JP2005250241A - Projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projector capable of projecting an image of uniform brightness to the whole screen by simply suppressing a phenomenon that the image is darkened on the peripheral part of the screen. <P>SOLUTION: Illumination light beams, i.e. image light beams, modulated by respective liquid crystal light valves 25a-25c are composited by a cross dichroic prism 27 and the composited image light beams are made incident on a projection lens 29. The image light made incident on the projection lens 29 is projected to a screen which is not shown. Since a retardation plate 28 having an aperture 28a on the center is stuck to the exit face 27c of the cross dichroic prism 27, a polarized light P can be made incident on the center part of a reflection mirror 16 and S polarized light can be made incident on the peripheral part of the reflection mirror 16. Thereby the reflection factor of the image light on the peripheral part of the projection mirror 16 can be increased and the phenomenon that the image projected to a translucent screen 18 is darkened on the periphery of the screen 18 can be suppressed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projector that projects a color image using a liquid crystal display panel or other light modulation device.

As an optical system constituting a conventional projector, there is an optical system in which modulated light of each color from a liquid crystal display panel illuminated with illumination light of each color is synthesized by a light synthesis member called a cross dichroic prism and projected as a color image. (See Patent Document 1). When such an optical system is incorporated into a rear projection type projector, the image light from the projection lens is reflected by a folding mirror and then passed through the screen in order to reduce the thickness of the projector.
JP 2000-206450 A

  However, in the projector as described above, the image at the center of the screen tends to be bright and the image at the periphery is dark. This is because, for example, the incident angle of the image light to the screen or mirror tends to be small in the central portion and large in the peripheral portion, and light amount loss is considered to occur in the peripheral portion.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a projector capable of easily projecting an image with uniform brightness on the entire screen while easily suppressing a phenomenon that an image in a peripheral portion of a screen becomes dark.

  In order to solve the above problems, a projector according to the present invention includes (a) a light modulating unit that is illuminated with illumination light having a predetermined polarization direction emitted from an illumination device, and modulates the illumination light, and (b) A projection optical system for forming a projection image of the image light formed by passing through the light modulation means, (c) a folding mirror for guiding the image light emitted from the projection optical system to the screen, and (d) the light modulation means And a polarization direction rotating unit that is arranged on the exit side and rotates the polarization direction of the image light at one of the central portion and the peripheral portion of the optical path cross section.

  In the projector described above, the polarization direction rotating means rotates the polarization direction of the image light in one of the central part and the peripheral part of the optical path cross section, so that the light attenuation at the peripheral part is centered by utilizing the polarization dependence characteristics of the folding mirror. It can be reduced compared with the dimming at the part. Therefore, it is possible to provide a projector that can project an image with uniform brightness on the whole.

  Further, in a specific aspect of the invention, in the projector, the polarization direction rotating unit includes a retardation plate partially disposed on a cross section of the optical path of the image light. In this case, the polarization direction can be easily rotated by the phase difference plate without loss of light amount.

  In another specific aspect of the present invention, the phase difference plate is disposed in the periphery of the optical path cross section of the image light. Here, the retardation plate is, for example, a λ / 2 wavelength plate. In this case, it is assumed that P-polarized image light is incident on the folding mirror, and the P-polarized light can be changed to S-polarized light at the peripheral portion. The reflectance can be increased relatively than the portion.

  Further, in another specific aspect of the present invention, the polarization direction rotating means includes a first retardation plate disposed entirely on the optical path cross section of the image light, and partially disposed on the optical path cross section of the image light. A second retardation plate. Here, the first and second retardation plates are, for example, λ / 2 wavelength plates. In this case, it is not necessary to use a donut-like retardation plate with a missing central portion, and the processing of the first and second retardation plates is simple.

  In another specific aspect of the present invention, the illumination device emits illumination light of each color, and the light modulation means is illuminated with illumination light of each color emitted from the illumination device, and illumination of each color. A light modulating device for each color that modulates the light, and a light combining member that emits image light obtained by combining the modulated light of each color that has passed through the light modulating device for each color. In this case, a color image can be projected by synthesizing image light from each color light modulation device.

  In another specific aspect of the present invention, the light combining member is a cross dichroic prism, and the polarization direction rotating means is attached to the exit surface of the cross dichroic prism. In this case, the polarization direction can be collectively rotated with respect to the color image light synthesized by the cross dichroic prism.

  In another specific aspect of the present invention, the polarization direction rotating means is attached to the optical element on the incident side of the projection optical system. In this case, it becomes easy to defocus the polarization switching boundary between the central portion and the peripheral portion by the polarization direction rotating means.

  In another specific aspect of the present invention, the polarization direction rotating means is attached to the optical element on the exit side of the projection optical system. In this case, it becomes easy to defocus the polarization switching boundary between the central portion and the peripheral portion by the polarization direction rotating means.

[First Embodiment]
FIG. 1 is a side view illustrating the overall structure of the projector according to the first embodiment of the invention. The projector 10 is a rear projection type device that displays an image by rear projection, and includes a projector main body 14 at the bottom of a case 12 that is a casing, and a reflection mirror 16 at the upper rear side in the case 12. 12 A transmission screen 18 is provided on the front surface. The image light emitted from the projector main body 14 travels obliquely upward and rearward along the optical axis OA1, is bent in the direction of the horizontal optical axis OA2 by the reflection mirror 16 that is a folding mirror, and enters the transmissive screen 18. The projector main body 14, the reflection mirror 16, and the transmissive screen 18 are positioned and fixed in the case 12 by means not shown.

  FIG. 2 is a block diagram conceptually illustrating the structure of the projector main body 14 in the projector 10 shown in FIG. The projector main body 14 includes a light source device 21 that generates light source light, a color division optical system 23 that divides the light source light from the light source device 21 into three colors of RGB, and illumination of each color emitted from the color division optical system 23. A light modulator 25 illuminated by light, a cross dichroic prism 27 that is a light combining member for combining modulated light of each color from the light modulator 25, and image light that has passed through the cross dichroic prism 27 is screened (not shown). And a projection lens 29 that is a projection optical system for projecting onto the projector. Among these, the light source device 21 and the color division optical system 23 constitute an illumination device for illuminating the light modulation unit 25. The light modulator 25 and the cross dichroic prism 27 function as a light modulator, and form color image light from illumination light.

  Here, the light source device 21 includes a light source lamp 21a, a pair of fly-eye optical systems 21d and 21e, a polarization conversion member 21g, and a superimposing lens 21i. Here, the light source lamp 21a is made of, for example, a high-pressure mercury lamp, and includes a concave mirror for collimating the light source light. The pair of fly-eye optical systems 21d and 21e is composed of a plurality of element lenses arranged in a matrix, and these element lenses divide the light source light from the light source lamp 21a and individually collect and diverge the light. The polarization conversion member 21g converts the light source light emitted from the fly-eye optical system 21e into only the S-polarized component perpendicular to the paper surface of FIG. 1 and supplies it to the next stage optical system. The superimposing lens 21i appropriately converges the illumination light that has passed through the polarization conversion member 21g as a whole, and enables superimposing illumination on the light modulation devices of the respective colors provided in the light modulation unit 25. That is, the illumination light that has passed through both the fly-eye optical systems 21d and 21e and the superimposing lens 21i passes through the color splitting optical system 23, which will be described in detail below. The liquid crystal light valves 25a to 25c are uniformly illuminated.

  The color division optical system 23 includes first and second dichroic mirrors 23a and 23b, three field lenses 23f, 23g, and 23h, and reflection mirrors 23m, 23n, and 23o. The first dichroic mirror 23a reflects R light and transmits G light and B light among the three colors of RGB. The second dichroic mirror 23b reflects G light and transmits B light out of the two colors of incident GB. In the color splitting optical system 23, white illumination light from the light source device 21 enters the first dichroic mirror 23a. The R light reflected by the first dichroic mirror 23a is guided to the first optical path OP1 as S-polarized light, and enters the field lens 23f for adjusting the incident angle via the reflecting mirror 23m. Further, the G light transmitted through the first dichroic mirror 23a and reflected by the second dichroic mirror 23b is guided to the second optical path OP2 as S-polarized light and enters the field lens 23g. Further, the B light that has passed through the second dichroic mirror 23b is guided to the third optical path OP3 as S-polarized light, and has an incident angle through the relay lenses LL1 and LL2 and the reflecting mirrors 23n and 23o for compensating for the optical path length difference. The light enters the field lens 23h for adjustment.

  The light modulation unit 25 includes three liquid crystal light valves 25a to 25c, each of which is a light modulation device, and three sets of polarizing filters 25e to 25g arranged so as to sandwich the liquid crystal light valves 25a to 25c. The R light guided to the first optical path OP1 enters the liquid crystal light valve 25a through the field lens 23f. The G light guided to the second optical path OP2 enters the liquid crystal light valve 25b via the field lens 23g. The B light guided to the third optical path OP3 enters the liquid crystal light valve 25c via the field lens 23h. Each of the liquid crystal light valves 25a to 25c is a non-light-emitting light modulation device for modulating the spatial intensity distribution of incident illumination light. The polarization states of the three colors of light incident on the liquid crystal light valves 25a to 25c are adjusted in units of pixels in accordance with drive signals or image signals input as electrical signals to the liquid crystal light valves 25a to 25c. . At that time, the polarization filters 25e to 25g adjust the polarization direction of the illumination light incident on the liquid crystal light valves 25a to 25c, and modulate the predetermined polarization direction from the light emitted from the liquid crystal light valves 25a to 25c. Light is extracted.

  The cross dichroic prism 27 includes a dielectric multilayer film 27a for reflecting R light and a dielectric multilayer film 27b for reflecting B light in a state of being orthogonal to each other. The cross dichroic prism 27 reflects the R light from the liquid crystal light valve 25a by the dielectric multilayer film 27a and emits the G light from the liquid crystal light valve 25b through the dielectric multilayer films 27a and 27b. The B light from the liquid crystal light valve 25c is reflected by the dielectric multilayer film 27b and emitted to the left in the traveling direction.

  On the exit surface 27c of the cross dichroic prism 27, a retardation plate 28 made of a flat, rectangular frame-shaped λ / 2 plate is attached. This retardation plate 28 rotates the polarization direction of the color image light that has passed through the cross dichroic prism 27 by 90 ° only at the periphery of the optical path cross section as a polarization direction rotating means. That is, on the exit surface 27c side of the cross dichroic prism 27, the color image light in the peripheral portion is converted from S-polarized light to P-polarized light with reference to both dielectric multilayer films 27a and 27b.

  FIG. 3 is a diagram illustrating the structure of the phase difference plate 28. The phase difference plate 28 attached to the exit surface 27c of the cross dichroic prism 27 has a rectangular outline, for example, and has a rectangular opening 28a at the center. The outline of the phase difference plate 28 and the central opening 28a have a similar shape with the center coincident. Since the color image light emitted from the cross dichroic prism 27 passes through the opening 28a of the phase difference plate 28 at the center of the optical path cross section, that is, around the optical axis OA, it is maintained as S-polarized light. Further, in the peripheral portion of the optical path cross section, that is, the portion away from the optical axis OA, the emitted color image light is converted from S-polarized light to P-polarized light by transmission through the phase difference plate 28. That is, the polarization direction of the image light emitted from the cross dichroic prism 27 is rotated by 90 ° only at the periphery of the optical path cross section. In the above example, the opening 28a of the retardation plate 28 has a rectangular shape close to a square, but the aspect ratio and size thereof are appropriately changed according to the shape and size of the irradiated surface of the liquid crystal light valves 25a to 25c. can do. Further, the opening 28a of the phase difference plate 28 can be circular or elliptical.

  Returning to FIG. 2, the projection lens 29 applies color image light emitted from the cross dichroic prism 27 and partially rotated in the polarization direction by the phase difference plate 28 onto the screen 18 via the reflection mirror 16. Project at an enlargement rate. At this time, the S-polarized light emitted from the cross dichroic prism 27 is converted into P-polarized light at the peripheral portion by the phase difference plate 28. That is, the color image light emitted from the cross dichroic prism 27 is S-polarized light at the central portion and P-polarized light at the peripheral portion. The above is the definition of the polarization plane with reference to the cross dichroic prism 27. However, for the reflection mirror 16 in FIG. 1, the plane (vertical plane) including the pair of optical axes OA1 and OA2 is the reference plane. The S-polarized light of the cross dichroic prism 27 becomes P-polarized light, and the P-polarized light of the cross dichroic prism 27 becomes S-polarized light. That is, the image light incident on the reflection mirror 16 is mainly P-polarized light at the central portion and mainly S-polarized light at the peripheral portion. Therefore, the image light incident on the peripheral part of the reflection mirror 16 is reflected with a high reflectance because the S-polarized light is dominant, and the image light incident on the central part of the reflection mirror 16 is dominant in the P-polarized light. Therefore, it is reflected with a relatively low reflectance. As a result, bright image light can be incident on the peripheral portion of the transmissive screen 18 so as to cancel out the light amount loss caused by the increase in the incident angle in the peripheral portion of the transmissive screen 18. An image with uniform brightness can be formed on the entire surface 18. The above retardation plate 28 is projected onto the transmissive screen 18 in a state where the focus is moderately blurred although it is close to the liquid crystal light valves 25a to 25c, so that the contour of the opening 28a can be prevented from being projected. An image with a smooth luminance distribution can be obtained.

  Hereinafter, the operation of the projector 10 according to the present embodiment will be described. The light source light from the light source device 21 is color-divided by the first and second dichroic mirrors 23a and 23b provided in the color-dividing optical system 23, and is incident on the corresponding liquid crystal light valves 25a to 25c as illumination light. Each of the liquid crystal light valves 25a to 25c is modulated by an image signal from the outside and has a two-dimensional refractive index distribution, and modulates illumination light in a two-dimensional space in units of pixels. As described above, the illumination light, that is, image light modulated by the liquid crystal light valves 25 a to 25 c is combined by the cross dichroic prism 27 and then enters the projection lens 29. The image light incident on the projection lens 29 is projected onto the screen 18 through the reflection mirror 16. At this time, since the phase difference plate 28 having the opening 28 a at the center is attached to the exit surface 27 c of the cross dichroic prism 27, P-polarized light is incident on the central portion of the reflecting mirror 16 and S is applied to the peripheral portion of the reflecting mirror 16. Polarized light can be incident. Therefore, the reflectance of the image light in the peripheral part of the reflection mirror 16 can be increased, and the phenomenon in which the image projected on the transmissive screen 18 becomes dark in the periphery can be suppressed.

[Second Embodiment]
Hereinafter, the projector according to the second embodiment will be described. This projector is obtained by modifying the projector 10 according to the first embodiment with respect to a phase difference plate 28 that is a polarization direction rotating unit.

  FIG. 4 is a diagram for explaining the structure of the polarization direction rotating device 128 incorporated in the projector according to the second embodiment. The polarization direction rotating device 128 is affixed to the exit surface 27c of the cross dichroic prism 27 as a polarization direction rotating means, and a base first retardation plate 128A attached so as to entirely cover the optical path section, and an optical path And an upper second retardation plate 128B attached to cover the center of the cross section, that is, the periphery of the optical axis OA. Since the first and second retardation plates 128A and 128B are both λ / 2 wavelength plates, the rotation of the polarization direction formed by the first retardation plate 128A is canceled by the second retardation plate 128B, and as a result In addition, the image light passing through the second retardation plate 128B passes through without being subjected to the rotating action in the polarization direction.

  By using the polarization direction rotating device 128 as described above, the image light emitted from the cross dichroic prism 27 remains S-polarized at the center of the optical path cross section and is S-polarized at the periphery of the optical path cross section. To P-polarized light. That is, the polarization direction of the image light emitted from the cross dichroic prism 27 is rotated by 90 ° only at the periphery of the optical path cross section. Therefore, as in the case of the first embodiment, the reflectance of the image light in the peripheral portion of the reflection mirror 16 can be increased, and the phenomenon that the image projected on the transmission screen 18 becomes dark in the periphery can be suppressed. it can.

  Since the polarization direction rotating device 128 used in the second embodiment is simply bonded to the rectangular retardation plates 128A and 128B, the processing is easy.

[Third Embodiment]
The projector according to the third embodiment will be described below. This projector is obtained by modifying the projector 10 of the first embodiment with respect to the mounting position of the phase difference plate 28.

  FIG. 5 is a diagram for explaining the arrangement of the phase difference plate 228 incorporated in the projector according to the third embodiment. In this case, the phase difference plate 228 is affixed to the incident surface of the incident lens 29 a among the lens elements 29 a and 29 b which are a large number of optical elements constituting the projection lens 29. Therefore, the S-polarized light incident on the projection lens 29 is converted into P-polarized light at the peripheral part by the phase difference plate 228, and passes through the central opening 228a as S-polarized light. That is, the image light emitted from the projection lens 29 is substantially S-polarized light at the central portion and substantially P-polarized light at the peripheral portion, so that the image light at the peripheral portion of the reflecting mirror 16 (see FIG. 1). Thus, it is possible to suppress a phenomenon in which an image projected on the transmission screen 18 (see FIG. 1) becomes dark in the vicinity.

  The retardation plate 228 described above can be replaced with a wave plate having a two-layer structure similar to the polarization direction rotating device 128 of the second embodiment shown in FIG.

[Fourth Embodiment]
The projector according to the fourth embodiment will be described below. This projector is obtained by modifying the projector 10 of the first embodiment with respect to the mounting position of the phase difference plate 28.

  FIG. 6 is a diagram illustrating the arrangement of the phase difference plate 328 incorporated in the projector according to the fourth embodiment. In this case, the phase difference plate 328 is affixed to the exit surface of the exit lens 29 b among the many lens elements 29 a, 29 b, etc. constituting the projection lens 29. Therefore, the S-polarized light emitted from the projection lens 29 is converted into P-polarized light at the peripheral portion by the phase difference plate 328, and passes through the central opening 328a as it is. That is, the image light emitted from the projection lens 29 is substantially S-polarized light at the central portion and substantially P-polarized light at the peripheral portion, so that the image light at the peripheral portion of the reflecting mirror 16 (see FIG. 1). Thus, it is possible to suppress a phenomenon in which an image projected on the transmission screen 18 (see FIG. 1) becomes dark in the vicinity.

  The retardation plate 328 described above can be replaced with a wave plate having a two-layer structure similar to the polarization direction rotating device 128 of the second embodiment shown in FIG.

[Fifth Embodiment]
Hereinafter, a projector according to a fifth embodiment will be described with reference to FIG. The projector 410 has a structure in which the projector main body 14 of the first embodiment is rotated by 90 ° around the optical axis OA. As a result, the definitions of the polarization planes of the cross dichroic prism 27 and the reflection mirror 16 coincide. That is, the phase difference plate 428 incorporated in the projector main body 14 is attached to the exit surface of the cross dichroic prism 27 and covers only the central portion around the optical axis OA. As a result, the image light emitted from the cross dichroic prism 27 passes through the phase difference plate 428 at the central portion of the optical path cross section, and thus is converted from S-polarized light to P-polarized light. At the peripheral portion of the optical path cross section, the phase difference plate 428 is converted. Does not pass through, so that it remains S-polarized light. As a result, the image light incident on the reflection mirror 16 is mainly P-polarized light at the central portion and mainly S-polarized light at the peripheral portion, so that bright image light can be incident on the peripheral portion of the transmission screen 18. .

  As described above, the present invention has been described according to the embodiment, but the present invention is not limited to the above embodiment. For example, in each of the above-described embodiments, the projector body is a so-called three-plate projector composed of three liquid crystal light valves 25a to 25c, but in a single-plate projector that combines a white light source and a color-type liquid crystal light valve. In addition, by arranging the retardation plates 28, 228, 328, 428 and the polarization direction rotating device 128 in the subsequent stage of the liquid crystal light valve, the peripheral screen 18 can be prevented from being dimmed.

  Further, in the first embodiment and the like, the opening 28a is formed in the retardation plate 28. By filling the opening 28a with a transparent material having no birefringence, the boundary between the central portion and the peripheral portion is formed. Thus, it is possible to prevent an optical path step from occurring with respect to the image light.

  In the above embodiment, the retardation plates 28, 228, 328, 428 and the polarization direction rotating device 128 are formed of λ / 2 wavelength plates. However, other types of wavelength plates (λ / 4 wavelength plates, etc.) are used. It can also be formed. In this case, the brightness enhancement amount in the vicinity can be adjusted to some extent.

  Further, the above retardation plates 28, 228, 328, and 428 may be for specific wavelengths, but can correspond to RGB colors. In this case, the optical path difference due to birefringence may be n + λ / 2 (n is a natural number different for each color of RGB).

It is a figure explaining the projector of 1st Embodiment. It is a figure explaining the optical system of the projector main body shown in FIG. It is a figure explaining the structure and attachment state of a phase difference plate. It is a figure explaining the polarization direction rotation apparatus in the projector of 2nd Embodiment. It is a figure explaining arrangement | positioning of the phase difference plate in the projector of 3rd Embodiment. It is a figure explaining arrangement | positioning of the phase difference plate in the projector of 4th Embodiment. It is a figure explaining the projector of 5th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Projector, 14 ... Projector main body, 16 ... Reflection mirror, 18 ... Transmission type screen, 21 ... Light source device, 21g ... Polarization conversion member, 23 ... Color division optical system, 23a, 23b ... Dichroic mirror, 25 ... Light modulation part 25a to 25c ... liquid crystal light valve, 27 ... cross dichroic prism, 27a, 27b ... dielectric multilayer film, 27c ... exit surface, 28 ... phase difference plate, 29 ... projection lens

Claims (8)

A light modulation means for illuminating with illumination light in a predetermined polarization direction emitted from the illumination device and modulating the illumination light;
A projection optical system for forming a projection image of the image light formed by passing through the light modulation means;
A folding mirror for guiding the image light emitted from the projection optical system to a screen;
A projector comprising: a polarization direction rotating unit that is disposed on the light exit side of the light modulation unit and rotates the polarization direction of the image light in one of the central part and the peripheral part of the optical path cross section.   The projector according to claim 1, wherein the polarization direction rotating unit includes a retardation plate partially disposed on a cross section of the optical path of the image light.   The projector according to claim 2, wherein the phase difference plate is disposed in a peripheral portion of an optical path cross section of image light.   The polarization direction rotating means includes a first retardation plate disposed entirely on the optical path section of the image light, and a second retardation plate partially disposed on the optical path section of the image light. The projector according to claim 1.   The illumination device emits illumination light of each color, and the light modulation unit is illuminated with illumination light of each color emitted from the illumination device, and modulates the illumination light of each color, respectively. 5. A projector according to claim 1, further comprising: a light combining member that emits image light obtained by combining the modulated light of each color that has passed through the light modulation device of each color.   6. The projector according to claim 5, wherein the light combining member is a cross dichroic prism, and the polarization direction rotating means is attached to an exit surface of the cross dichroic prism.   6. The projector according to claim 5, wherein the polarization direction rotating means is attached to an incident side optical element of the projection optical system. The projector according to claim 5, wherein the polarization direction rotating unit is attached to an optical element on an emission side of the projection optical system.

Images