Television – Holographic – Color tv
Reexamination Certificate
1999-07-16
2001-01-30
Le, Vu (Department: 2713)
Television
Holographic
Color tv
C348S051000, C348S739000, C348S750000, C348S790000, C345S005000, C345S006000
Reexamination Certificate
active
06181367
ABSTRACT:
TECHNICAL FIELD
This invention relates to viewing devices for video images, and more particularly to compact and lightweight video viewing device that can be adapted to a variety of applications including virtual reality viewing glasses and video monitors.
BACKGROUND OF THE INVENTION
Video viewing devices are in common use for a wide variety of applications. Cathode ray tube (“CRT”) displays have long been used for television viewing, and more recently as computer monitors. More compact devices for viewing video images, such as liquid crystal display (“LCD”) screens, have been developed as a substitute for CRT displays.
More recently compact, lightweight head mounted displays have been introduced as viewing devices for “virtual reality” systems. By providing a separate viewing device for each eye and appropriately varying the image viewable though each device, high-resolution stereographic video images may be displayed.
Another type of viewing device for video images are “heads up displays” (“HUD's”) that enable jet fighter pilots to process mentally a huge amount of information pertaining to both the space surrounding the aircraft and the condition and performance of the aircraft. This has led to the development of HUD's built into the transparent canopy of aircraft, as well as “head-mounted displays” and “visor displays.”
All of the above-described HUD's require light projected from a source display (such as a liquid crystal television screen) to travel some distance through air to a reflective, refractive or diffractive surface where the light is redirected to form a virtual image of the source display. A holographic optical element typically serves as a diffractive surface in such displays, and typically is highly color selective. However, it would be desirable to view a video image, particularly a three dimensional image, by directly generating a three-dimensional virtual image without the need for transmitting light from a source display through the air. If a technique could be found for avoiding the need to transmit light though the air over a substantial distance, the viewing device could be extremely compact, and could even closely resemble an ordinary pair of eyeglasses. The compact, lightweight and unobtrusive nature of such a viewing device would open up a multitude of new applications, such as allowing use as a monitor for a pocket-sized computer, a superior virtual reality viewing device, or as a prosthetic for deaf people to display visual cues derived from sound.
SUMMARY OF THE INVENTION
The inventive viewing device is adapted to display a virtual image corresponding to a video signal having a plurality of video lines in each video frame. A light generator selectively directs light beams into a first transparent plate at a plurality of respective locations along a surface of the first plate. The light beams are directed into the first plate in a manner that causes the light beams to propagate through the first plate with total internal reflection. An index of refraction modulator is positioned adjacent the first plate. The index of refraction modulator has a plurality of modulating elements at respective areas spaced apart from each other in the direction that the light propagates through the first plate. Each of the modulating elements is selectively controllable to either a first refractive index state or a second refractive index state responsive to a respective control signal. The first refractive index state causes the modulating element to have an index of refraction that is sufficiently different from the index of refraction of the first plate that the light beam remains internally reflected in the first plate in the area of the modulating element. The second refractive index state causes the modulating element to have an index of refraction that is sufficiently similar to the index of refraction of the first plate that a significant portion of the light beam exits the first plate in the area of the modulating element. An optical element positioned adjacent the index of refraction modulator controls the angle of divergence in the first direction of light exiting the first plate in the area of the modulating element. The light generator may be a plurality of light sources spaced apart along a surface of the first plate that are sequentially illuminated or a light beam that is scanned along a surface of the first plate. A color image may be generated by using a multicolor light generator, or by placing color selective modulating elements through which light passes as it exits the index of refraction modulator. The index of refraction modulator is preferably a layer of liquid crystal, and the modulating elements that control the refractive index of the liquid crystal layer are electrodes on opposite sides of the liquid crystal layer. The viewing device is driven by a video control circuit that receives a video signal corresponding to the intensity of a video image in each of a plurality of video lines. The video control circuit controls the intensity of each of the light beams in accordance with the amplitude of the video signal for each line. The video control circuit also generates control signals to cause each modulating element to be sequentially switched to its high index state responsive to a corresponding line of the video signal. A pair of the viewing devices may be mounted in a frame adapted to position each of the image display devices in front of a respective eye of an individual wearing the frame to allow stereoscopic viewing.
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DeVries P. David
Foster David H.
McGrew Stephen P.
Wink Roger F.
Dorsey & Whitney LLP
Le Vu
New Light Industries, Ltd.
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