Electrically Induced Photonic Structures in Cholesteric and Nematic Liquid Crystals

The latest studies of electrically induced photonic liquid crystal structures, performed at the Laboratory of Liquid Crystals of the Shubnikov Institute of Crystallography of the Russian Academy of Sciences, are reviewed. Due to the field-induced spatial modulation of the refractive index, these structure exhibit optical properties that are characteristic of photonic crystals. Two types of structures are discussed. The first is induced in cholesteric liquid crystals with spontaneous formation of a helical director distribution. The orientational transition to the state with a lying helix (i.e., axis lying in the layer plane) is considered. The second type includes homogeneous layers of nonchiral nematic liquid crystals, in which refractive index modulation is due to the effect of flexoelectric instability. In both cases the periodic boundary conditions for the molecular orientation are of fundamental importance. Both the methods for setting boundary conditions and the photonic properties of structures are considered.