Multipoint Magnetic Field Measurement Based on Magnetic Fluid and FSI-FLRD

We present a multipoint fiber magnetic field sensing system based on magnetic fluid (MF) and frequency-shifted interferometry fiber loop ringdown (FSI-FLRD). This system contains a number of cascaded sensing channels, and shares a common continuous-wave light source and slow electronics instead of a pulsed light source and high-speed electron devices as required in traditional multichannel FLRD techniques. Each sensing channel is formed by incorporating an MF-coated etched fiber as the sensing head inside a fiber ringdown loop. Each sensing head is mounted on a temperature control device. We experimentally fabricated a dual-channel FSI-FLRD magnetic field sensing system. First the system's temperature response was investigated, which indicates the MF-based sensing heads had temperature cross sensitivity. Then after keeping the temperature at 20 °C for improving testing accuracy and applying different magnetic fields, the two sensing channels were separately shown to have sensitivities of - 9.38×10
^-5
and - 2.28×10
^-5
/(km ·Oe) with a linear response in the range of 221-721 Oe. The obtained sensing channel stabilities were respectively 0.02% and 0.04%, which enhance more than one order of magnitude compared with those of most conventional FLRD techniques.