Improved second order nonlinear optical polymers by covalent attachment comparison of four different thermally stable systems

The practical implementation of polymers into electro-optic and nonlinear optical (NLO) devices requires thermally stable polymers with high optical nonlinearities. The nonlinear moieties (chromophores) can be either doped or covalently incorporated into the different classes of polymer matrices: polyimides, sol-gels, thermosetting, thermoplastic, etc. Although incorporation of covalently attached chromophores along with a means of thermally stabilizing the poling alignment involves difficult synthesis work, its advantages over doping, namely, high chromophore density reduced phase separation, and improved nonlinearity and thermal stability, make it the route of choice. We report here on four different approaches to improved long term thermal stability of the poling and the NLO effect. Two crosslinking polymers, one, “side-chain 1” in which the synthesized polymer contains the chromophore as a side chain and is crosslinked during poling to anchor both ends of the chromophore and one, “tri-linked” in which the synthesized chromophore containing prepolymer is crosslinked into a 3D polymer matrix during poling, are discussed. In the second material, the crosslinker also contains the chromophore to increase the chromophore loading. We also report on a polyimide material in which the chromophore is included as a side chain in the polyamic acid precursor polymer and immidization takes place during poling. In the fourth approach, the chromophore is covalently attached to a sol-gel system which is cured during poling