Abstract

We propose a new approach to design of thin-film optical waveguide sensors of fluid concentration. Thin film sensors are used for their compactness and robustness, and high sensitivity at plasmonic resonances. In order to replace the costly spectroscopic detection by a more economic power measurement a substantial increase in sensitivity of these sensors is needed. Here, we explore the sensitivity enhancement by applying a porous thin film [1] to a dielectric waveguide structure. The pores enable to a fluid to enter the film and change its average refractive index, thus substantially changing the effective index of the propagating mode. To secure high sensitivity, the corresponding phase changes are converted in the intensity changes by a Mach-Zehnder interferometer (MZI). The sensor sensitivity is calculated with respect to the refractive index of fluid n_f, thus keeping the consideration independent of the type of fluid.

© 2015 IEEE