Sensing of refractive index based on mode interference in a five-layer slab waveguide

We propose a refractive index sensor based on the mode interference in a five-layer waveguide. The propagation properties are analyzed by the coupled mode theory, and the function of the waveguide as a refractive index sensor is also explored based on simulation results. Taking into consideration a trade-off between the sensitivity and the size of the proposed sensor, we can get a very compact device of 10.8 μm×1 μm, and the sensing resolution of the proposed refractive index can reach 2.25×10−5 RIU for index change at around 1.455.