Low-loss polymer films with adjustable refractive index.

Solution-deposited polymer films with continuously adjustable refractive index (1.489-1.563) are made by blending in solution two polymers: polymethyl methacrylate (PMMA) and styrene-acrylonitrile copolymer (SAN). The dependence of index of refraction on composition was found to be linear, indicating the compatibility of the two polymers on a molecular basis. In films ~2 microm thick losses less than 0.2 dB/cm were measured. For thicker films (3.5 microm) an increased scattering loss was observed in high SAN content films.