JP4458390B2 - Reflective image display device using hologram color filter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflection type image display apparatus using a hologram color filter, and more particularly to a reflection type image display apparatus using a hologram color filter capable of projecting a bright and distortion-free image.
[0002]
[Prior art]
The present applicant has filed a number of patent applications regarding a hologram color filter and a transmissive color liquid crystal display device using the same. Also, a reflection type image display device in which this hologram color filter is applied to a reflection type liquid crystal display element or DMD (digital micromirror device) is disclosed in Japanese Patent Application Laid-Open No. 9-281919 (Japanese Patent Application No. 8-95289). Proposed in
[0003]
[Problems to be solved by the invention]
However, in Japanese Patent Application Laid-Open No. 9-281919, the reflected light from the reflective display element (reflective liquid crystal display element, DMD) is not reflected in the direction perpendicular to the surface of the display element, but is oblique. It will be reflected in the same way. When this reflected light is projected by the projection lens, the arrangement relationship between the display element and the projection lens becomes an inclining arrangement, and the optical arrangement is limited.
[0004]
The present invention has been made in view of such problems of the prior art, and its purpose is to diffract in the direction perpendicular to the surface of the reflective image display element, and to re-diffract to the illumination light source side by the hologram color filter. Another object of the present invention is to provide a reflection type image display apparatus using a hologram color filter capable of separating the displayed light from illumination light and displaying an image with small image distortion by a coaxially arranged projection optical system.
[0005]
[Means for Solving the Problems]
The reflection type image display device using the hologram color filter of the present invention that achieves the above object includes a hologram color filter comprising a repetition of element holograms that color-disperse and collect illumination light incident at an oblique incident angle and a reflection type A reflective image display device comprising a combination with a spatial modulation element, wherein the display light reflected by the reflective spatial modulation element and re-diffracted by the hologram color filter is emitted in a direction substantially opposite to the illumination light In the image display device, polarization separation means is disposed in the optical path of the illumination light to separate the display light from the illumination light.
[0006]
In this case, it is desirable that the polarization separation angle by the polarization separation means is substantially equal to the incident angle of the illumination light, and the display light is emitted substantially perpendicularly to the surface of the reflective spatial modulation element.
[0007]
Further, it is desirable that the reflective spatial modulation element rotates the polarization plane of incident light in accordance with the degree of modulation of the pixel.
[0008]
Further, the polarization separation means may be composed of a polarization separation prism or an array thereof, or may be composed of a holographic polarization beam splitter or a polarization beam splitter composed of a transmission type diffraction grating.
[0009]
Further, display light may be projected by a projection optical system.
[0010]
In the present invention, since the polarization separation means is arranged in the optical path of the illumination light so as to separate the display light from the illumination light, a bright and undistorted color image can be observed and displayed, and the projection image display device The projection optical system does not need to be tilted and the degree of freedom of the optical system is greatly improved.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a reflective image display device using a hologram color filter of the present invention will be described based on examples.
[0012]
The basic principle of the present invention is that, in a reflection type image display device using a hologram color filter as described in JP-A-9-281919, diffracted light that is split by the hologram color filter and incident on the reflection type image display element. Is set to be substantially perpendicular to the surface of the image display element, and the reflected light from the reflective image display element is diffracted again to the illumination light source side by the hologram color filter, and the direction of the polarization plane like the Wollaston prism The display light is separated from the direction of the illumination light by the polarization separation means that changes the emission direction according to the display light, and an image with small image distortion can be displayed. It can be projected.
[0013]
The illumination light incident angle of the hologram color filter and the polarization separation angle of the polarization separation means are set so that the display light separation direction by the polarization separation means is substantially perpendicular to the display surface of the reflective image display element. In that case, in the case of configuring as a projection image display device, it is not necessary to arrange the projection optical system in a tilted manner. Such a setting dramatically improves the degree of freedom of the optical system.
[0014]
Next, examples of the present invention will be described. First, referring to FIG. 3, the diffracted light, which is split by the hologram color filter 2 and is incident on the reflective image display element 5, particularly its central ray (the principal ray of the green component 7G) is incident on the surface of the image display element 5. The reflective image display device 1 set to be substantially vertical will be described.
[0015]
In FIG. 3, a reflective image display element 5 includes a transmissive spatial light modulator 3 made of, for example, a liquid crystal display element, and a reflective layer 4 such as an aluminum film disposed on the back surface of the transmissive spatial light modulator. 3 is regularly divided into pixels 3 ′, and the hologram color filter 2 is disposed on the front side (observation side) of the transmissive spatial light modulator 3. A black matrix (not shown) is arranged between the pixels 3 ′ of the transmissive spatial light modulator 3. Note that the distance between the hologram color filter 2 and the reflective layer 4 is selected to be approximately equal to the condensing distance (focal length) of each array-shaped micro-hologram 2 ′ constituting the hologram color filter 2.
[0016]
Here, the hologram color filter 2 includes three pixels adjacent to each other in the repetition period of the three primary color pixels R, G, and B of the transmissive spatial light modulator 3, that is, in the direction of the transmissive spatial light modulator 3. Corresponding to each of the 3 ′ sets, the holograms 2 ′ are arranged in an array at the same pitch as the repetition pitch, and the minute holograms 2 ′ are adjacent to each other in the direction in the drawing of the transmissive spatial light modulator 3. One micro-hologram 2 ′ is arranged corresponding to each set of three pixels 3 ′, and each micro-hologram 2 ′ is included in the illumination light 6 incident at an angle θ with respect to the normal line of the hologram color filter 2. The green component light 7G is formed in a Fresnel zone plate shape so as to be condensed substantially vertically near the center pixel G of the three primary color pixels R, G, B corresponding to the minute hologram 2 ′. It is. The micro-hologram 2 ′ is composed of a transmission type hologram such as a relief type, a phase type, and an amplitude type that has little or no wavelength dependency of diffraction efficiency, and diffracts at different diffraction angles depending on the wavelength.
[0017]
With this arrangement, when the white illumination light 6 is incident at an incident angle θ from the surface side of the hologram color filter 2, the wavelength dispersion is performed by the hologram color filter 2, and the condensing position for each wavelength is the surface of the hologram color filter 2. It is distributed in the direction parallel to. Among them, the red wavelength component 7R is near the surface of the reflective layer 4 at the position of the pixel R that displays red, and the green component 7G is near the surface of the reflective layer 4 at the position of the pixel G that displays green. By arranging the hologram color filter 2 so that the component 7B is diffracted and condensed near the surface of the reflection layer 4 of the pixel B that displays blue, each color component is hardly attenuated by the black matrix. Pass through each pixel 3 ', is reflected by the reflective layer 4, passes through the corresponding pixels R, G, and B again from the back side, and becomes light 8R, 8G, and 8B, respectively. The light enters the color filter 2 substantially perpendicularly, is re-diffracted by the hologram color filter 2 to become diffracted light 9, and is emitted in a direction substantially opposite to the illumination light 6.
[0018]
As described above, the reflected light 8 is re-diffracted by the hologram color filter 2 and is emitted in a direction substantially opposite to the illumination light 6, as described above, the hologram color filter 2 has little or no wavelength dependency of diffraction efficiency. For this reason, FIG. 4 shows an example of the wavelength dependence of the diffraction efficiency. FIG. 4 shows the diffraction efficiency when the illumination light 6 incident on the hologram color filter 2 is S-polarized light and P-polarized light, but there is little difference in diffraction efficiency regardless of whether the illumination light 6 is S-polarized light or P-polarized light. .
[0019]
Here, in the present invention, the diffraction components 7R, 7G, and 7B of the respective colors are incident on the pixels R, G, and B that display red, green, and blue of the transmissive spatial light modulator 3, respectively, and display of those pixels is performed. The transmissive spatial light modulator 3 is configured so as to be subjected to modulation of rotation of the polarization plane according to the state, and in the case of maximum modulation or minimum modulation when reflected by the reflective layer 4 and reciprocally passes through the pixel 3 ′ The surface is rotated 90 °. As such a transmissive spatial light modulator 3, for example, there is a TN liquid crystal display element, but in addition, an amplitude modulation transmissive spatial light modulator and a quarter-wave plate disposed on the incident side thereof. There are things that become.
[0020]
In this way, the diffracted light 7 that is spectrally divided by the hologram color filter 2 and enters the reflective image display element 5 (the diffracted components 7R, 7G, and 7B are collectively referred to as diffracted light 7), particularly its central ray (green component). In the reflective image display device 1 in which the 7G chief ray) is set to be substantially perpendicular to the surface of the image display element 5, the display light (diffracted light) 9 is emitted in a direction substantially opposite to the illumination light 6. However, the display light 9 cannot be separated from the illumination light 6 as it is, and is not suitable as a display device.
[0021]
Therefore, in the present invention, polarization separation means for separating the display light 9 from the illumination light 6 is used. As such a polarization separation means, a polarization separation prism such as a Wollaston prism, a Nicol prism, a Gran Thompson prism, a Gran Foucault prism, a Lotion prism, etc. can be used. Use of a holographic polarization beam splitter composed of a volume hologram proposed in JP-A-248417 and JP-A-7-234316, or a polarization beam splitter composed of a transmission diffraction grating proposed in JP-A-61-240204 it can. Furthermore, a polarization separation prism array in which polarization separation prisms are arranged in a plane on an array can be used. However, as will be apparent from the arrangement of FIGS. 1 and 2 to be described later, in the case of a polarized beam splitter that separates the S-polarized light and the P-polarized light so as to form an angle of 90 ° with each other, the display of the reflective image display device 1 is performed. It is not desirable because the arrangement is such that the surface is viewed from an oblique direction.
[0022]
FIG. 1 is an optical path diagram showing one embodiment of a reflection type image display apparatus using a hologram color filter according to the present invention. The reflection type image display apparatus 1 has the structure shown in FIG. 3, and a white light source 11 such as a metal halide lamp is used as the light source of the illumination light 6, and the Wollaston prism is used as polarization separation means in the optical path of the illumination light 6. 10 is arranged. The Wollaston prism 10 is set so that the separation angle between the S-polarized light and the P-polarized light is substantially equal to the incident angle θ of the illumination light 6 to the hologram color filter 2. A polarizing plate 12 is disposed in the optical path of the illumination light 6 incident on the Wollaston prism 10 from the light source 11.
[0023]
Because of this arrangement, the illumination light 6 emitted from the light source 11 becomes, for example, P-polarized light by the polarizing plate 12, and the illumination light 6 emitted from the Wollaston prism 10 remains P-polarized and has an incident angle θ with the hologram color filter 2 being used. The diffracted light 7 that is split into red, green, and blue components is incident on the reflective image display element 5 substantially perpendicularly, and the polarization plane changes from the P-polarized state according to the state of each pixel 3 ′. Upon receiving the rotation modulation, the reflected light 8 is incident on the hologram color filter 2 substantially perpendicularly from the back side, and is diffracted again to become the diffracted light 9. The diffracted light 9 enters the Wollaston prism 10 from the opposite side, and the modulated S polarization component in the diffracted light 9 is emitted from the illumination light 6 so as to form a separation angle θ with the illumination light 6 from the light source 11. The separated display light 9 ′ exits from the reflective image display device 1, and the display light 9 ′ is equivalent to exit from the reflective image display device 1 in the front direction. Therefore, a bright and undistorted color image can be observed by observing the display light 9 ′. Further, by arranging the projection lens 13 without decentering in the optical path of the display light 9 ′, a bright and undistorted color image can be projected on the screen 14. In the above arrangement, the polarizing plate 12 is not always necessary.
[0024]
FIG. 2 is an optical path diagram showing another embodiment of the reflection type image display apparatus using the hologram color filter according to the present invention. The reflection type image display apparatus 1 having the configuration shown in FIG. 3 is used, and a white light source 11 such as a metal halide lamp is used as the light source of the illumination light 6, and this implementation is performed as polarization separation means in the optical path of the illumination light 6. In the example, a holographic polarizing beam splitter 10 'disclosed in JP-A-7-248417 is arranged. The separation angle between the S-polarized light and the P-polarized light of the holographic polarizing beam splitter 10 ′ is set to be substantially equal to the incident angle θ of the illumination light 6 to the hologram color filter 2. A polarizing plate 12 is disposed in the optical path of the illumination light 6 incident on the holographic polarizing beam splitter 10 ′ from the light source 11.
[0025]
In this case, the illumination light 6 emitted from the light source 11 becomes P-polarized light, for example, by the polarizing plate 12, and the illumination light 6 emitted from the holographic polarization beam splitter 10 ′ is incident as P-polarized light. The diffracted light 7 that is incident on the hologram color filter 2 at an angle θ and is split into red, green, and blue components is incident on the reflective image display element 5 substantially perpendicularly, and P depends on the state of each pixel 3 ′. The polarization plane undergoes rotational modulation from the polarization state to become reflected light 8, enters the hologram color filter 2 from the back side substantially perpendicularly, and is diffracted again to become diffracted light 9. The diffracted light 9 is incident on the holographic polarization beam splitter 10 'from the opposite side, and the S-polarized component modulated in the diffracted light 9 is illuminated so as to form a separation angle θ with the illumination light 6 from the light source 11. The light 6 is separated from the light 6 to become display light 9 ′ and exits from the reflective image display device 1, and the display light 9 ′ is equivalent to exit from the reflective image display device 1 in the front direction. Therefore, a bright and undistorted color image can be observed by observing the display light 9 ′. Further, by arranging the projection lens 13 without decentering in the optical path of the display light 9 ′, a bright and undistorted color image can be projected on the screen 14. Also in this case, the polarizing plate 12 is not necessarily required.
[0026]
As described above, in the reflection type image display apparatus of the present invention, the illumination light 6 and the display light 9 are emitted in substantially opposite directions, but the display light 9 ′ is separated by the polarization separation means to produce the display light 9 ′. Since the display device 1 is arranged in front of the display device, a bright and undistorted color image can be observed and displayed. When configured as a projection image display device, the projection optical system does not need to be arranged in a tilted manner. The degree of freedom is greatly improved.
[0027]
As mentioned above, although the reflection type image display apparatus using the hologram color filter of the present invention has been described based on some embodiments, the present invention is not limited to these embodiments, and various modifications are possible. The transmissive spatial light modulator is not limited to the transmissive liquid crystal display element, and various spatial light modulators can be used. Furthermore, the reflective layer is not limited to a reflective layer such as an aluminum film, and a reflective layer using a hologram may be used.
[0028]
【The invention's effect】
As is clear from the above description, according to the reflective image display device using the hologram color filter of the present invention, the polarization separation means is arranged in the optical path of the illumination light so as to separate the display light from the illumination light. Therefore, a bright and undistorted color image can be observed and displayed, and when configured as a projection image display device, the projection optical system does not need to be tilted, and the degree of freedom of the optical system is dramatically improved.
[Brief description of the drawings]
FIG. 1 is an optical path diagram showing one embodiment of a reflective image display device using a hologram color filter according to the present invention.
FIG. 2 is an optical path diagram showing another embodiment of a reflective image display device using a hologram color filter according to the present invention.
3 is an optical path diagram of the reflective image display device used in FIGS. 1 and 2. FIG.
FIG. 4 is a diagram illustrating an example of wavelength dependency of diffraction efficiency of a hologram color filter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Reflection type image display apparatus 2 ... Hologram color filter 2 '... Micro hologram 3 ... Transmission type spatial light modulator 3' ... Pixel 4 ... Reflection layer 5 ... Reflection type image display element 6 ... Illumination light 7 ... Diffracted light 7R, 7G, 7B ... Diffraction spectroscopic component 8 ... Reflected light 8R, 8G, 8B ... Reflected light component 9 ... Diffracted light (display light)
9 '... display light 10 ... Wollaston prism 10' ... holographic polarization beam splitter 11 ... light source 12 ... polarizing plate 13 ... projection lens 14 ... screen

Claims (6)

A reflection-type image display device comprising a combination of a hologram color filter and a reflection-type spatial modulation element composed of repetition of element holograms that chromatically disperse and collect illumination light incident at an oblique incident angle, the reflection-type space In a reflective image display device in which display light reflected by a modulation element and re-diffracted by the hologram color filter is emitted in a direction substantially opposite to the illumination light, a polarization separation means is disposed in the optical path of the illumination light and the display is performed. A reflection-type image display device using a hologram color filter, wherein light is separated from the illumination light. The hologram according to claim 1, wherein a polarization separation angle by the polarization separation means is substantially equal to an incident angle of the illumination light, and the display light is emitted substantially perpendicularly to a surface of the reflective spatial modulation element. Reflective image display device using color filters. 3. The reflection type image display device using a hologram color filter according to claim 1, wherein the reflection type spatial modulation element rotates a polarization plane of incident light according to a modulation degree of a pixel. 4. A reflection type image display apparatus using a hologram color filter according to claim 1, wherein the polarization separation means comprises a polarization separation prism or an array thereof. 4. A reflection type image display apparatus using a hologram color filter according to claim 1, wherein the polarization separation means comprises a holographic polarization beam splitter or a polarization beam splitter comprising a transmission diffraction grating. . 6. The reflection type image display apparatus using a hologram color filter according to claim 1, wherein the display light is projected by a projection optical system.

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