Multimode input for dissipative sensing enhancement in whispering-gallery microresonators

摘要

Optical whispering-gallery mode (WGM) microresonators have been widely used as chemical sensors. In practice, most WGM sensing is based on either mode frequency shift (dispersive) or mode linewidth change (dissipative). However, WGM sensors based on the fractional change in throughput dip depth (dissipative) can offer better sensitivity under certain conditions. Recently it was demonstrated that for WGM dip-depth sensors multimode input can further improve the sensitivity as compared to single-mode input. This enhancement in sensitivity is achieved by using an asymmetric tapered fiber to couple light in and out of the microresonator. In this report, we develop a model which predicts the waist radius of the fabricated asymmetric tapered fiber. The radius predicted by the model is verified by measuring the beat length for the two fiber modes that are excited and couple into a WGM.