Abstract

On the basis of a model of the twisted nematic liquid crystal,¹ we analyze the effects of the twist angle and the input polarization angle on the reflective liquid-crystal intensity modulator with a polarizing beam splitter. When the input polarization is parallel to the front molecular director of the liquid crystal, the conventionally used 45° twist has a theoretical maximum reflectance of only 81%. However, a 63.6° twist angle yields the highest efficiency (theoretical maximum reflectance of 100%). If the light source is not monochromatic and has a narrow bandwidth, the dispersion effect tends to re duce the contrast, so a tradeoff between contrast and sensitivity must be made. We show that a configuration with 65-75° twist has an efficiency close to 100%, with continuously increasing sensitivity, but decreasing contrast, as the input polarization changes from 0° to -30°.

© 1990 Optical Society of America