HIGHLY STABLE COPOLYIMIDES FOR 2ND-ORDER NONLINEAR OPTICS

Nonlinear optical (NLO) copolyimides exhibiting high glass transition temperatures (T-g) and high thermal stabilities were synthesized to ac hieve long-term stability of optical nonlinearity at elevated temperat ures. The relationship between the chromophore loading level and the p hysical properties of the copolymers was studied. It was found that de creasing the chromophore loading level increased the glass transition temperature more than 40 degrees C. As a result, the stability of the electric field induced dipole orientation of the nonlinear optical chr omophores was enhanced. The second harmonic generation (SHG) signal ma intained 85% of its initial value after 700 h at 180 degrees C. Sizabl e second-order nonlinear optical coefficients and electro-optic coeffi cients were obtained.