High Sensitivity All Optical Fiber Conductivity-Temperature-Depth (CTD) Sensing Based on an Optical Microfiber Coupler (OMC)

• Published in: Journal of lightwave technology Vol. 37; no. 11; pp. 2739 - 2747
• Main Authors: Yu, Yang, Bian, Qiang, Lu, Yang, Zhang, Xueliang, Yang, Junbo, Liang, Linmei
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: All optical fiber sensing; Couplings; depth (pressure); Detection; Environmental monitoring; Fiber optics; Hydrophones; In situ measurement; Microfibers; Optical fiber sensors; Optical fibers; Optical measuring instruments; optical microfiber coupler; Pressure measurement; Rangefinding; Salinity; Salinity (geophysical); Seawater; Sensitivity; Tapering; Target detection; temperature; Temperature measurement; Temperature sensors; Water depth
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2018.2878475

An all optical fiber CTD sensor used in seawater based on an OMC is demonstrated. And the OMC is fabricated by fusing and tapering two twisted conventional communication fibers based on the improved flame-brushing method. By monitoring the sensing dips, in situ measurement of salinity, temperature, and depth (pressure) in seawater can be realized, respectively. Especially, the water depth (pressure) sensing function of the OMC is demonstrated for the first time, and the pressure sensitivity is 50 times higher than a bare fiber Bragg grating (with a wide pressure measurement range from 0 to 25 MPa). The highest sensitivities of salinity, temperature, and depth are 1596 pm/ 0 / 00 , 2326 pm/°C, and 169 pm/Mpa, respectively. These are high enough for the requirements of marine dynamic environmental monitoring and underwater target detection of fiber-optic hydrophone system. The all optical fiber CTD sensor demonstrated here show advantages of easy fabrication, compact structure, high sensitivity, low cost, and compatibility with the optical fiber system, which may find applications in multifunction optical sensors in ocean detections and other applications.