An environmental sensor based on an integrated optical whispering gallery mode disk resonator

In this report, we describe the fabrication and testing of an integrated optical whispering gallery mode resonator designed for use as an evanescent field environmental sensor. We use traditional photolithographic techniques to create 500 μm radius disk resonators in silicon oxy-nitride. The devices are overclad with a thin film of SiO2 to provide a suitable surface for subsequent chemical adhesion of organic compounds and protein layers. Tests performed with sucrose solutions indicate a sensitivity to surface index variations of Δn ∼ 1.0 × 10−5 refractive index units (RIU). We also demonstrate the ability of these devices to monitor protein layers binding to the surface.