JPH06117962A - Evaluation unit and regulating method for spatial optical modulation element - Google Patents

Abstract

PURPOSE:To obtain an evaluation unit and a regulating method for spatial optical modulation element which allows measurement in microregion, e.g. measurement of phase characteristics at a pixel unit of spatial optical modula tion element. CONSTITUTION:The evaluation unit for spatial optical modulation element comprises a spatial optical modulation element holder 6, a light source 1 for irradiating a spatial optical modulation element 7 held on the holder 6, and a parallel plate 8 arranged in the rear of the holder 6 while inclining against the optical axis. The evaluation unit further comprises a first optical detector 13 arranged in the rear of the parallel plate, and a second optical detector 18 arranged in the reflection optical path of the parallel plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for evaluating a spatial light modulator used in an optical information processing apparatus for optically executing image processing or image recognition in a visual recognition apparatus such as a robot.

[0002]

2. Description of the Related Art In recent years, it has been required for image processing or image recognition technology to process a larger number of pixels at a higher speed. Therefore, development of an optical information processing apparatus that responds to the above-mentioned demand by utilizing a high-speed parallel arithmetic function of light has become active. In these optical information processing apparatuses, for example, a spatial light modulator such as a liquid crystal display is used like the optical information processing apparatus described in Japanese Patent Application No. 63-287016. Unlike the case of being used for a display or the like, these spatial light modulators are required to have good characteristics in both amplitude and phase of transmitted light or reflected light. Therefore, the amplitude characteristic is generally evaluated from the light intensity characteristic measured using a spectrophotometer or the like, while the phase characteristic is measured using an interferometer.

[0003]

However, in an interferometer commercially available for measuring wavefront aberration of optical parts such as lenses and prisms, for example, in a minute region such as a phase characteristic in a pixel unit of a spatial light modulator. The measurement was impossible.

In view of the above problems, it is an object of the present invention to provide a spatial light modulation element evaluation apparatus which enables measurement in a minute region such as phase characteristics of the spatial light modulation element in units of pixels.

[0005]

A spatial light modulation element evaluation apparatus of the present invention for solving the above problems is a spatial light modulation element holding means and a spatial light modulation element held by this spatial light modulation element holding means. A light source for illuminating the element, a parallel plate arranged behind the spatial light modulation element holding means with an inclination with respect to the optical axis, and a first photodetector arranged behind the parallel plate are provided. A spatial light modulation element evaluation apparatus having a second photodetector arranged in the reflection optical path of the parallel plate.

Further, the adjusting method of the spatial light modulator evaluation apparatus of the present invention comprises a spatial light modulator holding means, a light source for irradiating the spatial light modulator held by the spatial light modulator holding means, and this space. A parallel flat plate is provided behind the light modulator holding means so as to be inclined with respect to the optical axis, and a first photodetector is arranged behind the parallel flat plate, and the parallel flat plate is provided in the reflection optical path. In a spatial light modulation element evaluation device having a second photodetector arranged, a straight line having a width of one pixel continuous in a first direction orthogonal to a plane including a normal line to the optical axis and the surface of the parallel plate. By displaying a plurality of voltage-applied pixel groups in the spatial light modulator in a second direction orthogonal to both the normal line and the first direction, a plurality of adjustment patterns are formed at a pitch of two pixels. , Of the tilt angle of the parallel plate with respect to the optical axis A method of adjusting the spatial light modulator evaluation apparatus characterized by integer.

[0007]

According to the spatial light modulator evaluation device having the above structure,
It is possible to provide a spatial light modulation element evaluation device that enables measurement in a minute region such as phase characteristics of the spatial light modulation element in units of pixels.

Further, according to the above adjusting method, there can be obtained an adjusting method of the spatial light modulation element evaluation device which enables precise adjustment of the inclination angle of the parallel plate with respect to the optical axis.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A spatial light modulator evaluation apparatus of the present invention will be described below with reference to the drawings. FIG. 1 is a side view of an embodiment of the spatial light modulator evaluation apparatus of the present invention.

In FIG. 1, 1 is a semiconductor laser, 2 is a collimator lens, 3 is a retardation plate, 4 is a first lens, and 5 is a lens.
Is a second lens, 6 is a spatial light modulation element holder, 7 is a spatial light modulation element, 8 is a parallel plate having a thickness d and having a front surface reflectance of R1 and a rear surface reflectance of R2. It is arranged at an angle of θ1 with respect to. 10 is the third lens, 1
1 is the 4th lens, 12 is the double pinhole, 13 is 2
Split photodetector, 14 is a mirror, 15 is a fifth lens, 1
6 is a sixth lens, 17 is a pinhole, and 18 is a photodetector.

Here, the first lens 4 and the second lens 5
Is a reduction optical system, and is configured to reduce the emitted light from the semiconductor laser 1 that is collimated by the collimator lens 2 and irradiate the spatial light modulator 7.

The phase difference plate 3 sets the polarization state of the light emitted from the semiconductor laser 1 to a state suitable for measurement. That is, the elliptically polarized light or the linearly polarized light is converted into the linearly polarized light having a predetermined angle with respect to the spatial light modulator 7. Also,
The third lens 10 and the fourth lens 11, and the fifth lens and the sixth lens constitute a magnifying optical system.

Next, the structure of the parallel plate 8 in the apparatus of this embodiment will be described with reference to FIGS. 2 and 3. 2 is a configuration diagram showing the relationship between the spatial light modulator 7 and the parallel plate 8, and FIG. 3 is a diagram showing reflection and refraction of light on the parallel plate.

In FIG. 2, 7 is a spatial light modulator, 7a and 7b are pixels forming the spatial light modulator 7, and 8 is a parallel plate. Further, P in the drawing is the pixel pitch forming the spatial light modulator 7, and L1 is the pixel 7
A shows the optical axis of the light ray that passes through a, and L2 shows the optical axis of the light ray that passes through the pixel 7b. Also, L
Reference numerals 1'and L2 'respectively denote reflected lights of the light rays L1 and L2 from the parallel plate 8.

Further, in FIG. 3, reference numeral 8 denotes a parallel plate having a thickness d, a refractive index n, a front surface reflectance R1 and a back surface reflectance R2, which is arranged at an angle of θ1 with respect to the light rays L1 and L2. There is.

First, the reflected lights L1 'and L of the light rays L1 and L2.
2'is matched, that is, the constitutional condition of the parallel plate 8 for shifting the light beam by one pixel is shown below. This condition is called the position condition. To satisfy the position condition, L
The distance a between the point where 1 is refracted on the front surface of the parallel plate 8 and reflected on the back surface and reaches the front surface again and the first incident point is a = P / c
It is necessary to satisfy the condition of os θ1.

On the other hand, regarding this a, assuming that the refraction angle of L1 is θ2, considering an isosceles triangle whose base is a in FIG.
= 2dtan θ2 holds. Therefore, P = 2
It becomes dtan θ2 cos θ1. Where sin θ1 = n
By applying the refraction law of sin θ2, the position condition can be expressed by the following equation (1).

[0018]

[Equation 1]

The thickness d, the refractive index n and the inclination angle θ1 with respect to the optical axis of the parallel plate 8 are determined so as to satisfy the position condition (1).

Next, the amplitude condition which determines the visibility of the interference fringes of the light rays L1 'and L2' thus overlapped will be described below. When the light rays L1 and L2 have the same amplitude and are set to 1, the amplitude of the light ray L1 ′ is given by R1 since it is only one reflection on the surface of the parallel plate 8.

On the other hand, the amplitude of the light ray L2 'is (1-R1) ²
Given by R2. Therefore, the transmittance of the pixel 7a is Ra,
When the transmittance of the pixel 7b is Rb, the amplitude condition is given by the equation (2).

[0022]

[Equation 2]

A parallel plate 8 is provided so as to satisfy this amplitude condition.
The front surface reflectance R1 and the rear surface reflectance R2 are determined.

The phase condition for determining the phase difference between the light rays L1 'and L2' for producing the interference fringes of the light rays L1 'and L2' is obtained as follows. The optical path length difference between the light ray L1 'and the light ray L2' is the optical path length difference in the air before entering the parallel plate 8, which is shown by b in FIG. It is the difference. That is, b = P
tan θ1 and n (2d / cos θ2). here,
If the Snell's rule is used for θ2, the phase condition can be expressed by equation (3).

[0025]

[Equation 3]

The thickness d, the refractive index n, and the inclination angle θ1 of some parallel plates 8 satisfying the above-mentioned position condition (1) satisfying the phase condition (3) are set.

The operation of the apparatus of this embodiment having the above configuration will be described below. First, the spatial light modulator holder-6
Among the pixels forming the spatial light modulation element 7 installed in the pixel 7, the pixel 7a of the pair of pixels 7a and 7b that are adjacent to each other is used as the reference, that is, no voltage is applied to the pixel 7a, A predetermined drive voltage is applied to 7b.

In this state, the light which is emitted from the semiconductor laser 1 through the second lens 5, the first lens 4, the phase difference plate 3 and the collimator lens 2 constitutes a spatial light modulator 7 which is a pixel. 7a and pixel 7b are illuminated.

As a result, the light ray L1 passing through the pixel 7a and the light ray L2 passing through the pixel 7b are partially reflected by the parallel plate 8 so that the respective reflected light rays L1 'and L2' overlap.
Interference occurs in the region where the reflected lights L1 'and L2' are superimposed. This interference intensity is determined by the pixel 7 to which the drive voltage is applied
It changes according to the phase change of the transmitted light at b. That is, it takes a maximum value when the phase difference between the transmitted lights of the pixels 7a and 7b is 0, and becomes 0 when the phase difference is π.

The interference light is reflected by the mirror 14, magnified by the fifth lens 15 and the sixth lens 16, and enters the photodetector 18 via the pinhole 17.
At this time, the pinhole 17 blocks light other than the target interference region. Further, at a distance P between adjacent pixels, aberrations other than the phase change due to the applied voltage, for example, distortion caused by the substrate, that is, a static phase difference can be substantially ignored. Therefore, by measuring the output of the photodetector 18, it is possible to evaluate the change in the phase of the transmitted light from an arbitrary pixel with respect to the applied voltage with reference to the adjacency.

On the other hand, the light rays L1 and L2 transmitted through the parallel plate 8 are expanded as parallel light while maintaining the pitch P by the third lens 10 and the fourth lens 11 and divided into two via the double pinhole 12. It is incident on the photodetector 13.
At this time, the double pinhole 12 separates the light ray transmitted through the pixel 7a and the light ray transmitted through the pixel 7b, and shields other light rays. Therefore, the light beam that has passed through the pixel 7a and the light beam that has passed through the pixel 7b enter the two detection portions of the two-divided photodetector 13, respectively.

Therefore, by comparing the outputs of the two detection portions of the two-divided photodetector 13, it is possible to evaluate the change in the intensity of the transmitted light from an arbitrary pixel with respect to the applied voltage with reference to the adjacent pixel.

As described above, according to this embodiment, it is possible to simultaneously measure both the amplitude and phase characteristics of the spatial light modulator in a minute area of at least one pixel unit. Furthermore, the third
Of the magnifying optical system including the lens 10 and the fourth lens 11 or the fifth lens 15 and the sixth lens 16 and the pinhole of the double pinhole 12 or the pinhole 17
It goes without saying that both the amplitude and phase characteristics of a region smaller than one pixel can be evaluated by appropriately setting the radius diameter. Further, although the transmissive spatial light modulator is described in the present embodiment, the same effect can be obtained also with the reflective spatial light modulator.

Next, an adjusting method of the spatial light modulator evaluation device according to claim 2 of the present invention will be described with reference to the drawings.

First, the structure of the adjustment pattern used in the adjustment method of the spatial light modulator evaluation apparatus will be described with reference to FIG. FIG. 4 shows an example of the adjustment pattern in the spatial light modulator evaluation apparatus shown in FIGS. 1, 2 and 3. The first direction in FIG. 4 is the direction orthogonal to the optical axis of the spatial light modulator evaluation device and the plane including the normal to the surface of the parallel plate 8. The second direction is a direction orthogonal to both the first direction and the optical axis of the spatial light modulator evaluation device. Further, in FIG. 4, the hatching portion shows the drive voltage applying portion, and the other portions show the voltage non-applying portion.

As shown by hatching in FIG. 4, the adjustment pattern has a plurality of linear voltage application pixel groups whose width is continuous in the first direction of one pixel and is arranged at a two-pixel pitch in the second direction. It is composed. That is, it is a pattern in which one pixel to which a voltage is applied in the second direction and one pixel which is a non-application portion are adjacently and alternately arranged.

Next, the adjusting pattern constructed as described above.
A method of adjusting the spatial light modulation element evaluation apparatus using the projector will be described below with reference to FIGS.

First, the adjustment pattern shown in FIG. 4 is displayed on the spatial light modulator 7. In this state, the second lens 5, the first lens 4, the phase difference plate 3, the collimator lens 2
The spatial light modulator 7 is irradiated with the light emitted from the semiconductor laser 1 via the laser. As a result, the light ray L1 that passes through the voltage application pixel of the adjustment pattern and the light ray L that passes through the non-application pixel
2 is partially reflected by the parallel plate 8.

Interference occurs in the area where the reflected light is superimposed. In order to generate the superposition of the reflected light, the parallel plate 8
Setting accuracy of about 0.1 degree is required so that the inclination angle θ1 with respect to the optical axis satisfies the positional condition shown in Expression 1. Therefore, it is extremely difficult to satisfy the above angle accuracy due to a processing error of the parallel plate 8, an assembly error, an optical axis error of the spatial light modulator evaluation device, and the like.

On the other hand, the interference intensity takes a maximum value when the phase difference between the light rays L1 and L2 is 0, and becomes 0 when the phase difference is π.
Therefore, using the adjustment pattern shown in FIG.
The light detector 1 is reflected by 14 and is magnified by the fifth lens 15 and the sixth lens 16 through the pinhole 17.
If the angle of inclination angle θ1 of the parallel plate 8 is adjusted so that the intensity of the light incident on 8 is maximized or minimized, the angle can be accurately determined regardless of the size and position of the pinhole 17 that determines the absolute value of the detected intensity. You can make adjustments.

Here, the parallel plate 8 is set so that the intensity of the light incident on the photodetector 18 becomes maximum or minimum.
Whether or not to adjust the inclination angle θ1 of 1 may be selected according to the characteristics of the spatial light modulator and the applied voltage.

[0042]

As described above, according to the spatial light modulation element evaluation apparatus of the present invention, it is possible to measure the phase characteristics of the spatial light modulation element in a pixel unit in a minute region.

Further, according to the adjusting method of the spatial light modulator evaluation apparatus of the present invention, it is possible to precisely adjust the inclination angle of the parallel plate in the spatial light modulator evaluation apparatus of the present invention with respect to the optical axis. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of a spatial light modulator evaluation apparatus of the present invention.

FIG. 2 is a relational diagram between a spatial light modulator and a parallel plate in the apparatus of the embodiment.

FIG. 3 is a diagram showing light reflection and refraction on a parallel plate of the apparatus of the embodiment.

FIG. 4 is a configuration diagram of an adjustment pattern used in the adjustment method of the present invention.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimator Lens 3 Phase Difference Plate 4 First Lens 5 Second Lens 6 Spatial Light Modulating Element Holder 7 Spatial Light Modulating Element 8 Parallel Plate 10 Third Lens 11 Fourth Lens 12 Double Pinhole 13 2 Division Photodetector 14 Mirror 15 Fifth lens 16 Sixth lens 17 Pinhole 18 Photodetector

Claims (2)

[Claims] 1. A spatial light modulation element holding means, a light source for illuminating the spatial light modulation element held by the spatial light modulation element holding means, and a tilt behind the spatial light modulation element holding means with respect to the optical axis. A parallel photoplate arranged in parallel with each other, a first photodetector arranged behind the parallel plate, and a second photodetector arranged in the reflection optical path of the parallel plate. Spatial light modulator evaluation system. 2. A spatial light modulation element holding means, a light source for illuminating the spatial light modulation element held by the spatial light modulation element holding means, and a tilt behind the spatial light modulation element holding means with respect to the optical axis. Evaluation of spatial light modulator having parallel flat plate arranged in parallel, first photodetector arranged behind the parallel flat plate, and second photodetector arranged in the reflection optical path of the parallel flat plate A method for adjusting a device, wherein a linear voltage application pixel group having a width of 1 pixel and continuing in a first direction orthogonal to a plane including a normal line of the surface of the parallel plate and the optical axis is defined by the normal line. By displaying on the spatial light modulator a plurality of adjustment patterns each having a two-pixel pitch in a second direction orthogonal to both the first direction and the first direction, the tilt angle of the parallel plate with respect to the optical axis can be adjusted. Adjustment method of spatial light modulator evaluation apparatus characterized by adjustment .