Vector magnetic field sensor based on coreless D-shaped fiber and magnetic fluid

A vector magnetic field sensor based on a ferrofluid-encapsulated coreless D-shaped fiber is proposed and demonstrated. The core of the singlemode fiber (SMF) is completely removed by fiber polishing technology, and the remaining part transformed into a multimode interference (MMI) waveguide. The exposed side-polishing plane enable the evanescent field to interact with surrounding magnetic fluid (MF). Relying on the non-circularly symmetric geometry of the coreless D-shaped fiber and the MF refractive index modulation by the orientation and intensity of the applied magnetic field, vector magnetic field sensing is achieved. The magnetic field response characteristics of the coreless D-shaped fibers with different residual thicknesses (RTs) are investigated. The experimental results show that a reduced RT yields enhanced sensitivity, and the magnetic field intensity sensitivity reaches -0.231 nm/mT and -0.483 dB/mT at a RT of 42.7 µm. The developed coreless D-shaped fiber sensor exclusively utilizes SMF, thereby offering a cost-effective scheme for the fabrication of vector magnetic field sensors.