Sensing properties of four-layered planar waveguides - Theoretical analysis

Optical waveguides are the fundamental components of chemical and biochemical evanescent wave sensors. Presented work focuses on the theoretical investigations of homogeneous sensitivity of four-layered composite planar waveguide composed of a silica-titania film and a titania film deposited on a glassy substrate in order of citing. Characteristics of a homogeneous sensitivity and a fundamental modes homogeneous sensitivity difference of such a structure are compared with the ones for a three-layered waveguide composed of silica-titania waveguiding film. Therefore the influence of a high refractive index titania film on homogeneous sensitivity characteristics of three-layered structure is given. It was shown that homogeneous sensitivity difference of fundamental modes of four-layered waveguide can be optimized with respect to thicknesses of each layer. For each value of a cover refractive index there exists the minimal thickness of the titania layer which maximizes the homogeneous sensitivity difference of fundamental modes.