Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2003-03-24
2004-10-19
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S636000, C353S031000
Reexamination Certificate
active
06807010
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to display systems that form a two-dimensional image on a display surface and more particularly relates to a color display apparatus using spatial light modulators that are illuminated by light from both incoherent light sources and laser light sources.
BACKGROUND OF THE INVENTION
Currently, promising solutions for digital cinema projection and home theater systems employ, as image forming devices, one of two types of spatial light modulators (SLMs): area SLMs and linear SLMs. An area spatial light modulator has a two-dimensional array of light-valve elements, each element corresponding to an image pixel. Each array element is separately addressable and digitally controlled to modulate transmitted or reflected light from a light source. There are two salient types of area spatial light modulators that are conventionally employed for forming images in digital projection and printing apparatus: Digital Micro-mirror Devices (DMDs) and Liquid-Crystal Devices (LCDs).
Prototype projectors using one or more DMDs have been demonstrated. DMD devices are described in a number of patents, for example U.S. Pat. No. 4,441,791 by Hornbeck, issued Apr. 10, 1984, titled “Deformable Mirror Light Modulator,” U.S. Pat. No. 5,535,047 by Hornbeck, issued Jul. 9, 1996, titled “Active Yoke Hidden Hinge Digital Micromirror Device,” U.S. Pat. No. 5,600,383 by Hornbeck, issued Feb. 4, 1997, titled “Multi-Level Deformable Mirror Device with Torsion Hinges Placed In A Layer Different From The Torsion Beam Layer,” and U.S. Pat. No. 5,719,695 by Heimbuch, issued Feb. 17, 1998, titled “Spatial Light Modulator With Superstructure Light Shield.” Optical designs for projection apparatus employing DMDs are disclosed in U.S. Pat. No. 5,914,818 by Tejada et al., issued Jun. 22, 1999, titled “Offset Projection Lens For Use With Reflective Spatial Light Modulators,” U.S. Pat. No. 5,930,050 by Dewald, issued Jul. 27, 1999, titled “Anamorphic Lens For Providing Wide-Screen Images Generated By A Spatial Light Modulator,” U.S. Pat. No. 6,008,951 by Anderson, issued Dec. 28, 1999, titled “Offset Projection Zoom Lens With Fixed Rear Group For Reflective Spatial Light Modulators,” and U.S. Pat. No. 6,089,717 by Iwai, issued Jul. 18, 2000, titled “Projector Apparatus.” LCD apparatus are described, in part, in U.S. Pat. No. 5,570,213 by Ruiz et al., issued Oct. 29, 1996, titled “Liquid Crystal Light Valve With Minimized Double Reflection” and U.S. Pat. No. 5,620,755 by Smith, Jr. et al., issued Apr. 15, 1997, titled “Inducing Tilted Perpendicular Alignment In Liquid Crystals.” Conventionally, area SLMs are provided filtered source illumination from a lamp or other broadband source. LCDs may be of either the reflective type (Liquid-Crystal On Silicon, or LCOS) or the transmissive type.
Linear SLMs, which could also be considered as one-dimensional spatial light modulators, have some advantages over the two-dimensional LCD and DMD area spatial light modulators described above. Inherent performance advantages for linear modulator arrays include the capability for higher resolution, reduced cost, and simplified illumination optics. In addition, linear arrays are more suitable modulators for laser light than are their two-dimensional counterparts. Grating Light Valve (GLV) linear arrays, as described in U.S. Pat. No. 5,311,360 by Bloom et al., issued May 10, 1994, titled “Method And Apparatus For Modulating A Light Beam” are one earlier type of linear modulator array that offers a workable solution for high-brightness imaging using laser sources, for example.
Recently, an electromechanical conformal grating device consisting of ribbon elements suspended above a substrate by a periodic sequence of intermediate supports was disclosed by Kowarz in commonly assigned U.S. Pat. No. 6,307,663, issued Oct. 23, 2001, titled “Spatial Light Modulator With Conformal Grating Device.” The electromechanical conformal grating device is operated by electrostatic actuation, which causes the ribbon elements to conform around the support substructure, thereby producing a grating. The device of '663 has more recently become known as the conformal GEMS device, with GEMS standing for Grating ElectroMechanical System. The conformal GEMS device possesses a number of attractive features. It provides high-speed digital light modulation with high contrast and good efficiency. In addition, in a linear array of conformal GEMS devices, the active region is relatively large and the grating period is oriented perpendicular to the array direction. This orientation of the grating period causes diffracted light beams to separate in close proximity to the linear array and to remain spatially separated throughout most of an optical system, providing a high degree of system flexibility and allowing the use of lower cost optics. When used with laser sources, GEMS devices provide excellent brightness, speed, and contrast.
Commonly assigned U.S. Pat. No. 6,411,425, issued Jun. 25, 2002, titled “Electromechanical Grating Display System With Spatially Separated Light Beams” and commonly assigned U.S. Pat. No. 6,476,848, issued Nov. 5, 2002, titled “Electromechanical Grating Display System With Segmented Waveplate,” (both to Kowarz et al.) disclose imaging systems employing GEMS devices in a number of printing and display embodiments. As with its GLV counterpart, a GEMS device modulates a single color and a single line of an for sequencing illumination and modulation data for each color to a single linear modulator or for combining separately modulated color images.
Among the recognized advantages of digital projection display employing spatial light modulators is an expanded color gamut, which allows displayed images to have improved color fidelity and appearance over images provided by conventional film-based or CRT-based projection systems. Color gamut is most readily visualized using the familiar tristimulus CIE color model developed by Commission Internationale de l'Eclairage (International Commission on Illumination), which shows the color space perceived by a standard human observer.
FIG. 1
a
shows the CIE color model, which represents a visible gamut
200
as a familiar “horseshoe” curve. Pure, saturated spectral colors are mapped to the “horseshoe” shaped periphery of visible gamut
200
. The interior of the “horseshoe” then contains all mappings of mixtures of colors, including mixtures of pure colors with white, such as spectral red with added white, which becomes pink, for example. Within visible gamut
200
, a device gamut
202
is typically represented by a triangle, with vertices approaching the curve of visible gamut
200
. In
FIG. 1
a
, device gamut
202
, as drawn, approximates the familiar gamut for standard SMPTE (Society of Motion Picture and Television Engineers) phosphors, for example.
As is well known in the color projection arts, it is desirable for a display device to provide as much of visible gamut
200
as possible in order to faithfully represent the actual color of an image and to provide vivid colors. The component colors of a display, typically Red, Green, and Blue (RGB) define the vertices of the polygon for device gamut
202
, thereby defining the area and shape of device gamut
202
.
One basic strategy, then, to increase the size of device gamut
202
is to use light sources that are spectrally pure, or have at least a high degree of spectral purity. Lasers, due to their inherent spectral purity, are particularly advantaged for maximizing device gamut
202
. Substantially monochromatic, laser sources effectively position vertices of device gamut
202
onto the periphery of visible gamut
200
.
A number of digital projector designs have been proposed for taking advantage of the favorable spectral qualities of laser sources. For example, U.S. Pat. No. 6,183,092 by Troyer, issued Feb. 6, 2001, titled “Laser Projection Apparatus With Liquid-Crystal Light Valves And Scanning Reading Beam,” U.S. Pat. No. 6,426,781 by Lee, issued Jul. 30, 2002, titled “Laser Video Projector,”
Epps Georgia
Harrington Alicia M.
Shaw Steven H.
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