JP2004045907A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a projector, which decreases in contrast as the lightness is increased and needs to have the lightness decreased to increase the contrast, to have both lightness and a high contrast. <P>SOLUTION: The angle of divergence of light made incident on a polarization beam splitter on the plane containing the incidence direction and reflection direction of a main light beam to and from the polarization beam splitter is made narrower than the angle of divergence of light irradiating a polarization beam splitter on a plane perpendicular to the above plane containing the main light beam. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a projection apparatus for projecting an image on a screen using a light valve element such as a liquid crystal panel or a reflection type image display element, for example, a liquid crystal projector apparatus, a reflection type image display projector apparatus, and a projection type display apparatus. And the like.
[0002]
[Prior art]
Conventionally, as described in, for example, JP-A-11-271683, a light source unit including a white light source and a reflector, and an optical device that modulates incident light based on an input video signal and performs light modulation according to the video signal. A video display element for forming an image, color separation / combination means for color-separating the light emitted by the light source unit and combining optical images of the respective colors from the video display element, and projection means for projecting the combined optical image 2. Description of the Related Art There is an image display device including projection means for displaying image light emitted from an image display element.
[0003]
[Problems to be solved by the invention]
In a projection type image display device, brightness and contrast are important performances, but it is difficult to achieve both brightness and contrast.
[0004]
In order to obtain brightness, it is necessary to increase light use efficiency, and there is a method of reducing the F value of illumination light. However, when the F value is reduced, the image becomes bright but the contrast is inferior, and it is difficult to achieve both the brightness and the contrast.
[0005]
It has been found that the deterioration of the contrast is caused by the sudden deterioration of the reflection performance when the incident angle of the polarizing beam splitter (hereinafter referred to as PBS) used in the color separation / combination means increases. This is related to the size of the angle of incidence on the reflecting surface. If the F value is reduced to obtain brightness, the angle of incidence of the light on the PBS increases and the reflection characteristics, that is, polarized light that must not be reflected, reflect. Then, a phenomenon occurs in which the polarized light to be reflected is transmitted without being reflected. As a result, light that should be reflected on the black display screen by the PBS so as not to reach the screen is transmitted through the PBS, leaking light to the black screen, and deteriorating the contrast.
[0006]
An object of the present invention is to provide an image display device that achieves both brightness and contrast in view of the above-described related art.
[0007]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a light source unit for irradiating light from a light source, and an optical image corresponding to a video signal by light-modulating the light radiated by the light source unit based on an input image signal. And a color separation / combination means for color-separating the light emitted by the light source unit and combining the optical images of the respective colors from the video display element, and a projection means for projecting the combined optical image. Wherein the color separation / combination means is configured to include a polarization beam splitter, and the principal ray is incident on the polarization beam splitter on a plane including a direction of incidence on the polarization beam splitter and a direction of reflection. The divergence angle of the light to be irradiated is narrower than the divergence angle of the light applied to the polarization beam splitter on a plane perpendicular to the plane and including the principal ray.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0009]
FIG. 1 is an optical configuration diagram showing one embodiment of the present invention, and shows an image display device 21 using three reflective video display elements 13 as light valves.
[0010]
The image display device 21 includes a light source unit 1 having a light source 2, and the light source 2 is a white lamp such as an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, a mercury xenon lamp, and a halogen lamp.
[0011]
Light emitted from the light bulb of the light source 2 is condensed and reflected by the elliptical, parabolic, or aspherical reflector 3.
[0012]
Light emitted from the light source unit 1 is a first array for forming a plurality of secondary light source images, which is constituted by a plurality of condenser lenses provided in a rectangular frame having substantially the same size as the exit aperture of the reflector 3. The light enters the lens 4. Furthermore, a second condenser lens is provided, which is arranged in the vicinity where the plurality of secondary light source images are formed, and forms the individual lens images of the first array lens 4 on the liquid crystal display element 13. Pass through the array lens 5. This emitted light is converted into a polarized light by a row of rhombic prisms each having a size approximately half the width of each lens and arranged so as to match the lateral pitch of the optical axis of each lens of the second array lens 5. The light enters the element 6. The prism surface is provided with a polarization separation film, and the incident light is separated by this polarization separation film into P-polarized light and S-polarized light. The P-polarized light goes straight through the polarization separation film as it is, and its polarization direction is rotated by 90 ° by the λ / 2 retardation plate 7 provided on the exit surface of this prism, and is converted to S-polarized light and emitted. On the other hand, the S-polarized light is reflected by the polarization splitting film, reflected again in the original optical axis direction in the adjacent rhombic prism, and emitted.
[0013]
The diaphragm 8 is a light-shielding plate having a hole. The hole has a length of 1 and is opened at a ratio of 0.7 horizontally to limit the vertical spread angle and the horizontal spread angle of light emitted from the polarization conversion element 3. .
[0014]
The collimator lenses 9a and 9b have a positive refracting power, have the function of further condensing the S-polarized light, and pass through the condenser lens 11 via the mirror 10 to form three reflective RGB liquid crystal display elements 13r for each color RGB. , 13g, and 13b, first, the color separation mirror 12 or a color separation prism (not shown) is used to divide the light into GB light and R light by a color separation prism, so that the contrast is improved exclusively for each wavelength region. Are incident on PBSs 14 and 15 which are the designed PBSs.
[0015]
That is, the R light is transmitted through the color separation mirror 12, then enters the R-dedicated PBS 14, and then is S-polarized light, is reflected toward the R-type reflective liquid crystal display element 13r, and irradiates it.
[0016]
The B light and the G light are reflected by the color separation mirror 12, pass through a specific wavelength selection wavelength plate 16a that changes the polarization direction only in a specific wavelength range, and convert the polarization of the B light from S-polarized light to P-polarized light. Then, the B light, which is the P-polarized light whose polarization has been converted, passes through the GB dedicated PBS 15 and irradiates the B dedicated reflective liquid crystal display element 13b. On the other hand, since the G light is an S-polarized light even after passing through the specific wavelength selection wavelength plate 16a, it is reflected by the GB dedicated PBS 15, and then illuminates the G dedicated reflective liquid crystal display element 13g. Of course, the above example is one specific example, and the embodiment is not limited to this.
[0017]
Thereafter, the polarization is converted by the reflection type image display device 13 dedicated to each color, the light is again incident on the PBSs 14 and 15 dedicated to each color, the S-polarized light is reflected, and the P-polarized light is transmitted.
[0018]
The reflection-type image display element 13 is provided with liquid crystal display units of the number corresponding to the pixels to be displayed (for example, 1365 pixels in width and 768 pixels in 3 colors). Then, the polarization angle of each pixel of the display element 13 changes in accordance with a signal driven from the outside, and the G light and the B light having the same polarization direction are detected by the PBS 15 and the R light is detected by the PBS 14. The amount of light passing through the PBS and the amount of light to be analyzed are determined by the relationship between the PBS 15 and the polarization degree of the PBS 15 and 14 for the polarized light having an intermediate angle. In this way, an image is projected according to a signal input from the outside. At this time, when the reflective image display element 13 performs black display, the polarization direction is the same as that of the incident light, and the light is returned to the light source side along the incident light path.
[0019]
By the way, the contrast can be improved by rotating and adjusting the λ / 4 retardation plates 17r, 17g, 17b disposed immediately before the reflective liquid crystal display elements 13r, 13g, 13b of each color.
[0020]
Thereafter, the light passes through a specific wavelength selection wavelength plate 16b that converts the polarization direction only in a specific wavelength range, and converts the polarization of the G light from P-polarized light to S-polarized light. The light incident on the specific wavelength selection wavelength plate 16b is such that G light is P-polarized light and B light is S-polarized light. Here, only G light is polarization-converted, so that both G light and B light are S-polarized light. And enters the PBS 18. The light of the R light transmitted through the R dedicated PBS 14 enters the PBS 18 as P polarized light. In the PBS 18, the R light and the GB light are color-combined again, and the light passes through a projection lens 19 such as a zoom lens and reaches a screen. The images formed on the reflective video display elements 13r, 13g, and 13b by the projection lens 19 are enlarged and projected on a screen to function as a display device. Power is supplied to the light source 2 and the image display element 13 by the power supply 20, and each of the driving circuits (not shown) drives the light source 2 and the image display element 13. Further, a color filter (not shown) for improving the color purity of the RGB light and a polarization filter (not shown) for obtaining a fixed polarized light are interposed in the optical path.
[0021]
Here, FIG. 2 shows the reflectance of the P-polarized light when the P-polarized light is incident on the PBS for reflecting the S-polarized light and transmitting the P-polarized light. In the figure, the horizontal axis represents the angle of incidence on the PBS, and the vertical axis represents the reflectance of P-polarized light. The horizontal direction indicates the reflectance of the P-polarized light with respect to the incident angle when the P-polarized light is incident on a plane including the incident direction and the reflection direction of the principal ray on the PBS. The vertical direction indicates the reflectance of the P-polarized light with respect to the incident angle when the P-polarized light is incident on a plane perpendicular to the plane including the incident direction and the reflection direction of the principal ray to the PBS and including the principal ray. . Ideally, when P-polarized light is incident, the reflectance of P-polarized light is zero.
[0022]
From FIG. 2, it can be seen that the reflection characteristics when the P-polarized light is incident on the plane including the incident direction and the reflection direction of the principal ray, and the reflection when the P-polarized light is incident on the plane including the principal ray and perpendicular to the plane. It is apparent that the characteristics are different, and that the reflection characteristics are significantly deteriorated in a plane including the incident direction and the reflection direction of the principal ray.
[0023]
This is because the reflection characteristics change due to the rotation of the polarization axis depending on the angle of incidence on the reflection surface, or the reflection performance is shifted depending on the angle of incidence because the reflection film is formed by laminating many thin films. In particular, in the case of incidence on a plane including the incident direction and the reflection direction of the principal ray, the reflection surface is inclined by 45 °, so that the angle of incidence on the reflection surface becomes large depending on the direction of incidence, so that the reflection characteristics change more remarkably. .
[0024]
Therefore, in this embodiment, the stop 8 is provided to limit the spread angle of light so that the length is 1 and the width is 0.7. As a result, when the G light and the B light are analyzed by the PBS 15 and the R light is analyzed by the PBS 14, the angle at which the reflection characteristic on the plane including the incident direction and the reflection direction of the principal ray is significantly deteriorated is reduced. Since there is little light, polarized light that should not be reflected is reflected, and the phenomenon that polarized light to be reflected is not reflected is less likely to occur. Therefore, it was possible to prevent the contrast from being significantly deteriorated due to the leakage of light from the PBS, and the brightness was reduced by about 15% due to the aperture, but the contrast was more than doubled as compared with the conventional technique without the aperture. In addition, since the angle distribution of the light from the light source decreases in brightness as the angle increases, the decrease in brightness can be suppressed to a small degree compared to the size of the aperture. As a result, the contrast can be reduced without significantly reducing the brightness. I could improve it.
[0025]
In the above-described embodiment, the stop is provided to limit the spread angle of light, but the present invention is not limited to this. The method of limiting the spread angle of the vertical and horizontal light to different sizes, that is, the principal point position of the collimator lens group on the image display element side of the illumination optical system may be different in the vertical and horizontal directions, and the conventional optical design Can be easily realized. For example, one or more cylindrical lenses may be provided in the collimator lens group of the illumination optical system. Unlike the diaphragm described in the above embodiment, such a configuration does not limit the light of the light source, and thus can realize a bright and high-contrast image display device.
[0026]
In each of the above embodiments, a three-panel image display device using three video display elements has been described. However, the present invention is not limited to the three-panel type image display device. It goes without saying that the present invention is also applicable to the case of a two-plate type using two elements, and the present invention is not limited to these embodiments.
[0027]
【The invention's effect】
According to the present invention, it is possible to achieve an image display device that maintains brightness and contrast by reducing the angle of incidence on the PBS in the horizontal direction, which is a cause of poor contrast.
[Brief description of the drawings]
FIG. 1 is a block diagram of an image display device according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing the reflectance of P-polarized light with respect to the angle of incidence of P-polarized light on PBS for explaining the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Light source unit, 2 ... Light source, 3 ... Reflector, 4 ... First array lens, 5 ... Second array lens, 6 ... Polarization conversion element, 7 ... 1/2 wavelength phase difference plate, 8 ... Stop, 9a, 9b ... Collimator lens, 10 ... Mirror, 11 ... Condenser lens, 12 ... Dichroic mirror, 13 ... Video display element, 13r ... Reflection type video display element, 13b ... Reflection type video display element for blue light, 13g ... Reflection type for green light Image display elements, 14, 15, 18: polarization beam splitters, 16a, 16b: specific wavelength selection wavelength plates, 17r, 17g, 17b: λ / 4 phase difference plate, 19: projection lens, 20: power supply, 21: image display apparatus.

Claims (4)

A light source unit that emits light from a light source; a video display element that forms an optical image corresponding to a video signal by optically modulating the light emitted by the light source unit based on an input image signal; An image display device comprising: a color separation / combination unit that performs color separation of the combined light and combines an optical image of each color from the video display element, and a projection unit that projects the combined optical image,
The color separation / combination unit is configured to include a polarization beam splitter, and a divergence angle of light incident on the polarization beam splitter on a plane including an incident direction and a reflection direction of the principal ray on the polarization beam splitter, An image display device characterized in that it is configured to be narrower than a spread angle of light applied to the polarizing beam splitter on a plane perpendicular to the plane and including a principal ray. The image display device according to claim 1, wherein the light source unit includes a diaphragm unit that limits a spread angle of light applied to the polarization beam splitter. An illumination optical system including a plurality of lenses for irradiating the light from the light source unit to the image display element,
The image according to claim 1, wherein principal plane positions of the plurality of lenses are different between a plane including an incident direction and a reflecting direction of the principal ray on the polarization beam splitter and a plane perpendicular to the plane. Display device. The image display device according to claim 3, wherein the plurality of lenses include a cylindrical lens.

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