JPS6231326B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image storage element in which an image conversion element that converts image information of incoherent light into image information of coherent light has a memory function.

Conventionally, in order to perform optical information processing such as Fourier transform, it is necessary to convert image information of incoherent light into image information of coherent light. is used to convert incoherent light image information into coherent light image information. As shown in the figure, the image conversion element includes a single crystal plate 1 having an electro-optic effect and a wavelength-dependent photoconductive effect, insulating layers 2, 2' provided on both sides of the single crystal plate 1, and transparent electrodes 3, 3'. It consists of Bi ₁₂ SiO ₂₀ and Bi ₁₂ GeO ₂₀ are usually used as the single crystal plate 1.
Thin films of polyparaxylylene, magnesium fluoride, mica, etc. are used as the insulating layers 2, 2', and In ₂ O ₃ , In ₂ O 3 are used as the transparent electrodes 3, _3' .
Composites of and SnO ₂ , thin films of Au or Pt, etc. are used.

When a voltage is applied to the single crystal plate 1 and the insulating layers 2, 2' by a power source 4 connected to the transparent electrodes 3, 3', in a steady state, the voltage V of the power source 4 causes the single crystal plate 1 and the insulating layers to For example, a potential distribution as shown by the solid line in FIG. 2 is obtained, which is determined by the thickness of the layers 2 and 2' and their dielectric constants. That is, a voltage of _E1 is applied to the single crystal plate 1. In this state, the original image 6 is irradiated with a light source 5 of incoherent light of a wavelength at which the single crystal plate 1 exhibits a photoconductive effect, and the reflected light from the original image 6 is transmitted through a lens 7 and a half mirror 8 into a single crystal. When an image is formed on the crystal plate 1, the irradiated area of the single crystal plate 1 has a potential distribution as shown by the broken line in FIG. That is, a voltage of _E2 is applied to the single crystal plate 1. The voltage E ₂ applied to this irradiated area is much weaker than the electric field E ₁ applied to the non-irradiated area, and as mentioned above, the single crystal plate 1 has an electro-optic effect. The non-irradiated area of the single crystal plate 1 exhibits large birefringence, while the irradiated area exhibits only slight birefringence. That is, a refractive index distribution corresponding to image information is formed on the single crystal plate 1.

In this way, after the image information of the original image 6 is formed as a refractive index distribution on the single crystal plate 1, the coherent light 9 having a wavelength at which almost no photoconductive effect of the single crystal plate 1 occurs is used as readout light, and this is polarized light. When the light 11 that has passed through the single crystal plate 1 is polarized into a linearly polarized wave by the half mirror 8 and then made into a linearly polarized wave by the half mirror 8, the light 11 that has passed through the single crystal plate 1 becomes an optical polarized wave according to the refractive index distribution of the single crystal plate 1. It receives a phase difference Γ. this light 11
The output light 13 obtained by detecting with the analyzer 12 is obtained when the polarizer 10 and the analyzer 12 are in the extinction position, and the readout light 9 is incident at an angle of 45° with respect to the optical axis of the single crystal plate 1. In this case, the light intensity is proportional to sin ² (Γ/2), so the incoherent image information of the original image 6 has been converted to coherent light image information, which can be used in optical information processing such as Fourier transform. It becomes possible to use it.

However, the electric field distribution in the single crystal plate 1 is maintained because free electrons and free holes generated by the incidence of reflected light from the original image 6 are trapped in the single crystal plate 1. Therefore, when the light irradiation from the light source 5 is stopped, the free electrons and free holes trapped in the single crystal plate 1 gradually recombine, or the insulating layers 2, 2' As the electric field distribution inside the single crystal plate 1 gradually becomes uniform, the refractive index distribution formed inside the single crystal plate 1 gradually becomes uniform. It becomes uniform within the single crystal plate 1. Therefore, the image information written on the single crystal plate 1 as a refractive index distribution gradually disappears. The storage time in this case is determined by the product ρ・ε of the resistivity ρ and dielectric constant ε of the single crystal plate 1, and the single crystal plate 1 is made of Bi ₁₂ SiO ₂₀ with high resistivity.
Alternatively, even if Bi ₁₂ GeO ₂₀ was used, the time was about 1 to 2 hours. Furthermore, when the voltage application is stopped, the free electrons and free holes trapped in the single crystal plate 1 quickly recombine, so the image information written as the refractive index distribution disappears. This will result in That is, when such an image conversion element is used, it is not possible to retain written image information for a long time.

An object of the present invention is to provide a memory function to an image conversion element that converts image information of incoherent light into image information of coherent light. Examples will be described in detail below.

FIG. 3 is a cross-sectional view of the image storage element of the present invention, which includes a single crystal plate 14 having an electro-optical effect and a wavelength-dependent photoconductive effect, an insulating layer 15 having ferroelectricity provided on both sides thereof, 15' and transparent electrodes 16, 16'. Single crystal plate 14
It has excellent properties such as a large photoconductive effect for writing light, a relatively low half-wave voltage, and the ability to easily obtain large, high-quality single crystals using the Czyochoralski method.
Bi ₁₂ SiO ₂₀ , Bi ₁₂ GeO ₂₀ is used, and the insulating layers 15 and 15' having ferroelectricity can generate residual polarization at several 100 V/μm, and the monocrystalline plate 14 has a high dielectric constant. The ability to provide a high electric field distribution and high insulation resistance (2×10 ¹⁴ Ω/cm
Above) Polyvinylidene fluoride is used for the following reasons: it can prevent the outflow of optical carriers, its breakdown voltage is as high as 100KV/mm, and it is relatively easy to obtain a thin film with a uniform thickness using a spinner, etc. use. Further, as the transparent electrodes 16, 16', a thin film of In ₂ O ₃ , Au, Pt, etc. is used.

In the present invention, a material having ferroelectric properties, that is, a ferroelectric material, is used as the insulating layers 15 and 15', and the image storage element has a memory effect by utilizing the fact that residual polarization occurs in the ferroelectric material. First, I will explain about ferroelectric materials. When an electric field E is applied to a crystal with ferroelectricity, the polarization P first becomes a curve
Varies along OAB. While the applied electric field E is very small, the polarization P changes along the curve OA, but when the electric field E is increased and E=Eb, the polarization P changes.
are all the same as the direction of the electric field E, and the entire crystal becomes one domain, and the subsequent electric field E
The polarization P is the curve C-B-Pr-D- with respect to the increase or decrease of
It changes along F-G-B-C. That is, the electric field E
Even if it becomes zero, residual polarization Pr remains.
Furthermore, in order to make this residual polarization Pr zero, it is necessary to apply a coercive electric field E _D to the crystal.

5A to 5F are explanatory diagrams of the operation of the image storage device according to the embodiment of the present invention shown in FIG. The same reference numerals as in the figures represent the same parts.

FIG. 3A shows the case where image information written as a refractive index distribution on the single crystal plate 14 of the image storage element is erased, and the transparent electrodes 16, 1
This is for the case where a voltage is applied to 6' by a power source 17 and a light beam 18 (hereinafter referred to as writing light 18) is irradiated to produce a photoconductive effect on the single crystal plate 14. In this way, the single crystal plate 14
exhibits a remarkable photoconductive effect, the applied voltage V is mostly applied to the insulating layers 15, 15', and the voltage V
If is sufficiently high, an electric field stronger than the coercive electric field E _D is applied to the single crystal plate 14, and the residual polarization distribution that remained in the insulating layers 15 and 15' depending on the shading of the past image is erased, all in the same direction. becomes polarized. In other words, the past recorded images have been erased. Further, the potential distribution of the image storage element at this time is as shown by the dotted line in FIG.

After erasing the past recorded image in this way, the irradiation of the writing light 18 is stopped and the polarity of the power supply 17 is reversed, as shown in FIG. It shall be indicated by a dotted line. After setting the image storage element to the state shown in FIG.
Although image information is written, here, in order to make the writing operation easier to understand, a case will be described in which only the upper half of the image storage element is irradiated with the writing light 18, as shown in FIG.

Since the single crystal plate 14 has a photoconductive effect as described above, the portion irradiated with the writing light 18 exhibits a remarkable photoconductive effect. Therefore, in the upper half of the image storage element, most of the voltage applied from the power supply 17 is applied to the insulating layers 15 and 15', so the potential distribution is shown by the dotted line in the upper half of the figure C. Become something. Further, the voltage distribution in the lower half of the image storage element, that is, the non-irradiated area, is maintained as it is as shown in FIG. B, as shown by the dotted line in the lower half of FIG.

Therefore, the electric field applied to the single crystal plate 14 is much larger in the lower half, which is the non-irradiated region, than in the upper half, which is the irradiated region. Therefore, as mentioned above,
Since the single crystal plate 14 has an electro-optic effect,
This means that image information has been written as a refractive index distribution.

When the image information is written as a refractive index distribution in this way, as shown in FIG. ) is made incident on the image storage element via the polarizer 20. A light beam 22 obtained by detecting the output light from this image storage element with a polarizer 20 and an analyzer 21 at the extinction position
As mentioned above, image information of incoherent light is converted into image information of coherent light.

Now, in the state shown in FIG. 5C, if the voltage application is stopped, the image information written as the refractive index distribution will be erased, but
5', residual polarization corresponding to the written image information is generated, as shown in FIG. 5E. The residual polarization of the upper half of the image storage element, that is, the irradiated area, and the residual polarization of the lower half of the image storage element, that is, the non-irradiated area, are:
As shown in the figure, the direction is opposite, so in the image storage element where residual polarization remains,
As shown in FIG. 5F, when a voltage is applied from the power supply 17 and the entire surface is irradiated with weak writing light 26 that does not reverse the polarization, the potential distribution of the image storage element is such that the generated carriers are concentrated near the residual polarization. Therefore, it is shown by the dotted line in Figure F. This potential distribution is almost the same as the potential distribution shown in Figure C, and therefore it means that the image information written in the image storage element as a refractive index distribution has been reproduced. The residual polarization generated in the insulating layers 15, 15' can be preserved semi-permanently by appropriately selecting the material of the insulating layers 15, 15'. Insulating layer 15, 15'
It can be preserved semi-permanently as the distribution of residual polarization generated in the process. Therefore, if the refractive index distribution corresponding to the written image information is reproduced as shown in F of the same figure, the image information written as shown in D of the same figure is converted into image information of coherent light. can be converted.

Also, when writing image information, the single crystal plate 1
The optical carriers generated in 4 are transferred to insulating layers 15, 1
Since the light carriers are attracted by the electric force of the polarization generated at 5', the optical carriers are not recombined, and the electric field distribution in the single crystal plate 14 can be maintained for a long time. Therefore, it is possible to reproduce clear images for a long time.

Next, as a single crystal plate 14, a 30mm plate with a (100) plane
After optically polishing both sides of this single crystal plate 14 to a flatness of λ/10 (λ is the wavelength of the readout light 19) using Bi ₁₂ SiO ₂₀ of ×30 mm ×0.5 mm, polyvinylidene fluoride was polished using dimethyl formaldehyde as a solvent. A 5% by weight solution is applied to both sides of the single crystal plate 14 to a thickness of 2 μm using a spinner, and this is heated at 140° C. for 30 minutes in an argon gas atmosphere to form insulating layers 15, 15'. Furthermore, the results of measuring the operating characteristics of an image storage element in which transparent electrodes 16 and 16' of In ₂ O ₃ were formed using the magnetron sputtering method and then subjected to poling processing will be described. In this case, the writing light 18 is
_The light _{from an}
Using 633nm light, as the original image of the written image
A mask pattern with rectangular shading of 10lP/mm was used. Further, as the power supply 17, a 1000V DC power supply was used.

In this way, by selecting the power supply 17, the writing light 18, the reading light 19, and the original image, and repeating the operations shown in FIGS. 5A to 5D, the readout image was a clear image with the same contrast as the original It was hot.
Further, no deterioration was observed in the readout image even during the readout operation for 6 hours while the readout light 19 remained irradiated. In order to further examine the memory characteristics, we stopped applying the voltage and left it in the daylight for one week, then applied a voltage of 1000V again and changed the intensity of the writing light 18 to 1/1 of the intensity when writing image information. Make it 10,
After the entire surface was irradiated, the readout light 19 was irradiated as shown in FIG. 5D, and a clear readout image could be obtained. Also, exactly the same characteristics were obtained when Bi ₁₂ GeO ₂₀ was used as the single crystal plate 14 and polyvinylidene fluoride was used as the insulating layers 15 and 15'.

FIG. 6 is a sectional view of another embodiment of the present invention, in which only one side of a single crystal plate 23 such as Bi ₁₂ SiO ₂₀ or Bi ₁₂ GeO ₂₀ having an electro-optic effect and a wavelength-dependent photoconductive effect is used. An insulating layer 24 made of a ferroelectric substance such as polyvinylidene fluoride is formed on the substrate, and a transparent electrode 2 made of a thin film of In ₂ O ₃ , Au, Pt or the like is further formed.
5,25' are formed.

When the above-mentioned experiment was conducted using this image storage element, it was possible to obtain exactly the same characteristics as an image storage element in which insulating layers were provided on both sides of a single crystal plate.
If the structure is such that the insulating layer 24 is provided only on one side of the single crystal plate 23, as in the image memory element shown in FIG. 6, the ferroelectric layer can be formed only once during the manufacture of the image memory element. There are advantages to saying that.

As explained above, in the present invention, an insulating layer made of ferroelectric material is provided on at least one side of a single crystal plate having an electro-optical effect and a wavelength-dependent photoconductive effect. It is possible to generate residual polarization in the insulating layer in accordance with the density of the image information obtained, and also to store this residual polarization. Therefore, there is an advantage that the image information written in the image storage element can be stored.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the configuration of a conventional image conversion element, FIG. 2 is an explanatory diagram of its operation, FIG. 3 is a sectional view of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of the characteristics of a ferroelectric material. FIG. 5 is an explanatory diagram of the operation of the image storage element of the present invention, and FIG.
The figure is a sectional view of another embodiment of the invention. 1, 14, 23 are single crystal plates, 2, 2', 15,
15', 24 are insulating layers, 3, 16, 16', 25,
25' is a transparent electrode, 4 and 17 are power sources, 5 is a light source,
6 is the original picture, 7 is the lens, 8 is the half mirror, 9,
19 is a readout light, 10 and 20 are polarizers, 11 is output light from an image conversion element, 12 and 21 are analyzers,
13 and 22 are output lights from the analyzer, and 26 is a weak writing light.

Claims (1)

[Scope of Claims] 1. A single crystal plate having an electro-optic effect and a wavelength-dependent photoconductive effect, a crystalline insulating layer having ferroelectricity provided on at least one side of the single crystal plate,
An image storage element comprising a transparent electrode that applies an electric field to the insulating layer and the single crystal plate. 2. The image storage element according to claim 1, wherein the single crystal plate is formed of bismuth silicon oxide (Bi ₁₂ SiO ₂₀ ). 3. The image storage element according to claim 1, wherein the single crystal plate is formed of bismuth germanium oxide (Bi ₁₂ GeO ₂₀ ). 4. Claim 1, wherein the insulating layer is formed of polyvinylidene fluoride.
The image storage device described in .