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.
The wedge display is a piece of wedge-shaped waveguide. Each time a ray reflects in the wedge, its angle relative to the
opposite side increases so that the critical angle is eventually reached and the ray emerges. Therefore, how far the ray
travels before emerging is determined by its injection angle. As a kind of projection display, the wedge-shaped
waveguide is a natural fit to holographic projection. In this paper, a new type of holographic display based on the wedge
panel is reported. The hologram projected into the wedge is generated by computer with a Spatial Light Modulator
(SLM 1280*1024), illuminated by a He-Ne laser. A method taking advantage of reverse ray tracing to correct keystone
distortion of the wedge display is introduced. By setting special patterns on the screen of the wedge panel and replacing
the projector at its thick end with a camera, keystone distortion information is recorded. The predistortion process adds
the distortion pattern from the camera to the original input images. Images with less distortion are shown on the screen
after the predistortion process.
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