Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-05-27
2001-10-16
Nguyen, Chanh (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S083000, C372S022000
Reexamination Certificate
active
06304237
ABSTRACT:
BACKGROUND OF THE INVENTION
A monochromatic red (R), green (G), and blue (B) light source having well color balanced white light output is a very desirable light source for many display applications, because it is known to be more efficient compared to other conventional incoherent “white light” light sources with red, green and blue filters. For example, used in conjunction with 3 channel, transmissive Liquid Crystal Display (LCD) panel modulator based projection display systems, the monochromatic R,G,B light source producing well color balanced white light can achieve at least 4 times higher optical efficiency than conventional high intensity incoherent light sources, such as Xenon lamps or Metal Halide lamps with red, green and blue filters.
However, the monochromatic R,G,B light source has to originate from some sort of lasers producing a visible spectrum of red, green and blue. As a result, all the past attempts to develop such light sources have had the following shortcomings.
1. Use of some sort of gas lasers as light sources. This results in unacceptably low wall plug efficiency and constant need of laser maintenance.
2. Some of the 3 primary wavelengths generated by the R,G,B laser light sources may not be suited for display use.
3. Some spatial light modulators used in display applications work well with continuous wave (cw) R,G,B laser light sources. The others need pulsed R,G,B laser light sources. It has been known to be very difficult to generate suitable R,G,B colors efficiently from cw laser designs, and pulsed laser light sources in the past have not been suited to couple with spatial light modulators, which require cw light sources, due to unacceptable long pulse duration.
4. The final problem associated with past R,G,B laser light sources is laser speckle, this phenomenon is considered to be a random interference pattern of intensity, which results from the reflection or transmission of highly coherent light from (or through) an optically rough surface (one whose local irregularities in depth are greater than one quarter of a wavelength from a laser light source). The speckle is very annoying to look at, and past attempts employed to minimize the speckle have been to vibrate the screens to disturb phase coherency associated with each wavefront.
SUMMARY OF THE INVENTION
The invention relates to a monochromatic, pulsed laser light source system; display systems employing the light source; and the method of providing the light source and displays.
The invention comprises a monochromatic R,G,B pulsed laser light source adapted for display applications, and particularly, LCD display systems. The light source includes a single or multiple laser master oscillator with a laser medium, for example, a neodymium (Nd)-containing laser medium, particularly, Nd:YVO
4
neodymium yttrium vanadate, to provide a pulsed, signal wave laser radiation, e.g., of about 1342 nm, 1047 nm arid 1064 nm and selected pulse width and pulse rate, and single or multiple laser power amplifier to amplify the power of the laser radiation. The light source includes single or multiple, preferably all solid state, non-linear frequency converters to receive and convert the amplified signal wave laser radiation to produce a green wavelength, e.g., about 532 nm or 523.5 nm; with slight spatial incoherency to reduce speckle, red wave length, e.g., about 626 nm to 629 nm with narrow spectrum incoherency to reduce speckle; and blue wave length, e.g., about 447 nm to 452 nm, which R,G,B wavelengths are particularly useful for color display purposes, such as when the light source is coupled with, and used in a three LCD display system, as hereinafter described.
The invention comprises a method by which speckle noise resulted from pulsed lasers may be reduced. Laser light produces a speckle noise, since it is so coherent. Speckle noise is reduced when R,G,B pulsed lasers are used as a light source, by introducing spatial incoherency in green light, by multimode operation and producing spectrum incoherency in red, which in combination reduces speckle noise.
Pulsed operation of the R,G,B laser light source is important, since pulsed operation permits the use of various non-linear frequency conversion processes, such as Optical Parametric Oscillation (OPO) and Sum of Frequency Mix (SFM) to produce visible wavelengths from the fundamental laser radiation of 1064 nm.
The invention includes display systems employing the monochromatic, pulsed laser light source, particularly for LCD display systems, since LCD panel (one of spatial light modulators) does not require pulse width modulation, the R,G,B pulsed laser light source may be coupled to three LCD panels (one panel for each primary color) to create a display system.
The invention presents a monochromatic R,G,B light source which incorporates:
a. solid state laser design which produces very high electrical to optical efficiency;
b. digital color space conversion electronics which transfers input video signal color space into R,G,B color space created by the monochromatic R,G,B light source, so that the resulting color spectrum is acceptable for display use;
c. a laser cavity design that operates at high pulse repetition rate (40-80 kHz range) and produces very short pulse (FWHM~7 ns range), or another design that operates at very high pulse repetition rate (>>1 MHz range) and produces ultra short pulse width (FWHM~100 ps range) with active modelock mechanism, which allows this monochromatic R,G,B light source to be coupled with many different spatial light modulators, which requires R,G,B light source that operates in cw or quasi-cw mode; and
d. a green laser design which produces multi-mode laser radiation (M
2
~10). The multi-mode operation of the laser helps increase the spatial incoherency, thus, reducing the speckle effect.
The invention will be described for the purposes of illustration only in connection with certain illustrated embodiments; however, it is recognized that those persons skilled in the art may make various additions, improvements, modifications and changes to the illustrated embodiments, without departing from the spirit and scope thereof.
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Corporation for Laser Optics Research
Nguyen Chanh
Ropes & Gray
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