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 the 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 anisotropy 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 polymer, while transverse-magnetic modes are evanescent. The implications of these data for amplified spontaneous emission and design of in-plane laser structures are discussed.