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<sub>2</sub>O<sub>5</sub> overlays. Sensitivity increases by a factor greater than 50, and a detection limit better than 5 × 10<sup>−7</sup> is obtained. This approach is broadly applicable to sensing at waveguide surfaces where the strength of evanescent fields dictates performance.
© 1999 Optical Society of America
(120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
(130.0130) Integrated optics : Integrated optics
(130.6010) Integrated optics : Sensors
(240.0310) Optics at surfaces : Thin films
Geoffrey R. Quigley, Richard D. Harris, and James S. Wilkinson, "Sensitivity Enhancement of Integrated Optical Sensors by Use of Thin High-Index Films," Appl. Opt. 38, 6036-6039 (1999)