Polarization-independent modulation for projection displays using small-period LC polarization gratings

Progress in the use of liquid-crystal polarization grating ( LCPG) to modulate unpolarized ( and polarized) light with a grating period as small as 6.3 mu m is reported. Similar to LCPGs formed at larger periods ( 11 mu m) reported previously, polarization-independent switching, predominantly three diffraction orders, maximum contrast ratios of similar to 100:1 for unpolarized broadband light, very low scattering, and diffraction efficiencies >= 98% continue to be observed. The smaller period led to an expected lower threshold voltage, even though the thickness was greater. Because the smaller grating period enables a brighter result from a Schlieren projection scheme for a microdisplay using the LCPG light valve, the inherent tradeoffs involved with both material and design parameters are discussed, and prospects for a polarization-independent projection display are commented upon.