Highly sensitive magnetic field measurement based on etched fiber Bragg grating and optoelectronic oscillator

Magnetic field as a kind of objective substance contains abundant physical information, so high sensitivity and resolution measurement for the magnetic field has great significance in scientific and industrial fields. In this work, we propose a novel fiber-optic magnetic field sensor by using an etched fiber Bragg grating (FBG) in conjunction with an OEO. A commercial FBG was firstly dipped into mixed hydrofluoric acid solution to remove cladding layer, and then was embedded with Fe3O4 magnetic fluid as sensing element. Incorporating the microwave photonic filter (MPF) in the OEO sensor, the oscillation frequency is determined by the magnetic field. Experimental results show that the oscillation frequency decreases with the increment of the magnetic field with sensitivity of 15.2Hz/Oe ranging from 3mT to 10mT, mainly because the refractive index of magnetic fluid was reduced sharply in this range. Since the proposed method transfers the measurement from the optical domain to electric domain, the interrogation speed, sensing sensitivity and resolution are significantly increased, offering potentials in many fields where the magnetic field measurement is required.