USOO5798 89A1 ‘ United States Patent {19] [11] Patent Number: 5,798,819 Hattori et a]. [45] Date of Patent: Aug. 25, 1998

[54] PROJECTION-DISPLAY APPARATUS AND 5.357.289 10/1994 Konno et a1. 353/33 METHOD PROVIDING [NIPROVED 5,575,548 11/1996 Lee ...... 353/31 iihlligglliTNEss OF PROJECTED FOREIGN PATENT DOCUMENTS

452634 2/1992 Japan ...... 353/8 [75] Inventors: Tetsuo HattorLYokohama; Yoshiro 457045 2/1992 Japan 353/8

, _ 0ikawa_, T0ky0_ , of Japan Primary Examiner—WilliamJapan Dowling...... [73] Asslgncc' Nlkon Corporahon' Tokyo‘ Japan Attorney, Agent, or Firm-Klarquist Sparkman Campbell 21 763 31 Leigh & Whinston. LLP [ 1 App 1. N 0 .: ,3 [57] ABSTRACT [22] Filed: Dec. 11, 1996 Methods and apparatus are disclose for obtaining a bright [30] Foreign ADI-‘million Priority Data projected color image. In a representative apparatus. polar ized beam splitters (one for each primary color of an image Dec. 12. 1995 [JP] Japan ...... 7-346367 to be Pl'OJ?ClCd)_ separate p-polanzed_ light_ and s~polar1zed, [51] Int. Cl.6 ...... 1 G03B 21/14 for each of the primary . Each separated s- and [52] US. Cl...... 353/33; 353/20; 353/31; p-polarized light for each color enters a respective spatial 349/9 light modulator. For each primary color. modulated light [58] Field of Search ...... 353/8. 20. 31. ?uxes Produced by the tW0 spatial light modulators which 353/33_ 34. 37; 349/5_ 3_ 9_ 15 perform modulation of the same image. are analyzed and integrated by the polarized beam splitters. The analyzed and [56] References Cited integrated light ?uxes for each primary color are color integrated. either by projection using separate projection U'S‘ PATENT DOCUMENTS lenses for each color, or by a cross-dichroic prism followed 4,127,322 11/1973 Jacobson et a1. .. by Projcc?on using a si?gl? 16118 5,028,121 7/1991 Baur et a1...... 5,172,254 12/1992 Atarashi et a1...... 353/20 16 Claims, 1 Drawing Sheet US. Patent Aug. 25, 1998 5,798,819

2056 204R 204B 203 202 FIG. 2 (Prior Art) 206

I --- -<--|:7-- ~ - - - - - — — -->-————— i 1 205B 201

213 215 217 219 5.798.819 1 2 PROJECTION-DISPLAY APPARATUS AND crystal become oriented suf?ciently to become birefringent. METHOD PROVIDING IMPROVED The birefringent locus causes any s‘polarized “reading” light BRIGHTNESS OF PROJECTED COLOR (entering from the right in FIG. 3) incident on the locus to IMAGE become circularly polarized. The circularly polarized light is re?ected by the mirror layer 215 and. as the re?ected light FIELD OF THE INVENTION again passes through the liquid-crystal layer 217. the light This invention pertains to projection-display apparatus. becomes p-polan'zed light and exits the spatied light modu more speci?cally to such apparatus operable to project a lator (toward the right in FIG. 3) as modulated light. color image de?ned by multiple spatial light modulators. When no ‘Writing” light impinges on a locus of the photoconductive ?lm 213. the impedance at that locus BACKGROUND OF THE INVENTION remains su?iciently high that a voltage potential does not develop across the liquid-crystal layer 217 at the locus. As A prior-art projection-display apparatus employing mul a result. molecules of the liquid (n'ystal at the locus do not tiple spatial light modulators and operable to project a color become birefringent. Any s-polarized “reading” light inci image is shown in FIG. 2. In the FIG. 2 apparatus. a white dent on the locus (from the right in FIG. 3) is optically illumination-light ?ux is emitted from a light source 201 that rotated according to the orientation of the liquid-crystal comprises. for example. a metal-halide or xenon lamp and molecules at the locus. is re?ected by the dielectric mirror re?ective parabolic mirror. The illumination-light ?ux typi 215. and again optically rotated according to the orientation cally passes through a ?lter (not shown) operable to absorb of the liquid-crystal molecules at the locus. The re?ected ultraviolet rays and a collimator (not shown) operable to 20 light exits the spatial light modulator unchanged as make parallel the rays comprising the illumination-light s-polarized light. ?ux. The illumination-light ?ux then enters a polarizing beam-splitter prism 202. The polarizing beam-splitter prism “Writing” light for the FIG. 2 embodiment is usually 202 comprises a beam-splitting layer 203 opaable to split supplied by three CRT screens (not shown). one for each primary color. The writing light is impinged on the respec the incident illumination-light ?ux into p-polarized light and 25 s-polarized light. The p-polarized light passes unaltered tive spatial light modulator 205B. 205R. 205G to “write” the through the beam-splitting layer 203 and is discarded. while video image for each color on these spatial light modulators. the s-polarized light is re?ected by the beam-splitting layer Light of a suitable wavelength for the particular photosen 203 and then separated into the three primary colors (. sitivity of the photoconductive film 213 in each spatial light modulator is used as the writing light for each modulator; for . ) by passage through a blue-re?ective dichroic 30 mirror 204B (which re?ects blue and passes red and green) example. red light is optimum when the photoconductive and through a red-re?ective dichroic mirror 204R (which ?lm 213 is an amorphous silicon hydride. re?ects red and passes green). The re?ected blue s-polarized Each spatial light modulator 205R. 205B. 205G modu light impinges as “reading” light on a “blue” spatial light lates the incident “reading” light (s-polarized light) as described above according to the writing light. The re?ected modulator 205B. The re?ected red s-polarized light 35 impinges as “reading" light on a “red” spatial light modu modulated light propagates in the opposite direction from lator 205R. The green s-polarized light impinges as “read the incident direction and returns again to the dichroic ing” light on a “green” spatial light modulator 2056. mirrors 204B. 204R. where the colors of re?ected modulated The spatial light modulators 205R. 205B. 205G are usu light are integrated. The color-integrated modulated light ally re?ective-type spatial light modulators having a cross propagates into the polarizing beam-splitter prism 202 in sectional structure as shown. e.g.. in FIG. 3. The spatial light which the s-polarized component of the color-integrated modulator of FIG. 3 comprises. from the “writing” light side light is re?ected by the beam-splitting layer 203 and dis (i.e.. the left side in FIG. 3). a ?rst transparent glass substrate carded; the p-polarized component of the color-integrated 211; a ?rst transparent conductive layer (e.g.. ITO ?lm) 212 light passes through the beam-splitting layer 203 and is projected by a projection lens 206 onto a screen (not shown). operable as a first transparent electrode; a photoconductive 45 layer 213 made. e.g.. from amorphous silicon hydride; a In the prior-art apparatus described above. color separa “light-blocking” layer 214 made from. e.g.. cadmium tion and color integration are performed by the same dich tellurium; a re?ective-mirror layer 215 made from. e.g.. roic mirrors 204B. 204R. However. apparatus are known in multiple layers of dielectric; a ?rst liquid-crystal orientation the prior art where color separation and color integration are layer 216 made from. e.g. polyimide; a liquid-crystal layer 50 performed by separate dichroic mirrors or dichroic prisms. 217 operable as a light-modulation layer. a second liquid The trend in projection-display technology is toward ever crystal orientation layer 218 made from. e.g.. polyimide; a brighter projected images. Unfortunately. in prior-art appa second transparent conductive layer (e.g.. 1T0 ?lm) 219 ratus such as described above. the image cannot be made as operable as a second transparent electrode; and a second bright as desired when projected onto. e.g.. a large screen transparent glass substrate 220. The thicknesses of the 55 such as a movie screen. This is because a portion of the light re?ective-mirror layer 215 and/or the liquid-crystal layer (5- or p-polarized portion) is discarded and thus does not 217 will ditfer according to the wavelength of light with contribute to the brightness of the projected image. which the spatial light modulator is used. but the basic structure is the same for each of the spatial light modulators SUIVIMARY OF THE INVENTION 205R. 205B. 205G. An alternating-current voltage is applied The present invention addresses the shortcomings of the between the ?rst and second transparent electrodes 212. 219. prior art described above. A key object of the invention is to When a “writing” light enters from the left side in FIG. 3 provide a projection-display apparatus operable to produce and impinges on a locus of the photoconductive ?lm 213. the a brighter projected image than prior-art projection-display impedance of the photoconductive ?lm at the locus apparatus. decreases. This causes a voltage potential to develop across 65 According to a preferred embodiment of a method accord the liquid-crystal layer at that locus. At the locus and in ing to the present invention. an illumination light ?ux is response to the voltage potential. molecules of the liquid separated into separate light ?uxes corresponding to the 5.798.819 3 4 primary colors making up the illumination light ?ux. For mary colors and to direct the illumination light flux to the each light ?ux corresponding to a primary color. a color separator. The color separator preferably comprises a p-polarized light ?ux and an s-polarized light ?ux are blue-re?ective dichroic mirror and a red-re?ective dichroic separated. Each p-polarized light ?ux and each s—polarized mirror situated in an X~con?guration relative to each other. light ?ux are separately modulated according to the image to Further according to a preferred embodiment. the first and be projected. preferably using separate spatial light modu second spatial light modulators for each primary-color illu lators. For example. for an illumination light ?ux comprising mination light ?ux comprises ?rst and second re?ective the three primary colors (red. green. and blue) a total of six spatial light modulators. and further preferably electrically spatial light modulators are employed. The resulting modu writing re?ective spatial light modulators. lated p-polarized light and modulated s-modulated light for l0 Further according to the preferred embodiment. each of each primary color are integrated. Finally. the integrated the polarizing beam splitters (one for each primary color) are modulated light ?uxes for each primary color are combined polarizing beam-splitter prisms. Such prisms preferably to produce a viewable image. have orthogonal surfaces on which the ?rst and second According to the preferred embodiment of the method. spatial light modulators are mounted. the integrated modulated light ?uxes for the primary colors 15 Further according to the preferred embodiment. the color are integrated (preferably by passage through a color integrator preferably comprises a crossdichroic prism that integrating prism) and collectively projected through a pro combines the integrated modulated light ?uxes from the jection optical system (e.g.. a projection lens) to a suitable polarizing beam splitters and delivers an integrated modu surface for viewing the image. Alternatively. the integrated lated light ?ux to a single projection lens for projection of modulated light ?uxes for each primary color are individu 20 the viewable image onto a surface. Alternatively. the color ally projected to form the color image on the surface on integrator can comprise separate projection lenses. one for which the image is projected. each primary color. that individually receive modulated light importantly. in methods according to the present ?ux from a corresponding polarizing and invention. one or the other of s-polarized light and project that light ?ux onto a surface where the primary-color p-polarized light is not discarded. Thus. the projected image 25 images are integrated into a single color image. I.e.. in the formed according to the method is appreciably brighter than alternative scheme. color integration is performed on the would be obtainable using prior-art methods and the same screen rather than before actual projection onto the screen. intensity of illumination light ?ux. An alternative embodiment of an apparatus according to Preferably. separating the p-polarized light from the 30 the present invention comprises a color separator. plural s-polarized light for each primary color prior to modulation. spatial light modulators and polarizing beam splitters. and a and integrating the p-polarized light and the s-polarized light color integrator. as described above. The color integrator is after modulation are performed using polarizing beam operable to integrate the integrated modulated light ?uxes splitter prisms. from the polarizing beam splitters to produce a light output. A preferred embodiment of an apparatus according to the 35 The alternative embodiment also comprises a projection present invention comprises a color separator. plural spatial optical system that is operable to project the light output and light modulators and polarizing beam splitters. and a color produce the color image on a surface for viewing. integrator. The color separator is situated relative to an In the foregoing embodiments. unlike projection-display illumination light ?ux comprising multiple primary colors. apparatus according to the prior art. two spatial light modu The color separator is operable to separate the illumination lators are used for each primary color rather than only one. light flux into separate primary-color illumination-light Thus. for the primary colors red. green. and blue. a total of ?uxes. For each primary color. the apparatus comprises ?rst six spatial light modulators are employed. Each primary and second spatial light modulators. one being operable to color of illumination light is polarization-divided into modulate. according to the image to be projected. an p-polarized light and s-polarized light; the polarization s-polarized primary-color illumination light ?ux and the 45 separated p~polarized illumination light ?uxes are separately other being operable to modulate a p-polarized primary incident on three spatial light modulators individually cor color illumination light ?ux. For example. if the illumination responding with each primary color. and the polarization light ?ux comprises the primary colors red. green. and blue. separated s-polarized illumination light ?uxes are separately the apparatus comprises two spatial light modulators for incident on three spatial light modulators individually cor each primary color. one modulator for s-polarized light and responding with each primary color. Thus. both spatial light one for p-polan'zed light of each primary color. Also for each modulators for each primary color perform modulation of primary-color illumination-light ?ux. the apparatus com the same image. Each primary color of modulated light is prises a separate polarizing beam splitter operable to: (a) then respectively analyzed and integrated. By combining. before modulation. split the primary-color illumination light for each primary color. modulated light ?uxes for both ?ux into a p-polarized light ?ux and an s-polarized light ?ux 55 p-polarized and s-polarized light (rather than using one and corresponding with the respective primary-color illumina discarding the other as in the prior art). a remarkably tion light ?ux for routing to the respective ?rst and second brighter projected image can be obtained compared to the spatial light modulators for each primary-color illumination prior art. light ?ux; and (b) integrate modulated light ?uxes produced In any of the embodiments of apparatus according to the by the ?rst and second spatial light modulators for each present invention. re?ective spatial light modulators or primary-color illumination light ?ux. Finally. the apparatus transmitting spatial light modulators can be used. Use of the comprises a color integrator operable to combine the inte re?ective type allows for a simpler and hence preferred grated light ?uxes from the polarizing beam splitters to structure because. for each primary color. a single polarizing produce the color image. beam splitter can be used as the . light analyzer. and Further according to a preferred embodiment. the appa 65 integrator for the modulated light corresponding to an ratus comprises a source of illumination light operable to image. Such a polarizing beam splitter has a “p-polarized” produce an illumination light ?ux comprising multiple pri light emission side and an “s-polarized" light emission side 5.798.819 5 6 (usually situated in orthogonal relationship). This allows the glass plate. Dielectric mirrors are also preferable because spatial light modulator for p-polarized light to be mounted to they are better than metallic minors in preserving the one such side. and the spatial light modulator for the randomly polarized nature of the light as the light is being spolarized light to be mounted to the other such side. re?ected therefrom. respectively. Each of the re?ected R. G. and B colored-light ?uxes then In addition. optically-Writing spatial light modulators can enters the respective polarizing beam-splitter prism 22R. be used rather than electrically-writing spatial light modu 22G. 22H. which are arranged relative to the respective lators. Use of electrically-writing spatial light modulators is planar mirrors 21R. 21G. 21B to receive the respective colored light ?ux. preferred because they eliminate the need for a writing In the polarizing beam-splitter prisms 22B. 22R. 226. the optical system that would comprise a CRT. relay lens. etc.; respective randomly polarized B. R. G light ?uxes are this more readily allows miniaturization. separated into p-polarized light and s-polarized light. The The foregoing and additional features and advantages of p-polarized light passes through and the s-polarized light is the present invention will be more readily apparent from the re?ected by the respective polarizing beam-splitter prism following detailed description. which proceeds with refer 22B. 22R. 226. ence to the accompanying drawings. 15 The blue p-polarized light. after having passed through the “blue” polarizing beam-splitter prism 22B. enters the BRIEF DESCRIPTION OF THE DRAWINGS spatial light modulator 23BP as “reading” light. The blue FIG. 1 is an oblique view showing the general construc s-polarized light. after having been re?ected by the “blue” tion of a preferred embodiment of a projection-display polarizing beam-splitter prism 22B. enters the spatial light apparatus according to the present invention. modulator 23BS as “reading” light Similarly. the red and FIG. 2 is an oblique view showing the general construc green p-polarized that have passed through the respec tion of a prior-art projection-display apparatus. tive “red” and “green" polarizing beam-splitter prisms 22R. 22G enter the respective spatial light modulators 23RP. FIG. 3 is a schematic sectional view of a representative 23G? as “reading” lights; and the red and green s-polarized 25 optically writing re?ective spatial light modulator usable lights that have been re?ected by the respective “red” and with the FIG. 1 embodiment. “green” polarizing beam-splitter prisms 22R. 22G enter the DETAILED DESCRIPTION spatial light modulators 23RS. 23GS as “reading" lights. In this embodiment. each of the spatial light modulators A preferred embodiment of a projection-display apparatus 23BP. 23BS. 23RP. 23RS. 23GP. ZSGS is preferably an according to the present invention is depicted in FIG. 1. electrically writing. re?ective spatial light modulator. most which represents the current best mode. The FIG. 1 embodi preferably such as disclosed in. e.g.. in Japan Kokoku Patent ment comprises an illumination-light source 10; a planar Publication No. I-[EI 5-82793. It will be appreciated that the mirror 15; a color separator 20 comprising a blue-re?ecting spatial light modulators 23BP. 23BS. 23RP. 23RS. 23GB dichroic mirror 20B and a red-re?ecting dichroic mirror 20R 35 23GS are not limited to such types; a variety of other types (the mirrors 20B. 20R collectively having an of electrically writing re?ective spatial light modulators can X-con?guration); planar mirrors 21R. 21G. 21B; polarizing be used alternatively. beam-splitter prisms 22B. 22R. 22G; spatial light modula The preferred type of electrically writing re?ective spatial tors 23BP. 23BS. 23GB 23GS. ZSRP. 23RS; and a cross light modulators comprise a transparent electrode (common dichroic prism 24. all preferably arranged relative to each electrode) formed over the entire surface of the spatial light other essentially as shown. modulator on the side at which “reading” light is incident. The illumination-light source 10 can be a conventional Multiple pixel electrodes are formed in a matrix on the type. normally comprising a concave re?ective mirror and a opposing side. and a liquid crystal layer is sandwiched source of white light. The source of white light is typically therebetween. Each of the pixel electrodes comprises a a metal halide lamp or xenon lamp. The concave re?ective 45 re?ective surface. such as of aluminum or other suitable mirror is situated rearwardly of the source of white light so re?ective metal. Each of the pixels also has associated as to re?ect rays from the source of white light and form therewith a switching circuit comprising MOS ?eld-etfect substantially parallel rays of illumination light propagating transistors (i.e.. thin-?lm transistors; abbreviated TF1‘) and along an optical axis AX. Light ?ux from the illumination capacitors. light source 10 normally passes through a UV-absorbing 50 At each pixel. a voltage can be applied across the asso~ ?lter and an IR-absorbing ?lter (not shown). ciated locus of the liquid crystal layer whenever the corre The optical axis AX of the illumination light is bent by the sponding MOS ?eld-e?ect transistor is switched on. An planar mirror 15 to allow the illumination light to enter the “electric ?eld controlled birefringence effect” (ECB) liquid color separator 20. The blue-re?ecting dichroic mirror 20B crystal material is used in the liquid crystal layer. In pixels and the red-re?ecting dichroic mirror 20R of the color 55 that are not turned on (i.e.. in which no voltage is applied separator 20 separate the incident white illumination light across the liquid crystal layer). polarized light entering the into a red light (R) ?ux. a green light (G) ?ux. and a blue pixels as “reading” light passes through the corresponding light (B) ?ux. The R. G. B ?uxes are each randomly loci in the liquid crystal layer without experiencing any polarized. change in polarization; the light is then re?ected by the The R. G. B ?uxes are re?ected by the planar mirrors 21R. re?ective portions of the corresponding pixel electrodes and 21G. 21B. respectively. to make the axes of the light ?uxes again passes through the corresponding loci in the liquid parallel with each other. The planar mirrors 21R. 21G. 21B crystal layer. without the light experiencing any net change can be made of re?ective metal. However. to minimize loss in polarization. to exit the spatial light modulator. Thus. light of light ?ux. it is preferable that the planar mirrors 21R. 21G. re?ected from pixels that are not turned on experiences no 21B be dielectric mirrors specially adapted to re?ect light of change in polarization relative to the incident light. the respective color. Dielectric mirrors typically comprise At pixels that are turned on (i.e.. in which a voltage is multiple thin-?lm layers formed by vacuum deposition on a applied across the corresponding loci in the liquid crystal 5.798.819 7 8 layer). the liquid crystal layer at the loci is birefringent. As celes triangular transverse section. The transparent members a result. light passing through each such pixel has a polar are cemented together to provide the cross-dichroic prism 24 ization plane that is rotated 90° With respect to the incident with a. preferably. square pro?le. A red~re?ecting dichroic polarized light. layer 24R and a blue—re?ecting dichroic layer 24B form an In will be appreciated from the foregoing that only light X-shaped inclusion between the mating surfaces of the re?ected from pixels that are turned on by corresponding transparent members. Preferably. each dichroic layer 24R. 24B is a multilayer lamination. to a desired thickness. of “write” signals experiences a change in polarization orien high-refractive-index titanium oxide (H02) ?lm and low tation. refractive-index silicon dioxide (SiO2) ?lm. Hence. the respective colors of s-polarized light entering Blue “analyzed” light (both 5- and p-polarized) that has the spatial light modulators 23BS. 23GS. 23RS as “reading” been integrated by the polarizing beam-splitter prism 22B is light are locally (at each pixel “turned on” by an electrical re?ected by the blue-re?ecting dichroic layer 24B; green ‘\vrite” signal) changed into p-polarized light as the light “analyzed” light (both s- and p-polarized) that has been re?ects from the respective spatial light modulators 23138. integated by the polarizing beam-splitter prism 226 is 2363. 23RS. At pixels that remain “o?”. the light re?ects as transmitted unchanged through the cross-dichroic prism 24; s-polarized light. Similarly. the respective colors of and red “analyzed” light (both s- and p-polarized) that has p-polarized light entering the spatial light modulators 23BP. been integrated by the polarizing beam-splitter prism 22R is 23GB 23RP as “reading” light are locally (at each pixel re?ected by the red-re?ecting dichroic layer 24R. Thus. the turned on by an electrical “write” signal) changed into various primary colors of “analyzed” light are color s-polarized light as the light re?ects from the respective integrated by and exit from the cross-dichroic prism 24. The spatial light modulators ZSBP. 23GP. 23RP. At pixels that color-integrated light is then projected by a projection lens remain “011'”. the light re?ects as p-polarized light. 25 onto a screen (not shown). In this embodiment. the same electrical “Write” signal is Therefore. both the p-polarized light and the s-polarized conducted to both spatial light modulators 23BS. 23BP; light associated with each primary color R. G. B of light receive modulation for the same video image in two respec thus. modulation of the same video image is performed tive spatial light modulators for each primary color. Without simultaneously by both spatial light modulators 23BS. discarding one of the p-polarized light or s-polarized light 23BP. Similarly. the same electrical “write” signal is con associated with any of the primary colors. all primary colors ducted to both spatial light modulators 23GS. 23GP; thus. of re?ected modulated light are analyzed and integrated. In modulation of the same video image is performed simulta other words. both the p-polarized light and the s-polarized neously by both spatial light modulators 23GS. 23GP. light. which were polarization-separated for modulation of Likewise. the same electrical “write” signal is conducted to each primary color. are integrated and thus utilized to form both spatial light modulators 23RS. 23RP; thus. modulation the projected color image. Consequently. a remarkably of the same video image is performed simultaneously by brighter projected color image can be obtained with an both spatial light modulators 23RS. ZSRP. apparatus according to this invention. compared to Modulated light re?ected from the spatial light modula 35 projection-display apparatus according to the prior art that tors 23135. 2368. 23RS enters the respective polarizing utilize only s-polarized or p-polarized light for each primary beam-splitter prisms 22B. 22G. 22R which allow only the color to form the projected color image. p-polarized light (i.e.. light that underwent a polarization It will be understood that any of various alternative change from “s” to “p") to be transmitted through (i.e.. embodiments of this invention are possible. For example. “analyzed” by) the beam-splitting layer in each polarizing although the color separator 20 is preferably a red-re?ecting beam-splitter prism 22B. 226. 22R. Similarly. modulated dichroic mirror crossed with a blue-re?ecting dichroic mir light re?ected from the spatial light modulators 23BP. 23GB ror (i.e.. a cross-dichroic mirror). a cross-dichroic prism can 23RP enters the respective polarizing beam-splitter prisms be used instead. Whenever a cross-dichroic mirror or a 22B. 226. 22R which allow only the s-polarized light (i.e.. cross-dichroic prism is used as the color separator. the light that underwent a polarization change from “p” to “s") light-path lengths from the illumination light source to the to be transmitted through (i.e.. “analyzed” by) the beam spatial light modulator for each primary color can be made splitting layer in each polarizing beam-splitter prism 22B. equal even if a light-path-correcting optical element is not 22G. 22R. used for each primary color R. G. B. Furthermore. since the The analyzed p-polarized blue light and the analyzed light-path lengths from each spatial light modulator to the s-polarized blue light are integrated by the polarizing beam 50 screen are the same (because the “write” image on each splitter prism 22B and enter the cross-dichroic prism 24. spatial light modulator is in a conjugate relationship with the which functions as a color integrator. In a similar manner. image on the screen relative to the projection lens). the analyzed p- and s-polarized green light and analyzed p- and light-path length from the illumination light source to the s-polarized red light are integrated by the cross-dichroic screen for each primary color can be made equal. Keeping prism 24. SS such path lengths substantially equal helps minimize color Hence. this embodiment and other embodiments accord variations caused by di?’erences in light-path lengths. ing to the present invention are distinguishable from the With respect to other alternative embodiments. a cross prior art because. according to the invention. each of the dichroic mirror rather than a aoss-dichroic prism 24 can be various colors B. G. R of both p-polarized light and used as the color integrator. In addition. dichroic mirrors s-polarized light. after being modulated and re?ected by the arranged parallel with each other. or dichroic mirrors respective spatial light modulator and after being "analyzed" arranged in a V-con?guration can also be used as the color by the respective polarizing beam-splitter prism 22B. 22G. separator and/or color integrator. In such instances. optics 22R. are integrated This is in stark contrast with the prior art for correcting lengths of light paths for one or more primary in which either the s-polarized light or the p-polarized light colors may be necessary to ensure that each light-path length is discarded before the colors are integrated. 65 through the respective polarizing beam-splitter prism to the The cross-dichroic prism 24 is preferably a prism com respective spatial light modulator is either different or equal prising four transparent members each having a right isos to the other light-path lengths. 5.798.819 9 10 According to another alternative embodiment. a com (e) passing the integrated modulated light ?uxes for each pound prism such as used for color separation in a conven primary color through a cross-dichroic prism to pro tional color television camera. in which three prisms are duce a color-image-forrning light ?ux. combined. can be used as the color separator and color 2. The method of claim 1. wherein. in step (e). the integrator. With such an embodiment. optics for correcting modulated light ?uxes for each primary color are combined light-path-length differences may be required as described to form a combined image before the combined image is above. projected to form the color image. 3. The method of claim 1. wherein. in step (e). the With respect to yet another alternative embodiment. trans modulated light ?uxes for each primary color are individu mitting spatial light modulators can be used instead of ally projected to form the color image on a projection 10 re?ective spatial light modulators. However. use of re?ec surface. tive spatial light modulators as in the preferred embodiment 4. The method of claim 1. wherein step (b) comprises allows a simpler construction of the apparatus. In addition. passing the light ?ux corresponding to each of the primary the polarizing beam-splitter prism corresponding to each colors through a respective polarizing beam-splitter prism. primary color of light can be used as the polarizer. analyzer. 15 5. The method of claim 4. wherein step (d) comprises and integrator for each modulated primary color of light passing the modulated s-polarized light and the modulated simply by situating one of the two spatial light modulators p-polarized light for each primary color through the respec for each primary color on the side of the respective polar tive polarizing beam-splitter prism. izing beam-splitter prism from which p-polarized light of 6. The method of claim 1. wherein step (e) comprises that color is emitted. and situating the other of the two spatial passing the color-image-forrning light ?ux through a pro light modulators for that color on the side of the respective jection lens. polarizing beam-splitter prism from which s-polarized light 7. An apparatus for producing a projected color image. of that color is emitted. comprising: Furthermore. whereas electrically writing spatial light (a) a color separator situated relative to an illumination modulators are preferably used. optically writing spatial 25 light ?ux comprising multiple primary colors. the color light modulators. such as shown in FIG. 3. can alternatively separator being operable to separate the illumination be used. If electrically writing spatial light modulators are light ?ux into separate primary-color illumination light used. a writing optical system. such as a CRT or relay lens. ?uxes; etc.. is not required. which is preferable from the standpoint (b) for each primary color. a ?rst spatial light modulator of miniaturization. operable to modulate. according to the image. an Furthermore. the preferred and alternative embodiments s-polarized primary-color illumination light ?ux and a described above are examples of projection-display appara second spatial light modulator operable to modulate. tus according to the present invention comprising a single according to the image. a p-polarized primary-color projection lens; i.e.. the various primary light colors R. G. B illumination light ?ux; are integrated in advance by a color integrator and the video 35 (c) for each primary-color illumination light ?ux. a sepa image is projected by a single projection lens. Alternatively. rate polarizing beam splitter operable to (i) split the for example. a three-projection-lens con?guration can also primary-color illumination light ?ux into a p-polarized be used in which color integration is performed on the screen light ?ux and an s-polarized light ?ux corresponding without using a color-integrating optical element I.e.. in with each primary-color illurninatiou light ?ux for such an alternative embodiment. the various primary colors routing to the respective ?rst and second spatial light R. G. B are individually projected onto the screen by three modulators for each primary-color illumination light projection lenses without any color integration being per ?ux. and (ii) integrate modulated light ?uxes from the formed prior to projection. ?rst and second spatial light modulators for each Whereas the invention has been described in connection primary-color illumination light ?ux; and with a preferred and various alternative embodiments. it will (d) a color integrator comprising a cross-dichroic prism be understood that the invention is not limited to those operable to combine the integrated modulated light embodiments. On the contrary. the invention is intended to ?uxes from the polarizing beam splitters to produce the encompass all alternatives. modi?cations. and equivalents as color image. may be included within the spirit and scope of the invention 8. The apparatus of claim 7. further comprising a source as de?ned by the appended claims. 50 of illumination light operable to produce an illumination What is claimed is: light ?ux comprising plural primary colors and to direct the 1. A method for forming a projected color image. com illumination light ?ux to the color separator. prising the steps: 9. The apparatus of claim 7. wherein the color separator (a) from a ?ux of illumination light comprising multiple comprises a blue-re?ective dichroic mirror and a red primary colors. separating light ?uxes corresponding to 55 re?ective dichroic mirror situated in an X-con?guration with the primary colors making up the illumination light each other. ?ux; 10. The apparatus of claim 7. wherein the ?rst and second (b) for each light ?ux corresponding to a primary color. spatial light modulators for each primary-color illumination separating a p-polarized light ?ux and an s-polarized light ?ux comprise ?rst and second re?ective spatial light light ?ux; modulators. (c) modulating the p-polarized light ?ux and the 11. The apparatus of claim 10. wherein the re?ective s-polarized light ?ux of each primary color according spatial light modulators are of an electrical writing type. to an image to be projected; 12. The apparatus of claim 7. wherein each of the polar (d) integrating the modulated p~polarized light and the izing beam splitters comprises a polarizing beam-splitter modulated s-polarized light for each primary color to 65 prism having orthogonal surfaces. form an integrated modulated light ?ux for each pri 13. The apparatus of claim 12. wherein the ?rst and mary color; and second spatial light modulators for each primary color are 5.798.819 11 12 mounted on adjacent orthogonal surfaces of the respective (d) a polarizing beam splitter for each primary color. each polarizing beam~splitter prism polarizing beam splitter being situated to (i) separate 14. The apparatus of claim 7. wherein the color integrator s-polarized light from p-polarized light in the primary comprises a projection lens. color illumination light ?ux from the color separator. 15. A projection-display apparatus. comprising: (ii) direct the s-polarized light to the respective ?rst (a) a light source operable to produce an illumination light spatial light modulator and direct the p-polarized light ?ux comprising plural primary colors; to the respective second spatial light modulator. and (b) a color separator operable to receive the illumination (iii) integrate the ?rst and second re?ected polarized light ?ux and separate the illumination light ?ux into light ?uxes from the respective ?rst and second spatial separate primary-color illumination light ?uxes; light modulators; (c) ?rst and second re?ective spatial light modulators for (e) a color integrator comprising a cross-dichroic prism each primary-color illumination light ?ux separated by operable to integrate the integrated modulated light the color separator. the ?rst re?ective spatial light ?uxes from the polarizing beam splitters and produce a modulator being operable to receive the respective light output; and primary-color illumination light flux and produce (t) a projection optical system operable to project the light therefrom a ?rst re?ected polarized light ?ux modu output and produce the color image on a surface for lated according to a desired image to be projected. and viewing. the second re?ective spatial light modulator being 16. The projection-display apparatus of claim 15. wherein operable to receive the respective primary-color illu the spatial light modulators are electrically writing spatial mination light ?ux and produce therefrom a second light modulators. re?ected polarized light ?ux modulated according to the image to be projected; UNITED STATES PATENT AND TRADEMARK OFFlCE CERTIFICATE OF CORRECTION

PATENT NO. : 5,798,819

DATED : August 25, 1998

INVENTOFHS) : HATTORI ET AL.

It is certified that error appears in the above~identi?ed patent and that said Letters Patent is hereby corrected as shown below:

On the. title page item [57],

Line 1 of the Abstract, "disclose" should be —-disclosed--.

Column 3, line 10, "s~modulated" should be —— s-polarized --.

Column 7, line 5, "In" should be --It—-.

Signed and Sealed this Ninth Day of November, 1999

Q. TODD DICKINSON