Simple structure of tapered FBG filled with magnetic fluid to realize magnetic field sensor

•The sensor can measure the magnetic field below the critical value of the magnetic fluid.•By tapering the FBG, a phase-shifted fiber is produced. The sensitivity of the sensor has been increased by 3 times.•After being encapsulated with a glass tube, the sensor has the potential to identify the direction of the magnetic field.•The manufacturing method of the sensor has high repeatability and low cost. A magnetic field sensor based on tapered FBG wrapped in magnetic fluid is proposed and experimented. The center of FBG is tapered to form a nanofiber, thereby enhancing the interaction between structure and magnetic fluid. The magnetic fluid's perception of the external magnetic field will affect the optical path of the nanofiber in the center of the tapered FBG, which is reflected in the transmission spectrum of the sensor. The manufacturing method is simpler and more sensitive to external changes. The experimental results show that the intensity change of the sensor has good linearity corresponding to magnetic flux density, and the sensitivity is 0.035 dB/mT. The sensor can also measure the magnetic field below the critical magnetic field. After packaging with a glass tube, the magnetic fluid has difference responses to different directions of the magnetic field.