Highly sensitive optic fiber vector magnetometer based on the Fabry-Perot interferometer and harmonic Vernier effect

This article experimentally validates a high-sensitivity vector magnetic field (MF) sensor based on two parallel Fabry-Perot interferometers (FPIs). Firstly, two standard single-mode fibers are interposed into a capillary tube to constitute a cantilever beam structure FPI₁. FPI₁ achieved a high axial strain sensitivity of 15.0 pm/µε. Then, FPI₁ was bonded with the magnetostrictive material Terfenol-D, and the sensitivity of its MF intensity and direction reached 91.43 pm/mT and -12.75 pm/°, respectively. Finally, a reference interferometer FPI₂ was matched to FPI₁ to constitute the harmonic Vernier effect sensor S₁. The average sensitivity of the MF intensity of S₁ reaches -4.308 nm/mT, and the MF direction sensitivity of S₁ reaches 892.3 pm/°. It amplifies the MF intensity and direction sensitivity of FPI₁ by 47 times and 33.0 times, respectively. Therefore, the proposed MF sensor can measure MF intensity and direction with high sensitivity. Additionally, the proposed sensor only involves fiber optic cutting, splicing, and cold bonding during the manufacturing process, without damaging the structure of the fiber optic. Therefore, it is easy to manufacture, highly reproducible, cost-effective, structurally robust, and easy to operate. It is one of the preferred choices for vector MF sensors in practical applications.