Highly Sensitive Dual-Channel Michelson Interferometer for Seawater Temperature and Salinity Sensing

A highly compact and superior sensitivity dual-channel Michelson interferometer for seawater temperature and salinity sensing is demonstrated, which is successively constructed by splicing single-mode fiber (SMF)–multimode fiber (MMF)–twin-core fiber (TCF) in sequence. Employing femtosecond laser microprocessing technology, two D-type microcavities are precisely fabricated on the dual fiber cores of the TCF for the purpose of temperature and salinity sensing. Furthermore, an enhanced high-reflectivity mirror is employed to improve the spectral contrast. The results obtained from the experiment illustrate that the proposed sensor demonstrates a remarkably stable temperature performance of −3.26 nm/°C in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$10~^{\circ }$ </tex-math></inline-formula>C–<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25~^{\circ }$ </tex-math></inline-formula>C. Besides, in the salinity interval of 5‰–40‰, a superior salinity sensitivity of −2.95 nm/‰ (equivalent to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-15~265$ </tex-math></inline-formula> nm/RIU) is proved. Moreover, the proposed sensor exhibits remarkable stability and high repeatability, thus proffering an innovative perspective for the surveillance of the marine environment.