Magnetic Field Sensing by Magnetic-Fluid-Coated Capillary Long-Period Fiber Gratings

Abstract

In this paper, we presented and experimentally investigated a novel magnetic field sensor based on magnetic-fluid (MF)-coated capillary long-period fiber gratings (CLPFGs). The CLPFGs with short length of no more than 10 mm and period of 1 mm were fabricated by point-to-point arc discharge method, and then infiltrated in an MF-filled glass tube forming a packaged MF-coated CLPFGs magnetic field sensors. A redshift in resonances of CLPFGs was brought out after packaging process, due to external refractive index changing. With the increasing external magnetic field, the intensity of resonant dips gradually decreased, which is caused by magnetostrictive effect together with refractive index variations. Moreover, CLPFGs with the same grating period and different grating lengths were comparatively investigated and analyzed. The resonant dips with larger transmissive depth present faster descend to the external magnetic field, result in higher sensitivity. The sensitivity of 0.036 dB/Oe could be obtained, when the CLPFGs has a grating length of 9 mm. What is more, the sensor is insensitive to temperature which can avoid the effect of temperature. The proposed MF-coated CLPFGs magnetic field sensor has potential applications in magnetic field systems.