JPH0464134B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides an electro-optic crystal that is arranged opposite to an electron source such as a photocathode or an electron gun configured in a vacuum container, and The present invention relates to a spatial light modulation device using a spatial light modulation tube that accumulates charges on the crystal surface to generate changes in the refractive index corresponding to the accumulated charges, and optically reads out the changes.

(Prior Art) First, the basic configuration of an air conditioning light modulation device will be briefly explained along with its operation.

FIG. 4 is a schematic diagram showing the basic configuration of the spatial light modulator.

Photocathode 4 on the inner surface of the glass container of the spatial light modulation tube 3
An image from an input pattern 1 irradiated with incoherent light is made incident through a lens 2 . At this time, the photocathode 4 emits photoelectrons corresponding to the incident image.

The photoelectrons are accelerated and passed through a focusing lens system 5,
The light is made incident on a microchannel plate (MCP) 6 and multiplied several thousand times.

These multiplied electrons are accumulated on the surface of an electro-optic crystal 8 made of LiNbO ₃ or the like on which a transparent electrode 8a is formed, and change the refractive index of this crystal 8 in accordance with the charge image.

When the electro-optic crystal 8 is irradiated with laser light from the laser light source 10 via the half mirror 9, a laser light image 11 (coherent image) is obtained.

This laser beam image allows coherent parallel optical calculations to be performed.

Note that instead of the laser light source 10, a white light source such as a halogen lamp may be used. In this case, it can be used as a projector using powerful light. A 55° cut LiNbO ₃ single crystal plate is suitable as the electro-optic crystal 8 of such a spatial light modulation tube.

LiNbO ₃ single-crystal plates are crystals that can be easily obtained from relatively large-area wafers, have a low half-wave voltage, are not photoconductive, and are baked at relatively high temperatures when degassing in a vacuum. It has the characteristic that it does not change even when it is used.

(Problems to be Solved by the Invention) As mentioned above, LiNbO ₃ single crystal has excellent characteristics, but according to the configuration of the conventional spatial light modulation tube, LiNbO ₃ has natural birefringence, so , ordinary light and extraordinary light are separated within the crystal, and as a result, these two light waves are modulated at different locations within the crystal, making it impossible to expect an improvement in resolution.

Furthermore, when reading with white light, wavelength purity is required because natural birefringent light has a large wavelength dependence. Therefore, it is virtually impossible to use white light. Furthermore, since the refractive index changes for ordinary light and extraordinary light differ depending on temperature, there is also the problem that the readout light is modulated by temperature changes. Both of these phenomena become noticeable as the crystal thickness increases, and in order to improve resolution, two crystals of the same type are bonded together via a transparent conductive film and one is processed to be thinner (patent application). (1983-171194), etc., became a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a spatial light modulator that can solve the problems related to the natural birefringence of the crystal plate and temperature changes.

(Means for Solving the Problems) In order to achieve the above object, the first method according to the present invention
The spatial light modulation device uses a spatial light modulation tube having an electron source configured in a vacuum container, an electro-optic crystal section that accumulates electrons emitted from the electron source and produces an optical change, and uses the electro-optic crystal section. In a spatial light modulation device that extracts an optical change in the electro-optic crystal section by reading out the section and irradiating the section with a light source, compensation is provided on the light source side of the electro-optic crystal section using the same material as the electro-optic crystal section and having substantially the same thickness. An optical element for rotating the plane of polarization of light by 90 degrees is arranged between the electro-optic crystal section and the compensation crystal.

Moreover, the second spatial light modulation device according to the present invention includes:
Using an electron source configured in a vacuum container and a spatial light modulation tube having an electro-optic crystal part that accumulates electrons emitted from the electron source and causes an optical change, the electro-optic crystal part is irradiated with a readout light source. In the spatial light modulation device for extracting optical changes in the electro-optic crystal section, a compensating crystal made of the same material and having substantially the same thickness as the electro-optic crystal section is disposed on the light source side of the electro-optic crystal section; An optical element for rotating the plane of polarization of light by 90° is arranged between the electro-optic crystal section and the compensation crystal, and an adjustment device that generates an electric field in the optical axis direction in the electro-optic crystal section or the compensation crystal. A power source is connected, and the optical path length of the electro-optic crystal section and the compensation crystal are made equal.

(Example) Hereinafter, the present invention will be described in more detail with reference to the drawings and the like.

FIG. 1 is a schematic diagram showing an embodiment of a first spatial light modulation device according to the present invention.

An image of the input pattern 1 is formed by a lens 2 on a photocathode of a spatial light modulation tube 3.

An electron image corresponding to the input optical image is focused on the input surface of the microchannel plate 6 by the accelerating and focusing electron lens system 5, and the multiplied electrons are caused to collide with the surface of the electro-optic crystal section 20. A charge image corresponding to the image of the input pattern 1 is formed on the surface of the electro-optic crystal section 20 .

As shown in FIG.
55° cut LiNbO ₃ crystal plates, 20a, 20b
They are bonded with, for example, an acrylic transparent adhesive via a transparent conductive film 20c so that they have the same crystal axis.

The thickness of crystal 20b is 5 mm, and the thickness of crystal 20a is 0.05 mm.
mm, and the surface 20e of the crystal plate 20a forms a charge accumulation surface. The charge storage surface 20e is coated with a dielectric mirror.

The refractive index of the crystal 20a changes due to the charge applied to the surface 20e of the crystal plate 20a, thereby modulating light.

The surface 20e of the crystal plate 20a can accumulate charges until the surface potential becomes equal to the potential of the mesh electrode 7.

Each part of the spatial light modulation tube 3 is equipped with a microchannel plate power supply 26 and a mesh electrode power supply 2.
7. An operating voltage is connected by a power source 28 for the back voltage of the crystal plate, and a power source 30 for the photocathode and acceleration focusing electrode.

The crystal half-wave plate 21 changes the polarization plane of the transmitted light.
It is an optical element that rotates 90°.

The compensation crystal 22 is made of a LiNbO ₃ crystal plate cut at 55°.

The compensation crystal 22 is arranged so that the direction of the crystal axis is optically parallel to the electro-optic crystal section 20. The thickness of the compensation crystal section 22 is 5.05 mm, which is equal to the sum of the thicknesses of the crystal plates 20a and 20b of the electro-optic crystal section.

The optical positional relationship between them is shown in an enlarged scale in FIG.

The light from the readout light source 24 passes through the polarizer 23
It becomes linearly polarized light, passes through a half mirror 9, a compensation crystal 22, a half-wave plate 21,
The light enters the electro-optic crystal section 20 in the spatial light modulation tube 3. The reflected light from the electro-optic crystal unit 20 passes through the half-wave plate 21 and the compensation crystal 22 again, is reflected by the half mirror 9, and passes through the analyzer 25 to form an output image 11.

As shown in FIG. 2, the readout light incident on a compensating crystal 22 made of LiNbO ₃ cut at 55° is separated into an ordinary ray o and an extraordinary ray e within the crystal 22.

The polarization planes of the lights exiting the compensation crystal 22 are each rotated by 90° by the half-wave plate 21 and are incident on the electro-optic crystal section 20 of the spatial light modulation tube 3 .
Here, the relationship between ordinary light and extraordinary light is reversed, and as shown in the figure, the two light waves coincide when they reach the modulated portion 20a.

In addition, in the embodiment described above, it is also possible to incorporate the half-wave plate 21 and the compensation crystal 22 into the spatial light modulation tube 3 as described later.

FIG. 3 is a schematic diagram showing an embodiment of a second spatial light modulation tube according to the present invention.

In this embodiment, a half-wave plate 21 and a compensation crystal 22 are provided within the spatial light modulation tube 3.

These optical positional relationships are no different from the embodiment shown in FIG.

In this embodiment, a transparent conductive film is also deposited on the surface 20d shown in FIG. adjust.

Thereby, the configuration is such that the initial phase shift can be finely adjusted.

Note that this fine adjustment of the initial phase shift can be similarly performed on the compensation crystal 22 side.

The configuration of other parts is shown in Figures 1 and 2 first.
This is no different from the embodiment device described with reference to the figures.

In each of the above-mentioned embodiments, deterioration in resolution could be removed by separating ordinary light and extraordinary light, and a resolution of 15 p/mm (50% modulation degree) could be obtained. Furthermore, we were able to obtain an output image using white light from a halogen lamp passed through a filter with a wavelength width of about 10 nm as a light source.

Furthermore, it was possible to provide a stable device whose output light intensity does not change even when the room temperature changes.

Various modifications can be made to each of the embodiments described in detail above within the scope of the present invention.

In each of the above embodiments, a photocathode was used as the electron image source of the spatial light modulation tube, but a type using an electron gun can also be used.

Furthermore, as the half-wave plate, a Fresnel-Rhom prism can also be used in addition to a quartz plate.

Moreover, although the electro-optic crystal section 20 has been described using two layers, it can also be used when one layer is used.

(Effects of the Invention) As described above, according to the present invention, two light waves separated by a crystal having natural birefringence can be configured to pass through exactly the same optical path length.
All conventional problems caused by natural birefringence can be solved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of a spatial light modulation device according to the present invention. FIG. 2 is an optical path diagram showing the main parts of the present invention in more detail. FIG. 3 is a schematic diagram showing still another embodiment of the spatial light modulation device according to the present invention. FIG. 4 is a schematic diagram showing an example of the configuration of a conventional spatial light modulation device. 1... Input pattern, 2... Lens, 3... Spatial light modulation tube, 4... Photocathode, 5... Accelerating and focusing electron lens system, 6... Microchannel plate,
7... mesh, 8... electro-optic crystal (conventional device), 9... half mirror, 10... light source, 11
... Output image, 12 ... Analyzer, 20 ... Electro-optic crystal part (present invention), 21 ... Half-wave plate, 22 ...
Compensation crystal, 23...Polarizer, 24...Light source for readout, 25...Analyzer, 26...Power source for microchannel plate, 27...Power source for mesh electrode, 28...For back voltage of crystal plate power supply, 29
...Power supply for adjustment, 30...Power supply for photocathode and acceleration focusing electrode.

Claims (1)

[Scope of Claims] 1. An electron source configured in a vacuum container, a spatial light modulation tube having an electro-optic crystal part that accumulates electrons emitted from the electron source and causes an optical change, and uses the electro-optic crystal. In a spatial light modulation device that extracts an optical change in the electro-optic crystal section by reading out the section and irradiating the section with a light source, compensation is provided on the light source side of the electro-optic crystal section using the same material as the electro-optic crystal section and having substantially the same thickness. 1. A spatial light modulation device, characterized in that a spatial light modulation device is configured by arranging a compensation crystal, and an optical element for rotating the plane of polarization of light by 90° between the electro-optic crystal section and the compensation crystal. 2. The spatial light modulator according to claim 1, wherein the optical element that rotates the polarization plane of the light by 90 degrees is a half-wave plate or a Fresnel-Rom prism. 3. The spatial light modulation device according to claim 1, wherein the optical element for rotating the plane of polarization of the light by 90 degrees and the compensation crystal are arranged outside the spatial light modulation tube. 4. The spatial light modulation device according to claim 1, wherein the optical element for rotating the polarization plane of the light by 90 degrees and the compensation crystal are disposed within a spatial light modulation tube. 5. The electro-optic crystal section is composed of a relatively thin electro-optic crystal plate provided with a transparent electrode on the back surface, and a relatively thick electro-optic crystal plate bonded to the electro-optic crystal plate via the transparent electrode. A spatial light modulator according to claim 1. 6. The spatial light modulator according to claim 1, wherein the thickness of the compensation crystal is approximately equal to the sum of the thicknesses of the relatively thin electro-optic crystal plate and the relatively thick electro-optic crystal plate. . 7 Using an electron source configured in a vacuum container and a spatial light modulation tube having an electro-optic crystal part that accumulates electrons emitted from the electron source and causes an optical change, the electro-optic crystal part is irradiated with a readout light source. In the spatial light modulation device for extracting optical changes in the electro-optic crystal section, a compensating crystal made of the same material and having substantially the same thickness as the electro-optic crystal section is disposed on the light source side of the electro-optic crystal section, An optical element for rotating the polarization plane of light by 90° is arranged between the electro-optic crystal section and the compensation crystal, and an adjustment device for generating an electric field in the optical axis direction in the electro-optic crystal section or the compensation crystal. A spatial light modulator, characterized in that the spatial light modulator is connected to a power source so that the optical path lengths of the electro-optic crystal section and the compensation crystal are equal.