Fiber-loop ring-down interrogated refractive index sensor based on an SNS fiber structure

In this paper, a fiber-loop ring-down interrogated refractive index sensor based on a single-mode-no-core-single-mode (SNS) fiber structure is reported. The influence of the wavelength and pulsewidth on the performance of the sensor are systematically investigated. Results show that the performance of the sensing system is strongly dependent on the interrogation wavelength and a narrower pulsewidth is helpful to avoid the disturbance of the relaxation oscillation. A method to determine the optimal interrogation wavelength was proposed. After determining the interrogation wavelength and pulsewidth, refractive index (RI) measurement was experimentally performed in the RI range of 1.3330-1.3539. And a cubic polynomial fitting was established between RI and ring-down time. In the linear region, a sensitivity of -3271 mu s/RIU was achieved. (C) 2017 Elsevier B.V. All rights reserved.