JPH06138446A - Optical modulator and projection type display device using the same - Google Patents

Abstract

PURPOSE:To provide the optical modulator having a good image contrast and the projection type display device using it. CONSTITUTION:A liquid crystal layer 94 is inserted and held between a transparent substrate 14 and a dielectric multi-layered film 93 and a light absorbing film 11 is formed on the flank of the transparent substrate 14, and a reflection preventive film 15 is formed by a V-coating system on the surface of the transparent substrate 14 and a counter electrode 13 which has a reflection preventing function is formed between the transparent substrate 11 and liquid crystal layer 94. An image is written from the reverse surface through a photoconductive layer 95. Light which is made incident from the side of the reflection preventive film 15 is scattered by the liquid crystal layer 94 and part of the scattered light is reflected by the border surface between the transparent substrate 14 and reflection preventive film 15 to return to the liquid crystal layer 94 again, but the transparent substrate 14 is thicker than specified, so the light is made incident on and absorbed by the light absorbing film 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a reflective spatial light modulator or writing light to input two-dimensional information such as an image or a data pattern, and uses the read light to input this two-dimensional information. The present invention relates to an optical writing type spatial light modulator (hereinafter, referred to as an optical modulator) having a function of displaying images and a projection type display device using the same.

[0002]

2. Description of the Related Art A conventional optical modulator is disclosed in Japanese Patent Laid-Open No. 2-93.
519 publication is illustrated. Hereinafter, a conventional optical modulator will be described with reference to the drawings.

FIG. 9 is a perspective view of a conventional optical writing type optical modulator. The light modulator includes a transparent substrate 96 such as glass with a transparent electrode 92b attached, a liquid crystal layer (liquid crystal composite) 94,
It is composed of a dielectric multilayer film 93 for total reflection and a photoconductive layer 95 to which a transparent electrode 92a is attached. The two transparent electrodes 92a and 92b are connected to the AC power supply 91. As the AC voltage generated by the AC power supply 91, an effective value V ₀ larger than the effective value of the AC voltage required to make the major axis of the nematic liquid crystal molecules in the liquid crystal layer 94 substantially coincide with the direction of the applied voltage is applied. Specifically, it is about 5 to 100V. The writing light 97 is incident on the photoconductive layer 95. On the other hand, the reading light 98
Enters from the transparent substrate 96 side, is totally reflected by the dielectric multilayer film 93, becomes display light 99, and is emitted to the substrate 96 side. Here, the liquid crystal layer 94 is, for example, as shown in FIG.
As shown in, the nematic liquid crystal 101 and its liquid crystal 10
1 of the ordinary refractive index n _o, the extraordinary refractive index n _e or LCD 101
Is composed of a polymer 102 having a refractive index approximately equal to any of the refractive indices n _x when randomly oriented, the polymer 1
The liquid crystal 101 is enclosed in 02. Alternatively, the liquid crystal 101 may be enclosed in a polymer 102 in the form of microcapsules.

In the liquid crystal layer 94, when the ordinary refractive index n _o of the liquid crystal 101 or the extraordinary refractive index n _e and the refractive index of the polymer 102 are substantially the same, the liquid crystal composite is directly sandwiched between the electrodes. , The refractive index of the liquid crystal 101 and the polymer 102 are different from each other when no voltage is applied between the electrodes, resulting in a scattering state. Is in a transparent state.

The photoconductive layer 95 is made of CdS, CdS.
e, Se, SeTe, GaAs, Bi ₁₂ SiO ₂₀ , Bi
_{It is made of 12} GeO ₂₀ , amorphous silicon film, or other material whose impedance changes drastically when exposed to light.

[0006] writing light irradiation time and the light non-irradiation of Z the impedance of the photoconductive layer 95, respectively _oN, and Z _OFF, the impedance of the liquid crystal layer 94 and the total reflection dielectric multilayer film 93, respectively Z _LC, Z _M Then, the optical modulator has the following relationship.

[0007]

[Equation 2]

Further, the thickness and the dielectric constant of the photoconductive layer 95 are t
₁ and ε ₁ , the thickness and the dielectric constant of the liquid crystal layer 94 are t ₂ and ε _{2, respectively.}
And the thickness and the dielectric constant of the total reflection dielectric multilayer film 93 are set to t ₃ and ε ₃ , respectively, the optical modulator

[0009]

[Equation 3]

Have a relationship of

Next, the operation of the conventional optical modulator will be described based on an example of a liquid crystal composite in which the ordinary refractive index n _o of the liquid crystal 101 and the refractive index n _{e of the} polymer 102 are substantially the same. .

In the absence of writing light, most of the voltage above (Equation 2) is applied to the photoconductive layer 95, and the applied voltage to the liquid crystal layer 94 is small. Therefore, the nematic liquid crystal molecule 10
1 corresponds to the irregular wall surface of the polymer 102, as shown in FIG.
Face in various directions as shown in (a). At this time, the nematic liquid crystal 101 is the polymer 1 surrounding the liquid crystal 101.
It has a refractive index (2n _o + n _e ) / 3 different from the refractive index n _{p of} 02.

Therefore, the read light 98 is scattered in the liquid crystal layer 94, and its output light intensity is minimized. Next, when the writing light 97 increases, the impedance of the photoconductive layer 95 decreases according to the intensity thereof, and the voltage applied to the liquid crystal layer 94 increases. When the intensity of the writing light 97 is sufficiently high, the long axis of the liquid crystal molecule 101 is directed to the direction of the electric field as shown in FIG. 10B, and the reading light 98 perpendicularly incident on the liquid crystal layer 94.
Respect, the nematic liquid crystal is considered ordinary refractive index n _o. Since n _o is with very close to the n _p, in this case the reading light 98 passes through without scattering, the reading light 98 after the element transmission is transmitted without scattering, reading light after element transmission, that is, the display The light intensity of the light 99 becomes maximum. When the light modulated as described above is projected on the screen, a projection display device is obtained.

[0014]

The light modulation layer formed as a change in the light scattering state, that is, in FIG. 10A, in order to convert an optical image on the liquid crystal layer 94 into a change in luminance, the light modulation is required. It is utilized that, when only light with a certain solid angle is extracted from the light emitted from the container, the amount of light entering the solid angle changes depending on the light scattering state. There are two types of this method, a center shield type and an aperture type. On the other hand, the center shield type is a method of blocking light from reaching the screen in the transparent state, and light not shielded by the shield plate reaches the screen when the light modulator is in the light scattering state. On the other hand, the aperture type utilizes light traveling in the direction of the directivity, and when the degree of scattering increases, the amount of light entering the projection lens from the light modulator decreases. The above-mentioned center-shielded type is advantageous in contrast, but has a problem that the configuration is complicated and the projected image is dark.

On the other hand, the aperture type has a simple structure,
Although a bright projected image can be obtained, there is a problem that the contrast of the projected image is not good as compared with the center-shielded type. This problem is common to an optical modulator that forms an optical image as a change in the light scattering state and a projection display device using the optical modulator. As a method for solving this problem, it is conceivable to reduce the solid angle of the projection lens, but this causes a decrease in the brightness of the projected image, and the feature that the projected image is bright is diminished.

The reflectance of the transparent electrode is a cause of lowering the contrast. The refractive index of medium 1 is n ₁ , medium 2
The reflectance R of light between the media 1 and 2 is expressed by the following equation, where n ₂ is the refractive index of

[0017]

[Equation 4]

Since the transparent electrode is usually made of ITO, the refractive index is about 2.0, and the substrate is glass, so the refractive index is about 1.52. The refractive indices n _x of the liquid crystal layer 94 is a scattering state is n _x ≒ 1.6 and the refractive index n _o of 1.52, 1.75 and extraordinary refractive index n _e ordinary. Therefore, the reflectance R ₁ between the substrate 96 and the ITO 96b is 1.9% from (Equation 4), the reflectance R ₂ between the ITO 96b and the liquid crystal layer 94 is 1.2%, and the reflection between the air and the glass substrate 96 is Rate R ₃
Is 4.2%, the total reflectance R is R = R ₁ + R ₂ + R ₃ = 7.3%. Since the reflectance R is light that does not enter the light modulation layer 94 and is reflected, it becomes unnecessary light and lowers the contrast.
That is, the contrast CR becomes 100 / 7.3≈15.

As described above, the conventional optical modulator cannot obtain a sufficient contrast. Therefore, even if a projection display device is configured using a conventional light modulator, it is not possible to expect high-contrast image display.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object thereof is to provide a light modulator having a good image contrast and a projection display device using the light modulator.

[0021]

According to the present invention of claim 1, there is provided a transparent substrate which transmits light, and a transparent thin film which is formed on the surface of the transparent substrate and has conductivity and a light reflection preventing function.
An optical modulator including the transparent thin film and a liquid crystal layer disposed between a light reflecting substrate having a light reflecting layer.

According to a sixteenth aspect of the present invention, there is provided a transparent substrate which transmits reading light, and a transparent thin film which is formed on the surface of the transparent substrate and has conductivity and a light reflection preventing function.
A liquid crystal layer arranged between the transparent thin film and a light reflecting substrate having a light reflecting layer, a light source means for emitting reading light to the liquid crystal layer through the transparent substrate, and a light reflecting layer modulated by the liquid crystal layer. And a projection optical means for projecting the light reflected from the screen onto a screen.

[0023]

According to the present invention of claim 1, the transparent thin film reflects light when light passes from the transparent substrate to the liquid crystal layer and when light reflected by the light reflecting substrate passes from the liquid crystal layer to the transparent substrate. To improve the contrast.

In the sixteenth aspect of the present invention, when the reading light emitted from the light source means passes from the transparent substrate to the liquid crystal layer, the light reflected by the light reflecting substrate and modulated by the liquid crystal layer is modulated by the liquid crystal layer. The transparent thin film suppresses the reflection of light when passing from the transparent substrate to the transparent substrate, and improves the contrast of the image projected on the screen by the projection optical means.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings showing its embodiments.

FIG. 1 is a sectional view of an optical modulator of an embodiment according to the present invention. Note that the following drawings are drawn as models and do not match the physical film thickness or shape.
In addition, parts unnecessary for explanation are omitted. The description will be focused on the differences from the conventional example.

In FIG. 1, the transparent substrate 14 is a glass substrate, and a counter electrode (transparent thin film) 13 also serving as an antireflection structure is formed on the surface in contact with the liquid crystal layer 94 which is a light modulation layer. Further, a space (not shown) or the like is provided between the counter electrode 13 and the dielectric multilayer film 93 so as to be held at a predetermined interval.
The liquid crystal layer 94 is sealed in the peripheral portion by the sealing resin 12. A photoconductive layer 95 is formed on the dielectric multilayer film 93,
A transparent electrode 92a is formed on the photoconductive layer 95,
The dielectric multilayer film 93, the photoconductive layer 95, the transparent electrode 92
a constitutes a light reflecting substrate. Here, the transparent substrate 14
Has a refractive index of 1.52, and the thickness t of the transparent substrate 14 is represented by the following equation, where d is the maximum diameter of the effective display area of the liquid crystal layer 94 and n is the refractive index of the transparent substrate 14.

[0028]

[Equation 5]

The light absorbing film 1 is formed on the side surface of the transparent substrate 14.
Black paint is applied as No. 1. This light absorbing film 11
Absorbs the light reflected on the exit surface of the transparent substrate 14 by 2
Prevents secondary scattered light.

As the liquid crystal material of the liquid crystal composite forming the liquid crystal layer 94, nematic liquid crystal, smectic liquid crystal and cholesteric liquid crystal are preferable, and a single or a mixture of two or more kinds of liquid crystal compounds or a substance other than the liquid crystal compounds is used. It may be. Among the above-mentioned liquid crystal materials, a cyanobiphenyl nematic liquid crystal having a relatively large difference between the extraordinary light refractive index n _e and the ordinary light refractive index n _o is preferable. Alternatively, a fluorine-based nematic liquid crystal having good light resistance and heat resistance is preferable.

A transparent substance is preferable as the polymer,
Further, although it may be any of a thermoplastic resin, a thermosetting resin, and a photocurable resin, it is preferable to use an ultraviolet curable resin from the viewpoint of ease of manufacturing process, separation from a liquid crystal phase, and the like. As a specific example, an ultraviolet curable acrylic resin is exemplified, and a resin containing an acrylic monomer or an acrylic oligomer which is polymerized and cured by ultraviolet irradiation is particularly preferable.

As such a polymer-forming monomer,
2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, neopentyl glycol acrylate, hexanediol diacrylate, diethylene glycol diacrylate, tripropylene glycol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol acrylate and the like.

Examples of the oligomer or prepolymer include polyester acrylate, epoxy acrylate and polyurethane acrylate.

A polymerization initiator may be used to accelerate the polymerization, and as an example, 2-hydroxy-2-
Methyl-1-phenylpropan-1-one (“Darocur 1173” manufactured by Merck), 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-
On (Merck "Darocur 1116"), 1-vidroxycyclohexyl phenyl ketone (Ciba-Gaiki "Irgacure 184"), benzyl methyl ketal (Ciba-Geigy "Irgacure 651") and the like. In addition, a chain transfer agent, a photosensitizer, a dye, a cross-linking agent and the like can be appropriately used in combination as optional components.

Although the ratio of the liquid crystal material of the liquid crystal composite is not specified here, it is generally about 20 to 90% by weight, preferably about 50 to 85% by weight.
If it is 20% by weight or less, the amount of liquid crystal droplets is small and the scattering effect is poor. On the other hand, when it is 90% by weight or more, the polymer and the liquid crystal tend to be phase-separated into upper and lower two layers, the ratio of the interface becomes small, and the scattering property is deteriorated. The structure of the polymer-dispersed liquid crystal layer changes depending on the liquid crystal fraction. When the content is about 50% by weight or less, the liquid crystal droplets exist as independent droplets.
When it is more than weight%, a continuous layer in which the polymer and the liquid crystal are intricately mixed with each other is formed.

The thickness of the liquid crystal layer 94 is preferably in the range of 5 to 25 μm, more preferably 8 to 15 μm. If the film thickness is thin, the scattering characteristics are poor and the contrast cannot be improved.

An antireflection film 15 for preventing reflection at the interface with air is formed on the surface of the transparent substrate 14. The antireflection film 15 includes a multi-coat method that reduces the reflectance in a relatively wide wavelength band of visible light and a V-coat method that reduces the reflectance in a specific wavelength band. In the case of an optical modulator used for a projection display device, the V coat method is adopted. This is because the light modulator used in the projection display device modulates light of each wavelength of red (R), green (G), and blue (B) light.
This is because a single optical modulator is used. That is, since the wavelength band received by each optical modulator is narrow, the V coat method is suitable for preventing reflected light as much as possible. Therefore, it is preferable that the optical modulator that modulates each of the R, G, and B lights be provided with an optimum V coat corresponding to the peak wavelength of the incident light. When white light is modulated, it is preferable to apply a multi-coat method.

In the multi-coat method, Al ₂ O ₃ has an optical film thickness of λ / 4, ZrO ₂ has an optical film thickness of λ / 2, and MgF ₂
Is formed by depositing a three-layer thin film having an optical film thickness of λ / 4. In the case of the V coat method, Y ₂ O ₃ has an optical film thickness of λ /
4. MgF ₂ is formed by vapor deposition of a two-layer thin film having an optical film thickness of λ / 4. It should be noted that SiO may be used instead of Y ₂ O ₂ , but since SiO has an absorption band for blue light, it is better to use Y ₂ O ₃ as the antireflection film of the optical modulator that modulates B light. . Also, who generally Y ₂ for direction of O ₃ is obtained a stable and good quality Y ₂ O ₃ is preferred.

Next, the operating principle of the above embodiment will be described.

FIG. 4 is a diagram showing a model of the optical modulator of the present invention. It is assumed that the liquid crystal layer 94 is sandwiched between the transparent substrate 14 and the dielectric multilayer film 93, and the thickness of the transparent substrate 14 is sufficiently larger than the size of the display area. Consider a case where thin parallel light is applied only to the minute area 41 centered on the point A in the display area without applying a voltage to the liquid crystal layer 94.

The light incident on the minute region 41 becomes scattered light 42 and is scattered, and reaches the emission surface 46. When the angle θ ₀ between the exit surface 46 and the scattered light 42 is less than or equal to the critical angle, it becomes the transmitted light ray 43, and when it is more than that, it becomes the reflected light ray 44. Reflected ray 44
Is again incident on the liquid crystal layer 94, and the scattered light 45 is emitted again forward. This corresponds to the formation of the secondary light source in the liquid crystal layer 94.

The luminance distribution of the re-emitted light from the liquid crystal layer 94 is rotationally symmetrical with respect to the thin incident parallel light. The brightness distribution of the re-emitted light has a ring shape.

When the scattered light emitted from a certain pixel enters another pixel even if it should originally be black-displayed, a secondary light source due to diffuse reflection is formed there, so that the brightness of the pixel originally supposed to be black-displayed. Will be higher.

From the above, the problem that the contrast of the projected image of the projection type display device using the liquid crystal layer is not good is
One of the causes is that the scattering gain of the optical modulator when no voltage is applied is large, but it is caused by the above mechanism. As the thickness t of the transparent substrate 14 increases, the brightness of the re-emitted light decreases. Therefore, increasing the thickness of the transparent substrate 14 improves the contrast of the displayed image.

As shown in FIG. 5, consider a case where two points giving the maximum diameter of the effective display area 51 of the liquid crystal layer are P and Q, and parallel light is irradiated only to a minute area 52 centered on the point P. The light emitted from the point P and reflected by the emission surface 46 causes the ring 53 by the re-emitted light to appear on the liquid crystal layer 94. At this time, in order to suppress the brightness of the re-emitted light in the entire effective display area 51, the point Q needs to exist inside the ring 53.
In other words, letting the length from point P to point Q be d,

[0046]

[Equation 6]

If the condition of is satisfied, the effective display area 51
As a whole, the increase in brightness due to unnecessary light is suppressed and the contrast is improved. Increasing the diameter of the ring 53 is the second action for improving the contrast of the present invention. Note that the present inventors have repeated various experiments and confirmed that if the maximum diameter of the effective display area 51 is smaller than the diameter of the ring 53, a practically sufficient effect of improving contrast can be obtained. in this case,

[0048]

[Equation 7]

It becomes Therefore, the thickness t of the transparent substrate 14
Should be selected so as to satisfy (Equation 7) (see Japanese Patent Application No. 4-145277 for details).

An example in which the surface of the transparent substrate 14 is concave will be described. As shown in FIG. 6, the transparent substrate 14 is made of the same material and has the same center thickness, only the emitting surface 46 is changed to a concave surface, and a minute area 41 centered on a point A in the display area without applying a voltage to the liquid crystal layer 94. Only thin parallel light is emitted from the incident side. Considering a ray that emerges from the point A on the liquid crystal layer 94, is reflected at the point B on the concave surface 46, and is incident on the point C on the liquid crystal layer 94, the exit surface 46 changes from a flat surface to a concave surface, so Since the distance from the virtual image of the minute region 41 to the point C becomes long, and the incident angle of the ray reflected at the point B and incident on the point C becomes large, the brightness of the re-emitted light from the point C decreases. Further, since the distance from the point A to the point C becomes long, the diameter of the ring becomes large. Therefore, by changing the emission surface 46 of the transparent substrate 14 from a flat surface to a concave surface, the brightness of the re-emitted light can be reduced and the contrast of the display image can be improved. This is
When the emitting surface of the transparent substrate 14 is concave, it means that the effect of improving the contrast is great even when the emitting surface is flat, even if the center thickness is thin. Therefore, it is not limited to (Equation 7).

Next, when the light is reflected by the ineffective surface (side surface), the light returns to the liquid crystal layer 94 and causes an increase in the brightness of the black display portion. This problem can be solved by providing the light absorbing means 11 on the ineffective surface 47 of the transparent substrate 14 to absorb unnecessary light, as shown in FIGS. 4 and 6. Furthermore, the transparent substrate 1
If an antireflection film is attached to the effective area of the exit surface 46 of No. 4, the reflectance of the exit surface 46 of the light emitted from the liquid crystal layer 94 at a small angle is reduced, so that the increase in brightness of the black display portion can be suppressed. The light absorbing means 11 corresponds to black paint or the like.

On the other hand, a counter electrode 13 having an antireflection function is formed on one surface (on the liquid crystal layer side) of the transparent substrate 14. Strictly speaking, ITO which is a transparent conductive thin film which becomes the counter electrode 13
An antireflection film is formed before and after the film. Hereinafter, the counter electrode having this antireflection structure is referred to as an antireflection electrode 13.

2A and 2B show the antireflection electrode 13
3 is a cross-sectional view showing an example of the configuration of FIG. The example of FIG. 2A is an antireflection electrode 13 having a three-layer structure, and 22 is an ITO film serving as a counter electrode. The film thickness d of the ITO film 22 is set so that the optical film thickness is approximately λ / 2. Peak wavelength of incident light λ
Is 550 nm, d = 1375Å (refractive index n≈2)
Before and after. The film thickness of the ITO film 22 is formed corresponding to λ. 21 and 23 are the refractive index of the transparent substrate 14 and ITO.
It is a thin film made of a material having a refractive index between that of the film 22. The thin films 21 and 23 are preferably formed of the same material and have the same film thickness. The film thickness of the thin films 21 and 23 is an optical film thickness nd = λ / 4. Although the change of the film thickness of the ITO film 22 has a great influence on the change of the reflectance of the peak wavelength, the thin film 21,
The change in the film thickness of 23 has relatively no effect. Note that n is a refractive index.

Materials for the thin films 21 and 23 include aluminum oxide (Al ₂ O ₃ ), yttrium oxide (Y ₂ O ₃ ), silicon monoxide (SiO), and magnesium oxide (Mg).
O), tungsten oxide (WO ₃ ), cerium fluoride (C
Examples include eF ₃ ), and lead fluoride (PbF ₂ ). Among them, Al ₂ O ₃ , Y ₂ O ₃ and CeF ₃ are preferable from the viewpoints of the stability of the substance, the light transmittance and the uniformity of the film. Also, SiO
With (n = 1.7), the reflectance can be made extremely small in a wide visible light range.

When λ is 550 nm, the thin films 21 and 23
When Al ₂ O ₃ (n = 1.63) is used for the film, the film thickness formed is in the range of d = 700Å to 1000Å, the ITO film (n≈
The film thickness of 2.0) 22 may be in the range of 1150Å to 1600Å. The thin film 23 lowers the voltage applied to the ITO film 22, but has almost no effect if d = 1000 Å or less. On the contrary, it is possible to prevent unnecessary substances from being eluted from the transparent substrate 14 and maintain the retention rate of the liquid crystal layer 94 for a long time. If the ITO film 22 is 1000 Å or more, the necessary and sufficient resistance value can be obtained by forming it by vapor deposition or sputtering at 200 ° or more. The thin film 21
Is Y ₂ O ₃ (n = 1.78), d = 650Å∼90
You can set it to 0Å.

From the examination result, when the refractive index n of the ITO film 22 is around 2.0, the use of Y ₂ O ₃ as the thin films 21 and 23 can make the reflectance extremely small over almost the entire visible light range. When the refractive index n of the film 22 is smaller than 1.9, the reflectance can be made extremely small in the visible light range by using Al ₂ O ₃ . However, this is the case where the refractive index of the liquid crystal layer 94 at the time of scattering is higher than the refractive index of the transparent substrate 14. The refractive index of the ITO film 22 also affects when the light incident on the liquid crystal layer 94 is scattered and the light again passes through the ITO film 22. When the refractive index is high, it is reflected and the liquid crystal layer 94 is reflected again.
Returning to, the rate of causing secondary scattering increases. Therefore, it is preferable to form the ITO film 22 with a refractive index as low as possible. From the above, the antireflection electrode 13 of this example
Then, the refractive index of the ITO film 22 is formed to be a little over 1.8, and the thin film 2
1, 23 were formed by using Al ₂ O ₃ (n≈1.63).

By forming the antireflection electrode 13 as described above, the reflectance of light can be greatly reduced, and when the band of modulated light is relatively narrow, the reflectance is 0.1% at the peak wavelength.
The following can be realized. As a matter of course, the ITO film 22 is configured or formed so that the AC voltage 91 can be applied. Instead of using the ITO film 22, a film of indium oxide, tin oxide or the like may be used. Also in that case, the thin films 21 and 23 may be laminated with an optical thin film that reduces the reflectance due to the optical interference effect. The ITO film in the present invention should be understood as a transparent conductive thin film.

The refractive index at the time of scattering of the liquid crystal layer 94, that is, the material selection is restricted for the following reason. Refractive indices n _x of the liquid crystal at the time of scattering the ordinary refractive index of the liquid crystal n _o, when the extraordinary refractive index was n _e (provided that _{n o <n e), n} x = (2n o + n e) / 3
Indicated by. Further, when the refractive index of the polymer is n _p , n _x changes depending on the content ratio of the liquid crystal and the polymer. It is preferable that the n _t ≒ n _x and the refractive index n _t of the transparent substrate 14. The antireflection electrode 13 ideally has the antireflection characteristic when the refractive indices of the front and rear media are equal.
Usually, the refractive index of the glass substrate used as the transparent substrate 14 of the optical modulator is 1.50 to 1.55, and most of them are around 1.52. Therefore, ideally n _x ′ should be around 1.52.

When a reflection type optical modulator is constructed, the light that does not enter the liquid crystal layer 94 and is reflected (hereinafter referred to as unnecessary interface reflected light) becomes a factor of lowering the contrast. In particular, the light reflected in the vicinity of the liquid crystal layer is projected on the screen as it is, so that the contrast is largely reduced. From the results of experiments and simulations, it was found that the refractive index difference between n _x and n _t must be within 0.15, and more preferably within 0.08. When a fluorine-based liquid crystal is used as the liquid crystal of the liquid crystal layer 94, n _x ≈n _t can be satisfied, which is preferable in that sense. Because the fluorine-based liquid crystal n _o is lower than the cyan biphenyl system is from 1.43 to 1.5, n _x is because can be realized from 1.47 to 1.57. Also, it has good heat resistance and is suitable for use in an optical modulator. However, since the difference Δn in refractive index between n _e and n _o is as small as 0.1 or less, the scattering characteristics are not very good. For this drawback, the cover may be covered by increasing the thickness of the liquid crystal layer 94.

The reflectance of the antireflection electrode 13 increases as it deviates from the peak wavelength, but there is no problem when the light modulator is used in a projection display device. This is because a projection display device that performs color display uses three light modulators of each color and the band of light modulated by each light modulator is narrow. The bandwidth of the light entering the optical modulator is G light, the half-width of the incident light for B light is about 50 nm, and the half width for R light is 90 nm.

Although the antireflection electrode 13 is a three-layer antireflection film in FIG. 2A, it may be a two-layer antireflection film as shown in FIG. 2B. However, in the case of a two-layer structure, it is not suitable to make the thicknesses of the respective thin films of the antireflection electrode 13 of the optical modulator common to R, G, and B. It is preferably formed according to the wavelength of the light modulated by the optical modulator. The antireflection electrode 13 having a two-layer structure will be described below.

The antireflection electrode 13 having a two-layer structure has a structure in which the thin film 24 is formed on the transparent substrate 14 and the ITO film 22 is formed thereon. The optical thickness of the ITO film 22 is λ / 2, and the thickness of the thin film 24 is λ / 4. λ is 55
If it is 0 nm, it is around d = 1375Å. ITO film 2
The film thicknesses of 2 and the thin film 24 are formed corresponding to the peak wavelength λ of the incident light.

The refractive index of the thin film 24 is 1.50 or more and 1.70.
The following is preferable. Furthermore, it is preferable to use a substance having a refractive index between the refractive index of the transparent substrate 14 and the refractive index n _x of the liquid crystal layer 94. For this reason, the refractive index is 1.
It is preferably 52 or more and 1.65 or less. Aluminum oxide Al ₂ O ₃ (n≈1.6) is used as a substance showing a refractive index in this range.
3) and cerium fluoride C _e F ₃ (n≈1.63).

As the antireflection thin film, in addition to the above, silicon monoxide (SiO), tungsten oxide (W
O ₃ ), lanthanum fluoride (LaF ₃ ), neodymium fluoride (Nd)
F ₃ ) may be used.

When λ is 550 nm, the thin film 24 is made of Al.
_{When 2} O ₃ (n≈1.63) is used, the film thickness formed is d =
In the range of 700Å to 1000Å, ITO film (n≈2.0)
The film thickness of 22 may be in the range of 1150Å to 1600Å. If the ITO film 22 is 1000 liters or more, a necessary and sufficient resistance value can be obtained by forming the ITO film 22 by vapor deposition or sputtering at 200 degrees or more. The antireflection electrode 13 having a two-layer structure exhibits V characteristics and the wavelength band of low reflectance is somewhat narrower than that of the three-layer structure, but it can be practically used.

FIG. 3 is a sectional view of an optical modulator of another embodiment. The difference from the embodiment of FIG. 1 is that the liquid crystal layer 94 is sandwiched between the dielectric multilayer film 93 and the counter substrate 32, and the transparent substrate 14 is optically coupled to the counter substrate 32 via the transparent adhesive 31. Is.

The counter substrate 32 is a glass substrate of about 1 mm, and the total thickness t of the counter substrate 32 and the transparent substrate 14 is d, the maximum diameter of the effective display area of the liquid crystal layer 94 is n, and the refractive index of the transparent substrate 14 is n. Then, it is expressed by the following equation.

[0068]

[Equation 8]

The light absorption film 11 is applied to a portion other than the effective display area. As shown in FIG. 3, it is applied to the side surfaces of the transparent substrate 14 and the counter substrate 32, but since the thickness of the transparent substrate 14 is usually sufficiently thicker than the thickness of the counter substrate 32, it is often applied only to the side surface of the transparent substrate 14. .

An antireflection electrode 13 as shown in FIG. 2A or 2B is formed on one surface of the counter substrate 32.
The configuration, characteristics, etc. are the same as those in the above embodiment.

The transparent adhesive 31 is an ultraviolet curable adhesive. The difference between the refractive index of the adhesive and the refractive index of the counter substrate 32 needs to be selected within 0.1. This is because light is reflected between substances having different refractive indexes. The reflectance R between substances having different refractive indexes is expressed by the following equation, where n ₁ is the refractive index of the medium A and n _{2 is} the refractive index of the medium B.

[0072]

[Equation 9]

Now, let the refractive index of the counter substrate 32 be n ₁ = 1.
52 and the refractive index of the adhesive 31 is n ₂ = 1.42,
From (Equation 7), the reflectance R is 0.12%, which exceeds 0.1%. If n ₂ = 1.47, the reflectance R is 0.03%
And becomes extremely small. The same reflected light causes the transparent substrate 14
Also occurs between the adhesive 31 and the adhesive 31. The difference in the refractive index as described above causes unnecessary interface reflected light of incident light and lowers the contrast. Therefore, the difference in refractive index between the adhesive 31 and the counter substrate 32 is within 0.1, preferably within 0.05. Many UV-curable adhesives have a refractive index close to that of glass, and are sufficient for this purpose. Further, it is not limited to the ultraviolet curable adhesive, and transparent silicone resin or the like can be used. The refractive index of the transparent silicone resin is 1.40 to 1.47. The transparent silicone resin has good heat resistance. In addition, a transparent epoxy adhesive, a liquid such as ethylene glycol, or the like can be used. A point to be noted is that an air layer is not generated in the adhesive 31 when the transparent substrate 14 is bonded to the counter substrate 32. If there is an air layer, the image quality becomes abnormal due to the difference in refractive index.

For the same reason, the refractive index of the transparent substrate 14 should be matched with that of the counter substrate 32. Ideally, it is preferable to use a glass substrate made of the same material as the counter substrate 32. Besides, a transparent resin such as an acrylic resin or a polycarbonate resin may be used. These have a refractive index close to that of glass, are relatively inexpensive, and can be easily formed into an arbitrary shape by pressing or the like.

By using the transparent substrate 14 in the optical modulator of the present invention, the secondary scattered light in the liquid crystal layer 94 can be prevented and the contrast can be improved. The effect of improving the contrast largely depends on the scattering property of the liquid crystal layer 94, the material, and the directivity of the incident light. As an example, the contrast is 30% or more when the liquid crystal layer is 10 μm or more, and 70 when the liquid crystal layer is close to the perfect diffusion property. % Or more.

The structure of the optical modulator is not limited to the structure shown in FIG. 1 or 3, and various modifications can be considered. An example thereof is shown in FIG.

The optical modulator shown in FIG. 7A is composed of an optical modulator 71, a plano-concave lens 14, and a transparent adhesive 31. An antireflection film 15 is formed on the light incident surface of the plano-concave lens 14, and a light absorption film 11 made of black paint is formed on the side surface of the plano-concave lens 14. The plano-concave lens 14 is made of acrylic resin by molding. As for the molding process, the same lens can be produced if a mold is used, so mass productivity is good.
When a projection display device is configured using this light modulator, the optical image on the liquid crystal layer 94 may be formed on the screen in a state where a plano-concave lens or the like is combined.
The above also applies to the following optical modulators. Here, by forming the transparent substrate 14 into a plano-concave lens, the thickness of the transparent substrate 14 does not depend on (Equation 6), and the secondary scattered light can be sufficiently prevented with a thin thickness.

FIG. 7B shows a plano-concave lens 14, a biconvex lens 72 and a transparent adhesive 31. A biconvex lens 72 is arranged close to the plano-concave lens 14. The radius of curvature of one convex surface of the biconvex lens 72 is equal to the radius of curvature of the concave surface of the plano-concave lens 14. A thin air gap is provided between the concave and convex surfaces. A light absorbing film 11 is formed on the side surface of the plano-concave lens 14, and an antireflection film is vapor-deposited on the concave surface of the plano-concave lens 14 and the biconvex surface of the biconvex lens 72. When a projection type display device is constructed using this light modulator, the projection lens is combined with the plano-concave lens 14 and the biconvex lens 72 to form an image on the optical image screen on the liquid crystal layer 94. Focus adjustment of the projected image is performed by moving the projection lens along the optical axis.

Also in this case, by connecting the plano-concave lens 14 to the exit side of the light modulator 71 and forming the light absorption film 11 on the side surface of the plano-concave lens 14, the case shown in FIG. 7A is obtained. Similarly, a projected image with good contrast can be obtained.

The optical modulator does not have a strong dependency on the incident angle, but when the incident angle of the incident light is large, the optical path length when passing through the liquid crystal layer 94 becomes long, so that the scattering characteristic changes. That is, if the incident angle of the light beam incident on the light modulator 71 differs depending on the location, the image quality of the projected image becomes non-uniform. On the other hand, in the case of the configuration shown in FIG. 7A, in order to reduce the radius of curvature of the concave surface, it is necessary to make convergent light with a large converging angle incident on the light modulator 71 or to increase the effective diameter of the projection lens. There is. The former has a problem that the image quality of the projected image becomes non-uniform because the image quality is not uniform depending on the location on the light modulator 71, and the latter has a problem that the projection lens becomes large and the cost becomes high. When the incident angle dependency of the scattering characteristics of the light modulator 71 is relatively large, the configuration as shown in FIG. 7B allows the light modulator 7 without increasing the size of the projection lens.
Since light that is nearly parallel to 1 can be made incident, it is easy to ensure the uniformity of the projected image.

The radius of curvature of the surface of the biconvex lens 72 on the side of the light modulator 71 may be the same as or smaller than the radius of curvature of the concave surface of the plano-concave lens 14. By doing so, the biconvex lens 72 enters the concave surface, so that the length from the liquid crystal layer 94 to the apex of the biconvex lens 72 on the projection lens side can be shortened.

FIG. 7C shows a configuration in which the surface of the transparent substrate 14 in contact with air is cut obliquely, and FIG. 7D shows a configuration in which it is cut into a conical shape. Further, FIG. 7E shows a configuration cut in an arc shape. A multi-coat or V-coat antireflection film 15 is formed on the surface in contact with air and glass, but it is difficult to completely set the reflectance to zero. In a reflection-type light modulator, unnecessary interface reflected light has a great influence on the projected image, and therefore must be extremely small. Liquid crystal layer 9
When the interface is oblique with respect to 4, the unnecessary interface reflected light is extremely rarely projected on the screen. Figure 7
As shown in (c) to (e) of FIG. 7, by making the interface curved or slanted, unnecessary reflected light can be significantly reduced and the contrast can be improved. FIG. 7F shows a short trumpet shape in which the surface of the transparent substrate 14 in contact with air is wider than the surface of the transparent substrate 14 in contact with the light modulator 71. The light absorption film 11 is formed on a portion other than the non-effective area of the transparent substrate 14. By adopting the configuration of FIG. 7F, the transparent substrate 1 is scattered by the liquid crystal layer 94.
The light reflected by the surface of No. 4 which contacts the air and returning to the liquid crystal layer 94 can be completely absorbed by the light absorbing film 11, and the contrast is improved.

Hereinafter, a projection type display device using the optical modulator of the present invention will be described. FIG. 8 is a configuration diagram of a monochrome display projection display device. Reference numeral 85 is the above-described optical modulator of the present invention. Although the optical modulator 85 is shown in FIG. 8 as having the configuration shown in FIG. 3, the present invention is not limited to this, and any optical modulator shown in FIG. 3 or 7 may be used. This also applies to other projection display devices described later.

The light source 83 is a lamp 83a, a concave mirror 83b,
It is composed of a filter 83c. The lamp 83a is a metal halide lamp or a xenon lamp.
The light including the color components of the three primary colors of B is emitted. Good contrast cannot be obtained without using a short arc lamp. A xenon lamp having an arc length of 2 mm or less is preferable. When using a metal halide lamp, one having an arc length of 4 mm or less is used. The concave mirror 83b is made of glass, and has a reflective surface on which a multilayer film that reflects visible light and transmits infrared light is deposited. The filter 83c is formed by depositing a multilayer film that transmits visible light and reflects infrared light and ultraviolet light on a glass substrate. Moreover, a color filter is inserted between the plane mirror 82 and the filter 83c as needed. The visible light included in the light emitted from the lamp 83a is reflected by the concave mirror 83.
It is reflected by the reflecting surface of b. The reflected light emitted from the concave mirror 83b is emitted after the infrared rays and ultraviolet rays are removed by the filter 83c.

The projection lens 81 is composed of a first lens group 81b on the light modulator 85 side and a second lens group 81a on the screen side, and a plane mirror is provided between the first lens group 81b and the second lens group 81a. 82 are arranged. Light modulator 8
The scattered light emitted from the pixel at the center of the screen of 5 is
After passing through the lens group 81b, about half is a plane mirror 82.
To the second lens group 81a without entering the plane mirror 82. The normal line of the reflecting surface of the plane mirror 82 is inclined 45 ° with respect to the optical axis 84 of the projection lens 81. The light from the light source 83 is reflected by the plane mirror 82, passes through the first lens group 81b, passes through the transparent substrate 14, and enters the liquid crystal layer 94. The reflected light from the dielectric multilayer film 93 is transmitted through the transparent substrate 14, the first lens group 81b, and the second lens group 81a in this order and reaches the screen 86. A light ray that exits from the center of the diaphragm of the projection lens 81 and goes toward the liquid crystal layer 94 is made substantially vertical to the liquid crystal layer 94, that is, telecentric. Substantially F of the projection lens
The value is F8.0 or more, preferably F10.0 or more.
This is necessary to get good contrast. Further, the surface of the transparent substrate 14 is multi-coated. Note that writing of an image is performed by writing light 97 through the photoconductive layer. The operation is the same as that of the conventional example, and thus the description thereof is omitted.

Here, in the case of modulating light having a long wavelength, it is preferable to increase the diameter of the water droplet liquid crystal of the liquid crystal composite.
For example, if the water-drop liquid crystal of the light modulator that modulates green light has an average particle diameter of 1.7 μm, the light modulator that modulates red light has a mean particle size of, for example, about 2.0 μm. This is because the scattering characteristics of the liquid crystal composite depend on the incident wavelength. The longer the wavelength to be modulated, the larger the average particle diameter of the water droplet liquid crystal, and the better the scattering characteristics. The average particle size can be adjusted by operating the ultraviolet irradiation conditions when the liquid crystal and the resin are phase-separated. Further, when the content ratio of the liquid crystal to the polymer is high, the liquid crystal does not become a water drop liquid crystal but a continuous layer is formed, but in this case, the average pore diameter of the polymer network is varied. This can also be adjusted by manipulating the ultraviolet irradiation conditions for phase separation.

FIG. 9 is a block diagram of a projection type display device of the present invention capable of color display. Here, for ease of explanation, 85a is an optical modulator of the present invention that modulates red light (R light), 85b is a modulator of the present invention that modulates blue light (B light), and 85c is a green light (G light). It will be described as the modulator of the present invention that modulates (light). Reference numeral 111a denotes a dichroic mirror that transmits R and B light and reflects G light.
Reference numeral 1b is a dichroic mirror that transmits R light and reflects B light, and 111c is a dichroic mirror for improving the optical purity of G light.

The light emitted from the lamp 83a is reflected by the mirror 8
The light is reflected by 2, and enters the first lens group 81b and then enters the dichroic mirror 111a. The dichroic mirror 111a transmits R and B lights and reflects G light. The reflected G light is further band-limited by the dichroic mirror 111c and enters the optical modulator 85c. This G
The full width at half maximum of light is 50 nm. The optical modulator 85c modulates the incident light based on the input video signal (image writing light 97). The modulated light again passes through the transparent substrate 14, is reflected by the dichroic mirrors 111c and 111a, and enters the first lens group 81b.

A part of the light scattered by the optical modulator 85c is reflected by the mirror 82 and returns to the light source 83 again. The other part is not condensed by the projection lens 81 and diverges.
The light straightened by the optical modulator 85c is the second lens group 81.
It is incident on a and projected on the screen 86. As described above, the G light modulation image is displayed on the screen.

On the other hand, the R and B lights are incident on the dichroic mirror 111b, and the dichroic mirror 111b transmits the R light and reflects the B light. The optical modulator 85a modulates the R light, and the optical modulator 85b modulates the B light. The modulated light is the same as the G light, and the scattered light is the second lens group 81a.
The straight light 81b is incident on the screen 86 and is projected on the screen 86. The R, G, B lights projected on the screen are superimposed to display a color image.

Here, a multi-coat type antireflection film is formed on the lens of the projection lens 81 to reduce unnecessary reflection as much as possible. Further, a V-coat type antireflection film adapted to each incident light is formed on the transparent plate 14 to reduce unnecessary light reflection.

As described above, according to the present invention, the transparent thin films are formed before and after the ITO of the counter electrode formed on one surface of the counter substrate or the transparent substrate of the optical modulator to form the three-layer structure or the two-layer structure. , ITO and counter substrate and IT
The reflectance between O and the liquid crystal can be significantly reduced. It is very easy to form, and very good results can be obtained when the wavelength of incident light to be modulated has a narrow band like a projection display device. An antireflection film is also formed on the surface in contact with air, and the total reflectance is 0.2% or less, which is very good.

In the above embodiment, an example in which the invention is applied to an optical writing type optical modulator has been described, but the present invention is not limited to this, and another optical modulator may be used as long as it is a reflection type optical modulator.

Further, in the above-mentioned embodiment, the light reflecting layer of the light reflecting substrate is constituted by the dielectric multilayer film 93, but the invention is not limited to this, and a type using another light reflecting layer such as metal may be used.

Further, in the projection type display device of FIGS. 8 and 9, the optical modulator shown in FIG. 3 is used as the optical modulator, but the present invention is not limited to this. It goes without saying that the optical modulator shown may be used.

Although it has been stated that the antireflection electrode 13 is formed of a two-layer or three-layer thin film, the present invention is not limited to this, and it is apparent that the antireflection electrode 13 can be formed by using an equivalent thin film technique. is there.

[0097]

As is apparent from the above description, according to the present invention, since the transparent thin film having the conductivity and the antireflection function of light is formed on the surface of the transparent substrate, the contrast of the optical modulator is improved. It has the advantage.

Further, when the light modulator of the present invention is used in a projection display device, there is an advantage that the contrast of a projected image is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an optical modulator of an embodiment according to the present invention.

FIG. 2A is a sectional view showing an example of the structure of a counter electrode, and FIG. 2B is a sectional view showing another example of the structure of a counter electrode.

FIG. 3 is a cross-sectional view showing the structure of an optical modulator of another embodiment according to the present invention.

FIG. 4 is an explanatory diagram illustrating an operation of the optical modulator of the present invention.

FIG. 5 is an explanatory diagram illustrating an operation of the optical modulator of the present invention.

FIG. 6 is an explanatory diagram illustrating an operation of the optical modulator of the present invention.

7 (a), (b), (c), (d), FIG.
(E), (f) is a block diagram of an optical modulator using a transparent substrate having various cross-sectional shapes.

FIG. 8 is a configuration diagram of a projection display apparatus according to an embodiment of the present invention.

FIG. 9 is a configuration diagram of a projection display device according to another embodiment of the present invention.

FIG. 10 is a perspective view of a conventional optical modulator.

11A and 11B are explanatory views of a conventional optical modulator.

[Explanation of symbols]

11 Light Absorption Film 12 Sealing Resin 13 Counter Electrode 14 Transparent Substrate 15 Antireflection Film 21, 23, 24 Al ₂ O ₃ Film 22 ITO Film 31 Transparent Adhesive 32 Counter Substrate 41, 52 Minute Area 42, 45 Scattered Light 43 Transmission Light ray 44 Reflected light ray 46 Emission surface 51 Effective display area 81 Projection lens 82 Planar mirror 83 Light source 85 Optical modulator

Claims (19)

[Claims] 1. A transparent substrate which transmits light, a transparent thin film formed on the surface of the transparent substrate and having conductivity and a light reflection preventing function, and a light reflecting substrate having the transparent thin film and a light reflecting layer. And a liquid crystal layer disposed between the light modulators. 2. The transparent thin film has a transparent conductive thin film on the liquid crystal layer side, and has a refractive index between the refractive index of the transparent substrate and the refractive index of the conductive thin film on the transparent substrate side. It has an antireflective film whose thickness is substantially equal to λ.
The optical modulator according to claim 1, wherein / 4 (λ is a peak wavelength of light incident on the transparent substrate) and the thickness of the conductive thin film is substantially λ / 2. 3. The optical modulator according to claim 2, wherein the antireflection thin film has a refractive index of 1.50 or more and 1.70 or less. 4. The transparent thin film is formed on both surfaces of the transparent conductive thin film and the conductive thin film, and has a refractive index between the refractive index of the transparent substrate and the refractive index of the conductive thin film. A thin film, and the thickness of the antireflection thin film is substantially λ /
4. The optical modulator according to claim 1, wherein 4 (λ is a peak wavelength of light incident on the transparent substrate), and the thickness of the conductive thin film is substantially λ / 2. 5. The optical modulator according to claim 4, wherein the antireflection thin film has a refractive index of 1.60 or more and 1.80 or less. 6. The light modulator according to claim 1, wherein the light reflection substrate has a photoconductive layer and a transparent conductive layer formed on a surface of the light reflection layer opposite to the liquid crystal layer. 7. The optical modulator according to claim 1, wherein the transparent substrate is one in which the first transparent plate and the second transparent plate are optically coupled by a transparent coupling member. 8. The optical modulator according to claim 7, wherein the difference between the refractive index of the transparent combination and the refractive index of the transparent substrate is within 0.1. 9. The optical modulator according to claim 1, wherein a surface of the transparent substrate is a concave surface. 10. The transparent substrate satisfies the following equation, where t is the center thickness, n is the refractive index, and d is the maximum diameter of the effective display area of the liquid crystal layer. Or 7
The described light modulator. [Equation 1] 11. The optical modulator according to claim 1, wherein an antireflection film is formed on the surface of the transparent substrate. 12. The optical modulator according to claim 1, wherein the difference between the refractive index of the liquid crystal layer in the light scattering state and the refractive index of the transparent substrate is 0.15 or less. 13. The light modulator according to claim 1, wherein the liquid crystal layer is a polymer-dispersed liquid crystal layer. 14. A polymer-dispersed liquid crystal layer having a water-droplet-shaped liquid crystal having an average particle diameter of 0.
5. The thickness is 5 μm or more and 3 μm or less.
3. The optical modulator according to item 3. 15. The optical modulator according to claim 1, wherein a light absorbing means is provided on a side surface of the transparent substrate. 16. A transparent substrate which transmits light for reading, a transparent thin film formed on the surface of the transparent substrate and having conductivity and a light reflection preventing function, and a light having the transparent thin film and a light reflection layer. A liquid crystal layer disposed between the reflective substrate, a light source means for emitting the reading light to the liquid crystal layer through the transparent substrate, and a light modulated by the liquid crystal layer and reflected from the light reflective layer. A projection-type display device, comprising: 17. The light reflecting substrate has a photoconductive layer and a transparent conductive layer formed on a surface of the light reflecting layer opposite to the liquid crystal layer, and an image is formed by irradiating the photoconductive layer with light. 17. The projection display device according to claim 16, further comprising an optical writing unit for writing. 18. The projection optical means has an optical path separation system for separating the light emitted from the light source means into a plurality of optical paths, and an optical path combination system for combining the light modulated by the liquid crystal layer into one optical path. The projection display device according to claim 16 or 17. 19. The projection display device according to claim 16, wherein the film thickness of the transparent thin film is formed so as to correspond to the peak wavelength of modulated light.