JPS62100729A - Optical image element - Google Patents

Abstract

PURPOSE:To improve the contrast ratio of the output image of an optical image element by constituting said element of a composite insulating layer consisting of a single crystal plate and amorphous diamond films and transparent electrodes. CONSTITUTION:Thin films consisting of oxide such as silicon dioxide, zirconia, alumina or yttrium oxide are formed as protective films on the surfaces of the single crystal 1 and thereafter amorphous diamond films which are insulating layers 2,2' are deposited thereon. The transparent electrodes 3, 3' are provided on the surfaces of such thin films. The amorphous diamond films are formed by a plasma CVD method in gaseous methane flow. Since the substrate temp. is low in this case, the optically uniform films are obtd. without the oxygen deficiency on the surface of the single crystal by the dissipation of oxygen from bismuth silicon oxide which is the substrate or the generation of the exfoliation and cracking of the films by the difference in the coefft. of thermal expansion. Then contrast ratio of output image of the optical image element is thus improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical image device that performs incoherent-coherent conversion of images, temporary storage of images, etc. using a single crystal plate having an electro-optic effect and a photoconductive effect.

FIG. 1 is a diagram showing the structure of an optical image element. Single crystal plate 1
, an insulating layer 2.2', a transparent electrode 3.3' and a power source 4. The single crystal plate 1 is a single crystal having an electro-optical effect and a wavelength-dependent photoconductive effect, such as bismuth silicon oxide (BiuSiO2o) or bismuth germanium oxide (Bi+gGeO2o),
An electric field is applied via the insulating layer 2.2' by means of the transparent electrode 3.3'. 7 is a polarizer, and 9 is an analyzer. This optical image element is used, for example, to convert an image of incoherent light into an image of coherent light, or to temporarily store an image. For example, it operates as follows. .

When the voltage V of the power supply 4 is applied to the single crystal plate 1 and the insulating layer 2.2' by the transparent electrode 3.3', in a steady state, the thickness of the single crystal plate 1 and the insulating layer 2.2', respectively A constant potential distribution determined by the dielectric constant of is generated inside the optical image element. In this state, when an incoherent) 2 written image 5 of a wavelength at which the single crystal plate 1 exhibits a photoconductive effect is focused on the single crystal plate 1, a potential distribution corresponding to the written image 5 is formed in the irradiated area. . That is, due to the photoconductive effect of the single crystal plate 1, electron-hole pairs are generated according to the spatial light intensity distribution of the image, and these electron-hole pairs are connected to each transparent electrode 3.3 according to the polarity of each. ', and is trapped at the interface between the insulating layer 2.2' and the single crystal plate 1, forming a potential distribution.

Since the single crystal plate 1 has an electro-optical effect, its refractive index changes according to the above-mentioned potential distribution, and eventually a refractive index distribution corresponding to the written image 5 is formed.

When using the aforementioned bismuth silicon oxide as the pre-crystal plate 1, this crystal plate has a high resistance (approximately 101
7Ω·am), the aforementioned electron-hole pairs remain in a trapped state, and the written image 5 is accumulated in the optical image element.

After the written image 5 is formed and stored as a refractive index distribution on the single crystal plate l, coherent light of a wavelength that causes almost no photoconductive effect in the single crystal plate l is read out as read light 6, and is linearly polarized by a polarizer 7 to form a single When the light 8 is incident on the crystal plate 1, the light 8 transmitted through the single crystal plate 1 is subjected to an optical phase difference according to the refractive index distribution of the single crystal plate 1. Therefore, the output light 10 obtained by detecting the transmitted light 8 with the analyzer 9 becomes light having an optical intensity distribution again, and as a result, the incoherent written image is converted into a coherent image.

In the optical image element, the insulating layer 2.2' is to prevent carriers generated inside the single crystal plate 1 from flowing out to the power source 4, so it needs to have a high insulation resistance value and also be transparent to light. Therefore, it is naturally required that the film be an optically homogeneous transparent thin film.

Therefore, the material for the insulating layer 2.2' must have a high insulation resistance value and be able to easily form an optically homogeneous transparent thin film. Furthermore, for the reasons described below, it is necessary that the breakdown voltage value and dielectric constant be large.

Generally, there is a relationship as shown in the following equation between the output light intensity T of the optical image element and the applied voltage Vl of the single crystal plate l.

However, vx is a half-wave voltage and is a constant determined by the following equation.

λ.

...(2) V
The maximum contrast ratio is obtained when 1=vX. Therefore, when using the optical image device, the power source 4 is normally set so that the VXQ applied voltage is applied to the single crystal plate 1.

In order to apply a voltage of Vx to the single crystal plate 1, in the structure shown in FIG. 1, the voltage of the power source 4 must not be greater than vx. Now, the thickness and dielectric constant of the single crystal plate l are di,
ε1, the thickness and dielectric constant of the insulating layer 2.2' are d2. ε2
Then, the voltage v1 applied to the single crystal plate 1 is given by the following equation.

become. Therefore, in order to keep the voltage V of the power source 4 low and apply a predetermined voltage to the single crystal plate 1, if the thickness dl of the single crystal plate 1 and the dielectric constant ε1 are constant, then the insulating layer 2.2'
It is desirable that the thickness d2 is small and the dielectric constant ε2 is large. The thickness d2 is limited by the breakdown voltage value of the insulating layer 2.2', and if it is made too small, electrical breakdown will occur, so the larger the dielectric constant ε2 is, the more the insulating layer 2.2
′.

In this way, the insulating layer 2.2' needs to satisfy the above conditions, and conventionally it is made of polyparaxylylene, mica plate,
Various materials such as silicone insulating oil have been proposed. However, although these conventional insulating materials can provide nearly satisfactory results in terms of insulation resistance, breakdown voltage, and the ability to easily form optically homogeneous and transparent thin films, their relatively low dielectric constant There was a drawback that the voltage V of No. 4 had to be increased.

For example, when polyparaxylylene is used, its dielectric constant ε2 is 3.0, so ε1=56, d1=20
d2-5 on 0μm bismuth silicon oxide
When the insulating layer 2.2' is formed with a thickness of μm, the power supply and
This results in approximately 1/2 of a voltage V of 1 being applied to the insulating layer. Therefore, half-wave voltage Vx of bismuth-silicon oxide single crystal = 3.9KV (however, in equation (2), λ = 633μm, no = 2.54.γ, 1 = 5X
10" m/V), it was necessary to apply a voltage of 7.5 KV, which is approximately twice that voltage. Repeated application of such high voltage deteriorates the polymer membrane. Electrical characteristics sometimes deteriorated significantly.Also, there was a drawback that the polymer film absorbed moisture in the atmosphere, resulting in lower insulation characteristics and deterioration of device characteristics.

An object of the present invention is to provide an optical image element that solves the above-mentioned drawbacks and has significantly improved characteristics.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a diagram showing all embodiments of the optical image device of the present invention.

The optical image element of the present invention is different from conventional optical image elements in that amorphous diamond, which has excellent properties, is used as the insulating layer 2.2', and that bismuth-silicon oxide single crystal 1 and amorphous diamond are used. By applying a thin film of an oxide such as silicon dioxide, zirconia, alumina, or yttrium oxide, which has a high specific resistance and dielectric constant, as a protective film for the single crystal 1 on one or both of the insulating layers 2 and 2'. be.

Amorphous diamond film has a relatively high insulation resistance value (volume resistivity) of 109 to 1010 Ω・cm, and a dielectric constant of 4 to 5, which is higher than conventional polyvaraxylylene or silicone insulating oil, and the film is highly uniform. This is an insulating film that has excellent properties in terms of density.

Amorphous diamond film is produced by plasma CVD (Chemical vapor deposition) in a methane gas flow.
dep.

5ition) method. In this case, since the substrate temperature is as low as approximately 100°C, oxygen vacancies may occur on the single crystal surface due to oxygen escaping from the bismuth silicon oxide substrate, or film peeling or cracking may occur due to differences in thermal expansion coefficients. It is possible to obtain a film that is optically uniform without any problems.

However, on the other hand, an amorphous diamond film is formed by dissociating and depositing methane gas using the plasma CVD method.
2 is generated. Therefore, the bismuth silicon oxide single crystal substrate is placed in a highly reducing atmosphere of RF impression, high temperature (100° C.), and hydrogen gas atmosphere, and oxygen vacancies occur from the surface of the single crystal.

In the present invention, bismuth silicon oxide single crystal l
In order to solve the problem of oxygen vacancies in the single crystal 1, an insulating film with relatively high resistance and high dielectric constant is first formed on the surface of the single crystal 1 (oxides such as silicon dioxide, zirconia, alumina, and yttrium oxide are used). The optical image element is constructed by applying a thin film of 1 as a protective film and then depositing an amorphous diamond film as an insulating layer 22'.

Examples of the present invention in which silicon dioxide 5i02 is used as the protective film will be described in more detail below. After forming a silicon dioxide film with a thickness of about 1000A on both sides of a bismuth silicon oxide single crystal plate with a thickness of 300μm by vapor deposition, CVD, sprocketing, or spinner method, heat treatment was performed at about 500'C. to densify the film. Thereafter, an amorphous diamond film is formed by plasma CVD. Substrate temperature is approximately 100°
An amorphous diamond film of about 1 μm was obtained by vapor phase growth in methane gas of C1 about I×10′ rorr. This amorphous diamond film had a film thickness uniformity of ±5% or less, and was a good film with no cracks or peeling. A transparent electrode is provided on the surface of this thin film, and a power source 4
When voltage V was applied, 94% of the applied voltage ■ was applied to the single crystal plate, and the image contrast ratio was approximately 40 dB.
and about 20 when using a conventional polyparaxylylene membrane.
Significant improvement over d13. Furthermore, similar characteristics to those described above were confirmed when zirconia, alumina, or yttrium oxide was applied as a protective film.

As explained above, the optical image element of the present invention has an insulating film 2.2.
' is composed of an amorphous diamond film created by plasma CVD and a thin film of oxides such as silicon dioxide, zirconia, alumina, and yttrium oxide as a protective film for bismuth silicon oxide single crystal. Since the dielectric constant is large, there is an advantage that the power supply voltage can be set lower than the conventional voltage value. Therefore, when used with the same power supply voltage value as the conventional one, the present invention has the advantage that the voltage applied to the single crystal plate 1 is higher than that of the conventional one, so that the output image contrast ratio of the optical image element is improved. There is.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an optical image element. 1: Single crystal plate 2.2': Insulating layer 3.3': Transparent electrode 4: Power source 5: Writing light 6: Readout light (incident light) 7: Polarizer 8: Readout light (transmitted light) 9: Detection photon
10: Output light V: Power supply voltage dl: Single crystal plate thickness d,: Insulating layer thickness

Claims (2)

[Claims] (1) A composite insulating layer consisting of a single crystal plate having an electro-optic effect and a photoconductive effect, an amorphous diamond film provided on one side or both sides of the single crystal plate, and the composite insulating layer and the single crystal plate. An optical image device comprising: a crystal plate; and a transparent electrode that applies an electric field to the crystal plate. (2) The optical image element according to claim 1, wherein the protective layer comprises silicon dioxide, zirconia, alumina,
An optical image element characterized by being made of an oxide such as yttrium oxide.