Uniform scattering patterns from grating-diffuser cascades for display applications

A cascade of a thick grating and a thin diffuser is shown to scatter radiat ion efficiently and uniformly over a wide angle. Cascading the grating with a diffuser causes the single-beam power spectrum of the diffuser to be rep licated at each diffraction angle of the grating. The grating period is cho sen so that the first diffraction order falls near the one-half point of th e power-spectrum peak of the diffuser. The relative strengths of the diffra ction orders are optimized to obtain uniformity of the resulting intensity distribution in the plane of the diffraction orders. The intensity distribu tion in the perpendicular plane is governed solely by the diffuser. Such a cylindrical system is considered on the basis of the requirements for proje ction TV's of a large horizontal span (100 degrees) and a narrower vertical span (similar to 15 degrees). Broadband illumination is studied by conside ration of three simultaneously illuminating wavelengths. Experimental resul ts are given for a cascade of a grating formed in photoresist and an etched -glass diffuser. (C) 1999 Optical Society of America.