Magnetic Field Sensor Based on Microfiber Sagnac Loop Interferometer and Ferrofluid

We demonstrate a novel compact optical magnetic field sensor composed of a single-mode microfiber sagnac loop interferometer (SMSLI) and ferrofluid (FF). The refractive index of FF cladding in the twist area of SMSLI is changed with the externally applied magnetic field, which makes the dip-wavelength of the SMSLI transmission spectra shift. The experimental results show that the transmission spectrum of the proposed sensor shifts regularly with the change of externally applied magnetic field intensity. When the magnetic field intensity increased from 0 to 600 Oe, the dip-wavelength of transmission spectrum shifted nearly 200 pm. In addition, a minimal detectable magnetic field strength of the sensor responding to the 50-Hz alternating magnetic field was demonstrated to be similar to 3 Oe experimentally.