Ultrahigh Sensitivity Surface Plasmon Resonance Magnetic Field Sensor Based on Side-Core Inscribed Capillary Fiber

An ultrahigh sensitivity surface plasmon resonance (SPR) magnetic field sensor based on side-core inscribed capillary fiber (SCICF) is proposed. The SCICF has an extremely simple fiber structure with only a Ge-doped core inscribed silica capillary. Based on SCICF, the magnetic field sensor is constructed by arranging a metal wire externally tangent to the Ge-doped core and filling magnetic fluid (MF) into the capillary to detect the magnetic field by using the SPR effect. Systematic analysis and optimization of the structure parameters of the core, the metal wire, and the capillary are performed by utilizing the finite element method (FEM). In addition, the magnetic field sensitivity, resolution, figure of merit (FOM), and manufacturing tolerance are discussed. Simulation results indicate that the maximum sensitivity reaches up to 274000 pm/mT within a magnetic field range from 35 to 200 Oe, which is nearly three orders of magnitude higher than most optical fiber magnetic field intensity sensors. Moreover, the sensor shows the best resolution of 3.65 nT and the best FOM of 6.091 mT $^{-{1}}$ when the magnetic field intensity is 35 Oe. The SCICF-SPR magnetic field sensor featuring high magnetic field sensitivity, simple structure, and ease of filling has immense potential in geological exploration and biological medicine.