Compact magnetic-field sensor based on optical microfiber Michelson interferometer and Fe3O4 nanofluid.

We report a magnetic-field sensor by merging the advantages of optical fiber Michelson interferometers with that of magnetic fluid. Compact and low-cost optical fiber Michelson interferometers were first fabricated by a high-frequency CO2 laser, and then they were inserted into glass capillaries with water-based Fe3O4 magnetic fluid as sensing elements. The sensing characteristics have been investigated and the experimental results show that the reflective spectrum of the fiber-magnetic sensor linearly shifted with the change of the magnetic-field strength that is perpendicular to the axial of the devices. The fiber-magnetic sensor with interference arm’s diameter of 50 μm is most sensitive to the external magnetic field, and the sensitivity is up to 64.9  pm/mT, which is 20 times higher than that of 125 μm diameter.