Television – Video display – Projection device
Patent
1997-06-23
1999-11-23
Kostak, Victor R.
Television
Video display
Projection device
348750, 348757, H04N 574
Patent
active
059909838
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to image projectors using lasers for a source of light. More specifically, it relates to projection display systems wherein solid state microlasers or heterostructure diode lasers, or both, are employed in the projection of high resolution full-color images.
BACKGROUND ART
Rapid advances in processing of information have placed ever increasing demands on the display systems which transfer critical information to the decision makers in a variety of settings. One serious limitation has been in the area of the quality of display systems meeting the demands of high frame rates and high resolution with compact, cost effective, and efficient optical sources.
Two basic principles, light-modulation and direct emission, are used in video projectors. In a light-modulation design, a beam of light passes through an optical array which is capable of switching individual display elements (pixels) on or off. Liquid crystal display (LCD) panels are common light modulators. Other, more exotic modulators, such as oil films and deformable micro-mirrors, are also available. Direct-emission projectors emit their own-light. The most common direct-emission device is the CRT projector, used in home TV projectors and in high power versions for large screen industrial use. Direct-emission projectors are inherently simpler than light-modulation projectors. Conceptually, the direct emission projector consists only of a controllable light source and optics. The evolution of the CRT projector illustrates how, owing to its inherent simplicity, a direct-emission display mechanism can be readily produced and later scaled-up to higher brightness and resolution levels.
As the resolution requirement of high definition television (HDTV) and computer displays increase, CRT-based projectors reach some basic physical limits. A breakthrough is necessary to extend the resolution and brightness limits of this mainstream projection technology. Unfortunately, there are very few viable direct-emission technologies, so designers have looked for other ways to project video and computer information. The result is a host of light-modulation projectors using many different techniques. However, projectors of this type share a set of common problems. One of them is the need for an efficient light source which maximizes the amount of light that is passed through the modulator. Also, the modulation device must be scalable to a reasonably small size. The design issues associated with these needs are difficult and complex, and in many cases they directly limit the achievable results.
To better understand the nature of limitations associated with previous technology, it becomes instructive to review briefly the operating characteristics of four principal contenders in the video projection arena. In order of review, these can be identified as CRT projectors, light valve projectors, passive-matrix panels and active-matrix panels.
CRT Projectors: Projection CRTs are similar to conventional monochrome CRTs, except that they are operated at much higher beam currents. Color systems are built using three independent CRT systems, each with its own lens. The user must make periodic convergence adjustments to bring the three beams into color registration. Attempts to produce single-lens projectors, where the three color tubes are internally converged at the factory, have not been widely accepted.
Light Valve Projectors: Light valve projectors have been developed to overcome some of the deficiencies of the CRT projectors. An advantage of light valve systems is that the light source and modulating element are decoupled. Light valve projectors based on the electron beam oil film light valve were developed over 25 years ago. In such systems, an oil film is used as the image source. Intensity of the projected light is controlled by the amplitude of the deformation of the oil film. However, they are very complex, bulky, expensive, and are difficult to set up and maintain.
An alternative to the oil film approach is provided by the LCD li
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Assa Shlomo
Flint Graham
Hargis David E.
Kostak Victor R.
Laser Power Corporation
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