In-situ all-fiber conductivity-temperature-depth (CTD) sensitive-enhanced sensor for marine environment measurement

Abstract

Conductivity-temperature-depth (CTD) measurement occupies a pivotal position in marine environment detection. However, the electronic devices or systems are highly susceptible to corrosion under these conditions, resulting in frequent failures. Herein, an in-situ all-fiber CTD sensitive-enhanced sensor integrated by T-shaped Fabry-Perot interferometer (T-FPI) and temperature-compensated Fiber Bragg Grating (TC-FBG) is proposed and experimentally demonstrated. The T-FPI is composed by input single-mode fiber (SMF) and vertically affixed hollow-core fiber (HCF) with polishing process of CO2-laser, constructing a channel for seawater flowing. The channel is employed for measuring the CTD characteristic of the seawater. In addition, a TC-FBG is integrated on the input SMF to eliminate in-situ temperature crosstalk. Experimental results present that the highest sensitivities achieve 16.78 nm/(mol/L), 9.27 pm/℃, and 62.86 nm/MPa for salinity temperature, and pressure measurement, respectively. Meanwhile, the resolution of the sensor is tested as 0.107 ℃, 0.016 mol and 15.024 KPa, respectively. Compared with CTD sensors based on electronic devices or systems, the proposed sensor updates the sensing performance, volume, cost and anti-corrosive quality.