2ND-ORDER OPTICAL NONLINEARITY ON A MODIFIED SOL-GEL SYSTEM AT 100-DEGREES-C

Second-order nonlinear optical (NLO) properties of polymeric materials have been widely studied.1 Polymeric materials have become competitive with inorganics for nonlinear optical applications such as fast waveguide electrooptic modulation and frequency-doubling devices provided the nonlinearity shows reasonable stability at ambient temperatures. The noncentrosymmetric alignment of the NLO chromophores that results from the poling process is not in a state of thermodynamic equilibrium. Therefore, the alignment would relax to a random configuration in the absence of a poling field. To prevent the randomization of the poled molecules, the NLO chromophores are usually incorporated in a polymer which has a high glass transition temperature (Tg). This is due to the fact that the molecular orientational motion is closely associated with the Tg of the polymer. Moreover, enhanced temporal stability of second-order NLO properties in a poled polymer system can be obtained when a certain degree of cross-linking is introduced. In the cross-linked polymer, the NLO moieties are either incorporated or covalently bound into a rigid polymer network and are much less likely to relax to random orientation. The polymers can be cross-linked by thermal meansle, f, 2or by photochemical means.3. © 1992, American Chemical Society. All rights reserved.