Optical characterization of microfiber loop resonator towards humidity sensing

Abstract

Microfiber loop resonator (MLR) fabricated by using silica fiber for relative humidity (RH) sensing application is reported. The silica fiber was tapered to achieve waist diameter of 5 μm using flame brushing technique. The MLR with a 300 μm diameter loop microfiber was formed by manually twisted the tapered fiber. Initially, the effect of whispering gallery modes (WGMs) on the MLR was observed. Transmission mode spectra were observed to determine the number of resonated wavelength and quality factor (Q-factor). The Q-factor for MLR is observed to be > 105 which is a good attribution for sensing application. A significant response to RH from 35% to 85% was observed due to the change of resonating behaviour of MLR across the RH range. The sensing sensitivity increased by a factor of 8.15 in MLR compared to the straight microfiber (SF) structure. As the RH increased, the output power of the MLR decreased linearly from -43.05 dBm to -46.81 dBm with linearity and resolution of 95.91% and 0.153% RH respectively.