Ultrasensitive Magnetic Field Sensor Based on Fabry–Perot Interferometer and Magnetostrictive Material

An ultrasensitive fiber optic magnetic field sensor based on Fabry-Perot interferometer (FPI1) and magnetostrictive material Terfenol-D is proposed. A low fineness FPI1 made by inserting a tapered two-mode fiber (TMF) into a hollow-core fiber (HCF). Due to the increased effective length of strain, FPI1 is particularly sensitive to axial strain. Then, the magnetostrictive material Terfenol-D is bonded to FPI1. Due to the excellent stretching properties of Terfenol-D under the action of a magnetic field, FPI1 adhered to Terfenol-D also has high sensitivity to the magnetic field. The experiment found that in the large magnetic field range of 9.7-92.4 mT, the magnetic field sensitivity of FPI1 reached 1.67 nm/mT. In order to further improve the sensitivity of FPI1 to magnetic fields, we connected a magnetic field insensitive air cavity FPI2 in parallel with FPI1 to form the Vernier effect, further amplifying the magnetic field sensitivity of FPI1. In the range of 13.08-21.93 mT, the magnetic field sensitivity was amplified to 36.43 nm/mT, which is 21.8 times the sensitivity of a single FPI1, which is currently the highest known magnetic field sensitivity. The sensor structure also has good repeatability and stability and low-temperature crosstalk. It is expected to become one of the best options for highly sensitive magnetic field detection.