状況は一律ではなく、表示される環境が明るい場合には「コントラストは多少低くても、明るい画像」が求められるし、暗い室内で投影画像を表示する場合には、よりコントラストの高い画像の投影が望まれる。
【０１１３】
従って、第１、第２の波長選択性リターダにおける少なくとも一方の、光束光路に対する傾き角を可変にする（請求項９）と、コントラストを優先するときは、第１及び／または第２の波長選択性リターダの傾きを調整して、前述したフレア光強度の小さいコントラストの高い画像を投影し、投影画像の明るさを優先するときは、傾き角を０として第１、第２の波長選択性リターダの分光特性が同一となるようにすることにより、明るい画像を投影できるようになる。
【０１１４】
また、明るさを「より優先」したい場合は偏光子２４を取り外せるようにすれば、より光利用効率を高くすることができる。偏光子２４を取り外すと、結像光路中の平板が無くなるため、ライトバルブと投射レンズとの間の光路長がずれるが、偏光子を取り外した後に、ガラス部材などの平行平板を挿入することにより上記光路長のずれを補正することができる。
【０１１５】
上に説明した「偏光ビームスプリッタの特性」は説明の簡単のために単純化しているが、実際は蒸着やスパッタリングなどによる薄膜製造技術により作成可能な性能としては制約が生じ、細かなリップルやうねりがある。この発明に用いる偏光ビームスプリッタの特性としては、照明ランプの発光スペクトルに応じ、また、波長選択性リターダの特性にあわせて、フレア光を低減できるように最適設計すればよく、照明ランプの発光スペクトルにあわせた主波長で前述の条件を満たせば十分である。
【０１１６】
具体的には「照明ランプの各波長に対する発光エネルギーと、偏光ビームスプリッタの偏光分離膜の特性を、各波長毎に掛け合わせた値」を波長について積分した値で比較すればよく、使用する光源の波長に応じ、最適な分光特性とすればよい。
【０１１７】
即ち、照明ランプの発光強度分布をＥ(λ)としたとき、例えば、請求項４記載の場合の例であると、偏光ビームスプリッタに要求される「条件：Ｔｓ＜１−Ｔｐ」を満足する特性は、
∫Ｅ(λ)Ｔｓ(λ）ｄλ＜∫Ｅ(λ)（１−Ｔｐ(λ）)ｄλ （５）
あるいは、さらに比視感度関数：ｖ(λ) を加えて
∫Ｅ(λ)Ｔｓ(λ)ｖ(λ)ｄλ＜∫Ｅ(λ)(１−Ｔｐ(λ))ｖ(λ)ｄλ （６）
の関係に置き換えればよい。他の場合も同様である。なお、上記（６）、（７）式において、積分領域は「可視領域」である。
【０１１８】
【発明の実施の形態】
以下、具体的な実施の形態を説明する。繁雑をさけるため、混同の虞がないと思われるものについては、全図面を通じて同一の符号を用い、既に、図１において説明したものについては説明を省略する。
【０１１９】
図３に示す実施の形態は、偏光ビームスプリッタ１２の透過率：Ｔｓ、Ｔｐが条件：Ｔｓ＞（１−Ｔｐ）を満足するものであり、白色照明光Ｌ１は、偏光ビームスプリッタ１２に対してＰ偏光として入射する。第１及び第２の波長選択性リターダ１０、２２は赤色帯域の偏光を９０度変換する素子で「同一の分光特性」を有する。
【０１２０】
この実施の形態では、第２の波長選択性リターダ２２を光束光路に対して傾けることにより「分光特性シフト効果」により、その分光特性を「波長選択性リターダ１０の分光特性に対して短波長側」へシフトさせることにより、投影画像のコントラスト向上を図っている。
【０１２１】
なお、図３において、符号１５は、ライトバルブ１８、２０に対するライトバルブ１６の光路長を調整するための透明平行平板を示している。
【０１２２】
図４に示す実施の形態では、偏光ビームスプリッタ１２の透過率：Ｔｓ、Ｔｐが条件：Ｔｓ＜（１−Ｔｐ）を満足するものであり、白色照明光Ｌ１は、偏光ビームスプリッタ１２に対してＰ偏光として入射する。第１及び第２の波長選択性リターダ１０、２２は、赤色帯域の偏光を９０度変換する素子で「同一の分光特性」を有する。
【０１２３】
この実施の形態では、第１の波長選択性リターダ１０を光束光路に対して傾けることにより「分光特性シフト効果」により、その分光特性を「波長選択性リターダ２２の分光特性に対して短波長側」へシフトさせることにより、投影画像のコントラスト向上を図っている（請求項４）。
【０１２４】
図５に示す実施の形態では、偏光ビームスプリッタ１２の透過率：Ｔｓ、Ｔｐが条件：Ｔｓ＞（１−Ｔｐ）を満足するものであり、白色照明光Ｌ１は、偏光ビームスプリッタ１２に対してＳ偏光として入射する。第１及び第２の波長選択性リターダ１０、２２は、赤色帯域の偏光を９０度変換する素子で「同一の分光特性」を有する。
【０１２５】
この実施の形態では、第１の波長選択性リターダ１０を光束光路に対して傾けることにより「分光特性シフト効果」により、その分光特性を「波長選択性リターダ２２の分光特性に対して短波長側」へシフトさせることにより、投影画像のコントラスト向上を図っている（請求項５）。
【０１２６】
図６に示す実施の形態では、偏光ビームスプリッタ１２の透過率：Ｔｓ、Ｔｐが条件：Ｔｓ＞（１−Ｔｐ）を満足するものであり、白色照明光Ｌ１は、偏光ビームスプリッタ１２に対してＰ偏光として入射する。第１及び第２の波長選択性リターダ１０、２２は、青色帯域の偏光を９０度変換する素子で「同一の分光特性」を有する。
【０１２７】
符号１４０は、偏光ビームスプリッタ１２を透過した光を、赤色帯域光と緑色帯域光とに分離するダイクロイックプリズム（色分離素子）、符号１５Ａは、ライトバルブ１６、２０に対して、ライトバルブ１８の光路長を調整するための透明平行平板を示している。
【０１２８】
この実施の形態では、第１の波長選択性リターダ１０を光束光路に対して傾けることにより「分光特性シフト効果」により、その分光特性を「波長選択性リターダ２２の分光特性に対して短波長側」へシフトさせることにより、投影画像のコントラスト向上を図っている（請求項７）。
【０１２９】
図６の実施の形態において、偏光ビームスプリッタ１２の透過率：Ｔｓ、Ｔｐが条件：Ｔｓ＜（１−Ｔｐ）Ｔｐを満足するものである場合には、図６の構成において、白色照明光Ｌ１を偏光ビームスプリッタ１２に対してＳ偏光状態で入射させるようにすれば、第１の波長選択性リターダ１０を光束光路に対して傾けることにより「分光特性シフト効果」により、その分光特性を「波長選択性リターダ２２の分光特性に対して短波長側」へシフトさせることにより、投影画像のコントラスト向上を図ることができる（請求項８）。
【０１３０】
図３〜図６に示した実施の形態においては、色分離素子としてのダイクロイックプリズム１４、１４０は、そのダイクロイック膜が光束光路に対し４５度方向に傾斜し、各色光を互いに９０度をなすように分離するものであった。
【０１３１】
色分離素子における色分離性能をさらに向上させるために、入射角度を３０度、１５度等の「より低い入射角度」を実現するようにダイクロイック膜を設定してもよい。
【０１３２】
図７は、このような場合の実施の１形態を示している。
図５の実施の形態の変形例として説明すると、この例は、ダイクロイック膜への入射角を１５度に設定した場合の例である。
「色分離素子」は３つのプリズム部分１４−１、１４−２、１４−３で構成され、プリズム部分１４−２と１４−３との境界面にダイクロイック膜１４Ｂが形成されている。偏光ビームスプリッタ１２側から入射する光は、プリズム部分１４−１、１４−２を透過し、ダイクロイック膜１４Ｂで２色の光に分離される。
【０１３３】
ダイクロイック膜１４Ｂを透過した光はプリズム部分１４−３を透過して第３のライトバルブ２０を照明し、反射されて入射光路を逆進して偏光ビームスプリッタ１２に戻る。
【０１３４】
プリズム部分１４−１との間に空気間隙ＡＧを設けられたプリズム部分１４−２は、ダイクロイック膜１４Ｂで反射された光を、空気間隙ＡＧ側表面で全反射するように、硝材・空気間隙ＡＧの傾斜角度を設定されており、全反射した光でライトバルブ１８を照明する。もちろん、光路長に余裕があれば、空気間隙部を持たせない構成とすることができる。
【０１３５】
図８は、請求項２記載の投影装置の、実施の１形態を示している。
直線偏光状態の白色照明光Ｌ１を、第１の波長選択性リターダ１０に入射させ、この第１の波長選択性リターダ１０を通過した光のうち、偏光方向が変化した波長帯域光：Ａと偏光方向が変化しない波長帯域光：ＮＡを、偏光ビームスプリッタ１２により２光路に分離し、分離された一方の波長帯域光：Ａを第１のライトバルブ１６への照明光とし、他方の波長帯域光：ＮＡを時間的色分離手段１７によって２色の光：ＢおよびＣに時間的に分離し、分離された光：Ｂ、Ｃを交互に第２のライトバルブ２０Ａへの照明光とし、第１のライトバルブ１６に照明光：Ａに対する画像を表示すると共に、第２のライトバルブ２０Ａに照明光：Ｂ、Ｃに対する画像を、時間的色分離手段１７の時間的な色分離に同期して表示し、各照明光：Ａ、Ｂ、Ｃを画像に従って変調された映像光：ＬＡ、ＬＢ、ＬＣとし、これら各映像光を合成した合成光：ＬＴを、第２の波長選択性リターダ２２を介して偏光子２４に入射させ、この偏光子２４を介して結像光学系２６によりスクリーン上に投射してカラー画像を表示する。
【０１３６】
第１の波長選択性リターダ１０と第２の波長選択性リターダ２２とは「同一もしくは波長スライド同一の分光特性」を持つ素子であり、第１および第２の波長選択性リターダの少なくとも一方が「光束光路に対して傾け」て配置される。
【０１３７】
図４に示した実施の形態の変形例として説明すると、偏光ビームスプリッタ１２の透過率：Ｔｓ、Ｔｐは条件：Ｔｓ＜（１−Ｔｐ）を満足し、白色照明光Ｌ１は、偏光ビームスプリッタ１２に対してＰ偏光として入射する。第１及び第２の波長選択性リターダ１０、２２は赤色帯域の偏光を９０度変換する素子で「同一の分光特性」を有する。
【０１３８】
そして、図示の如く、第１の波長選択性リターダ１０を光束光路に対して傾けることにより「分光特性シフト効果」により、その分光特性を「波長選択性リターダ２２の分光特性に対して短波長側」へシフトさせることにより、投影画像のコントラスト向上を図っている。
【０１３９】
時間的色分離手段１７は、偏光ビームスプリッタ１２を透過した２色の光：青色帯域光と緑色帯域光を時間的に分離する手段であり、青色帯域光を透過させ、緑色帯域光を遮断する第１フィルタと、青色帯域光を遮断し、緑色帯域光を透過させるような第２フィルタとを高速回転させ、ライトバルブ２０Ａに入射する照明光を青色帯域光・緑色帯域光に高速で交互に切換えるようになっている。
【０１４０】
ライトバルブ２０Ａには、照明光が青色帯域光であるときは青色画像を、照明光が緑色帯域光であるときは緑色画像を表示する。
【０１４１】
「時間的色分離手段」は、偏光ビームスプリッタ１２とライトバルブ２０Ａの間に設ける必要は必ずしも無く、時間的色分離手段を偏光ビームスプリッタ１２への白色照明光の入射側に設けるようにしても良い。
【０１４２】
この場合には、例えば、マゼンタ光（青色帯域光と赤色帯域光）を透過させ、緑色帯域光を遮断するフィルタと、緑色帯域光を透過させ、マゼンタ光を遮断するフィルタとを、白色照明光に対して時間的に切り換えることにより、偏光ビームスプリッタ１２へ入射する光を、マゼンタ光と緑色帯域光とに分離するようにできる。偏光ビームスプリッタ１２に入射したマゼンタ光のうち、赤色帯域光は偏光ビームスプリッタ１２により青色帯域光と分離されるので、結局、ライトバルブ２０Ａに入射する光は、青色帯域光と緑色帯域光に時間的に分離される。
【０１４３】
時間的色分離手段を、偏光ビームスプリッタの入射側に設ける場合、黄色光（赤色帯域光と青色帯域光）を透過させ、緑色帯域光を遮断するフィルタと、黄色光を遮断し、緑色帯域光を透過させるフィルタとを、白色照明光に対して時間的に切り換えることによっても、上記と同様の結果が得られる。
【０１４４】
白色照明光の光源ランプが、例えば、超高圧水銀ランプであるような場合、発光スペクトルにおける赤色帯域光の輝度が不足しがちであり、他の色の光とのバランスをとる上でも、赤色帯域光が、常にライトバルブ１６に対して照射されているようにするためには、マゼンタ光を透過させ、緑色帯域光を遮断するフィルタと、黄色光を透過させ、青色光を遮断するフィルタとを、白色照明光に対して時間的に切り換えるようにすればよく、このようにすれば、時間的色分離手段を偏光ビームスプリッタ１２とライトバルブ２０Ａとの間に配設したのと同じ効果を得ることができる。
【０１４５】
時間的色分離手段としては、上記の「フィルタを高速切り換えするもの」の他に、例えば、ＳＩＤ ’００ ｄｉｇｅｓｔ．Ｖｏｌ３１，Ｐ９２に記載された「カラースイッチ」という色選択性透過素子を用いることもできる。
【０１４６】
図９は、図５の実施の形態の変形例を示している。
この例では、明るさを「より優先」したい場合に、偏光子２４を結像光路外に取り外せるようにし、光利用効率をより高めるようにしたものである。偏光子２４は、図９（ｂ）に示すように、透明なダミー平行平板２５と一体に形成されている。ダミー平行平板２５は、偏光子２４を結像光路外に取り外した際の「結像光路におけるライトバルブと投射レンズとの間の光路長のずれ」を補正するように構成されている。
【０１４７】
偏光子２４とダミー平行平板２５との切り換えは、ユーザによる手動によって行うようにしても良いし、適宜の駆動手段により行うようにしても良い。切り換えには、スライド移動、回転移動、その他の切り換え方式を適宜利用できる。あるいは、偏光子２４やダミー平行平板２５をそれぞれ、ホルダ等の保持部材に固定し、投影装置外から保持部材ごと完全に取り外し、あるいは交換可能なようにしておいても良い。
【０１４８】
偏光子２４とダミー平行平板２５とを切り換えることは、図５の実施の形態のみならず、上に説明した各実施の形態（図１（ａ）の物を含む）の場合にも、適用できることは言うまでもない。
【０１４９】
上に説明してきた投影装置に用いられる光源には、ハロゲンランプ、キセノンランプ、メタルハライドランプ、超高圧水銀ランプなどが用いられる。効率よく照度を得られるように、リフレクターで反射集光させてもよい。
【０１５０】
偏光変換器は、従来からある偏光ビームスプリッタアレイと波長板を組み合わせた偏光変換器で構成され、一方向の偏光方向に効率よく変換される偏光変換器を用いても良い。
【０１５１】
さらに、偏光度を向上させ、コントラスト性能を確保したい場合は、入射光の偏光変換器の後に直線偏光子を挿入したり、偏光ビームスプリッタを用いたりして偏光度を向上させると効果的である。とくに、偏光ビームスプリッタを用いた場合は、直線偏光子であった場合は光吸収のために発熱し、性能を低下させる場合もあるが、偏光ビームスプリッタでは不要な偏光成分を反射あるいは透過させ、スプリッタ内に蓄積させないため、光吸収による発熱を極力抑えることが可能となる。ＵＳＰ６２３４６３４記載のWire-Grid Polarizer（グリット偏光子）といわれるプレートタイプの偏光ビームスプリッタを用いてもよい。
【０１５２】
もちろん、このような偏光子は、照明レンズ側のみならず投射レンズ側に配置してもよい。また、グリット偏光子は、照明光と投影光の光路分離合成用として用いてもよい。ライトバルブを効率よく照明する光学系としての照明用集光素子は、インテグレータと呼ばれるフライアイレンズの組合せでライトバルブへ照射される照度ムラを低減させる集光素子や、コンデンサーレンズと組み合わせてライトバルブへ効率よく導く集光素子を用いることができる。
【０１５３】
必要に応じて偏光変換器を構成する偏光ビームスプリッタアレイピッチにあわせたレンズアレイを組み合わせた構成などを採用できる。また、光源として、より高出力レーザ光源など、偏光性の高い光源を用いることが可能である場合は、偏光変換器を省略することも可能である。
【０１５４】
【発明の効果】
以上に説明したように、この発明によれば新規な投影装置を実現できる。この発明の投影装置は、上述の如く、投影画像におけるコントラストを有効に高めることができる。
【０１５５】
また、必要に応じ、あるいは所望により、コントラストに優先して投影画像の明るさを増大させることができる。
【図面の簡単な説明】
【図１】１対の波長選択性リターダにおいて、一方の分光特性を他方の分光特性に対して短波長側へシフトさせることにより、投影画像におけるフレア光強度を減少できることを説明するための図である。
【図２】波長選択性リターダの分光特性シフト効果を説明するための図である。
【図３】投影装置の実施の１形態を説明するための図である。
【図４】投影装置の実施の別形態を説明するための図である。
【図５】投影装置の実施の他の形態を説明するための図である。
【図６】投影装置の実施の他の形態を説明するための図である。
【図７】投影装置の実施の他の形態を説明するための図である。
【図８】投影装置の実施の他の形態を説明するための図である。
【図９】投影画像の明るさをより優先させるために、偏光子を結像光路外に取り外せるようにした実施の形態の１例を説明するための図である。
【符号の説明】
１０ 波長選択性リターダ
１２ 偏光ビームスプリッタ
１４ ダイクロイックプリズム
１６ ライトバルブ
１８ ライトバルブ
２０ ライトバルブ
２２ 波長選択性リターダ
２４ 偏光子
２６ 投射レンズ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a projection apparatus, and more particularly to a projection apparatus for color image projection that displays an image on a light valve and uses a wavelength selective retarder and a polarization beam splitter.
[0002]
[Prior art]
As a projection device for enlarging and projecting an image displayed on a liquid crystal panel or the like on a display medium such as a screen, a “liquid crystal projector” has recently been widely used for displaying video reproduction images, computer data, and the like. Among them, the “three-panel liquid crystal projector” used for color video presentations has a high penetration rate because the video is high definition.
[0003]
A liquid crystal panel is generally called a “light valve”, and can change the polarization state of output light with respect to linearly polarized input light in units of pixels.
[0004]
On the other hand, there is known a “wavelength selective retarder” that can provide “half-wave retardation” between ordinary rays and extraordinary rays in linearly polarized light in a desired wavelength band. The retardation for a half wavelength can be given to “light in a wavelength band that can be arbitrarily set as a design condition”.
[0005]
A three liquid crystal projector using a wavelength selective retarder has been proposed (for example, US Pat. No. 6,183,091).
[0006]
Such a three-liquid crystal projector is described as “a wavelength band in which the polarization direction is changed among the lights that have passed through the first wavelength-selective retarder when white illumination light in a linearly polarized state is incident on the first wavelength-selective retarder. Light: A wavelength band light whose polarization direction does not change from A: NA is separated into two optical paths by a polarization beam splitter, one of the separated wavelength band lights: A is used as illumination light to the first light valve, and the other wavelength Band light: NA is further separated into two colors of light: B and C by a color separation element, the separated light: B is used as illumination light for the second light valve, and light: C is sent to the third light valve. The first to third light valves display images, and the illumination lights A, B, and C are image lights modulated in accordance with the images: LA, LB, and LC. Synthesized synthesized light: LT, second wavelength Through 択性 retarder is incident on the imaging optical system is a projection device "is projected onto a screen to display a color image by the imaging optical system.
[0007]
The polarizing beam splitter used in such a projection apparatus “transmits P-polarized light and reflects S-polarized light” is an ideal case, and is ideal for a wide wavelength band such as the visible region. It is not always possible to exhibit excellent optical characteristics. Although it is not impossible to realize a polarization beam splitter having ideal optical characteristics, it is not practical because it would cost enormous costs if it was to be realized.
[0008]
When an actual polarization beam splitter is used, the “light / dark contrast in the enlarged color image to be displayed” is lowered due to the non-ideal characteristics. Then, in the actual projection apparatus as described above, the problem is how to improve the contrast.
As a result of the inventor's research aimed at improving the contrast, the “relationship between spectral characteristics” of the first and second wavelength selective retarders affects the contrast in relation to the characteristics of the polarizing beam splitter. I found out.
[0009]
In addition, when the wavelength selective retarder is tilted with respect to the optical path of the light beam passing through the wavelength selective retarder, the spectral characteristic of the wavelength selective retarder shifts to the short wavelength side on the wavelength axis (hereinafter referred to as wavelength selective retarder). It was found that “spectral characteristic shift effect” can be used for contrast control of a projected image.
[0010]
[Problems to be solved by the invention]
It is an object of the present invention to improve the contrast of a projected image by a projection device by using a spectral characteristic shift effect in a wavelength selective retarder.
[0011]
It is another object of the present invention to make it possible to select improvement in contrast and improvement in brightness according to whether priority is given to contrast or brightness in a projected image.
[0012]
[Means for Solving the Problems]
The projection apparatus according to claim 1, wherein the wavelength of the polarization direction of the light that has passed through the first wavelength-selective retarder is allowed to enter the linearly polarized white illumination light into the first wavelength-selective retarder. Band light: A and wavelength band light whose polarization direction does not change: NA is separated into two optical paths by a polarization beam splitter, one wavelength band light: A is used as illumination light for the first light valve, and the other Wavelength band light: NA is further separated into two colors of light: B and C by the color separation element, the separated light: B is used as illumination light for the second light valve, and light: C is the third light. Illumination light to the bulb, images are displayed on the first to third light valves, and each illumination light: A, B, C is image light modulated in accordance with the above image: LA, LB, LC, and each of these images Combined light: LT is the second wavelength selection It is incident on the polarizer through sexual retarder, a projection device, "which displays a color image projected on the screen by the imaging optical system through the polarizer, characterized by the following points.
[0013]
That is, the first and second wavelength-selective retarders are elements having “same spectral characteristics that are the same or the same wavelength slide”, and at least one of the first and second wavelength-selective retarders is “with respect to the light beam optical path. Tilted ”.
[0014]
The projection apparatus according to claim 2, wherein the wavelength of the polarization direction of the light that has passed through the first wavelength-selective retarder is allowed to enter the linearly polarized white illumination light into the first wavelength-selective retarder. Band light: A and wavelength band light whose polarization direction does not change: NA is separated into two optical paths by a polarization beam splitter, one wavelength band light: A is used as illumination light for the first light valve, and the other Light of the wavelength band: NA is temporally separated into two colors of light: B and C by temporal color separation means, and the separated lights: B and C are alternately used as illumination light to the second light valve, An image for illumination light: A is displayed on the first light valve, and an image for illumination light: B, C is displayed on the second light valve in synchronization with the temporal color separation of the temporal color separation means. , Each illumination light: A, B, C according to the above image The adjusted image light: LA, LB, LC, and the combined light: LT, which is obtained by synthesizing these image lights, is incident on the polarizer via the second wavelength selective retarder, and the above-described connection is made via this polarizer. A projection apparatus that displays a color image by projecting onto a screen by an image optical system, and is characterized by the following points.
[0015]
That is, the first wavelength-selective retarder and the second wavelength-selective retarder are elements having “the same or the same wavelength slide spectral characteristics”, and at least one of the first and second wavelength-selective retarders is “ Inclined with respect to the light beam path.
[0016]
Some supplementary explanation.
“Linear polarization state white illumination light” is white light substantially in a linear polarization state and is used for illumination of a light valve. The “white light” in this case has component light that can display a color image.
[0017]
As the “light valve”, a transmissive type can be used, but a reflective type can be preferably used. The reflection type light valve has a reflection surface on one side of the liquid crystal, and controls the polarization direction by utilizing the polarization plane turning function of the liquid crystal. When light is incident, the light is transmitted through the liquid crystal, reflected by the reflecting surface, and transmitted through the liquid crystal and emitted.
[0018]
When the voltage applied to each pixel of the liquid crystal is controlled, the rotation angle of the polarization plane during reciprocation of the liquid crystal is controlled, so that the distribution of the polarization direction in the emitted light can be controlled according to the voltage applied to the pixel. Thus, an image can be displayed.
[0019]
Unlike the transmissive type, the “reflective light valve” does not require a black matrix, so that there is no problem of pixel area reduction due to the black matrix, and a bright image can be displayed. Further, when a reflective light valve is used, the polarization beam splitter can be “shared with light separation and synthesis”.
[0020]
The “spectral characteristic” in the wavelength selective retarder is a characteristic with respect to wavelength of the efficiency that gives “retardation for half wavelength” between ordinary rays and extraordinary rays in linearly polarized light. For example, in the case of a transmission-type wavelength-selective retarder, when white light in a P-polarized state is transmitted through this, the intensity of P-polarized light in the transmitted light: F (normalizes the intensity of incident white light as 1) is a wavelength. : When expressed as a function of λ and F (λ), the intensity of the S-polarized light in the transmitted light is {1-F (λ)}.
[0021]
Such F (λ) and {1-F (λ)} are referred to as “spectral characteristics of the wavelength selective retarder”. Therefore, the fact that the first and second wavelength selective retarders have the same spectral characteristics means that the spectral characteristics: F (λ) of these wavelength selective retarders are the same.
[0022]
Further, the spectral characteristic “same wavelength slide” means that the spectral characteristic of one wavelength selective retarder: F (λ) is F (λ−Δλ) of the other wavelength selective retarder. Refers to cases.
That is, the spectral characteristic: F (λ−Δλ) of the other wavelength-selective retarder is the same as the spectral characteristic: F (λ) of one wavelength-selective retarder if it is slid in the wavelength axis direction by the wavelength: Δλ. Be the same. Of course, even if the spectral characteristics of the first and second wavelength selective retarders are the same or the wavelength slides are the same, it does not mean the “mathematical identity” of the two spectral characteristics, but is essentially the same. It is.
[0023]
“Inclining the wavelength-selective retarder with respect to the optical axis of the light beam” means that the wavelength-selective retarder is inclined with respect to a plane perpendicular to the optical axis of the light beam incident on the wavelength-selective retarder.
[0024]
The “temporal color separation means” in the projection apparatus according to claim 2 is means for temporally separating a light beam (B + C) containing two colors of light: B and C into these component lights: B and C. For example, a first filter that transmits light: B and blocks (or reflects) light: C, and a second filter that blocks (or reflects) light: B and transmits light: C are luminous fluxes. It is possible to use one that switches alternately in time with respect to (B + C). The temporal color separation means can be disposed between the polarizing beam splitter and the second light valve, but can also be provided on the incident side of the polarizing beam splitter as will be described later.
[0025]
The projection apparatus according to claim 1 or 2, wherein both the first and second wavelength-selective retarders are elements that convert polarized light in the red band by 90 degrees, and one of the first and second wavelength-selective retarders is used. It can be configured to be “tilted with respect to the light beam optical path” (claim 3). When the spectral characteristics of the first and second wavelength-selective retarders are “same wavelength slide”, the red bands swirling the polarization are shifted from each other by the wavelength: Δλ (about several tens of nm).
[0026]
In the projection device according to claim 3, the transmittances Tp and Ts of the P-polarized light and the S-polarized light in the polarizing beam splitter are:
Condition: Ts <1-Tp
The first wavelength-selective retarder is tilted with respect to the light beam optical path, and “P-polarized white illumination light is incident on the polarization beam splitter” can be made incident on the first wavelength-selective retarder. (Claim 4).
[0027]
In the projection apparatus according to claim 3, the transmittances Tp and Ts of the P-polarized light and the S-polarized light in the polarizing beam splitter are:
Condition: Ts> 1-Tp
The first wavelength-selective retarder is tilted with respect to the light beam optical path, and “S-polarized white illumination light is incident on the polarization beam splitter” can be made incident on the first wavelength-selective retarder. (Claim 5).
[0028]
The projection apparatus according to claim 1 or 2, wherein both the first and second wavelength selective retarders are elements that convert blue band polarized light by 90 degrees, and one of the first and second wavelength selective retarders is used. It can be configured to be “tilted with respect to the light beam optical path” (claim 6).
[0029]
In the projection device according to claim 6, the transmittances Tp and Ts of the P-polarized light and the S-polarized light in the polarizing beam splitter are:
Condition: Ts> 1-Tp
The first wavelength-selective retarder is tilted with respect to the light beam optical path, and “P-polarized white illumination light is incident on the polarization beam splitter” can be made incident on the first wavelength-selective retarder. (Claim 7).
[0030]
In the projection apparatus according to claim 6, the transmittances Tp and Ts of the P-polarized light and the S-polarized light in the polarizing beam splitter are:
Condition: Ts <1-Tp
The first wavelength-selective retarder is tilted with respect to the light beam optical path, and “S-polarized white illumination light is incident on the polarization beam splitter” can be made incident on the first wavelength-selective retarder. (Claim 8).
[0031]
In the projection apparatus according to any one of claims 1 to 8, at least one of the first and second wavelength-selective retarders can change the tilt angle with respect to the light beam optical path (claim 9). .
[0032]
In the projector according to claim 1 or 2, the wavelength selective retarder tilted with respect to the light beam optical path is preferably a first wavelength selective retarder (claim 10).
[0033]
The conditions in claims 4, 5, 7, and 8 (the relationship between the magnitudes of Ts and 1-Tp), the polarization conversion band (the wavelength region in which the wavelength selective retarder converts 90 degrees of polarized light), and the illumination light (white illumination light) The polarization state is summarized as follows.
[0034]

[0035]
In short, when using a transmissive light valve, the polarization beam splitter that separates the illumination light and the polarization beam splitter that synthesizes the light are generally separate, but in such a case, separate polarization beams are used. As the splitter, those having the same characteristics, that is, those having the same “transmittance: Ts and transmittance: Tp” are used. In such a case, the “polarization state of the white illumination light incident on the first wavelength-selective retarder” in the above description means the polarization state with respect to the polarization beam splitter that separates the light.
[0036]
When a reflective light valve is used, light can be separated and combined by the same polarization beam splitter. In this case, the transmittance: Ts, Tp, and the polarization state of the illumination white light are the polarizations. The beam splitter is uniquely determined.
[0037]
The principle of the present invention and the “spectral characteristic shift effect” in the above-described wavelength selective retarder will be described below.
[0038]
FIG. 1A schematically shows an example of a projection apparatus using a polarizing beam splitter and a wavelength selective retarder. In the figure, reference numeral 10 denotes a first wavelength selective retarder, and reference numeral 12 denotes a polarizing beam splitter. Reference numeral 14 denotes a dichroic prism, reference numerals 16, 18 and 20 denote reflective light valves, reference numeral 22 denotes a second wavelength selective retarder, and reference numeral 24 denotes a polarizer.
[0039]
For the sake of concreteness of explanation, it is assumed that the wavelength selective retarders 10 and 24 have a function of “converting red band polarized light (hereinafter referred to as red band light) by 90 degrees”.
[0040]
When the white illumination light L1 in the linear polarization state (for the sake of concreteness of description, the P-polarization state with respect to the polarization beam splitter 12) is incident on the first wavelength-selective retarder 10, it passes through the wavelength-selective retarder 10. Due to the spectral characteristics of the wavelength-selective retarder 10, the red band light: A becomes “S-polarized with respect to the polarization beam splitter 12 by“ polarization direction turning 90 degrees ”due to polarization conversion, and becomes the other wavelength band light ( (Blue / green band light): NA is not subjected to polarization conversion, and enters the polarization beam splitter 12 with the original P-polarized state.
[0041]
After passing through the wavelength-selective retarder 10, the red band light: A is polarized and converted into S-polarized light, so that it is reflected by the polarization separation film 12 A of the polarization beam splitter 12 and becomes illumination light for the first light valve 16. . Blue / green band light: Since NA maintains a P-polarized state, it passes through the polarization separation film 12A of the polarization beam splitter 12 and enters the dichroic prism 14.
[0042]
The dichroic prism 14 is a “color separation element” and separates blue / green band light: NA into blue band light: B and green band light C by a dichroic film 14A. The separated blue band light: B becomes the illumination light for the second light valve 18, and the green band light: C becomes the illumination light for the third light valve 20.
[0043]
When an image is displayed on the first to third light valves 16, 18, 20 by “controlling the voltage application of each liquid crystal pixel according to the image signal”, the polarization direction of the illumination light changes in the pixel to which the voltage is applied. That is, each illumination light: A, B, and C is “reflected according to the above image (as a change in polarization direction)” and reflected, and travels backward in the incident optical path.
[0044]
The light returned from the light valve 16 to the polarization beam splitter 12 is transmitted through the polarization beam splitter 12 with the light component “converted into the P polarization state with respect to the polarization beam splitter 12” by the light valve 16, and the red video light: LA It becomes. The reflected light (blue video light: LB) from the light valve 18 is reflected by the dichroic prism 14 and is combined with the reflected light (green video light: LC) (from the light valve 20) that passes through the dichroic prism 14 and is polarized beam splitter. 12 is incident.
[0045]
The polarization beam splitter 12 reflects the light component that has been converted into the S-polarized state by the light valve from the light incident from the dichroic prism 14 side. The reflected light is green image light: LB, blue image light: LC, and is combined with red image light: LA by the light valve 16 to become combined light: LT.
[0046]
The combined light: LT is transmitted through the second wavelength selective retarder 22, but at this time, the polarization state of the red image light: LA is polarization-converted from the P-polarized state to the S-polarized state, and the other image light: LB, LC It will be aligned with the polarization state. The combined light LT having the same polarization state is transmitted through the polarizer 24, and at this time, the P-polarized component mixed as noise light is removed.
[0047]
The light L2 that has passed through the polarizer 24 enters a projection lens 26 that is an “imaging optical system”, and is projected on a screen (not shown) by the action of the projection lens 26 to form an image as an “enlarged color image”.
[0048]
FIG. 1B schematically shows the spectral characteristics of the wavelength selective retarder 10. That is, the vertical axis in FIG. 1B indicates the conversion efficiency (spectral intensity of light in a predetermined polarization direction transmitted through the wavelength selective retarder 10), and the horizontal axis indicates the wavelength.
[0049]
When the white illumination light L1 is in the P-polarized state, the portion indicated by the solid line is the conversion efficiency (corresponding to F (λ) described above) for converting the P-polarized state to the S-polarized state. Of L1, the red band light is rotated 90 degrees in the polarization direction to become S-polarized light. The broken line portion represents the intensity of the P-polarized light transmitted through the wavelength selective retarder 10 and corresponds to the aforementioned {1-F (λ)}.
[0050]
When the polarization state of the incident white light L1 is S-polarized light, the light intensity distribution after passing through the wavelength selective retarder 10 is as indicated by a broken line for S-polarized light and as indicated by a solid line for P-polarized light in FIG. Become.
[0051]
In the wavelength region indicated by the symbol “ξ” in FIG. 1B (the boundary between the green band and the red band), “the conversion efficiency (solid line) increases monotonously as the wavelength increases”. That is, in this wavelength region: ξ, “the light in the initial P-polarized state and the light in the S-polarized state after polarization conversion are mixed”. Wavelength region: ξ is referred to as “intermediate band for rotating the polarization direction by 90 degrees”. In addition, a point where a broken line and a solid line intersect in this intermediate region: CP is referred to as a “cross point”.
[0052]
An actual wavelength-selective retarder always has “an intermediate band in which P-polarized light and S-polarized light are mixed” in the spectral characteristics of transmitted light after polarization conversion. Considering the intermediate band: ξ, a part of the light in the intermediate band: ξ passes through the polarizing beam splitter 12 as “green band light”, and a part thereof is reflected by the polarizing beam splitter 12 as “red band light”. .
[0053]
Thus, the presence of the intermediate band obscures “color division according to wavelength” by polarization conversion, and therefore the presence of the intermediate band causes a decrease in contrast.
[0054]
On the other hand, if the transmittance of the S-polarized light in the polarizing beam splitter 12 is Ts and the transmittance of the P-polarized light is Tp, “the transmittance of the S-polarized light: Ts is 0% with respect to the light of various incident angles, It is difficult to realize a “polarization beam splitter having a transmittance Tp of 100%” in terms of design and manufacturing, and the polarization beam splitter is generally used within an incident angle range of illumination light: 0 to several tens of degrees. Therefore, the design is made so that the characteristics are improved with priority given to either Tp or Ts. For example, when priority is given to reducing Ts, the incident angle range is 0 to several tens of degrees. In general, Tp is set to several tens% or more and Ts is set to several% or less.
[0055]
In the projection apparatus as shown in FIG. 1A, the presence of the intermediate band in the wavelength selective retarders 10 and 22 and the imperfection of Tp and Ts in the polarization beam splitter 12 act to generate “flare light”. This causes a decrease in contrast in the projected image.
[0056]
Hereinafter, a decrease in contrast will be described. The light reflected by the polarization beam splitter 12 (red band light) and the light transmitted through the polarization beam splitter 12 (green / blue band light) will be considered individually. It is assumed that the white illumination light L1 is P-polarized with respect to the polarization beam splitter 12 as shown in the figure.
[0057]
The S-polarized light component: As and the P-polarized light component: Ap of the light intensity after passing through the first wavelength-selective retarder 10 are incident illumination light L1 because the incident illumination light L1 to the wavelength-selective retarder 10 is P-polarized light. Spectral intensity distribution: W, S polarization component is cross transmittance (solid line portion in FIG. 1B): T1N, P polarization component is parallel transmittance (dashed line portion in FIG. 1B): T1P Respectively, as follows.
As = W · T1N Ap = W · T1P.
[0058]
Then, the S-polarized light component: Bs and the P-polarized light component: Bp of the amount of light reflected by the polarization beam splitter 12 use the transmittances: Ts, Tp,
Bs = As (1-Ts) = W · T1N (1-Ts)
Bp = Ap (1-Tp) = W · T1P (1-Tp)
Thus, these component lights become illumination light for the red light valve 16.
[0059]
Consider flare light in “dark output” when the display image should be “black”.
Assuming that the red light valve 16 is not modulated “during dark output” and the illumination light is reflected 100% while maintaining its polarization direction, the above components: Bs and Bp are directly applied to the polarization beam splitter 12. Return.
[0060]
As the flare light at the time of dark output, in this case, only the amount that passes through the polarizing beam splitter 12 and travels toward the projection lens 26 may be considered. Then, the S-polarized light component: Cs and the P-polarized light component: Cp that return from the light valve 16 to the polarizing beam splitter 12 and pass therethrough are:
Cs = Bs · Ts = W · T1N (1-Ts) Ts
Cp = Bp · Tp = W · T1P (1-Tp) Tp
These are incident on the second wavelength selective retarder 22.
[0061]
Of this incident light (light from the light valve 16), the S-polarized component: Ds and the P-polarized component: Dp that pass through the second wavelength-selective retarder 22 are the cross-transmittance T2N of the wavelength-selective retarder 22; Parallel transmittance: T2P is applied to Cs and Cp as follows.
[0062]

These light components are incident on the polarizer 24.
[0063]
In this case, the polarizer 24 is an element that transmits only S-polarized light in order to “transmit the bright display light”. Therefore, among the transmitted light components, the P-polarized component: Dp is cut and the S-polarized light is transmitted. Component: Only Ds goes to the projection lens. Since the dark output is considered, this S-polarized component: Ds becomes a flare light component.
[0064]
Next, when the same consideration is given to the light (green band light and blue band light) transmitted through the polarization beam splitter 12, first, the S polarization component: Bs ′ and the P polarization component: Bp ′ transmitted through the polarization beam splitter 12. Is as follows.
[0065]
Bs ′ = As · Ts = W · T1N · Ts
Bp ′ = Ap · Tp = W · T1P · Tp
These component lights are separated into two colors by the dichroic prism 14 and become illumination lights for the blue and green light valves 18 and 20. At the time of dark output, these illumination lights are reflected by the light valves 18 and 20 while maintaining the polarization direction at the time of incidence. It is only necessary to consider only the component reflected back to the polarization beam splitter 12 that becomes flare light during dark output.
[0066]
The S-polarized light component: Cs ′ and P-polarized light component: Cp ′ reflected by the polarizing beam splitter 12 are set to reflectivity at the light valves 18 and 20 as 100%, respectively.
Cs ′ = Bs ′ (1-Ts) = W · T1N · Ts (1-Ts)
Cp ′ = Bp ′ (1−Tp) = W · T1P · Tp (1−Tp)
It becomes.
[0067]
When these components: Cs ′ and Cp ′ light enter the second wavelength-selective retarder 22 and pass through the second wavelength-selective retarder 22, the S-polarized components: Ds ′ and P-polarized components of the transmitted light: Dp ′ is

Of these component lights, the P-polarized component: Dp ′ is cut by the polarizer 24, so the flare component toward the projection lens 26 is only the S-polarized component: Ds ′.
[0068]
Therefore, the flare light among the white illumination light L1 incident on the first wavelength-selective retarder 10 during dark output is the S-polarized component: Ds and the S-polarized component calculated immediately above: Sum of Ds':

It becomes.
[0069]
Considering “T1N · T2P” and “T1P · T2N” in the right parenthesis of the equation (1), as described above, T1N is the cross transmittance in the wavelength selective retarder 10 (the solid line portion in FIG. 1B). T1P is the parallel transmittance (the broken line portion in FIG. 1B).
[0070]
Therefore, if the first and second wavelength selective retarders 10 and 22 have the same spectral characteristics and the spectral characteristics are as shown in FIG. 1B, the product: T1N · T2P is As shown in FIG. 1C, it is the product of the transmittance of the P-polarized component in the wavelength-selective retarder 22 (broken line) and the transmittance of the S-polarized component in the wavelength-selective retarder 10 (solid line). It is equal to the area of the hatched part.
[0071]
On the other hand, the product: T1P · T2N is, as shown in FIG. 1D, the transmittance of the P-polarized component in the wavelength selective retarder 10 (solid line) and the transmittance of the S-polarized component in the wavelength selective retarder 22 (broken line). And is equal to the area of the hatched portion in the figure.
[0072]
In this case, since the wavelength selective retarders 10 and 22 have the same spectral characteristics, the products: T1N · T2P and T1P · T2N are equal to each other.
[0073]
However, the spectral characteristics of the wavelength-selective retarder 22 are as shown in FIG. 1B, and the spectral characteristics of the wavelength-selective retarder 10 are the left side (short wavelength side) of FIG. ), The product: T1N · T2P has the transmittance (dashed line) of the P-polarized component in the wavelength-selective retarder 22 and the wavelength-selective retarder 10 as shown in FIG. Is the product of the transmittance (solid line) of the S-polarized light component at, and is equal to the area of the hatched portion in FIG. This area is larger than the area of the “hatched portion” shown in FIG.
[0074]
On the other hand, the product: T1P · T2N is, as shown in FIG. 1 (f), the transmittance of the P-polarized component in the wavelength selective retarder 10 (solid line) and the transmittance of the S-polarized component in the wavelength selective retarder 22 (broken line). Product, which is 0 in the case of the figure.
[0075]
On the other hand, the products in the formula (1): T1N · T2P and coefficients multiplied by T1P · T2N: Ts (1-Ts) and Tp (1-Tp) are determined by the characteristics of the polarization separation film 12A of the polarization beam splitter 12. .
[0076]
As a characteristic of the polarizing beam splitter 12, the S-polarized light reflectance is increased (that is, the S-polarized light transmittance is decreased), and the P-polarized light transmittance is set to several tens of percent to ensure the extinction ratio of transmitted light (Ts). <Characteristics satisfying 1−Tp), for example, consider the case of Ts = 0.01 and Tp = 0.8. Then
Ts (1-Ts) = 0.0099
Tp (1-Tp) = 0.16
Thus, Ts (1-Ts) is only about 6% of Tp (1-Tp).
[0077]
Then, in the right side of the expression (1) that gives the intensity of flare light at the time of dark output, the value in parentheses is “0.0099 · T1N · T2P + 0.16 · T1P · T2N)”, and T1N · T2P is somewhat large. However, since the value of Ts (1-Ts) is as small as 0.0099, the influence is small.
[0078]
On the other hand, the value of T1P · T2N has a larger value of Tp (1−Tp), which is a coefficient thereof, as 0.16.
[0079]
In this case, as described above, “the spectral characteristic of the wavelength selective retarder 22 is as shown in FIG. 1B, and the spectral characteristic of the wavelength selective retarder 10 is the cross point in FIG. If the CP is shifted to the left side (short wavelength side) in the figure, and the products: T1N · T2P, T1P · T2N are as shown in FIGS. 1 (e) and 1 (f) Since the product: T1P · T2N is 0, the value in the parentheses on the right side of the equation (1) is “0.0099 · T1N · T2P”, and the product: T1N · T2P is somewhat large, but the coefficient is as small as 0.0099. As a whole, the value becomes small, and the intensity of flare light can be effectively reduced.
[0080]
In the case of FIGS. 1C and 1D, since T1N · T2P = T1P · T2N, the size of the right side of the equation (1) is “2W {0.1699T1N · T2P}”. In the case of FIGS. 1E and 1F, even if the size of T1N · T2P is twice the size of T1N · T2P in FIG. 1C, the right side of equation (1) Is 0.0198T1N · T2P, which is only 12% in the case of FIGS. 1 (c) and 1 (d).
[0081]
That is, when the polarized reflection beam splitter 12 satisfies the characteristic “Ts <1−Tp”, when the white illumination light L1 is incident on the polarization beam splitter 12 as P-polarized light, the second wavelength selective retarder 22 is used. If the “spectral characteristic of the second wavelength-selective retarder 2 is shifted to the short wavelength side” is used as the spectral characteristic of the first wavelength-selective retarder 10, the flare light intensity is effective. It will be possible to reduce it.
[0082]
The case where the white illumination light L1 is incident on the polarization beam splitter 12 in the P-polarized state has been described above. In the configuration of FIG. 1A, considering the case where the white illumination light L1 is incident on the polarization beam splitter 12 as S-polarized light, the same consideration as above (the calculation process is the same as the above case and is omitted). ), The flare light equation corresponding to the above equation (1) is as follows.
[0083]

It becomes.
[0084]
This value is obtained by exchanging the coefficients: Tp (1-Tp) and Ts (1-Ts) applied to the products: T1N · T2P and T1P · T2N in the equation (1) when white illumination light is incident as P-polarized light. It has become.
[0085]
In this case, considering the case of Ts <(1-Tp) as the characteristic of the polarization beam splitter, the magnitude relationship of the coefficients is Tp (1-Tp) << Ts (1-Ts). The product having (1−Ts) as a coefficient: T1P · T2N may be reduced. To achieve this, the spectral characteristic of the second wavelength-selective retarder 22 is “first wavelength-selective retarder”. By using the “10 spectral characteristics shifted to the short wavelength side”, the value of equation (2) can be reduced to effectively reduce the intensity of flare light.
[0086]
The case where the characteristic of the polarization beam splitter 12 is “Ts <(1−Tp)” has been described above, but the case where the magnitude relationship of the above characteristics is reversed, that is, “Ts> (1−Tp)”. In the case, the reverse is true. That is, in this case, when the white illumination light is incident on the polarizing beam splitter 12 as P-polarized light, the spectral characteristic of the second wavelength selective retarder 22 is expressed as “the spectral characteristic of the first wavelength selective retarder 10 is tilted to the short wavelength side”. When the white illumination light is incident as S-polarized light, the spectral characteristic of the first wavelength selective retarder 10 is “second wavelength selectivity”. The intensity of the flare light can be effectively reduced by using the retarder 22 whose spectral characteristic is shifted to the short wavelength side.
[0087]
In the case of the apparatus configuration as shown in FIG. 1A, considering the case where the spectral characteristics of the wavelength-selective retarders 10 and 22 “convert the polarization in the blue band by 90 degrees”, in this case, the intensity of flare light In order to reduce this effectively, the following should be done.
[0088]
That is, when the characteristic of the polarization beam splitter 12 is “Ts> (1-Tp)”, when the white illumination light is incident as P-polarized light, the spectral characteristic of the first wavelength selective retarder 10 is “second”. The intensity of the flare light can be effectively reduced by using the wavelength selective retarder 22 whose spectral characteristic is shifted to the short wavelength side, and when the white illumination light is incident as S-polarized light, the second By using the spectral characteristic of the wavelength selective retarder 22 that “shifts the spectral characteristic of the first wavelength selective retarder 10 to the short wavelength side”, the intensity of flare light can be effectively reduced.
[0089]
When the characteristic of the polarization beam splitter 12 is “Ts <(1−Tp)”, when the white illumination light is incident as P-polarized light, the spectral characteristic of the second wavelength-selective retarder 22 is “first”. In this case, the intensity of flare light can be effectively reduced by using the one in which the spectral characteristic of the wavelength selective retarder 10 is slid to the short wavelength side, and when the white illumination light is incident as S-polarized light, the first The intensity of flare light can be effectively reduced by using “the spectral characteristic of the second wavelength selective retarder 22 shifted to the short wavelength side” as the spectral characteristic of the wavelength selective retarder 10.
[0090]
As described above, in the projection apparatus having the configuration as shown in FIG. 1A, the first and second wavelength-selective retarders depend on the characteristics of the polarization beam splitter and whether the polarization state of the white illumination light is P-polarized light or S-polarized light. It has been explained that it is possible to “reduce the flare light intensity at the time of dark output and improve the contrast” by making the spectral characteristics of each other “wavelength shifted”.
[0091]
Therefore, in order to apply such a principle, it is only necessary to combine the first and second wavelength selective retarders having the spectral characteristics of “same wavelength slide” with each other. As the first and second wavelength selective retarders, those having the same spectral characteristics or the same wavelength slide are combined, and one or both of the wavelength selective retarders are “tilted with respect to the light beam optical path”. The contrast is improved by utilizing the “spectral characteristic shift effect”.
[0092]
Spectral characteristics shift effect is “When the wavelength selective retarder is tilted with respect to the optical path of the light beam, the spectral characteristics of this retarder remain in its shape (wavelength is shown on the horizontal axis and conversion efficiency is shown on the horizontal axis). ”Shift to the short wavelength side”.
[0093]
As a specific example, FIG. 2A shows a spectral characteristic 2-1 (tilt angle) when a wavelength-selective retarder having a spectral characteristic for polarizing green band polarized light by 90 degrees is tilted with respect to the light beam optical path. : 0), 2-1 (tilt angle: 20 degrees), and 2-3 (tilt angle: 30 degrees). It can be seen that as the tilt angle increases, the spectral characteristics shift to the short wavelength side while maintaining shape identity.
[0094]
FIG. 2B shows the relationship between the tilt angle (incident angle of the light beam optical path) with respect to the wavelength selective retarder shown in FIG.
The spectral characteristic shift effect is not a phenomenon specific to a specific wavelength selective retarder, but is a general phenomenon for wavelength selective retarders in general. The amount of shift of spectral characteristics due to the spectral characteristic shift effect depends on the design of the wavelength selective retarder.
[0095]
In order to realize the above-described “improvement of contrast by reducing flare light”, it is necessary to slide the spectral characteristics of the first and second wavelength selective retarders in the wavelength direction. In this configuration, a “spectral characteristic shift amount” between wavelength selective retarders is determined by design, and a pair of wavelength selective retarders whose spectral characteristics are shifted from each other by such a shift amount. Need to create.
[0096]
On the other hand, when the “spectral characteristic shift effect” is used, a pair of wavelength-selective retarders having the same spectral characteristics prepared in advance are combined, and one or both retarders are tilted with respect to the light beam optical path to adjust the tilt angle. Thus, it is possible to easily realize a state in which the flare light intensity can be minimized.
[0097]
Also, by combining a pair of wavelength-selective retarders that are “wavelength slides identical” to each other, it is easy to adjust the amount of shift in spectral characteristics between wavelength-selective retarders in a wider wavelength range by using the spectral characteristic shift effect. Can be done.
[0098]
As described above, the pair of wavelength selective retarders can be tilted with respect to the optical path of the light beam. However, considering the adjustment of the tilt angle, it is preferable to tilt only one of the wavelength selective retarders. In that case, if the second wavelength selective retarder on the side closer to the projection lens is tilted, astigmatism occurs in the imaged light beam, so that “the same optical path length (optical thickness) as the second wavelength selective retarder is set. It is necessary to design a device that takes into account the effects of astigmatism, such as canceling astigmatism by tilting the parallel flat plate that has the reverse, and considering that the back focus of the projection lens increases, It is preferable to incline the first wavelength selective retarder used on the side (claim 10).
[0099]
As described above, when the first wavelength selective retarder is tilted, when the wavelength selective retarder is “an element that converts the polarization in the red band by 90 degrees”, the transmittance of the P-polarized light and the S-polarized light in the polarizing beam splitter: Tp And Ts satisfy the condition: Ts <1-Tp, P-polarized white illumination light may be incident on the polarizing beam splitter (Claim 4). When the polarization transmittances: Tp and Ts satisfy the condition: Ts> 1-Tp, S-polarized white illumination light may be incident on the polarization beam splitter.
[0100]
Further, when the wavelength selective retarder is “an element that converts blue band polarized light by 90 degrees”, the transmittance of the P-polarized light and the S-polarized light in the polarizing beam splitter: Tp and Ts are: Condition: Ts> 1− When Tp is satisfied, P-polarized white illumination light is incident, and when the transmittance of T-polarized light and S-polarized light in the polarizing beam splitter: Tp and Ts satisfy the condition: Ts <1−Tp, If S-polarized white illumination light is incident on the polarization beam splitter, the contrast can be improved by tilting the first wavelength selective retarder (claims 7 and 8).
[0101]
Next, “an improvement in the brightness of the projected image”, which is another subject of the present invention, will be described. The intensity of flare light at the time of dark output has been described above. If the same consideration is made for bright output, the following is obtained.
[0102]
As in the above description, taking the apparatus configuration of FIG. 1A as an example, the polarization beam splitter 12 in the case of P-polarized illumination (white illumination light is incident on the polarized beam splitter 12 in the P-polarized state). In the reflected light, the S-polarized component: Bs and the P-polarized component: Bp are respectively
Bs = As (1-Ts) = W · T1N (1-Ts)
Bp = Ap (1-Tp) = W · T1P (1-Tp)
In the bright output, since the polarization direction is changed by the light valve 16 and reflected, the S-polarized component: RBs and the P-polarized component: RBp of the light reflected by the light valve 16 are exchanged by switching the above Bs and Bp. Conversion efficiency of the valve 16: multiplied by η, ie
RBp = Bs · η RBs = Bp · η
It becomes.
[0103]
For the bright output, it is only necessary to consider the amount of light that passes through the polarization beam splitter 16. The S-polarized component: RBs is multiplied by the transmittance Ts, and the P-polarized component: RBp is multiplied by Ts.
Cs = RBs · Ts = Bp · η · Ts = W · T1P (1-Tp) Ts · η
Cp = RBp · Tp = Bs · η · Tp = W · T1N (1-Ts) Tp · η
Light passes through the polarization beam splitter 12 and enters the second wavelength selective retarder 22.
[0104]
S-polarized light component: Ds and P-polarized light component: Dp passing through the second wavelength selective retarder 22 are respectively

In this case, since the polarizer 24 is an element that transmits only the S-polarized light so as to transmit the bright output light, the component: Dp is cut, and only the component: Ds. Heads toward the projection lens 26.
[0105]
When the same consideration is made for the light component: NA (green / blue band light) transmitted through the polarizing beam splitter 12,
Bs ′ = As · Ts = W · T1N · Ts
Bp ′ = Ap · Tp = W · T1P · Tp
Is directed to the dichroic prism 14 and separated into two colors by the dichroic prism 14 to become illumination light for the light valves 18 and 20. Of the light reflected after the polarization direction is changed by these light valves 18 and 20, the component toward the projection lens 26 is the component reflected by the polarization beam splitter 12, and the reflection component by the polarization beam splitter 12 is P About polarization component and S polarization component
Cs ′ = Bp ′ (1-Ts) η = W · T1P · Tp (1-Ts) η
Cp ′ = Bs ′ (1-Tp) η = W · T1N · Ts (1-Tp) η
It becomes.
[0106]
These lights are incident on the second wavelength-selective retarder 22, and S-polarized component: Ds ′ and P-polarized component: Dp ′ that pass through the second wavelength-selective retarder 22 are:

It becomes.
[0107]
Among these, the P-polarized light component: Dp ′ is cut by the polarizer 24, and the S-polarized light component: Ds ′ is directed to the projection lens 26.
[0108]
Therefore, the total amount of light toward the projection lens 26 is

Thus, the amount of bright output light depends on the product of the characteristics (Ts, Tp) of the polarization beam splitter 12 and the spectral characteristics of the first and second wavelength-selective retarders 10 and 22, respectively.
[0109]
Equation (3) is maximized when (T1P · T2P + T1N · T2N) in the right parenthesis is maximized, which means that the bright output light is “the spectral characteristics of the first and second wavelength selective retarders are It means that it becomes maximum when it is “same”.
[0110]
When the same consideration as described above is performed for S-polarized light,

(4) is the same as (3).
[0111]
That is, the brightness of the projected image does not depend on the polarization direction of the illumination light, and is maximized when the first and second wavelength selective retarders 10 and 22 have the same polarization characteristics.
[0112]
The situation where the projection image is displayed is not uniform. When the display environment is bright, a `` bright image even if the contrast is somewhat low '' is required, and when displaying the projection image in a dark room, It is desired to project an image with higher contrast.
[0113]
Accordingly, when the tilt angle with respect to the light beam optical path is variable in at least one of the first and second wavelength selective retarders (claim 9), when priority is given to contrast, the first and / or second wavelength selection is performed. When adjusting the inclination of the characteristic retarder and projecting the above-described image with high flare light intensity and high contrast and giving priority to the brightness of the projected image, the inclination angle is set to 0 and the first and second wavelength selective retarders are used. By making the spectral characteristics of the same the same, it becomes possible to project a bright image.
[0114]
In addition, when it is desired to give priority to brightness, if the polarizer 24 can be removed, the light utilization efficiency can be further increased. When the polarizer 24 is removed, there is no flat plate in the imaging optical path, so the optical path length between the light valve and the projection lens is shifted. After removing the polarizer, a parallel flat plate such as a glass member is inserted. The deviation of the optical path length can be corrected.
[0115]
The above-mentioned "characteristics of the polarizing beam splitter" has been simplified for the sake of simplicity, but in reality, there are restrictions on the performance that can be created by thin film manufacturing technology such as vapor deposition and sputtering, and there are fine ripples and waviness. is there. The characteristics of the polarization beam splitter used in the present invention may be optimally designed to reduce flare light according to the emission spectrum of the illumination lamp and the characteristics of the wavelength selective retarder. It is sufficient if the above-mentioned conditions are satisfied with the dominant wavelength according to the above.
[0116]
Specifically, it is only necessary to compare the value obtained by integrating the “emission energy for each wavelength of the illumination lamp and the characteristics of the polarization separation film of the polarizing beam splitter for each wavelength” integrated with respect to the wavelength. According to the wavelength of the light, the optimum spectral characteristics may be obtained.
[0117]
That is, when the emission intensity distribution of the illumination lamp is E (λ), for example, in the case of claim 4, the “condition: Ts <1-Tp” required for the polarization beam splitter is satisfied. The characteristics are
∫E (λ) Ts (λ) dλ <∫E (λ) (1-Tp (λ)) dλ (5)
Alternatively, add a specific luminous efficiency function: v (λ)
∫E (λ) Ts (λ) v (λ) dλ <∫E (λ) (1-Tp (λ)) v (λ) dλ (6)
It may be replaced with the relationship. The same applies to other cases. In the above formulas (6) and (7), the integration region is the “visible region”.
[0118]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments will be described. In order to avoid complications, the same reference numerals are used throughout the drawings for those that are not likely to be confused, and the description of those already described in FIG. 1 is omitted.
[0119]
In the embodiment shown in FIG. 3, the transmittance: Ts, Tp of the polarizing beam splitter 12 satisfies the condition: Ts> (1-Tp), and the white illumination light L1 is compared with the polarizing beam splitter 12. Incident as P-polarized light. The first and second wavelength selective retarders 10 and 22 are elements that convert polarized light in the red band by 90 degrees and have “same spectral characteristics”.
[0120]
In this embodiment, the second wavelength-selective retarder 22 is tilted with respect to the optical path of the light beam, so that the spectral characteristics are shifted to the short wavelength side with respect to the spectral characteristics of the wavelength-selective retarder 10. ”To improve the contrast of the projected image.
[0121]
In FIG. 3, reference numeral 15 indicates a transparent parallel plate for adjusting the optical path length of the light valve 16 relative to the light valves 18 and 20.
[0122]
In the embodiment shown in FIG. 4, the transmittance: Ts, Tp of the polarizing beam splitter 12 satisfies the condition: Ts <(1−Tp), and the white illumination light L1 is compared with the polarizing beam splitter 12. Incident as P-polarized light. The first and second wavelength selective retarders 10 and 22 are elements that convert polarized light in the red band by 90 degrees and have “same spectral characteristics”.
[0123]
In this embodiment, the first wavelength-selective retarder 10 is tilted with respect to the optical path of the light beam, so that the spectral characteristic shifts to the short wavelength side with respect to the spectral characteristic of the wavelength-selective retarder 22. ”To improve the contrast of the projected image.
[0124]
In the embodiment shown in FIG. 5, the transmittance: Ts, Tp of the polarizing beam splitter 12 satisfies the condition: Ts> (1−Tp), and the white illumination light L1 is compared with the polarizing beam splitter 12. Incident as S-polarized light. The first and second wavelength selective retarders 10 and 22 are elements that convert polarized light in the red band by 90 degrees and have “same spectral characteristics”.
[0125]
In this embodiment, the first wavelength-selective retarder 10 is tilted with respect to the optical path of the light beam, so that the spectral characteristic shifts to the short wavelength side with respect to the spectral characteristic of the wavelength-selective retarder 22. ”To improve the contrast of the projected image.
[0126]
In the embodiment shown in FIG. 6, the transmittances Ts and Tp of the polarizing beam splitter 12 satisfy the condition Ts> (1−Tp), and the white illumination light L1 is compared with the polarizing beam splitter 12. Incident as P-polarized light. The first and second wavelength-selective retarders 10 and 22 are elements that convert blue band polarized light by 90 degrees and have “same spectral characteristics”.
[0127]
Reference numeral 140 denotes a dichroic prism (color separation element) that separates the light transmitted through the polarization beam splitter 12 into red band light and green band light. Reference numeral 15A denotes the light valve 18 with respect to the light valves 16 and 20. A transparent parallel plate for adjusting the optical path length is shown.
[0128]
In this embodiment, the first wavelength-selective retarder 10 is tilted with respect to the optical path of the light beam, so that the spectral characteristic shifts to the short wavelength side with respect to the spectral characteristic of the wavelength-selective retarder 22. To improve the contrast of the projected image.
[0129]
In the embodiment of FIG. 6, when the transmittances: Ts and Tp of the polarizing beam splitter 12 satisfy the condition: Ts <(1-Tp) Tp, the white illumination light L1 in the configuration of FIG. Is made incident on the polarizing beam splitter 12 in the S-polarized state, the spectral characteristic is changed to “wavelength” by tilting the first wavelength-selective retarder 10 with respect to the optical path of the light beam and by “spectral characteristic shift effect”. By shifting the spectral characteristic of the selectivity retarder 22 to the short wavelength side, the contrast of the projected image can be improved (claim 8).
[0130]
In the embodiment shown in FIGS. 3 to 6, the dichroic prisms 14 and 140 as the color separation elements are arranged such that the dichroic films are inclined in the direction of 45 degrees with respect to the light beam optical path so that each color light forms 90 degrees with each other. Were separated.
[0131]
In order to further improve the color separation performance of the color separation element, the dichroic film may be set so as to realize a “lower incidence angle” such as an incident angle of 30 degrees or 15 degrees.
[0132]
FIG. 7 shows an embodiment of such a case.
If it demonstrates as a modification of embodiment of FIG. 5, this example is an example at the time of setting the incident angle to a dichroic film | membrane to 15 degree | times.
The “color separation element” includes three prism portions 14-1, 14-2, and 14-3, and a dichroic film 14B is formed on the boundary surface between the prism portions 14-2 and 14-3. The light incident from the polarization beam splitter 12 side passes through the prism portions 14-1 and 14-2, and is separated into two colors of light by the dichroic film 14B.
[0133]
The light that has passed through the dichroic film 14B passes through the prism portion 14-3, illuminates the third light valve 20, is reflected, travels backward in the incident optical path, and returns to the polarization beam splitter 12.
[0134]
The prism portion 14-2 provided with the air gap AG between the prism portion 14-1 and the glass material / air gap AG so that the light reflected by the dichroic film 14B is totally reflected on the surface of the air gap AG. The light valve 18 is illuminated with totally reflected light. Of course, if there is a margin in the optical path length, it is possible to adopt a configuration in which no air gap is provided.
[0135]
FIG. 8 shows an embodiment of the projection apparatus according to claim 2.
The linearly polarized white illumination light L1 is incident on the first wavelength-selective retarder 10, and among the light that has passed through the first wavelength-selective retarder 10, the wavelength band light having a changed polarization direction: A and polarized light The wavelength band light whose direction does not change: NA is separated into two optical paths by the polarization beam splitter 12, and one of the separated wavelength band lights: A is used as illumination light for the first light valve 16, and the other wavelength band light is used. : NA is temporally separated into two colors of light: B and C by the temporal color separation means 17, and the separated lights: B and C are alternately used as illumination light to the second light valve 20 A, and the first An image for the illumination light: A is displayed on the light valve 16 and the images for the illumination light: B, C are displayed on the second light valve 20 A in synchronization with the temporal color separation of the temporal color separation means 17. Each illumination light: A, B, C The image light modulated in accordance with the image: LA, LB, LC, and the combined light: LT obtained by synthesizing these image lights is incident on the polarizer 24 via the second wavelength selective retarder 22. The image is projected onto the screen by the imaging optical system 26 via the color image.
[0136]
The first wavelength-selective retarder 10 and the second wavelength-selective retarder 22 are elements having “same spectral characteristics with the same or wavelength slide”, and at least one of the first and second wavelength-selective retarders is “ Inclined with respect to the light beam path.
[0137]
As a modification of the embodiment shown in FIG. 4, the transmittance: Ts, Tp of the polarizing beam splitter 12 satisfies the condition: Ts <(1−Tp), and the white illumination light L1 is converted into the polarizing beam splitter 12. Is incident as P-polarized light. The first and second wavelength selective retarders 10 and 22 are elements that convert polarized light in the red band by 90 degrees and have “same spectral characteristics”.
[0138]
Then, as shown in the figure, the first wavelength-selective retarder 10 is tilted with respect to the optical path of the light beam so that the spectral characteristic shifts to a shorter wavelength side than the spectral characteristic of the wavelength-selective retarder 22. ”To improve the contrast of the projected image.
[0139]
The temporal color separation means 17 is means for temporally separating the two colors of light transmitted through the polarizing beam splitter 12: blue band light and green band light, and transmits the blue band light and blocks the green band light. The first filter and the second filter that blocks the blue band light and transmits the green band light are rotated at high speed, and the illumination light incident on the light valve 20A is alternately converted into blue band light and green band light at high speed. It is designed to switch.
[0140]
The light valve 20A displays a blue image when the illumination light is blue band light, and displays a green image when the illumination light is green band light.
[0141]
The “temporal color separation unit” is not necessarily provided between the polarization beam splitter 12 and the light valve 20A, and the temporal color separation unit may be provided on the incident side of the white illumination light to the polarization beam splitter 12. good.
[0142]
In this case, for example, a filter that transmits magenta light (blue band light and red band light) and blocks green band light and a filter that transmits green band light and blocks magenta light are used as white illumination light. By switching over time, the light incident on the polarization beam splitter 12 can be separated into magenta light and green band light. Of the magenta light incident on the polarizing beam splitter 12, the red band light is separated from the blue band light by the polarizing beam splitter 12, so that the light incident on the light valve 20A eventually becomes a blue band light and a green band light. Separated.
[0143]
When the temporal color separation means is provided on the incident side of the polarization beam splitter, a filter that transmits yellow light (red band light and blue band light) and blocks green band light, and blocks yellow light and green band light. The same result as described above can be obtained by temporally switching the filter that transmits the light with respect to the white illumination light.
[0144]
When the light source lamp of white illumination light is, for example, an ultra-high pressure mercury lamp, the luminance of the red band light in the emission spectrum tends to be insufficient, and the red band is also necessary for balancing with the light of other colors. In order to ensure that light is always applied to the light valve 16, a filter that transmits magenta light and blocks green band light and a filter that transmits yellow light and blocks blue light are provided. The white illumination light may be switched with respect to time, and in this way, the same effect as when the temporal color separation means is disposed between the polarization beam splitter 12 and the light valve 20A can be obtained. be able to.
[0145]
As the temporal color separation means, in addition to the above-described “High-speed filter switching”, for example, SID '00 digest. A color selective transmission element called “color switch” described in Vol31, P92 can also be used.
[0146]
FIG. 9 shows a modification of the embodiment of FIG.
In this example, when it is desired to prioritize the brightness, the polarizer 24 can be removed from the imaging optical path to further improve the light utilization efficiency. The polarizer 24 is integrally formed with a transparent dummy parallel plate 25 as shown in FIG. The dummy parallel plate 25 is configured to correct “the deviation of the optical path length between the light valve and the projection lens in the imaging optical path” when the polarizer 24 is removed from the imaging optical path.
[0147]
Switching between the polarizer 24 and the dummy parallel plate 25 may be performed manually by a user or may be performed by an appropriate driving unit. For switching, sliding movement, rotational movement, and other switching methods can be used as appropriate. Alternatively, the polarizer 24 and the dummy parallel plate 25 may be fixed to a holding member such as a holder so that the holding member can be completely removed or replaced from the outside of the projection apparatus.
[0148]
Switching between the polarizer 24 and the dummy parallel plate 25 can be applied not only to the embodiment of FIG. 5 but also to the above-described embodiments (including the one of FIG. 1A). Needless to say.
[0149]
As the light source used in the projection apparatus described above, a halogen lamp, a xenon lamp, a metal halide lamp, an ultrahigh pressure mercury lamp, or the like is used. In order to obtain illuminance efficiently, the light may be reflected and condensed by a reflector.
[0150]
The polarization converter may be a polarization converter that includes a conventional polarization beam splitter array and a wave plate combined with each other, and that is efficiently converted into one polarization direction.
[0151]
Furthermore, when it is desired to improve the degree of polarization and ensure contrast performance, it is effective to improve the degree of polarization by inserting a linear polarizer after the polarization converter of incident light or using a polarizing beam splitter. . In particular, when a polarizing beam splitter is used, if it is a linear polarizer, it generates heat due to light absorption, which may reduce performance, but the polarizing beam splitter reflects or transmits unnecessary polarization components. Since it is not stored in the splitter, it is possible to suppress heat generation due to light absorption as much as possible. A plate-type polarizing beam splitter called a Wire-Grid Polarizer (grit polarizer) described in USP 6234634 may be used.
[0152]
Of course, such a polarizer may be arranged not only on the illumination lens side but also on the projection lens side. The grit polarizer may be used for optical path separation and synthesis of illumination light and projection light. The light condensing element as an optical system that efficiently illuminates the light valve is a light valve that is combined with a condenser element that reduces uneven illuminance irradiated to the light valve by combining a fly-eye lens called an integrator, and a condenser lens. It is possible to use a condensing element that efficiently guides the light.
[0153]
If necessary, it is possible to adopt a configuration in which a lens array is combined with a polarization beam splitter array pitch that constitutes a polarization converter. In addition, when a light source with high polarization such as a higher-power laser light source can be used as the light source, the polarization converter can be omitted.
[0154]
【The invention's effect】
As described above, according to the present invention, a novel projection apparatus can be realized. As described above, the projection apparatus of the present invention can effectively increase the contrast in the projection image.
[0155]
Further, the brightness of the projected image can be increased in preference to the contrast as necessary or desired.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining that, in a pair of wavelength selective retarders, flare light intensity in a projected image can be reduced by shifting one spectral characteristic to the short wavelength side with respect to the other spectral characteristic. is there.
FIG. 2 is a diagram for explaining a spectral characteristic shift effect of a wavelength selective retarder.
FIG. 3 is a diagram for explaining one embodiment of a projection apparatus.
FIG. 4 is a diagram for explaining another embodiment of the projection apparatus.
FIG. 5 is a diagram for explaining another embodiment of the projection apparatus.
FIG. 6 is a diagram for explaining another embodiment of the projection apparatus.
FIG. 7 is a diagram for explaining another embodiment of the projection apparatus.
FIG. 8 is a diagram for explaining another embodiment of the projection apparatus.
FIG. 9 is a diagram for explaining an example of an embodiment in which a polarizer can be removed from an imaging optical path in order to give higher priority to the brightness of a projected image.
[Explanation of symbols]
10 Wavelength selective retarder
12 Polarizing beam splitter
14 Dichroic prism
16 Light valve
18 Light valve
20 Light valve
22 Wavelength selective retarder
24 Polarizer
26 Projection lens

Claims (10)

A linearly polarized white illumination light is incident on the first wavelength-selective retarder, and among the light that has passed through the first wavelength-selective retarder, the wavelength band light having a changed polarization direction: A and the polarization direction are changed. Wavelength band light: NA is separated into two optical paths by a polarizing beam splitter,
One of the separated wavelength band lights: A is used as illumination light for the first light valve, and the other wavelength band light: NA is further separated into two colors of light: B and C by the color separation element. Light: B is illumination light to the second light valve, light: C is illumination light to the third light valve,
An image is displayed on the first to third light valves, and the illumination lights: A, B, C are image lights modulated in accordance with the image: LA, LB, LC, and these image lights are synthesized. Light: LT is a projection device that displays a color image by causing light to enter a polarizer through a second wavelength-selective retarder and projecting the light onto the screen by an imaging optical system through the polarizer.
The first wavelength-selective retarder and the second wavelength-selective retarder are elements having the same spectral characteristics or the same wavelength slide, and at least one of the first and second wavelength-selective retarders is used as a light beam optical path. A projection apparatus characterized by being arranged at an angle with respect to the projection apparatus. A linearly polarized white illumination light is incident on the first wavelength-selective retarder, and among the light that has passed through the first wavelength-selective retarder, the wavelength band light having a changed polarization direction: A and the polarization direction are changed. Wavelength band light: NA is separated into two optical paths by a polarizing beam splitter,
One of the separated wavelength band lights: A is used as illumination light for the first light valve, and the other wavelength band light: NA is temporally separated into two colors of light: B and C by temporal color separation means. Separated light: B and C are alternately used as illumination light to the second light valve,
An image for illumination light: A is displayed on the first light valve, and an image for illumination light: B, C is displayed on the second light valve in synchronization with temporal color separation of the temporal color separation means. Each of the illumination lights: A, B, C is converted into image lights: LA, LB, LC modulated according to the image, and the combined light: LT obtained by synthesizing these image lights is used as a second wavelength selective retarder. A projection device that displays a color image by being incident on a polarizer through the polarizer and projected on a screen by an imaging optical system through the polarizer,
The first wavelength-selective retarder and the second wavelength-selective retarder are elements having the same spectral characteristics or the same wavelength slide, and at least one of the first and second wavelength-selective retarders is used as a light beam optical path. A projection apparatus characterized by being arranged at an angle with respect to the projection apparatus. The projection apparatus according to claim 1 or 2,
The first and second wavelength selective retarders are elements that convert polarized light in the red band by 90 degrees, and one of the first and second wavelength selective retarders is arranged to be inclined with respect to the light beam optical path. Projection device characterized. The transmittance of T-polarized light and S-polarized light in the polarizing beam splitter: Tp and Ts in the projection device according to claim 3
Condition: Ts <1-Tp
Satisfied,
The first wavelength selective retarder is tilted with respect to the beam path,
A projection apparatus, wherein a P-polarized white illumination light is incident on a polarization beam splitter to a first wavelength selective retarder. The transmittance of T-polarized light and S-polarized light in the polarizing beam splitter: Tp and Ts in the projection device according to claim 3
Condition: Ts> 1-Tp
Satisfied,
The first wavelength selective retarder is tilted with respect to the beam path,
A projection apparatus, wherein S-polarized white illumination light is incident on a polarization beam splitter to a first wavelength selective retarder. The projection apparatus according to claim 1 or 2,
The first and second wavelength-selective retarders are elements that convert polarized light in the blue band by 90 degrees, and one of the first and second wavelength-selective retarders is disposed inclined with respect to the light beam optical path. Projection device characterized. 7. The projector according to claim 6, wherein the transmittances Tp and Ts of the P-polarized light and the S-polarized light in the polarizing beam splitter are:
Condition: Ts> 1-Tp
Satisfied,
The first wavelength selective retarder is tilted with respect to the beam path,
A projection apparatus, wherein a P-polarized white illumination light is incident on a polarization beam splitter to a first wavelength selective retarder. The projection apparatus according to claim 6.
Transmittance of P-polarized light and S-polarized light in the polarizing beam splitter: Tp and Ts
Condition: Ts <1-Tp
Satisfied,
The first wavelength selective retarder is tilted with respect to the beam path,
A projection apparatus, wherein S-polarized white illumination light is incident on a polarization beam splitter to a first wavelength selective retarder. 9. The projection apparatus according to claim 1, wherein an inclination angle of at least one of the first and second wavelength selective retarders with respect to the light beam optical path is variable. The projection apparatus according to claim 1 or 2,
A projection apparatus characterized in that a wavelength selective retarder tilted with respect to a light beam optical path is a first wavelength selective retarder.

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