Vectorial Magnetic Field Sensing by Magnetic-Fluid-Infiltrated Eccentric Fiber Bragg Grating

A novel miniature magnetic-fluid (MF)-infiltrated eccentric fiber Bragg grating (EFBG) vectorial magnetic field sensor was proposed and experimentally demonstrated. An EFBG with a length of 10 mm and an eccentric distance of $2~\mu \text{m}$ was written in a standard single-mode fiber by a point-to-point femtosecond laser (FSL) writing process, which was then sealed in an MF-infiltrated glass capillary (GC) to form the magnetic-field-sensitive structure. Through the refractive index and absorption modulation of the MF under the influence of external magnetic fields, the transmission intensities at the resonant wavelengths of cladding modes are accordingly changed. Transmission at these resonant wavelengths can be used as the magnetic field sensing quantity. Experiments show that the sensor can sensitively respond to both strength and direction of the magnetic field. A sensitivity of about 0.042 dB/Oe in a magnetic field strength range of 0–120 Oe was found.