P-167: FDTD and Elastic Continuum Analysis of the Liquid Crystal Polarization Grating

Abstract

liquid crystal polarization grating (LCPG) has advantages of polarization independence of the zero diffraction order, nearly 100% diffraction efficiency in the first orders, and higher resolution capability over previously reported binary LC gratings. Here we analyze the LCPG, an electrically controlled, polarization-independent light modulator using the finite- difference time-domain (FDTD) method and the elastic continuum theory. The optical performance is studied and critical electrical parameters for a LCPG cell are presented. 1. Introduction of liquid crystal (LC) light modulators operating on unpolarized light have been proposed in an effort to overcome the substantial losses in conventional LC displays that require polarized light. Most prominently, Bos and coworkers suggested several potentially efficient and polarization-independent diffraction gratings using liquid crystals (1-4). These approaches, however, face crucial limitations for real applications due to their binary nature: fabrication difficulty and the easy appearance of defects. They therefore tend to have inherently large periods that result in many diffraction orders with small diffraction angles. A newly demonstrated liquid crystal polarization grating (LCPG) (5) is a switchable diffractive optical element with a continuously varying, periodic, anisotropic index profile. As shown in Fig. 1(a), this can be embodied as a nematic director that follows (6): n(x) = ˆ cos(x / ) + ˆ y sin(x /) + ˆ (0) (1)