3 February 2009 Parabolic transition region curve for a wedge projection display
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A wedge shaped flat panel projection display can be made by combining a slab waveguide with a tapered "wedge" waveguide sector. The sudden angle transition between the flat slab-waveguide surface and the tilted wedge-waveguide surface, sometimes called the 'kink' in a conventional wedge flat panel screen design, causes the rays which are incident at the flat slab-waveguide surface just before the kink to overlap with the rays which are incident at the tilted wedge-waveguide surface just after the kink. This paper identifies the 'kink' problem by using the reverse ray tracing technique, where parallel rays are traced from the wedge-waveguide surface back to the receiving end of the slab-waveguide. We propose a parabolic curved transition region to be inserted between the slab and the wedge waveguide as the solution to this problem, as the parabolic curved surface replaces the 'kink' with a smoother angle change between the flat and the tilted waveguide surfaces, to avoid the rays overlapping. The parabolic curve is designed to introduce collimation for the rays projected from a point light source to avoid inducing convergence or divergence to the rays which are incident at the parabolic curved surface. A thick wedge design consisting of the slab, parabola and wedge waveguides is demonstrated in this paper which shows how the ray overlapping problem for a conventional slab-wedge waveguide design can be solved.
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Kuan Wen Chen, Adrian Travis, Shun Yi Tan, Tim Wilkinson, "Parabolic transition region curve for a wedge projection display", Proc. SPIE 7232, Emerging Liquid Crystal Technologies IV, 72320U (3 February 2009); doi: 10.1117/12.807833; https://doi.org/10.1117/12.807833

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