Microfiber Coupling Structures for Magnetic Field Sensing With Enhanced Sensitivity

Two kinds of magnetic field sensors based on Sagnac loop and knot resonator configurations with microfiber coupling structures are proposed and investigated experimentally. The designed sensors are made from the microfiber coupler, whose coupling region is coated with magnetic fluid. The as-fabricated sensors have the same sensing/coupling region, but the achieved sensitivities are greatly different, which are 19.4 and 171.8 pm/Oe for the microfiber Sagnac loop and microfiber knot resonator structures, respectively. Comparing with the microfiber Sagnac loop and other similar microfiber knot resonator (or silicon microring) sensing structures, the sensitivity of the as-designed microfiber knot resonator sensing structure is enhanced significantly. The underlying mechanisms are expounded physically in terms of the microscopic formation of the coupling region and the essence of interference for the microfiber knot resonator structure. The designed structures could potentially lead to highly sensitive magnetic field sensors and other new-fashioned magneto-optical photonic devices.