Simultaneous Measurement of Seawater Salinity and Temperature With Composite Fiber-Optic Interferometer

• Published in: IEEE transactions on instrumentation and measurement Vol. 71; pp. 1 - 8
• Main Authors: Zhao, Yong, Zhao, Jian, Peng, Yun, Tong, Rui-Jie, Cai, Lu
• Format: Journal Article
• Language: English
• Published: New York IEEE 2022; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Composite interference structure; Error analysis; Fabry-Perot interferometers; femtosecond laser micromachining; Fiber optics; fiber-optic sensor; Laser machining; Mach-Zehnder interferometers; Micromachining; Optical fiber sensors; Optical fibers; Optical waveguides; Refractivity; Salinity; Salinity (geophysical); Seawater; seawater salinity; Sensors; Temperature measurement; Temperature sensors; Waveguides
• ISSN: 0018-9456; 1557-9662
• DOI: 10.1109/TIM.2021.3137855

A seawater salinity and temperature simultaneous measurement sensor is proposed and demonstrated in this article, which consists of a Fabry-Perot interferometer (FPI) and Mach-Zehnder interferometer (MZI) composite fiber-optic structure. The femtosecond laser micromachining technique is used to modify the single-mode fiber (SMF) and inscribe three consecutively connected waveguides, in which the modified areas are corroded by hydrofluoric (HF) acid to form in-fiber channels. One internal channel forms a FPI and is selectively filled with the low refractive index UV adhesive to measure temperature. The other channel is combined with the waveguide structure to constitute a MZI, which has a wavelength shift response to salinity and temperature variations. In theoretical modeling, the sensing performances of the composite interference structure are analyzed separately. The experimental results show that the salinity and temperature sensitivities are −2.323 nm/‰ and 2.176 nm/°C, respectively. Besides, the repeatability, stability, and measurement error are tested, which shows that the sensor has good sensing performance and has the potential for seawater parameter measurements.