Miniaturized FPI-FBG integrated sensor for parallel monitoring of magnetic field and magnetic fluid refractive index

In this paper, a sensor combining Fabry–Perot interferometer (FPI) with fiber Bragg grating (FBG) is designed, fabricated, and experimentally demonstrated as an excellent alternative to traditional sensors to detect the magnetic field and refractive index (RI), simultaneously. The sensor comprises a magnetostrictive Ni-Fe alloy coated on partially-unclad FBG, connecting the two reflecting surfaces of the micro-FPI cavity. The magnetostrictive analysis shows that magnetostriction reaches the maximum value at 59.3% Ni concentration. The sensor performance test was conducted on the RI of magnetic fluid and external magnetic field changes. The probe sensitivity was found to be as high as 625.38 nm/RIU and 7.71 nm mT −1 , respectively. A matrix for simultaneous measurement of the magnetic field and RI was constructed using these sensitivity values. The stability of the sensor system over more than 300 h is at a satisfactory level. Considering the accurate FBG modulation and particular design of the experiment proposed by this method, the resolution of 1.69 × 10 −4 RIU and 0.016 mT for magnetic fluid and magnetic field could be achieved, respectively, which can meet the sensing demand for a wide range of applications.