Simultaneous measurement of salinity, temperature and pressure in seawater using optical fiber SPR sensor

Abstract

A new fiber optic reflective probe is designed for simultaneous detection of salinity, temperature, and pressure in seawater. As far as we know, it is the first time that these three parameters are measured by an integrated reflex optical fiber sensor. Surface Plasmon Resonance effect inspire by an Au film coated on the fiber’s surface. Photonic crystal fiber (PCF) is chosen as an ideal mode-excitation field. Slow spreading cladding pattern provide a possibility for simultaneous existence of multiple SPR resonance dips. Two kinds of sensitive films (PDMS, SU-8) are coated outside the Au film at different sections. This design makes it possible to form three different sensitive areas, and then three distinct SPR resonance dips appear by optimizing the structure’s parameters. In calibration experiments of an optimized probe, the maximum sensitivity of 0.560 nm/ g/kg, −1.802 nm/°C, and 2.838 nm/MPa are obtained respectively for salinity, temperature, and pressure measurement. Meanwhile, transmission matrix coefficients are determined for cross-sensitive demodulation. This design will have great practical potential if more optimization and process treatments are carried out in the future.