Highly Sensitive Salinity/Refractive Index Sensor based on Fiber Ring Laser with Tapered Fiber

In this paper, a fiber ring laser with single mode fiber - tapered no core fiber - single mode fiber structure (STNS structure) was proposed and demonstrate to be an ultrahigh sensitive refractive index and salinity sensor. The laser located at $\sim 1555$ nm, with a narrow 3-dB bandwidth of 0.06 nm and high signal-to-noise ratio of $\sim 45\mathbf{dB}$. The NaCI salinity sensitivity and RI sensitivity of our designing were 0.627 nm/(g/L) and 3761.2 nm/RIU, respectively, with a good linearity of 0.998. It has potential to be widely applied in chemical and biological analysis, ocean monitoring and protection of ecosystems.