Recent progress in developing highly efficient and thermally stable nonlinear optical polymers for electro-optics

Abstract

Recent development of high-performance nonlinear optical polymers for electro-optics (E-O) is reviewed in this paper. A highly efficient and thermally stable nonlinear optical (NLO) chromophore, namely 2-[4-(2-{5-[2-(4-{Bis-(<i>tert</i>-butyl-dimethyl-silanyloxy)-ethyl]-amino}-phenyl)-vinyl]-thiophen-2-yl}-vinyl)-3-cyano-5-trifluoromethyl-5<i>H</i>-furan-2-ylidene]-malononitrile, has been prepared and incorporated in amorphous polycarbonate (APC) composites. The result from high electric field poling shows a very large E-O coefficient (r₃₃ = 94 pm/V at 1.3 &#956;m), ~80% of which can be maintained at 85 °C for more than 500 hours. In addition to this guest/host sysytem, a high T<i>g</i> side-chain polymer, derived from a 3-D cardo-type polimide with dendron-encapsulated chromophores as pendent groups has also been synthesized and characterized. A high degree of chromophore dipole orientation and a large r₃₃ of 71 pm/V at 1.3 &#956;m can be achieved in this poled polyimide. More than 90% of its E-O activity can be maintained at 85 °C for more than 600 hours. To access the full potential of poled polymers for device applications, we have developed a new lattice-hardening approach to overcome the "nonlinearity-stability-tradeoff" of conventional thermoset methods. By using the Diels-Alder lattice-hardening process, we can achieve the same high poling efficiency and large r₃₃value as in a guest-host system while maintaining good thermal stability seen in densely-crosslinked polymers. By modifying the electronic properties of the crosslinking reagents, we can fine-tune the processing temperature window of the Diels-Alder reactions to achieve hardened materials with optimal properties.