P-209: Evaluation of Projection Schemes for the Liquid Crystal Polarization Grating Operating on Unpolarized Light

Abstract

We report on our first experimental comparison of polarizationindependent projection schemes using the liquid crystal polarization grating (LCPG) modulator as the active element. This recently-demonstrated LC grating has unique diffraction properties, and we evaluate its performance using the bright- and dark-field Schlieren configurations and consider its use with a TIR-prism assembly. Each scheme shows promise for highbrightness and good-contrast projection for different applications. 1. Introduction crystal polarization gratings (LCPGs) show great promise as projection display modulators of unpolarized light, exhibiting high contrast and experimentally-demonstrated 100% diffraction efficiency [1]. This type of modulator is particularly suited for mobile, battery-powered “pocket” projectors that demand high contrast and brightness with minimal power consumption. As with the other types of projection display systems using diffractive modulators, the contrast and brightness of our system depends on the projection scheme employed. Since the principle of operation in the LCPG is distinct from previous LC gratings, we anticipate comparably improved projected image properties (contrast and brightness). As only very limited experimental and theoretical investigations into LCPG switches have been carried out (and none utilizing a realistic projection scheme), here we report on the first examination of such. This information should strongly inform the design of any realistic projection system based on the LCPG modulator. The key feature of our polarization-independent modulator is the diffractive LCPG, whose operation and structure is outlined in Fig. 1. This grating is unique from conventional gratings in that only three orders (m=±1,0) are present, and its diffraction efficiency for unpolarized light follows [1]: