JPH02262613A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain the image forming device which can display an image with superior color reproducibility by specifying the twist angle of liquid crystal molecules of a liquid crystal light valve. CONSTITUTION:An optical recording type liquid crystal light valve is constituted by forming a transparent electrode 202 made of ITO and a dielectric multi- layered mirror 204 consisting of a photoconductor layer 203 and a dielectric multi-layered film on a transparent substrate 201 and then forming a transparent electrode 205 of ITO as an opposite substrate, and then sealing liquid crystal 207 through the transparent substrate 206. Twisted nematic liquid crystal is used as the liquid crystal 207 and the twist angle of the liquid crystal is set to 175 to 210 deg. by an orienting film formed on a dielectric multi-layered mirror 204 and the transparent electrode 205. When the twist angle of liquid crystal molecules is set within this range, the reflectivity is >=90% and almost 100% reflectivity is obtained at a 193 deg. twist angle. Consequently, the highest reflectivity is obtained with the wavelength of light irradiating the liquid crystal light valve, so that the image with superior color reproducibility is displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application 1] The present invention relates to an improvement in an image forming apparatus that displays a full-color image using an optical recording type liquid crystal light valve having a photoconductor layer and a liquid crystal layer.

[Prior Art] An image forming apparatus that displays a full-color image using a conventional optical recording type liquid crystal light valve having a photoconductor layer and a liquid crystal layer is disclosed in Japanese Patent Laid-Open No. 150937-1983. , using three liquid crystal light valves in which the twist angle of the liquid crystal molecules is 45 degrees, images corresponding to R, G, and B of the image are formed on each liquid crystal light valve, and multiple color-selective polarizing beam splitters and dichroic separators are used. By combining these, white light was made monochromatic, guided to a liquid crystal light valve, and the image formed was read out.

[Problem to be Solved by the Invention] However, in the above-mentioned conventional technology, the wavelength dependence of the reflectance of the liquid crystal light valve used is determined by the relationship between the layer thickness in μm of the liquid crystal layer and the refractive index anisotropy Δn. The problem is that the color reproducibility of the formed image is poor because it is sensitive to the product Δn-d and it is difficult to optimize the wavelength of the light irradiated to the liquid crystal light valve.

Therefore, the present invention solves these problems,
The purpose is to provide an image forming device that can display images with excellent color reproducibility using a liquid crystal light valve that can be easily optimized for the wavelength of light irradiated onto the liquid crystal light valve. There is a particular thing.

The image forming apparatus of the present invention includes (1) an image forming apparatus that displays a color image using a plurality of reflective liquid crystal light valves each having a photoconductor layer and a liquid crystal layer and forming images optically; The twist angle of the liquid crystal molecules of the light valve is from 175 degrees to 210 degrees.
2. The product Δn-d of the refractive index anisotropy Δn of the liquid crystal of the reflective liquid crystal light valve and the layer thickness d of the liquid crystal layer is within the range of 2. 0.95λ≦△ for the wavelength λ of the light
3. R and G readout lights for visualizing images formed on the plurality of reflective liquid crystal light valves.

A wavelength separation function that monochromates the wavelength corresponding to B, and irradiates it onto the plurality of reflective liquid crystal light valves, and R, G, which is reflected by the plurality of reflective liquid crystal light valves.
B. It is characterized by having a dichroic element that simultaneously has a function of synthesizing light corresponding to wavelengths. 4. The dichroic element is characterized by having two types of wavelength selection surfaces orthogonal to each other.

[Example 1] An image forming apparatus according to an example of the present invention is shown in FIGS. 1 to 3.
This will be explained according to the diagram.

101.102.103 is an optical recording type liquid crystal light valve that has a photoconductor layer and a liquid crystal layer and forms an image optically, and as shown in FIG.
A transparent electrode 202 made of ITO is formed on a transparent electrode 202 made of ITO, and a photoconductor M2O3 and a dielectric multilayer mirror 204 made of a dielectric multilayer film are fabricated. A liquid crystal 207 is sealed therein. In this embodiment, the liquid crystal 207 uses a twisted nematic liquid crystal, and the twist angle of the liquid crystal is defined by an alignment film (not shown) formed on the dielectric multilayer mirror 204 and the transparent electrode 205, and this twist angle is 175°. to 210'. 20
Reference numeral 8 indicates writing light irradiated onto the photoconductor layer, and reference numeral 209 indicates reading light. In addition, 210 is a transparent electrode 202.2
This is a power supply for applying an electric field to the liquid crystal light valve via 05. Table 1 shows the detailed configuration of the liquid crystal light valve. In this example, a small amount of boron is used as the photoconductor layer.
Intrinsic amorphous silicon with re-addition was used, but it is also possible to use one with a PIN structure.
S, S e, OP C, single crystal silicon, B
SO etc. can also be used.

Table 1 shows 104, 105, and 106 the reflective liquid crystal light valve and cathode ray tubes 107, 108, which are image supply means, respectively.
This is a Royal equal-magnification imaging optical system that optically couples 109 tube surfaces, and specifically uses a rod lens array in which a large number of gradient index rod lenses are arranged on a plane. Also,
In addition to rod lens arrays, it is also possible to use a coupling means using an erect equal-magnification imaging optical system configured using multiple microlens arrays in which a large number of microlenses exhibiting lens characteristics due to refractive index distribution are formed on a plane. Yes, also
It is also possible to combine a plurality of micro-diameter fibers using a fiber microplate arranged on a plane. 110, 111, and 112 are power supplies for driving the reflective liquid crystal light valves 101, 102, and 103, respectively, and apply an electric field through the transparent electrode in the reflective liquid crystal light valve, similar to 210 in FIG. . Cathode ray tube 101
．． An image based on signals corresponding to RGB of the image is displayed from a video signal source (not shown) on 102 and 103, and this image is guided to the reflective liquid crystal light valve by the aforementioned rod lens array and irradiated onto the photoconductor layer. be done. The video signal supplied to each cathode ray tube is a normal video signal that is color demodulated and separated into RGB signals, and then supplied to one of the cathode ray tubes for each color. A black and white image is displayed. In the area where the photoconductor layer was irradiated with light, the impedance of the photoconductor layer changes, and the impedance ratio with the liquid crystal layer changes, and the electric field that was applied to the liquid crystal layer at the time of light irradiation changes. When irradiated with light, an electric field is applied and the alignment state of the liquid crystal changes, and the light that enters from the liquid crystal layer side is reflected by the dielectric multilayer mirror and receives retardation from the liquid crystal while exiting, forming an image. Ru. The principles of the above image formation are as described in detail in the prior art and related documents mentioned above.

In this way, the reflective liquid crystal light valve 101.102
．． Image information corresponding to RGB of the image to be displayed is formed on the image display 103. 113 is a readout light source for visualizing the above-mentioned image information, and uses a xenon lamp, a halogen lamp, a metal halide lamp, or the like. It is best to add a reflector to this readout light source to increase the efficiency of using the light emitted from the light source.In addition, an infrared filter is added to block the heat absorbed by the reflective liquid crystal light valve and other optical components. It is even better to add an ultraviolet blocking filter to prevent deterioration of the liquid crystal inside the liquid crystal light valve. The readout light emitted from the readout light source 113 is separated into S-polarized light and P-polarized light by the polarization beam splitter 114. Figure 1 shows the case where the S-polarized light component reflected by the polarizing beam splitter is used for display, but when displaying the P-polarized light component, the arrangement of the projection lens described later and the readout light source described above must be exchanged. This makes it possible, and the matters described below hold in exactly the same way. Further, the polarizing beam splitter 114 desirably has good polarization characteristics over the entire visible light range, and must sufficiently maintain the whiteness of the light emitted from the light source. The light that has passed through the polarizing beam splitter 114 enters a dichroic prism 115, which is a dichroic element, and is separated into three colors, RBG, and each monochromatic light is irradiated onto a reflective liquid crystal light valve. FIG. 3 is a diagram showing the vicinity of the dichroic prism 115.

The dichroic prism 115 is made up of four right-angled prisms pasted together, and the pasting surfaces 301.
302 is coated with a dielectric multilayer film and functions as a surface for separating two orthogonal wavelengths. The dielectric multilayer film formed on the bonding surface 301 has R(
The dielectric multilayer film formed on the bonding surface 302 reflects light with a wavelength corresponding to B (blue) in white light and transmits light with other wavelengths. It is set to reflect light of certain wavelengths and transmit light of other wavelengths. Therefore, polarizing beam splitter 1
The light 303 that has passed through the dichroic prism 1
15 separates by wavelength, 304 red light (R), 3
05 becomes blue light (B), and the bonding surface 301.30
The light 306 that has passed through both of the liquid crystal light valves becomes green light (G) and is irradiated onto each reflective liquid crystal light valve. As mentioned above, reflective liquid crystal light valve 101.102.10
3, images corresponding to R, G, and B of the image are formed, but in FIG.
This shows the case where a G image is formed on top. Light 304.305 wavelength separated by dichroic prism 115
．． The light 306 enters each reflection type liquid crystal light valve, and while being reflected by the dielectric multilayer mirror, the liquid crystal light rays 306 enter the dichroic prism again. 307, 308, and 309 each indicate the light reflected by the reflective liquid crystal light valve. Light 309 containing green (G) image information passes through the dichroic prism as it is, and light 307 containing red (R) image information is reflected by the dielectric multilayer film on the bonding surface 301 inside the dichroic prism, and becomes blue ( The light 308 containing the image information in B) is transmitted to the bonding surface 30 in the dichroic prism.
The RGB lights are reflected by the dielectric multi-MW on 2, and the RGB lights are combined into 310 beams and sent to the polarizing beam splitter 11.
4 again. Of the light in which the RGB three colors are combined and which enters the polarizing beam splitter 114, only the light whose polarization plane has been rotated by 906 among the light which entered the reflective liquid crystal light valve is transmitted, and is guided to the projection lens 116 and sent to the screen. 11
7 will be displayed on the screen.

When we investigated in detail the conditions for the twist angle of the liquid crystal molecules of the optical recording type liquid crystal light valve used in the image forming apparatus shown in this example, we found that the reflectance was within the range of 175° to 2106° for any wavelength. It was found that the reflectance was 90% or more, and furthermore, the reflectance was almost 100% at a twist angle of 193°.

Therefore, the twist angle of the liquid crystal molecules is preferably 193°, and in order to increase the reflectance of the liquid crystal light valve, it is necessary to set the twist angle of the liquid crystal molecules within the range of at least 175° to 210°. Furthermore, the product Δn−d of the refractive index anisotropy Δn of the liquid crystal and the layer F[d of the liquid crystal layer is also optimized for the wavelength of the light that is made monochromatic by the dichroic prism and irradiated. Figure 4 is △n
-d=0.58 and the twist angle of the liquid crystal molecules set to 193 degrees, the reflectance of an optical recording type liquid crystal light valve in the absence of an electric field was measured using a polarizing beam splitter. In the optical recording type liquid crystal light valve shown in Figure 4,
The reflectance is set to have a peak at a wavelength of 550 nm. The wavelength at which the reflectance peaks can be set to any value within visible light by changing Δn−d. The solid line in FIG. 5 shows the relationship between Δn-d and the wavelength at which the reflectance of the optical recording type in the absence of an electric field has its peak.

The center wavelength of the light separated by the dichroic prism shown in this embodiment is the same as that of the optical recording type liquid crystal light valve 101.
The light irradiated on 102 is λ = 630 nm, the light irradiated on 102 is λ = 550 nm, and the light irradiated on 103 is λ = 48
00m. Therefore, 0゜95λ≦△n-d≦1.1
If it is within the range of 5λ, the influence on the color purity etc. of the formed image can be ignored, but the reflection type liquid crystal light valve 101
is Δn-d=0.65.102 is Δn-d=0.58,
When 103 is set to Δn-d = 0.50, the reflectance is highest for the wavelength of the light irradiated to each liquid crystal light valve, and it is possible to display images with excellent color reproducibility. It is desirable to do so.

The dotted line in FIG. 5 indicates the Δn-
This is the relationship between d and the wavelength at which the reflectance has a peak. Compared to the optical recording type liquid crystal light valve in which the twist angle of the liquid crystal molecules is 193 degrees as shown in this example, the change in the peak wavelength of reflectance is sensitive to the fluctuation of △n・d, and the spectral characteristics of the dichroic prism are In order to optimize the optical recording type liquid crystal light valve according to this, the gap margin of the liquid crystal layer must be small, and as a result, the color purity of the displayed image will deteriorate. On the other hand, in the optical recording type liquid crystal light valve shown in this embodiment, the change in the peak wavelength of reflectance is gradual with respect to the change in Δn-d, so optimization can be performed relatively easily.

In addition, in this embodiment, a cathode ray tube was used as a means for writing an image on the liquid crystal light valve, but the laser light modulated by the video signal is two-dimensionally scanned by a polygon scanner, an acousto-optic modulator, a galvano scanner, etc., and the liquid crystal light valve is The photoconductor layer may be irradiated.

[Effects of the Invention] As described above, according to the present invention, the reflectance of the liquid crystal light valve can be easily made to have a peak in accordance with the wavelength of the light that is made monochromatic by the dichroic prism and irradiated onto the liquid crystal light valve. The color purity of the displayed image has been improved and images closer to natural colors can now be obtained.

In addition, the twist angle of the liquid crystal molecules has been optimized to improve contrast and brightness, further improving image display quality and improving brightness, making it possible to reduce the amount of light from the light source. As a result, the temperature rise of the liquid crystal light valve itself due to irradiation light has been reduced, improving the reliability and lifespan of the liquid crystal light valve.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is a diagram showing a reflective liquid crystal light valve according to an embodiment of the present invention. FIG. 3 is a diagram showing the vicinity of a dichroic prism according to an embodiment of the present invention. FIG. 4 is a diagram showing the reflectance of a liquid crystal light valve according to an embodiment of the present invention. FIG. 5 is a diagram showing the relationship between Δn-d and the wavelength λ at which the reflectance of the liquid crystal light valve has a peak, according to an embodiment of the present invention. Rhythm, photoconductor layer, liquid crystal layer and above Applicant: Seiko Epson Co., Ltd. Representative Patent Attorney Masayoshi Kamiyanagi (and 1 other person) 101, 102, 103 ・ Bulb 104, 105, 106 ・ Zuray 107, 108, 109 ・ Reflective type LCD light Selfoclen t! i-pole ray tube/dichroic tube Figure 2 Figure 4

Claims (4)

[Claims] (1) In an image forming apparatus that displays a color image using a plurality of reflective liquid crystal light valves that have a photoconductor layer and a liquid crystal layer and perform image formation optically, the liquid crystal molecules of the reflective liquid crystal light valve Twist angle from 175 degrees to 21
An image forming apparatus characterized in that the image forming apparatus is within a range of 0 degrees. (2) The product Δn·d of the refractive index anisotropy Δn of the liquid crystal of the reflective liquid crystal light valve and the layer thickness d of the liquid crystal layer is 0.95λ with respect to the wavelength λ of the light irradiated to the reflective liquid crystal light valve. ≦
2. The image forming apparatus according to claim 1, wherein Δn·d≦1.15λ. (3) The readout light for visualizing images formed on the plurality of reflective liquid crystal light valves is made monochromatic to wavelengths corresponding to R, G, and B, and the wavelengths are irradiated onto the plurality of reflective liquid crystal light valves. An image forming apparatus comprising a dichroic element having a separation function and a function of combining light corresponding to R, G, and B wavelengths reflected by the plurality of reflective liquid crystal light valves. (4) The image forming apparatus according to claim 1, wherein the dichroic element has two types of wavelength selection surfaces orthogonal to each other.