JP2599832B2 - Manufacturing method of spatial light modulator - Google Patents

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 (PROM, Pockels Readout Optical MRAM) using a single crystal having an electro-optical effect and a photoconductive effect, such as a Bi ₁₂ SiO ₂₀ (BSO) single crystal.
odulator).

[0002]

2. Description of the Related Art Among spatial light modulators, a PR using a single crystal having an electro-optical effect and a photoconductive effect such as a BSO single crystal is used.
The OM element converts the light intensity distribution of the written image information into a charge distribution in the single crystal plate by using the photoconductive effect of the single crystal and stores it. Is converted into an intensity distribution of the readout light. Therefore, this type of spatial light modulator is composed of the single crystal plate, the insulating layer sandwiching the single crystal plate, and the transparent electrode.

Conventionally, such a spatial light modulator has been constituted by using the single crystal plate whose both surfaces are optically polished, and a parylene thin film or a cleaved film (insulator) of mica. Also,
There has been a method in which an insulating layer is formed by vapor deposition. But,
Since the parylene thin film has a low dielectric strength, the electro-optical effect characteristics of the single crystal cannot be sufficiently exhibited. Since the mica film has an inherent birefringence, the electro-optical effect characteristics of the element are complicated, and it is difficult to produce a uniform large-area thin plate having a uniform thickness. Poor yield during formation.

In particular, in a spatial light modulator for converting an incoherent light image into a coherent light image, the single crystal plate is tapered to prevent interference fringes caused by multiple reflections at the end face of the BSO single crystal. It is being considered to provide one. At this time, the required taper angle varies depending on the element and the device, but needs to be, for example, about 15 minutes. Therefore, when manufacturing a spatial light modulator, the single crystal plate is processed into a tapered shape, and an insulating plate and an electrode plate are sequentially bonded to both surfaces thereof.

However, when the single crystal plate is placed on a processing base, ground, optically polished, and then bonded, the bonding stress is unevenly applied to the single crystal when the adhesive is cured. Distortion occurs in the single crystal, which causes wavefront aberration of light transmitted through the element. Further, even if the single crystal plate having a thickness of several hundred μm is tapered by itself, for example, a load is applied to one side of the single crystal plate and grinding is performed. It is difficult, and the direction of this taper cannot be determined.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to increase the area of a spatial light modulator, to provide a high yield when processing an insulating layer, and to form a uniform and uniform insulating layer. It is an object of the present invention to provide a method for manufacturing such a spatial light modulator. Further, an object of the present invention is to form a single crystal layer having a large-area electro-optical effect and a photoconductive effect, and a high yield,
It is an object of the present invention to provide a method of manufacturing a spatial light modulator capable of reducing a wavefront aberration in the single crystal layer.

[0007]

According to a method of manufacturing a spatial light modulator according to the present invention, an insulating plate having a thickness of 2 mm or more made of optical glass is adhered to a substrate having a transparent electrode, and an end face of the insulating plate is formed. After processing to form an insulating layer having a thickness of 5 to 30 μm, at least an electro-optic crystal layer, a transparent electrode, and a substrate are provided on the insulating layer. Further, the method for manufacturing a spatial light modulator according to the present invention includes the step of forming a Bi ₁₂ Si film on a substrate having a transparent electrode and an insulating layer made of optical glass.
Bonding the O ₂₀ single crystal and LiNbO ₃ composed of one or more single crystals selected from the group consisting of thickness 2mm or more electro-optic crystal plate, the thickness of 30~500μm by processing the end surface of the electro-optic crystal plate After forming the electro-optic crystal layer of
At least a transparent electrode and a substrate are provided on the electro-optic crystal layer.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a method for manufacturing a spatial light modulator according to an embodiment of the present invention will be described with reference to FIGS. First, the substrate 1 is prepared. As a material of the substrate 1, it is necessary to use an optical glass such as borosilicate glass, blue plate glass, and BK-7 glass. Next, the transparent electrode film 2 is formed on the substrate 1 by vapor deposition or the like. Then, 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, Bi ₁₂ S having an electro-optical effect and a photoconductive effect is formed on the surface side of the insulating layer 4.
A single crystal plate 5 made of iO ₂₀ single crystal or LiNbO ₃ single crystal is bonded, and an end face 5a of the single crystal plate 5 is ground and optically polished to form a single crystal layer 7 as shown in FIG.

On the other hand, separately from this, a transparent electrode film 2 is formed on the substrate 1 by vapor deposition or the like, the insulating plate 3 is bonded to the substrate 1, and the end face 3a of the insulating plate 3 is ground and optically polished.
The insulating layer 4 as shown in FIG. Then, as shown in FIG. 4, the adhesive insulating layer 4 is bonded to the single crystal layer 7 to obtain a spatial light modulator.

According to such a manufacturing method, the end face of the insulating plate 3 having a thickness of 2 mm or more is ground and optically polished to form the insulating layer 4, and the insulating layer 4 having a thickness of 5 to 30 μm is formed. Therefore, unlike the method in which an insulating thin plate thinned from the beginning is bonded to the single crystal plate, the insulating layer does not bend at the stage of bonding the two, so that the insulating layer has a more uniform and uniform thickness than before. The layer 4 can be formed, the yield in the bonding step is improved, and the area of the insulating layer 4 can be increased. Here, it is necessary that the thickness of the insulating plate 3 be 2 mm or more, whereby deformation during bonding of the insulating plate 2 can be prevented, the thickness of the insulating layer 4 can be made uniform, and variation in withstand voltage can be prevented. And device destruction due to electric discharge can be prevented.

Further, the thickness of the single crystal plate 5 needs to be as thick as 2 mm or more. Since the single crystal layer 7 is formed by grinding and optically polishing the end face 5a of the single crystal plate 5, unlike the method in which an electro-optical crystal layer thinned from the beginning is bonded to a substrate or the like, the single crystal plate 5 does not bend at the bonding stage, so that the single crystal layer 7 more uniform than before can be formed, the yield in the bonding stage is improved, and the electro-optical crystal layer 7 Large area is also possible.

When the thickness of the single crystal plate 5 is 2 mm or less, stress is unevenly applied to the single crystal when the adhesive is cured,
The single crystal layer 4 is distorted, causing a wavefront aberration of light transmitted through the element. Further, the thickness of the single crystal layer 4 is 30 to 500 μm.
Polish until it reaches m. In FIG. 4, one of the insulating layers 4 may be omitted. Such a spatial light modulation device itself is known as an object.

Next, in the spatial light modulator using coherent light such as laser light as readout light, as described above, it is necessary to taper the single crystal layer 7 in order to prevent the occurrence 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 the tapered surface 8 to obtain a state shown in FIG. In this state, the processing base 6
The lower side surface 9 and the tapered surface 8 have a predetermined taper angle, for example,
For 15 minutes, the tapered surface 8 and the end surface 5a of the single crystal plate 5 are parallel. And, along the broken line A, the single crystal plate 5
Is horizontally ground and then optically polished, the main surfaces on both sides of the single crystal layer 7 have a predetermined taper angle, that is, 15 degrees.
Make a minute.

When the single crystal layer 7 is tapered by such a method, pressure is uniformly applied over the entire surface of the single crystal plate 5 at the stage of grinding, so that processing with high plane accuracy can be performed. become. In the processing base 6,
Only by 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 be freely determined.

Next, a preferred example of the processing base 6 will be described. FIG. 5 shows that the processing base 6 according to the preferred embodiment has a tapered surface 8.
FIG. 6 is an enlarged side view of the processing base 6 as viewed from the side. On the tapered surface 8 side of the processing base 6, a net-like recess 6a is formed by crossing vertical and horizontal linear recesses orthogonal to each other. It is arranged in a shape. When the substrate 1 is temporarily fixed to the tapered surface 8 of the processing base 6, an adhesive layer is interposed between the substrate 1 and the projection 6b.
At this time, assuming that the tapered surface 8 is flat, even if a pressure is uniformly applied to the entire substrate 1 at the time of the temporary fixing, the thickness of the adhesive layer is inevitably shifted. When the plate 5 is ground, a thickness error due to this occurs. On the other hand, in this example, if pressure is applied evenly to the entire substrate 1, excess adhesive than the average escapes to the mesh concave portion 6 a before curing, and as a result, the thickness of the adhesive layer becomes constant, The processing accuracy of the single crystal plate 5 can be further improved.

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 at about 80 ° C. is used for temporary fixing. However, if this adhesive is used, the single crystal layer 7 has a different coefficient of thermal expansion from the substrate 1. In this case, the flatness of the end face becomes poor, 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 the organic solvent, the adhesive is dissolved by ultrasonic cleaning, Separate 1. According to this method, the flatness of the end face of the single crystal layer 7 can be favorably maintained, and the occurrence of cracks in the single crystal layer 7 can be prevented. In the embodiment, the pure edge layer 4 is formed after the insulating plate 3 is ground and then optically polished. However, the optical polishing may be performed after the insulating plate 3 is etched.

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 having a thickness of 3 mm is prepared.
The end face 3a is ground by a surface grinder, sand-ground, and further optically polished by using 1) cerium oxide and 2) colloidal silica in this order, and a 10 μm-thick borosilicate glass insulating layer. 4 was formed. Also, 2.7mm thick BS
An O single crystal plate 5 was prepared and bonded to the insulating layer 4.
Also, 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 base 6. The slope with respect to the lower surface 9 of the tapered surface 8 is 0 degrees 15 minutes, the width of the net-shaped recess 6a is 2 mm, the width of the planar square projection 6b is 5 mm, and the recess is
The depth of 6a was 0.5 mm, and the thickness of the entire processing base 6 was 4 mm. Then, the surface is ground by a surface grinder on the end face 5a side of the BSO single crystal plate 5, then polished by sand, optically polished using colloidal silica as abrasive grains, and BS having a center thickness of 300 μm.
An O single crystal layer 7 was formed.

The borosilicate glass substrate 1 of this sample was peeled from the processing substrate 6 by a normal heating peeling method (Comparative Example). On the other hand, using 1,1,1-trichloroethane as a solvent, ultrasonic cleaning was performed by an ultrasonic cleaning machine for 15 minutes, and the borosilicate glass substrate 1 was separated from the processing substrate 6 (Example). Then, when an interferometer photograph was taken of each of the above samples, the photographs of FIG. 7 (Example) and FIG. 8 (Comparative Example) were obtained. Here, since the stripe pattern shows contour lines at intervals of 0.3 μm, the size of the unevenness is within 0.3 μm in the sample of the example, and the sample of the comparative example has the unevenness of 3 μm or more.

Next, an experiment was conducted on transmitted wavefront distortion.
That is, when coherent light such as laser light is transmitted through the sample, the electromagnetic wave front of the transmitted light varies due to inhomogeneity and distortion of the sample. The spatial light modulator having such distortion cannot be used for applications such as optical image processing and optical information processing. Therefore, the transmitted wavefront distortion was evaluated for each of the following samples. Specifically, laser light is passed through a circular pinhole having a diameter of about 10 μmφ, the laser light passing through this pinhole is transmitted through the sample, and projected on a screen several meters away from the sample. If the beam shape projected on the screen is circular, it can be said that there is no distortion,
If there is a transmitted wavefront distortion, the beam shape is deformed from a perfect circle.

A) BSO wafer, LiNbO ₃ wafer, BK-7 glass, blue plate glass (all thickness 2 m)
When the laser light was transmitted through m), no transmitted wavefront distortion was observed. b) The above BSO wafer, LiNbO ₃ wafer,
When BK-7 glass and blue plate glass (all thickness 2 mm) were bonded to blue plate glass and laser light was transmitted,
In each case, no transmitted wavefront distortion was observed. c) A BSO wafer having a thickness of 2 mm was bonded to a blue plate glass, and laser light was transmitted as it was. The bonded BSO wafer was ground and optically polished as described above to a thickness of 50 μm or a thickness of 100 μm, respectively, and a laser beam was transmitted. No transmitted wavefront distortion was observed for any of these samples. d) Thickness 2 mm, 3 mm, 300 μm
Were bonded and the transmitted wavefront distortion was inspected as described above. As a result, when the thickness of the BSO wafer is 2 mm or 3 mm, a screen projection image as shown in the photograph of FIG. 9 is obtained, and the thickness of the BSO wafer is 300 mm.
In the case of μm, a screen projection image as shown in the photograph of FIG. 10 was obtained. From this, it can be seen that when a BSO wafer having a thickness of 300 μm is bonded to a soda lime glass, transmitted wavefront distortion occurs.

[0022]

According to the present invention, an insulating plate is adhered on a substrate, and an end face of the insulating plate is processed to form an insulating layer. Unlike the method of bonding to a single crystal plate having a conductive effect, the insulating layer does not bend at the bonding stage, so that a more uniform insulating layer can be formed than before, and the yield at the bonding stage is improved. The size of the insulating layer can be increased.

According to the present invention, the single crystal plate is bonded to a substrate, and the end surface of the single crystal plate is processed to form the single crystal layer. Unlike the method in which the single crystal plate is bonded to a substrate or the like, the single crystal plate does not bend at the bonding stage, so that a single crystal layer more uniform than before can be formed, and the yield in the bonding stage is improved. In addition, the area of the electro-optic crystal layer can be increased.

[Brief description of the drawings]

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 where an insulating layer is formed by grinding and optically polishing the 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 a state immediately before bonding a substrate after forming an insulating layer 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 obtained by peeling a substrate from a processing base by ultrasonic cleaning using an organic solvent.

FIG. 8 is an interferometer photograph of a sample obtained by peeling a substrate from a processing substrate by a heating method.

FIG. 9 is a photograph showing a screen projection image obtained by transmitting a laser beam to a sample obtained by bonding a BSO wafer having a thickness of 2 mm and 3 mm to a soda lime glass.

FIG. 10 is a photograph showing a screen projection image obtained by transmitting a laser beam to a sample obtained by bonding a BSO wafer having a thickness of 300 μm to a soda lime glass.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base 2 Transparent electrode film 3 Insulating plate 3a End surface of insulating plate 4 Insulating layer 5 Electro-optical crystal plate 5a End surface of electro-optical crystal plate 6 Processing substrate 6a Reticulated recess 6b Projection 7 Electro-optical crystal layer 8 Tapered surface

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoji Tange 2-38-2, Okamachi, Mizuho-ku, Nagoya-shi, Aichi Prefecture 2-2, Okashioru, NGK-shi 3-21-21 (56) References JP-A-2-245721 (JP, A) JP-A-59-166916 (JP, A) JP-A-54-128358 (JP, A) Jpn. JP, U)

Claims (6)

(57) [Claims] 1. An insulating plate made of optical glass having a thickness of 2 mm or more is adhered to a substrate having a transparent electrode, and an end surface of the insulating plate is processed to form an insulating layer having a thickness of 5 to 30 μm. A method for manufacturing a spatial light modulator, comprising: providing at least an electro-optic crystal layer, a transparent electrode, and a substrate on the insulating layer. 2. A Bi ₁₂ SiO ₂₀ single crystal and an L ₁₂ substrate are provided on a substrate having a transparent electrode and an insulating layer made of optical glass.
An electro-optic crystal plate having a thickness of 2 mm or more made of one or more single crystals selected from the group consisting of iNbO ₃ is bonded, and the end face of the electro-optic crystal plate is processed to have a thickness of 30 to 500 μm.
Forming the electro-optic crystal layer, and then providing at least a transparent electrode and a substrate on the electro-optic crystal layer. 3. The electro-optic crystal plate is bonded to the substrate having the transparent electrode and the insulating layer, and then the substrate is bonded to the tapered surface of the processing base having a tapered surface. 3. The method for manufacturing a spatial light modulation device according to claim 2, wherein an end face of the crystal plate is formed by grinding and optical polishing to form a taper to form an electro-optic crystal layer. 4. A net-shaped concave portion is formed in the tapered surface of the processing base, and when the substrate is temporarily fixed to the tapered surface of the processing base, a gap between the substrate and the projection of the tapered surface is formed. 4. The method for manufacturing a spatial light modulation device according to claim 3, wherein an adhesive layer is interposed in the substrate, and pressure is applied to the substrate to move excess adhesive to the net-shaped recess before curing. 5. The method according to claim 1, wherein the processing base, the substrate, and the adhesive layer bonding the substrates are immersed in an organic solvent, and the organic solvent is penetrated into the mesh-shaped concave portion by ultrasonic cleaning to perform the bonding. The method according to claim 4, wherein the processing substrate and the substrate are separated by dissolving an agent layer. 6. An electro-optic crystal layer is formed by grinding and optically polishing an end face of the electro-optic crystal plate, and bonding an insulating plate made of optical glass on a substrate having a transparent electrode. The method for manufacturing a spatial light modulation element according to claim 2, wherein the electro-optical crystal layer and the insulating layer are bonded after forming an insulating layer by grinding and optically polishing an end face of the element.