Bistable twisted nematic liquid-crystal optical switch

Abstract

In this letter, we describe a bistable twisted nematic (BTN) liquid-crystal device optimized for use in a fiber optical system. The device configuration is optimized so that the states of polarization for the two bistable states are linear and orthogonal to each other for a linearly polarized input light. This optimization is accomplished by the use of the Poincaré sphere method. Using this method, we obtained the analytical forms of the optimization conditions. Several different optimized conditions are obtained. In order to experimentally explore the use of the BTN structure in optical latching switches, one optimized structure (11.25° and −348.75° twists, dΔn/λ=0.496) is studied in the infrared region by the measurement of the output state of polarization. The experimental results agree well with our theoretical predictions. This study also suggests that transmissive BTN displays with high contrast are possible by the use of these optimized conditions with nonparallel and noncross polarizer configurations.