JPH04296716A - Special optical modulator - Google Patents

Abstract

PURPOSE:To prevent the occurrence of interference fringes due to reflection from transparent electrode films and transparent adhesive layers when coherent light for readout is passed through a special optical modulator. CONSTITUTION:Transparent electrode films 2A, 2B are formed on the surfaces of substrates 1A, 1B and insulating layers 4A, 4B are stuck to the insides of the films 2A, 2B with transparent adhesive layers 3A, 3B. An electro-optical crystal layer 6 made of a Bi12SiO20. single crystal, etc., is held between the insulating layers 4A, 4B by adhesion. The optical path of the transparent electrode films 2A, 2B is made 0.47-0.52 time the wavelength of coherent light for readout passed through the resulting special optical modulator.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is directed to a Pockels Read Optical Modulator (PROM).
The invention relates to spatial light modulators such as optical modulators.

0002

[Prior Art] Among spatial light modulators, Bi12SiO
20 (BSO) A PROM element using a single crystal is
Utilizing the photoconductivity of the BSO single crystal, the light intensity distribution of written image information is converted into a charge distribution within the single crystal plate and accumulated, and then the electro-optic effect generated by the electric field created by this charge distribution is utilized. This converts it into the intensity distribution of readout light. Therefore, this type of spatial light modulator is a BSO
It consists of a single crystal plate, an insulating layer surrounding it, and a transparent electrode.

In particular, in a PROM element that converts an incoherent optical image into a coherent optical image,
In order to prevent interference fringes from occurring in images read out by coherent light, the electro-optic crystal layer is provided with a taper. Therefore, the pair of main surfaces of this layer are inclined at a predetermined angle with respect to each other, but this angle varies depending on the element or device, and needs to be about 15 minutes or more, for example. As a result, the pitch of interference fringes generated in the readout light image is reduced to such an extent that it cannot be discerned with the naked eye.

0004

[Problem to be solved by the invention] However, the inventor of the present invention
When the electro-optic crystal layer was tapered by about 15 minutes and read-out experiments using laser light were carried out, it was found that minute interference fringes still appeared in the read-out light image.

An object of the present invention is to eliminate interference fringes that are not directly caused by reflection between a pair of principal surfaces of an electro-optic crystal layer, as described above.

[0006]

[Means for Solving the Problems] The present invention provides an electro-optic crystal layer, an insulating layer provided on at least one side of the electro-optic crystal layer, a glass substrate on which a transparent electrode film is formed, and a glass substrate of the glass substrate. A spatial light modulation element having at least a transparent adhesive layer bonding the insulating layer and the surface on which the transparent electrode film is formed, wherein the optical path length of the transparent electrode film is the readout of the spatial light modulation element. This relates to a spatial light modulator whose wavelength is 0.47 times or more and 0.52 times or less the wavelength of coherent light.

[0007]

[Function] The present inventor mainly concerns PROM elements.
As a result of examining interference fringes in readout images using coherent light, we found that reflections at the two interfaces of the transparent electrode film and reflections at the transparent adhesive layer, which had been overlooked until now, are the causes of interference fringes. They discovered this and completed the present invention. According to the present invention, by setting the optical path length of the transparent electrode film to 0.47 times or more and 0.52 times or less the wavelength of the coherent light for readout of the spatial light modulation element, the contrast of the interference fringes due to the above reflection is achieved. This made it possible to make it so thin that it was difficult to see it in the readout image. This principle will be described later.

[0008]

[Example] First, a PROM suitable for applying the present invention
An example of an element is shown below. FIG. 1 is a cross-sectional view of such a PROM device. First, for example, a quadrilateral substrate 1A is prepared. The substrate 1A is preferably formed of glass such as synthetic quartz glass or borosilicate glass. This board 1
A transparent electrode film 2A is formed on the surface of A by a vapor deposition method or the like. At this time, a transparent electrode film 2 is placed on the corner part of the substrate 1A.
Preferably, a lead portion is formed for connecting A to an external power source.

Next, an insulating plate of a predetermined thickness is bonded to the surface of the substrate 1A via a transparent adhesive layer 3A. Next, this insulating plate is ground and optically polished to form an insulating layer 4A as shown in FIG. Then, an electro-optic crystal plate is adhered and fixed to the surface of the insulating layer 4A via a transparent adhesive layer 5A. In this state, the surface of the electro-optic crystal plate is ground and optically polished to form an electro-optic crystal layer 6 of a predetermined thickness, as shown in FIG. This electro-optic crystal layer 6 is provided with an inclination or taper of, for example, about 15 minutes.

On the other hand, in exactly the same manner as described above, FIG.
As shown in , a transparent electrode film 2B having a lead portion is formed on the surface of the substrate 1B, and an insulating plate is bonded to the surface of the substrate 1B via a transparent adhesive layer 3B so as to cover the transparent electrode film 2B. do. This insulating plate is then ground and optically polished to form an insulating layer 4B of a predetermined thickness. This insulating layer 4B
is adhered to the electro-optic crystal layer 6 by a transparent adhesive layer 5B. In this way, the PROM element shown in FIG. 1 is constructed.

In the PROM element shown in FIG. 1, the insulating layers 4A and 4B are provided on both sides of the electro-optic crystal layer 6, but it is also possible to omit one of the insulating layers. In addition, a pair of transparent electrode films 2A and 2B are respectively attached to the substrate 1A.
, 1B, and the electro-optic crystal layer 6 and the insulating layers 4A, 4B are sandwiched between the pair of transparent electrode films 2A and 2B, but as described above, when one of the insulating layers 4B is omitted, , one transparent electrode film 2B can also be formed on the surface of the electro-optic crystal layer 6 by vapor deposition.

Here, in FIG. 1, the transparent electrodes 2A, 2
The optical path length of B is set to be 0.47 times or more and 0.52 times or less the wavelength of the coherent light for reading out of this spatial light modulation element. That is, according to the research of the present invention, it has become clear that the cause of interference fringes that is not due to reflection at the end face of the electro-optic crystal layer 6 is due to reflection at the end faces of the transparent electrode films 2A, 2B and the transparent adhesive layer 3A. Ta. By limiting the optical path length of the transparent electrode film as described above, no interference fringes were observed even when reflections in the transparent electrode film and the transparent adhesive layer were taken into consideration as a whole.

Furthermore, in order to prove this point, a model experiment conducted by the present inventor will be described. First, a sample having the configuration shown in FIG. 2 was prepared, and the transmittance of this sample was measured. That is, an antireflection film 7 is formed on the surface of a synthetic quartz glass substrate 8 having a square planar shape with a side of 40 mm and a thickness of 3 mm.
A was formed. In addition, In2O3 is applied to the surface of the substrate 8 opposite to the anti-reflective film 7A by electron beam evaporation.
A transparent electrode film 9 made of a mixture of and Sn2O3 was formed.

Furthermore, an antireflection film 7B was formed on the surface of the insulating plate 11 made of synthetic quartz glass. The transparent electrode film 9 and the insulating plate 11 were bonded together with a transparent adhesive layer 10. As the material of the transparent adhesive layer 10, a two-component optical epoxy resin with a refractive index n=1.56 was used.

In this sample, an electro-optic crystal layer was not used to eliminate the effects of reflection and interference fringes caused by the electro-optic crystal layer. Further, antireflection films 7A and 7B were provided on the surfaces of the glass substrate 8 and the insulating plate 11 to eliminate the influence of reflection on these surfaces. Thereby, the influence of reflection by the transparent electrode film 9 and the transparent adhesive layer 10 can be measured.

Here, for convenience, the optical path length n of the transparent electrode film 9
The following relational expression is set between d and the wavelength λ of the coherent light for reading. nd=aλ Then, the sample of FIG. 2 was irradiated with a laser beam of λ=633 nm to obtain each graph shown in FIGS. 3 to 7. However, in order to also investigate the influence of reflection on the transparent adhesive layer 10, the layer thickness of the transparent adhesive layer 10 was also changed in each of FIGS. 3 to 7.

In the example shown in FIG. 3, the transparent adhesive layer 10
The layer thickness was set to 0 μm. The peak of a is about 0.50, and the transmittance changes slowly. When the present inventor visually observed the transmitted light, no interference fringes were observed in the transmitted light if the transmittance was 99.5% or more. This point was the same in each example shown in FIGS. 4 to 7. When a=0.46 to 0.54, the transmitted light was 99.5% or more.

In the example shown in FIG. 4, the transparent adhesive layer 1
The film thickness of 0 was set to 0.7 μm. Therefore, this optical path length is 0.7×1.56 μm, and λ=633 μm
It was approximately 1.7 times as large. In this case, it was found that the transmittance oscillated and changed due to the influence of the transparent adhesive layer 10. It was also found that the peak of transmittance does not exist at a=0.50, but rather the minimum value of transmittance exists near a=0.50. Also, a=0.45 to 0.56
Within this range, the transmittance was 99.5% or more.

In the example shown in FIG. 5, the transparent adhesive layer 1
The thickness of 0 was set to 1.7 μm. Therefore, this optical path length is 1.7 × 1.56 μm, which is approximately 4.2 of λ.
It was double that. Moreover, compared to the graph of FIG. 4, the intervals between vibrations are further narrowed. Also, a=0.46 to 0.
In the range of 53, the transmittance was 99.5% or more.

In the example shown in FIG. 6, the transparent adhesive layer 1
The thickness of 0 was set to 2.7 μm. Therefore, this optical path length is 2.7 × 1.56 μm, which is approximately 6.7 of λ.
It was double that. Even when compared with the graph of FIG. 5, the intervals between vibrations are even smaller. Also, a=0.4
The transmittance was 99.5% or more in the range of 7 to 0.52. Further, the local maximum values are around 0.48 and 0.51.

In the example shown in FIG. 7, the thickness of the transparent adhesive layer 10 was 3.7 μm. Therefore, this optical path length is
It was 3.7×1.56 μm, which was about 8.4 times λ. Also, compared to the graph of FIG. 6, the intervals between vibrations are even smaller. Also a=0.45~0.53
The transmittance was 99.5% or more in the range of . Furthermore, the number of local maximum peaks increases from two to three in the range where the transmittance is 99.5% or more. If the transparent adhesive layer becomes even thicker, the above-mentioned vibrations become even finer, and the number of peaks within the transmittance range of 99.5% or more increases accordingly.

[0022] If we combine the above experiments, a=0.47~
If it is in the range of 0.52, the transmittance will be 99.5% or more, and interference fringes due to the transparent electrode film and transparent adhesive layer will no longer be observed.

In reality, it is better to make the transparent adhesive layer thinner.
This is advantageous because it reduces the voltage drop and improves the performance of the device. However, there are limitations due to the properties of the optical adhesive, and there is some variation in the layer thickness during manufacturing. For example, when the present inventor conducted an experiment using the above-mentioned epoxy optical adhesive having a refractive index n=1.56, the average layer thickness was 1.
7 μm, with a maximum error of ±1 μm. However, even if such manufacturing variations are taken into account, a=0.47
If it is in the range of ~0.52, no interference fringes will occur, as described above.

[0024]

According to the present invention, since the optical path length of the transparent electrode film is set to 0.47 times or more and 0.52 times or less the wavelength of the coherent light for reading out the spatial light modulator, the transparent electrode film and The contrast of interference fringes due to reflection at the interface of the transparent adhesive layer can be reduced to such an extent that it cannot be seen in the readout light image.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a PROM element.

FIG. 2 is a front view showing an experimental sample.

FIG. 3 is a graph showing the relationship between a and transmittance when the thickness of the transparent adhesive layer is 0 μm.

FIG. 4 is a graph showing the relationship between a and transmittance when the thickness of the transparent adhesive layer is 0.7 μm.

FIG. 5 is a graph showing the relationship between a and transmittance when the thickness of the transparent adhesive layer is 1.7 μm.

FIG. 6 is a graph showing the relationship between a and transmittance when the thickness of the transparent adhesive layer is 2.7 μm.

FIG. 7 is a graph showing the relationship between a and transmittance when the thickness of the transparent adhesive layer is 3.7 μm.

[Explanation of symbols]

1A, 1B, 8 Substrate 2A, 2B, 9 Transparent electrode film 3A, 3B, 10 Transparent adhesive layer 4A, 4B
Insulating layer 6 Electro-optic crystal layer

Claims (1)

[Claims] 1. An electro-optic crystal layer, an insulating layer provided on at least one side of the electro-optic crystal layer, a glass substrate on which a transparent electrode film is formed, and a glass substrate on which the transparent electrode film of the glass substrate is formed. A spatial light modulation element having at least a transparent adhesive layer for bonding a side surface and the insulating layer, wherein the optical path length of the transparent electrode film is 0.0.5 times the wavelength of coherent light for readout of the spatial light modulation element. 47 times more, 0
．． A spatial light modulation element that is 52 times or less.