A review of light-induced bistability in liquid crystals

This review aims to summarise one of the most intriguing phenomena in the nonlinear optics of liquid crystals: optical bistability, in which two distinct output transmission states can exist for a single input light intensity. Since the earliest experiments on the orientational optical response of liquid crystals, achieving purely optical first-order orientational transitions, analogous to first-order phase transitions, has resisted straightforward realisation for several decades. Such transitions are characterised by an abrupt change in the orientational state and the presence of a bistability region in which two stable orientational states are realised. Distinct orientational structures lead to different states of the transmitted light, manifested, for example, as variations in the power, beam divergence, or polarisation of the output beam. This nontrivial behaviour is of fundamental interest because it reflects the nonlinear coupling between the light field and liquid-crystal orientational structures or phases. Furthermore, optical bistability in liquid crystals is promising for various applications, including optical computing, optical switches, shutters, and logic elements.