Optical fiber magnetic field sensor based on multi-mode fiber and core-offset structure

A magnetic field sensor based on a magnetic fluid (MF)-coated intermodal interferometer is proposed and experimentally demonstrated. It is fabricated by a core-offset structure between two segments of multi-mode fibres (MMF), a spherical structure is formed in the end of the second segment MMF. The core-offset section can be used to excite the core mode to the cladding, then the core and cladding modes will interference at the spherical structure due to the optical path difference caused by the refractive index difference. Two interference valleys of the interferometer integrated with MF under different magnetic field intensities have been experimentally analysed. The experimental results exhibit that the sensor possesses a magnetic field sensitivity of −0.187 nm/mT by monitoring the wavelength shift at the magnetic field intensity from 0 to 20mT, and the optical power attenuation at specific wavelength with a magnetic field has a maximum sensitivity of 0.228 dB/mT.