JP4637370B2 - Optical system for forming modulated color images - Google Patents

Description

【００５６】
好適な実施の形態の本実施例は、第１クリーンアップ偏光子１９０としての染色Ｓ配向偏光子の前に、光源１７５としての水晶ハロゲン灯を含む。出力は、光学的スペクトル検光子（不図示）を用いて計測した。この実例は、フリースタンド(free-standing)反射防止（ＡＲ）コーティングされた要素を用いて組み立てられた。第１および第２リターダスタック１６０，１７０は、広域帯域反射防止コーティング窓部の間に接合されるとともに第１ビームスプリッタ１１０の入出力ポートに貼り付けられる圧力感応接着剤を有する。第２ビームスプリッタ１２０としての赤／青二色性鏡板は、Ｓ偏光光を受け入れるように、第１ビームスプリッタ１００のＰＢＳコーティングに平行に配置される。反射型変調器１３０，１４０，１５０は、５００ｎｍ（青色）、５６０ｎｍ（緑色）、６４４ｎｍ（赤色）における１／４波長リターデーションとなるようアルミ鏡にリターデーション薄板をかぶせることによって作成された。反射防止コーティングガラス窓部はリターデーションフィルム全体にわたっており、率整合(index match)をはかっている。反射型変調器１３０，１４０，１５０は、光学システム１００の適切な出力ポートに取り付けられた。第２クリーンアップ偏光子１９５を出射する再結合光は、光学スペクトル偏光子の入力と結合する。透過スペクトルは、各々のポートのパネルを物理的に回転し、かつ出力を記録することにより、発生させられた。最大の透過は約４５°配向で生じ、最小の透過は０°配向で生じて、前者を後者で正規化することによってコントラスト比のデータひと組を得た。各々の帯域の正確な絶対透過率が、３個の場が検知素子へ同時的に結合していく許容誤差のために、動作状態データからは抽出できないことは、当業者であれば直ちに理解される。図１１、図１２、図１３および図１４は、光学スペクトル検光子によって計測した本発明の好適な実施の形態による反射光学性の計測出力を示している。計測結果は明らかにイエローとシアン中のノッチを現している。軸上コンスタント比は、可視スペクトルにわたって高く、例えば約５００：１よりも大きい。
【００５７】
軸上の色域は、ＳＭＰＴＥ基準で要求される水準をはるかに上回っており、この好適な実施の形態は色域とシステム輝度を結合している。さらにより高い輝度でさえ、色座標を犠牲にすることによって、得ることが可能である。輝度を高くする好適な方策のひとつは、間原色光の非動作状態での漏れを増加させることを防止しつつ第１および第２リターダスタック１６０，１７０がより大きな遷移帯域の重なりとなるように設計することによって、第１および第２リターダスタック１６０，１７０の遷移勾配を大きくするか、または、ノッチ濃度を減らすことである。
【００５８】
輝度を高くする他の好適な方策は、第１と第２のリターダスタック１６０，１７０に対して異なるリターデーション値を用いることである。この設計は同じ波長に対して対称ではないので、シアンとイエローの中に異なるノッチ濃度を得ることができる。ある場合には、シアンノッチを完全に避けること、例えば５７８ｎｍの光を８０％−９０％遮断することにより、適切な色座標を得ることができる。ノッチの濃度はデューティ比(duty ratio)の相違によって決定され、ここでは、第１と第２リターダスタック１６０，１７０の間の緑色ノッチの相対幅と遷移勾配によって測られる。この実施例では、両スタックは隣接して積層された１４層の膜を含み、光源１７５の緑色線（５４５ｎｍ）とイエロー線（５７８ｎｍ）とを区別する遷移勾配を与えている。よってこの方策は、各々のノッチを高い程度でブロックするものとなる。
【００５９】
図１１および図１２に示されているように、第１リターダスタック１６０の緑色出力の最初の極小は、第２リターダスタック１７０のマゼンタ出力の最初の極小と一致し、したがって、マゼンタノッチの高濃な遮断がもたらされる。第２リターダスタック１７０のマゼンタ出力は、４９１ｎｍと６１９ｎｍで８５％の透過率である。
【００６０】
本発明の好適な実施の形態は、色光路を形成したり結合したりするのにリターダスタック（ＲＳ）技術を用いることで角度感応性を低減するという利点をも持っている。二色性鏡、コレステリックフィルムやホログラフィックフィルムなどのような、関連技術の色スプリッタは物理的に２個の光路を形成し、遷移帯域特性を決定している。ＲＳ１６０，１７０は色を偏光によってコード化しおり、それによって遷移帯域特性を決定することができるが、ＲＳ１６０，１７０は共線形伝搬場要素を物理的に分離しない。それで、光はスタックに実質的に垂直に入射し、それによって角度感応性が最小化される。したがって、各々のフィルムの光学軸が面内に沿っている場合には、垂直入射からの小さな逸れに対するリターダンス変動は角度について２次である。色光路を形成するために用いられている第１（ＰＢＳ）コーティングが実質的に傾けられているとしても（典型的には偏倚角が４５°）、この好適な実施の形態はシステムのｆ数にわたってニュートラル(neutral)な偏光効率を提供する。二つの機能を分けることで、角度感応性が非常に減少する。
【００６１】
さらなる角度感応性の減少は、この好適な実施の形態において、特殊化されたリターデーションフィルムを用いることによって実現される。実質的に小さな角度非感応性のリターデーションは、複合(compound)リターダ若しくは２軸性単一リターダのいずれかを用いることにより実現することができる。例えば、２軸性リターデーションフィルムは、高分子基板を面方向にとフィルム法線方向に沿った両方に引き伸ばすことによって作成することができる。フィルム法線方向に沿ったリターデーションが面方向リターデーションの実質的に半分であるときには、入射角に対する波長変動は実質的にささいなものになる。
【００６２】
非垂直の小さな逸れに対して、最大リターデーション変動は角度について４次である。このようなフィルムは、半強度点のスペクトル変動をささいなものにしてしまう。表２は、平行偏光子間の第２リターダスタックだけについての計測データを示している。支配的なスペクトルが、半頂角１５°に対して最大変動０．５ｎｍで赤方に変動することを結果は示している。個のような構成においては、第１ビームスプリッタ１１０（ＰＢＳ）は色分離能力の限界となる要因を代表する。
【００６３】
【表２】
５４５ｎｍにおけるリターダンスが１．５波長の１４層の第２リターダスタック１７０の角度に対する半強度点のスペクトル変動；４個の方位角が与えられている

【００６４】
コントラスト比の非軸上の計測は、図１８の構成で第２ビームスプリッタ１２０（二色性鏡）を取り除いたものを用いて、緑色光に対して行われた。準平行な(qusi-collimated)白色光は２５ｎｍＦＷＨＭで５５０ｎｍの透過帯域(bandpass)を用いてフィルタされた。光学強度計を用いて、Ｐ回転（ＰＢＳコーティング法線を含む平面内）およびＳ回転に対する角度の関数として強度が記録された。緑色パネルの配向が４５°で計測された強度によって正規化することによって、パネルの配向が０°の強度までコントラスト比を求めた。表３に与えられた結果は、コントラスト比が入射角に対して落ちていきながらも、妥当なｆ数にわたって高くありつづけており、視覚円錐(viewing cone)は極めて等方的である。
【００６５】
【表３】
入出力リターダスタックを用いた緑色光のコントラスト比

【００６６】
比較の目的のため、同一条件下でフィリップスプリズムが計測された。同一の手続きを行い、緑色スペクトルのコントラスト比が配向の関数として計測された。Ｐ回転の結果は許容できるコントラスト比であったものの、表４に示すように、Ｓ回転のコントラスト比は非常に劣化したものであった。
【００６７】
【表４】
フィリップスプリズムを用いた緑色光のコントラスト比

【００６８】
図１５は、本発明の他の好適な実施の形態による３パネル反射型光学システムを表す。この好適な実施の形態は、図４に関連する上述の特徴を含んでおり、さらに、光が反射型光学システムを通り抜けるときに光の強度を大きくするための第１および第２ダブラー(doubler)１１５，１２５も含む。第１および第２のダブラーは好ましくはインバータであって、強誘電性(ferroelectric)液晶ディスプレイのために光の強度を増大する。
【００６９】
図１５に示したように、光源１７５からの白色光は、第１クリーンアップ偏光子１９０によって偏光されて、第１リーダスタック１６０によって第１の原色が一つの偏光状態にかつその補色が直交偏光状態に沿うようにコード化される。第１の原色は、第１ビームスプリッタ１１０を透過し、分離された光路を平衡させるために使用される部分を経由する。第１の原色は第１光ダブラー１１５を透過した、第３反射型変調器１５０によって空間的に変調されて、第１光ダブラー１１５を透過され戻る。次に、第１の原色は第１ビームスプリッタ１１０によって反射されて、第２リターダスタック１７０、第２クリーンアップ偏光子１９５、および必要があれば第２凸レンズ系１８２を通ってシステムを出射する。
【００７０】
第１の原色の補色は、第１ビームスプリッタ１１０で反射されて、第２光ダブラー１２５を通過した後に第２と第３の原色に分割される。第２の原色は、色分離器１２０によって反射された後、第２反射型変調器１４０によって空間的に変調されて、第２光ダブラー１２５を透過するために色分離器１２０によって再び反射される。第３の原色は、色分離器１２０を透過し、第１反射型変調器１３０によって空間的に変調されて、色分離器１２０を再び透過する。第２と第３の原色は結合されて、第２光ダブラー１２５と、システム１００を第２リターダスタック１７０を通って出射するために第１ビームスプリッタ１１０とを透過する。第２リターダスタック１７０は、同じ偏光状態を有する結合された補色と第１の原色とを、第２クリーンアップ偏光子１９５と第二凸レンズ系１８２を通じて、透過させる。
【００７１】
コントラスト比を向上するために、図４の実施の形態の中間リターダスタックがビームスプリッタ１１０と色分離器１２０の間に位置していてもよい。
【００７２】
図１６は、本発明のさらに他の好適な実施の形態による光学システム２００を表し、第１、第２、第３および第４偏光ビームスプリッタ２０５，２１０，２１５，２２０と、第１、第２、第３および第４リターダスタック２６０，２６５，２７０，２７５を含んでいる。この実施例において、以下、第１、第２および第３の原色はそれぞれ青色、赤色および青色とする。これらの色は例示のためのものであって、当業者に容易に理解されるところによりこれらの色の順序は所望のものに変えることができる。
【００７３】
光源１７５からの白色光は、第１リターダスタック２６０によって、青色光が一つの偏光状態に沿いその補色のイエロー光が直交偏光状態に沿うように偏光される。第１偏光ビームスプリッタ（ＰＢＳ）５２０は青色を透過させ、かつ、イエローを反射する。第２リターダスタック２６５は、赤色／シアンまたは緑色／マゼンタのリターダスタックであって、赤色を一つの偏光状態にかつ緑色をその直交偏光状態にコード化する。第１および第２反射型変調器１３０，１４０はそれぞれ赤色光と緑色光を変調する。その後、第２ＰＢＳ２１０は赤色光を透過させかつ緑色光を反射する。第３リターダスタック２７０は、赤色および緑色光を第３ＰＢＳ２１５によって第４リターダスタック２７５を通過する一つの偏光状態へと再結合される。第４ＰＢＳ２２０は、第１ＰＢＳ２１５からの青色光を第３反射型変調器１５０へと透過し、この第３変調器は青色光を変調して第４ＰＢＳ２２０へと反射し返す。第４ＰＢＳ２２０は青色光を第３ＰＢＳ２１５へ反射し、第３ＰＢＳが青色光を第４リターダスタック２７５へ反射する。第４リターダスタック２７０は、すべての三原色、赤色、緑色および青色を同じ偏光状態へと回転して、その結合スペクトルを出力する。
【００７４】
本発明の好適な実施例による色分離および結合構造ならびに方法は、リターダスタックと中性偏光スプリッタを用いて別個の色光路を形成するものである。これは反射型別光路投映器に用いられ、特にシリコンディスプレイ上の反射型液晶に適用される。リターダスタック（ＲＳ）技術は、偏光によって色の分離を行うために用いられる。直交する偏光状態から物理的に別の光路を形成する構造と結びついて、色分割が実現される。リターダスタックは、平坦な透過帯域(passband)および阻止帯域(stopband)特徴と、狭い遷移帯域幅と、低い色クロストークとを発生する。関連技術の二色性ビームスプリッタとは違い、ＲＳ技術は偏光性に基づいている。これは色と偏光の両方の処理をここに記載したように簡便な構成にまとめた投映器で行うことを可能にする。
【００７５】
以上の実施の形態は、単に説明のためのものであって、本発明の限定を構成するものではない。本発明の教示は、他の型の装置にも容易に適用することができる。本発明の記載は説明することを意図としており、特許請求の範囲を限定するものではない。幾多の置換、改良、変形、は当業者にとって明らかである。例えば、第２ビームスプリッタが第1ビームスプリッタ１００で反射された光に作用するか、第1ビームスプリッタを透過した光に作用するか、のいずれでもよいことは当業者には容易に理解される。特許請求の範囲において、機能手段節(means-plus-function clause)は言及された機能を実行する個々に記載された構造と、構造的均等物のみならず、均等の構造物をも含むことが意図されている。
【図面の簡単な説明】
本発明を、以下の図を参照することにより詳細に説明する。図において同じ参照番号は、同じ構成要素を指している。
【図１】図１（ａ）および図１（ｂ）は、関連技術の反射型ディスプレイの構成を表し、ここで単一偏光の光は第１ポートを通って導入され、かつ第２ポートを通って反射型ＬＣＤパネルへ向かって透過されることを示す。
【図２】 図２は、本発明の好ましい実施の形態による、リターダスタックおよびＰＢＳ偏光色スプリッタを示す。
【図３】 図３は、本発明の他の好ましい実施の形態による、光学システムを表す。
【図４】 図４は、本発明のさらに他の好ましい実施の形態による、３パネル反射型ディスプレイシステムを含む光学システムを表す。
【図５】 図５は、本発明のさらに他の好ましい実施の形態による、他の３パネル反射型ディスプレイシステムを含む光学システムを表す。
【図６】 図６は、図５の３パネル反射型ディスプレイシステムの等価展開配置で、反射型ディスプレイシステムが非動作状態(off-state)にあることを表す。
【図７】 図７は、図５の３パネル反射型ディスプレイシステムの他の等価展開配置で、反射型ディスプレイシステムが非動作状態(off-state)にあることを表す。
【図８】 図８は、図５の３パネル反射型ディスプレイシステムの等価展開配置で、反射型ディスプレイシステムが動作状態(on-state)にあることを表す。
【図９】 図９は、図５の反射型ディスプレイシステムに対する遷移帯域(transition band)を表す。
【図１０】 図１０は、図５の反射型ディスプレイシステムが非動作状態にある場合の、当該反射型ディスプレイシステムを通る光漏れを示す。
【図１１】 図１１は、図５の反射型ディスプレイシステムの測定出力を示す。
【図１２】 図１２は、図５の反射型ディスプレイシステムの測定出力を示す。
【図１３】 図１３は、図５の反射型ディスプレイシステムの測定出力を示す。
【図１４】 図１４は、図５の反射型ディスプレイシステムの測定出力を示す。
【図１５】 図１５は、本発明による、図１４に示す光学システムの変形例を表す。
【図１６】 図１６は、本発明の他の好ましい実施の形態による、３パネル反射型ディスプレイシステムを含む光学システムを表す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to image formation. The present invention particularly relates to an optical system using a color selective polarizing element for forming a color image.
[0002]
[Prior art]
Related art optical projection systems use transmissive thin film transistor (TFT) liquid crystal display (LCD) panels. Multi-layer deposited thin film dichroic beam splitters that are tilted with respect to the axis of incident light have been used to create physically separate paths. Each of these optical paths corresponds to a part of the spectrum of the additive primary color band of red, green, and blue (RGB). The LCD in each light path controls the level of locally transmitted light in a particular primary color band. The modulated or imagery light is recombined with an isotropic coating and a full color image is projected onto the front or near projection screen.
[0003]
In transmission mode, the LCD is placed between crossed polarizers so that a high contrast ratio is obtained for most LC electro-optic modes. In the reflective mode, light is incident on the LCD panel substantially perpendicularly, but as a similar arrangement, as described in the parent application incorporated above by reference, a polarizing beam splitter (PBS) is directly connected to the panel. Make sure it is in front.
[0004]
One type of polarizing beam splitter is a tilted thin-film stack having four ports that reflects and transmits the light spectrum based on its polarization. The PBS ideally functions as a broadband reflection element for a light spectrum polarized along one axis and as a transmission element for a light spectrum polarized along an orthogonal axis. A dichroic beam splitter ideally reflects or transmits a light spectrum based only on the frequency of the light.
[0005]
The full-color optical path type projector includes a plurality of reflective LCD panels, a plurality of dichroic beam splitters for creating three color optical paths, a polarizing beam splitter for each reflective LCD panel, and a convex lens. It is also possible to use further optical elements for recombining the images before. This is cumbersome and expensive.
[0006]
Instead, a single polarizing beam splitter is used, followed by a Philips prism to separate and combine the three color optical paths. In this configuration, the color separation / combination structure is effectively disposed between the polarizer and the analyzer. It is an advantage from the standpoint of the number of components that the light paths of the three colors share the same PBS.
[0007]
[Problems to be solved by the invention]
However, it is required for the high contrast ratio that the Philips prism maintain the polarization of the input state for each color optical path so that the light efficiently exits the port. This condition must be maintained such that the contrast ratio over the f-number of the system is on average 100: 1 and ideally exceeds 200: 1. A clean-up polarizer and, in some cases, additional polarizing optics, such as a quarter wave plate, provides a contrast ratio between the LCD panel and the prism. Used to improve.
[0008]
In the Philips prism, red and blue are first reflected by the dichroic coating and then total internally reflected (TIR) before entering the LCD. The modulated polarized light then returns along the same optical path. The spectral characteristics of this dichroic coating are strongly dependent on the angle of incidence and cause substantial cross-talk between the color channels. To help solve the crosstalk problem, a “double notch” filter (DNF) is often inserted that substantially blocks mid-band light such as True Cyan and True Yellow. This DNF is also a multi-layer coating, but since it is used near normal incidence, changes to the angle of incidence are less sensitive. Even if averaged over the f-number of the system, the light density at the notch is small.
[0009]
Thus, the related art three-panel reflective projection system uses PBS, DNF and Philips prisms, each consisting of three prisms, two of which have a dichroic mirror coating. In order to improve the operability of a transmissive system using a reflective LCD panel, there is a need for a configuration that reduces the cost and complexity while improving the contrast ratio and throughput.
[0010]
In the related art, multilayer thin film coatings are used for color manipulation in the projection system. This technique meets the requirements for high efficiency and high power operation of projection. Furthermore, a steep transition slope desired to maximize brightness can be achieved while meeting the criteria of color coordinates. However, the gradient isotropic coating reduces the polarizing property, particularly in a system having a small f-number. In LCDs, the polarization must be accurately maintained in order to reduce dark state leakage. Furthermore, dichroic mirrors have an angle sensitive half-power wavelength that varies substantially with the angle of incidence.
[0011]
In order to create a physically separate optical path using a dichroic mirror, the layer is often substantially tilted with respect to the axis of incident light. This significantly increases the spectral variation due to small angular deviations relative to the deflection angle. In the worst case, when the deflection angle is 45 °, the wavelength (spectrum) variation is approximately linear with respect to the angle change.
[0012]
Essentially, the apparent thickness of each layer of the thin film stack decreases with the non-normal incidence angle, resulting in a blue shift in the spectrum. If there is a declination angle, there will be both blue and red shifts in the plane of incidence. Such angular sensitivity limits the f-number of color manipulation systems, particularly LCD projectors.
[0013]
A reflective silicon display panel is very well known as a related technology. The most well known reflective silicon display panel is a VLSI active matrix panel that has been processed to have a high fill ratio or flat fill ratio and high visible reflectivity. Alternatively, the polysilicon panel can be made to function as a reflective display. In a VLSI panel, a thin liquid crystal film is sandwiched between a silicon chip and a cover glass covered with a transparent conductor, typically indium tin oxide (ITO). The liquid crystals can be either nematic or smectic materials, both of which are well supported by documents in the field. Liquid crystals are anisotropic media and respond to an electric field by changing their orientation. This changes the polarization state of the light propagating through the liquid crystal.
[0014]
1 (a) and 1 (b) illustrate a related art reflective display configuration in which light in a single polarization state is incident. As shown in FIG. 1 (a), light enters the polarizing beam splitter (PBS) 10 through the first port 12, and then reflects off the second port 14 toward the reflective LCD panel 20. The LCD panel 20 reflects the light back, passes through the second port 14 and the PBS 10, and the light exits from the third port 16. In FIG. 1 b, light enters PBS 10 through third port 16, passes through PBS 10, and exits second port 14. The LCD panel 20 reflects light back through the second port 14, and the light is reflected by the PBS 10 and exits from the first port 12.
[0015]
The polarization state of the reflected light is locally modulated by the voltage-dependent distribution of LC molecules in each pixel of the LCD panel 20. This polarized image is converted to an actual gray shade image using an analyzer. In a retroreflective arrangement as shown in FIGS. 1 (a) and 1 (b), light is introduced and analyzed using PBS 10. FIG. This PBS 10 will effectively position the LCD panel 20 between the intersecting polarizers, allowing light to pass through the system and ultimately to the convex lens.
[0016]
[Means for Solving the Problems]
The present invention is directed to substantially solving one or more problems arising from the limitations and disadvantages of the related art.
[0017]
Another object of the present invention is to improve the contrast ratio and the throughput of the reflective LCD system, and at the same time suppress the complexity and cost.
[0018]
Another object of the present invention is to reduce the f-number of the color manipulation system while maintaining the contrast ratio.
[0019]
In commonly owned U.S. Pat. No. 5,751,384, the entire contents of which are hereby incorporated by reference, create separate color light paths and combine the separate color light paths to form a single light path. Thus, it has been found that a retarder stack can be used in combination with a neutral polarization splitter. This technique has its own advantages, particularly with respect to angular sensitivity.
[0020]
The present invention converts a first spectrum of incident light from a light source along a first polarization state, and converts a second spectrum of the incident light from the light source into a second polarization state different from the first polarization state. An input retarder that transforms along, a first beam splitter that is optically coupled to the input retarder and that transmits the first spectrum as a transmission spectrum, and a second beam splitter that reflects the second spectrum as a reflection spectrum; Can be realized in whole or in part by an optical system having a beam splitter including
[0021]
The present invention is also entirely based on a system that splits incident light from a light source into red, green and blue component color bands by passing each color through a physically different light path. Or it can implement | achieve partially. At least two of these optical paths are formed by a stacked retardation film and a polarizing beam splitter (PBS). By creating different optical paths, each color band can be processed independently. According to a preferred embodiment of the present invention, such processed light can be combined to form a single optical path, again using a retarder stack (RS) and PBS. The present invention is particularly suitable for a projector using a reflective liquid crystal in a silicon display panel.
[0022]
The present invention can be realized in whole or in part by combining the operations of color and polarization in order to manufacture another optical path type projector having a simple structure based on the reflective display panel. A retarder stack (RS) element forms an orthogonally polarized primary color from a polarized input. In this illustrative embodiment, all four ports of the PBS are used and the PBS functions as a color splitter. A dichroic beam splitter can be used to further divide the port containing the subtractive primary color band. In one embodiment of this reflection type, all three optical paths are recombined and analyzed by the input PBS. A full color image can also exit from a fourth port of PBS that has not been used so far. Thus, a full color projector according to the present invention will require only one PBS coating and one dichroic color-splitting coating with one or two retarder stacks.
[0023]
The present invention can also be realized in whole or in part by improving the polarization operation associated with the color optical system in order to obtain a high contrast ratio. In connection with the dichroic splitter, due to the low angular sensitivity presented by the retarder stack of the present invention, the projector of the present invention also has a high contrast ratio as a result.
[0024]
The present invention can also be implemented in whole or in part by providing a wide color gamut with minimal hardware. It is an aspect of the present invention that it has been found that an exit retarder stack that handles light leakage from a PBS can also be used to perform an inter-band notch filtering operation. Auxiliary notch filters are often used in related art systems that use Philips prisms, which eliminates the need for them. Using separate input and exit retarder stacks, the inter-primary light, such as that generated by a metal halide lamp, is reduced or reduced by this clean-up polarizer. Can be erased. This eliminates the need for a separate double notch filter (DNF).
[0025]
The invention can also be realized in whole or in part by providing an optical system that exhibits high overall throughput or brightness, such as a reflective LCD projector. This is achieved by manipulating the color band by laminating a lossless polymeric retarder film, matching the reflectance between the retarder films, and minimizing the number of high loss polarizers. . It is further achieved by eliminating the need for an auxiliary filter to remove interprimary light.
[0026]
Additional advantages, objects and features of the invention will be set forth in part in the description which follows and will be apparent to those skilled in the art upon attempting to practice the invention or may be learned from the practice of the invention. . These objects and advantages of the invention will be realized and attained as particularly pointed out in the appended claims.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described in detail below with reference to the drawings. The same reference numbers in the figures represent the same or similar components in each figure. “Retarder”, “retarder stack”, “spectrum”, “complementary spectrum”, “spatial light modulator”, “doubler”, etc. The various elements and terms are described and / or defined in the original application. That is, such terms in this description are used to correspond to the meanings set forth in these original applications. FIG. 2 shows a polarization color separator 45 that can produce two polarization color paths in accordance with a preferred embodiment of the present invention. The polarization color separator 45 includes a retarder stack (RS) 30 and a polarization beam separator (PBS) 40. Details of the construction and operation of the retarder stack 30 are apparent in the original application incorporated by reference above.
[0028]
In operation, polarized incident light from a light source (not shown) is directed to the retarder stack 30. An optional polarizer 50 can be used when the incident light is not polarized or to increase the contrast ratio of the polarized incident light. This retarder stack 30 accepts polarized incident light, converts the polarization of one primary color into one polarization state S (λ), and converts the polarization of its complementary color into an orthogonal polarization state (1-S (λ)). To do. In the embodiment shown in FIG. 2, the PBS 40 is oriented so that the complementary color is reflected by the PBS 40 and its primary color is transmitted through the PBS 40.
[0029]
FIG. 3 depicts a projection system 55 according to one embodiment of the present invention. The projection system 55 includes input / output retarder stacks 60, 80, reflective spatial modulators 65, 75, PBS 70, and a cleanup polarizer 90. In the present embodiment, these reflective spatial modulators 65 and 75 are liquid crystal spatial modulators. However, as will be understood by those skilled in the art, any reflective spatial modulator may be employed in this embodiment and in the embodiments described below that show reflective liquid crystal spatial modulators for illustrative purposes. In operation, at least partially polarized incident light propagates through the input retarder stack 60 so that the input retarder stack 60 follows a primary color in one polarization state and a polarization state orthogonal to its complementary color. Polarize.
[0030]
Retarder stacks 60 and 80 are optically coupled to the polarizing beam splitter. As used herein, the expression “optically coupled” means that light that has passed through or reflected from one optical element is incident on the next optical element directly or through one or more intermediate optical elements. It refers to all configurations. For the retarder stack 60, light transmitted through this stack enters the PBS 70 through the first port, and the first one of the colors is reflected by the PBS 70 through the second port. The polarizing beam splitter of the present invention is capable of splitting light into different polarizations, in particular, capable of splitting light into orthogonal polarization states and directing them along a substantially orthogonal output optical path. It is selected from all elements that can be attached.
[0031]
The primary color spectrum is modulated and reflected by the LCD 65 through the second port, enters the PBS 70, and is output from the third port. The complementary color spectrum is transmitted through the fourth port through the PBS 70, modulated by the LCD 75, and reflected back toward the PBS 70. The PBS 70 reflects the complementary color spectrum, and the complementary color spectrum is emitted from the third port together with the primary color spectrum. Light propagates through an output retarder stack 80 that encodes both the primary color spectrum and the complementary color spectrum along the same polarization state. The cleanup polarizer 90 then polarizes the light to improve the contrast ratio and block crosstalk light before output.
[0032]
FIG. 3 shows that PBS leakage can be minimized by placing the output retarder stack 80 at the exit port. This restores the desired light to a single polarization state, so that the cleanup polarizer 90 blocks all crosstalk light.
[0033]
FIG. 4 represents an optical system 100 according to yet another preferred embodiment of the present invention. The system 100 includes a first beam splitter 110, a color separator 120, first, second and third reflective modulators 130, 140, 150, first and second retarder stacks 160, 170, First and second clean-up polarizers 190 and 195, a polarization conversion array 185, first and second optical lenses 180 and 182, and a light source 175 are included. Independent lenses 108 and 182 are schematically depicted in FIG. 4, but these lenses are simply focused so as to include one or more optical elements as is known in the art. It is understood that it represents an optical system of collimating and projection. In general, any optical system capable of focusing and projecting can be used as elements 180 and 182. In this embodiment, the beam splitter 110 is a PBS that transmits or reflects light based on its polarization, and the color separator 120 typically transmits or reflects light based on its wavelength. A dichroic beam splitter. Furthermore, the first, second, and third reflective spatial modulators 130, 140, and 150 in this embodiment are selected from liquid crystal modulators, and can be nematic on silicon, FLC on silicon, or the like. The light source 75 is an incandescent lamp, a laser, a light emitting diode (LED), an ultra high pressure metal halide lamp (UHP), an ultra high pressure mercury lamp, a fusion lamp, and other light sources.
[0034]
In FIG. 4, the light from the light source 175 can be collimated and converted by the polarization conversion array 185 before being polarized by the first cleanup polarizer 190. The first retarder stack 160 encodes the first primary color along one polarization state and the complementary color along the orthogonal polarization state. In this embodiment, the beam splitter 110 reflects this complementary color and transmits its primary color. The color separator 120 separates the reflected complementary color into second and third primary colors, and the separated second and third primary colors are separated by the first and second reflective modulators 130 and 140. Modulated. The first primary color is spatially modulated by the third reflective modulator 150. The first, second and third primary colors are spatially modulated by the polarization of light in accordance with the image information supplied from each reflective modulator 130, 140, 150.
[0035]
This separated light is then recombined. The spatially modulated second primary color light passes through the color separator 120 and the beam splitter 110, respectively. The spatially modulated third primary color light is reflected by the color separator 120 and passes through the first beam splitter 110. The spatially modulated first primary color light is reflected by the first beam splitter 110. The second and third primary color lights are recombined to create a spatially modulated complementary color and pass through the second retarder stack 170 along with the spatially modulated first primary color. The second retarder stack 170 rotates the S-polarized first primary color into P-polarized light and does not affect the P-polarized spectrum of the complementary color. Thereby, the first primary color spectrum and the complementary color spectrum are integrated into a modulated white light passing through the second cleanup polarizer 195 and then output through the optical projection lens 182. Each primary color of the modulated white light has an equal path length through the system 100.
[0036]
FIG. 5 represents an optical system including another three-panel reflective display system according to yet another preferred embodiment of the present invention. FIG. 6 represents an equivalent deployment configuration in the off-state of the three-panel reflective display system of FIG. 5 for easy tracking of polarization. It should be understood that in all of these drawings, the same components are identified by the same reference numerals. Therefore, repeated explanation is omitted here for the sake of brevity.
[0037]
In FIG. 5, incident white light from a light source may be linearly polarized using a polarization conversion array (not shown) to increase efficiency, or may be polarized by a cleanup polarizer (not shown). The first retarder stack 160 is here an input green / magenta (IGM) stack, and allows incident white light to pass along with blue and red light and orthogonally polarized green light. In this embodiment, green light is P-polarized and exits the IGM, and reverse spectrum or complementary magenta light is S-polarized. In this embodiment, since the beam splitter 110 is a PBS, it transmits only green light and reflects magenta light.
[0038]
In the non-operating (dark) state shown in FIG. 6, light is reflected from the reflective modulators 130, 140, and 150 without changing the polarization state (SOP) as follows. These reflective modulators are red, blue and green LCDs in this embodiment, respectively. Red and blue light are separated by a color separator. This color separator is a dichroic splitter in this embodiment. Blue B and true cyan C are reflected to the second reflective modulator (blue LCD) 140, and true yellow Y and red R are transmitted to the first reflective modulator (red LCD) 130. The reflected light returns without changing the SOP and is recombined by the color separator 120. The light returning to the beam splitter 110 maintains S polarization and is therefore efficiently reflected by the beam splitter 110. As a result, all the light is emitted from the input port, and the contrast ratio is very high in the approximation at this stage.
[0039]
In practice, the first beam splitter 110 has a finite polarization efficiency. In many cases, the leakage of P-polarized light into the S port is 10 times greater at normal incidence than the leakage of S-polarized light into the P port.
[0040]
Important green light reflected by the first beam splitter 110 (ε _p = 2-4%) and trivial light from the reverse spectrum transmitted by the first beam splitter 110. In fact, for an f-number with an incident angle as small as ± 12 °, ε _p = 40%. Thus, a cleanup polarizer 195 is required to maintain the contrast ratio over a typical projection f number.
[0041]
FIG. 7 shows ε when the system of FIG. 5 is in the dark (non-operating) state. _s Is ε _p Represents light leakage through the system under the assumption that it can be ignored. In the non-operating state, the first beam splitter 110 is (1-ε _p ) Is reflected by the third reflective modulator 150 without changing the SOP. This is analyzed by the first beam splitter, and ε _p (1-ε _p ) Leaks to the output port. Ε reflected by the first beam splitter 110 _p Green incident light is split by a color separator (dichroic splitter) and returned by the first and second reflective modulators 130 and 140 without changing the SOP.
[0042]
The green reflected light reflected by the first beam splitter (PBS) 110 is then combined by the dichroic splitter and returned to the PBS 110. This P-polarized light is ε by PBS110. _p (1-ε _p ) Leaks and combines with leaks from other parts of the system. Due to the lack of system coherence, these components are combined on an essentially a power basis. It is assumed that light consisting of the reverse spectrum (complementary color) is efficiently reflected by PBS 110 and contributes relatively little to the contrast ratio of the system.
[0043]
According to the example in this preferred embodiment, in order to keep the constant ratio high, in addition to the clean-up polarizer 195 crossing the input polarizer, here a second output green / magenta (OGM) stack. A retarder stack 170 is located at the exit port. The second retarder stack 170 converts the P-polarized light transmitted by the PBS 110 into S-polarized light without affecting the blue and red colors. The green leak is then blocked by the cleanup polarizer 195.
[0044]
FIG. 8 is an equivalent deployment of the three-panel reflective display system of FIG. 5 and shows that the reflective display system is in a white (on) state. The light propagation of FIG. 8 is performed because the first, second and third reflective modulators 130, 140, 150 modulate and polarize the light so that it is orthogonal to the SOP of the incident light. Is different. The spectrum reflected by the first reflective modulator 130 passes through the color separator 120, which in the preferred embodiment is a dichroic beam splitter, and is then reflected by the second reflective modulator 140. Combined with the resulting spectrum. This combined spectrum is a complementary color of the first primary color and is transmitted through the first beam splitter 110, the second retarder stack 170, and the second cleanup polarizer 195. The spectrum reflected by the third reflective modulator 150 is reflected by the first beam splitter 110 and combined with the complementary color combined spectrum. This primary color spectrum is then polarized by the second retarder stack so that its SOP matches the complementary color SOP and exits the system.
[0045]
In the preferred embodiment, R and Y light is modulated by a red LCD (first reflective display 130) and B and C light is blue LCD (second reflective display). 140). In this embodiment, all four colors enter the first beam splitter 110 in the P-polarized regression path. The first beam splitter 110 reflects all S-polarized green light and transmits all P-polarized (BCYR) light.
[0046]
In this preferred embodiment example, the second retarder stack 170 (OGM) is different in design from the first retarder stack 160 (IGM). The OGM has a wider magenta notch than the IGM so that a substantial portion of the intensity in the C and Y bands is rotated 90 °. So, OGM has the dual function of demodulating the green light SOP, to maximize the contrast ratio and to discard the C and Y band parts to improve the color gamut. ing.
[0047]
In this preferred embodiment example, the green light does not pass through a tilted isotropic coating in the optical path between the first beam splitter 110 and the third reflective modulator 150. This maximizes the contrast ratio of green light, which has the greatest impact on the degree of system contrast ratio. In the series of optical paths of the related art Philips prism, green light is efficiently transmitted through four tilted isotropic stacks. In the Philips prism, as a result, loss occurs with respect to the reproducibility of the polarization, particularly for light rays that are not in a plane that includes the stack normal direction (S rotation).
[0048]
In the example of this preferred embodiment, the light reflected from the first beam splitter 110 is here preferably a dichroic splitter (designed to have a green half-power point ( It enters the color separator 120 which is a mirror. Element 120 separates and combines blue and red light. By removing the green light from this port, the performance required for the color separator 120 is relaxed, but no light is present in the transition band, so the transition band characteristics are not established. . As such, the degree of spectral transition is small, so the crosstalk between the first and second reflective modulators 130, 140 (red and blue LCD) is relatively small and hence the loss of color performance is Relatively small. The polarization-modulated light from the first and second reflective modulators 130 and 140 is recombined by the element 120 and then analyzed by the beam splitter 110.
[0049]
The color separator is typically a dichroic splitter that functions as a color selective mirror that substantially reflects all of one primary color band and substantially transmits all of its complementary color bands. Although often steep, there is a finite transition band with both transmitted and reflected spectral element portions. Since this mirror is tilted with respect to the axis of the incident light, this dichroic splitter can be considered to have a linear eigenstate. This characteristic can be determined by examining transmitted / reflected fields with polarization parallel and perpendicular to the plane of incidence. Polarized light projections along both eigenstates cause such collinearly propagating fields retardation and consequently affect the SOP. Dichroic mirrors typically have non-overlapping S and P polarization transition bands. This separation depends on the central wavelength, the specific stack design and the angle of incidence. Beyond this transition band, substantially all the light is reflected or transmitted, but this configuration does not affect the degree of polarization. In a band that separates the two transmission spectra, this configuration acts like a polarizing beam splitter.
[0050]
During the operating state, the LCD rotates the light by 90 °, but light of a wavelength such that the dichroic splitter reflects S-polarized light and transmits P-polarized light is rejected at the fourth port of the dichroic splitter. This results in a notch that can improve the color coordinates in principle. However, if this band erodes the primary color band at an angle within the f number of the system, substantial transmission loss results.
[0051]
According to a preferred embodiment of the present invention, to minimize the transition bandwidth for the combined spectrum of S and P, the dichroic splitter is substantially zero polarizing properties (10 at half intensity point). -15 nm separation), thereby maximizing the throughput of blue and red light with minimal f-number. As described above, in this embodiment, the first retarder stack 160 (IGM) encodes green in one polarization state and magenta along the orthogonal polarization state. The first beam splitter 110 as a polarizing beam splitter then transmits green light and reflects magenta, thereby removing the green spectral portion from the port included in the second (dichroic) splitter 120. As shown in FIG. 9, which represents the transition band of the preferred embodiment of FIG. 5, this dichroic splitter transition band is green so that the angular sensitivity does not affect the chrominance of each output. Located in. In order to keep the blue (or red) reflectivity and the red (or blue) transmission high over the entire f-number of the system, a suitable dichroic splitter has a half-intensity point located substantially in the center of this band. Have.
[0052]
Since there is no additional filter, light entering the transition band of the first and second retarder stacks 160 and 170 is shared between the two ports of the first beam splitter 110 as shown in FIG. Is done. Since the IGM and OGM stack designs are made independently, their interaction can produce the desired color operability. In accordance with a preferred embodiment of the present invention, the polarization of light generated with a strong source emission such as 578 nm is controlled to maximize the contrast ratio of the system. This interaction is illustrated in the following example where the same stack is used for both input and exit ports. At a half-intensity point of the retarder stack, for example at a wavelength in the yellow band, the intensity is ideally divided equally by the first PBS beam splitter 100. The SOP generated by this stack is 45 ° linear polarization, but any SOP with equal projection along the PBS eigenpolarizations is possible. As shown in FIG. 10, P-polarized light leaks into the output port of the PBS 110 from both the green and magenta ports. In this case, the second retarder stack 170 rotates the light leakage to a non-optimum 45 °. Thereby, substantially half of the light leakage passes through the clean-up polarizer. The contrast drops rapidly to about 10: 1 at this wavelength.
[0053]
To overcome this limitation, the contrast ratio is maximized by fabricating first and second retarder stacks that suitably handle the SOPs of inactive light leaking through the first PBS beam splitter (110). . One strategy to increase the contrast is to add a film to raise the transition slope and keep the transition band away from intense light source emission. A preferred strategy is to create the first retarder stack 160 (IGM) so that its transition band does not overlap the second retarder stack 160 (OGM) transition band. Since the S-polarized light maintains a constant ratio, the spectrum is separated by the stack 170 (OGM) to the extent that the P-polarized leakage typically rotates, for example, about 90 °. In the preferred embodiment, the first and second retarder stacks 160, 170 are zero-overlap.
[0054]
An example of a full-color three-path projector according to a preferred embodiment describes both contrast ratio and color enhancement. The orientation of the first and second retarder stacks is shown in Table 1 for both stacks using z-stretched (Nz = 0.5) polycarbonate film. The orientation of both stacks is symmetric about the same wavelength, so the cyan and yellow notch characteristics are essentially the same. The retardation is 1.5 wavelengths at 545 nm, preferably 535 nm. Although the red color is slightly deviated from the optimum, the interaction between the stacks is invariant to the wavelength, and this example represents this embodiment.
[0055]
[Table 1]
Orientation of first retarder stack 160 (IGM) and second retarder stack 170 (OGM) to provide 1.5 wavelength at 545 nm

[0056]
This example of the preferred embodiment includes a quartz halogen lamp as the light source 175 before the dyed S-oriented polarizer as the first cleanup polarizer 190. The output was measured using an optical spectrum analyzer (not shown). This example was assembled using free-standing anti-reflective (AR) coated elements. The first and second retarder stacks 160 and 170 have a pressure sensitive adhesive that is bonded between the wideband anti-reflective coating window and affixed to the input and output ports of the first beam splitter 110. The red / blue dichroic end plate as the second beam splitter 120 is arranged in parallel to the PBS coating of the first beam splitter 100 so as to receive S-polarized light. The reflective modulators 130, 140, and 150 were created by covering a retardation thin plate on an aluminum mirror so as to obtain a quarter wavelength retardation at 500 nm (blue), 560 nm (green), and 644 nm (red). The anti-reflective coating glass window spans the entire retardation film and is index matched. Reflective modulators 130, 140, 150 were attached to the appropriate output ports of optical system 100. The recombined light exiting the second cleanup polarizer 195 combines with the input of the optical spectral polarizer. The transmission spectrum was generated by physically rotating the panel of each port and recording the output. Maximum transmission occurred at about 45 ° orientation and minimum transmission occurred at 0 ° orientation, and a set of contrast ratio data was obtained by normalizing the former with the latter. Those skilled in the art will readily appreciate that the exact absolute transmittance of each band cannot be extracted from the operating state data due to the tolerance that the three fields are simultaneously coupled to the sensing element. The 11, 12, 13 and 14 show the reflected optical measurement output according to the preferred embodiment of the present invention as measured by an optical spectrum analyzer. The measurement results clearly show notches in yellow and cyan. The on-axis constant ratio is high across the visible spectrum, for example greater than about 500: 1.
[0057]
The on-axis color gamut is well above the level required by the SMPTE standard, and this preferred embodiment combines the color gamut and system brightness. Even higher brightness can be obtained by sacrificing color coordinates. One suitable measure to increase the brightness is to prevent the first and second retarder stacks 160 and 170 from overlapping a larger transition band while preventing an increase in leakage of inter-primary light in a non-operating state. By designing, the transition slope of the first and second retarder stacks 160, 170 is increased or the notch concentration is decreased.
[0058]
Another suitable measure to increase the brightness is to use different retardation values for the first and second retarder stacks 160,170. Since this design is not symmetric for the same wavelength, different notch densities can be obtained in cyan and yellow. In some cases, proper color coordinates can be obtained by avoiding cyan notches altogether, for example by blocking 80% -90% of 578 nm light. The density of the notch is determined by the difference in duty ratio, here measured by the relative width of the green notch between the first and second retarder stacks 160, 170 and the transition slope. In this example, both stacks include 14 layers stacked adjacent to each other to provide a transition gradient that distinguishes the green line (545 nm) and yellow line (578 nm) of the light source 175. This strategy thus blocks each notch to a high degree.
[0059]
As shown in FIGS. 11 and 12, the first minimum of the green output of the first retarder stack 160 coincides with the first minimum of the magenta output of the second retarder stack 170, and thus the high density of the magenta notch. Will be cut off. The magenta output of the second retarder stack 170 has a transmittance of 85% at 491 nm and 619 nm.
[0060]
The preferred embodiment of the present invention also has the advantage of reducing angular sensitivity by using retarder stack (RS) technology to form and combine color optical paths. Related art color splitters, such as dichroic mirrors, cholesteric films and holographic films, physically form two optical paths to determine the transition band characteristics. Although RS 160, 170 encodes color by polarization and thereby can determine the transition band characteristics, RS 160, 170 does not physically separate the collinear propagation field elements. Thus, light enters the stack substantially perpendicularly, thereby minimizing angular sensitivity. Thus, when the optical axis of each film is in-plane, the retardance variation for small deviations from normal incidence is quadratic in angle. Even though the first (PBS) coating used to form the color optical path is substantially tilted (typically 45 ° deviating angle), this preferred embodiment is the f-number of the system. Provides neutral polarization efficiency over a wide range. By separating the two functions, the angle sensitivity is greatly reduced.
[0061]
Further angular sensitivity reduction is achieved in this preferred embodiment by using specialized retardation films. Substantially small angle insensitive retardation can be achieved by using either a compound retarder or a biaxial single retarder. For example, a biaxial retardation film can be made by stretching a polymer substrate both in the plane direction and along the film normal direction. When the retardation along the film normal direction is substantially half of the surface direction retardation, the wavelength variation with respect to the incident angle becomes substantially trivial.
[0062]
For small non-vertical deviations, the maximum retardation variation is fourth order in angle. Such films neglect the spectral variation at the half-intensity point. Table 2 shows the measurement data for only the second retarder stack between parallel polarizers. The results show that the dominant spectrum varies red with a maximum variation of 0.5 nm for a half apex angle of 15 °. In such a configuration, the first beam splitter 110 (PBS) represents a factor that limits the color separation capability.
[0063]
[Table 2]
Spectral variation of the half-intensity point with respect to the angle of the 14th second retarder stack 170 with a retardance at 545 nm of 1.5 wavelengths; 4 azimuth angles are given

[0064]
The non-axial measurement of the contrast ratio was performed on green light using the configuration shown in FIG. 18 except that the second beam splitter 120 (dichroic mirror) was removed. Quasi-collimated white light was filtered at 25 nm FWHM with a 550 nm bandpass. Using an optical intensity meter, the intensity was recorded as a function of angle to P rotation (in the plane containing the PBS coating normal) and S rotation. By normalizing the green panel orientation with an intensity measured at 45 °, the contrast ratio was determined up to an intensity of 0 ° panel orientation. The results given in Table 3 show that the contrast cone continues to be high over a reasonable f-number while falling with respect to the angle of incidence, and the viewing cone is very isotropic.
[0065]
[Table 3]
Contrast ratio of green light using input / output retarder stack

[0066]
For comparison purposes, Philips prisms were measured under the same conditions. The same procedure was followed and the green spectrum contrast ratio was measured as a function of orientation. Although the result of P rotation was an acceptable contrast ratio, as shown in Table 4, the contrast ratio of S rotation was very deteriorated.
[0067]
[Table 4]
Contrast ratio of green light using a Philips prism

[0068]
FIG. 15 illustrates a three-panel reflective optical system according to another preferred embodiment of the present invention. This preferred embodiment includes the features described above in connection with FIG. 4 and further includes first and second doublers for increasing the intensity of light as it passes through the reflective optical system. 115 and 125 are also included. The first and second doublers are preferably inverters and increase the light intensity for a ferroelectric liquid crystal display.
[0069]
As shown in FIG. 15, the white light from the light source 175 is polarized by the first cleanup polarizer 190, and the first primary stack is made into one polarization state by the first reader stack 160 and its complementary color is orthogonally polarized. Coded to fit the situation. The first primary color passes through the first beam splitter 110 and passes through the portion used to balance the separated light path. The first primary color is spatially modulated by the third reflective modulator 150 that has passed through the first optical doubler 115 and is transmitted back through the first optical doubler 115. The first primary color is then reflected by the first beam splitter 110 and exits the system through the second retarder stack 170, the second cleanup polarizer 195, and, if necessary, the second convex lens system 182.
[0070]
The complementary color of the first primary color is reflected by the first beam splitter 110, and after passing through the second optical doubler 125, is divided into the second and third primary colors. The second primary color is reflected by the color separator 120 and then spatially modulated by the second reflective modulator 140 and reflected again by the color separator 120 for transmission through the second optical doubler 125. . The third primary color passes through the color separator 120, is spatially modulated by the first reflective modulator 130, and passes through the color separator 120 again. The second and third primary colors are combined and transmitted through the second optical doubler 125 and the first beam splitter 110 for exiting the system 100 through the second retarder stack 170. The second retarder stack 170 transmits the combined complementary color and the first primary color having the same polarization state through the second cleanup polarizer 195 and the second convex lens system 182.
[0071]
In order to improve the contrast ratio, the intermediate retarder stack of the embodiment of FIG. 4 may be located between the beam splitter 110 and the color separator 120.
[0072]
FIG. 16 shows an optical system 200 according to still another preferred embodiment of the present invention, which includes first, second, third and fourth polarizing beam splitters 205, 210, 215, 220, and first, second. , Third and fourth retarder stacks 260, 265, 270, 275. In this embodiment, hereinafter, the first, second and third primary colors are blue, red and blue, respectively. These colors are exemplary and the order of these colors can be varied as desired, as will be readily understood by those skilled in the art.
[0073]
White light from the light source 175 is polarized by the first retarder stack 260 so that the blue light follows one polarization state and the complementary yellow light follows the orthogonal polarization state. The first polarization beam splitter (PBS) 520 transmits blue and reflects yellow. The second retarder stack 265 is a red / cyan or green / magenta retarder stack that encodes red into one polarization state and green into its orthogonal polarization state. The first and second reflective modulators 130 and 140 modulate red light and green light, respectively. Thereafter, the second PBS 210 transmits red light and reflects green light. The third retarder stack 270 is recombined with red and green light into a polarization state that passes through the fourth retarder stack 275 by the third PBS 215. The fourth PBS 220 transmits the blue light from the first PBS 215 to the third reflective modulator 150, and the third modulator modulates the blue light and reflects it back to the fourth PBS 220. The fourth PBS 220 reflects blue light to the third PBS 215, and the third PBS reflects blue light to the fourth retarder stack 275. The fourth retarder stack 270 rotates all three primary colors, red, green and blue to the same polarization state and outputs its combined spectrum.
[0074]
A color separation and combining structure and method according to a preferred embodiment of the present invention uses a retarder stack and a neutral polarizing splitter to form separate color optical paths. This is used in a reflection type separate optical path projector, and is particularly applied to a reflection type liquid crystal on a silicon display. Retarder stack (RS) technology is used to perform color separation by polarization. In combination with a structure that physically forms another optical path from orthogonal polarization states, color division is realized. The retarder stack generates flat passband and stopband features, a narrow transition bandwidth, and low color crosstalk. Unlike related art dichroic beam splitters, RS technology is based on polarization. This makes it possible to perform both color and polarization processing with a projector that is organized in a simple configuration as described herein.
[0075]
The above embodiments are merely illustrative and do not constitute a limitation of the present invention. The teachings of the present invention can be readily applied to other types of devices. The description of the invention is intended to be illustrative and not limiting of the scope of the claims. Numerous substitutions, improvements, and variations will be apparent to those skilled in the art. For example, those skilled in the art will readily understand that the second beam splitter may act on the light reflected by the first beam splitter 100 or on the light transmitted through the first beam splitter. . In the claims, a means-plus-function clause may include not only the individually described structures performing the functions mentioned, but also structural equivalents, as well as equivalent structures. Is intended.
[Brief description of the drawings]
The invention will be described in detail with reference to the following figures. In the figures, the same reference numbers refer to the same components.
FIG. 1 (a) and FIG. 1 (b) depict a related art reflective display configuration in which single polarized light is introduced through a first port and a second port It is transmitted through the reflective LCD panel.
FIG. 2 shows a retarder stack and a PBS polarization color splitter, according to a preferred embodiment of the present invention.
FIG. 3 represents an optical system according to another preferred embodiment of the present invention.
FIG. 4 represents an optical system including a three-panel reflective display system according to still another preferred embodiment of the present invention.
FIG. 5 represents an optical system including another three-panel reflective display system according to yet another preferred embodiment of the present invention.
FIG. 6 is an equivalent deployment of the three-panel reflective display system of FIG. 5 showing that the reflective display system is in an off-state.
7 represents another equivalent deployment of the three-panel reflective display system of FIG. 5 when the reflective display system is in an off-state.
FIG. 8 is an equivalent deployment of the three-panel reflective display system of FIG. 5, showing that the reflective display system is in an on-state.
FIG. 9 represents a transition band for the reflective display system of FIG.
FIG. 10 illustrates light leakage through the reflective display system when the reflective display system of FIG. 5 is in a non-operating state.
FIG. 11 shows the measured output of the reflective display system of FIG.
12 shows the measured output of the reflective display system of FIG.
13 shows the measured output of the reflective display system of FIG.
FIG. 14 shows the measured output of the reflective display system of FIG.
FIG. 15 shows a variation of the optical system shown in FIG. 14 according to the invention.
FIG. 16 represents an optical system including a three-panel reflective display system according to another preferred embodiment of the present invention.

Claims (43)

An optical system,
A plurality of stacked retarders for converting a first spectrum of incident light from a light source into a first polarization state and converting a second spectrum of the incident light into a second polarization state different from the first polarization state ; An input retarder stack having
The input retarder stack and optically coupled to, and reflects the converted the second spectrum the first spectrum which is converted into the first polarization state to the transmission vital the second polarization state, on the basis of the polarization a beam splitting unit having a first beam splitter for separating the light,
A first spatial modulator optically coupled to the beam splitting unit, modulating the first spectrum and reflecting the modulated first spectrum to the beam splitting unit;
A second spatial modulator optically coupled to the beam splitting unit, modulating the second spectrum and reflecting the modulated second spectrum to the beam splitting unit;
Have
The beam splitting unit combines the modulated first spectrum and the modulated second spectrum into a combined spectrum;
It said beam splitting unit optically coupled to, converts the polarization of the coupled spectrum to a substantially single polarization state, characterized by further comprising an output retarder stack having a plurality of stacked retarder . The optical system according to claim 1 , wherein the first polarization state is orthogonal to the second polarization state. 3. The optical system according to claim 1 , wherein the first spectrum and the second spectrum are selected from at least one of blue light, red light, and green light. The optical system according to any one of claims 1 to 3 , further comprising an input polarizer that is optically coupled to the input retarder stack, polarizes the incident light, and transmits the input light to the input retarder stack. It is characterized by having. 4. The optical system according to claim 1 , further comprising: a polarization conversion array that optically couples with the input retarder stack and converts the polarization of the incident light into an input polarization state. 5. It is characterized by having. The optical system according to claim 1 , further comprising an input lens positioned between the input retarder stack and the light source. The optical system according to any one of claims 1 to 6 , wherein the light source is selected from one of an incandescent lamp, a laser, a light emitting diode, an ultra high pressure mercury lamp, and a fusion lamp. And 8. The optical system according to claim 1 , wherein the output retarder stack has a transition band that does not overlap a transition band of the input retarder stack. 9. 8. The optical system according to claim 1 , wherein the separation of the half-intensity points of the input retarder stack and the output retarder stack is approximately between 5 nm and 40 nm. . 10. The optical system according to any one of claims 1 to 9 , further comprising an output polarizer that is optically coupled to the output retarder stack. 11. The optical system according to any one of claims 1 to 10 , further comprising an output lens optically coupled to the output retarder stack and receiving and transmitting the coupled spectrum. The optical system according to any one of claims 1 to 11 , further comprising a second beam splitter,
The second beam splitter accepts the second spectrum that is reflected from the first beam splitter, passes through a predetermined portion of the second spectrum, further and the remaining portion of the second spectrum have a second beam splitter for reflecting a third spectrum,
The second spatial modulator modulates the predetermined part of the second spectrum and reflects the modulated second spectrum to the dividing unit . The optical system according to any one of claims 1 to 11 , wherein at least one of the first spectrum and the second spectrum includes at least one band of a plurality of wavelengths. 14. The optical system according to claim 13 , wherein the at least one band of a plurality of wavelengths has a full-width-half-maximum value of at least 70 nm. 14. The optical system according to claim 13 , wherein the at least one band of multiple wavelengths has a full-width-half-maximum of at least 97 nm. 14. The optical system according to claim 13 , wherein the at least one band of a plurality of wavelengths defines a color. 17. The optical system of claim 16 , wherein the color has an additive mixed primary color. 17. The optical system of claim 16 , wherein the color has a subtractive mixed primary color. 17. The optical system according to claim 16 , wherein the color has a substantially pure color. It is characterized by that. The optical system according to any one of claims 1 to 11 , wherein at least one of the first spectrum and the second spectrum is an approximate square wave. 21. The optical system of claim 20 , wherein the approximate square wave has one or more maximum transmissions in the transmission band and one or more minimum transmissions in the stopband. It is characterized by. 21. The optical system of claim 20 , wherein the approximate square wave transition band slope is less than 40 nm. 21. The optical system of claim 20 , wherein the approximate square wave transition band slope is less than 25 nm. 24. The optical system according to any one of claims 1 to 23 , wherein the retarder stack comprises at least two retarder films. 25. The optical system according to claim 24 , wherein the two retarder films comprise polymer retarder films. 25. The optical system according to claim 24 , wherein the two retarder films have a thin film. 25. The optical system according to claim 24 , wherein the two retarder films comprise between 2 and 7 retarder films. 25. The optical system according to claim 24 , wherein the two retarder films comprise between 8 and 20 retarder films. The optical system according to claim 12 , comprising:
Said beam splitting unit optically coupled to a third spatial modulator for reflecting to the beam splitting section to the third spectral as modulation and modulation third spectrum, with further having,
The beam splitting unit combines the modulated first, second, and third spectra into a combined spectrum. 30. The optical system of claim 29 , wherein the light is modulated according to color image information associated with a spectrum of each of the first, second and third spatial modulators. 31. The optical system according to claim 30 , wherein the first, second and third spatial modulators are liquid crystal modulators. 13. The optical system according to claim 12 , wherein the first beam splitter includes a polarizing beam splitter that transmits and reflects light based on polarization. 33. The optical system according to claim 32 , wherein the second beam splitter includes a dichroic beam splitter that transmits light in the first predetermined wavelength band and reflects light in the second predetermined wavelength band. It is characterized by having. 34. The optical system of claim 33 , further comprising:
A first optical doubler positioned between the first beam splitter and the second beam splitter;
And a second optical doubler positioned between the first beam splitter and the first spatial modulator. 35. The optical system according to any one of claims 1 to 34 , further comprising optical projection optics that are optically coupled to the combined spectrum to form an optical projector. It is characterized by that. The optical system according to claim 12 , comprising:
Optically coupled between the first beam splitter and the second beam splitter to align the predetermined portion of the second spectrum along a third polarization state and to align the third spectrum with the third polarization. A first intermediate retarder adapted to be aligned along a fourth polarization state different from the state;
The second beam splitter is a polarization beam splitter. 30. The optical system of claim 29 , further comprising:
A third beam splitter optically coupled between the first spatial modulator and the first beam splitter and reflecting the first polarization transmission spectrum;
And a fourth beam splitter optically coupled between the third beam splitter and the second beam splitter for coupling the first, second and third modulation spectra. The optical system according to claim 37 , further comprising:
A second intermediate retarder optically coupled between the second beam splitter and the fourth beam splitter is provided. 40. The optical system of claim 38 , wherein the output retarder stack is optically coupled to the fourth beam splitter. The optical system according to claim 12 , further comprising:
And a third spatial light modulator optically coupled to the second beam splitter for modulating the third spectrum. 41. The optical system according to claim 40 , further comprising:
A first optical doubler positioned between the first beam splitter and the second beam splitter to increase the predetermined portion of the second spectrum and the intensity of the third spectrum;
A second optical doubler positioned between the first beam splitter and the first spatial modulator to increase the intensity of the first spectrum. A method for creating a modulated color image, comprising:
An input retarder stack having a plurality of stacked retarders encodes the first primary color from the white light source along the first polarization state and the complementary color along the second polarization state;
Directing the first primary color to the first spatial modulator to modulate the image data for the first primary color,
Directing the complementary color to a color separator to separate the complementary color into a second primary color and a third primary color;
Directing the second primary color to a second spatial modulator to modulate the image data for the second primary color,
Directing the third primary color to a third spatial modulator to modulate the image data for the third primary color,
Recombining the first, second, and third modulation primaries so that the first, second, and third modulation primaries have substantially the same polarization state by an output retarder stack having a plurality of stacked retarders It is characterized by doing. An optical system for creating a modulated color image,
An input retarder stack having a plurality of stacked retarders that encodes a first primary color from a white light source along a first polarization state and encodes its complementary color along a second polarization state;
A first polarizing beam splitter that directs the first primary color to the first spatial modulator and directs the complementary color to the color separator to modulate the image data for the first primary color;
Accepting the complementary color, separating the complementary color into a second primary color and a third primary color, and directing the second primary color to the second spatial modulator to modulate the image data for the second primary color; A color separator that directs the third primary color to a third spatial modulator to modulate image data for the third primary color;
An output retarder stack having a plurality of stacked retarders that recombine the first, second, and third modulation primaries such that the first, second, and third modulation primaries have substantially the same polarization state It is characterized by having.

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