Analysis of a Magnetic Field Sensor Based on a Sagnac Interferometer Using a Magnetic Fluid-Filled Birefringent Photonic Crystal Fiber

A magnetic field sensor based on a Sagnac interferometer using a magnetic fluid-filled birefringent photonic crystal fiber (MF-BPCF) was proposed and studied by finite element method. Two large air holes in the birefringent photonic crystal fiber were designed to fill with magnetic fluid. The MF-BPCF in the proposed Sagnac interferometer acted as the sensing head. As magnetic field perpendicular to the MF-BPCF, magnetic fluid was anisotropic. The characteristics of the output spectrum of the Sagnac interferometer was simulated. The results showed that when the phase difference phi satisfied integer multiples of 2 pi, several dip wavelengths appeared. Not only the intensity but also the direction of the magnetic field was measured. The measuring sensitivity could be further promoted by making the dip wavelength approach lambda(Bg)=0.