Reflective Optical Fiber Sensor Based on Dual Fabry Perot Cavities for Simultaneous Measurement of Salinity and Temperature

A reflective optical fiber sensor that is composed of two Fabry Perot cavities is proposed for temperature and salinity measurement. One of the Fabry Perot cavity which is fabricated by offset splicing is exposed to the ambient directly to sense the ambient salinity, the other is employed to compensate for the temperature coupling effect. A thin layer of the gold film is coated on the refractive index change interface, which makes the spectrum quality is no longer limited by the refractive index difference between the two sides of the interface. By applying the frequency division multiplexing (FDM) technique and cavity length demodulation technology, the measurement range is no longer restricted to the free spectrum range (FSR), which can realize salinity measurement in the full measurement range. The proposed sensor can realize the salinity sensitivity better than 50 nm/parts per thousand and temperature sensitivity of 6.85 nm/degrees C in the cavity length domain. It is promising for salinity measurement application for its merits of low cost, easy fabrication, and long sensing distance.