Inverted Rib Waveguides - Theoretical Analysis of Sensing Properties

Optical waveguides are fundamental components of chemical and biochemical evanescent wave sensors. Presented work is devoted to theoretical investigations of homogeneous and surface sensitivity characteristics of the inverted rib waveguide structure. The inverted rib waveguide discussed in this paper is composed of an ion-exchange based channel waveguide formed in a glassy substrate and a uniform, high refractive index, sol-gel derived $SiO_2-TiO_2$ film. Characteristics of a homogeneous sensitivity, a surface sensitivity and fundamental modes sensitivity differences in function of a uniform film thickness and a maximal refractive index contrast of the gradient index channel waveguide are given. The influence of the $SiO_2-TiO_2$ film thickness on sensitivity characteristics is discussed. The analysis is carried out on a bases off the effective index method used with the transfer matrix method.