SMF Taper Evanescent Field-Based RI Sensor Combined With Fiber Loop Ring Down Technology

Abstract

A composed refractive index (RI) sensor based on evanescent field-fiber loop ring down was demonstrated. The ring-down time would be changed with the intensity loss near the tapered single-mode fiber (SMF), which is related to the RI of the test solutions. The feasibility of the sensing scheme was proved theoretically and experimentally. Results showed that the sensitivity of this simple scheme could reach to $-388.581~\mu \text{s}$ per RI unit (RIU) and the detection limit below $2.57\times 10^{-5}$ RIU was achieved. Moreover, a PDMS detection cell was specially designed to enhance the structure’s mechanical strength and the signal’s stability. The proposed RI sensor is attractive due to its high detection sensitivity, fast response, and insensitivity to light source fluctuations beyond what conventional RI sensors can offer.