<title>Improvement in the performance of evanescent wave chemical sensors by special waveguide structures</title>

Abstract

Evanescent wave sensors based on single mode waveguides are attractive but have rather low sensitivities for gaseous species and suffer degradation from surface contaminants. We propose the use of a thin, high-index loading film on a silica waveguide to enhance the field strength at the guide surface and to correct measurements for surface contamination by launching the two polarisation modes. Resonant structures also enhance sensitivities when matched to the absorption characteristics of a gas.