Sensing characteristics of a MF-filled photonic crystal fiber Sagnac interferometer for magnetic field detecting

A highly sensitive magnetic field sensor based on Sagnac interferometer consisted of a polarization maintaining photonic crystal fiber (PCF) filled with magnetic fluid (MF) is proposed and demonstrated. The refractive index of MF is sensitive to magnetic field H and the fiber Sagnac interferometer is sensitive to refractive index, so the sensing structure of our magnetic field sensor is designed. The water-based nanoparticles Fe3O4 is used which possesses low refractive index. The refractive index of MF follows the Langevin function and changes linearly with magnetic field H in our considerable magnetic field region. The parameters of lambda, B(lambda, H) on the influences of sensitivity are analyzed. We find a new phenomenon the two dip wavelengths shift in the opposite direction as magnetic field increases. The phenomenon is explained by group birefringence Bg which decreases and its sign changes as magnetic field increases. The sensitivity increases infinitely near the special wavelength related with zero-point Bg. The average sensitivities are 384 pm/Oe (51,569 nm/RIU), -430 pm/Oe (-57,747 nm/RIU) which turn out pretty well and the R-squares are 0.98113, 0.98415 respectively for the detected range 410-600 Oe. (C) 2016 Elsevier B.V. All rights reserved.