Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2000-03-09
2002-02-26
Phan, James (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S201100, C359S204200, C359S216100, C348S210990
Reexamination Certificate
active
06351324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to scanning projection and display systems. More particularly, it relates to projection and display systems that scan one or more modulated laser beams to generate an image.
2. Description of Related Art
Rapid advances in information processing and video production have made it technically possible to provide high resolution video images. However, the quality of the video images seen by a viewer is severely limited by the systems that project the image on a screen. The lack of suitable display systems has been a significant factor in preventing widespread application of high resolution video projectors. Generally, the available projection display systems are either very expensive, or they do not provide a high quality image at high frame rates and high resolution, and with sufficient brightness. If available at an affordable cost, high resolution projection displays would have widespread and diverse uses such as projection TV for consumers and businesses, projectors for meeting room and auditoriums, flight simulators for military uses, and movie projectors for theatres.
Two basic principles, direct emission and light modulation, are commonly used in video projectors. Direct-emission projectors emit their own light. The most common direct emission device is the CRT projector used in home TV projectors. High power versions of CRT projectors have been used for large screen industrial use. In a CRT projector, an electron beam is appropriately modulated to excite phosphors, which in turn generates the color of each pixel in the image that is projected onto a screen.
To display a video (i.e. moving) image, a sequence of frames are displayed very rapidly on the CRT screen. Each frame must be fully scanned by a single electron beam within a very short time period. For example, for a 60 Hz frame refresh rate, each frame must be scanned in less than {fraction (1/60)} of a second. Because a frame is defined by a number of adjacent lines, each line must be scanned within a small fraction of the frame period, depending upon the size of the display. For example, in a standard 640×480 pixel format, each of 480 lines must be scanned in less than 3.5 microseconds (i.e. 3.5×10
−6
second). Of course, larger pixel formats (e.g. 800×600 or 2000×1000 have a greater number of pixels and lines, and therefore such larger formats require correspondingly faster line scans.
Despite the large number of lines that are scanned, direct-emission projectors have a relatively straightforward design that conceptually consists of only a controllable light source and optics. The evolution of the CRT projector to its present state 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. However, as resolution and brightness requirements increase, CRT-based projectors reach some physical limits and therefore, other ways to project video and computer information have been proposed and developed.
Light-modulation projectors have been proposed in which red, green, and blues lasers are individually modulated and combined to generate a full color image on a projection screen. In light-modulation projectors, laser radiation is modulated in a modulator array that switches individual display elements (pixels) on or off. Liquid crystal display (LCD) panels are common light modulators. Other modulators, such as acousto-optic modulators, oil film modulators, and deformable micro-mirrors (DMDs), are also available.
Light modulation projectors can be classified depending upon whether the modulated beam is scanned or not. Generally, a non-scanning projector requires a two-dimensional modulator array large enough to have a one-to-one relationship with the screen pixels, and each pixel is constantly illuminated. For example each array pixel in a 640×480 DMD array is directly mapped onto a screen pixel. However, non-scanning systems have demanding electronics requirements due to the large number of pixels that must be accessed simultaneously, and the available modulators are difficult and expensive to scale up to such sizes. Unfortunately, in the context of large high resolution displays, the available two-dimensional modulators have a limited pixel count. As a point of reference, present-day full-color LCD-based and DMD-based display systems are limited to pixel counts of less than 10
6
, while some displays require pixel counts of 2×10
6
and greater. Furthermore, the brightness of the projected display in constant illumination systems is low at higher pixel counts because the fractional area of the pixels decreases at higher densities, thereby reducing light output. The design issues associated with such constant illumination systems are difficult and complex, and in many cases they directly limit the achievable results.
In order to overcome the limitations and problems inherent in non-scanning projection systems that constantly illuminate each pixel, scanning architectures have been developed in which multiple laser beams are very rapidly scanned across a screen to create an image. The concept of scanning a single modulated laser beam is similar to the concept of scanning an electron beam in the familiar CRT monitor widely used for computers and TVs. However, a practical system for scanning an electron beam is very different from a practical system for scanning a modulated laser beam. Laser scanning configurations have practical hardware limitations on the modulation rate and the scanning rate. Particularly, the available light modulators are limited in bandwidth. Further bandwidth limitations are imposed by the scanner and scanning configuration. A typical two-dimensional (2D) scanner uses a polygon scanner for horizontal scanning and a galvanometer-actuated mirror (a “galvo mirror”) for vertical scanning, both of which have limited bandwidth (i.e. scanning rate). Although some high bandwidth polygon scanners are available, they are very expensive and impractical. Galvo mirrors are much less expensive, but they have much smaller bandwidth, and are plagued with nonlinearities.
To address the limitations of scanning speed and modulation bandwidth, parallel scanning systems have been proposed in which multiple modulated laser beams are scanned simultaneously, thereby reducing the scanning speed and modulation bandwidth requirements, such as disclosed in U.S. Pat. No. 5,534,950 issued Jul. 9, 1996 and PCT publication WO95/10159, published Apr. 13, 1995.
Parallel scanning techniques (architectures) used in prior multi-beam laser display systems can be divided into three basic techniques for purpose of discussion. These three scanning architectures are termed herein: (1) vernier, (2) paintbrush, and (3) pushbroom. In these scanning architectures, the image space can be treated as being divided into bands, which are defined as groups of adjacent lines. Typically, the number of lines in each band is equal throughout the image space, for example one parallel scanning system for a 640×480 format has 48 bands, each band including ten lines.
In the vernier scan architecture, multiple modulated laser beams simultaneously write multiple bands. Each band is written by a laser beam that is scanned across the screen to write a first line, then deflected to a next line in the band, then scanned to write the next line, and so forth until all the lines in the band have been written. Multiple beams are used to scan multiple bands in parallel; for example, one system may include 64 modulated laser beams that are vertically arranged with a spacing between adjacent beams of about {fraction (1/64)} of the screen height. The 64 beams write 64 bands in parallel in the image space.
In the paintbrush scan architecture, the laser beams are closely aligned in a vertical arrangement so that all lines in one band are written simultaneously. For example if a band has 64 lines, then 64 closely-positioned
Law Offices of James D. McFarland
Phan James
Photera Technologies, Inc.
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