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Projection Type Video Image Display Device Videobildanzeigegerät Nach Dem Projektionsprinzip Dispositif D’Affichage D’Images Vidéo Du Type Projecteur

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Projection Type Video Image Display Device Videobildanzeigegerät Nach Dem Projektionsprinzip Dispositif D’Affichage D’Images Vidéo Du Type Projecteur Europäisches Patentamt & (19) European Patent Office Office européen des brevets (11) EP 0 871 338 B1 (12) EUROPEAN PATENT SPECIFICATION (45) Date of publication and mention (51) Int Cl.: of the grant of the patent: H04N 9/31 (2006.01) 02.08.2006 Bulletin 2006/31 (21) Application number: 98302024.9 (22) Date of filing: 18.03.1998 (54) Projection type video image display device Videobildanzeigegerät nach dem Projektionsprinzip Dispositif d’affichage d’images vidéo du type projecteur (84) Designated Contracting States: • Yamagishi, Shigekazu DE FR GB Takatsuki-shi, Osaka 569-11 (JP) (30) Priority: 10.04.1997 JP 9191897 29.05.1997 JP 13948397 (74) Representative: Crawford, Andrew Birkby et al A.A. Thornton & Co., (43) Date of publication of application: 235 High Holborn 14.10.1998 Bulletin 1998/42 London WC1V 7LE (GB) (73) Proprietor: MATSUSHITA ELECTRIC INDUSTRIAL (56) References cited: CO., LTD. EP-A- 0 537 708 EP-A- 0 731 603 Kadoma-shi, Osaka 571-8501 (JP) EP-A- 0 752 608 US-A- 5 541 673 (72) Inventors: • Hatakeyama, Atsushi Ibaraki-shi, Osaka 567 (JP) Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 0 871 338 B1 Printed by Jouve, 75001 PARIS (FR) 1 EP 0 871 338 B1 2 Description same shape. Moreover, on the X- shaped glued surface, a reflection layer of dielectric film or the like having a Technical Field of the Invention selective reflection characteristic (or selective transmis- sion characteristic) of a specific color is formed, and a [0001] The present invention relates to a projection 5 blue light reflection plane 1051B and a red light reflection type display device for separating a white color luminous plane 1051R are provided. flux from a light source into three color luminous fluxes [0008] Color lights modulated according to the video of red, blue and green, optically modulating these lumi- signal corresponding to the colors by the modulating nous fluxes through a light valve, recombining modulated means 100B, 100G, and 100R composed of incident side luminous fluxes of each color after optical modulation, 10 polarizer 107, liquid crystal light valve 101, and exit side and magnifying and projecting an image on a screen. polarizer 102 are combined by the dichroic prism 105 More particularly, the invention relates to a structure for (color light combining means), and projected on a screen preventing light crosstalk or the like in a dichroic prism (not shown) through a projection lens 106 which is pro- for composing color light combining means in an optical jection optical means. system of such projection type display device. 15 [0009] Herein, the modulated luminous flux of each color passing through the modulating means 100B, Background of the Invention 100G, 100R either passes through the dichroic prism 105, or is reflected by the blue light reflection plane 1051B [0002] A projection type display device mainly com- or is reflected by the red light reflection plane 1051R for prises a light source, color light separating means for20 composing the X-shaped reflection plane, and is emitted separating a white color luminous flux emitted therefrom to the side of the projection lens 106. into color luminous fluxes of three primaries, three liquid [0010] However, a slight portion of the light is not re- crystal light valves for optically modulating separated lu- flected by blue light reflection plane 1051B or the red light minous fluxes of each color, color light combining means reflection plane 1051R for composing the X-shaped re- for combining modulated luminous fluxes of the optically 25 flection plane, but passes through, and may reach up to modulated colors through these liquid crystal light valves, the back side of the liquid crystal light valve 101 for com- and a projection lens for magnifying and projecting the posing the modulating means 100B, 100R confronting combined modulated luminous flux on a screen. each other across the dichroic prism 105. [0003] Fig. 8 is a conceptual diagram showing a basic [0011] For example, the blue modulated luminous flux constitution of a conventional projection type display de- 30 passes through the blue light reflection plane 1051B of vice. Referring to Fig. 8, the process until an image is the dichroic prism 105, leaves the red luminous flux in- magnified and projected on a screen is described. cident plane 105R, and enters the back side of the liquid [0004] A natural light emitted from a light source 201 crystal light valve 101 of the red color modulating means passes through an illuminating optical system composed 100R. of a first integrator 202a, a reflection mirror 207, and a 35 [0012] Similarly, the red modulated luminous flux second integrator 202b, and goes toward a first dichroic passes through the red light reflection plane 1051R of mirror 203 which passes blue and reflects green and red. the dichroic prism 105, leaves the blue luminous flux in- [0005] The blue light passing through the first dichroic cident plane 105R, and enters the back side of the liquid mirror 203 is reflected by a reflection mirror 207B, fo- crystal light valve 101 of the blue color modulating means cused by a field lens 205B, and reaches modulating40 100B. means 100B. On the other hand, of the green light and [0013] Furthermore, the green modulated luminous red light, the green light is reflected by a second dichroic flux may be slightly reflected by the red light reflection mirror 204 which reflects green and passes red, and is plane 1051R or blue light reflection plane 1051B of the focused by a field lens 205G, and reaches modulating dichroic prism 105, and may enter the back side of the means 100G. 45 liquid crystal light valve 101 of the red color modulating [0006] The red light passes through the second dich- means 100R and the back side of the liquid crystal valve roic mirror 204, and is focused by a field lens 205R 101 of the blue color modulating means 100B. through first relay lens 206a, reflection mirror 207R, sec- [0014] In this way, if the light enters from the back side ond relay lens 206b, and reflection mirror 207R, and of the liquid crystal light valve 101 into the liquid crystal reaches modulating means 100R. Herein, the color lights 50 light valve 101, the liquid crystal light valve 101 may mal- modulated by the modulating means 100B, 100G, 100R function and other adverse effects may be caused. according to the video signal corresponding to the colors [0015] Thus, it is a first problem that the light emitted are put into a dichroic prism 105. from modulating means for other color enters the back [0007] Fig. 7 is a detailed diagram of modulating side of the liquid crystal light valve 101 for each color as means and color light combining means shown in Fig. 8. 55 leak light from the dichroic prism 105 to cause adverse As the color light combining means, generally, the dich- effects on the liquid crystal light valve 101, and in partic- roic prism 105 is used, and this dichroic prism 104 is ular the effect is greater by the blue light which is light at composed by mutually gluing four triangular prisms of the shorter wavelength side. 2 3 EP 0 871 338 B1 4 [0016] Moreover, the modulated luminous fluxes of vented from being passed through, and the color light red, blue and green passing through the modulating which must be passed through the color light combining means for each color may be slightly reflected by the means is prevented from being reflected. Hence, the incident planes 105B, 105G, 105R of each dichroic prism color light returning in the direction of the light valve and the exit side polarizer surface 102S, and may enter 5 through the color light combining means is shut off. each liquid crystal light valve 101 from the back side as [0024] Therefore, the color light entering from the back return light. side of the light valve is shut off, and malfunction of the [0017] Such return light is one of the factors to cause light valve is prevented. As a result, a sharp video image malfunction of the liquid crystal light valve 101 as men- is obtained. tioned in the first problem, and hence it is a second prob- 10 lem. Brief Description of the Drawings [0018] To solve these problems, hitherto, it has been proposed to install an absorption type filter between the [0025] color combining means and modulating means as dis- closed in Japanese Laid- open Patent No. 8-184797. The 15 Fig. 1 is a block diagram of embodiment 1 of a pro- absorption type filter is, however, small in the degree of jection type video image display device of the inven- freedom for setting the spectral characteristic, and is not tion. sufficient to prevent the harmful light completely depend- Fig. 2 is a block diagram of embodiment 2 of a pro- ing on the color light (EP-A-537 708). If composed to jection type video image display device of the inven- prevent completely, the transmission rate of the usable 20 tion. color lights is decreased. Fig. 3 is a block diagram of embodiment 3 of a pro- [0019] In document EP-A-0 731 603 a projection type jection type video image display device of the inven- display is disclosed making use of phase plate to prevent tion.
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