JPH06175092A - Spatial optical modulation element - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an interference pattern of reflected light caused by a transparent electrode. CONSTITUTION:Transparent insulating films 3 and 4 are provided on both sides of a BSO crystal body 1. A laminated body formed by laminating transference electrode films 9 and 10 and reflection preventing films 7 and 8 on glass substrates 11 and 12 is attached and connected to the transparent insulating film. By such constitution, the reflected light from the transparent electrode is prevented, and then the undesired interference pattern is prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial light modulator using an electro-optic crystal such as BSO.

[0002]

2. Description of the Related Art Conventionally, as a spatial light modulator using an electro-optic crystal material, a PROM element (Pockels Readable Optical
Modulator) is known. In this PROM element, for example, Bi ₁₂ SiO ₂₀ single crystal (BS
O) is used, a transparent insulating film is formed on one side or both sides of the BSO single crystal, and a transparent electrode film is formed on these transparent insulating films, so that the glass substrates are adhesively bonded to each other. Image information is written by utilizing the photoconductive effect, and image information is read by utilizing the Pockels effect. That is, when writing image information, writing light is irradiated with a DC bias voltage applied to the PROM element to form polarized charges corresponding to the image information inside the element to perform image recording, and the information is recorded. When the image information is read out, linearly polarized light is projected in a DC bias or non-biased state, and the image information is read out by utilizing the Pockels effect based on the polarization charge formed inside. When the image recording / reproducing apparatus using the PROM element is used, an incoherent light image can be converted into a coherent light image and an optical Fourier transform can be performed, so that various advantages can be achieved in image analysis.

[0003]

When recording or reproducing information on a PROM element, coherent light such as laser light is often used. Therefore, when using a PROM element, it is extremely important to prevent the occurrence of interference patterns in order to record a clear image. However, the refractive index of each material layer constituting the PROM element is BS
O is 2.53, the transparent insulating film is 1.46, the transparent electrode film is 1.90, and the glass substrate is 1.46, and the refractive index is discontinuous from the light incident side to the light emitting side. Therefore, reflection occurs at the interface between each material layer, and when recording and reproducing with coherent light, the reflected light at each interface interferes with each other,
As a result, undesired interference fringes occur. In the case of an irregular pattern, this interference fringe is recorded as noise, which has been a major obstacle in recording and reproducing a clear image.

Therefore, an object of the present invention is to realize a spatial light modulator capable of preventing the occurrence of an irregular interference pattern due to the reflected light generated at the interface of each material layer and recording and reproducing clear image information. .

[0005]

A spatial light modulator according to the present invention includes an electro-optical crystal body that generates electric charges according to the amount of writing light, and transparent insulating films formed on both sides of the electro-optical crystal body. And a transparent electrode film adjacent to each of these transparent insulating films, wherein
An antireflection film is formed on at least one transparent electrode film of the individual transparent electrode films.

[0006]

[Function] Since the transparent electrode film generally has a high refractive index,
In a spatial light modulator using a transparent electrode film, a mismatch in refractive index occurs at the front and rear interfaces of the transparent electrode film, resulting in unwanted reflected light. Therefore, in the present invention, the antireflection film is formed so as to be in direct contact with the transparent electrode film.
At this time, since the film thickness of the transparent electrode film can be made extremely thin, the transparent electrode and the antireflection film are laminated in consideration of the refractive index and the film thickness of the transparent electrode so as to exhibit the antireflection effect as a whole. . According to this structure, it is possible to simultaneously remove the reflection on both the incident surface and the emission surface of the transparent electrode film. As a result, even when an image is recorded / reproduced using coherent light, it is possible to prevent the generation of an unwanted interference pattern and record / reproduce a clear image.

[0007]

1 is a sectional view showing the structure of an example of a spatial light modulator according to the present invention. In this example, a transmissive PROM element will be described as an example. As an electro-optical crystal, the thickness is 30
A 0 μm Bi ₁₂ SiO ₂₀ single crystal plate (BSO plate) 1 is used. Epoxy resin layer that is a transparent adhesive on both sides of this BSO plate (refractive index 1.56, thickness 1.5 μm)
The transparent insulating layers 3 and 4 made of synthetic quartz glass (thickness 10 μm, refractive index 1.46) are bonded to each other via 2 via adhesive. Antireflection films 7 and 8 are provided on the transparent insulating layers 3 and 4 via transparent adhesives 5 and 6, respectively. Further, on the antireflection films 7 and 8, a transparent electrode film (thickness 400
Å and refractive index 1.90) respectively. Furthermore, on the transparent electrode films 9 and 10, a glass substrate (thickness 3 mm, refractive index 1.4
6) Place. When manufacturing this PROM element, the transparent electrode film 9 is formed on the glass substrate 11 by vacuum evaporation, the antireflection film 7 is vacuum evaporated on this transparent electrode film 9, and this laminated structure is bonded by epoxy resin. Join. Similarly, on the glass substrate 12 side, the transparent electrode 10 and the antireflection film 8 are sequentially laminated on the glass substrate 12 by vacuum vapor deposition. Further, connection terminals 13 and 14 are provided on the transparent electrode films 9 and 10, respectively, and an electric field is applied to the BSO plate 1 via these connection terminals.

Next, a method of recording and reproducing image information on this PROM element will be described. Bi ₁₂ SiO ₂₀ has photoconductivity with respect to blue light, and therefore, wavelength light in the blue region is used as writing light. When writing light is projected from the direction of the arrow, a charge corresponding to the writing light intensity is generated due to the photoconductive effect of the BSO plate. At this time, when a DC bias voltage is applied between the terminals 13 and 14, the charges generated by the photoconductive effect are polarized and held as polarized charges for image recording. On the other hand, when playing back the recorded image information,
Reproduction light (light having a wavelength other than blue light, for example, red light) is projected toward the PROM element. When polarization charges are formed inside the BSO plate, an electric field having an intensity corresponding to the polarization charges is formed, and birefringence occurs. Therefore, when linearly polarized light is projected as the reproduction light, elliptically polarized light corresponding to the polarization charge is emitted from the PROM element. It can be reproduced as an image.

On the other hand, in the PROM element having the above-mentioned structure, there is a portion where the refractive index is discontinuous. For example, since the refractive index of the transparent electrode film is 1.90, which is higher than the refractive index of the surrounding members, the transparent electrode film Reflection occurs at the front and back interfaces. Also, B
The SO single crystal also has a refractive index of 2.53, which is much higher than the refractive index of the epoxy resin film that is a surrounding member thereof, so that reflection occurs at the interface before and after that. For writing and reproducing an image in the PROM element, an argon ion laser having a wavelength of 488 nm and a helium neon laser having a wavelength of 633 nm are often used as light sources. Since these laser lights have high coherence, if there are two reflecting surfaces, the lights repeatedly reflect between them and interfere with each other to form interference fringes. The interference fringes generated at the time of writing and reproducing make the reproduced image unclear. Due to the multiple reflection between the both surfaces of the BSO single crystal among the above-mentioned reflecting surfaces existing in the PROM element, and the multiple reflection between the transparent electrode film and the surface of the BSO single crystal adjacent to the transparent electrode film. The interference fringes generated have a high contrast and adversely affect the reproduced image. Therefore, in the present invention, a taper is provided so that the surface of the BSO plate 1 on the light emission side is inclined by 25 minutes with respect to the surface orthogonal to the optical axis. By forming the taper in this way, the light incident surface 1a of the BSO plate 1 among the causes of the interference film described above is generated.
The interference pattern formed by the reflected light at 1 and the reflected light at the light emitting surface 1b becomes a regular interference pattern, and therefore does not become noise, and the adverse effect due to reflection can be removed.

Next, of the above-mentioned two sets of causes of interference fringes, consideration will be given to the multiple reflection on the latter set of the transparent electrode film and the surface of the BSO single crystal adjacent to the latter. In order to eliminate the influence of interference fringes by forming a taper between them as in the case described above, it is necessary to form a taper in the insulating layer sandwiched between both reflection layers. However, variations in the thickness of the insulating layer caused by this taper make the characteristics of the element non-uniform, which adversely affects the element characteristics. Another method of removing interference fringes is to provide an antireflection film on either surface of a set of reflecting surfaces to reduce the reflectance of that surface. In this case, it is conceivable to provide an antireflection film on the BSO surface or the transparent electrode film surface. But,
In the former case, when the antireflection film has a low electrical resistivity,
When the image is stored in the PROM element, the charge moves through the antireflection film, so that the distribution of the charge generated in the element is disturbed and the reproduced image is deteriorated. Therefore, a high-resistivity antireflection film is required. However, it is difficult to manufacture an antireflection film having a high resistivity. Therefore, it is not desirable to provide an antireflection film on the surface of BSO. On the other hand, the antireflection film provided on the surface of the transparent electrode is not required to have the above-mentioned electrical characteristics, so that it is easy to manufacture. Further, since both the transparent electrode film and the antireflection film can be integrally formed by a film forming method such as a vacuum vapor deposition method or a sputtering method, both can be formed in one step, which is also advantageous in streamlining the steps. Therefore, in this example, the antireflection films 7 and 8 are provided on the exit surface and the entrance surface of the transparent electrode films 9 and 10, respectively, to eliminate the occurrence of the interference pattern due to the reflected light. The reflection on the transparent electrode films 9 and 10 is
The interference pattern is generated on both the incident surface and the emission surface, and the interference pattern is generated between the reflected light on the incident surface and the reflected light on the emission surface. Therefore, it is possible to eliminate the occurrence of the interference pattern by removing one of the reflected lights on the incident surface or the exit surface. However,
If it is possible to remove both the reflected light on the incident surface and the emitted surface, then P
Multiple reflections occurring between the ROM device and other interfaces are reduced, and noise can be further reduced. Further, if the transparent electrode films 9 and 10 are made thin, the reflected light on both the incident surface and the emission surface can be removed by appropriately laminating the transparent electrode film and the antireflection film.
Therefore, in this example, when the antireflection films 7 and 8 are laminated on the transparent electrodes 9 and 10, the film thickness and the refractive index of the transparent electrode film are taken into consideration in both the incident surface and the emission surface of the transparent electrode film. They are integrally laminated so that the reflected light becomes almost zero as a whole. With such a configuration, the reflected light on the incident surface and the exit surface can be removed by forming only one antireflection film, and the generation of noise during recording and reproduction can be further reduced. Thus, as the antireflection film, for example, a laminated structure of TiO ₂ and SiO ₂ can be used.

FIG. 2 shows the reflection characteristics when a transparent electrode film and an antireflection film are laminated on a glass substrate. In this example,
A 0.04 μm thick indium tin oxide film was used as the transparent electrode film, and a laminated body of TiO ₂ and SiO ₂ was used as the reflection removal film. In FIG. 2, the horizontal axis represents wavelength (nm),
The vertical axis represents the reflectance (%). As is clear from FIG.
It was possible to reduce the reflectance to 0.3% or less for the writing light having the wavelength of 488 nm, and to reduce the reflectance to 0.01% or less for the reproducing light having the wavelength of 633 nm.

Next, the effect of the antireflection film will be described. FIG. 3 is a projection photograph at the time of reproducing when a white background pattern is recorded when the antireflection film of the PROM element shown in FIG. 1 is not formed, and FIG. 4 is a projection photograph when the antireflection film is formed. As shown in FIG. 3, when there is no antireflection film, a strong interference pattern occurs. On the other hand, when the antireflection film is formed, the interference pattern is almost removed.

FIG. 5 is a sectional view showing a modification of the spatial light modulator according to the present invention. This example shows an example applied to a reflective PROM element. A metal reflective film 21 is formed on one side of the BSO plate 20 by vapor deposition. The metal reflection film 21 is made of a metal film of titanium, aluminum or the like,
It functions not only as a reflective layer but also as an electrode. Epoxy resin layer 2 on the other side of BSO plate 20
Insulating film 23 is provided via 2. A glass substrate 25 and a transparent electrode film 2 are formed on the insulating film 23 via an epoxy resin 24.
A laminated body of 6 and the antireflection film 27 is provided. Writing and reproducing of information is performed by projecting writing light and reproducing light from the glass substrate 25 side. Also in this example, an undesired interference pattern is generated by the reflected light generated by the mismatch of the refractive index before and after the transparent electrode film. Therefore, by forming the antireflection film 27 on the transparent electrode film 26, it is possible to prevent the occurrence of an interference pattern and record and reproduce a clear image.

The present invention is not limited to the above-described embodiments, and various changes and modifications can be made. For example, a transparent PRO
In the M element, the antireflection films are formed on the transparent electrode films on both sides of the BSO plate respectively, but of course, even when the antireflection film is formed only on the transparent electrode film on one side, an undesired interference pattern is generated. It can be sufficiently reduced.

Further, in the above-mentioned embodiments, the antireflection film is formed between the transparent electrode film and the transparent insulating film, but the antireflection film is provided on either the light incident side or the light emitting side of the transparent electrode film. Even if formed, the same effect can be achieved.

[0016]

As described above, according to the present invention,
Since the antireflection film is integrally laminated on the transparent electrode film with a large refractive index, the reflected light generated at the interface of the transparent electrode film can be reduced, and therefore a clear image without interference patterns can be recorded. And can be replayed. Moreover, since the transparent electrode film and the antireflection film are integrally laminated in the same process, the manufacturing process is facilitated.

[Brief description of drawings]

FIG. 1 is a sectional view showing a configuration of an example of a spatial light modulator according to the invention.

FIG. 2 is a graph showing the reflection characteristics of a laminate of a transparent electrode film and an antireflection film.

FIG. 3 is a photograph showing a projected image in the case where there is no reflection preventing film.

FIG. 4 is a photograph showing a projected image with an antireflection film.

FIG. 5 is a sectional view showing a modified example of the spatial light modulator according to the present invention.

[Explanation of symbols]

 1 BSO plate 2, 5, 6 epoxy resin layer 3, 4 transparent insulating film 7, 8 antireflection film 9, 10 transparent electrode film 11, 12 glass substrate

Claims (4)

[Claims] 1. An electro-optical crystal body that generates electric charges according to the amount of writing light, transparent insulating films formed on both sides of the electro-optical crystal body, and transparent electrode films adjacent to these transparent insulating films. A spatial light modulation element comprising: an antireflection film formed on at least one transparent electrode film of the two transparent electrode films. 2. An electro-optic crystal body that generates electric charges according to the amount of writing light, a transparent electrode film provided on one side of the electro-optic crystal body via an insulating film, and the electro-optic crystal body. A spatial light modulation element comprising a reflective electrode film provided on the other side of the above, wherein an antireflection film is formed on the transparent electrode film. 3. The antireflection film is laminated on the transparent electrode film so as to remove reflected light at both interfaces of the transparent electrode film.
Alternatively, the spatial light modulator according to item 2. 4. The spatial light modulator according to claim 1, wherein one surface of the electro-optic crystal body is formed so as to be inclined with respect to a surface orthogonal to an optical axis. .