Light scanner with cylindrical lenses

Details Light scanner with cylindrical lenses Light scanner with cylindrical lenses

2001-02-22

2003-09-23

Phan, James (Department: 2872)

Optical: systems and elements

Deflection using a moving element

C359S205100, C359S209100, C359S210100

Reexamination Certificate

active

06624919

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to improved scroll scanning systems, and in particular, to systems which provide imaging of scrolling multiple color bands across a single-panel reflective or transmissive display device in a video projector.
BACKGROUND OF THE INVENTION
A known color projection display system includes a monochromatic flat panel display device that is, in operation, sequentially illuminated with light. The modulated light pattern from the display device is then projected onto a display surface. For color projection, monochromatic light sources or selectively filtered light sources are sequentially scanned over the flat panel display device at a repetition rate sufficient that the human eye perceives a single color image. The human eye thus integrates this “color sequential” display of three separate images into a “single” image. By providing a single flat panel display device, a common optical path is provided for all colors, and convergence and misregistration errors are substantially eliminated.
To provide efficient illumination of the flat panel display device, it is preferred to split white light from a projector lamp into the three basic colors, which are simultaneously employed. Since the components are simultaneously employed, the light output from the projector lamp is efficiently employed. This technique requires that portions of the flat panel display device simultaneously present portions of pixel images for each of the colors. In order to make efficient use of the flat panel display and to avoid degradation of the resolution, each color is ideally presented as a rectangular stripe which scrolls down the panel, sequentially illuminating all regions of the flat panel display device. This technique therefore requires that pixel data for each of the respective colors be updated between the respective color stripe illumination.
In a rotating prism scanning system, the rotating prism assembly repeatedly scans the red, green, and blue bands through a pair of relay lenses, which image the spatially-separated scanning colored light bands onto a light valve panel having an array of pixels. The scanning colored light bands are separated from each other by one-third of the panel height. Each time a light band of one color leaves the bottom of the array, a corresponding light band of the same color appears at the top of the array and begins its scan. Before each colored light band passes over a respective row of pixels, the pixel image data must be loaded into the column conductors while the respective row is selected, and the pixel elements allowed to settle. Because, in this case, three different rows (or bands of rows) will be illuminated substantially simultaneously by the three different colored light bands, either three separate column conductors and drivers must be provided for each column of pixels, or the data must be provided sequentially to the column conductors at three times the video line rate.
The simultaneous use of a substantial portion of the available red, green and blue light through a single light valve panel provides optical efficiencies comparable to that of three-panel systems employing similar types of light valve panels. However, by using only a single panel, the need to mechanically converge different color images formed on different panels is eliminated, and system cost and size is reduced. Additionally, beam combining dichroic filters are not needed, which leads to additional savings. See, Peter Janssen, “A Novel Single Light Valve High Brightness HD Color Projector”, Society For Information Display (SID), Technical Paper, France 1993; Shimizu, Jeffrey, “Single Panel Reflective LCD Projector”, SPIE (1999).
Typically, the flat panel display device is a thin film transistor (TFT) liquid crystal display (LCD) device, having, for example, a resolution of 1280 by 1024 pixels. Since the image is projected, the display device may be relatively small, i.e., less than about 6 cm. Further, the preferred mode of operation is a reflective mode, which allows use of thinner layers of liquid crystal light modulation material and correspondingly faster response times, since the light passes through the liquid crystal twice. Display technologies other than TFT may be employed, for example known silicon on insulator LCD display devices. Further, the “projection” need not be over a large area, and, for example, a similar technology may be employed in so-called heads-up displays and virtual reality goggles. See, U.S. Pat. Nos. 5,673,059 and 5,642,129, expressly incorporated herein by reference.
In order to achieve the scrolling illumination, scanning mechanisms have been proposed with moving color filters or with static color separation combined with an optical scanning mechanism like a rotating prism. The moving color filter solutions so far have been less light efficient because they tend to discard at least two thirds of the available white light to achieve individual color components. Static color separation, e.g. with dichroic mirrors, is generally much more light efficient because all color components can be used simultaneously. However, in these dichroic mirror systems, the problem is then in designing a scanning mechanism that converts the static color stripes into a useful scrolling color stripe pattern.
One known scanning mechanism is a rotating prism. It suffers, however, from low quality imaging of the color stripes, and it is generally very difficult to achieve uniform scanning for all color components in a single scanning element. Multiple scanning element systems have been proposed, employing rotating prisms (either separated or physically joined), which offer better scan-speed uniformity (for the different color light bands) and scan-speed linearity (for each light band) than the single-prism system, but are less compact. See, U.S. Pat. Nos. 5,845,981, 5,608,467, 5,548,347, 5,532,763, 5,528,318, 5,508,738, 5,416,514 and 5,410,370, expressly incorporated herein by reference.
For a scrolling scanner system, the ideal scan transformation function is:
x
o
(
t
)/
X
=(
t/T+x
i
/X
) modulo 1,
with X being the total height of input and output beam, x
i
being the ray height in the input beam, x
o
being the corresponding ray height in the output beam as a function of time, T being the frame period, and t being the time. (The modulo 1 operation returns a value between 0 and 1, equal to the non-integer fraction of the operand. It is the same as the fract ( ) function in common computer languages.) This concept is similar to so-called “aliasing”, in this case the integer portion of the function being undeterminable based on the state of the output. It is noted that only the phase of the output ray depends on the input ray height in the beam; the actual output swings always from 0 to X, independently from the input ray height. This means that the scanner has to perform a different geometrical transformation for different incoming ray heights, or aberrations will result in the scrolling light band output.
In one known system, a rotating prism is provided, having a central axis of rotation and an even number of facets symmetrically disposed around the axis. A light source projects parallel beams of the three different respective colors through the prism. Central illumination rays for each of the respective color bands are propagated along a respective path that is directed at the axis of rotation. The ray paths of the outer edges of each color band are directed to converge at an angle a=(n+1/3mb), where n is equal to any non-negative integer (i.e. 0, 1, . . . ), m is equal to 1 or 2, and b=360° divided by the number of prism facets. A combination of optical components is arranged to intercept the illumination rays after their passage through the prism, and to guide and converge the illumination rays, seeking to form on the panel spaced-apart light bands having mutually parallel central illumination rays which scan across the panel as the prism is rotated. The optical elements (i.e. the prism, the lens

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