Computer graphics processing and selective visual display system – Plural physical display element control system – Optical means interposed in viewing path
Reexamination Certificate
1998-08-25
2001-09-25
Brier, Jeffery (Department: 2672)
Computer graphics processing and selective visual display system
Plural physical display element control system
Optical means interposed in viewing path
C345S008000, C353S020000, C359S853000
Reexamination Certificate
active
06295039
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to display systems, and more particularly, to the illumination of display systems in which a plurality of pixels generate an image by reflecting light from one or more light sources.
BACKGROUND OF THE INVENTION
simplify the following discussion, the present invention will be discussed in terms of displays utilized in head mounted computer displays; however, it will be apparent to those skilled in the art from the following discussion that the present invention may be applied to other types of displays. Head-mounted computer displays may be viewed as “eye glasses” that are worn by the user to view images created by a computer or other video source. The image seen by each eye is generated on a display screen having a two dimensional array of pixels.
In one type of display, each pixel is a small mirror that is covered by a “shutter” that is controlled by the voltage of the mirror. The shutter is constructed from a layer of liquid crystal on the mirrors. The voltage controls the state of the liquid crystal on top of the pixel so as to modulate the reflected light. A light source illuminates the pixels and the modulated reflected light from the pixels is imaged into the eye of the viewer. The imaging optics typically consist of lenses that magnify the pixels and form a virtual image. The light source is typically constructed from 3 LEDs that emit different colors.
For this type of display to function properly, the intensity of light reflected by each micro-mirror must be independent of the pixel's location in the display. In addition, each pixel must appear to be an independent light source. The illumination must be both spatially and angularly uniform, with the angular extent given by the acceptance angle (f-number) of the imaging optics. In prior art systems these constraints are met by converting the three point light sources into a diffuse light beam that strikes the display at right angles to the plane of the mirrors. The light source utilizes a condenser lens to collimate or slightly diverge the light to match the telecentricity of the imaging optic and an array of micro-lenses or a diffuser in the collimated light beam to provide the required diffusion. Since the light source must be outside the field of view of the user so as not to block the image generated by the display, a half silvered mirror is used to illuminate the display while allowing light reflected by the display to reach the eye of the viewer.
This prior art solution to the illumination problem has several problems. First, the distance between the first imaging optic and the display must be at least as great as the shortest dimension of the display to provide room for the half-silvered mirror. Second, the illuminator requires a condenser lens and diffuser which must be at least as large as the display. These constraints lead to a bulky display. Both the size and the weight of this type of display are objectionable.
To collimate the light source, all of the LEDs must be very close to the focal point of the collimating lens and limited in size so as to simulate a single point source and properly mix the colors of the LEDs. This constraint limits the size of the LEDs, and hence, the maximum intensity of light from the display. In addition, the half-silvered mirror decreases the brightness of the display, since only one fourth of the light in the collimated beam actually reaches the viewer's eye.
Broadly, it is the object of the present invention to provide an improved illumination system for a reflective display.
It is a further object of the present invention to provide a display system that does not require the use of a half-silvered mirror to illuminate the pixels.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a display that includes an array of reflective pixels, a linear light source; and a reflector. The reflector includes a cylindrical surface preferably having a parabolic cross-section, the axis of the cylindrical surface being parallel to the linear light source. The linear light source is positioned relative to the reflector such that light from the linear light source is collimated by the reflector onto the array of reflective pixels. The reflector is constructed from a material that is partially reflecting. The linear light source preferably includes a plurality of light emitting diodes and an optical diffuser. In a color display, the light emitting diodes comprise diodes having different emission spectra. In one embodiment of the invention, the reflector is constructed from a material that reflects light of a first linear polarization while transmitting light having a linear polarization orthogonal to the first linear polarization. In this embodiment, each pixel in the array of reflective pixels preferably includes a polarization rotating cell that rotates the linear polarization vector of light reflected by the pixel in response to the receipt of an electrical signal by the pixel.
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Heffner Brian L.
Mertz Pierre H.
Agilent Technologie,s Inc.
Blackman Anthony J.
Brier Jeffery
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