Effect of Structure on Sensitivity of Magnetic Field Sensor Based on Non-Adiabatic Tapered Optical Fiber With Magnetic Fluid

Magnetic field sensor based on non-adiabatic tapered optical fiber (NATOF) surrounded with magnetic fluid (MF) has a potential to detect ultra-weak magnetic field. In order to improve the sensitivity of the magnetic field sensor, this paper investigated the effect of structure on sensitivity. The interference occurring between the modes in cladding and MF was analyzed to obtain the relationship between sensitivity and diameter of the tapered waist. Experiments were carried out to verify the proposed relationship. The experiments indicated when the diameter was larger than dispersion turning point ( $8.75 ~\mu \text{m}$ ), the sensitivity of the sensor decreased with the diameter of the tapered waist. The largest sensitivity obtained in the experiment is 6.567 nm/mT under a weak magnetic flux density range from 0 mT to 5 mT. This result is instructive for the manufacture of sensors with specific sensitivity.