Thermally stable nonlinear polymers promise optoelectronic integration
Optically responsive molecules that can survive the high temperatures of microelectronics processing have been successfully inserted into polyimides by scientists at the IBM Almaden Research Center (San Jose, CA). The resulting nonlinear polymer can withstand the severe requirements of integrated-circuit production, so it could eventually enable nonlinear optical components to be fully integrated with electronic circuitry. The researchers said some of the nonlinear polyimides can be used for more than 1000 hours at temperatures above 225°C without any measurable reduction in nonlinearity and can be held at temperatures above 300°C for tens of minutes without degradation or activity loss. Activity is obtained by attaching a dipolar chromo phore to the polymer backbone and raising this system above its glass transition temperature in the presence of an electric field to orient the dipolar chromophores, then returning it to a lower temperature and removing the poling field.
For practical applications, chromophores exhibiting large optical nonlinearities must be combined with materials having good thermal stability; this may require years of further research. Nonetheless, an optoelectronic device incorporating a nonlinear optical polymer is expected to operate at higher frequencies than conventional devices and may function in a high-speed computer clock at several orders of magnitude faster than currently available. Such polymers could also become relatively inexpensive alternatives for nonlinear crystals now used as modulators in telecommunications applications.