Magnetic field sensor based on S-shaped and core-offset fusion splicing structure of single-mode fiber coated with magnetic fluid

Abstract Tunable refractive index characteristics of magnetic fluid have important research value in magnetic field sensing. In this paper, a magnetic field sensor based on S-shaped and core-offset fusion splicing structure of single-mode fiber coated with magnetic fluid is proposed and demonstrated. The proposed sensing structure is based on Mach-Zehnder interference principle and is coated with magnetic fluid. The basic idea of structural design is to first excite the fiber cladding mode by using an S-shaped fusion splicing structure, and then use the core-offset fusion splicing structure to achieve the interference between the cladding mode and the core mode. The refractive index of the magnetic fluid changes with the magnetic field strength, resulting in the variation in the transmission spectrum of the sensor. The experimental results show that the sensitivity of the sensor is 33.14 pm/Oe in the range of the magnetic field strength of 0–75 Oe, and the interference valley wavelength increases linearly with the increase of the magnetic field strength. Therefore, the fabricate process of the sensing structure only requires two simple fusion splicing operations of ordinary single-mode fiber, which has the characteristics of low cost, simple structure, easy processing, and high sensitivity, so it has broad application prospects.