JP2613701B2 - 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 for modulating a light beam into a two-dimensional spatial light pattern according to an input electric signal.

[0002]

2. Description of the Related Art As a conventional electric address type spatial light modulator, a liquid crystal light shutter used for a liquid crystal display is known.

The above-mentioned liquid crystal optical shutter has two polarizing plates,
It is composed of two glass plates on which transparent electrodes are deposited and a liquid crystal sandwiched between these glass plates, and the liquid crystal molecules are arranged by being twisted by 90 ° between the two glass plates.

When a liquid crystal twisted by 90 ° is sandwiched between two polarizing plates whose polarization directions are orthogonal to each other so that light does not pass through, the incident light rotates the polarization plane by 90 ° along the direction of the liquid crystal molecules. Is transmitted.

However, when a voltage is applied to the transparent electrode, the liquid crystal molecules are erected and the twist is removed, and the light is blocked because the plane of polarization of the incident light does not rotate. That is, the liquid crystal optical shutter functions as an electrical transmittance modulator for light rays.

Further, if liquid crystal molecules are stacked and arranged in the same direction without using a polarizing plate so that twisting does not occur between two glass plates, it is possible to change only the phase of light by applying a voltage. it can. This indicates that the liquid crystal molecules exhibit the same refractive index anisotropy (birefringence) as a uniaxial crystal having an optical axis in the major axis direction, and the light polarization direction (electric field oscillation direction)
Alternatively, changing the direction of the liquid crystal molecules changes the refractive index.

As a method of applying a voltage to the liquid crystal of the spatial light modulator, there are a simple matrix driving method and an active matrix driving method.

In the simple matrix driving method, an electrode for conducting a current is wrapped around a grid, and an electric signal is sent at the same timing in the vertical and horizontal directions. This is a method of applying a voltage.

On the other hand, the active matrix driving method is as follows.
In addition to the above-described electrode structure, this is a method in which an active element (transistor) is attached to each pixel and a voltage is applied to each pixel.

[0010]

Since the spatial resolution of the above-mentioned conventional electric address type spatial light modulator is determined by the size of the pixel, the spatial resolution increases as the pixel size is reduced and the density is increased. . However, in the above-described conventional spatial light modulator, it is necessary to provide an electrode, an active element, and the like for each pixel, and there is a problem that the density of the pixels is limited and the spatial resolution cannot be improved.

The present invention has been made in view of the above-described problems of the conventional electric address type spatial light modulator, and provides a spatial light modulator capable of improving the spatial resolution without changing the size of a pixel.

[0012]

Means for Solving the Problems In order to solve the above problems,
According to the present invention, there is provided a first light modulating means having a first surface composed of a plurality of pixels intersecting an optical axis and capable of changing a refractive index of each pixel by a predetermined method, A second light modulating means having a second surface composed of a plurality of pixels intersecting the axis and capable of changing the refractive index of each pixel by the predetermined method; The modulating means is arranged on the optical axis such that one of the plurality of pixels constituting the second surface overlaps with at least two of the plurality of pixels constituting the first surface in the traveling direction of light. And the amount of phase modulation of the overlapping portion is determined by the amount of phase modulation by the first light modulating means and the amount of phase modulation by the second light modulating means, and the overlapping portion functions as one pixel. A spatial light modulation device is provided.

[0013]

The first light modulating means has a first surface composed of a plurality of pixels intersecting with the optical axis. The first light modulating means changes the refractive index of each pixel by a predetermined method, and the second light modulating means. The means has a second surface composed of a plurality of pixels intersecting the optical axis, and changes the refractive index of each pixel by a predetermined method to form the second surface with respect to the light traveling direction. At least a part of the pixel to be arranged is arranged on the optical axis so as to overlap the pixel constituting the first surface, and changes the phase of the light transmitted through the first light modulation means and the second light modulation means.

[0014]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of a spatial light modulator according to the present invention.

FIG. 1 shows the configuration of a first embodiment of the spatial light modulator of the present invention.

The spatial light modulator shown in FIG. 1 is composed of the same electric address type liquid crystal spatial light modulators (hereinafter, referred to as spatial light modulators) 10 and 20 as a first light modulating means and a second light modulating means. Have been.

The spatial light modulators 10, 20 are configured such that the refractive index of each pixel changes by applying a voltage, and only the phase of light can be changed. And
The spatial light modulators 10, 20 are arranged on the same optical axis such that their planes are orthogonal to the optical axis.

The spatial light modulator 10 is arranged on the light source side with respect to the spatial light modulator 20. The spatial light modulator 20 is arranged in a horizontal direction of one pixel in a direction of an arrow a perpendicular to the optical axis. Are shifted by a distance equal to half the length of.

Therefore, the pixels 11 and 12 of the spatial light modulator 10 and the pixels 21 and 22 of the spatial light modulator 20 can be viewed from the optical axis direction as follows.
The positional relationship is as shown in FIG.

As shown in FIG. 2, the phase modulation amount of the portion A is determined only by the phase modulation amount of the pixel 11, but the phase modulation amount of the portion B is obtained by adding the phase modulation amounts of the pixels 11 and 21. It will be.

For this purpose, when the phase modulation amount of the portion A, that is, the phase modulation amount of the pixel 11 is determined in advance, the phase modulation amount obtained by subtracting the phase modulation amount of the pixel 11 from the desired phase modulation amount of the portion B is obtained. To the pixel 21.

Further, since the phase modulation amount of the portion C is the sum of the phase modulation amounts of the pixels 21 and 12, the phase modulation amount obtained by subtracting the phase modulation amount of the pixel 21 from the desired phase modulation amount is calculated as the pixel modulation amount. Give to 12.

Hereinafter, the amount of phase modulation is similarly obtained for the portion D, and the amount of phase modulation is similarly determined for all pixels.

As a result, the phase is modulated in units of a portion where each pixel of each of the spatial light modulators 10 and 20 overlaps,
Since the area of the portion where the pixels overlap is half the area of the pixels, a spatial resolution twice as large as that of each of the spatial light modulators 10 and 20 can be achieved.

Since the phase modulation amount is determined by one pixel of each part at both ends, the phase modulation amount is smaller by one pixel than the other parts, it may not be used by means of light shielding or the like. It is possible.

If the number of spatial light modulators to be used is further increased, the spatial resolution can be further improved in accordance with the number. In that case, the phase of the light is 2π (36
0 °) or more, it does not matter.

That is, if the phase of the light is changed by 2π, the phases of the light become equal, so that the phase modulation of the light generally ranges from 0 to 2π.
The phase modulation pattern may be spatially the same even if the phase is changed by 2mπ (m is 0 or a positive integer) in the entire space.

In the above-described embodiment, two identical spatial light modulators are used. However, it is also possible to use a spatial light modulator in which the pixels themselves are previously shifted by half the pixel pitch.

Using such a spatial light modulator,
This is particularly effective in the case of a spatial light modulator in which pixels do not match when moved in parallel in the direction perpendicular to the optical axis. Such an example will be described below as a second embodiment.

FIG. 3 shows the configuration of a second embodiment of the spatial light modulator according to the present invention.

The spatial light modulator of FIG. 3 includes two spatial light modulators 30 and 40. These spatial light modulators
Numerals 30 and 40 change the refractive index of each pixel by applying a voltage and change only the phase of light.

The spatial light modulators 30 and 40 are arranged on the same optical axis so that their surfaces are orthogonal to the optical axis.

The spatial light modulator 30 is arranged on the light source side with respect to the spatial light modulator 40. Each spatial light modulator
Pixels 30 and 40 are formed concentrically, and the spatial light modulator 30
And the pixel of the spatial light modulator 40 are arranged to be shifted by a distance corresponding to a half of their radial width.

Therefore, when viewed from the optical axis direction, for example, the pixel
The pixels 31 and 41 have a positional relationship as shown in FIG.
Overlap at the B 'part.

As in the case of the first embodiment described above, B '
Can be determined as the sum of the phase modulation amounts of the pixels 31 and 41. Further, the phase modulation amount of the portion A ′ is determined by the phase modulation amount of the pixel 31 and the spatial light modulator.
The phase modulation amount of a pixel (not shown) on the inner side of the pixel 41 on the pixel 40 is determined as the sum, and the phase modulation amount of the portion C ′ is determined by the phase modulation amount of the pixel 41 and the spatial light modulator 30. Upper pixel 31
Is determined as the sum of the phase modulation amounts of the pixels (not shown) outside the pixel.

Similarly, the phase modulation amounts of the other parts are determined as the sum of the phase modulation amounts of the pixel of the spatial light modulator 30 and the pixel of the spatial light modulator 40 overlapping the pixel 30. And the radial width of the part where the pixels overlap is
Since the width is half of the width of each pixel, the spatial resolution is improved twice as much as when the spatial light modulator 30 or the spatial light modulator 40 is used alone.

When two identical spatial light modulators in which pixels are formed concentrically are used and they are displaced in the direction orthogonal to the optical axis as in the first embodiment,
Although the spatial resolution is improved, the rotational symmetry with respect to the optical axis is lost in that case.

As shown in FIG. 5, in the case of the spatial light modulators 50 and 60 in which concentric pixels are further divided in the circumferential direction, for example, the spatial light modulator 60 is connected to a predetermined position around the optical axis. By rotating by an angle, the circumferential length of the portion where each pixel overlaps is halved. Therefore, in this case, the spatial resolution in the circumferential direction can be doubled.

The spatial light modulator that changes the phase of light has been described above as an example. However, the present invention can of course be applied to a spatial light modulator that rotates the plane of polarization of light and modulates light intensity with a polarizing plate. In addition, the spatial resolution can be increased without changing the size of the pixel.

At this time, even if the polarization plane is rotated by 2π or more by superimposing the pixels, if the polarization plane rotates by 2π, the polarization state returns to the original polarization state, so that there is no problem.

In each of the embodiments described above, the case of the transmission type electric address type spatial light modulator has been described. However, the present invention is also effective in the case of the reflection type electric address type spatial light modulator. In addition, by arranging the pixels so as to partially overlap with each other, the spatial resolution can be increased without changing the size of the pixels.

In the above-described embodiment, the spatial light modulator is orthogonal to the optical axis. However, the spatial light modulator need not necessarily be orthogonal, and each pixel partially overlaps in the optical axis direction. What is necessary is just to arrange | position as follows.

[0043]

According to the spatial light modulator of the present invention, the spatial light modulator has the first surface composed of a plurality of pixels intersecting the optical axis, and changes the refractive index of each pixel by a predetermined method. A first light modulating means capable of changing the refractive index of each pixel by a predetermined method, the second light modulating means having a second surface composed of a plurality of pixels intersecting the optical axis. Since the second light modulating means is disposed on the optical axis such that at least a part of the pixels constituting the second surface overlap with the pixels constituting the first surface in the light traveling direction. The optical characteristics of the overlapping pixels can be set by the respective optical characteristics of the overlapping pixels, and the area of the overlapping portions can be smaller than the area of each pixel. Spatial resolution can be easily achieved without reducing It can be.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment of a spatial light modulator according to the present invention.

FIG. 2 is an enlarged view showing a part of the spatial light modulator of FIG. 1;

FIG. 3 is a diagram showing the configuration of a second embodiment of the spatial light modulator of the present invention.

FIG. 4 is an enlarged view showing a part of the spatial light modulator of FIG. 3;

FIG. 5 is a diagram showing a modification of the spatial light modulator of FIG.

[Explanation of symbols]

 10, 20, 30, 40, 50, 60 spatial light modulators 11, 12, 21, 22, 31, 41 pixels

Continued on the front page (72) Inventor Terutaka Tokumaru 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Yoshio Okada 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation

Claims (1)

(57) [Claims] A first light modulating means having a first surface composed of a plurality of pixels intersecting with an optical axis and capable of changing a refractive index of each pixel by a predetermined method; A second light modulating means having a second surface composed of a plurality of pixels intersecting the axis and capable of changing the refractive index of each pixel by the predetermined method; multiple light modulating means, constituting the second surface with respect to the traveling direction of the light
A plurality of image that one of the pixels constituting the first surface
The optical modulator is disposed on the optical axis so as to overlap with two or more of the elements, and the amount of phase modulation of the overlapping portion is equal to the first optical modulation.
And the phase modulation amount by the second light modulating means.
Is determined by the amount of phase modulation, and the overlapping portion is one pixel
A spatial light modulator that functions as a device.