A novel optical fiber magnetic field sensor based on Mach-Zehnder interferometer integrated with magnetic fluid

In this paper, a novel Magnetic fluid-filled optical fiber sensor consisting of a multimode-single mode-multimode (MM-SM-MM) fiber structure has been proposed and experimentally demonstrated. The proposed sensor is based on a Mach-Zehnder interferometer, which is fabricated by splicing a section of uncoated single mode fiber between two short sections of multimode fibers with a fiber fusion splicer. The micro-structure is sealed in a Magnetic fluid-filled capillary tube and the magnetic field sensing probe is formed. 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 0.6 mT to 21.4 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 99.586%. The achieved sensitivity of the proposed magnetic field sensor is 0.12306 nm/mT. Furthermore, we also proposed the corresponding building methods of the measurement system based on the MM-SM-MM structure. It turned out that a voltage change indirectly reflects the change of the external magnetic field strength. This therefore provides the potential to fiber-based magnetic field sensing applications.