JPS63165819A - Method for correcting shading of space light modulator - Google Patents

Abstract

PURPOSE:To correct the shading of crystal thickness by previously accumulating electrostatic charge corresponding to the distribution of reading light intensity obtained when uniform charge is accumulated in an electro-optical substance in a space light modulator. CONSTITUTION:Uniform input light beam are radiated to an opto-electric cathode 31 in the space light modulator 3 to accumulate uniform charge on the surface of an electro-optical crystal plate 34. Then, coherent light is radiated from the rear face of the plate 34 to obtain light intensity distribution shown in Fig.(A). As shown in Fig.(B), the uneven thickness of the crystal which is the cause of shading is formed. The distribution is recorded on a photographing film 101 and erasing light beams corresponding to the light intensity distribution are made incident upon the cathode 31 through the film 101 to previously accumulated the charge corresponding to the light intensity distribution on the surface of the plate 34. Thus, the shading can be corrected by previously accumulating the charge corresponding to the light intensity distribution based upon the difference of thickness of the crystal on the crystal plate 34.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a shading correction method for a spatial light modulator.

In the present invention, shading refers to non-uniformity in the brightness of an image resulting from a difference in natural birefringence due to non-uniformity in the thickness of the electro-optic crystal of the spatial light modulator.

(Prior Art) The basic configuration of a spatial light modulation device will be explained with reference to FIG.

A photocathode 31 is formed on the inner surface of the entrance surface of the vacuum-tight container of the spatial light modulation tube.

An electro-optic crystal 34 is placed opposite the photocathode 31 .

This electro-optic crystal 34 has natural birefringence, and a transparent electrode is provided on the rear surface.

A secondary electron collecting electrode 33 is provided on the photocathode side of the electro-optic crystal 34.
A microchannel plate 32 is provided between the photocathode 31 and the photocathode 31 .

An input image 1 is illuminated by an incoherent light source 10 and projected by a lens 2 onto a photocathode 31 of a spatial light modulation tube 3 .

The input optical image is converted into a photoelectron image at the photocathode 31, and the converted electron image is focused on the input surface of the microchannel plate 32.

The electron image is doubled by the microchannel plate 32 to form an electron image on the surface of the 55° cut LiNb○3 single crystal plate 34.

Here, the light from the laser light source 4 is magnified by the objective lens 5,
After removing excess diffracted light through the pinhole 6, the polarizer 7 aligns the polarization direction with the X-axis (or y-axis) of the crystal.

It is input from the B-plane side as linearly polarized light in a direction of 45° from the axis).

Since the refractive index in the x and y directions within the crystal 34 is different, a phase difference occurs between the components in the x direction and y' direction of the incident light, and the light is generally output as elliptically polarized light.

When this output light passes through an analyzer 11, only one polarization direction is extracted, and a coherent optical image modulated by the input image 1 is obtained on the screen 12.

(Problems to be Solved by the Invention) In writing to the spatial light modulation tube 3, the charge is uniformly set to M.
Due to the non-uniformity of the electro-optic crystal thickness,
The brightness of the image also becomes non-uniform.

As mentioned above, this is called shading in the present invention.

The thickness l and the phase difference 1'o of this crystal 34 are expressed by the following equation.

ro=(2π/λ) (ne'-no)x2J In the current crystal polishing technology, the thickness uniformity is limited to about the wavelength λ, so this shading always occurs.

Below, regarding this shading with reference to drawings, etc.
I will explain in more detail.

Even when charges are accumulated uniformly, shading occurs due to differences in crystal thickness, as shown in FIG. 4(A).

FIG. 4(B) shows the crystal cut and the thickness direction exaggerated.

The phase difference between points a and b on the crystal is given by the following equation.

△"o = (2π/λ) (ne'-no) .

FIGS. 5A and 5B show the relationship between the charge σ and the brightness I at points a and b.

The relationship between the amount of surface charge σ at points a and b and the brightness I of the output light is shifted left and right depending on the thickness of the crystal.

In other words, to uniformly make the entire area the darkest, a charge of σa is required at point a, and a charge of σa is required at point A.
Only b is required.

FIG. 6(C) shows the cross section of FIG. 4(B) with the required charge plotted on the vertical axis.

An object of the present invention is to provide a shading correction method for a spatial light modulator that can easily correct the shading of the above-mentioned spatial light modulator.

(Means for Solving the Problems) In order to achieve the above object, a shading correction method for a spatial light modulator according to the present invention includes an electron source, an electron source emitted from the electron source, and an optical change. In a spatial light modulator that is made of an electro-optical material that has natural birefringence that causes , and whose optical changes are read out using external light,
Shading correction is performed by pre-accumulating charges in the material corresponding to the readout light intensity distribution in a state where the material is uniformly charged.

(Examples) Hereinafter, the method of the present invention will be explained in more detail with reference to Examples.

FIG. 1 is a schematic diagram for explaining a shading correction method using photographic film.

When a uniform charge is applied to the spatial light modulation tube 3, the distribution of the crystal thickness appears as bright and dark, as explained with reference to FIG.

In the figure, 110 is a shank for input light.

111 is a shutter for erasing light.

If this image is photographed and erasing light is irradiated through the film 101, the charge distribution due to the erasing light will be as shown in FIG. 6, and the output image will have uniform brightness.

FIG. 2 is a schematic diagram for explaining a shading correction method using feedback.

First, the shutter 112 is opened to uniformly charge the spatial light modulation tube 3 with uniform light. Next, by closing the shutter 112 and opening the shutter 113, the output image is
/2 plate 103 provides feedback to the input surface of the spatial light modulation tube 3 through the analyzer 102.

The intensity of the feedback light will have a distribution as shown in FIG. 6, and if the feedback light is used for erasure, the output image will have uniform brightness.

Based on a similar principle, in an EBSLM (light valve), shading due to non-uniformity of crystal thickness is corrected by modulating the beam of erasing light to perform erasing.

(Effects of the Invention) As explained in detail above, the shading correction method for a spatial light modulator according to the present invention includes an electron source, and accumulates electrons emitted from the electron source to correct natural birefringence that causes optical changes. In a spatial light modulator of a type that is made of an electro-optic material and whose optical changes are read out using external light,
The device is configured to perform shading correction by accumulating in the material in advance charges corresponding to the readout light intensity distribution in a state where the material is multiplied by M uniform charges.

The method can be realized using a simple device as described above.

This method makes it possible to correct shading caused by minute variations in crystal thickness that are unavoidable in crystal processing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a first configuration (using photographic film) for carrying out the method of the invention. FIG. 2 is a schematic diagram showing a second configuration (feedback type) for implementing the method of the invention. FIG. 3 is a schematic diagram for explaining the principle of the spatial light modulation device. FIG. 4 is a schematic diagram showing an example of occurrence of shading in a spatial light modulation device using an electro-optic crystal plate. FIG. 5 is a graph showing the relationship between brightness and charge accumulated at a point with a specific thickness. FIG. 6 is a graph showing an example of the distribution of charges necessary to obtain uniform brightness. l... Input image 2... Lens 3... Spatial light modulation tube 4... Laser 5... Objective lens 6... ... Pinhole plate 7 ... Analyzer 8 ... Collimating lens 9 ...
Half mirror 10... White light source 11... Polarizer 12... Screen 31... Photocathode 32... Micro channel plate 33...
...Secondary electron collecting electrode 34... Electro-optic crystal plate (55° cut LiN
bo3 wafer) 35... Output window 100.104... Half mirror 101... Photographic film 102... Analyzer 103... λ/2 plate 110, 111, 112, 113... shutter 105
...Mirror Patent Applicant Hamamatsu Photonics Co., Ltd. Agent Patent Attorney Hisashi Inoro Figure 5 A underground and bjl! Point @Cargo amount and light 8sb Figure 6 Procedural amendment document March 3, 1986

Claims (3)

[Claims] (1) A spatial light modulator consisting of an electron source and an electro-optic material having natural birefringence that accumulates electrons emitted from the electron source and causes optical changes, and reads out the optical changes using external light. A shading correction method for a spatial light modulator, wherein shading correction is performed by pre-accumulating in the substance a charge corresponding to a readout light intensity distribution in a state in which a uniform charge is accumulated in the substance. (2) Accumulation of charges corresponding to the readout light intensity distribution is achieved by irradiating erasing light onto the incident surface of the spatial light modulation tube through a film corresponding to the readout light with uniform charges accumulated in the material. A shading correction method for a spatial light modulator according to claim 1, which is obtained. (3) Accumulation of charge corresponding to the readout light intensity distribution means that the readout light is λ
2. The shading correction method for a spatial light modulator according to claim 1, wherein the shading correction method is obtained by feedback to the input surface of the spatial light modulation tube through a /2 plate and an analyzer.