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US 6,334,685 B1Granted
Segmented light pipe apparatus and method for increasing luminous efficiency of single light-valve, color video projection displays
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A color sequential video projector (10) employs a color modulating device (22) and a segmented light pipe (30) that coact to provide a high luminous efficiency. The color modulating device splits polychromatic light into three different colored light beams (24, 26, 28) that are positionally stationary, but alternate mutually exclusive colors sequentially with time such that each pixel of a light valve (48) is exposed to all three colors during an image frame time. The segmented light pipe receives the three light beams and forms three adjacent color bands that are precisely aligned on the light valve. Because all three colors of light are constantly illuminating the light valve, light losses are substantially eliminated. The color modulating device employs multiple color wheels (82, 84, 86) each having filter segments (90, 92, 94) that form the three light beams by reflecting the alternating, mutual exclusive colors as the wheels rotate. Alternative embodiments employ one, two, or three color wheels having flat or conically-shaped filter segment surfaces. The segmented light pipe includes three rectangular glass cores (70, 72, 74) surrounded by a low index cladding (78) and having their abutting faces (76) coated with a thin, low refraction index coating. The light pipe input apertures (32, 34, 36) receive three roughly shaped light beams, homogenize them, and provide at three output apertures (38, 40, 42) uniformly bright rectangular light beams. A precision achromatic lens (44) images the uniform light beams onto the light valve such that seams between the beams are imaged to within one micron of accuracy and are parallel to the light valve pixel rows.
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