Optical tuning and switching of photonic defect modes in cholesteric liquid crystals

Optical tuning of photonic defect modes in cholesteric liquid crystals is demonstrated based on a contrast in the pitch length. Two-photon laser lithography was performed in a cholesteric helix to leave an unpolymerized region in the center to act as a structural defect. The unpolymerized region was then substituted by an azobenzene dye-doped cholesteric liquid crystal which exhibits a pitch shortening upon ultraviolet exposure. Reversible shifting or on-off switching of the defect mode was realized as a result of selectively inducing a pitch shortening of the cholesteric liquid crystal at the defect and changing the contrast in the pitch length between the bulk and defect. (c) 2007 American Institute of Physics.