Magnetic Fluid-Filled SMF–MMF-Axially-Offset-Spliced NCF–SMF Structure for Vector Magnetic Field Sensing

This paper proposes and demonstrates an all-fiber vector magnetic field sensor based on a cascade structure of single-mode fiber (SMF)–multimode fiber (MMF)–no-core fiber (NCF)–SMF. The sensor employs an axial-offset splicing technique to asymmetrically connect the NCF to both the MMF and the output SMF, thereby constructing a composite waveguide structure with strong modal coupling characteristics. This asymmetric geometry effectively modulates the mode-field distribution of the propagating light, enhances the interaction between the evanescent field in the fiber cladding and the external magnetic fluid, and enables significant responses to both magnetic field intensity and direction. Experimental results show that with a 6 μm axial offset applied to the NCF, the sensor exhibits excellent sensing performance within a magnetic field range of 8–24 mT, achieving amagnetic field intensity sensitivity of –974 pm/mT and a directional sensitivity of –821 pm/°. It also reaches a temperature sensitivity of –1205 pm/°C in the 25–55 °C range. The sensor offers advantages of simple fabrication, low cost, and high sensitivity, demonstrating promising potential for multidisciplinary sensing applications.