Highly sensitive magnetic field sensing probe based upon compact Fabry–Perot interferometer combined with Galfenol rod

Abstract A novel ultra sensitive magnetic field (MF) sensing probe based upon a compact Fabry–Perot interferometer (FPI) and a Galfenol rod is presented and experimentally validated. The sensor consists of a single-mode fiber fused to a quartz capillary, with a PVA film applied to the capillary’s end face to create an interferometer with three reflective surfaces. The distance between the three reflecting surfaces is carefully adjusted to match and generate a vernier effect (VE) spectrum through interference of the three reflecting surfaces. Finally, the interferometer is pasted onto the end face of the Galfenol rod to create an MF sensor. When an external MF is applied, the Galfenol rod undergoes expansion and contraction, altering the optical path difference of the interferometer and causing the shift of the interference spectrum. By monitoring the changes in the spectral envelope caused by the VE, a higher MF sensitivity is achieved. Experimental findings demonstrate that the sensor achieves the MF’s sensitivity of −6.733 nm mT−1, 25.4 times greater than that of a single sensing FPI1. In summary, this MF sensor is simple to fabricate, cost-effective, structurally durable, and highly sensitive, making it a promising solution for practical MF sensing applications.