Optical fiber magnetic field sensor based on cascaded down-taper and spherical structure

Abstract

An optical fiber magnetic field sensor using intermodal interferometer coated by magnetic fluid (MF) is proposed. The interferometer consists of down-taper and spherical structure formed on the standard single-mode fiber (SMF) by a fusion splicer. Since the refractive index (RI) of the MF is sensitive to external magnetic field, the interferometer coated by MF can be used for magnetic field sensing. Two interference valleys of the interferometer integrated with ferrofluid under different magnetic field intensities have been experimentally analyzed. The experimental results show that there is a linear relationship between the valley wavelength shift and magnetic field intensity for a range of 0 to 20 mT, and the maximum sensitivity reaches up to −0.195 nm/mT. In the range of 0 to 12 mT, the variation of transmission loss at valley wavelength with a magnetic field has a maximum sensitivity of 0.106 dB/mT.