Magnetic field sensing using magnetic-fluid-filled optofluidic ring resonator

A magnetic field sensor based on the silica optofluidic ring resonator is proposed and experimentally demonstrated for the first time. Magnetic fluid is filled in the core of the microcapillary to experience the strength change of the applied magnetic field. When the whispering gallery modes circulate in the wall of the microcapillary, it can experience the increasing refractive index of magnetic fluid with the increase in the magnetic field strength, leading to the redshift of the resonant wavelength. The maximum sensitivity of 75.7 pm/mT and figure of merit of 105 T^?1 are realized, respectively, corresponding to a large dynamic magnetic field range from 15 to 125 mT. By optimizing the concentration of the kerosene-based magnetic fluid, the detection limit of 2.2 mT and the measurement resolution of 0.9 mT are achieved, respectively. This work provides a novel magnetic field sensing scheme with high performance using the optofluidic ring resonator and further broadens its applications.