Magnetic fluid enabled hexagonal fiber grating for vector magnetic field sensing

Optical fiber magnetic field sensors play a crucial role in aerospace and medical fields due to their high sensitivity, fast response time, and resistance to electromagnetic interference. Most current research primarily focuses on detecting magnetic field intensity; however, the magnetic field is a vector field with both intensity and direction, making vector magnetic field measurement significantly important in various fields. Here, we experimentally demonstrated a vector magnetic field sensor using a magnetic fluid (MF) enabled hexagonal fiber grating. Such a specialty optical fiber device features strong asymmetric evanescent field distribution along the index perturbed area, from which the overcoated MF can sense the external magnetic field. When the fiber magnetometer operated at the dispersion turning point, a maximum sensitivity of 10.48 nm/mT was achieved within a range of 0–20.7 mT, which is one order of magnitude greater than that of conventional fiber grating sensors. Utilizing the polygon optical fiber, our demonstrated device simultaneously achieves a maximum orientation sensitivity of 1.17 nm/deg within a range of 0°–30°. This hexagonal fiber grating as an excellent vector magnetic field sensor may be used in military, aerospace, medical sectors, etc.