The proportion of power carried in the superstrate medium by the guided modes of integrated optical waveguides can be increased by the addition of a thin high-index film. Enhanced refractive-index sensing is demonstrated with channel waveguide Mach-Zehnder interferometers with Ta(2)O(5) overlays. Sensitivity increases by a factor greater than 50, and a detection limit better than 5 x 10(-7) is obtained. This approach is broadly applicable to sensing at waveguide surfaces where the strength of evanescent fields dictates performance.
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Quigley et al. (1999) studied this question.