Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-12-20
2001-03-06
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S252000
Reexamination Certificate
active
06198566
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an optical switching device (light valve) used for optical communication, optical operation, an optical storage, an optical printer, a picture display device, etc. and, more particularly, to a picture display device and an optical switching device applicable to a projection apparatus or the like.
2. Background Art
A picture display device such as a projector primarily employs a liquid crystal display device
900
that uses liquid crystal as an optical switching device as shown in
FIG. 21
which provides a schematic configuration thereof. The liquid crystal display device
900
formed of a polarizers
901
and
908
, glass plates
902
and
903
, transparent electrodes
904
and
905
, and liquid crystals
906
and
907
provides pixel display by applying a voltage between the transparent electrodes to change the orientations of liquid crystal molecules thereby to rotate polarizing surfaces. Images are presented by using a liquid crystal panel constituted by pixels which are formed of such optical switching devices (liquid crystal cells) and are two-dimensionally arranged, and by adjusting an applied voltage to control the orientations of liquid crystal molecules so as to perform gray-scale representation.
Liquid crystal, however, exhibits poor fast-response characteristic and operates at a response speed of only about a few milliseconds at most. There has been another problem in that the polarizers deteriorate light utilization efficiency of liquid crystal, and an attempt to obtain a higher contrast ratio considerably adds to power consumed. For this reason, as a picture display device that is required to provide still higher picture quality, there have recently been demands for a picture display device capable of providing brighter display with more accurate gray scale representation than a liquid crystal display apparatus.
In recent years, a picture display device has been under study that employs an optical switching device capable of quickly turning light ON/OFF by bringing an optical switching assembly, which is equipped with a light transmitting micro prism capable of extracting light, close to a light guiding member that is capable of transmitting light by means of total reflection so as to extract evanescent light (evanescent wave) and by a minute movement of about one wavelength or less. The picture display device employing such an optical switching assembly is expected to be able to provide brighter picture display with higher contrast since the picture display device is capable of operating at faster speed because of a shorter moving distance and also capable of enhancing light utilization efficiency. However, the picture display device utilizing evanescent light is still in a developing phase, and it has not yet necessarily become able to provide higher efficiency of light utilization and high-quality images with higher contrast.
Accordingly, an object of the present invention is to provide a picture display device capable of enhancing the efficiency of light utilization so as to provide higher quality pictures with higher contrast by optimizing a picture display device employing an optical switching device utilizing evanescent light, particularly by optimizing a path or the like of an incoming light ray applied to a display area provided on a total reflection surface. Another object of the invention is to provide an optical switching device ideally suited for such a picture display device.
DISCLOSURE OF THE INVENTION
To these ends, a picture display device in accordance with the present invention employs a micro prism to extract and reflect an evanescent wave, and is designed so that light is applied to the micro prism from two symmetric directions. Therefore, the picture display device in accordance with the present invention has a light guiding member equipped with a total reflection surface capable of transmitting an incoming light ray for image display by means of total reflection, an optical switching assembly attached to a display area of the total reflection surface, and a light source assembly capable of applying an incoming light ray to at least the display area, wherein the optical switching assembly is equipped with a plurality of light transmitting extracting surfaces that can be moved to a first position where they are close to an extracting distance or less at which evanescent waves (evanescent light) leaking from the display area can be extracted, and a second position where they are away from the extracting distance or farther, and a plurality of micro prisms that reflect the light extracted from the extracting surfaces toward the light guiding member; and the light source assembly or the light guiding member are arranged so that an incoming light ray can be applied from two directions that are symmetrical in relation to the display area. Furthermore, an arrangement is made so that an incoming light ray is applied to the micro prisms of the optical switching assembly from both sides so as to increase the intensity of an outgoing light ray per pixel. Thus, brighter images can be obtained, and ON/OFF contrast can also be increased.
In order to extract evanescent light leaking from an incoming light ray that is totally reflected on the total reflection surface and to emit it as a vertical outgoing light ray, a triangular micro prism that has an appropriate apex angle and extends along the total reflection surface is suitably used. By radiating an incoming light ray from two symmetric directions to the micro prism, the incoming light ray can be reflected by two prism surfaces having different angles with the apex being located therebetween. This makes it possible to obtain an outgoing light ray that is approximately twice as intense as that obtained when an incoming light ray is applied from one direction. Moreover, the outgoing light ray is emitted from the entire micro prism constituting one pixel, permitting a seamless image with no gap between pixels to be obtained. Hence, the present invention makes it possible to provide a picture display device capable of displaying brighter, higher-quality images by using evanescent light.
Preferably, the light source assembly or the light guiding member is configured so that the entire display area is irradiated by an incoming light ray that is not reflected in the display area. If the light source assembly or the light guiding member is configured so that an incoming light ray that has been reflected by a part of the display area is applied to another display area, then the intensity of the incoming light ray radiating another display area changes depending on whether the optical switching assembly of the display area to which the incoming light ray is applied first is ON or OFF. Hence, there is a likelihood that the light intensity of an outgoing light ray for displaying an image changes according to a display area or an image mode, or the intensity of an incoming light ray becomes insufficient in another display area, and an outgoing light ray produced by ON/OFF of the switching assembly may not be obtained with a resultant failure to display an image. To avoid this problem, the entire display area is radiated by an incoming light ray that has not been reflected in the display area. This enables an incoming light ray of a constant intensity to be applied to all switching assemblies of the display area regardless of operating states of other switching assemblies. Hence, deterioration of image quality such as a chipped image or a reduced contrast can be prevented.
An incoming light ray can be applied to a display area from two directions by installing a light source assembly on one side of the light introducing assembly and by installing a reflecting surface on a side opposing an incident surface through which light from the light source assembly enters the light guiding member, with the total reflection surface being located therebetween. As the reflection surface, one that utilizes total reflection to reflect an incoming light
Takeda Takashi
Yonekubo Masatoshi
Dang Hung Xuan
Seiko Epson Corporation
Watson Mark P.
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