JP3722300B2 - Hologram color filter - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a holographic color filter, and more particularly to a holographic color filter that makes it possible to use convergent light and divergent light other than parallel light as illumination light and greatly improve the utilization efficiency of illumination light.
[0002]
[Prior art]
Conventionally, a backlight is indispensable for display in a color liquid crystal display device using an absorption color filter such as a pigment or a dye. However, just using white light as it is from behind the color liquid crystal display device, its utilization efficiency is very low. The main reasons are as follows.
[0003]
(1) The area occupied by the black matrix other than the cells of each color is large, and the light hitting it is wasted.
(2) Among white light incident on each pixel, the color components that pass through the color filters of R (red), G (green), and B (blue) are limited, so other complementary color components are wasted. End up.
(3) There is a loss due to absorption by the color filter.
[0004]
In order to solve such a problem, as shown in FIG. 5, for example, a microlens array 2 is installed in front of the color filter 1, and a white light backlight 3 is condensed on the color filter cells R, G, and B, respectively. By doing so, a method for increasing the utilization efficiency of the backlight 3 is conventionally known. In FIG. 5, reference numeral 4 denotes a black matrix provided between the color filter cells R, G, and B.
[0005]
However, even with this method, since the white light 3 cannot be applied to each color filter cell R, G, B by being split, it is impossible to solve the problem (2).
[0006]
Furthermore, Japanese Patent Laid-Open No. 4-60538 proposes a liquid crystal projector that improves the light utilization efficiency by using three dichroic mirrors and a microlens array without using such a color filter. In this case, the absorption color filter using the above-mentioned pigments, dyes and the like is not necessary, and the above problems (1) to (3) are solved and the brightness of the color image is improved, but three dichroic mirrors are used. Since this is necessary, the optical system / device becomes large and bulky. In addition, there is a problem that the cost becomes high.
[0007]
In view of such circumstances, the present applicant used a color filter using a hologram and the same in Japanese Patent Application No. 5-12170 in order to greatly improve the utilization efficiency of a backlight for liquid crystal display and the like. A liquid crystal display device was proposed.
[0008]
Further, a liquid crystal projection display device that displays a bright color image on a screen by changing the liquid crystal display device using such a hologram color filter to a projection type has been proposed in Japanese Patent Application No. 5-242292.
[0009]
[Problems to be solved by the invention]
By the way, the above-mentioned hologram color filter is composed of a condensing microelement hologram array, and each element hologram is composed of a computer generated hologram having the same interference fringe pattern or a duplicate hologram thereof, and is incident on any element hologram. The incident angles of the backlights to be used are all the same, and a parallel light beam is used as the backlight.
[0010]
However, the diameter of the liquid crystal display device is often smaller than the aperture of a condensing optical system such as a parabolic mirror or a positive lens of the illumination light source device, or projection for projecting light emitted from the liquid crystal display device In order to reduce the diameter of the lens, the backlight is convergent. When such convergent light is used as a backlight, when all the element holograms of the hologram color filter have the same interference fringe pattern, the backlight is not incident on the surrounding element hologram at the designed incident angle. Therefore, the color components wavelength-dispersed by the element hologram are incident not only on the corresponding color separation pixels but also on the adjacent color separation pixels, and color mixing occurs, which causes a decrease in color purity.
[0011]
The present invention has been made in view of such problems of the prior art, and its purpose is to reduce color purity when illumination is performed using a backlight other than a parallel light beam such as a convergent light beam or a divergent light beam. It is an object to provide a hologram color filter having good color reproducibility without inviting.
[0012]
[Means for Solving the Problems]
The hologram color filter of the present invention that achieves the above object comprises an array in which condensing element holograms are periodically arranged, and the white light incident on each element hologram at a predetermined incident angle has a wavelength in a direction along the recording surface. In a hologram color filter that disperses and condenses spectrally, the interference fringe pattern of each element hologram varies depending on the position so that the incident angle of white light incident on each element hologram varies depending on the position of each element hologram. In addition, the interference fringe pattern includes element holograms that are asymmetrical not only in a specific direction in which element holograms are periodically arranged but also in a direction orthogonal thereto, and a black liquid crystal display in which a black matrix is arranged between pixels It is used for an apparatus.
[0013]
In this case, the hologram color filter can be produced by one or more times of duplication using a computer generated hologram as an original. The white light incident on the hologram color filter includes convergent light, divergent light, or light in which converged light and divergent light are mixed depending on the location in the cross section of the light beam.
[0014]
[Action]
In the present invention, since the interference fringe pattern of each element hologram differs according to its position so that the incident angle of white light incident on each element hologram differs according to the position of each element hologram, Even if convergent light other than parallel light, divergent light, or the like is used, the color components wavelength-dispersed by each element hologram are incident only on the corresponding color separation pixels, and the color purity of the display is not reduced due to color mixing. It does not occur, and the use efficiency of illumination light can be greatly improved.
[0015]
【Example】
Hereinafter, the hologram color filter of the present invention will be described based on examples.
[0016]
First, a liquid crystal display device using a hologram color filter according to the present invention will be described with reference to a sectional view of FIG. In the figure, a hologram array 5 constituting a color filter is arranged on the backlight 3 incident side of a liquid crystal display element 6 regularly divided into liquid crystal cells 6 '(pixels). On the back surface of the liquid crystal display element 6, a black matrix 4 provided between the liquid crystal cells 6 'is disposed. In addition to the above, polarizing plates (not shown) are disposed on the incident side of the hologram array 5 and the emission side of the liquid crystal display element 6. In addition, an absorption type color filter that passes light of colors corresponding to R, G, and B color separation pixels is additionally arranged between the black matrix 4 as in the conventional color liquid crystal display device. You may do it.
[0017]
The hologram array 5 corresponds to the repetition period of the color separation pixels of R, G, and B, that is, the repetition pitch corresponding to each set of three liquid crystal cells 6 'adjacent in the direction in the plane of the liquid crystal display element 6. The micro holograms 5 'are arranged in an array at the same pitch. The micro holograms 5' are arranged in groups of three liquid crystal cells 6 'adjacent to each other in the direction of the surface of the liquid crystal display element 6 and arranged one by one. Each of the minute holograms 5 'is incident on the normal component of the hologram array 5 at an angle θ (this angle differs for each minute hologram 5'). Is condensed in a Fresnel zone plate shape so as to be condensed on the liquid crystal cell G at the center of the three color separation pixels R, G, B corresponding to the minute hologram 5 '. The micro-hologram 5 'is formed of a transmission type hologram such as a relief type, a phase type, and an amplitude type, which has little or no wavelength dependency of diffraction efficiency. Here, the fact that the diffraction efficiency has no or little wavelength dependency means that the diffraction efficiency is not a type that diffracts only a specific wavelength and the other wavelengths do not diffract, such as a Lippmann hologram. The wavelength also means what is diffracted, and the diffraction grating having less wavelength dependency of the diffraction efficiency diffracts at different diffraction angles depending on the wavelength.
[0018]
Due to such a configuration, the white backlight 3 that is incident on the normal line at a different angle θ with respect to the normal line from the surface opposite to the liquid crystal display element 6 of the hologram array 5 is incident. Depending on the wavelength, the diffraction angle by the minute hologram 5 ′ is different, and the condensing position for each wavelength is dispersed in a direction parallel to the surface of the hologram array 5. Among them, the red wavelength component is at the position of the liquid crystal cell R that displays red, the green component is at the position of the liquid crystal cell G that displays green, and the blue component is at the position of the liquid crystal cell B that displays blue. By arranging the hologram array 5 so as to be diffracted and condensed, each color component passes through each liquid crystal cell 6 'with almost no attenuation in the black matrix 4, and the liquid crystal cell 6' at the corresponding position is passed through. Color display according to the state can be performed.
[0019]
As described above, by using the hologram array 5 as a color filter, each wavelength component of the conventional color filter backlight can be incident on each liquid crystal cell 6 'without absorption without any waste. Can be improved.
[0020]
Further, the liquid crystal display device having the configuration shown in FIG. 3 can be used as it is as a direct-view type liquid crystal display device, or as a spatial light modulation element for projection display and used as a liquid crystal projection display device. FIG. 4 is a cross-sectional view of a liquid crystal projection display device. The first polarizing plate 12 is close to or integrally with the incident side of the hologram array 5, and the second polarizing plate is close to or integrally with the exit side of the liquid crystal display element 6. The polarizing plate 13 is disposed. The color liquid crystal display device 11 is illuminated by the backlight 3 composed of white convergent light or divergent light from the illumination device 14 composed of a combination of, for example, a metal halide lamp 15 and a parabolic mirror 16. The display image modulated by is passed through a field lens 17 disposed in the vicinity of the liquid crystal display device 11, is enlarged by the projection lens 18, and is enlarged and formed on the screen 19, so that a bright projection image can be obtained.
[0021]
In the above description, the backlight 3 is considered to be regarded as parallel light having a constant incident angle with respect to all the minute holograms 5 ′. However, in reality, when the backlight 3 is viewed as a whole, it is a convergent light. In many cases, the light is divergent light, or the light is a mixture of convergent light and divergent light depending on the location in the beam cross section. For example, in the case of the liquid crystal projection display device as shown in FIG. 4, the diameter of the liquid crystal display device 11 is smaller than the aperture of the parabolic mirror 16, and the projection for projecting light emitted from the liquid crystal display device 11 is performed. In order to reduce the diameter of the lens 18, it is convenient if the backlight 3 is convergent light. When such convergent light is used as the backlight 3, if all the micro holograms 5 ′ of the hologram color filter 5 are formed of the same interference fringe pattern, the incident angle on the peripheral micro hologram 5 ′ is as designed. Therefore, the color component dispersed in wavelength by the micro-hologram 5 ′ is incident not only on the corresponding color separation pixels but also on the adjacent color separation pixels, and color mixing occurs. It causes a decrease in purity.
[0022]
Therefore, in the present invention, for each micro-hologram 5 ′ on the hologram color filter 5, a light-condensing interference fringe pattern having wavelength dispersion corresponding to the incident angle θ at that position is formed. This is shown in FIG. FIG. 1A is a front view of a hologram color filter 5 in which minute holograms 5 ′ are arranged in a triangle shape, and the center when a converging backlight 3 is incident on this hologram color filter 5 from the right side in the figure. FIG. 1B and FIG. 1C schematically show the interference fringe pattern of the micro-hologram 5 'and the interference fringe pattern of the micro-hologram 5' near the lower right corner, respectively. In this case, since the incident angle θ of the backlight 3 is different at the center of all the small holograms 5 ′, the interference fringe patterns are also correspondingly different. The interference fringe pattern of the minute hologram 5 'in the left-right direction including the central portion where the backlight 3 has no y-direction component is symmetrical in the vertical direction as shown in FIG. However, since the incident angle is different between the vicinity of the right end and the vicinity of the left end, the fringe interval of the interference pattern as shown in FIG. Further, in the vicinity of the upper side and the lower side where the backlight 3 has a component in the y direction, the wavelength component of G, which is the central wavelength to be dispersed, is condensed at the center of the corresponding color aperture of the black matrix 4. Therefore, as shown in FIG. 1C, the interference fringe pattern is asymmetrical in the vertical direction, and the incident angle is different between the vicinity of the right corner and the vicinity of the left corner. Note that the direction of wavelength dispersion by the micro-holograms 5 ′ near the upper side and the lower side is not completely the y direction because the backlight 3 has a component in the y direction, but the vertical direction of the openings of the black matrix 4 This is not a problem because the y-direction component of the dispersion can be made smaller than the size of.
[0023]
Thus, in the present invention, for each micro-hologram 5 'on the hologram color filter 5, a condensing interference fringe pattern having wavelength dispersion corresponding to the incident angle θ of the backlight 3 at that position and Therefore, the color components wavelength-dispersed by each micro-hologram 5 ′ are incident only on the corresponding color separation pixels, and the color purity of the display does not deteriorate due to the color mixture.
[0024]
Incidentally, since the varying all of the fringe pattern of the fine hologram 5 'is time, etc. will be applied at the top of the plot, as shown the hologram color filter 5 in FIG. 2 for example is divided into several zones Z ₁₁ to Z _NM Even if the interference fringe patterns of the minute holograms 5 ′ in one zone Z _nm are all drawn in the same manner and are different between the zones, an approximately good hologram color filter 5 can be obtained. Note that such zoning is desirably performed in consideration of local uniformity of the light direction distribution in the backlight 3.
[0025]
In the above embodiment, the backlight 3 is premised on the convergent light. However, as described above, the present invention is not limited to this, and the backlight 3 is not limited to divergent light or light that is a mixture of convergent and divergent light depending on the location in the light beam cross section. Also in the case of the backlight 3 including parallel light, the interference fringe pattern of all the minute holograms 5 ′ is made different by the same principle, or the hologram color filter 5 is divided into several zones Z _{11 to} Z _NM. All the interference fringe patterns of the minute holograms 5 ′ in _nm are made the same and different between the zones.
[0026]
By the way, as described above, the original hologram hologram filter 5 is produced as a computer generated hologram by electron beam drawing or the like assuming that the incident angle of the backlight 3 differs depending on the position of the minute hologram 5 '. The filter 5 is produced by duplication from an original plate made of this computer generated hologram. At that time, the reproduction illumination light irradiated from the original side in close contact with the hologram sensitive material does not need to be non-parallel light such as the convergent light as the backlight 3. Thus, the hologram color fill 5 having different incident angles of the backlight 3 can be duplicated. However, in this case, since the hologram array has a slightly short condensing distance due to the gap between the original plate and the hologram photosensitive material, the first copy product is made the original plate according to the copying method of Japanese Patent Application No. 7-148609, and it is separated again. The hologram color filter 5 having the same interference fringe pattern group as that of the computer generated hologram original is copied by irradiating the reproduction illuminating light traveling in the opposite direction to that at the time of the first copy and making a copy again. .
[0027]
As described above, the hologram color filter of the present invention has been described based on the embodiments. However, the present invention is not limited to these embodiments, and various modifications can be made.
[0028]
【The invention's effect】
As is clear from the above description, according to the hologram color filter of the present invention, the interference fringe pattern of each element hologram is different so that the incident angle of the white light incident on each element hologram differs depending on the position of each element hologram. Since it differs depending on the position, even if convergent light other than parallel light, divergent light, etc. is used as illumination light, the color components wavelength-dispersed by each element hologram are incident only on the corresponding color separation pixels. Thus, the color purity of the display does not decrease due to color mixing, and the use efficiency of the illumination light can be greatly improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a hologram color filter according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining zoning according to a modification of the present invention.
FIG. 3 is a cross-sectional view of a liquid crystal display device using a hologram color filter according to the present invention.
4 is a cross-sectional view when the liquid crystal display device of FIG. 3 is configured as a liquid crystal projection display device.
FIG. 5 is a diagram for explaining an illumination method of a conventional liquid crystal display device.
[Explanation of symbols]
3 ... Backlight 4 ... Black matrix 5 ... Hologram array (hologram color filter)
6 ... Liquid crystal display element 5 '... Micro hologram 6' ... Liquid crystal cell 11 ... Color liquid crystal display device 12 ... First polarizing plate 13 ... Second polarizing plate 14 ... Illuminating device 15 ... Metal halide lamp 16 ... Parabolic mirror 17 ... field lens 18 ... projection lens 19 ... screen _{Z 11, ~, Z nm,} ~, Z NM ... zone

Claims (3)

In a hologram color filter which consists of an array in which condensing element holograms are periodically arranged, and spectrally collects the white light incident on each element hologram at a predetermined incident angle by wavelength dispersion in the direction along the recording surface,
The interference fringe pattern of each element hologram is different depending on the position so that the incident angle of white light incident on each element hologram is different depending on the position of each element hologram, and the interference fringe pattern is different from the element hologram. Hologram color filter characterized in that it includes an element hologram that is asymmetric not only in a specific direction periodically arranged but also in a direction perpendicular thereto, and is used in a color liquid crystal display device in which a black matrix is arranged between pixels .   2. The hologram color filter according to claim 1, wherein the hologram color filter is produced by one or more duplications using a computer generated hologram as an original.   2. The hologram color filter according to claim 1, wherein the white light incident on the hologram color filter is convergent light, divergent light, or light in which converged light and divergent light are mixed depending on a location in a light beam cross section.

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