20 May 1999 Projection optics for reflective light valves
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Reflective x-Si backplanes allow projection displays to evolve toward higher pixel count and greater miniaturization, extending the range of competitive application. As light valve area A is reduced, projector output into solid angle S equalsV (pi) NA2 can in many cases be considered to decrease roughly as approximately (A*S)0.5, with the 0.5 exponent representing typical microdisplay operating in a regime that is neither purely brightness-limited nor purely power-limited. Polarization modulation entails a modified scaling approximately (A*S/2)0.5; color sequential operation, approximately (1/3)*(A*S)0.5; spatially divided single-light-valve RGB projection, approximately (A*S/3)0.5. Projection lenses for three-light-valve system must provide an increased working distance to accommodate a color recombiner. Zoom lens are often required in front projectors, and rear projection usually entails a short lens-to-screen distance. It has become cost-effective to use plastic aspherical elements to meet these requirements. Periodic strip-PBS arrays have been widely adopted for polarization recycling, but aperiodic homogenizers are sometimes used to correct the uneven magnification and symmetry limitations of conic reflectors. Bright-state and dark-state beams must occupy distinct etendues in the half space above a reflective light valve, creating a vulnerability to crosstalk. Crosstalk from a polarizing beamsplitter gives rise to a residual background intensity approximately 0.3*NA2, unless a quarterwave corrector is used. Crosstalk can also arise from stress birefringence in prism substrates. Stray light makes an indirect contribution to background, but can sometimes be corrected by filtering.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Alan E. Rosenbluth, Rama Nand Singh, "Projection optics for reflective light valves", Proc. SPIE 3634, Projection Displays V, (20 May 1999); doi: 10.1117/12.349348; https://doi.org/10.1117/12.349348


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