Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2001-11-14
2002-08-20
Sangmau, Hemang (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S040000, C385S901000, C359S222100, C359S295000
Reexamination Certificate
active
06438282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an optical switching device (light valve) for use in optical communication, optical processing, optical memory devices, optical printers, image display devices, etc., and more particularly, to an optical switching device suitable for use in an optical image display device and to an optical image display device.
2. Background Art
Conventionally, an optical switching device using a liquid crystal is known in the art.
FIG. 43
schematically illustrates an optical switching device
900
according to a conventional technique. As shown in
FIG. 43
, the optical switching device
900
includes polarizers
901
and
908
, glass plates
902
and
903
, transparent electrodes
904
and
905
, and liquid crystals
906
and
907
. In this optical switching device, optical switching is performed by applying a voltage between the transparent electrodes so as to modify the orientations of liquid crystal molecules thereby rotating the polarization plane. A conventional image display device is produced by disposing such optical switching devices (liquid crystal cells) in a two-dimensional fashion into the form of a liquid crystal panel. In this image display device, representation of gray scales is accomplished by controlling the alignment of liquid crystal molecules by adjusting the applied voltage.
However, liquid crystals are slow in response. The response time of liquid crystals is several msec at best. This makes it difficult to employ optical switching devices using a liquid crystal in applications which need a short response time, such as optical communication, optical processing, an optical memory such as a hologram memory, an optical printer, etc. Another problem of optical switching devices using a liquid crystal is a reduction in the light utilization efficiency caused by a polarizer.
In the art of the image display device, increasingly high image quality is required. To meet such a requirement, it is needed to provide an optical switching device capable of representing gray scales more precisely than optical switching devices using a liquid crystal.
Thus, it is an object of the present invention to provide a low-loss optical switching device capable of responding at a high speed. It is another object of the present invention to provide an optical switching device capable of forming a high-quality image with a uniform contrast.
DISCLOSURE OF THE INVENTION
According to the present invention, to achieve the above objects, there is provided an optical switching device which extracts evanescent light from a light guide capable of transmitting light by means of total reflection, wherein extraction of light is performed when a light-transmissive extraction plane of a switching part is brought into contact with the light guide. Light can be turned on and off at a high speed by moving the switching part by a small distance nearly equal to one wavelength or less. The switching part is formed to be of a reflective type. The light guide, the optical switching part, and driving means for driving the switching part are disposed in this order in a direction in which light is illuminated, thereby forming the optical switching device in a multilayer structure. Thus, an optical switching device can be realized which can output a large amount of light with a low loss and which can respond at a high speed. That is, the switching part according to the present invention includes: the light guide with a total reflection plane capable of transmitting light by means of total reflection; the switching part including a light-transmissive extraction plane capable for extracting evanescent light leaking through the total reflection plane; and driving means for moving the switching part to a first position at which the extraction plane is within an extraction range which allows an evanescent light to be extracted and a second position at which the extraction plane is out of said extraction range, wherein the light guide, the switching part and the driving means are disposed in this order in a direction in which light is output.
In the optical switching device according to the present invention, the light guide, the switching part, and the driving means for driving the switching part may be disposed one on another in this order into a multilayer structure in which the functions of the light guide, the switching part, and the driving means are implemented in the respective layers substantially independently of one another. This makes it possible to easily optimize the respective parts. In the optical switching device according to the present invention, light is reflected by the switching part toward the light guide, and no light passes through the driving means. Therefore, it is possible to optimize the driving means without having to consider optical conditions.
This allows the switching part to be supported on the driving means, and thus it becomes unnecessary for the light guide to have a structure on the side facing the optical switching part. Thus, the light guide can be constructed in the form of a simple flat panel. Because the light guide is not required to include a part for supporting the switching part, the entire area of the light guide on the side where the total reflection plane is formed can be used as a plane through which light is extracted, that is, as a plane the switching part is brought into contact with. Thus it is possible to realize an optical switching device having a large aperture area through which light is output, that is, having a large aperture ratio, which allows a large amount of light to be output. Furthermore, by employing the panel structure, it becomes possible to use a plane opposite to the total reflection plane as an output plane through which the extracted light is output to the outside. The driving means may be formed on an integrated circuit substrate for controlling the driving means. The optical switching device may be integrated with an integrated circuit chip for controlling an image.
A pixel may be formed by one or a combination of a plurality of optical switching devices according to the present invention. If a plurality of optical switching devices are disposed in a two-dimensional fashion, and if the light guide is adapted to be capable of transmitting white light or three primary color light, an image display device can be obtained. This image display device can display a high-resolution image at a high speed. Furthermore, the image display device can be constructed into the form of a multilayer structure, which allows the image display device to be produced at low cost. The image display device may be integrated with an integrated circuit chip.
To realize the switching part of the reflective type, a light outputting member for outputting extracted light may be formed using a microprism or a light-dispersive material such that light extracted through the extraction plane is reflected by the light outputting member. The direction of the output light may be controlled so that light is output in a direction substantially perpendicular to the total reflection plane.
The driving means may include a supporting member for elastically supporting the switching part and electrostatic driving means for driving the switching part by means of electrostatic force acting between a pair of electrodes whereby the switching part may be moved to the first and second positions. Preferably, the supporting member urges the switching part at the first position toward the light guide when no electrostatic force is exerted by the electrostatic driving means. The electrostatic driving means can be easily controlled by electric power. However, the driving force provided by the electrostatic driving means varies with a variation in voltage or current. In contrast, a driving force provided by an elastic element is stable because it is generated mechanically. In view of the above, the supporting member formed of an elastic material is employed to stably generate a driving force thereby urging the extraction pla
Ito Hirokazu
Kamijima Shunji
Takeda Takashi
Yonekubo Masatoshi
Rojas, Jr. Omar
Sangmau Hemang
Seiko Epson Corporation
Watson Mark P.
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