Ultrafast Response Reflective Fiber-Optic Salinity Sensor

In this work, a series of fiber-optic salinity sensors were prepared. The sensing principle of salinity sensor is the changes of reflection coefficient and evanescent wave attenuation with salinity. The spectral intensity received by the spectrometer was linearly related to salinity. To improve performance, the sensor tapers were reduced to increase the incident angle at the end and enhance evanescent waves. By optimizing the taper, the sensitivity of sensor 4 can be improved as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.70\times 10^{-{3}}$ </tex-math></inline-formula>/‰ with linearity 99.99% within the salinity range from 5.001‰ to 40.003‰. Benefited from the cone structure, which was not easy to retain water, the response time of the sensor was just 0.1 s. These sensors exhibited excellent stability and satisfactory reversibility. In addition, the signal-to-noise ratio (SNR) of sensor 4 can reach as high as 65.411. The outstanding performances above demonstrated that the prepared fiber-optic salinity sensors are promised to be a new approach for salinity detection in practical applications.