Ultrahigh Sensitivity Surface Plasmon Resonance Magnetic Field Sensor Based on D-Shape Four-Hole Fiber

A surface plasmon resonance (SPR) sensor based on a D-shape four-hole fiber (DFHF) is proposed for ultrahigh sensitivity magnetic field detection. By means of side-polishing, one of the air holes in the four-hole fiber is opened, allowing an Al wire to be positioned in close proximity to the core and immersed in the magnetic fluid (MF) for magnetic field sensing. The sensor is analyzed by the finite element method (FEM), and the core diameter, air hole diameter, and Al wire diameter are optimized. The magnetic field sensitivity, resolution, figure of merit (FOM), and manufacturing tolerance of the optimized sensor are determined. The results show that the DFHF-SPR magnetic field sensor can detect magnetic fields between 35 and 150 Oe with a maximum magnetic field sensitivity of 176 000 pm/mT, which are 1–2 orders of magnitude higher than that of similar magnetic field sensors. At a magnetic field of 35 Oe, the optimal resolution and maximum FOM are 5.68 nT and 7.93 mT<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{-{1}}$ </tex-math></inline-formula>, respectively. The DFHF-SPR magnetic field sensor, which has high sensitivity and does not require difficult filling in manufacturing, has large commercial potential in magnetic field environmental monitoring, biomedicine, and other fields.