Nematic liquid crystal phase-gratings for reflective spatial light modulators

The twisted nematic liquid crystal phase grating, using patterned alignment with opposite twist angles for reflective spatial light modulators, is analyzed with respect to operating mode, diffraction efficiency and operating voltage including the effect of disclination lines between opposite twist domains. In general, the high-field diffractive modes have lower operating voltages, slower response time and relatively higher contrast ratio than zero-field diffractive modes. We describe a high-field diffractive mode with a twist angle of approximately +/-54 degrees for opposite twist domains which achieves an optical efficiency of nearly 100% and an estimated contrast ratio greater than 300:1 for monochromatic light.