Optical Nonlinearities of Guest-Host-Polymer Structures

Abstract

Until recently, attempts to take advantage of the large second-order optical nonlinearities of certain conjugated organic molecules in devices were limited to neat crystalline materials, since the requirements for a noncentrosymmetric bulk phase could be met with molecular and polymeric crystals that happen to condense in a noncentrosymmetric point group.[1] The large dipoles that are often observed in these molecules made the growth of optical quality and robust crystals difficult. More recently, mixed systems consisting of the nonlinear optical molecules incorporated into polymer glasses, liquid crystals, and liquid crystal polymers have been investigated.[2] The difficulties in processing that are required to obtain optical quality materials are reduced. For second-order nonlinearities, an alignment process, such as electric field poling, is required to break the center of symmetry inherent in these materials. However, the reduction in number density and alignment attainable with realistic poling fields requires molecules with exceptionally large nonlinear optical susceptibilities in order to obtain bulk materials with nonlinear coefficients large enough to produce sensible devices.