Journal
OPTICS AND LASER TECHNOLOGY
Volume 164, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.optlastec.2023.109523
Keywords
CTD sensor; Lamellar PI coating; Fiber Bragg Grating; Fiber Fabry-Perot Interferometer
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In this paper, an integrated and compact fiber-optic CTD sensor for simultaneous measurement of ocean temperature, salinity, and pressure is proposed. Experimental results demonstrate high sensitivity, high resolution, high reliability, anti-electromagnetic interference, compact size, and low cost of the proposed sensor.
Conductivity, temperature and depth (CTD) are the three most important parameters of the marine environment. In this paper, an integrated and compact fiber-optic CTD sensor for simultaneous measurement of ocean tem-perature, salinity (conductivity) and pressure (depth) is proposed. A bare fiber Bragg grating (FBG) for tem-perature measurement, an FBG with lamellar polyimide (PI) coating for salinity measurement and a diaphragm-based extrinsic Fabry-Perot interferometer (DEFPI) for pressure measurement are connected in series with only one single fiber to form a multiplexed sensing system for CTD detection. The salinity sensing mechanism based on the water diffusion model of the lamellar PI coating is presented. A mold for curing the lamellar PI coating is fabricated and the curing process is introduced in detail. Experimental setup is built for temperature, salinity and pressure measurement. The wavelength-division multiplexing (WDM) technology combined with Gaussian fitting method and the cross-correlation demodulation algorithms are employed to demodulate the measurand from the spectrum. The Gaussian elimination method is used to eliminate the cross-sensitivity effects of the three meas-urands. Experimental results show that a sensitivity of 10 pm/degrees C, 141 pm/(mol/L) and 520 nm/MPa for tem-perature, salinity and pressure measurement, respectively, has been realized. Resolution measurements show that a resolution of 0.1 degrees C, 0.01 mol and 1.5 KPa for temperature, salinity and pressure measurement, respec-tively, is achieved. The repeatability of the proposed CTD sensor is also be investigated and a repeatability of 0.73 % FS, 0.72 % FS and 0.1 % FS for temperature, salinity and pressure measurement, respectively, has been obtained. The proposed fiber-optic CDT sensor has the advantages of high-sensitivity, high resolution, high reliability, anti-electromagnetic interference, compact size and low cost, which has great application potential in ocean exploration.
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