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Side-Polished Single-Mode-Multimode-Single-Mode Fiber Structure for the Vector Magnetic Field Sensing

A vector magnetometer, composed of a side-polished single-mode-multimode-single-mode fiber structure coated with ferrofluids, is proposed and investigated. The side-polishing of the multimode fiber can expose the evanescent field to the surrounding ferrofluids, whose refractive index in the vicinity of the polished surface can be tuned by both the intensity and direction of the applied magnetic field, thus in turn realizing the magnetic vector sensing. The sensing principles are illustrated in details, and the sensing performances, especially the dependence on the residual thickness (RT) of the side-polished multimode fiber, are well investigated experimentally. It is found that the decrease of the RT can significantly improve the sensitivity to both the magnetic field intensity and the direction, and the highest intensity and direction sensitivities of −0.053 nm/Oe and −5.68 nm/degree have been achieved respectively, when the RT reduces to 50.5 μm. The proposed vector magnetometer, featuring the advantages of simple structure, low cost, and ease of fabrication, can find the potential applications in the fields such as industry, military, and environment.