JP3162816B2 - Optical writing type spatial light modulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical writing type spatial light modulator having a function of inputting two-dimensional optical information such as an image or a data pattern by using a writing light and displaying the information by a reading light. The present invention relates to a projection type image display device using intensity conversion, a wavelength conversion device for optical images, and an optical writing type spatial light modulation device applicable to an incoherent light / coherent light conversion device.

SUMMARY OF THE INVENTION The present invention relates to an optical writing type spatial light modulator capable of writing and reading two-dimensional optical information such as images in parallel, and is formed on a resin thin film having high affinity. By using a liquid crystal-resin composite containing liquid crystal droplets with uniform particle size, high resolution,
The contrast, sensitivity, and uniformity are obtained.

[0003]

2. Description of the Related Art A conventional light-writing type spatial light modulator using a light-scattering liquid crystal layer and a photoconductive layer which does not require a polarizing plate and has a high light transmittance as shown in FIG. Light modulation elements are known (references: K. Takizawa, H. Kikuchi,
H. Fujikake, Society for Information Displays (SID) I
nternational Symposium Digest of Technical Papers
Vol.22, p.250-p.253,1991).

[0004] An optical writing type spatial light modulator shown in FIG. 1 has a transparent substrate 101 formed in a plate shape and a transparent substrate 10.
7, a plate-shaped transparent electrode 102a laminated on one surface (the left surface in FIG. 7), and one surface (FIG. 7) of the transparent electrode 102a.
, A plate-like liquid crystal / resin composite 103 laminated on the left side), and a plate-like dielectric multilayer film 104 laminated on one surface (the left side in FIG. 7) of the liquid crystal / resin composite 103
When a plate-like light-absorbing layer 105 laminated on the side (left side in FIG. 7) a face of the dielectric multilayer film 104, Bi ₁₂ S
A plate-shaped photoconductive layer 1 made of iO ₂₀ and laminated on one surface (the left surface in FIG. 7) of the light absorbing layer 105
06, and a plate-shaped transparent electrode 102b laminated on one surface (the left surface in FIG. 7) of the photoconductive layer 106.

The liquid crystal / resin composite 103 is composed of a transparent resin 108 composed of an epoxy resin or the like and a liquid crystal such as a nematic liquid crystal.
And liquid crystal droplets 109 dispersed in the form of droplets.

When driven by a driving AC voltage supplied from a driving AC power supply 111 via a lead wire 110, an optical image of the writing light 112 incident from the left side of FIG. 7 is converted into a voltage pattern. This voltage pattern drives the liquid crystal (resin) composite.

At this time, the reading light 113 is read from the right side of FIG.
Is irradiated, the written optical image is emitted as the display light 114.

[0008]

By the way, the above-mentioned conventional optical writing type spatial light modulator has the following problems.

That is, in such an optical writing type spatial light modulator, the liquid crystal droplet 109 of the liquid crystal / resin composite 103 is formed.
The characteristics are degraded due to the variation in.

That is, when the particle size of the liquid crystal droplets 109 greatly varies, the maximum resolution of the liquid crystal / resin composite 103 is limited by the size of the largest liquid crystal droplets 109, so that a high definition display image is obtained. There was a problem that it was difficult to obtain.

The liquid crystal / resin composite 103 has liquid crystal droplets 109 of various sizes, and the driving voltage of each liquid crystal droplet 109 is different. In contrast, the light transmittance shows a gradual increase. For this reason, when the thin or thin photoconductive layer 106 which is indispensable for high resolution is used, the change in the voltage distribution between the photoconductive layer 106 and the liquid crystal / resin composite 103 due to light irradiation alone is not enough.
Since the liquid crystal / resin composite 103 is not sufficiently transparent, a high-contrast display image cannot be obtained. On the other hand, in order to obtain a sufficient contrast, strong writing light is required. There was a problem that cannot be secured.

Further, when forming the liquid crystal droplet 109,
Subtle surface states (flatness, contamination, etc.) of transparent electrode 102a and dielectric multilayer film 104 sandwiching liquid crystal / resin composite 103
Therefore, there is a problem that it is difficult to form a uniform liquid crystal / resin composite 103.

The transparent electrode 102a and the dielectric multilayer 1
Since the generation of the liquid crystal droplets 109 is affected by the material of the liquid crystal 04, there is a problem that the reproducibility of the liquid crystal / resin composite 103 is poor.

The present invention has been made in view of the above circumstances, and has been made in consideration of the above circumstances. An optical writing type device capable of reducing the size of liquid crystal droplets and making them uniform, thereby greatly improving resolution, contrast, sensitivity, and uniformity. The purpose is to obtain a spatial light modulator.

[0015]

In order to achieve the above object, an optical writing type spatial light modulator according to the present invention has a transparent resin thin film having high wettability with respect to liquid crystal at both ends,
A transparent resin having a predetermined refractive index, a nematic liquid crystal having an ordinary light refractive index equivalent to the transparent resin, a cholesteric liquid crystal, a smectic liquid crystal, or a liquid crystal-resin composite in which a mixed liquid crystal of these liquid crystals is dispersed; A photoconductive layer which is in close contact with the liquid crystal / resin composite and whose impedance changes according to writing light;
And a transparent electrode formed so as to sandwich the resin composite from both sides and to which a driving AC voltage is applied.

[0016]

In the optical writing type spatial light modulator having the above-mentioned structure, a nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal having an ordinary light refractive index equivalent to the transparent resin is added to a transparent resin having a predetermined refractive index. Alternatively, a mixed liquid crystal of these liquid crystals is dispersed to form a liquid crystal / resin composite. At both ends of the liquid crystal / resin composite, a transparent resin thin film having high wettability (also called affinity) for the liquid crystal is laminated. Further, a photoconductive layer whose impedance changes according to the writing light is laminated so as to be in close contact with the liquid crystal / resin composite, and a transparent electrode is formed so as to sandwich the photoconductive layer and the liquid crystal / resin composite from both sides. Then, an AC voltage is applied between the transparent electrodes to drive the electrodes.

[0017]

【Example】

<< Overall Structure >> FIG. 1 is a configuration diagram showing an embodiment of an optical writing type spatial light modulator according to the present invention.

The optical writing type spatial light modulator shown in FIG. 1 has a transparent substrate 1, a transparent electrode 2, a liquid crystal / resin composite 3,
A photoconductive layer 4 and a transparent electrode 5 are provided.
When the writing light 8 for inducing the photoconductive effect of the photoconductive layer 4 is incident from the left side in FIG. 1 in a state where the writing is performed by the driving AC voltage supplied from the driving AC power supply 7 through the The light image of the light 8 is converted into a voltage pattern, and the liquid crystal / resin composite 3 is driven by the voltage pattern. At this time, readout light having a wavelength with low absorption and low sensitivity of the photoconductive layer 4 from the left side of FIG. When 9 is incident,
A part of the reading light 9 is emitted as scattered light 10 and the stored light image is emitted as display light (straight light) 11.

The transparent substrate 1 is made of a transparent material such as glass and is a portion to be a substrate of the optical writing type spatial light modulator, and a transparent electrode 2 is laminated on one surface side thereof.

The transparent electrode 2 is a thin film adhered to one surface of the transparent substrate 1 by a method such as vapor deposition, and is connected to one voltage output terminal of a driving AC power supply 7 via the lead wire 6.

The photoconductive layer 4 is made of Bi ₁₂ SiO ₂₀ or Bi ₁₂ whose electric impedance decreases with respect to the incidence of the writing light 8.
GeO ₂₀ , CdS, Se, amorphous Se, Si, amorphous Si, amorphous SiC, SeTe, amorphous SeTe, SeAs, amorphous SeAs,
This layer is made of GaAs, GaP, or the like. One surface of the layer is in close contact with the liquid crystal / resin composite 3, and the other surface is in close contact with the transparent electrode 5.

The transparent electrode 5 is a thin film adhered to one surface of the photoconductive layer 4 by a method such as vapor deposition, and is connected to the other voltage output terminal of the driving AC power supply 7 via the lead wire 6.

The liquid crystal / resin composite 3 has an affinity between the transparent resin 12 formed in a plate shape, the liquid crystal droplets 13 dispersed almost uniformly in the transparent resin 12, and the liquid crystal and the transparent resin 12. (High wettability), and transparent resin thin films 14 and 15 of 1 μm or less disposed on both surfaces of the transparent resin 12.
And functions as a light modulation layer of the optical writing type spatial light modulation element.

[0024] As the liquid crystal constituting the liquid crystal droplets 13 is of a refractive index n _p equivalent value of the ordinary refractive index n _o is a transparent resin 12, the refractive index anisotropy Δn (= n _e -n _o ) Is used as large as possible.

As the liquid crystal satisfying such conditions, a nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal, or a mixed liquid crystal of these liquid crystals having a large refractive index anisotropy Δn is used. In order to obtain high speed, a nematic liquid crystal having low viscosity and high elasticity is suitable. Among them, cyanobiphenyl-based, terphenyl-based, pyridine-based, pyrimidine-based and tolan-based nematic liquid crystals having a large refractive index anisotropy Δn are most suitable.

As the transparent resin 12, an acrylic resin or a methacrylic resin having a refractive index n _p of about 1.52,
Epoxy resin, urethane resin, polystyrene, polyvinyl alcohol, or a copolymer thereof (eg, an acryl / urethane copolymer) is used.

The resin thin films 14 and 15 include:
In order to prevent reflection, a resin having a refractive index equivalent to that of the transparent resin 12, for example, a resin having the same or the same component as the transparent resin 12, is used. Polyvinyl alcohol is optimal.

<< Procedure for Producing Liquid Crystal / Resin Composite >> Next, the procedure for producing the liquid crystal / resin composite 3 will be described.

First, the liquid crystal droplets 13 and the constituent materials of the transparent resin 12 are mixed to form a homogeneous solvent, and then the homogeneous solvent is applied to the transparent electrode 2 and the photoconductive layer 4 to which the resin thin films 14 and 15 have been previously attached. Pour in between.

Further, by curing the components of the transparent resin 12 by using a method such as photo-curing, heat-curing, and reaction-curing, the liquid crystal components are rapidly insolubilized and turned out (phase-separated) to provide sufficient light. A liquid crystal / resin composite 3 having a film thickness of 5 μm or more necessary for obtaining scattering is produced.

Another manufacturing procedure is as follows.
3 and the transparent resin 12 were dissolved in a common solvent, and the uniform solution was roll-coated on the photoconductive layer 4 provided with the resin thin film 15, or the uniform solution was provided with the resin thin film 14. After roll coating on the transparent electrode 2, the solvent component is volatilized.

Thereafter, the photoconductive layer 4 side and the transparent electrode 2 side are pressed against each other to obtain 5 μm necessary for obtaining sufficient light scattering.
A liquid crystal / resin composite 3 having a thickness of not less than m is prepared.

In this case, in the conventional method, the liquid crystal droplet 13
The growth of is easily affected by the interface of a different substrate which is not familiar with the liquid crystal, and the particle size is likely to vary greatly. However, in the present invention, the resin thin films 14 and 15 are used in any of the methods. Problems do not occur. In addition, when a resin thin film is used only for one substrate, a considerable improvement effect can be obtained, which is effective.

In such an optical writing type spatial light modulator, the smaller the liquid crystal droplet 13 is, the higher the particle size uniformity and the higher the resolution can be. In the method of manufacturing the resin composite 3, it is desirable to rapidly form the liquid crystal / resin composite 3 because the faster the curing of the transparent resin 12, the smaller the size of the liquid crystal droplet 13 can be made.

However, in order to scatter visible light of various wavelengths almost uniformly, it is necessary to set the particle size of the liquid crystal droplets 13 to 0.5 μm or more. Since it decreases, 0.5 to 10 μm is practically appropriate.

Note that the liquid crystal droplets 13
Are large, the liquid crystal droplets 13 are connected to each other,
The transparent resin 12 may have a spongy body shape or a three-dimensional network structure. In addition, these liquid crystal / resin composites 3
Most are self-supporting, so that the film thickness can be easily controlled and the area can be increased.

However, when the transparent resin 12 is soft,
To support the side surface of the liquid crystal / resin composite 3, the transparent electrode 2
A spherical or fibrous spacer may be provided between the photoconductive layer 4 and the photoconductive layer 4.

<< Experimental Example >> As an example, a sample of the liquid crystal / resin composite 3 produced as a trial is composed of two transparent electrodes (In ₂ O ₃ :
Sn), a resin thin film is formed by a polyvinyl alcohol film (having a refractive index of about 1.55), and a refractive index anisotropy Δ
n large nematic liquid crystal (Merck Japan BL
-008, n _o = 1.527, crystal-by n _e = 1.807) and photocurable acrylic urethane resin (Norland Products _{NOA-65, n o = 1.524} )
The resin composite 3 is formed.

For this purpose, first, an aqueous solution of polyvinyl alcohol (concentration: 1 w%) is spin-coated on a transparent electrode (20%).
(00 rotations / minute, 120 seconds)
A polyvinyl alcohol thin film is applied to a thickness of 0.05 μm to form a resin thin film.

Next, a nematic liquid crystal and an acrylic urethane resin are mixed at a weight ratio of 1: 1. A spherical spacer having a diameter of 10 μm is added in an amount of 0.1% by weight, and then a transparent electrode on which a resin thin film made of polyvinyl alcohol is adhered. Insert between substrates.

Further, ultraviolet rays (wavelength 365 nm, intensity 30
mW / cm 2), resulting in a uniform liquid crystal / resin composite (10 μm thick) having liquid crystal droplets 13 having a particle size of 2 to 3 μm.
3 was obtained.

The solid line in FIG. 2 is a table showing the relationship between the light transmittance and the applied voltage of the liquid crystal / resin composite 3 produced as a trial.

As is apparent from this figure, the rise of the liquid crystal / resin composite 3 using the resin thin film indicated by the solid line is steeper than that in the case where the resin thin film indicated by the dotted line is not used. You can see that.

FIG. 3 shows the result of trial production of the liquid crystal / resin composite 3 using transparent electrode substrates on which stripes having various line widths are patterned, and the resolution of the liquid crystal / resin composite 3 itself was measured.

From this figure, it can be seen that when the resin thin film is provided on the transparent electrode, a higher resolution is obtained as compared with the case where no resin thin film is provided. It can be seen that the resolution is improved accordingly.

Therefore, in order to increase the resolution of the liquid crystal / resin composite 3, the liquid crystal droplets 13 may be formed quickly on an affinity resin. This makes it possible to increase the resolution of the optical writing type spatial light modulator.

Based on these results, Bi ₁₂ SiO
₂₀ to the 500 μm thick photoconductive layer 4
A transparent electrode 5 made of n ₂ O ₃ : Sn is formed, and a transparent substrate 1 made of glass is formed on a transparent substrate 1.
A transparent electrode 2 composed of n ₂ O ₃ : Sn is formed, and a liquid crystal / resin composite 3 is formed between the transparent electrode 2 and the photoconductive layer 4 by the above-described method.
A prototype of an optical writing type spatial light modulator having an effective area of was produced.

<< Operation of Embodiment >> Next, the operation of this embodiment shown in FIG. 1 will be described with reference to FIGS.

First, as shown in FIG. 4, when the writing light 8 does not enter, most of the driving voltage is applied to the photoconductive layer 4 having a higher resistivity than the liquid crystal / resin composite 3, so that the liquid crystal The arrangement direction (orientation) of the liquid crystal molecules of the resin composite 3 becomes irregular for each liquid crystal droplet 13 due to the regulating force of the resin interface.

As a result, the reading light 9 transmitted through the photoconductive layer 4 is repeatedly reflected and refracted by the mismatch between the refractive indices of the liquid crystal droplet 13 and the transparent resin 12, and is strongly scattered.

On the other hand, as shown in FIG. 5, when the writing light 8 is incident, the impedance of the photoconductive layer 4 is reduced, so that a part of the voltage distributed to the photoconductive layer 4 is reduced. Move to side 3.

At this time, since the size of the liquid crystal droplets 13 is uniform, the orientation of the liquid crystal molecules (positive dielectric anisotropy) in each liquid crystal droplet 13 is aligned in the direction of the electric field at a time. It approaches the refractive index of the liquid crystal droplets 13 in the ordinary refractive index n _o, becomes equal to the refractive index n _p of the transparent resin 12.

As a result, the refractive index mismatch is eliminated,
The incident read light 9 passes through the liquid crystal / resin composite 3 as it is.

Here, if only the straight traveling light (display light) 11 is extracted by the optical system, an optical image of the display light modulated by the writing light 8 can be obtained, and the intensity and wavelength of the optical image can be converted. Become.

At this time, since the rise of the light transmittance versus applied voltage curve of the liquid crystal / resin composite 3 is steep, a light image having a high contrast ratio can be obtained with weak writing light 8.

As described above, in this embodiment, the resin thin films 14 and 15 having an affinity for the liquid crystal and the transparent resin 12 are provided at both ends of the liquid crystal / resin composite 3 so that the liquid crystal / resin composite 3 can be formed. In the above, the size of the liquid crystal droplets 13 is made uniform, thereby minimizing the degradation of the resolution due to the particle properties of the liquid crystal droplets 13, and further, the light transmittance versus the applied voltage of the liquid crystal / resin composite 3. Since the voltage curve is steep, the photoconductive layer 4 can be made thin, and the liquid crystal / resin composite 3 can be made sufficiently transparent with weak writing light 8.

As a result, high resolution, high sensitivity and high contrast can be realized. Further, the transparent substrate 1
And the substrate surface of the photoconductive layer 4 is undercoated with the resin thin films 14 and 15, so that the formation of the liquid crystal / resin composite 3 is not affected by the surface condition or material of the substrate sandwiching the liquid crystal / resin composite 3. , High uniformity and reproducibility can be obtained.

In the above-described embodiment, the read light utilization factor of the element (maximum intensity of display light / intensity of read light)
However, in order to improve the read light utilization rate, a dielectric multilayer film for reflecting the read light 9 is provided between the liquid crystal / resin composite 3 and the photoconductive layer 4 as shown in FIG. 2
0 and a light absorbing layer 21 that absorbs the leaked read light may be sequentially laminated to separate the read light 9 and the write light 8.

In this case, the writing light 8 and the reading light 9
Are respectively incident from the photoconductive layer 4 and the liquid crystal / resin composite 3 side, and the reflected light (display light) of the reading light 9 is intensity-modulated in accordance with the intensity of the writing light 8. Note that the reading light 9
When a wavelength at which the photoconductive layer 4 has no sensitivity is used, the light absorbing layer 21 becomes unnecessary. Further, instead of the dielectric multilayer film 20, a finely divided metal film such as aluminum or chromium can be used.

The optical writing type spatial light modulator of the present invention can be used as a projection type image display device using a light intensity conversion function, a wavelength conversion device of an optical image, and an incoherent light / coherent light conversion device. It is.

[0061]

As described above, according to the present invention, the size of the liquid crystal droplet can be made small and uniform.
This greatly improves resolution, contrast, sensitivity, and uniformity.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical writing type spatial light modulator according to the present invention.

FIG. 2 is a table showing an example of the relationship between the light transmittance of a liquid crystal / resin composite used in an optical writing type spatial light modulator according to the present invention and an applied voltage.

FIG. 3 is a table showing an example of the relationship between the resolution of a liquid crystal / resin composite used in an optical writing type spatial light modulator according to the present invention and the intensity of ultraviolet light during film formation.

FIG. 4 is a schematic diagram showing an operation example of the optical writing type spatial light modulator shown in FIG.

FIG. 5 is a schematic diagram showing an operation example of the optical writing spatial light modulator shown in FIG.

FIG. 6 is a configuration diagram showing another embodiment of the optical writing type spatial light modulator according to the present invention.

FIG. 7 is a configuration diagram showing an example of a conventionally known optical writing type spatial light modulator.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transparent substrate 2 transparent electrode 3 liquid crystal / resin composite 4 photoconductive layer 5 transparent electrode 6 lead wire 7 driving AC power supply 12 transparent resin 13 liquid crystal droplets 14, 15 resin thin film

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-110524 (JP, A) JP-A-3-221919 (JP, A) JP-A 4-141629 (JP, A) JP-A-3-141 17630 (JP, A) JP-A-59-216126 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/135 G02F 1/1334 G02F 1/1333

Claims (6)

(57) [Claims] 1. A transparent resin thin film having high wettability with respect to liquid crystal is formed on both ends, and a transparent resin having a predetermined refractive index has an ordinary light refractive index equivalent to the transparent resin. A nematic liquid crystal, a cholesteric liquid crystal, a smectic liquid crystal, or a liquid crystal / resin composite in which a mixed liquid crystal of these liquid crystals is dispersed; and a photoconductive layer that is in close contact with the liquid crystal / resin composite and changes in impedance according to writing light. And a transparent electrode formed to sandwich the photoconductive layer and the liquid crystal / resin composite from both sides and to which a driving AC voltage is applied. 2. The optical writing type spatial light modulator according to claim 1, wherein a dielectric multilayer film for reflecting light is laminated and inserted between the photoconductive layer and the liquid crystal / resin composite. 3. The optical writing type spatial light modulator according to claim 2, wherein a light absorbing layer for absorbing light is inserted between the photoconductive layer and the dielectric multilayer film. 4. The optical writing spatial light modulator according to claim 1, wherein the resin thin film is formed of polyvinyl alcohol having high wettability to the liquid crystal and the transparent resin. 5. The optical writing according to claim 1, wherein the liquid crystal / resin composite is formed by any one of light curing, heat curing, reaction curing, and solvent evaporation of the transparent resin. Type spatial light modulator. 6. The liquid crystal constituting the liquid crystal / resin composite is any one of a cyanobiphenyl-based liquid crystal, a terphenyl-based liquid crystal, a pyridine-based liquid crystal, a pyrimidine-based liquid crystal, and a tolan-based liquid crystal. 4. The optical writing spatial light modulator according to any one of items 4 and 5.