Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-10-12
2001-05-15
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S259000, C359S315000, C359S322000, C359S022000, C356S329000
Reexamination Certificate
active
06233083
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light modulation apparatus for modulating a light beam two-dimensionally and outputting the same, and an optical information processing system for applying a predetermined optical process to a light beam output from the light modulation apparatus.
2. Description of the Related Art
As an optical information processing system for modulating a light beam two-dimensionally and applying an optical process to the modulated light beam, an optical information recording and reproducing system using a so-called holographic memory (hereinafter referred to as an optical memory system) is known.
The optical memory system records an input signal in a holographic memory as a recording medium as follows. A recording signal light is applied with the spatial light modulation two-dimensionally based on the input signal. For the spatial light modulation of the input signal, a transparent type spatial light modulation apparatus comprising a plurality of pixels (specifically, a liquid crystal television comprising a plurality of pixels, or the like) is used. By interference between the recording signal light applied with the spatial light modulation and a recording reference light output independently, a two-dimensionally diffracted light is produced. Then, the image formed by the diffracted light is recorded in the holographic memory as the two-dimensional information corresponding to the input signal.
As the holographic memory, for example, a volume type hologram recording element formed by laminating a plurality of lithium niobate layers is used.
On the other hand, the above-mentioned optical memory system can reproduce the input signal by reading the two-dimensional information from the holographic memory wherein the two-dimensional information is recorded. The reproducing operation is executed as follows. A reproducing reference light is directed on the two-dimensional information on the holographic memory. At the time, the reproducing reference light is directed to the holographic memory with the same incident angle as the above-mentioned recording reference light. Then, the reflected light obtained thereby is received by a light receiving apparatus having a plurality of pixels. Accordingly, a light receiving signal is obtained from each pixel of the light receiving apparatus. Then, the original input signal is reproduced using the light receiving signals.
In the above-mentioned optical memory system, in order to correctly reproduce the original input signal from the holographic memory, it is needed that the relationship in position between the spatial light modulation apparatus and the light receiving apparatus is accurately determined and fixed. Furthermore, it is needed to set the holographic memory at a precise position.
However, if a movable portion is included in the spatial light modulation apparatus or the light receiving apparatus, or if the holographic memory itself is replaced frequently, displacement or positioning error may be generated in the optical memory system. The displacement in the spatial light modulation apparatus, the displacement in the light receiving apparatus, or the displacement of the holographic memory causes the displacement between the pixels in the spatial light modulation apparatus and the pixels in the light receiving apparatus. If such a displacement is generated, the original input signal cannot be reproduced correctly.
Specifically, if the displacement is generated, reflected light corresponding to a light beam output from a certain pixel in the spatial light modulation apparatus may not be incident on the correct pixel of the light receiving apparatus. In this case, the original input signal may not be reproduced correctly.
More specifically, in the normal state without displacement, for example, it is presumed that the reflected light corresponding to the light beam output from the pixel at the i row j column in the spatial light modulation apparatus is incident on the pixel at the I
1
row J
1
column in the light receiving apparatus. In this case, if displacement is generated by replacement of the holographic memory or the like, the reflected light to be incident on the pixel at the I
1
row J
1
column may be incident on the pixel at the I
2
row J
2
column. As a result, a correct light receiving signal is not obtained, so that the original input signal cannot be reproduced correctly.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a light modulation apparatus capable of removing an influence of displacement of a movable portion or a detachable part and therefore executing the accurate optical process, and to provide an optical information processing system using the light modulation apparatus.
A light modulation apparatus in accordance with an aspect of the present invention includes: a light modulation device comprising a plurality of first light transmission control elements each for controlling an amount of transmission of a light beam, for generating and applying a modulation light beam representing a modulation signal by controlling the amount of transmission of the light beam in each of the plurality of first light transmission control elements in accordance with the modulation signal; and a detection light beam generating device that always allows transmission of a part of the light beam for generating and applying a detection light beam for detecting a displacement of an irradiation position of the modulation light beam.
The light modulation apparatus in accordance with the present invention generates and applies the detection light beam for detecting a displacement of the irradiation position of the modulation light beam. Therefore, in a light receiving apparatus, the displacement of the irradiation position of the modulation light beam can be detected by using the detection light beam so that the influence of the displacement can be removed when the received modulation light beam are processed. Furthermore, in the light modulation apparatus in accordance with the present invention, the detection light beam is generated by using a part of the light beam which is used for generating the modulation light beam. Therefore, the detection light beam can be generated easily, and the construction of the light modulation apparatus can be simplified.
In the aforementioned light modulation apparatus, a modulation panel may be added, and the detection light beam generating device may includes a second light transmission control element that always allows transmission of a part of the light beam. Furthermore, a modulation area and a detection area may be formed on the modulation panel. In this case, the modulation area and the detection area are separated from each other, the plurality of first light transmission control elements are arranged in the modulation area, and the second light transmission control element is placed in the detection area.
In this light modulation apparatus, the detection light beam is generated by transmitting the light beam through the second light transmission control element placed in the detection area. On the other hand, the modulation light beam is generated by the first light transmission control elements arranged in the modulation area. Since the modulation area and the detection area are separated from each other, the detection light beam is separated from the modulation light beam in location. That is, the irradiation position of the detection light beam is separated from the irradiation position of the modulation light beam in a light receiving apparatus. Therefore, the light receiving apparatus can accurately and easily detects the detection light beam.
In aforementioned light modulation apparatus, a quadrilateral panel may be used as the modulation panel. In this case, the modulation area whose area is smaller than the area of the quadrilateral modulation panel is formed at the center of the quadrilateral modulation panel, the plurality of first light transmission control elements are arranged in th
Ben Loha
Ladas & Parry
Pioneer Corporation
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