JPH04256920A - Manufacture of spatial optical modulating element - Google Patents

Abstract

PURPOSE:To make the area of the spatial optical modulating element large, to improve the yield at the time of machining an insulating layer and a single crystal layer, to make the insulating layer and single crystal layer homogeneous, and to reduce a wave front aberration when the spatial optical modulating element which uses single crystal such as Bi12SiO20 single crystal having electrooptic effect and photoconductive effect is manufactured. CONSTITUTION:An insulating plate is adhered onto a substrate 1 which has a transparent electrode film 2 and the end surface of this insulating plate is machined to form the insulating layer 4. Further, a single crystal plate 5 is adhered to the insulating layer 4 and the end surface 5a of the single crystal plate 5 is ground and optically polished to form the single crystal layer. A taper surface 8 is formed preferably on a surface 6 for machining, the substrate 1 is adhered to the tapered surface e8, and the single crystal plate 5 is machine along a surface A parallel to the lower flank of the substrate for machining.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to Bi12SiO20
(BSO) Spatial light modulator (PROM, P
Ockels Readout Optical Mo
dulator).

0002

2. Description of the Related Art Among spatial light modulators, a PROM element using a single crystal having an electro-optic effect and a photoconductive effect, such as a BSO single crystal, uses the photoconductive effect of the single crystal to write image information. The light intensity distribution is converted into a charge distribution within a single crystal plate and stored, and then converted into a readout light intensity distribution using the electro-optic effect produced by the electric field created by this charge distribution. Therefore, this type of spatial light modulation element is composed of the single crystal plate, an insulating layer sandwiching the single crystal plate, and transparent electrodes.

Conventionally, such a spatial light modulation element has been constructed using the above-mentioned single crystal plate whose both sides are optically polished and a parylene thin film or a mica cleavage film (insulator). Also,
There is a method of forming an insulating layer by vapor deposition. but,
Since the parylene thin film has a low dielectric strength voltage, it cannot fully exhibit the electro-optical effect characteristics of the single crystal. Mica films have inherent birefringence, which complicates the electro-optic properties of the device, and makes it difficult to create thin plates with uniform thickness and large area, making it difficult to create insulating layers. Yield during formation is poor.

[0004] In particular, in spatial light modulation elements that convert an incoherent light image into a coherent light image, it has been considered to provide a taper in the single crystal plate in order to prevent interference fringes. The size of the taper angle required at this time varies depending on the element and device, but for example, 1
It needs to be about 5 minutes long. Therefore, when manufacturing a spatial light modulator, the single crystal plate is processed into a tapered shape,
Insulating plates and electrode plates are successively glued to both sides.

However, if the single crystal plate is placed on a processing base, subjected to grinding processing and optical polishing, and then bonded, adhesive stress is applied non-uniformly to the single crystal when the adhesive hardens. Distortion occurs in the single crystal, causing wavefront aberration of light transmitted through the element. Furthermore, even if the single crystal plate with a thickness of several hundred μm is individually taper-processed, the precision of the taper angle cannot be improved because the grinding process is performed by applying a load to one side of the single-crystal plate. It is difficult to determine the direction of this taper.

[0006]

[Problems to be Solved by the Invention] An object of the present invention is to make it possible to increase the area of a spatial light modulator, to achieve a high yield when processing an insulating layer, and to form an insulating layer with a uniform thickness and homogeneity. An object of the present invention is to provide a method for manufacturing a spatial light modulation element. Another object of the present invention is to be able to form a single crystal layer having a large area of electro-optic effect and photoconductive effect, and to have a high yield.
It is an object of the present invention to provide a method for manufacturing a spatial light modulation element that can reduce wavefront aberration in the single crystal layer.

[0007]

[Means for Solving the Problems] The present invention involves bonding an insulating plate onto a substrate having a transparent electrode, processing the end face of the insulating plate to form an insulating layer, and then applying at least an electric current on the insulating layer. The present invention relates to a method of manufacturing a spatial light modulator characterized by providing an optical crystal layer, an insulating layer, and a substrate. Also,
The present invention involves bonding an electro-optic crystal plate onto a substrate having a transparent electrode and an insulating layer, processing the end face of the electro-optic crystal plate to form an electro-optic crystal layer, and then forming an electro-optic crystal layer on the electro-optic crystal layer. The present invention relates to a method for manufacturing a spatial light modulator, characterized in that at least an insulating layer and a substrate are provided on the top of the spatial light modulator.

[0008]

Embodiments First, a method of manufacturing a spatial light modulator according to an embodiment of the present invention will be described with reference to FIGS. 1 to 4. First, a substrate 1 is prepared, and a glass substrate or the like is used as the substrate 1. Next, a transparent electrode film 2 is formed on the substrate 1 by vapor deposition or the like. After bonding the insulating plate 3 to the substrate 1, the end face 3a of the insulating plate 3 is ground and optically polished to form an insulating layer 4 as shown in FIG.

Next, as shown in FIG. 3, a single crystal plate 5 having an electro-optical effect and a photoconductive effect is placed on the surface side of the insulating layer 4.
The end face 5a of the single crystal plate 5 is ground and optically polished to form the single crystal layer 7 as shown in FIG.

Separately, a transparent electrode film 2 is formed on the substrate 1 by vapor deposition or the like, an insulating plate 3 is bonded to the substrate 1, and the end surface 3a of the insulating plate 3 is ground and optically polished.
An insulating layer 4 as shown in FIG. Then, as shown in FIG. 4, the insulating layer 4 of this adhesive is adhered to the single crystal layer 7 to obtain a spatial light modulation element.

According to this manufacturing method, since the insulating layer 4 is formed by grinding and optically polishing the end face of the relatively thick insulating plate 3, the insulating thin plate made into a thin film is used from the beginning. Unlike the method of bonding to a crystal plate, the insulating layer does not curve during the bonding process, making it possible to form the insulating layer 4 with a more uniform and homogeneous thickness than before. The yield has improved, and furthermore, it has become possible to increase the area of the insulating layer 4. The thickness of the insulating plate 3 is preferably 1 mm or more. If the thickness of the insulating plate 3 is less than 1 mm, it will be deformed during adhesion, and the thickness of the insulating layer 4 will not be uniform.
This can cause variations in dielectric strength and element destruction due to discharge. More preferably, it is 1.5 mm or more, and even more preferably 2 mm or more. Further, the thickness of the insulating layer 4 is preferably 5 to 30 μm.

[0012] Furthermore, the thickness of the single crystal plate 5 is preferably relatively thick, such as 1 mm or more. Since the single crystal layer 7 is formed by grinding and optically polishing the end surface 5a, unlike the method of bonding a thin electro-optic crystal layer to a substrate etc. from the beginning, the adhesion of the single crystal plate 5 is difficult. The monocrystalline layer 7 does not undergo any curvature during the process and is therefore more homogeneous than before.
It has become possible to form the electro-optic crystal layer 7, the yield at the adhesion stage has improved, and it has also become possible to increase the area of the electro-optic crystal layer 7. More preferably, the thickness of the crystal plate 5 is 1.5 mm or more, and more preferably 2 mm or more.

[0013] If the thickness of the single crystal plate 5 is 1 mm or less, stress will be applied unevenly to the single crystal during curing of the adhesive, and
Distortion occurs in the single crystal layer 4, causing wavefront aberration of light transmitted through the element. Moreover, the thickness of the single crystal layer 4 is 30 to 50
0 μm is preferred.

Next, in a spatial light modulator that uses coherent light such as a laser beam as readout light, as described above, it is necessary to tape the single crystal layer 7 in order to prevent the generation of interference fringes. There is. For this purpose,
In this embodiment, a processing base 6 having a tapered surface 8 of, for example, 15 minutes is prepared in advance, and the substrate 1 is temporarily fixed to this tapered surface 8 to form the state shown in FIG. In this state, the lower surface 9 of the processing base 6 and the tapered surface 8 form a predetermined taper angle, for example, 15 minutes, and the tapered surface 8 and the end surface 5a of the single crystal plate 5 are parallel. Then, when the single crystal plate 5 is ground horizontally along the broken line A and then optically polished, the main surfaces on both sides of the single crystal layer 7 form a predetermined taper angle, that is, 15 minutes.

[0015] If the single crystal layer 7 is tapered by such a method, pressure is applied evenly over the entire surface of the single crystal plate 5 during the grinding process, so processing with good planar accuracy is possible. become. In addition, in the processing base 6,
By simply setting the taper angle between the lower surface 9 and the tapered surface 8 to a predetermined angle, the accuracy of the taper angle in the single crystal layer 7 can be maintained, and the direction of the taper can also be freely determined.

Next, a preferred example of the processing base 6 will be explained. FIG. 5 shows a processing base 6 according to a preferred example with a tapered surface 8.
FIG. 6 is an enlarged side view of this processing base 6, which is an enlarged plan view seen from the side. On the tapered surface 8 side of the processing base 6, a net-like recess 6a is formed by intersecting vertical and horizontal linear recesses that are perpendicular to each other.
are formed, the protrusions 6b are separated from each other by the mesh-like recesses 6a, and the protrusions 6b are arranged in a grid pattern vertically and horizontally. When temporarily fixing the substrate 1 to the tapered surface 8 of the processing base 6, an adhesive layer is interposed between the substrate 1 and the projections 6b. At this time, assuming that the tapered surface 8 is flat, even if pressure is applied uniformly to the entire substrate 1 during temporary fixing, the thickness of the adhesive layer will inevitably be uneven, and therefore the single crystal When the plate 5 is ground, an error in thickness occurs due to this. On the other hand, in this example, if pressure is applied evenly to the entire substrate 1, the adhesive in excess of the average will escape to the reticulated recesses 6a before curing, and as a result, the thickness of the adhesive layer will be constant. The processing accuracy of the single crystal plate 5 can be further improved.

Further, after the single crystal plate 5 is ground and optically polished, it is necessary to separate the substrate 1 from the processing base 6. Usually, an adhesive that can be removed by heating to about 80° C. is used for temporary fixing, but if this adhesive is used, the single crystal layer 7 will have a different coefficient of thermal expansion from the substrate 1. The flatness of the end face of the crystal layer 7 deteriorates or cracks occur in the crystal layer 7 due to deformation. In contrast, in this embodiment, an organic solvent in which the adhesive is soluble is prepared, at least the adhesive layer is immersed in this organic solvent, the adhesive is dissolved by ultrasonic cleaning, and the processing substrate 6 is removed from the substrate. Separate 1. With this method, the flatness of the end face of the single crystal layer 7 can be maintained well, and the occurrence of cracks in the single crystal layer 7 can also be prevented. In the embodiment, the insulating plate 3 was ground and then optically polished to form the pure edge layer 4, but the insulating plate 3 may be etched and then optically polished.

A more specific experimental example will be described. A borosilicate glass substrate 1 provided with a transparent electrode film 2 was prepared. In addition, a borosilicate glass insulating plate 3 with a thickness of 3 mm is prepared, and its end face 3a is surface ground with a surface grinder, sand-polished, and the abrasive grains used are 1) cerium oxide and 2) colloidal silica in this order. optically polished to a thickness of 10 μm.
An insulating layer 4 made of borosilicate glass was formed. Further, a BSO single crystal plate 5 having a thickness of 2.7 mm was prepared and bonded to the insulating layer 4. In addition, a processing base 6 as shown in FIGS. 5 and 6 is prepared,
The substrate 1 was bonded to the tapered surface 8 of the processing substrate 6. The slope of the tapered surface 8 with respect to the lower surface 9 is 0 degrees and 15 minutes, the width of the reticulated recess 6a is 2 mm, and the width of the projection 6b having a square plane is 5 mm.
The depth of the recess 6a was 0.5 mm, and the overall thickness of the processing base 6 was 4 mm. And BSO single crystal plate 5
The end surface 5a of the end face 5a was ground by a surface grinder, then sand-polished, and optically polished using colloidal silica as an abrasive grain to form a BSO single crystal layer 7 having a center thickness of 300 μm.

[0019] Regarding this sample, the borosilicate glass substrate 1 was peeled off from the processing base 6 by a normal peeling method using heating (comparative example). On the other hand, using 1,1,1-trichloroethane as a solvent, ultrasonic cleaning was performed for 15 minutes using an ultrasonic cleaner to peel the borosilicate glass substrate 1 from the processing base 6 (Example). Then, when interferometer photographs were taken for each of the above samples, the photographs shown in FIG. 7 (Example) and FIG. 8 (Comparative Example) were obtained. Here, since the striped pattern shows contour lines with an interval of 0.3 μm, the size of the unevenness in the example sample is 0.3 μm.
The roughness remains within 3 μm, and the sample of the comparative example has irregularities with a size of 3 μm or more.

Next, an experiment was conducted regarding transmitted wavefront distortion. That is, when coherent light such as a laser beam is transmitted through a sample, the electromagnetic wave front of the transmitted light varies due to non-uniformity, distortion, etc. of the sample. A spatial light modulation element having such distortion cannot be used for applications such as optical image processing and optical information processing. For this reason, the transmitted wavefront distortion was evaluated for each of the following samples. Specifically, a laser beam is passed through a circular pinhole with a diameter of approximately 10 μm φ, and the laser beam that has passed through the pinhole is transmitted into the sample and projected onto a screen several meters away from the sample. If the beam shape projected onto the screen is circular, it can be said that there is no distortion, but if there is distortion in the transmitted wavefront, the beam shape deforms from a perfect circle.

a) BSO wafer, LiNbO
3 When laser light was transmitted through a wafer, BK-7 glass, and blue plate glass (all 2 mm thick), no transmitted wavefront distortion was observed in any of them. b) The above BSO wafer, LiNbO3 wafer, BK-7 glass, blue plate glass (all thickness is 2
mm) was adhered to blue plate glass and laser light was transmitted through it, and no transmitted wavefront distortion was observed in either case. c) A BSO wafer with a thickness of 2 mm was adhered to blue plate glass, and laser light was allowed to pass through it. The bonded BSO wafer was also ground and optically polished as described above to a thickness of 50 μm or 100 μm, respectively, and laser light was transmitted therethrough. No transmitted wavefront distortion was observed in any of these samples. d) Blue plate glass, thickness 2mm, 3mm, 300
Each .mu.m BSO wafer was glued together and inspected for transmitted wavefront distortion as described above. As a result, when the thickness of the BSO wafer is 2 mm and 3 mm, a screen projection image as shown in the photograph in Figure 9 is obtained, and when the thickness of the BSO wafer is 300 μm, a screen projection image as shown in the photograph in Figure 10 is obtained. A projected image was obtained. From this, the thickness is 30
It can be seen that when a 0 μm BSO wafer is bonded to blue plate glass, transmitted wavefront distortion occurs. In order to obtain a device without transmitted wavefront distortion, the thickness of the BSO wafer when bonded must be 1 mm or more.

[0022]

According to the present invention, an insulating plate is bonded onto a substrate and the end face of this insulating plate is processed to form an insulating layer, so that the thin insulating plate can be made thin from the beginning to produce electro-optical effects and optical effects. Unlike the method of bonding to a single crystal plate that has a conductive effect,
The insulating layer does not curve during the bonding process between the two, making it possible to form a more homogeneous insulating layer than before, improving the yield at the bonding process, and making it possible to increase the area of the insulating layer. became.

Further, according to the present invention, since the single crystal plate is bonded onto a substrate and the end face of the single crystal plate is processed to form the single crystal layer, the single crystal thin plate is made thin from the beginning. Unlike the method of bonding single-crystal plates to substrates, etc., there is no curvature in the single-crystal plate during the bonding process, making it possible to form a more homogeneous single-crystal layer than before, and improving the yield at the bonding step. However, it has also become possible to increase the area of the electro-optic crystal layer.

[Brief explanation of the drawing]

FIG. 1 is a front view showing a state immediately before bonding an insulating plate to a substrate.

FIG. 2 is a front view showing a state in which an insulating layer is formed by grinding and optically polishing an insulating plate.

FIG. 3 is a front view showing a state in which a substrate is bonded to a processing base and a single crystal plate having an electro-optical effect and a photoconductive effect is bonded to an insulating layer.

FIG. 4 is a front view showing the state of the substrate after forming the insulating layer, just before it is bonded to the single crystal layer.

FIG. 5 is a plan view showing a processing base according to a preferred example.

FIG. 6 is a side view showing a processing base according to a preferred example.

FIG. 7 is an interferometer photograph of a sample in which the substrate was peeled off from the processing base by ultrasonic cleaning using an organic solvent.

FIG. 8 is an interferometer photograph of a sample in which a substrate is peeled off from a processing base by a heating method.

FIG. 9 is a photograph showing a screen projection image obtained by transmitting a laser beam through a sample obtained by bonding a BSO wafer with a thickness of 2 mm and 3 mm to blue plate glass.

FIG. 10 is a photograph showing a screen projection image obtained by transmitting laser light through a sample obtained by bonding a BSO wafer with a thickness of 300 μm to blue plate glass.

[Explanation of symbols]

1. Foundation 2 Transparent electrode film 3 Insulating board 3a　End face of insulating plate 4 Insulating layer 5 Electro-optic crystal plate 5a End face of electro-optic crystal plate 6 Processing base 6a　Net-like recess 6b Protrusion 7 Electro-optic crystal layer 8 Tapered surface

Claims (6)

[Claims] 1. An insulating plate is bonded onto a substrate having a transparent electrode, an insulating layer is formed by processing the end face of the insulating plate, and then at least an electro-optic crystal layer, an insulating layer and a substrate are formed on the insulating layer. A method for manufacturing a spatial light modulator, comprising: 2. An electro-optic crystal plate is bonded onto a substrate having a transparent electrode and an insulating layer, and an end face of the electro-optic crystal plate is processed to form an electro-optic crystal layer. 1. A method of manufacturing a spatial light modulator, comprising providing at least an insulating layer and a substrate thereon. 3. After bonding an electro-optic crystal plate onto a substrate having a transparent electrode and an insulating layer, the substrate is bonded to the tapered surface of a processing base having a tapered surface, and the end face of the electro-optic crystal plate is bonded to the tapered surface of a processing base having a tapered surface. 3. The method for manufacturing a spatial light modulator according to claim 2, wherein the electro-optic crystal layer is formed by grinding and optically polishing the electro-optic crystal layer. 4. The method for manufacturing a spatial light modulator according to claim 3, wherein a net-like recess is formed in the tapered surface of the processing base. 5. The method for manufacturing a spatial light modulator according to claim 4, wherein the adhesive bonding the tapered surface and the base is removed by ultrasonic cleaning using an organic solvent. 6. Grinding and optically polishing the end face of the electro-optic crystal plate to form the electro-optic crystal layer, bonding an insulating plate onto a substrate having a transparent electrode, and grinding the end face of the insulating plate. After processing and optical polishing to form an insulating layer,
3. The method for manufacturing a spatial light modulator according to claim 2, wherein the electro-optic crystal layer and the insulating layer are bonded.