A refractive index sensor based on fiber cavity ring-down spectroscopy

Fiber cavity ring-down(CRD) technology has attracted widespread attentions for its high sensitivity, and has extensive applications in many fields requiring high sensitivity measurement. In this paper, we propose and implement a refractive index sensor based on fiber CRD spectroscopy. A pulse of light passes through a loop resonator formed by two high-splitting ratio couplers and comes out repeatedly. A segment of similar to 4cm fiber with thin cladding was designed as a refractive index sensor and inserted into the fiber cavity. The sensor appeared different transmission losses with different surrounding refractive indices, which can be measured by detecting the ring-down curves. The experimental results show that the system has a linear response to the surrounding refractive index with a sensitivity of 182.17 mu s /RIU in the range of 1.3575 similar to 1.4430 at the center wavelength of 1553nm.