Photomodulation of liquid crystal orientations for photonic applications

Two types of photomodulation of orientations of liquid crystals (LCs) are reviewed: 1) order-disorder phase transitions of LCs induced by photochemical reactions of photochromic molecules and 2) order-order alignment change of LCs (change in LC directors) induced by photochemical reactions or without photochemical events. Both processes produce a large refractive-index modulation, which forms the basis of a range of photonic applications. Various modes of photomodulation of orientations of LCs with plausible mechanisms and their possible applications in photonics are described.