JP2599831B2 - Spatial light modulator and method of manufacturing the same - 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 such as a Pockels readout light modulator.

[0002]

2. Description of the Related Art Among spatial light modulators, a PROM (Pockels Rea) using a silicon oxide bismuth Bi ₁₂ SiO ₂₀ (BSO) single crystal.
dout Optical Modulator) The device uses the photoconductivity of BSO single crystal to convert the light intensity distribution of the written image information into a charge distribution in the single crystal, accumulates it, and then generates an electric field generated by the electric field created by this charge distribution. The optical effect is used to convert the read light into an intensity distribution. Therefore, this type of spatial light modulator is composed of a BSO single crystal plate, an insulating layer surrounding the BSO single crystal plate, and a glass substrate on which a transparent electrode is formed.

In particular, in a spatial light modulator for converting an incoherent light image into a coherent light image, it has been studied to provide a taper on a BSO single crystal plate in order to prevent interference fringes. At this time, the required taper angle varies depending on the element and the device, but needs to be, for example, about 15 minutes. For this reason, when manufacturing a spatial light modulator, a BSO single crystal plate is processed into a tapered shape, and an insulating plate and an electrode plate are sequentially bonded to both surfaces thereof.

[0004]

However, the present inventor has
A pair of glass insulating plates and a pair of glass substrates having transparent electrodes were attached to both sides of such a BSO single crystal plate, respectively, to produce a PROM element, and a laser beam was applied to observe the transmitted light image. It was found that interference fringes appeared as image noise.

An object of the present invention is to substantially eliminate interference fringes not directly caused by a tapered electro-optical crystal layer in a spatial light air conditioner using coherent light as read light.

A spatial light modulator according to the present invention comprises: a glass substrate; a transparent electrode film provided on the glass substrate;
The glass substrate is provided with a glass insulating layer optically bonded to the transparent electrode film side of the glass substrate, and an electro-optical crystal plate optically bonded to the insulating layer, wherein the glass substrate and the insulating layer are of the same type. Characterized in that the thickness decreases continuously from one end face of the glass substrate to the other end face facing this end face. Also,
The method for manufacturing a spatial light modulator according to the present invention is such that a transparent electrode film is formed on the main surface of a glass flat plate having a constant thickness, and an insulating plate made of the same kind of glass as the glass flat plate is optically bonded thereon.
The insulating plate is optically polished to form an insulating layer, this glass flat plate is fixed on an inclined surface, the glass flat plate is cut along a horizontal plane, and the thickness is continuously increased from one end surface to the other end surface. The method is characterized in that a glass substrate which is reduced in number is produced, and an electro-optic crystal layer is formed on the insulating layer.

[0007]

The present inventor studied the generation of interference fringes due to the above-mentioned spatial light modulator, and found that the interference fringes were reflected on the coherent light reflected on the opposing main surfaces (the widest surface) of the glass substrate. Was found to have been caused.
Then, by continuously changing the thickness of the glass substrate between the pair of opposed end surfaces of the glass substrate (hereinafter, sometimes referred to as tapering the glass substrate), the glass is formed. It is possible to substantially eliminate interference fringes caused by reflection on both main surfaces of the substrate. In addition, the glass substrate and the insulating layer are made of the same type of glass so that they behave integrally when viewed optically, and the glass substrate is tapered to cause reflection at the main surface of the insulating layer. Interference fringes were also successfully prevented.

[0008]

1 and 2 are schematic front views each showing an example of a PROM element according to an embodiment of the present invention. In the example of FIG. 1, the thickness of the substrate 1 decreases continuously from one end surface 1a of the glass substrate 1 to the other end surface 1b.
The insulating layer 2 is formed on one of the main surfaces of the first and second substrates. The pair of glass substrates 1 are opposed to each other so as to sandwich the insulating layer 2 inside, and the substrates 1 are oriented such that one end surfaces 1a are located on the same side of the substrate 1.
An electro-optic crystal layer 3 made of BSO single crystal or the like is formed between the pair of insulating layers 2 opposed to each other. Since this PROM element 4 performs reading with coherent light,
Also in the electro-optic crystal layer 3, the layer thickness decreases continuously from one end face 3a to the other end face 3b (that is, the electro-optic crystal layer 3 is tapered).

The PROM element 14 shown in FIG. 2 has substantially the same structure as the element 4 shown in FIG. 1, but one end surface 1a of a pair of substrates 1 facing each other is located on the opposite side in the drawing. It differs in that it is located.

In FIG. 1 and FIG. 2, an optical adhesive is used to bond between the glass substrate 1 and the insulating layer 2 and between the insulating layer 2 and the electro-optic crystal layer 3, respectively. Also,
A transparent electrode (not shown) is formed on the surface of the glass substrate 1.

According to the PROM elements 4 and 14 shown in this embodiment,
Since the glass substrate 1 is tapered, interference fringes caused by reflection of coherent light on the pair of main surfaces of the glass substrate 1 can be prevented. In particular,
Since the interval L of the interference fringes in the read light image is approximately inversely proportional to the taper angle θ of the glass substrate 1, the interval L is reduced by increasing the taper angle θ, and the interference fringes are reduced. When the interval L becomes smaller than the resolution, the interference fringes become invisible.

The taper angle at which the interval L of the interference fringes becomes smaller than the resolution depends on the wavelength of light and the refractive index of the glass substrate. For example, a Pyrex glass substrate is used, and a He-Ne laser having a wavelength of 633 nm is used as readout light. When used,
The taper angle must be at least 25 minutes.

For the same reason, when the electro-optic crystal layer 3 is formed of BSO single crystal, the crystal layer 3
Is required to be about 15 minutes or more.

However, the present inventor has found that in this case, a new problem of interference fringes occurs. That is, in the above case, in FIG. 2, one main surface A of the crystal layer 3 and the outer main surface B of the glass substrate 1 form an angle of 15 minutes, but the refractive index of the glass substrate 1 is Since the refractive index is smaller than the refractive index in 3, the distance difference caused by the 15-minute angle between the main surfaces A and B is canceled out, and a new interference fringe is generated due to the reflection between the main surfaces A and B. It was done. However, the present inventor succeeded in eliminating interference fringes caused by reflection between the main surfaces A and B by forming the antireflection film 5 on the surface of the main surface B.

Next, a method of manufacturing the PROM element as shown in FIGS. 1 and 2 will be described with reference to FIGS. 3 (a) to 3 (e). First, a glass flat plate 11 is prepared. As a material of the glass flat plate 11, a material having high hardness such as Pyrex glass, borosilicate glass, or synthetic quartz glass is preferable. Next, the transparent electrode film 6 is formed on the flat plate 11 by vapor deposition or the like. Then, after bonding the insulating plate 12 to the flat plate 11, the end face of the insulating plate 12 is ground and optically polished to form the insulating layer 2 as shown in FIG. In (b), (c), (d), and (e), the transparent electrode film 6 is not shown.

Next, as shown in (d), the insulating layer 2 is bonded to the inclined surface 7a of the jig 7. At this time, the inclination angle of the inclined surface 7a is set in advance to be equal to the predetermined taper angle of the glass substrate 1. Assuming that the taper angle is, for example, 30 minutes, when the glass flat plate 11 is fixed on the jig 7, a pair of main surfaces of the glass flat plate 11 form an angle of 30 minutes with respect to the horizontal plane C. When the glass plate 11 is ground and optically polished along the horizontal plane C, a tapered glass substrate 1 is obtained as shown in FIG.

When the glass substrate 1 is tapered by such a method, a glass flat plate is formed at the stage of grinding.
Since pressure is evenly applied over the entire surface of 11, the curvature can be prevented, and the resulting wavefront aberration can be reduced. Further, in the jig 7, the accuracy of the taper angle of the glass substrate 1 can be maintained only by setting the inclination angle of the inclined surface 7a to a predetermined angle.

Next, the glass substrate 1 is placed on the inclined surface of the jig 17.
After bonding and fixing to 17a, the electro-optic crystal flat plate 13 is bonded to the insulating layer 4 and fixed. However, in (e), the glass substrate 1 is oriented so that one main surface 1a is located below the inclined surface 17a and the other principal surface 1b is located above the inclined surface 17a. Then, the electro-optic crystal flat plate 13 is ground and optically polished along the horizontal plane D to form the electro-optic crystal layer 3 as shown in FIGS. At this time, the slope
The inclination angle 17a is the sum of the taper angle in the electro-optic crystal layer 3 and the taper angle in the glass substrate 1. For example, if the taper angle of the substrate 1a is 30 minutes and the taper angle of the crystal layer 3 is 15 minutes, the inclination angle of the inclined surface 17a must be 45 minutes.

Separately, a glass substrate 1 is manufactured according to the processes shown in FIGS. 3A and 3B, and the insulating layer 2 formed on the substrate 1 is bonded to the electro-optic crystal layer 3. ,
The PROM element shown in FIG. 1 or 2 is obtained. At this time, by changing the direction of the taper of the glass substrate 1 to be bonded last,
One of the PROM elements shown in FIGS. 1 and 2 is obtained.

After reaching the stage of FIG. 3D, another process can be followed. For example, as shown in FIG. 4, if a jig 27 having an inclined surface 27a having an inclination angle smaller than the taper angle of the glass substrate 1 is used, the taper angle of the glass substrate 1 and the inclination of the inclined surface 27a are reduced. The difference from the angle is the taper angle of the electro-optic crystal layer 3. For example, assuming that the taper angle of the glass substrate 1 is 30 minutes and the taper angle of the crystal layer 3 is 15 minutes, it is sufficient that the inclined surface 27a has an angle of 15 minutes with respect to the horizontal plane E. The angle of inclination may be 15 minutes. According to this method, when performing the grinding along the horizontal plane E, the inclination angle of the inclined surface of the jig is smaller than the inclination angle in the case of FIG. Flat plate 13 is less likely to be distorted. Next, the other glass substrate 1 is prepared in the same manner as described above, and the insulating layer 2 formed thereon is adhered to the electro-optic crystal layer 3 to obtain the structure shown in FIG.
Can be obtained.

The embodiment will be described more specifically. First, as shown in FIG. 3A, each side is 40 mm square and 3 mm thick.
Prepare a flat plate 11 made of synthetic quartz glass of
The transparent electrode film 6 of mm was formed by vapor deposition. Then (b)
As shown in the figure, an insulating plate 12 made of synthetic quartz glass having a side of 40 mm and a thickness of 3 mm was bonded to the transparent electrode film side of the substrate 11 with an epoxy adhesive for optical use. Then, the insulating plate 12 was ground and optically polished using a surface grinder and a polishing grinder in this order to form an insulating layer 2 having a thickness of 10 μm.

Next, as shown in (d), the insulating layer 2 was bonded to the inclined surface 7a having an inclination angle of 30 minutes, and the synthetic quartz glass substrate 11 was ground and optically polished along the horizontal plane C. Insulating layer 2
Was separated from the jig 7. Also, as shown in (e), each side is 30mm square and 3mm thick cut along the crystal axis (001).
The BSO single crystal flat plate 13 was bonded to the insulating layer 2 with an optical epoxy adhesive. Further, the glass substrate 1 was bonded to the inclined surface 17a having an inclination angle of 45 minutes, and the BSO single crystal flat plate 13 was ground and optically polished along the horizontal plane D to form the BSO single crystal layer 3.

Separately, the synthetic quartz glass substrate 1 having a taper angle of 30 minutes as described above along FIGS. 3A and 3B.
Then, the insulating layer 2 was optically bonded to the BSO single crystal layer 3 to produce the PROM element 4 shown in FIG.

Further, in the above, the flat plate 11 made of synthetic quartz glass is not tapered, and is used as it is as a substrate.
A PROM element of a comparative example was manufactured.

Then, each PR of the above-mentioned inventive examples and comparative examples was
Using an OM element and a readout device schematically shown in FIG. 5, generation of interference fringes was examined.

That is, a He-Ne laser (633 nm) 22 is
Then, the beam was expanded by the objective lens 23 and the collimating lens 24, and was irradiated to the PROM element 4 (or the PROM element of the comparative example) through the polarizer 25. A DC voltage of 5 KV is applied to the PROM element by the DC power supply 26, and the laser beam is modulated by the Pockels effect. The light transmitted through the PROM element then passes through the analyzer 28, is collected by the condenser lens 29, and forms an image on the film 30. Polarizer 25 and analyzer
28 and cross Nicol state.

As a result of photographing an image on the film as described above, when the conventional PROM element was used, fine interference fringes were seen as shown in the photograph of FIG.
When the element was used, no interference fringes were seen as shown in FIG.

[0028]

According to the present invention, in the spatial light modulator, the thickness of the glass substrate is continuously reduced from one end surface to the other end surface of the glass substrate. The interference fringes resulting from the reflection on both principal surfaces can be made very fine and substantially eliminated. In addition, the glass substrate and the insulating layer are made of the same type of glass so that they behave integrally when viewed optically, and the glass substrate is tapered to cause reflection at the main surface of the insulating layer. Interference fringes were also successfully prevented.

According to the manufacturing method of the present invention, the glass flat plate is fixed on the inclined surface, and the glass flat plate is ground along the horizontal plane, so that the glass flat plate is continuously moved from one end surface to the other end surface. Since the glass substrate whose thickness is gradually reduced is made, the glass plate is placed on the inclined surface at the stage of grinding, so the entire surface of the glass plate is ground at the stage of grinding. Pressure is evenly applied and no excessive force is applied locally. Accordingly, it is possible to prevent the glass flat plate from being curved, and to reduce the wavefront aberration associated therewith. Further, the accuracy of the taper angle in the glass substrate can be maintained only by setting the inclination angle of the inclined surface at a predetermined angle with respect to the horizontal plane.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing a PROM element according to an embodiment of the present invention.

FIG. 2 is a schematic front view showing a PROM element according to an embodiment of the present invention.

FIGS. 3 (a), (b), (c), (d) and (e) are schematic views showing a manufacturing method for tapering a glass substrate and an electro-optic crystal layer.

FIG. 4 is a schematic front view for explaining another method for tapering the electro-optic crystal layer.

FIG. 5 is a schematic diagram showing an imaging device for measuring the occurrence of interference fringes.

FIG. 6 is a photograph showing a light image read by a laser beam when a PROM element of a comparative example is used.

FIG. 7 is a photograph showing an optical image read by a laser beam when the PROM element of the present invention is used.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 1a One end face 1b The other end face 2 Insulating layer 3 Electro-optic crystal layer 4, 14 PROM element 5 Antireflection film 6 Transparent electrode film 7, 17, 27 Jig 7a, 17a, 27a Inclined surface C, D , E horizontal plane

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Shoji Tange 2-38-2, Okamachi, Mizuho-ku, Nagoya-shi, Aichi Prefecture, Japan hill dormitory (56) References JP-A-63-168618 (JP, A) JP-A-63-118183 (JP, A) JP-A-54-48262 (JP, A)

Claims (3)

(57) [Claims] 1. A glass substrate, a transparent electrode film provided on the glass substrate, a glass insulating layer optically bonded to the transparent electrode film side of the glass substrate, A spatial light modulator comprising an electro-optic crystal plate optically bonded to the glass substrate, wherein the glass substrate and the insulating layer are formed of the same type of glass, and from one end face of the glass substrate. A spatial light modulator, wherein the thickness continuously decreases toward the other end face facing the end face. 2. The glass substrate and the insulating layer are made of a material selected from the group consisting of Pyrex glass, bismuth borosilicate glass, and synthetic quartz glass. Spatial light modulator. 3. A transparent electrode film is formed on a main surface of a glass flat plate having a constant thickness, an insulating plate made of the same kind of glass as the glass flat plate is optically bonded thereon, and the insulating plate is optically polished. An insulating layer is formed, this glass flat plate is fixed on an inclined surface, and the glass flat plate is cut along a horizontal plane, and the thickness of the glass flat plate continuously decreases from one end surface to the other end surface. A method for manufacturing a spatial light modulation element, comprising forming a substrate and forming an electro-optic crystal layer on the insulating layer.