| 摘要 |
A hollow light guide with opposed first and second sections having parall el directions of translational symmetry and confocal, parabolic cross-sectional shape. The light guide may be a prism light guide, or other hollow light guide such as a metallic mirror light guide or a multi-layer dielectric light guide. The cro ss- sectional shapes have vertices separated by a distance which does not exceed about three times (preferably, about 2.5 times) the focal length of the shapes.</S DOAB>
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