Optical fiber magnetic field sensor with thin clad LPFG cascaded FBG structure

In this paper, an optical fiber magnetic field sensor is proposed for simultaneous measurement of magnetic field strength and temperature. The proposed sensor is composed of a thin-clad long-period fiber grating (LPFG) and fiber Bragg grating (FBG). The fiber cladding is corroded by hydrofluoric acid (HF) to improve the measurement sensitivity of the sensor probe. By using the different sensitive characteristics of LPFG and FBG to external changes, the effect of double parameter measurement and temperature compensation is achieved, thus improving the accuracy of LPFG magnetic field strength measurement. The experimental results show that the temperature sensitivity of LPFG and FBG of 8 pm/°C and 85.7 pm/°C of the proposed sensor respectively in the temperature range of 35–85 °C, and the magnetic field sensitivity of 65 pm/mT of the proposed sensor in the range of magnetic field strength of 4–20 mT. Compared with the LPFG- FBG thermomagnetic sensor without corrosion of optical fiber cladding, the magnetic field sensitivity of the proposed sensor is increased by 1.88 times.