An All-Fiber Magnetic Field Sensor Based on Dual-S-Shaped Optic Fiber Integrated With Magnetic Fluid

In this paper, magnetic fluid (MF), a new type of optical functional nanomaterial with interesting optical characteristics under the external magnetic field is adopted to form a novel fiber-optic magnetic field sensor. The proposed sensor is based on Mach-Zehnder interferometer and has a dual-S-shaped structure. The S-shaped structure is fabricated by splicing two overlapping single-mode fibers with a fiber fusion splicer. The magnetic field sensing probe was made by inserting the fiber-optic micro-structure in an MF-filled capillary tube. Variations in an external magnetic field is seen to cause changes in the refractive index of MF. This tunable change in the refractive index with magnetic field strengths between 0 and 20 mT produces a shift in the position of the peak of the wavelength. The shift of the valley wavelength with magnetic field intensity has a good linearity of up to 99.634%. The achieved sensitivity of the proposed magnetic field sensor is 0.2904 nm/mT, which is a several-fold improvement on most of the other reported MF-based magnetic field sensors. Furthermore, we have built the corresponding circuit-based measurement system and have shown that a voltage change, associated with the results, indirectly reflects the change of the external magnetic field strength. This, therefore, provides the potential to fiber-based magnetic field sensing applications.