OPTICAL ANISOTROPY OF POLYMERIC FILMS MEASURED BY WAVE-GUIDE PROPAGATION MODE DETERMINATION

Extruded thin films of a liquid-crystalline charge-conjugated rigid-rod polymer poly (p -phenylenebenzobisthiazole), PBT, and a semicrystalline thermoplastic polyethylene-terephthalate (Mylar) were fabricated and examined for film thickness, refractive index, and linear attenuation coefficient. Optical waveguide modes were successfully induced on the polymeric films using a prism coupler at lambda = 633 and 1300 nm. Highly consistent thickness values were obtained for the polymeric films. In addition, the anisotropic nature of the optical properties was determined using TE and TM propagation modes. A refractive index as high as 2.3 was observed on PBT film. The refractive index data suggested that the PBT and Mylar films were optically anisotropic with refractive indices n(perpendicular-to) (out-of-plane) invariably smaller than n(parallel-to) (in-plane). Large anisotropy was also discovered in the linear attenuation coefficient alpha, with alpha(perpendicular-to)/alpha(parallel-to) almost-equal-to 50 for the Mylar films. Complementary polarimetric and spectroscopic interference measurements were also applied to investigate the optical anisotropy of the extruded polymeric films.