JP2636037B2 - Optical image conversion device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical image conversion element using a single crystal having a photoconductive effect and an electro-optical effect, and more specifically, to a flat plate made of the single crystal. When electrodes are attached to both sides or one side via an insulating plate, at least the single crystal and the insulating plate are bonded by an optical bonding (optical contact) method so that optical and electrical characteristics can be improved. The present invention relates to an optical image conversion device.

[Prior art] The optical image conversion element is a PRCM (Pockeles Readout Optical
Modulator) element, which belongs to the spatial light modulator. That is, input information having a spatial distribution,
For example, given intensity modulation to input light information such as images,
It is an element that works to obtain output light information.

More specifically, the optical image conversion element is irradiated with X-rays or blue light to write and store image information,
By irradiating the red light at the time of reading, modulation is applied to the red light in accordance with the stored information to obtain output image information, and the process of storing and outputting is performed by erasing the stored information. It has the property of being able to be repeated many times.

Therefore, the usage of the optical image conversion element operating in this way is as follows: image color conversion, X-ray image detection, gradation adjustment,
Contour enhancement, ITC conversion, parallel logic operation, etc. can be listed. That is, in color conversion, blue light is used for writing light and red light is used for reading light by utilizing the characteristic that the same image as a recorded image is output by using light having a uniform intensity distribution as reading light. This allows the color of the image to be converted from blue to red. As described above, the X-ray image can be detected by reading out the recorded image because the X-ray can be used as the writing light as described above. Further, when performing an appropriate operation at the time of reading a recorded image for tone adjustment and contour emphasis, processing such as adjustment of the density of the read image, inversion of negative / positive, and emphasis of the contour can be performed. The ITC conversion refers to a process that can convert an image composed of incoherent light into an image composed of coherent light using a laser as readout light. In this case, an image formed by coherent light can be subjected to various optical processes such as Fourier transform, holographic process, and the like, so that the process by ITC transform has a wide range of useful applications. The parallel logical operation means that the intensity of an image is made to correspond to a binary level of a high level or a low level, an image from which certain logical information is read is used as a readout light, and an appropriate operation is given at the time of readout, so that the recorded information and Means that a logical operation such as a logical product or a logical sum is performed during the operation, and the result of the operation can be extracted as an output image. At this time, a plurality of data can be processed in parallel in time using the parallel characteristics of light, so that a high-speed logical operation can be performed.

As described above, an optical image conversion element having various application fields is an element utilizing the photoconductive effect and electro-optical effect of a single crystal such as bismuth silicon oxide Bi ₁₂ SiO ₂₀ (hereinafter, referred to as BSO). Here, the photoconductive effect refers to the effect that when light enters a dielectric or semiconductor, a carrier charge proportional to the incident light is generated, the resistivity decreases, and a photocurrent can be caused to flow by applying a voltage. Say. For example,
When the single crystal is BSO, this effect is large for X-rays and blue light, and hardly occurs for red light.

On the other hand, the electro-optic effect here means the Pockels effect, which means that when an electric field is applied to a single crystal, the refractive index of the single crystal shows birefringence according to the magnitude of the electric field,
N _o, n _e shaft can be in a direction perpendicular to the electric field when the single crystal is BSO. Therefore, the linearly polarized light incident parallel to the electric field is transmitted as elliptically polarized light having an ellipticity according to the magnitude of the electric field.

FIG. 1 shows the basic configuration of an optical image conversion element having such an attribute. In the figure, an optical image conversion element indicated by reference numeral 2 includes a single crystal plate having a photoconductive effect and an electro-optical effect, for example, a BSO single crystal 4.
A transparent electrode 8 is attached to both sides of the substrate via an insulating plate 6.

Next, the operation procedure of the optical image conversion device 2 configured as described above will be described with reference to FIGS. First, FIG. 2a
As shown in (1), a voltage source 10 is connected between the transparent electrodes 8, and a predetermined DC voltage is applied. In this case, the image conversion element 2
Potential gradient E _n of the internal (n = 1, 2), as shown by reference numeral E ₁ in FIG. A, become spatially uniform electric field in the BSO single crystal within 4. Incidentally, it displayed separately for the prior art top and bottom portions region of the BSO single crystal 2 about a potential gradient E _n in order to facilitate understanding of that time, if the number of the subscript n have the same value the same It represents a potential gradient.

Therefore, at the time of writing, as shown in FIG. 2B, the lower half area 2a of the optical image conversion element 2 is shielded, and blue light or light 14 having an image by X-rays is made incident only on the upper half area 2b. . In this case, positive and negative carriers 16 and 18 represented by reference numerals or are generated in the BSO single crystal 4 according to the amount of incident light 14. The carriers 16 and 18 thus generated move to both end surfaces of the BSO single crystal 4 by Coulomb force due to the external electric field generated by the voltage source 10.
Further, further movement is prevented by the presence of the insulating plate 6, and the carriers 16 and 18 are accumulated on both end surfaces of the BSO single crystal 4. The density of the polarized accumulated carriers 16, 18 corresponds to the information of the writing light intensity. In this case, the polarized carriers 16, 18 create an electric field in the opposite direction to the external electric field. Therefore, the electric field applied to the crystal is the sum of the external electric field and the electric field generated by carriers 16 and 18. In other words, the electric field in the crystal becomes smaller as the greater part of the carrier density (reference potential gradient E _2). As a result, the information of the written image is replaced by the electric field intensity distribution in the BSO single crystal 4. In this state, when the light image conversion element 2 is kept in a dark place, the BSO single crystal 4 becomes an insulator again, so that the polarized carriers 16 and
18 is kept as it is, and the image information is recorded for a long time.

Next, a case where a negative image is output at the time of reading will be described. In this case, as shown in FIG. 2c, light 20 having no photoconductive effect, that is, light 20 which does not destroy the written information, for example, red light 20 having a small light intensity is incident. Then, the linearly polarized light transmitted through the polarizer (not shown) is converted into elliptically polarized light according to the electric field distribution in the BSO single crystal 4 and passes through the BSO single crystal 4. Next, a red light 22 having image information having a light intensity distribution according to an electric field distribution is output through an analyzer (not shown) arranged orthogonal to the polarizer. Red light with this image information
Reference numeral 22 has information of a negative image with respect to the original image.

Next, when reading a positive image, the electric field in the BSO single crystal 4 is reduced by the carriers 16 and 18 by short-circuiting the voltage source 10 and setting the external electric field to zero value at the time of reading, as shown in FIG. only it becomes generated electric field (see potentials gradient E _3). In this state, the red light 22 having image information has information of a positive image with respect to the original image.

Next, when erasing the written image, as shown in FIG. 2E, when the transparent electrodes 8 are short-circuited and irradiated with red light 24 having a high light intensity, the polarized carriers 16 and 18 are recombined. And return to the original state. In this case, the zero level potential gradient E ₄ because no voltage is applied to the single crystal.

[Problem to be Solved by the Invention] The optical image conversion element that operates as described above is actually configured as shown in FIG. That is, BSO single crystal 4
When the insulating plate 6 and the transparent electrode 8 are attached to both sides of the substrate, they are attached via optical adhesive layers 32 and 34 such as epoxy resin.

However, by interposing such optical adhesive layers 32 and 34, the voltage applied to the BSO single crystal 4 is reduced due to the thickness of the adhesive, and the voltage of the voltage source required for forming an image is reduced. The disadvantage of having to raise it arises. In addition, unevenness in brightness of the read image occurs due to the unevenness of the thickness of the optical adhesive layers 32 and 34. Further, curing and shrinkage of the optical adhesive layers 32 and 34 occur, whereby the BSO single crystal 4, the insulating plate 6, and the transparent electrode 8 are distorted, and as a result, the read image is distorted. In addition, bubbles may be mixed in the optical adhesive layers 32 and 34, and in this case, the read image is distorted. In addition, the crystal is slightly distorted due to the piezoelectric effect of the BSO single crystal 4 caused by further applying a voltage to the BSO single crystal 4, and the optical adhesive layer 32 already hardened due to the distortion absorbs the strain stress. There is a possibility that the insulating plate 6 cannot be completely separated from the BSO single crystal 4. Furthermore, the interface between the adhesive layers 32 and 34 and BS
There are various inconveniences in that the influence of interference fringes due to multiple reflection of light in the O single crystal 4 is likely to occur, and as a result, the read image is deteriorated.

The present invention has been made in order to overcome all of the above-mentioned disadvantages. At least the bonding between a single crystal such as BSO and an insulating plate is performed by optical bonding (optical contact) so that the bonding can be performed without using an adhesive. Accordingly, it is an object of the present invention to provide an optical image conversion element having excellent characteristics without optical distortion.

Means for Solving the Problems In order to solve the above problems, the present invention provides a single crystal plate having a photoconductive effect and an electro-optic effect, and an insulating plate attached to at least one side of the single crystal plate And an electrode layer for applying an electric field to the single crystal plate via the insulating plate, wherein at least the opposing surfaces of the single crystal plate and the insulating plate are polished and then pressed against each other. In this case, the single crystal plate and the insulating plate are brought into an optically bonded state.

The present invention also provides a single crystal plate having a photoconductive effect and an electro-optic effect, an insulating plate attached to at least one side of the single crystal plate, and applying an electric field to the single crystal plate via the insulating plate. In the optical image conversion device provided with the electrode plate to perform, after polishing the respective surfaces of the single crystal plate and the insulating plate and the electrode plate, respectively, and then by pressing each other, the single crystal plate and the insulating plate and the electrode plate and Is in an optically bonded state.

[Operation] When producing an optical image conversion element comprising a single crystal plate having a photoconductive effect and an electro-optic effect, an insulating plate and an electrode layer or an electrode plate, at least a contact surface between the single crystal plate and the insulating plate is polished. After being brought into close contact with each other, a predetermined load was applied to make an optically bonded state, whereby an optical pixel conversion element having excellent electrical and optical characteristics was obtained.

Examples Next, preferred examples of the optical image conversion device according to the present invention will be described, and the details will be described below with reference to the accompanying drawings.

In FIG. 4, reference numeral 50 denotes a single crystal plate having a photoconductive effect and an electro-optical effect.
Bi ₁₂ SiO ₂₀ , Bi ₁₂ GeO ₂₀ or the like is employed. This single crystal plate 50
The insulating plates 52 and 54 and the transparent electrode plates 56 and 58 made of a metal oxide or the like are arranged in parallel with each other using a processing jig (not shown) in a state separated from both side surfaces 50a and 50b.

Here, as the insulating plates 52 and 53, optical glass or single crystal is adopted, and as the optical glass, borosilicate glass, quartz glass, or the like is adopted.
Mica, LiNbO ₃ , LiTaO _{3 and the} like are employed. The electrode plates 56, 58 are made of optical glass, for example, borosilicate glass as a base material, and the side surfaces 56a, 58b of the electrode plates 56, 58 are entirely made of In ₂ O ₃ , SnO 2. A metal oxide such as ₂ is deposited to form a transparent electrode.

Then, the side surfaces 50 of the single crystal plate 50 and the insulating plates 52 and 54
a, 50b, 52a, 52b, 54a, 54b and the insulating plate 5 of the electrode plates 56, 58
The side surfaces 56b and 58a facing the 2 and 54 are optically polished, respectively. Their surface roughness (center line average roughness: _Ra ) is 0.1
μm or less, and preferably 0.02 μm or less in order to minimize light scattering. Further, their flatness can be set to 2λ (λ = 546 nm) or less, but problems such as easy peeling and interference fringes may occur, and are preferably λ or less, more preferably λ or less.
/ 2 or less is desirable.

Side surfaces 50a, 50b, 52a, 52b, 54a, 54b, 56a, 56b and 5 of the single crystal plate 50, the insulating plates 52, 54 and the electrode plates 56, 58
The size of 8a, 58b is 1 to 200 mm square, preferably 10 to 200 mm.
100mm square. Further, the thickness of the single crystal plate 50 is 0.05
55 mm, preferably 0.3-0.8 mm. Further, the thickness of the insulating plates 52 and 54 is 0.002 to 1 mm when the material is glass or mica, preferably 0.01 to 0.03 mm.
mm. When using LiNbO ₃ or LiTaO ₃ single crystal as its material, the thickness is 0.01 to 5 mm, preferably 0.1 to 1 m.
m.

In such a configuration, first, dirt, dust, and the like on the side surfaces 50a, 50b, 52a, 52b, 54a, 54b, 56b, and 58a (hereinafter, these are collectively referred to as a side surface A) are removed. Next, the side portions A to be bonded are brought into contact with each other, and are held and brought into close contact with each other by pressure bonding. As a result, the optically polished side portions A are brought into an optically bonded (optical contact) state. In addition, as a method for achieving an optically bonded state, it is possible to bring together the plates to be bonded in pure water, then take out the bonded plates and dry until the water becomes a molecular film. Can be mentioned. In the above-described embodiment, the electrode plates 56 and 58 are omitted, and the thickness of the insulating plates 52 and 54 is increased and the thickness of the insulating plates 52 and 54 is set to the side portions 52a and 54b.
It goes without saying that the electrode layer may be formed by depositing a metal oxide such as In ₂ O ₃ or SnO ₂ .

The optical image conversion device thus produced operates substantially the same as the description shown in FIGS. 2A to 2E. In this case, since the optical image conversion device according to the present embodiment does not use an adhesive such as an epoxy resin for bonding, various advantages such as image unevenness caused by the adhesive can be advantageously obtained. Can be

 Hereinafter, specific examples will be described.

Example 1 Bi ₁₂ SiO ₂₀ produced by a pulling method, 30 mm from a single crystal
A (100) single crystal plate of × 30 mm × 800 μm ^t was cut out, and both surfaces were optically polished to a flatness of λ / 4. 40mm as insulating plate
Using borosilicate glass of × 40 mm × 30 μm ^t , as the electrode plate, a borosilicate glass optically polished to a flatness λ / 4 of 40 mm × 40 mm × 4 mm ^t with an ITO film which is a metal oxide film attached It was used.

After bonding the insulating plates to both sides of the single crystal plate and bonding them to each other by optical bonding (optical contact), the electrode plates are further bonded to both sides and pressed to each other. The optical image conversion element was produced by bonding using a bonding method.

On the other hand, for comparison, a single-crystal plate and an insulating plate were bonded with an optical adhesive, and then an electrode plate was bonded on both sides with an optical adhesive to produce an optical image conversion element according to the related art.

When a He-Ne laser was transmitted through the device fabricated by this method and the transmitted wavefront and the spatial frequency spectrum were observed, favorable characteristics without wavefront aberration were obtained as compared with the device using an adhesive. The characteristics are shown in Table 1.

In Table 1, the half-wavelength voltage is a voltage corresponding to the image writing voltage, and the resolution (lp / mm) indicates the number of black and white line pairs that can be confirmed in a width of 1 mm.

In addition, the durability of the optical image conversion device according to the present example, such as thermal shock resistance, was significantly improved as compared with the conventional method using an adhesive.

Example 2 30 mm × 3 from Bi ₁₂ SiO ₂₀ single crystal produced by the pulling method
A plate of (100) plane of 0 mm × 800 μm ^t was cut out, and both sides were optically polished to a flatness of λ / 4. 40mm × 40mm as insulating plate
× 10μm ^t mica plate, electrode plate 40mm × 40mm ×
A borosilicate glass optically polished to a flatness λ / 4 of 4 mm ^{t with} an ITO film attached to one side surface was used.

After attaching an insulating plate to both sides of the single crystal plate and bonding them by an optical bonding (optical contact) method, bonding an electrode plate to both sides thereof and bonding them by an optical bonding (optical contact) method to produce an image conversion element. did. The characteristics were almost the same as those of the device shown in Table 1.

Example 3 Bi ₁₂ SiO ₂₀ produced by a pulling method, 30 mm from a single crystal
A (100) single crystal plate of × 30 mm × 300 μm ^t was cut out and both surfaces were optically polished to a flatness of λ / 4. 40mm as insulating plate
× 40 mm × 300 μm ^t LiNbO ₃ is used, and the electrode plate is 40 mm
A borosilicate glass optically polished to a flatness λ / 4 of × 40 mm × 4 mm ^{t with} an ITO film was used.

After attaching an insulating plate to one side of the single crystal plate and bonding by an optical bonding (optical contact) method, an electrode plate is bonded to both sides thereof and bonding by an optical bonding (optical contact) method to form an image conversion element. Produced.

In the above embodiments, Pyrex glass (trade name of Corning) or BK7 glass can be used as the borosilicate glass.

[Effects of the Invention] As described above, according to the present invention, when manufacturing an optical image conversion element, the bonding surface between a single crystal plate having a photoconductive effect and an electro-optical effect and an insulating plate is optically polished, Adhesion is performed by optical bonding (optical contact) method. For this reason, since an adhesive is not used for bonding, distortion of a read image when using the optical image conversion element generated due to the adhesive, or the influence of interference fringes or the like is completely eliminated. The voltage of the power supply required for image detection can be reduced without reducing the voltage applied to the single crystal due to the thickness of the adhesive, and an optical image conversion element with extremely improved optical and electrical characteristics can be obtained. .

As described above, the present invention has been described with reference to the preferred embodiments. However, the present invention is not limited to these embodiments, and various improvements and design changes can be made without departing from the gist of the present invention. Of course.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining the principle of an optical image conversion device, FIGS. 2a to 2e are diagrams for explaining the operation of the optical image conversion device, and FIG. FIG. 4 is an exploded configuration view of the optical image conversion device according to the present invention, and FIG. 5 is a configuration explanatory diagram of the optical image conversion device in an optically bonded state according to the present invention. 50 single crystal plate, 52, 54 insulating plate 56, 58 electrode plate 50a, 50b, 52a, 52b, 54a, 54b side surface 56a, 56b, 58a, 58b side surface

Claims (8)

(57) [Claims] 1. A single crystal plate having a photoconductive effect and an electro-optic effect, an insulating plate attached to at least one side of the single crystal plate, and an electric field applied to the single crystal plate via the insulating plate. In the optical image conversion device provided with an electrode layer, the surfaces of the single crystal plate and the insulating plate facing each other are polished at least, and then the single crystal plate and the insulating plate are optically bonded to each other by pressure bonding. An optical image conversion device, characterized in that: 2. The optical image conversion device according to claim 1, wherein
The surface roughness (R _a ) of the contact surface between the single crystal plate and the insulating plate is 0.1
An optical image conversion device having a thickness of not more than μm and a flatness of not more than 2λ. 3. The optical image conversion device according to claim 1, wherein the material of the insulating plate is optical glass. 4. The optical image conversion device according to claim 1, wherein the material of the insulating plate is a single crystal. 5. A single crystal plate having a photoconductive effect and an electro-optic effect, an insulating plate attached to at least one side of the single crystal plate, and applying an electric field to the single crystal plate via the insulating plate. In the optical image conversion device provided with the electrode plate to perform, after polishing the respective surfaces of the single crystal plate and the insulating plate and the electrode plate, respectively, and then by pressing each other, the single crystal plate and the insulating plate and the electrode plate and An optical image conversion element characterized by having an optically bonded state. 6. The optical image conversion device according to claim 5, wherein
An optical image conversion device, wherein _a surface roughness (R _a ) of _a contact surface between a single crystal plate, an insulating plate and an electrode plate is 0.1 μm or less and a flatness is 2λ or less. 7. The optical image conversion device according to claim 5, wherein the insulating plate is made of optical glass. 8. The optical image converter according to claim 5, wherein the material of the insulating plate is a single crystal.