Microsphere-Based Fiber-Optic Magnetic Field Sensor Utilizing Whispering Gallery Mode and Fabry-Perot Cavity

This paper presents a novel fiber-optic magnetic field (MF) sensor integrating dual sensing modes of whispering gallery mode (WGM) and Fabry-Perot interferometer (FPI). By coupling barium titanate microspheres with quartz capillaries to generate WGM, an F-P interferometer is formed between the spherical surface of the microspheres and the gas cavity. Innovatively, a magnetostrictive composite material composed of Terfenol-D particles dispersed in epoxy resin is used to uniformly encapsulate the sensing structure. Through MF-induced orientation alignment, the magnetostrictive strain generated under external MF is directly transferred to the resonant microsphere, inducing measurable wavelength shifts. Experimental results demonstrate that the sensor achieves a sensitivity of 3 pm/mT within the 0 - 118 mT measurement range, with hysteresis error below 1.2%. The solid design eliminates liquid medium requirements, significantly enhancing structural reliability and environmental robustness. This research provides a new paradigm for high-sensitivity miniaturized magnetic detection, showing promising application potential in industrial non-destructive testing and biological magnetic sensing domains.