A novel salinity sensor with high-resolution and large dynamic range based on optical Fabry-Pérot cavity

A novel salinity sensor based on Fabry-Pérot cavity (F-P cavity) was proposed and demonstrated experimentally. This sensor adopts the frequency dither locking method to lock the laser frequency to the resonant frequency of the F-P cavity. The resonant frequency shifts with the salinity of the solution inside the F-P cavity. Experimentally, such a salinity sensor has demonstrated a resolution of ∼ 2 × 10−4 PSU (corresponding to ∼ 4 × 10−8 RIU), a dynamic range of ∼ 42 PSU and a response time of 49 ms.