Measurement of PT-PEK-c polymer film parameters using the quasi-wavegusde m-line method

摘要

A coupling prism is commonly used to feed light into a waveguide to measure m-line coupling angles and thereby determine thin film parameters. This method has been demonstrated both for real wave-guides and for quasi-waveguides [1-4]. A quasi-waveguide differs from a real waveguide in that the former is a structure with the refractive index of the guiding film less than that of the prism. In the quasi-waveguide the light is guided by the film-substrate interface while the reflection at the film-prism boundary is leaky. Usually, the film in a quasi-waveguide structure is isotropic. However, many non-linear-optical polymer films are anisotropic. This is because, in order to obtain high electro-optic coefficients, the non-linear chromophores of material are aligned by polarization and the polymer film becomes a uniaxial film with its optical axis along the direction of polarization. In this paper we shall show that it is possible to measure the main parameters of an anisotropic polymer film, that is its refractive indices and thickness, by coupling light through the prism into the modes of a quasi-waveguide.