Design and characterization of composite planar polarimetric interferometer

This paper presents the design and theoretical characterization of a composite uniform-gradient planar waveguide polarimetric interferometer. Presented structure is composed of an Ag⁺↔Na⁺ ion-exchange based waveguide formed in Borosilicate 33 glass substrate and a uniform, sol-gel based, silica-titania film. Characteristics of homogeneous sensitivity difference for TE₀-TM₀, TE₀-TE₁ and TM₀-TM₁ modes in function of the uniform film refractive index and the gradient waveguide refractive index profile are given. Because thermal annealing is an inseparable part of the sol-gel process, the gradient index waveguide is subjected to a rediffusion process. The original refractive index profile is flattened. It was shown that a presence of the gradient waveguide increases sensitivity differences over values which can be obtained for single layer uniform silica-titania waveguides. Moreover, it was shown that a range of uniform film thickness values, for which sensitivity difference of the composite structure is maximized, is downshifted to a range which can be much easier obtained with a sol-gel process.