Seawater temperature and salinity sensing based on in-fiber Michelson-Fabry-Perrot hybrid interferometer employing frequency domain decomposition method

Abstract:

In this letter, we propose an in-fiber Michelson-Fabry-Perrot (M-FP) hybrid interferometer for the simultaneous meas-urement of seawater temperature and salinity. The sensor head consists of two parallel hetero Fabry-Perrot cavities fabri-cated on the end face of the twin core fiber. A fiber fusion taper is used to split and recouple the light in the two cores. In this case, the Vernier effect can be obtained which can greatly enhance the sensitivity and solve the problem of tempera-ture cross-sensitivity. Different from the traditional demodulation method based on envelop detection, we employed fre-quency domain decomposition method (FDDM) to demodulate the sensing signal. The simulation results indicate that the proposed sensor has high sensitivity to salinity and temperature. Thanks to the merits of high sensitivity, ease of fabrica-tion and small footprint, the proposed seawater temperature and salinity sensor would have potential applications in ma-rine science, food industry and ocean ranching.

Key words:fiber hydrid interferometer; frequency domain decomposition; seawater sensing; cross-sensitivity