High-precision magnetic field sensor based on phase-shift fiber loop ring-down technique and FBG-magnetostrictive structure

A high-precision fiber-optic magnetic field sensor based on the phase-shift fiber-optic loop ring-down (PS-FLRD) technique and the structure of fiber Bragg grating (FBG) bonding to a magnetostrictive rod is proposed and experimentally demonstrated. A coarse wavelength division multiplexer (CWDM) is inserted into the fiber loop and serves as an optical edge filter (OEF) to provide wavelength-dependent transmittance. Due to the linear response of the CWDM, the wavelength shift of the FBG induced by the external magnetic field is linearly converted to a transmittance change of the fiber loop, which is reflected in the phase shift. Consequently, a relationship between the phase shift and the magnetic field applied to the FBG is established. The experimental results show a good linear relationship between the phase shift and the magnetic field. For magnetic field strengths ranging from 0 to 880 Gs, the measured sensitivity is 0.0056 deg/Gs with a resolution of approximately 18 Gs. Furthermore, the proposed scheme demonstrates excellent stability and repeatability, remaining unaffected by power fluctuations, which provides a promising solution for magnetic field sensing.