Temperature compensated magnetic field sensor based on magnetic fluid infiltrated cascaded structure of micro-tapered long-period fiber grating and fiber Bragg grating

Magnetic fluid (MF) infiltrated fiber-optic interference structures can be used to realize miniature magnetic field sensor for various applications needing sensitive magnetic field measurement, however, these sensors are typically also sensitive to temperature variations. To solve the problem of temperature cross sensitivity, an MFinfiltrated micro-tapered long-period fiber grating (MT-LPFG) and a femtosecond laser inscribed fiber Bragg grating (fsFBG) cascaded sensing structure is proposed and demonstrated. The MT-LPFG is fabricated by a fused tapering method under the illumination of a CO2 laser and is inserted into a glass capillary infiltrated with MF for magnetic field measurement, and the fsFBG is cascaded to the MT-LPFG for temperature measurement. Through the simultaneous monitoring of the resonant wavelength shift of the MT-LPFG and the Bragg wavelength shift of the fsFBG, temperature and magnetic field strength can be simultaneously extracted through a sensitivity coefficient matrix. As a result, the influence of the temperature on the MF-infiltrated MT-LPFG can be effectively compensated. Experimental results show that a magnetic field strength sensitivity of 21.86 pm/Oe can be achieved in a magnetic field strength range of 10-80 Oe and a temperature range of 30-60 & DEG;C.