Optical Bistability in Nematic Liquid Crystals.

Available from UMI in association with The British Library. The high degree of parallelism offered through the interconnect freedom of digital optical processing may be realised at a moderate total power level with bistable devices operating in the 1-100 muW regime. This thesis approaches the requirement of low operating power through utilisation of the large thermo -optic nonlinearities to be found in nematic liquid crystals. A study is thus made of the thermal and optical properties of one specific liquid crystal, with regard to maximising the change in refractive index with absorbed power. This material is used as the nonlinear spacer medium in a number of Fabry-Perot structures the respective performance of which, both theoretically and experimentally, identify an optimal cavity design which produced critical optical power levels of 13.3 muW, allowing the demonstration of all-optical bistability in a passive device at 20 muW. Bistable switching is also demonstrated over the 514-830 nm range, using gas and solid-state diode laser sources. Though such low powers allow a high degree of parallelism from conventional (typically 10 W) laser sources, to quantify the overall potential processing rate experimental characterisation of the dynamic response of these devices is conducted, with a simple theoretical model presented. Though, in principle, all required logic functions may be obtained from combinations of bistable characteristics and individual biassing levels, consideration is also given to novel cavity designs and materials that allow logical operations based on alternative transfer characteristics in both power and polarisation state.