JP2001166148A - Picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device which makes displaying light emitted in the front side of a screen (in the direction vertical to a display element surface and an HCF(holographic color filter) surface), which is the appropriate observing position, in a 'reflective' display device which is equipped with the HCF and constructed so as to make light pass the HCF twice as illuminating and displaying light. SOLUTION: The HCF which is provided with a polarized light hologram, having a function to produce diffracted rays with high diffraction efficiency as regards light with a specified polarized light component, as an element (array) is adopted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device using a holographic color filter (hereinafter, referred to as HCF), and more particularly to a space such as a liquid crystal display device and a digital micromirror device (DMD) type display device. The present invention relates to an image display device obtained by combining a light modulation unit and an HCF.

[0002]

2. Description of the Related Art Conventionally, a backlight is indispensable for a display in a color liquid crystal display device using an absorption color filter made of a pigment, a dye or the like. However, if white light is simply irradiated from behind the color liquid crystal display device, its utilization efficiency is very low. The main reasons are as follows.

(1) The area occupied by the black matrix other than the cells of each color is large, and the light hit there is wasted. (2) Among white light incident on each pixel, R (red), G
Since the color components passing through the (green) and B (blue) color filters are limited, other complementary color components are wasted. (3) There is a loss due to absorption by the color filter.

In order to solve such a problem, for example, a microlens array is installed in front of a color filter,
2. Description of the Related Art There has been conventionally known a method of concentrating a white light backlight on color filter cells R, G, and B to increase the use efficiency of the backlight.

However, even with this method, it is not possible to irradiate the white light 3 to each of the color filter cells R, G, B in a spectral manner, so that the problem (2) cannot be solved.

Further, a liquid crystal projector in which the use efficiency of light is improved by using three dichroic mirrors and a microlens array without using such a color filter has been proposed in Japanese Patent Application Laid-Open No. Hei 4-60538. In this case, the above-mentioned absorption color filters using pigments, dyes, etc. become unnecessary, and the above-mentioned problems (1) to (3) are solved, and the brightness of the color image is improved, but three dichroic mirrors are required. Because of the necessity, the optical system and the device become large and bulky. In addition, there is a problem that the cost becomes high.

In order to solve these problems, Japanese Patent Application No. 5-12170 discloses a color filter (HCF) using a hologram and a color filter (HCF) in order to greatly improve the use efficiency of a backlight for a liquid crystal display. A liquid crystal display device using the same has been proposed. The HCF according to the above proposal transmits and diffracts a white backlight with spectral distribution by using a hologram having no selectivity (a small amount) of a diffraction wavelength, and corresponds to light of components in the R, G, and B wavelength ranges, respectively. It functions to make it enter a liquid crystal cell of a desired color. That is, the above-described liquid crystal display device relates to a “transmission type” liquid crystal display device.

On the other hand, a liquid crystal display device is disclosed in
As shown in JP-A-177176 and JP-A-9-152597, there is a type in which the back electrode is a reflective electrode to improve the aperture ratio of the liquid crystal and the light use efficiency. These liquid crystal display devices are not limited to projection type display devices that project display images or ambient light (special light sources in devices such as backlights and edge lights) because of their high light use efficiency. It has been increasingly used for direct-view display devices that use ambient light such as illumination light.

A digital micromirror device (DMD) has also been proposed as a display element capable of two-dimensional display by deformation of a minute mirror. This is shown in FIG.
As shown in the perspective view of FIG. 2A, a minute mirror M corresponding to each pixel is two-dimensionally arranged, and a mirror M 'at a predetermined address is tilted about a diagonal line, thereby obtaining a mirror M'.
A two-dimensional pattern is displayed by reflecting light incident from a certain direction on a mirror in a direction different from that of a mirror that is not tilted (see IEEE Spectrum Vol. 30,
No. 11, pp. 27-31). FIG. 6B shows a support driving structure of each mirror M. Each of the mirrors M has a pair of support posts P set up on the silicon substrate S at one diagonal angle.
By applying a voltage to one of a pair of electrodes E provided on the substrate S on the back side of the mirror M, the electrostatic force causes the mirror to be driven about the diagonal line between the hinges T as an axis. The plane of M is rotated.

Therefore, examples in which HCF is applied to these "reflection type" display elements have been proposed in Japanese Patent Application Laid-Open Nos. 9-281917 and 9-281777.

An example of a "reflection type" image display device using an HCF will be described below. FIG. 3 schematically shows a sectional view of an embodiment of a reflection type image display device using an HCF. In this embodiment, a reflective liquid crystal display element 56 is used as a spatial light modulator. In the figure,
The HCF 66 is spaced apart on the front side (observation side) of the liquid crystal display element 56 which is regularly divided into pixels 57. A reflection layer 58 such as an aluminum film is disposed on an electrode on the back surface of the liquid crystal display element 56. Note that the distance between the HCF 66 and the reflective layer 58 is selected to be substantially equal to the focusing distance (focal length) of the micro hologram 65 '(array).

The HCF 66 is provided with the R, R,
A cycle in which pixels of G and B color components (referred to as “color separation pixels”) are repeated, that is, the liquid crystal display element 56
Holograms 65 'arranged in an array at the same pitch as the repetition pitch corresponding to each set of pixels adjacent to each other in the direction (left and right) in the plane of FIG. The micro hologram 65 ′ has three (R, G, B) color separation pixels 57 adjacent to the liquid crystal display element 56 in the direction (left and right) in the plane of the paper of FIG.
One pixel is arranged corresponding to one pixel forming a set.
Each micro hologram 65 ′ converts the green component light 51 G of the illumination light 55 incident at an angle θ with respect to the normal of the HCF 66 from the pixels (one set) corresponding to the micro hologram 65 ′. Are formed in a Fresnel zone plate shape so as to converge light near the center color separation pixel G.

The minute hologram 65 ′ has a relief type, a phase type, and no or little wavelength dependence of diffraction efficiency.
It consists of a transmission type hologram such as an amplitude type. Here, the fact that the wavelength dependence of the diffraction efficiency does not exist or is small means that a specific wavelength is diffracted and other wavelengths hardly diffract as in a Lippmann hologram.
A diffraction grating that diffracts any wavelength with one diffraction grating means that a diffraction grating whose diffraction efficiency has little wavelength dependence diffracts at different diffraction angles depending on the wavelength.

With such an arrangement, when the white illumination light 55 is incident from the front side of the HCF 66 at an angle θ with respect to the normal to the surface of the HCF 66, the wavelength is dispersed by the HCF 66, and the condensing position for each wavelength is It is dispersed in a direction parallel to the HCF66 plane. Among them, the red wavelength component 51R is
Near the surface of the reflective layer 58 at the position of the pixel R for displaying red,
The green component 51G is diffracted and condensed near the surface of the reflective layer 58 at the position of the pixel G for displaying green, and the blue component 51B is diffracted and condensed near the surface of the reflective layer 58 of the pixel B for displaying blue. , HCF 66, each color component is incident on each pixel 57 with almost no attenuation by the black matrix, is reflected by the lower reflective layer 58, and is incident again on the HCF 66. In this case, the HCF 66 In this case, the transmitted light 52R and 52R constituting the display light are not diffracted.
G and 52B enter the observer's eyes. Transmitted light 52
R, 52G, and 52B are pixels 57R, 57G, and 57B that display red, green, and blue, respectively, and are subjected to intensity modulation according to the respective display states. , And a full-color image is obtained by combining them.

The reflected light 52R, 52G, 52B is HCF
In order to be transmitted without being diffracted by the
R, 51G, 51B) and reflected light (52R, 52G, 52).
It is important that the optical axes in B) are different. The incident light (51R, 51G, 51B) and the reflected light (52R, 52R)
If the optical axes of G and 52B) are close to each other, the function of selecting the diffraction angle of the hologram cannot be used. That is, the fact that the optical axes of the incident light and the reflected light are close means that the reflected light (52R, 52G, 51G, 52G, 51B) is diffracted from the hologram in the same direction as the incident light (51R, 51G, 51B). 52
B) means returning, but in such a case, in the normal direction of the surface of the liquid crystal display element 56, the incident light and the reflected light pass around their optical axes.

When light is incident on a hologram having diffraction angle selectivity from a direction exactly opposite to the direction in which the light is diffracted and emitted, the incident light is diffracted by the hologram. In the above case, the reflected light (52R, 52G, 52G, 52G, 51B) is again incident on the HCF 66 surface from a direction exactly opposite to the incident light (51R, 51G, 51B) in the normal direction of the HCF 66 surface.
52B) is again diffracted by the HCF 66, and is transmitted and diffracted in the direction of the white illumination light 55 and emitted. Therefore, when the optical axes of the incident light and the reflected light are close, the reflected light (52R, 5R)
2G, 52B) is again diffracted by the HCF 66, and most of the reflected light is diffracted in the direction of the light source, and the utilization efficiency as display light is reduced.

[0017]

As described above, the HCF
Then, it is generally necessary to make the illumination light obliquely enter the color filter surface. For this reason, many components of light reflected on the surface of the HCF cause a decrease in light use efficiency and a decrease in S / N due to generation of noise light.

Furthermore, a "reflection type" using a conventional HCF
In the display device of (1), the light reflected by the reflective display element is HCF
In order to prevent the light from diffracting again and returning to the illumination light source direction, the optical axis of the illumination light incident on the device and the optical axis of the light reflected (already diffracted) by the display element must be different. There is.

On the other hand, in a liquid crystal display device, since the intensity of light is modulated by the optical rotation of the liquid crystal, when light is transmitted obliquely through the liquid crystal layer, the optical path length of the light transmitted through the liquid crystal layer is different from the design value, and the display value is different. This causes a reduction in pattern contrast and color reproducibility. Therefore, in general, it is desirable for the liquid crystal display element to transmit light perpendicularly to the liquid crystal surface. In a direct-view display device, an observer generally looks at the display device from the front of the display screen,
This is a condition under which an image can be observed with the least distortion.

In a projector-type display device (a system in which an image projected from the device is viewed), a special optical system is required in order to form light obliquely emitted from the display element surface on a screen. So, the optical system becomes large,
Since the cost of the optical system increases and the aberration of the optical system increases, it is desirable that the light is emitted perpendicular to the display element surface.

As described above, in a general display element, it is desirable that light is emitted in a direction perpendicular to the display element surface.
In the case of a “reflection type” display element, the reflection surface is positioned parallel to the display element surface, so that when HCF is employed, the R, G, and B light that has been diffracted and dispersed enters the display element. Later, when the light was reflected and emitted as display light, it could not be emitted perpendicular to the display element surface.

According to the present invention, in a "reflection type" display device using an HCF, light of each color (the center of the optical axis) separated by a color filter is vertically incident on a display element surface such as a liquid crystal display element. The display light (the center of the optical axis) reflected and emitted by the display element is not diffracted again by the HCF, and the front of the screen at a proper observation position (the direction perpendicular to the display element surface and the HCF surface). It is another object of the present invention to provide a display device capable of emitting light to the display device.

[0023]

In order to achieve the above object, the light (center of the optical axis) diffracted by the HCF and emitted is H.
For light that is perpendicular to the CF surface and that is incident again perpendicularly to the HCF surface, characteristics that do not cause diffraction by the HCF are required. In the present invention, an HCF having a polarization hologram having a function of generating a diffracted light with high diffraction efficiency with respect to light of a specific polarization component as an element (array) is employed as the HCF.

The present invention provides a white light source, a hologram
In an image display device comprising at least an HCF in which an array is arranged in a matrix and spatial modulation means for defining a display pattern, the HCF diffracts light of a specific polarization direction with high diffraction efficiency. A polarization hologram having a function of generating light is used as an element (array), and as a diffraction function of the polarization hologram, green component light of light in the visible wavelength range is focused to a specific focus in a direction substantially perpendicular to the hologram surface. And the white illumination light source is configured to irradiate the HCF with white light of a substantially linearly polarized component at a specific angle.

<Action> An HCF having a polarization hologram having a function of generating diffracted light with high diffraction efficiency as an element (array) for light of a specific (linear) polarization component is employed, and the HCF is formed at a specific angle. By adopting a white illumination light source that irradiates white light of a substantially linear polarization component, surface reflection on the HCF surface can be reduced, and almost all of the light rays incident on the HCF can be diffracted and dispersed. Therefore, the use efficiency of the illumination light is improved, and the component of the noise light can be reduced.

If the light incident on the HCF from the white illumination light source and the polarization direction of the light emitted from the HCF are different, the light reflected from the optical axis of the diffracted light from the HCF and emitted (display light) If the polarization direction of the diffracted light at the HCF is different from the polarization direction of the reflected light (display light) even if the optical axis of The reflected light (display light) can be transmitted without being diffracted by the HCF. Therefore, it is possible to both make the diffracted light (spectralized light) by the HCF incident on the surface constituting the spatial modulation means and emit the display light.

In an HCF using a hologram having no (less) diffraction wavelength selectivity, since the spectral action of the hologram is used, illumination light is obliquely incident on the hologram surface. Polarization holograms are holograms that have a strong diffraction effect on light in a specific polarization direction, and are known to exhibit higher light utilization efficiency with respect to a specific polarization direction than ordinary holograms.

Since the light capable of exhibiting such high utilization efficiency is linearly polarized light in a specific direction, it is desirable that the light incident on the polarization hologram is linearly polarized in advance. (Claim 1)

As described above, in an HCF using a hologram having no (small) diffraction wavelength selectivity, illumination light is obliquely incident on the hologram surface. The angle of the incident light increases (H
The surface reflection on the HCF surface increases as the distance from the HCF surface increases.

FIG. 5 is a graph showing the intensity of reflected light when light is incident from a medium having a refractive index of n ₁ = 1.0 to a medium having a refractive index of n ₂ = 1.5. Rs is R for s-polarized light.
When p is p-polarized light, (Rs + Rp) / 2 indicates an average of two polarized states, that is, a state of normal white illumination light in which various polarized states are mixed.

FIG. 5 shows that the reflectance of the p-polarized light increases after the reflectance becomes 0 at a certain specific angle (ψb = 56.3 ° in the figure). Therefore, HC
By setting the illumination light to F to be p-polarized light, it is possible to reduce reflected light on the HCF surface, improve light use efficiency, and reduce noise light. (Claim 3)

For example, when light is incident from a medium (air) having a refractive index n ₁ = 1.0 to a medium having a refractive index n ₂ = 1.5, the reflectance becomes 0 at an angle of 56.3 °. . As can be seen from FIG. 5, when the incident angle is in the range of 40 ° to 60 °, the HCF shows a lower surface reflectance than the reflectance when the illumination light is incident from the front, and further increases the illumination light. Thus, it is possible to expect the effect of improving the use efficiency of the device and reducing the noise of the display light. (Claim 4)

The angle at which the “reflectance = 0” is called the “Brewster angle” and is determined from the refractive index of the medium. Assuming that the refractive index of the medium 1 is n ₁ and the refractive index of the medium 2 is n ₂ , the Brewster angle B is obtained from the following relational expression. tan (B) = n ₂ ÷ n ₁

Although a polarization hologram can diffract light in a specific polarization direction almost completely, many polarization holograms also have a diffractive action on a polarization plane in a direction perpendicular to the direction. When an HCF composed of a polarization hologram is used, if a liquid crystal display element is used as the spatial modulation means, light having a polarization component orthogonal to a specific polarization direction causes a decrease in contrast.

Therefore, when a liquid crystal display element is used as the spatial modulation means and a non-linearly polarized light source is used as the illumination light source, it is desirable to use two or more polarizing plates in addition to the polarization hologram. (Claim 7)

In this case, when the direction of the polarizing plate used on the illumination light side is adjusted to the direction of polarization of the polarization hologram which acts strongly, the utilization efficiency becomes highest. (Claim 8)

Further, by utilizing the polarization hologram for the HCF, the use of the reflection type spatial modulation means as the spatial modulation means has more advantages.

As described above, in the display device, it is desirable that the display light is emitted in a direction perpendicular to the display element surface. However, in the case of the “reflection type” display element, the reflection surface is parallel to the display element surface. Therefore, in a display device using a conventional HCF, display light reflected and emitted cannot be emitted perpendicularly to the display element surface.

The polarization hologram is used for the HCF, and the HCF is used.
When the light incident on the polarization hologram is linearly polarized light and the direction of the light coincides with the polarization direction of the polarization hologram which acts strongly, the incident light (illumination light) is almost diffracted and spectrally separated.

When the polarization plane is rotated by a liquid crystal or a retardation plate while being spatially modulated by the spatial modulation means and reflected, the display light whose polarization plane is orthogonal to the incident light is incident on the HCF again. Will be. Since the HCF is a polarization hologram, most of the display light is transmitted without being diffracted and used for displaying an image. (Claim 2)

As described above, if a polarization hologram is used for an HCF, incident light (diffraction light) and display light can be separated without being affected by the hologram incident angle selectivity. It becomes possible to emit display light in a direction perpendicular to the reflective display element surface using the spatial modulation means.

As described in J. Tsujiuchi, “Holography” (Shokabosha), pp. 65-68, the angle dependence (synonymous with the incident angle selectivity) of the hologram depends on the thickness of the hologram layer. And tends to become stronger as the thickness increases. Therefore, when the incident light and the display light are to be separated due to the angle dependence of the hologram, the hologram layer becomes thick. However, when the hologram layer is thick, light absorption by the hologram layer causes a reduction in light use efficiency and coloring of display light, which leads to deterioration in image quality of a display pattern.

By using a polarization hologram, it is not necessary to increase the thickness of the hologram layer to impart angle dependency, and even when the diffraction efficiency is theoretically set to 100%, the amount of change in the optical path length at that thickness is small. λ / 2 (λ is the wavelength of light)
It is sufficient that the thickness of the hologram is 5 times the theoretical optical path length change amount of λ / 2, even if the actual disturbance of the stripe structure of the hologram is considered. For example, it has been found that if the degree of modulation of the refractive index of the hologram is 0.01 or more, sufficient performance is exhibited if the thickness of the hologram layer is 4 μm to 20 μm. (Claim 10)

In particular, by using a polarization hologram composed of a birefringent material and a non-birefringent material as the polarization hologram, the polarization hologram can be formed without limiting the incident angle and the thickness of the hologram layer. Since it is possible to have dependencies, it is possible to set these conditions more freely. (Claim 11)

In the case of the reflection type spatial modulation element, in the HCF, light is transmitted twice when the illumination light is incident and when the display light is emitted, and the two polarization planes at that time need to be orthogonal.
Therefore, the polarizing plate that determines the polarization direction of the illumination light is HC
If the display light is disposed at a position close to F, the emitted display light also passes through the polarizing plate. However, when a polarization hologram HCF is used for the reflective spatial light modulator, the illumination light passing through the color filter and the polarization plane of the display light are orthogonal to each other. Would be. Therefore, it is desirable to arrange the polarizing plate that determines the polarization direction of the illumination light at a position where the display light emitted from the color filter does not enter and does not adhere to the HCF. (Claim 9)

When a spatial modulation means such as a DMD is used instead of a liquid crystal display element as the reflection type spatial modulation means, H
After passing through the CF, it is necessary to rotate the polarization plane until the light is reflected by the spatial modulation means and passes through the color filter again. Therefore, between the color filter and the spatial modulation means,
It is effective to arrange a phase difference plate. (Claim 5)

Since the HCF can be processed into a film, the workability is improved by bringing the HCF into close contact with the retardation film via an adhesive layer or the like. (Claim 6)

When the HCF of the present invention is used as a projector-type display element, it is easily imagined that the HCF will be exposed to intense illumination light and become extremely hot. However, a certain distance is required between the HCF of the present invention and the reflection part of the display element, and it is impossible to make them completely adhere. Therefore, it is important that the thermal deformation ratio of HCF is a low value.

For example, in the case of a hologram array in which 500 element holograms having a relatively wide allowable range are arranged, 1/5
If there is a deformation of 00, the displacement will occur completely and the HC
F is not available. In recent years, display devices having more pixels have been put into practical use, and the thermal deformation ratio of HCF needs to be 0.2% or less. (Claim 12)

Further, in order to prevent warpage due to deformation, it is desirable to bond HCF to a substrate such as glass. In this case, a light-curing type, which is hardly deformed or deteriorated by light or heat, is cured by ultraviolet rays. It is desirable to use a type of adhesive. (Claim 13)

[0051]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image display device using an HCF according to the present invention will be described below. FIG. 1 shows a schematic cross-sectional view of an example of a reflection type image display device using an HCF composed of a polarization hologram. In this example, a reflective liquid crystal display element 5 is used as the spatial light modulating means.
6 is used. In the figure, an HCF 65 composed of a polarization hologram is arranged at a distance from the front side (observation side) of the liquid crystal layer 56 which is regularly divided into pixels 57. The liquid crystal element 56 has a reflective electrode 58 arranged on the back surface, and a transparent electrode is arranged on the front surface side (not shown). Note that the distance between the HCF 65 and the reflective electrode 58 is
It is set substantially equal to the focusing distance (focal length) of the minute hologram 65 '.

Also in this case, the HCF 65 determines the repetition period of the R, G, and B color pixels of the pixel 57, that is, the three color pixels adjacent to each other in the direction of the pixel of the liquid crystal display device (left and right). Corresponding to each of the sets, they are arranged in an array at the same pitch as the repetition pitch thereof, and are arranged such that the center of each minute hologram 65 'and the center of the liquid crystal pixel for G overlap each other. Is HCF
Illumination light 5 incident at an angle θ with respect to the normal to the 65 surface
5, the light 51G of the green component in the small hologram 6
It is formed in a Fresnel zone plate shape so as to converge light near the pixel G at the center of the three color separation pixels R, G, B corresponding to 5 ′.

The micro hologram 65 ′ has a relief type, a phase type, and no or little wavelength dependence of diffraction efficiency.
It consists of a transmission type hologram such as an amplitude type. Further, the minute hologram 65 'is a polarization hologram, which shows a strong diffraction efficiency on a specific polarization plane.

The polarization hologram is disclosed in JP-A-6-30092.
As shown in FIG. 5 of Japanese Patent Application Laid-Open No. 1 (1993) -1992, a method of forming a lattice layer by a proton exchange region and a phase compensation film of a dielectric using a lithium niobate substrate as a birefringent crystal as a substrate, A volume hologram is realized by a method using a liquid crystal polymer as disclosed in Japanese Patent Application Laid-Open No. 10-265531, and further, by forming a layer structure of a birefringent material such as liquid crystal and a non-birefringent material. There are various ways to do this.

These polarization holograms can realize a hologram having a strong polarization dependence (having a strong diffraction efficiency on a specific polarization plane) without depending on the incident angle or the structure of the hologram. In addition, it is also possible to realize a polarization hologram having polarization dependency by giving illumination light under special conditions using a normal volume hologram that does not use a birefringent material.

With such an arrangement, when white illumination light 55 of linearly polarized light in the polarization direction having the strongest diffractive action of HCF is made incident from the surface side of HCF 65 at an incident angle θ,
The wavelength is dispersed by diffraction at the HCF 65, and the light condensing position for each wavelength is dispersed in a direction parallel to the HCF 65 surface. Among the wavelength-dispersed lights, the light of the center wavelength G is diffracted in the normal direction with respect to the HCF plane by the HC.
F is designed. This is because, as described above, it is desirable to emit display light to the front of the device (the direction perpendicular to the display screen).

The red wavelength component 51R is near the surface of the reflective electrode 58 at the position of the pixel R for displaying red, and the green component 51G is for the reflective electrode 58 at the position of the pixel G for displaying green.
Near the surface of the pixel B, a blue component 51B is a pixel B for displaying blue.
By arranging the HCF 65 so as to diffract and condense light in the vicinity of the surface of the reflective electrode 58, the respective color components pass through the liquid crystal layer 56 with little attenuation, are reflected by the reflective electrode 58, and Through the liquid crystal layer 56 from the back side again.

When the light passes through the liquid crystal layer 56 twice, the illumination light is rotated on the plane of polarization in a direction perpendicular to the direction of the incident light. Therefore, the light reflected by the reflection electrode 58 and incident on the HCF 65 is light in the polarization direction of the HCF 65 having a low diffraction efficiency, and is hardly diffracted, so that the transmitted light 52R, 52
G, 52B and enters the observer's eye. Further, the transmitted light 52 is emitted almost perpendicular to the HCF plane. The components 51R, 51G, and 51B of each color enter the pixels R, G, and B that display red, green, and blue, respectively, and receive intensity modulation according to the display state of those pixels to reach the eyes of the observer. Therefore, a color image can be displayed by a combination of the modulation states of the pixels R, G, and B.

Linearly polarized white light 5 incident on the HCF 65
5 at an angle θ of about 56.3 ° with respect to HCF65.
If the polarization hologram is made to be incident with polarized light and the HCF is made to strongly diffract the p-polarized light, the component of the light reflected on the surface of the HCF 65 can be made almost zero. In addition,
Improvement of efficiency and S / N by combining linearly polarized illumination light 55 and polarized light HCF65, and effect of preventing reflected light on polarized light HCF65 surface by combination of p-polarized illumination light and polarization hologram that strongly diffracts p-polarized light Is not limited to the reflective display element as in this embodiment, and the same effect can be expected with a transmissive display element such as a transmissive liquid crystal.

As a white light source, a cold-cathode tube is often used in a direct-view image display device, and a meta-halide lamp or a krypton rank is often used in a projector-type image display device. These light sources are generally a mixture of light of various polarization directions.

Therefore, it is necessary to convert a white light source into linearly polarized light in order to provide the effect of the polarized light HCF as in the present invention. FIG. 2 is an explanatory diagram illustrating a display device according to an example including a white light source that converts light into linearly polarized light using a polarizing plate. When the white illumination light 54 having a random polarization direction is transmitted through the polarizing plate 62 (having a function of extracting linearly polarized light), it is selected as the illumination light 55 having only the linearly polarized light. Then, after passing through the polarized light HCF 65, the light is incident / reflected on the reflective display element 56 and again incident on the polarized light HCF 65. After passing through the polarized HCF as it is, the display light 52
And emitted.

At this time, the display light 52 is first polarized HCF.
Is a light having a polarization plane whose polarization directions are orthogonal to each other. Therefore, when the display light 52 emitted from the polarized light HCF passes through the polarizing plate 62, most of the display light is blocked, resulting in a very dark display image. Therefore, the polarizing plate 62 needs to be arranged at a position where the display light 52 does not adhere to the polarization HCF 65 so that the display light 52 is not transmitted. In the example shown in FIG. 2, a polarizing plate is used as a polarizing element. However, any element that generates linearly polarized light from random polarized light, such as a polarizing beam splitter, does not impair the effects of the present invention.

FIG. 4 is an explanatory view showing a display device of the present invention according to an example in which a digital micromirror device (DMD) 68 shown in FIG. 6 is used as a spatial light modulator disposed on the back side of the polarization HCF 65. Yes, center of HCF and D
The green micromirror of the MD is arranged so as to be coincident in the normal direction of the HCF surface, and the light split by the HCF 65 passes through the phase difference plate 69, and thereafter, the red diffraction component 51R, the green diffraction component 51G, and the blue light Near the position where each of the diffraction components 51B converges, the micro mirror 59 (59
(R, 59G, 59B).

With this arrangement, in the case of the state shown in FIG. 4, since the positions of the pixels B and G are modulated,
The reflected lights 52G and 52B are reflected in a direction substantially normal to the HCF, whereas the pixels R are not modulated, so that the reflected light 52R is emitted in a direction different from the reflected lights 52G and 52B. When a λ / 4 wavelength plate is used as the phase difference plate 69, the light transmitted through the phase difference plate 69 again by the micromirror is in a direction in which the polarization plane is orthogonal to the linearly polarized illumination light 55. HCF65 is transmitted as it is.
Therefore, for example, by projecting only the light emitted in the direction perpendicular to the HCF plane onto a screen by a lens, it is possible to display and observe a color image by a projection method.

[0065]

As described above, according to the present invention,
In a “reflection type” display device using an HCF, light (center of the optical axis) of each color separated by a color filter is vertically incident on a display element surface such as a liquid crystal display element.
The display light (the center of the optical axis) reflected and emitted by the display element is
A display device capable of emitting light in front of a screen at a proper observation position (a direction perpendicular to the display element surface and the HCF surface) without being diffracted again by the HCF is provided. In the display device of the present invention, the surface reflection on the HCF surface is reduced, and almost all of the light incident on the HCF can be diffracted and dispersed, so that the efficiency of use of illumination light is improved, and noise light is reduced. It is possible to reduce the brightness, and bright and high-quality display light (video) is visually recognized.

[0066]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a reflection-type image display device using an HCF composed of a polarization hologram according to the present invention.

FIG. 2 is an explanatory diagram illustrating a display device according to an example including a white light source that converts light into linearly polarized light using a polarizing plate.

FIG. 3 is a cross-sectional view showing an example of a conventional “reflection type” image display device using an HCF.

FIG. 4 is a digital micromirror device (DMD)
FIG. 4 is an explanatory diagram showing a display device of the present invention according to an example using a device.

FIG. 5 shows a case where light is converted from a medium having a refractive index n ₁ = 1.0 to a refractive index n _2.
4 is a graph showing the intensity of reflected light when the light is incident on a medium of 1.5.

FIGS. 6A and 6B are explanatory views showing a digital micromirror device (DMD). FIG. 6A is a perspective view, and FIG.

[Explanation of symbols]

 51R, 51G, 51B: Diffraction spectral components 52R, 52G, 52B: Reflection (transmission) display light 54: White illumination light 55: Illumination light (linearly polarized light) 56: Reflective liquid crystal display element 57: Pixel (liquid crystal) 58: Reflection Layers 59R, 59G, 59B: Micro mirrors 61, 62 ... Polarizer 65: Polarized HCF 65 '... Micro hologram (array) 66 ... HCF 66': Micro hologram 68: Digital micro mirror device (DMD)

Claims (14)

[Claims] An image display apparatus comprising at least a white light source, a holographic color filter having a configuration in which hologram arrays are arranged in a matrix, and spatial modulation means for defining a display pattern. -A color hologram is used as an element (array) with a polarization hologram that has the function of generating diffracted light with high diffraction efficiency for light in a specific polarization direction. Of the light in the visible wavelength range, the green component light is transmitted and diffracted so as to be condensed at a specific focal point. The white illumination light source irradiates the holographic color filter with white light of a substantially linear polarization component at a specific angle An image display device characterized in that: 2. An image display apparatus according to claim 1, wherein said spatial modulation means is a reflection type spatial modulation means having means for reflecting incident light and emitting a display pattern. 3. The image display device according to claim 1, wherein the white light is incident on the holographic color filter as p-polarized light whose electric field vector is in the incident plane direction. 4. The image display device according to claim 3, wherein the white light is incident at an angle of 40 ° to 60 ° with respect to the normal direction of the holographic color filter surface. 5. The image display device according to claim 1, wherein a phase difference plate is arranged between the holographic color filter and the spatial modulation means. 6. The image display device according to claim 5, wherein the holographic color filter and the retardation plate are integrated in close contact with each other. 7. The image display device according to claim 1, wherein two or more polarizing elements are provided on the optical path in addition to the holographic color filter. 8. At least one of the polarizing elements is located between the white illumination light source and the holographic color filter, and the light emitted from the polarizing element is substantially linearly polarized light, and the polarization component is holographically polarized light. The image display device according to claim 7, wherein the polarization directions are arranged so that the diffracted light is emitted most strongly from the color filter. 9. The holographic color filter according to claim 8, wherein at least one of the polarizing elements located between the white illumination light source and the holographic color filter is arranged so as not to be in close contact with the holographic color filter. Image display device. 10. A polarization hologram constituting a holographic color filter is a volume phase transmission hologram, wherein the hologram has a thickness in a range of 4 μm to 20 μm, and has a refractive index modulation degree of 0. 0
The image display device according to claim 1, wherein the number is one or more. 11. The image display device according to claim 1, wherein the polarization hologram constituting the holographic color filter has a region having birefringence and a region having no birefringence. 12. The image display device according to claim 1, wherein the polarization hologram constituting the holographic color filter has a thermal deformation ratio at 80 ° C. of 0.2% or less. 13. The image display device according to claim 1, wherein the polarization hologram constituting the holographic color filter is configured to be adhered to a substrate with a photo-curable adhesive. 14. The image display device according to claim 1, wherein the image display device is a projection type device for projecting a display image.