JPS63253919A - Optical image converter - Google Patents

Abstract

PURPOSE:To decrease the voltage to be impressed on an optical image converting element by using the constitution in which image reading out light is passed plural times in the optical image converting element. CONSTITUTION:Writing and reading out of the image are executed by utilizing the optical image converting element 1 such as, for example, bismuth silicon oxide (BSO) signal crystal, the electrical properties of which change with an optical effect. A reflecting member 12 which passes the reading out light 6 plural times through the optical image converting element 1 at the time of image reading out is provided on this device. The voltage to be impressed on, the BSO single crystal 1 is previously set at a relatively low value and in turn, the reading out light 6 is passed plural times through the same region within the BSO 1, by which the phase delay of one passage is added and the sufficient half wavelength phase delay is obtd. The voltage to be impressed on the optical image converting element 1 is thereby decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a photoimage conversion element, such as bismuth silicon oxide (
B112S1020. Hereinafter referred to as rBSOJ. ) The present invention relates to an optical image conversion device that writes and reads optical images by utilizing electro-optic effects such as photoconductive effects and electro-optic effects possessed by single crystals.

(Prior Art) Optical image conversion elements such as BSO have traditionally had the function of converting an incoherent optical image into a coherent optical image, and have therefore been studied in various ways as elements for two-dimensional image processing using light. There is.

In addition, various applications as two-dimensional optical memory and two-dimensional displays are also being researched. A typical example of BSOs is PROM (Pockels Readout Optical Memory), which utilizes the vertical-order electro-optic effect of a BSO single crystal.

The basic structure of this PROM is B5O4 as shown in Figure 4.
It has a structure in which an insulating layer (parylene) 42 is provided on both surfaces of one wafer, and a transparent electrode (indium oxide>A) 43 is further provided thereon.

First, a write operation is performed as follows. B50
When a two-dimensional image is formed on the surface of 85041 with voltage applied to both sides of B5041, carriers are generated in the crystal according to the intensity of human light due to the photoconductivity of B5041, and these carriers cause the crystal screen to The voltage applied to is reduced. As a result, the human power light image is recorded in the crystal as a voltage distribution corresponding to the intensity distribution. Readout then takes advantage of the birefringence caused by the voltage applied to the crystal. That is, the BSO is parallel to the wafer surface and perpendicular to each other.
The refractive index is different for linearly polarized light in two directions (X direction and X direction).

Therefore, for example, as shown in FIG.
Intensity Ii consisting of linearly polarized light in the bisecting directions of the direction and the X direction
The coherent light is made incident on B5O41. Then, due to the birefringence of BSO, the local voltage V between both surfaces of the crystal
Depending on , the incident linearly polarized light locally becomes elliptically polarized (Pockels effect).

Therefore, by placing an analyzer 52 perpendicular to the incident polarization direction on the output side, it is possible to read out a human light image recorded as the intensity distribution of coherent light corresponding to the voltage distribution on the B5041 surface. At this time, the output light intensity ■0゛ is as follows. However, V is a local voltage and Vπ is a half-wavelength voltage.

Generally, blue light with a wavelength of around 440 nm, which is most sensitive to BSO, is used as input image writing light, and red light or infrared light, which has low sensitivity, is used as image reading light.

The recorded image is erased by irradiating the entire surface with blue light. As described above, BSO is excellent as an optical image conversion element in terms of sensitivity, resolution, response speed, etc., but its high half-wavelength voltage (for example, 3900 V at wavelength 633nl11, 5600V at wavelength 830nh+) severely limits its usage. has been done. In addition, the BSO element has an optical oil property, and as the light passes through the crystal, the plane of polarization rotates, so there is a problem that the actual half-wave voltage further increases.

(Problems to be Solved by the Invention) The present invention provides optical image conversion when writing and reading various image information using an optical image conversion element having properties such as a photoconductive effect and an electro-optic effect. The object of the present invention is to provide a high-resolution optical image conversion device that reduces the voltage applied to an element.

(Means for solving the problem) In an optical image conversion device that writes and reads images using an optical image conversion element whose electrical properties change due to optical action, when reading out the image, A reflecting member is provided that allows light to pass through the optical image conversion element multiple times.

(Embodiment) FIG. 1 is a schematic diagram of an embodiment of the present invention. In the figure, reference numeral 1 denotes an optical image conversion element having an electro-optic effect such as a photoconductive effect or an electro-optic effect, such as a BSO. 2 and 2' are insulating films, and 3 and 3' are transparent electrodes.

10 is an antireflection film provided on one transparent electrode 3' side. Reference numeral 11 denotes an opening provided for each pixel. 12
is a reflective portion, which is provided for each pixel in a part of one transparent electrode 3 side. 13a is a concave substrate having a plurality of condensing reflecting surfaces 13 having a constant refractive power, which are provided integrally or independently on the transparent electrode 3' side.

Further, the light collecting reflective surface 13 is provided corresponding to each pixel. Reference numeral 5 indicates manual image writing light, and reference numeral 6 indicates image reading light, which is composed of, for example, linearly polarized light having a polarization axis in a plane parallel to the plane of the paper. Reference numeral 14 denotes a wavelength selection filter which has a spectral characteristic of transmitting light having the wavelength of the writing light 5 and reflecting light having the wavelength of the reading light 6. 15 is a polarizing beam splitter 116 is a coherent optical image read out.

Next, the basic operation of this embodiment will be explained using BSO as an example.

When the BSO is irradiated with writing light in the absorption wavelength range for the BSO, carriers are excited within the BSO, and due to the photoconductive effect, the carriers move due to a pre-applied voltage and are trapped at the boundary between the crystal and the insulating film. . The electric field caused by the trapped carriers acts in the direction of canceling the applied electric field,
A voltage distribution is formed in the BSO single crystal according to the irradiation amount, that is, according to the manual image intensity distribution.

Here, before the writing light is irradiated, the applied voltage is applied to the BSO single crystal plate surface. At this time, if the applied voltage is set to a half-wavelength voltage, the BSO can be arranged so that the two optical axes Ox and Oy correspond to the X direction and the If readout light with a polarization plane is incident in a direction that is 45 degrees to
Due to the birefringence generated in the BSO, the output light of the readout light becomes linearly polarized light orthogonal to the polarization direction of the incident light.

Next, in the state after the write light is irradiated, the applied voltage changes according to the input image intensity distribution, and the polarization state of the read light changes according to the voltage distribution corresponding to the amount of change at this time.

For example, when sufficiently strong light is incident on a certain region, the initial applied voltage is completely canceled out, no electric field is applied to the BSO single crystal in this region, the BSO single crystal becomes isodirectional, and the polarization state of the readout light changes. The light is emitted in the same linearly polarized state as when the light is emitted. The wavelength of the readout light is within the transmission wavelength range for the BSO single crystal so as not to cause a photoconductive effect.

If the polarization axes of the polarizer and analyzer for the BSO are set perpendicular to each other, a negative type will be obtained in which the amount of readout light will decrease according to the irradiation amount of the writing light, and on the other hand, if they are made parallel, a positive type will be obtained. . Taking the screw type as an example, the voltage applied to the BSO single crystal and the phase delay amount Δ of the two optical axes Ox and Oy
The relationship between φ is where the wavelength is λ and the refractive index of the BSO single crystal is n. ,1
If the electro-optic coefficient is γ41, then Δφ−(2π/λ) no y 41 (V b −
V c)...(2). Also, the relationship between the phase delay amount Δφ and the amount of transmitted light ■0 is 70-I-5in2 (Δφ/2) -- where ■ is the intensity of the incident light amount.
-----(3). Here, vb is a voltage previously applied to the BSO single crystal, and Vc is a cancellation voltage generated by carriers.

The transmitted light ff1lo is maximum when Δφ=π, and the applied voltage at this time is the half-wave voltage V with respect to the wavelength of the readout light.
It is π.

Since the maximum value of 1Vb-Vcl is vb, it is sufficient to set vb to Vπ in order to increase the dynamic range of IO/I. However, in this embodiment, vb
is set to a relatively low value, and instead, the readout light is applied multiple times to the same area in the BSO as shown in Figure 1.
By passing, the phase delay of one pass is added,
It is characterized by obtaining a sufficient half-wavelength phase delay.

In particular, in this embodiment, the optical activity is canceled by making the readout light pass through the BSO single crystal multiple times. As a result, the applied voltage required for the BSO single crystal in this example is 1/the number of times the half-wave voltage passes.

Next, the operation of the embodiment shown in FIG. 1 will be explained. 1st
In the figure, an applied voltage is applied to the BSO 1 via the transparent electrode 3°3'. The writing light 5 is B from the right direction.
After entering the SO1 and being reflected by the reflection section 12 on the left end surface,
Ejects from the incident side. During this time, light is absorbed by the BSO single crystal and carriers are formed. The readout light 6 has, for example, a polarization plane parallel to the plane of the paper, passes through the BSO 1 from the aperture 11 via the polarization beam splitter 15 from the left side, and reaches the concave portion 13 provided as a condensing reflective surface. The readout light 6 reflected by the concave portion 13 passes through the BSOl again and is reflected by the reflecting portion 12 on the left end surface other than the opening 11, and is reflected by the BSOl.
It enters SO1.

Repeat this kind of repetition multiple times.

Thereafter, in this embodiment, as shown in the figure, the readout light 6 is configured to be at the same incident position of the aperture 11, that is, the reciprocating path of the light returns halfway.

In addition, each element may be set so that the readout light 6 is emitted from another adjacent opening 11a, for example, as shown in FIG. 2.

In this embodiment, the refractive power of the concave portion 13 and the set position of the reflecting portion 12 are determined depending on the number of times the readout light goes back and forth.

In particular, each element is set so that the readout light 6 does not diverge while reciprocating within the BSO and before being emitted. Opening 1
Of the readout light emitted from 1 or lla, B50I
The readout light modulated by the polarization beam splitter 15 reflects the readout light, that is, the light having a polarization plane perpendicular to the plane of the paper,
The light is guided to a predetermined position as a coherent optical image.

In the above explanation, BSO was used as the electro-optic crystal, but in the present invention, for example, Bi1□GeO□ is used. (
BGO), Bj, 2Ti 02o, Ba2Na Nb5
0,5(BNN), GaAs, ZnS, CdS, B
a Ti 03. Li Nb O3, Li Ta 03
Electro-optic crystals such as the following are also suitable.

Further, the concave substrate 13a having the concave portion 13 has an upper appearance,
It has a shape in which cylindrical lenses or fly's-eye lenses are lined up two-dimensionally, and it can be used with so-called molding methods such as replica, compression, and injection, ion,
It can be obtained using a dry etching method using plasma or the like, or a photolithography method using a photosensitive resin such as a resist.

Instead of the above concave substrate, refractive power may be obtained by forming a refractive index distribution in the substrate by a method such as ion exchange.

In addition, in this embodiment, if the number of times the readout light passes through the BSOl is small or the opening is wide, or the divergence of the readout light is not a problem, a simple flat part may be used instead of the concave part. good.

FIG. 3 is a schematic diagram of another embodiment of the BSO element used in the optical image conversion device of the present invention. The BSO element shown in the figure is manufactured as follows.

First, an AI film is deposited on a transparent glass substrate 17 to a thickness of 2000 mm, and then a line width of 70 mm is coated using photoresist (Microposit 1350 (manufactured by Shipley) is used here).
A grid-like A1 pattern 18 with a pitch of 100 μm and a pitch of 100 μm was obtained. On top of this, 1000 pieces of Zr07 (zirconium oxide) 19 were attached as an insulating film, and a (100)-plane BSO crystal 20 polished to a thickness of 100 μm was adhered with a transparent adhesive. ZrO as an insulating film on the opposite side to the pasting side.
219 was deposited by 2,000 people, and ITO (indylum tin oxide) 21 was deposited by 1,200 people as a transparent electrode.

Next, a replica agent is dripped from above, and the master substrate is pressed to form a cylinder lens array-shaped concave surface 2 as shown in the figure.
I got 2.

The above film structure is BSO(n-1,5), Zr
02(n-2,1,λ/2)I To (n=1.8
, λ/4), replica (n=1.5), and B50
- Has an anti-reflection effect between replicas. A cold filter 23 made of a dielectric multilayer film is formed on the concave surface of the replica, and has the characteristic of reflecting infrared light but transmitting visible light.

On the outside of the device having the above configuration, a polarizing beam splitter is arranged on the side opposite to the concave surface 22 at an angle of 450 with respect to the device surface.

Next, to explain the operation when the BSO element shown in FIG. 3 is placed in the position shown in FIG.
A voltage is applied between the electrode and the ITO electrode. A manual image as shown in FIG. 1 is illuminated with blue light as a writing light and imaged on the BSO surface. The portion irradiated with the writing light changes due to the electric field. The readout light uses a semiconductor laser with a wavelength of 8300 nm, and after passing through a polarizing beam splitter, it enters the element with a polarization direction parallel to the plane of the paper. The incident light reciprocates approximately 10 times within the element and exits from the aperture. At this time, the polarized light component in the direction perpendicular to the paper surface increases depending on the intensity of the writing light, and only that component is reflected by the polarizing beam splitter.

By using the reflected light at this time, a coherent optical image by semiconductor laser light is obtained.

Another configuration of the BSO element is, for example, by forming an ITO film to a thickness of 1000 nm on a Gaussian substrate 17 shown in FIG. are arranged in a grid pattern with a line width of 40 μm and a pitch of 60 μm.

The rest of the configuration is the same as the configuration shown in FIG. In this case an electrostatic field is applied between both ITO electrodes. In this embodiment, the resolution of the optical image is improved because the pitch of the grid pattern is finer, and because the writing light passes through the element almost once (in the embodiment shown in Fig. 3, it is reflected by the AI pattern). (at least two passes) compared to the embodiment of FIG. However, since the effective amount of light is reduced, the sensitivity is low. In addition, various configurations can be adopted depending on the purpose.

(Effects of the Invention) According to the present invention, by adopting a configuration in which the image readout light passes through the optical image conversion element multiple times as described in n1,
It is possible to achieve an optical image conversion device that can be used in a wide range of applications by reducing the voltage applied to the optical image conversion element.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention, and FIG. 2 is a schematic diagram of an embodiment of the present invention. FIG. 3 is a schematic diagram of a portion of another embodiment of the present invention;
FIGS. 4 and 5 are explanatory diagrams of conventional optical image conversion devices, respectively. In the figure, 1 and 20 are B5O12, 2' is an insulating plate, and 3.3'
, 21 is a transparent electrode, 5 is a writing light, 6 is a reading light,
10 is an antireflection film; 11. lla is an aperture, 12 is a reflective part, 13 is a concave part, 14 is a wavelength selection filter, 15 is a polarizing beam splitter, 116 is a coherent optical image, 17 is a glass substrate, and 18 is an AI pattern.

Claims (4)

[Claims] (1) In an optical image conversion device that writes and reads images using an optical image conversion element whose electrical properties change due to optical action, when reading out the image, readout light is transmitted to the optical image conversion element. An optical image conversion device characterized by comprising a reflecting member that allows the light to pass through the image multiple times. (2) A part of the optical image conversion element is provided with an opening for inputting the readout light, and the reflecting member receives the readout light that enters through the opening and passes through the optical image conversion element. 2. The optical image conversion device according to claim 1, wherein the optical image conversion device is provided as a part of the optical image conversion device and/or independently of the optical image conversion device for re-incidence. (3) The optical image conversion device according to claim 2, wherein the aperture is provided corresponding to each pixel. (4) The optical image conversion device according to claim 3, wherein a part of the reflecting member is a light collecting reflecting surface and is provided corresponding to each pixel.