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 transmission 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 disclosed 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. a reflected light beam from reentering the light valve. Fig. 4 is a block diagram of embodiment 4 of a pro- [0020] It is hence an object of the invention to present 25 jection type video image display device of the inven- a projection type video image display device comprising tion. an optical system capable of solving such problems. Fig. 5 is a block diagram of embodiment 5 of a projection type video image display device of the inven- Summary of the Invention tion. 30 Fig. 6 is a block diagram of embodiment 6 of a pro- [0021] A projection type video image display device of jection type video image display device of the inven- the invention comprises: tion. Fig. 7 is a detailed drawing of modulating means and a light source for emitting a white light in one direc- color combining means of a conventional projection tion, 35 type video image display device. color light separating means for separating the white Fig. 8 is a conceptual diagram showing a basic con- light from the light source into three color lights of stitution of a conventional projection type video im- red light, blue light and green light, age display device. modulating means comprising light valves for modulating the polarized lights contained in the luminous 40 Reference Numerals fluxes from the color light separating means, and producing a video image, [0026] color light combining means for combining the modulated luminous fluxes after being modulated by the 100B Blue light modulating means modulating means, and 45 100R Red light modulating means projection optical means for projecting the combined 100G Green light modulating means luminous flux obtained by the color light combining 101 Liquid crystal light valve means on a screen. 102 Exit side polarizer 102S Face side of exit side polarizer [0022] Moreover, a dichroic filter having characteris- 50 103a First quarter-wave plate tics for selectively passing and selectively reflecting the 103aS Face side of first quarter-wave plate color lights from the modulating means, and a quarter- 103b Second quarter-wave plate wave plate are both disposed between the color light 103bS Face side of second quarter-wave plate combining means and the modulating means positioned 104 Dichroic filter on an optical path of at least one color light of the three 55 104S Face side of dichroic filter color lights of the red light, blue light and green light. 105 Dichroic prism (color light combining means) [0023] In this constitution, the color light which must 105B Blue light incident plane be reflected by the color light combining means is pre- 105R Red light incident plane

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105G Green light incident plane ing and selectively reflecting the color lights from the 1051B Blue light reflection plane modulating means is disposed between the color light 1051R Red light reflection plane combining means and the modulating means positioned 106 Projection lens (projection optical means) on an optical path of at least one color light of the three 107 Incident side polarizer 5 color lights of the red light, blue light and green light, and 108 Polarizing direction converting means (half- a first quarter-wave plate is disposed between the dich- wave plate) roic filter and the modulating means. 108S Face side of half-wave plate [0029] In other different projection type video image 201 Light source display device, conforming to the above constitution, 202a First integrator 10 a dichroic filter having characteristics for selectively pass- 207 Reflection mirror ing and selectively reflecting the color lights from the 202b Second integrator modulating means is disposed between the color light 203 First dichroic mirror combining means and the modulating means positioned 207B Reflection mirror on an optical path of at least one color light of the three 205B Field lens 15 color lights of the red light, blue light and green light, 100B Modulating means a first quarter-wave plate is disposed between the dich- 204 Second dichroic mirror roic filter and the modulating means, and 205G Field lens a second quarter-wave plate is disposed between the 100G Modulating means dichroic filter and the color light combining means. 206a First relay lens 20 [0030] In other different projection type video image 207R Reflection mirror display device, conforming to the above constitution, 206b Second relay lens a polarizer is disposed at the light exit side of the modu- 207R Reflection mirror lating means, 205R Field lens a dichroic filter having characteristics for selectively pass- 100R Modulating means 25 ing and selectively reflecting the color lights from the modulating means is disposed between the color light Detailed Description of the Invention combining means and the modulating means positioned on an optical path of at least one color light of the three [0027] A projection type video image display device of color lights of the red light, blue light and green light, the invention comprises: 30 a first quarter-wave plate is disposed between the dichroic filter and the modulating means, and a light source for emitting a white light in one direc- a second quarter-wave plate is disposed between the tion, dichroic filter and the color light combining means. color light separating means for separating the white [0031] In other different projection type video image light from the light source into three color lights of 35 display device, conforming to the above constitution, red light, blue light and green light, a dichroic filter having characteristics for selectively pass- modulating means comprising light valves for mod- ing and selectively reflecting the color lights from the ulating the polarized lights contained in the luminous modulating means is disposed between the color light fluxes from the color light separating means, and pro- combining means and the modulating means positioned ducing a video image, 40 on an optical path of at least one color light of the three color light combining means for combining the mod- color lights of the red light, blue light and green light, ulated luminous fluxes after being modulated by the a first quarter-wave plate is disposed between the dich- modulating means, and roic filter and the modulating means, projection optical means for projecting the combined a second quarter-wave plate is disposed between the luminous flux obtained by the color light combining 45 dichroic filter and the color light combining means, and means on a screen, polarizing direction converting means is disposed be- wherein a dichroic filter having characteristics for se- tween the second quarter-wave plate and the color light lectively passing and selectively reflecting the color combining means. lights from the modulating means, and a quarter- [0032] In other different projection type video image wave plate are both disposed between the color light 50 display device, conforming to the above constitution, combining means and the modulating means posi- a polarizer is disposed at the light exit side of the modu- tioned on an optical path of at least one color light lating means, of the three color lights of the red light, blue light and a dichroic filter having characteristics for selectively pass- green light. ing and selectively reflecting the color lights from the 55 modulating means is disposed between the color light [0028] In other projection type video image display de- combining means and the modulating means positioned vice, conforming to the above constitution, on an optical path of at least one color light of the three a dichroic filter having characteristics for selectively pass- color lights of the red light, blue light and green light,

4 7 EP 0 871 338 B1 8 a first quarter-wave plate is disposed between the dich- inated by this constitution. roic filter and the modulating means, [0038] Concerning the second problem of the modu- a second quarter-wave plate is disposed between the lated luminous flux of blue color slightly reflected by the dichroic filter and the color light combining means, and blue color incident plane 105B of the dichroic prism 105 polarizing direction converting means is disposed be- 5 and the face side of the dichroic filter 104S, and entering tween the second quarter-wave plate and the color light each liquid crystal light valve 101 from the back side as combining means. return light, the return light from the incident plane 105B [0033] In other different projection type video image of the blue light of the dichroic prism is eliminated by the display device, conforming to the above constitution, function of the first quarter-wave plate 103a at the mod- a polarizer is disposed at the light exit side of the modu- 10 ulating means side as described below. lating means, [0039] The blue polarized light emitted from the exit a dichroic filter having characteristics for selectively pass- side polarizer 102 for composing the blue light modulating and selectively reflecting the color lights from the ing means100B passes through the first quarter-wave modulating means is disposed between the color light plate 103a at the modulating means side, and becomes combining means and the modulating means positioned 15 elliptical polarized light or circular polarized light, and on an optical path of at least one color light of the three passes through the dichroic filter 104. Herein, the optical color lights of the red light, blue light and green light, axis of the first quarter-wave plate 103a is disposed so a first quarter-wave plate is disposed between the dich- as to be nearly 45 degrees to the axis of the incident blue roic filter and the modulating means, linear polarized light. The blue luminous flux slightly re- polarizing direction converting means is disposed be- 20 flected by the blue luminous flux incident plane 105B of tween the dichroic filter and the color light combing the dichroic prism 105 becomes an inverse elliptical po- means, closely to the color light combining means, and larized light orcircular polarized light, and passes through a second quarter-wave plate is disposed between the the dichroic filter 104 as return light, and becomes a po- dichroic filter and the color light combining means. larized light rotated by nearly 90 degrees from the oscil- [0034] In the foregoing constitutions, two quarter- wave 25 lation direction of the polarized light when emitted from length plates by joining the first quarter-wave plate and the modulating means through the first quarter-wave second quarter-wave plate may function as one half- plate 103a. The polarized light enters the exit side polar- wave plate. izer 102 and is absorbed, and hence does not reach the [0035] In these constitutions, the first quarter-wave back side of the liquid crystal light valve 101. That is, plate and second quarter- wave plate may be individually 30 malfunction and other adverse effects by the return light disposed so that the polarized light from the modulating reflected by the blue light incident plane 105B of the di- means may enter as the light in the polarizing direction chroic prism are eliminated. determined by the color light combining means. [0040] Similarly, the return light reflected by the face side of the dichroic filter 104S enters the exit side polar- Embodiment 1 35 izer 102 and is absorbed by the function of the first quarter-wave plate 103a at the modulating means side, and [0036] Fig. 1 is a schematic block diagram for explain- hence does not reach the back side of the liquid crystal ing embodiment 1, in which a first quarter-wave plate light valve 101. That is, malfunction and other adverse 103a is disposed at the modulating means side between effects by the return light reflected by the face side of the the blue color modulating means 100B and the dichroic 40 dichroic filter 104S are eliminated. prism 105 as the color light combining means shown in [0041] As for the liquid crystal light valve 101 used in Fig. 7 relating to the prior art, and further a dichroic the modulating means of red light and green light, the filter104 having a function of selectively passing and se- same effects are obtained by the function of the dichroic lectively reflecting the color light is inserted. filter 104 for each color and the first quarter-wave plate [0037] This constitution solves the first problem that 45 103a at the modulating means side disposed in the di- the color light emitted from modulating means for other chroic filter 104. color enters the back side of the liquid crystal light valve [0042] However, it is not required to insert into all op- 101 using the liquid crystal for blue color as leak light tical paths, but it may be inserted at least in one optical from the dichroic prism 105 to cause adverse effects. path depending on the degree of adverse effects of cross- Since the inserted dichroic filter 104 has the function of 50 talk due to harmful light. The effects of the present inven- selectively passing and selectively reflecting the color tion are readily obtained by inserting the quarter wave light, only the modulated blue light is passed, and the plate and dichroic filter in the conventional system shown leak light (a slight green light and red light) emitted in Fig. 8, and it is advantageous that the optical parts through the dichroic prism 105 is reflected to the color used in the color light combining means and modulating light combining means, and hence does not reach the 55 means are not required to be particular parts. Although blue color modulating means side. That is, malfunction not mentioned specifically, the constituent optical mem- and other adverse effects by leak light to the back side bers are coated with anti-reflection treatment (generally of the liquid crystal light valve 101 for blue color are elim- AR coating) on the surface contacting with the air.

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Embodiment 2 [0048] In a second configuration, both the first quarter- wave plate 103a at the modulating means side and the [0043] Fig. 2 is a schematic block diagram showing second quarter-wave plate 103b at the color light com- embodiment 2. At the color light combining means side bining means are disposed on the same optical axis. That of the dichroic filter 104 comprising the first quarter- wave 5 is, the two quarter-wave plates are designed to act as plate 103a of the modulating means side disposed at the one half-wave plate. In this case, however, if the dichroic modulating means side in embodiment 1, further, a sec- prism 105 is used as the color light combining means, it ond quarter-wave plate 103b of color light combining is necessary to enter by S-polarized light on the prism means side is provided. reflection plane, and the transmission axis direction of [0044] The color light emitted from the modulating10 the exit side polarizer 102 of the modulating means of means for color light directing toward the back side of red light and blue light is the oscillation direction (P-po- the liquid crystal light valve 101 for blue color as leak light larized light) vertical to the S- polarized light on the prism from the dichroic prism 105 passes through the second reflection plane. quarter-wave plate 103b at the color light combining [0049] Thus, in the constitution in which the polarized means side, and becomes an elliptical polarized light or 15 light passing through one quarter-wave plate is nearly a circular polarized light, and is reflected by the dichroic perfect circular polarized light, the depending on the color mirror 104 to be return light, and becomes an inverse light combining means, the oscillation direction of the po- elliptical polarized light or circular polarized light, and larized light emitted from the modulating means may be passes again the second quarter- wave plate103b at the limited in the vertical direction or horizontal direction, and color light combining means side. In this constitution, the 20 the oscillation direction of the polarized light delivered axis of polarization of the incident leak light is a polarized from the modulating means may not be used nearly at light rotated on the axis of polarization by nearly 90 de- 45 degrees. grees, and returns reversely to the optical path from [0050] Incidentally, it is not required to insert the first which it is emitted. The polarized light of the return light quarter-wave plate 103a at the modulating means side rotated nearly 90 degrees on the axis of polarization is 25 and the second quarter- wave plate 103b at the color light absorbed by the exit side polarizer 102 of each optical combining means in all optical paths, but they may be path, and hence does not reach the back side of the liquid inserted at least in one optical path depending on the crystal light valve 101. degree of adverse effectsof crosstalk due to harmful light. [0045] In the foregoing embodiment 1, if the leak light The effects of the present invention are readily obtained as the return light by reflecting to the color light combining 30 by inserting the quarter wave plate and dichroic filter in side by the dichroic mirror 104 returns reversely to the the conventional system shown in Fig. 8, and it is advan- optical path from which it is emitted while being attenu- tageous that the optical parts used in the color light com- ated, and reaches the back side of the modulated liquid bining means and modulating means are not required to crystal light valve 101, a new problem may occur, and be particular parts. Although not mentioned specifically, such new problem is solved by the constitution of this 35 the constituent optical members are coated with anti- re- embodiment. flection treatment (generally AR coating) on the surface [0046] As for the liquid crystal light valve 101 used in contacting with the air. the modulating means of red light and green light, the same effects may be obtained by the function of the di- Embodiment 3 chroic filter 104 for each color and the second quarter- 40 wave plate 103b at the color light combining means pro- [0051] Fig. 3 is a schematic block diagram showing vided in the dichroic filter 104. However, the configuration embodiment 3. The first quarter-wave plate 103a of the of the optical axis of the second quarter- wave plate 103b modulating means side composed in embodiment 2 is at the color light combining means side and the optical disposed closely to the exit side polarizer 102, instead axis of the first quarter- wave plate 103a at the modulating 45 of the dichroic filter 104. In this constitution, the polarized means side may be considered in two manners. light emitted from the exit side polarizer 102 passes [0047] In a first configuration, the optical axis of the through the first quarter-wave plate 103a, and becomes first quarter-wave plate 103a is orthogonal to the optical an elliptical polarized light or circular polarized light, but axis of the second quarter-wave plate 103b. It is intended the return light reflected by the face side of the first quar- not to change the axis of the polarized light from each 50 ter-wave plate 103aS passes again the first quarter- wave modulating means toward the projection lens 106. In this plate103a. Hence, the polarized light is a polarized light case, however, if the dichroic prism 105 is used as the rotated by nearly 90 degrees from the oscillation direction color light combining means, it is necessary to enter by of the polarized light emitted from the exit side polarizer S-polarized light on the prism reflection plane, and the 102. Therefore, the return light is absorbed by the exit transmission axis direction of the exit side polarizer 102 55 side polarizer 102, and does not reach the liquid crystal of the modulating means of red light and blue light is the light valve 101. oscillation direction of S-polarized light on the prism re- [0052] The return light from the face side of the dichroic flection plane. mirror 104S also receives a similar action, and does not

6 11 EP 0 871 338 B1 12 reach the liquid crystal light valve 101. Thus, according embodiment 5. Closely to the second quarter- wave plate to the constitution of embodiment 3, adverse effects of 103b at the color light combining means side in embod- leak light due to other color light can be eliminated almost iment 3, a half-wave plate 108 is provided. In this consti- completely. tution, the light leaving the half-wave plate 108 can be [0053] The problems are thus eliminated about the re- 5 rotated into a polarized light in the optimum oscillation turn light left over slightly in embodiment 1 and embodi- direction for the color light combining means 105, and ment 2 (that is, the return light reflected by the face side hence it is free from restrictions by the incident light con- of the exit side polarizer 102S attributable to the differ- dition limited by the color light combining means 105 and ence between the refractive index of the exit side polar- the exit light by the modulating means 105. As a result, izer 102 and the refractive index of air, and the return 10 the application range of the light emitted from the mod- light reflected by the face side of the first quarter-wave ulating means 101 can be expanded. For example, if the plate 103aS at the modulating means side attributable oscillation direction of the polarized light leaving the mod- to the difference between the refractive index of the first ulating means 101 is an oscillation direction of about 45 quarter-wave plate 103a at the modulating means side degrees, it is possible to process without problem. and the refractive index of air). 15 [0058] Incidentally, it is not required to constitute as [0054] Incidentally, it is not required to constitute as specified above in all optical paths, but it may be consti- specified above in all optical paths, but it may be consti- tuted at least in one optical path depending on the degree tuted at least in one optical path depending on the degree of adverse effects of crosstalk due to harmful light. Al- of adverse effects of crosstalk due to harmful light. Al- though not mentioned specifically, the constituent optical though not mentioned specifically, the constituent optical 20 members are coated with anti-reflection treatment (gen- members are coated with anti-reflection treatment (generally AR coating) on the surface contacting with the air. erally AR coating) on the surface contacting with the air. Embodiment 6 Embodiment 4 25 [0059] Fig. 6 is a schematic block diagram showing [0055] Fig. 4 is a schematic block diagram showing embodiment 6. The second quarter- wave plate 103b and embodiment 4. Closely to the second quarter- wave plate half-wave plate 108 composed in embodiment 5 are dis- 103b at the color light combining means side in embod- posed closely to the color light combining means 105. In iment 2, a half-wave plate 108 is provided as the polar- this constitution, the problems are eliminated about the izing direction converting means. In this constitution, the 30 return light left over slightly in embodiment 5 (that is, the light leaving the half-wave plate 108 can be rotated into return light reflected by the face side of the half-wave a polarized light in the optimum oscillation direction for plate 108S attributable to the difference between the re- the color light combining means, and hence it is free from fractive index of the half-wave plate 108 and the refractive restrictions by the incident light condition limited by the index of air, and the return light reflected by the face side color light combining means and the exit light from the 35 of the color light combining means 105S attributable to modulating means 101. As a result, the application range the difference between the refractive index of the color of the light leaving the modulating means 101 can be lightcombining means 105 and the refractive index of air). expanded. For example, if the oscillation direction of the [0060] Newly, moreover, the return light reflected by polarized light leaving the modulating means 101 is an the face side of the second quarter-wave plate 103bS oscillation direction of about 45 degrees, it is possible to 40 attributable to the difference between the refractive index process without problem. of the second quarter-wave plate 103b at the color light [0056] Incidentally, it is not required to constitute as combining side and the refractive index of air, and the specified above in all optical paths, but it may be consti- return light reflected by the face side of the dichroic mirror tuted at least in one optical path depending on the degree 104S attributable to the difference between the refractive of adverse effects of crosstalk due to harmful light. The 45 index of the dichroic filter 104 and the refractive index of effects of the present invention are readily obtained by air are rotated by the first quarter- wave plate 103a at the inserting the quarter wave plate and dichroic filter in the modulating means side to be polarized lights rotated on conventional system as shown in Fig. 8, and it is advan- the axis of polarization by about 90 degrees to the axis tageous that the optical parts used in the color light com- of polarization emitted from the exit side polarizer 102, bining means and modulating means are not required to 50 and reach the exit side polarizer 102. be particular parts. Although not mentioned specifically, [0061] The polarized light of the return light rotated by the constituent optical members are coated with anti- re- about 90 degrees is absorbed by the exit side polarizer flection treatment (generally AR coating) on the surface 102 in each optical path, and does not reach the liquid contacting with the air. crystal light valve. 55 [0062] Thus, according to the constitution of embodi- Embodiment 5 ment 6, adverse effects of the leak light due to other color lights and adverse effects of return light reflected by the [0057] Fig. 5 is a schematic block diagram showing intervening optical parts can be eliminated almost com-

7 13 EP 0 871 338 B1 14 pletely. 3. A projection type video image display device of claim [0063] Incidentally, it is not required to constitute as 2, wherein said first quarter- wave plate contacts said specified above in all optical paths, but it may be consti- dichroic filter. tuted at least in one optical path depending on the degree of adverse effects of crosstalk due to harmful light. Al- 5 4. A projection type video image display device of claim though not mentioned specifically, the constituent optical 1, wherein said quarter-wave plate has a plurality of members are coated with anti-reflection treatment (gen- quarter-wave plates, erally AR coating) on the surface contacting with the air. a first quarter-wave plate of said plurality of quarter- [0064] As described herein from embodiment 1 to em- wave plates is disposed between said dichroic filter bodiment 6, according to the constitution of the invention, 10 and said modulating means, and it is possible to prevent the light passing through without a second quarter-wave plate of said plurality of quar- being reflected in the exit direction on the X-shaped re- ter-wave plates is disposed between said dichroic flection plane of the dichroic prism, or the light reflected filter and said color light combining means. by the X-shaped reflection plane, from reaching the side of the liquid crystal light valve. Further, the exit light is 15 5. A projection type video image display device of claim prevented from returning as being reflected by the dich- 4, wherein said first quarter- wave plate contacts said roic prism incident plane or exit plane. Therefore, it is dichroic filter, and said second quarter- wave plate is possible to shut off the light entering the back side of the contacting with said dichroic filter. liquid crystal light valve without heading toward the optical path advancing direction through the dichroic prism. 20 6. A projection type video image display device of claim It hence avoid the problems such as malfunction of the 1, wherein a polarizer is disposed at the light exit liquid crystal light valve due to light irradiation from the side of said modulating means, reverse direction of the optical path. As a result, a clear said quarter-wave plate has a plurality of quarter- projection image is obtained. wave plates, 25 a first quarter-wave plate of said plurality of quarter- wave plates is disposed between said dichroic filter Claims and said modulating means, and a second quarter-wave plate of said plurality of quar- 1. A projection type video image display device com- ter-wave plates is disposed between said dichroic prising: 30 filter and said color light combining means.

a light source for emitting a light in one direction, 7. A projection type video image display device of claim color light separating means for separating the 6, wherein said first quarter- wave plate contacts said white light from said light source into three color polarizer, and said second quarter-wave plate con- lights of red light, blue light and green light, 35 tacts said dichroic filter. modulating means comprising light valves for modulating polarized lights contained in lumi- 8. A projection type video image display device of claim nous fluxes from said color light separating 1, wherein said quarter-wave plate has a plurality of means, and producing a video image, quarter-wave plates, color light combining means for combining the 40 a first quarter-wave plate of said plurality of quarter- modulated luminous fluxes after being modulat- wave plates is disposed between said dichroic filter ed by said modulating means, and and said modulating means, projection optical means for projecting a com- a second quarter-wave plate of said plurality of quar- bined luminous flux obtained by said color light ter-wave plates is disposed between said dichroic combining means on a screen, 45 filter and said color light combining means, and wherein a dichroic filter having characteristics polarizing direction converting means is disposed for selectively passing and selectively reflecting between said second quarter-wave plate and said said color lights from said modulating means, color light combining means. and a quarter-wave plate are both disposed between said color light combining means and said 50 9. A projection type video image display device of claim modulating means positioned on an optical path 8, wherein said first quarter- wave plate contacts the of at least one color light of said three color lights face side of said dichroic filter, and said second quar- of the red light, blue light and green light. ter-wave plate contacts the other side of said dichroic filter. 2. A projection type video image display device of claim 55 1, wherein said quarter-wave plate is disposed be- 10. A projection type video image display device of claim tween said dichroic filter and said modulating means. 8, wherein said polarizing direction converting means contacts said second quarter-wave plate.

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11. A projection type video image display device of claim contacts said polarizing direction converting means. 8, wherein said first quarter- wave plate contacts the face side of said dichroic filter, said second quarter- 19. A projection type video image display device of claim wave plate contacts the other side of said dichroic 17, wherein said polarizing direction converting filter, and said polarizing direction converting means 5 means is a half-wave plate. contacts said second quarter-wave plate. 20. A projection type video image display device of 12. A projection type video image display device of claim claims 4, 6, 13, or 17, wherein two quarter-wave 8, wherein said polarizing direction converting length plates by joining said first quarter-wave plate means is a half-wave plate. 10 and said second quarter- wave plate function as one half-wave plate. 13. A projection type video image display device of claim 1, wherein a polarizer is disposed at the light exit 21. A projection type video image display device of claim side of said modulating means, 4 or 6, wherein each one of said first quarter-wave said quarter-wave plate has a plurality of quarter- 15 plate and said second quarter-wave plate is dis- wave plates, posed so that the polarized light from said modulat- a first quarter-wave plate of said plurality of quarter- ing means may enter as the light in the polarizing wave plates is disposed between said dichroic filter direction determined by said color light combining and said modulating means, means. a second quarter-wave plate of said plurality of quar- 20 ter-wave plates is disposed between said dichroic 22. A projection type video image display device of claim filter and said color light combining means, and 1, wherein said light valve contains a liquid crystal polarizing direction converting means is disposed material having a function of light transmission and between said second quarter-wave plate and said light shut-off. color light combining means. 25 23. A projection type video image display device of claim 14. A projection type video image display device of claim 1, wherein said color light combining means com- 13, wherein said first quarter-wave plate contacts prises a plurality of prisms, and has a function of said polarizer, and said second quarter-wave plate passing at least one of said red light, said blue light, contacts said dichroic filter. 30 and said green light, and reflecting at least one of the others. 15. A projection type video image display device of claim 14, wherein said polarizing direction converting means contacts said second quarter-wave plate. Patentansprüche 35 16. A projection type video image display device of claim 1. Projektions-Videobildanzeigevorrichtung, umfas- 13, wherein said polarizing direction converting send: means is a half-wave plate. eine Lichtquelle zum Aussenden eines Lichts in 17. A projection type video image display device of claim 40 eine Richtung, 1, wherein a polarizer is disposed at the light exit eine Farblichttrenneinrichtung zum Trennen side of said modulating means, des weißen Lichts von der Lichtquelle in drei said quarter-wave plate has a plurality of quarter- Farblichter aus rotem Licht, blauem Licht und wave plates, grünem Licht; a first quarter-wave plate of said plurality of quarter- 45 eine Modulationseinrichtung, die Lichtventile wave plates is disposed between said dichroic filter zum Modulieren polarisierten Lichts, das in and said modulating means, Lichtströmen von der Farblichttrenneinrichtung polarizing direction converting means is disposed enthalten ist, umfasst und ein Videobild erzeugt; between said dichroic filter and said color light com- eine Farblichtkombiniereinrichtung zum Kombi- bining means, closely to said color light combining 50 nieren der modulierten Lichtströme, nachdem means, and sie von der Modulationseinrichtung moduliert a second quarter-wave plate of said plurality of quar- wurden; und ter-wave plates is disposed between said dichroic Projektionsoptikeinrichtung zum Projizieren ei- filter and said color light combining means. nes kombinierten Lichtstroms, der durch die 55 Farblichtkombiniereinrichtung erzielt wurde, auf 18. A projection type video image display device of claim einen Bildschirm; 17, wherein said first quarter-wave plate contacts wobei sowohl ein dichroitisches Filter mit Eigen- said polarizer, and said second quarter-wave plate schaften zum selektiven Leiten und selektiven

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Reflektieren der Farblichter von der Modulati- und der Modulationseinrichtung angeordnet ist; onseinrichtung als auch eine Viertelwellenplatte eine zweite Viertelwellenplatte der Vielzahl von Vier- zwischen der Farblichtkombiniereinrichtung telwellenplatten zwischen dem dichroitischen Filter und der Modulationseinrichtung, die auf einem und der Farblichtkombiniereinrichtung angeordnet Lichtweg von wenigstens einem Farblicht aus 5 ist; und den drei Farblichtern des roten Lichts, blauen eine Polarisationsrichtungskonvertiereinrichtung Lichts und grünen Lichts positioniert sind, ange- zwischen der zweiten Viertelwellenplatte und der ordnet sind. Farblichtkombiniereinrichtung angeordnet ist.

2. Projektions-Videobildanzeigevorrichtung nach An- 10 9. Projektions-Videobildanzeigevorrichtung nach An- spruch 1, wobei die Viertelwellenplatte zwischen spruch 8, wobei die erste Viertelwellenplatte die Vor- dem dichroitischen Filter und der Modulationsein- derseite des dichroitischen Filters berührt und die richtung angeordnet ist. zweite Viertelwellenplatte die andere Seite des dichroitischen Filter berührt. 3. Projektions-Videobildanzeigevorrichtung nach An- 15 spruch 2, wobei die erste Viertelwellenplatte das di- 10. Projektions-Videobildanzeigevorrichtung nach An- chroitische Filter berührt. spruch 8, wobei die Polarisationsrichtungskonver- tiereinrichtung die zweite Viertelwellenplatte be- 4. Projektions-Videobildanzeigevorrichtung nach An- rührt. spruch 1, wobei die Viertelwellenplatte eine Vielzahl 20 von Viertelwellenplatten aufweist, 11. Projektions-Videobildanzeigevorrichtung nach An- eine erste Viertelwellenplatte der Vielzahl von Vier- spruch 8, wobei die erste Viertelwellenplatte die Vor- telwellenplatten zwischen dem dichroitischen Filter derseite des dichroitischen Filters berührt, die zweite und der Modulationseinrichtung angeordnet ist; und Viertelwellenplatte die andere Seite des dichroiti- eine zweite Viertelwellenplatte der Vielzahl von Vier- 25 schen Filter berührt und die Polarisationsrichtungs- telwellenplatten zwischen dem dichroitischen Filter konvertiereinrichtung die zweite Viertelwellenplatte und der Farblichtkombiniereinrichtung angeordnet berührt. ist. 12. Projektions-Videobildanzeigevorrichtung nach An- 5. Projektions-Videobildanzeigevorrichtung nach An- 30 spruch 8, wobei die Polarisationsrichtungskonver- spruch 4, wobei die erste Viertelwellenplatte das di- tiereinrichtung eine Halbwellenplatte ist. chroitische Filter berührt und sich die zweite Viertel- wellenplatte mit dem dichroitischen Filter in Kontakt 13. Projektions-Videobildanzeigevorrichtung nach An- befindet. spruch 1, wobei ein Polarisator an der Lichtaustritts- 35 seite der Modulationseinrichtung angeordnet ist, 6. Projektions-Videobildanzeigevorrichtung nach An- die Viertelwellenplatte eine Vielzahl von Viertelwel- spruch 1, wobei ein Polarisator an der Lichtaustritts- lenplatten aufinreist, seite der Modulationseinrichtung angeordnet ist, eine erste Viertelwellenplatte der Vielzahl von Vier- die Viertelwellenplatte eine Vielzahl von Viertelwel- telwellenplatten zwischen dem dichroitischen Filter lenplatten aufweist, 40 und der Modulationseinrichtung angeordnet ist; eine erste Viertelwellenplatte der Vielzahl von Vier- eine zweite Viertelwellenplatte der Vielzahl von Vier- telwellenplatten zwischen dem dichroitischen Filter telwellenplatten zwischen dem dichroitischen Filter und der Modulationseinrichtung angeordnet ist; und und der Farblichtkombiniereinrichtung angeordnet eine zweite Viertelwellenplatte der Vielzahl von Vier- ist; und telwellenplatten zwischen dem dichroitischen Filter 45 die Polarisationsrichtungskonvertiereinrichtung zwi- und der Farblichtkombiniereinrichtung angeordnet schen der zweiten Viertelwellenplatte und der Farb- ist. lichtkombiniereinrichtung angeordnet ist.

7. Projektions-Videobildanzeigevorrichtung nach An- 14. Projektions-Videobildanzeigevorrichtung nach An- spruch 6, wobei die erste Viertelwellenplatte den Po- 50 spruch 13, wobei die erste Viertelwellenplatte den larisator berührt und die zweite Viertelwellenplatte Polarisator berührt und die zweite Viertelwellenplat- das dichroitische Filter berührt. te das dichroitische Filter berührt.

8. Projektions-Videobildanzeigevorrichtung nach An- 15. Projektions-Videobildanzeigevorrichtung nach An- spruch 1, wobei die Viertelwellenplatte eine Vielzahl 55 spruch 14, wobei die Polarisationsrichtungskonver- von Viertelwellenplatten aufweist, tiereinrichtung die zweite Viertelwellenplatte be- eine erste Viertelwellenplatte der Vielzahl von Vier- rührt. telwellenplatten zwischen dem dichroitischen Filter

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16. Projektions-Videobildanzeigevorrichtung nach An- Revendications spruch 13, wobei die Polarisationsrichtungskonver- tiereinrichtung eine Halbwellenplatte ist. 1. Dispositif d’affichage d’images vidéo du type à projection comprenant : 17. Projektions-Videobildanzeigevorrichtung nach An- 5 spruch 1, wobei ein Polarisator an der Lichtaustritts- une source de lumière destinée à émettre une seite der Modulationseinrichtung angeordnet ist, lumière dans une direction, die Viertelwellenplatte eine Vielzahl von Viertelwel- un moyen de séparation de lumière de couleur lenplatten aufinreist, destiné à séparer la lumière blanche provenant eine erste Viertelwellenplatte der Vielzahl von Vier- 10 de ladite source de lumière en trois lumières de telwellenplatten zwischen dem dichroitischen Filter couleur de lumière rouge, de lumière bleue et und der Modulationseinrichtung angeordnet ist; de lumière verte, die Polarisationsrichtungskonvertiereinrichtung zwi- un moyen de modulation comprenant des val- schen dem dichroitischen Filter und der Farblicht- ves de lumière destiné à moduler des lumières kombiniereinrichtung eng an der Farblichtkombinier- 15 polarisées contenues dans des flux lumineux einrichtung angeordnet ist; und provenant dudit moyen de séparationde lumière eine zweite Viertelwellenplatte der Vielzahl von Vier- de couleur, et à produire une image vidéo, telwellenplatten zwischen dem dichroitischen Filter un moyen de combinaison de lumière de couleur und der Farblichtkombiniereinrichtung angeordnet destiné à combiner les flux lumineux modulés ist. 20 après avoir été modulés par ledit moyen de modulation, et 18. Projektions-Videobildanzeigevorrichtung nach An- un moyen optique de projection destiné à pro- spruch 17, wobei die erste Viertelwellenplatte den jeter un flux lumineux combiné obtenu par ledit Polarisator berührt und die zweite Viertelwellenplat- moyen de combinaison de lumière de couleur te die Polarisationsrichtungskonvertiereinrichtung 25 sur un écran, berührt. dans lequel un filtre dichroïque ayant des carac- téristiques pour transmettre sélectivement et ré- 19. Projektions-Videobildanzeigevorrichtung nach An- fléchir sélectivement lesdites lumières de cou- spruch 17, wobei die Polarisationsrichtungskonver- leur depuis ledit moyen de modulation, et une tiereinrichtung eine Halbwellenplatte ist. 30 plaque quart d’onde sont tous les deux disposés entre ledit moyen de combinaison de lumière de 20. Projektions-Videobildanzeigevorrichtung nach den couleur et ledit moyen de modulation positionné Ansprüchen 4, 6, 13 oder 17, wobei zwei Viertelwel- sur un trajet optique d’au moins une lumière de lenlängenplatten durch Verbinden der ersten Vier- couleur parmi lesdites trois lumières de couleur telwellenplatte und der zweiten Viertelwellenplatte 35 de la lumière rouge, de la lumière bleue et de la als eine Halbwellenplatte arbeiten. lumière verte.

21. Projektions-Videobildanzeigevorrichtung nach An- 2. Dispositif d’affichage d’images vidéo du type à pro- spruch 4 oder 6, wobei jede der ersten Viertelwel- jection selon la revendication 1, dans lequel ladite lenplatte und der zweiten Viertelwellenplatte so an- 40 plaque quart d’onde est placée entre ledit filtre di- geordnet ist, dass das polarisierte Licht von der Mo- chroïque et ledit moyen de modulation. dulationseinrichtung als das Licht in der Polarisati- onsrichtung, die von der Farblichtkombiniereinrich- 3. Dispositif d’affichage d’images vidéo du type à pro- tung bestimmt wurde, eintreten kann. jection selon la revendication 2, dans lequel ladite 45 première plaque quart d’onde vient en contact avec 22. Projektions-Videobildanzeigevorrichtung nach An- ledit filtre dichroïque. spruch 1, wobei das Lichtventil ein Flüssigkristallma- terial mit einer Lichtdurchlass- und Lichtsperrfunkti- 4. Dispositif d’affichage d’images vidéo du type à pro- on umfasst. jection selon la revendication 1, dans lequel ladite 50 plaque quart d’onde comporte une pluralité de pla- 23. Projektions-Videobildanzeigevorrichtung nach An- ques quart d’onde, spruch 1, wobei die Farblichtkombiniereinrichtung une première plaque quart d’onde de ladite pluralité eineVielzahl vonPrismen umfasst und eine Funktion de plaques quart d’onde est placée entre ledit filtre zum Weiterleiten wenigstens eines des roten Lichts, dichroïque et ledit moyen de modulation, et des blauen Lichts und des grünen Lichts und zum 55 une seconde plaque quart d’onde de ladite pluralité Reflektieren wenigstens eines der anderen aufweist. de plaques quart d’onde est placée entre ledit filtre dichroïque et ledit moyen de combinaison de lumière de couleur.

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5. Dispositif d’affichage d’images vidéo du type à pro- que quart d’onde est en contact avec l’autre côté jection selon la revendication 4, dans lequel ladite dudit filtre dichroïque et ledit moyen de conversion première plaque quart d’onde est en contact avec de direction de polarisation est en contact avec ladite ledit filtre dichroïque, et ladite seconde plaque quart seconde plaque quart d’onde. d’onde est en contact avec ledit filtre dichroïque. 5 12. Dispositif d’affichage d’images vidéo du type à pro- 6. Dispositif d’affichage d’images vidéo du type à projection selon la revendication 8, dans lequel ledit jection selon la revendication 1, dans lequel un po- moyen de conversion de direction de polarisation est lariseur est placé du côté sortie de lumière dudit une plaque demi-onde. moyen de modulation, 10 ladite plaque quart d’onde comporte une pluralité de 13. Dispositif d’affichage d’images vidéo du type à pro- plaques quart d’onde, jection selon la revendication 1, dans lequel un po- une première plaque quart d’onde de ladite pluralité lariseur est placé du côté sortie de lumière dudit de plaques quart d’onde est placée entre ledit filtre moyen de modulation, dichroïque et ledit moyen de modulation, et 15 ladite plaque quart d’onde comporte une pluralité de une seconde plaque quart d’onde de ladite pluralité plaques quart d’onde, de plaques quart d’onde est placée entre ledit filtre une première plaque quart d’onde de ladite pluralité dichroïque et ledit moyen de combinaison de lumière de plaques quart d’onde est placée entre ledit filtre de couleur. dichroïque et ledit moyen de modulation, 20 une seconde plaque quart d’onde de ladite pluralité 7. Dispositif d’affichage d’images vidéo du type à pro- de plaques quart d’onde est placée entre ledit filtre jection selon la revendication 6, dans lequel ladite dichroïque et ledit moyen de combinaison de lumière première plaque quart d’onde est en contact avec de couleur, et ledit polariseur, et ladite seconde plaque quart d’on- un moyen de conversion de direction de polarisation de est en contact avec le filtre dichroïque. 25 est placé entre ladite seconde plaque quart d’onde et ledit moyen de combinaison de lumière de cou- 8. Dispositif d’affichage d’images vidéo du type à pro- leur. jection selon la revendication 1, dans lequel ladite plaque quart d’onde comporte une pluralité de pla- 14. Dispositif d’affichage d’images vidéo du type à pro- ques quart d’onde, 30 jection selon la revendication 13, dans lequel ladite une première plaque quart d’onde de ladite pluralité première plaque quart d’onde est en contact avec de plaques quart d’onde est placée entre ledit filtre ledit polariseur, et ladite seconde plaque quart d’on- dichroïque et ledit moyen de modulation, de est en contact avec ledit filtre dichroïque. une seconde plaque quart d’onde de ladite pluralité de plaques quart d’onde est placée entre ledit filtre 35 15. Dispositif d’affichage d’images vidéo du type à pro- dichroïque et ledit moyen de combinaison de lumière jection selon la revendication 14, dans lequel ledit de couleur, et moyen de conversion de direction de polarisation est un moyen de conversion de direction de polarisation en contact avec ladite seconde plaque quart d’onde. est placé entre ladite seconde plaque quart d’onde et ledit moyen de combinaison de lumière de cou- 40 16. Dispositif d’affichage d’images vidéo du type à pro- leur. jection selon la revendication 13, dans lequel ledit moyen de conversion de direction de polarisation est 9. Dispositif d’affichage d’images vidéo du type à pro- une plaque demi-onde. jection selon la revendication 8, dans lequel ladite première plaque quart d’onde est en contact avec le 45 17. Dispositif d’affichage d’images vidéo du type à pro- côté face dudit filtre dichroïque et ladite seconde pla- jection selon la revendication 1, dans lequel un po- que quart d’onde est en contact avec l’autre côté lariseur est placé du côté sortie de lumière dudit dudit filtre dichroïque. moyen de modulation, ladite plaque quart d’onde comporte une pluralité de 10. Dispositif d’affichage d’images vidéo du type à pro- 50 plaques quart d’onde, jection selon la revendication 8, dans lequel ledit une première plaque quart d’onde de ladite pluralité moyen de conversion de direction de polarisation est de plaques quart d’onde est placée entre ledit filtre en contact avec ladite seconde plaque quart d’onde. dichroïque et ledit moyen de modulation, le moyen de conversion de direction de polarisation 11. Dispositif d’affichage d’images vidéo du type à pro- 55 est placé entre ledit filtre dichroïque et ledit moyen jection selon la revendication 8, dans lequel ladite de combinaison de lumière de couleur, à proximité première plaque quart d’onde est en contact avec le dudit moyen de combinaison de lumière de couleur, côté face dudit filtre dichroïque, ladite seconde pla- et

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une seconde plaque quart d’onde de ladite pluralité de plaques quart d’onde est placée entre ledit filtre dichroïque et ledit moyen de combinaison de lumière de couleur. 5 18. Dispositif d’affichage d’images vidéo du type à projection selon la revendication 17, dans lequel ladite première plaque quart d’onde est en contact avec ledit polariseur, et ladite seconde plaque quart d’onde est en contact avec ledit moyen de conversion 10 de direction de polarisation.

19. Dispositif d’affichage d’images vidéo du type à projection selon la revendication 17, dans lequel ledit moyen de conversion de direction de polarisation est 15 une plaque demi-onde.

20. Dispositif d’affichage d’images vidéo du type à projection selon les revendications 4, 6, 13 ou 17, dans lequel deux plaques d’une longueur quart d’onde, 20 en réunissant ladite première plaque quart d’onde et ladite seconde plaque quart d’onde, fonctionnent en tant qu’une seule plaque demi-onde.

21. Dispositif d’affichage d’images vidéo du type à pro- 25 jection selon la revendication 4 ou 6, dans lequel chacune de ladite première plaque quart d’onde et de ladite seconde plaque quart d’onde est placée de façon à ce que la lumière polarisée provenant dudit moyen de modulation puisse entrer en tant que la 30 lumière dans la direction de polarisation déterminée par ledit moyen de combinaison de lumière de couleur.

22. Dispositif d’affichage d’images vidéo du type à pro- 35 jection selon la revendication 1, dans lequel ladite valve de lumière contient un matériau de cristaux liquides ayant une fonction de transmission de lu- mière et de coupure de lumière. 40 23. Dispositif d’affichage d’images vidéo du type à projection selon la revendication 1, dans lequel ledit moyen de combinaison de lumière de couleur com- prend une pluralité de prismes, et a une fonction de transmission d’au moins une de ladite lumière rouge, 45 de ladite lumière bleue, et de ladite lumière verte, et de réflexion d’au moins l’une des autres.

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