Index of refraction and waveguiding in thin films of a conjugated polymer which exhibits stimulated emission

We report variable angle spectroscopic ellipsometry (VASE) measurements on thin films of a soluble derivative of poly-paraphenylenevinylene (PPV) in t he emission region of the spectrum. We find that the films are birefringent , with a higher and more dispersive index of refraction for light polarized with its electric field in the plane of the film. Physically, this anisotr opy is explained by preferential in-plane orientation of the polymer chains ; a result of this orientation is that on typical substrates such as glass and quartz, only transverse-electric waveguide modes propagate in the polym er, while transverse-magnetic modes are evanescent. The implications of the se data for amplified spontaneous emission and design of in-plane laser str uctures are discussed.