A high-finesse fiber optic Fabry–Perot interferometer based magnetic-field sensor

• A compact extrinsic Fabry–Perot interferometric sensor based on a TbDyFe rod for the measurement of weak dc magnetic fields is demonstrated.
• A high-finesse extrinsic Fabry–Perot cavity is fabricated to improve the magnetic sensitivity.
• The white-light interferometry is utilized to detect the absolute length of the Fabry–Perot cavity.
• The sensor exhibits a high magnetic resolution of 25 nT with the TbDyFe rod at length of 16 mm.

A high-finesse extrinsic Fabry–Perot interferometric sensor for the measurement of weak dc magnetic fields is demonstrated. The Fabry–Perot cavity is formed by aligning the fiber end-face and the TbDyFe rod end-face, and each end-face is coated by a mirror with a micro-lens. The length of the TbDyFe rod is changed by the variation of an applied dc magnetic field, leading a change of the Fabry–Perot cavity length. By interrogating the white-light interferometric spectrum, the wavelength of the resonant peak is tracked and the length of the Fabry–Perot cavity is obtained. The sensor exhibits a high sensitivity of 1510 nm/mT with a magnetic resolution of 25 nT.