Optical Fiber EFPI Cavity Magnetic Field Sensor Based on the Magnetostrictive Effect

Magnetic field measurement plays an extremely important role in various fields, such as earthquake-generating mechanisms, resource exploration, and national defense security. Addressing the current issues of low sensitivity and susceptibility to temperature in optical fiber magnetic field sensors, a high-sensitivity optical fiber extrinsic Fabry–Perot interferometer (EFPI) cavity magnetic field sensor based on the coupling of giant magnetostrictive material (GMM) and a Fabry–Perot (F–P) cavity is proposed. The sensor employs TbDyFe material as the sensing element and utilizes neodymium–iron–boron to provide a bias magnetic field, enhancing the conversion efficiency of the GMM rod. An F–P cavity is formed by precisely aligning the end face of a single-mode optical fiber with the smooth surface of a permanent magnet. When the external magnetic field changes, the length of the GMM rod changes accordingly, which in turn causes a variation in the length of the F–P cavity. Experimental results show that within the range of 0– $150~\mu $ T, the highest sensitivity of the sensor reaches 676 nm/mT, corresponding to a magnetic field resolution of 147 nT. A fiber Bragg grating (FBG) temperature decoupling method is proposed to perform temperature compensation on the sensor and correct the magnetic field measurement results, thereby solving the problem of cross-sensitivity to temperature. The designed sensor features a compact structure and simple fabrication, providing a reference for the development of high-sensitivity optical fiber magnetic field sensors.