Optical fiber magnetic field sensing based on an optoelectronic oscillator with a prestressed and pre-magnetized enhanced-responsivity structure

This paper presents a magnetic field responsivity-enhancement sensing system, which comprises a magnetic field enhanced-responsivity fiber Bragg grating (FBG) sensing unit and a microwave photonic demodulation system utilizing an optoelectronic oscillator (OEO). The enhanced-responsivity structure integrates a mechanical stress coupling mechanism and a magnetic field bias, applying both prestress and pre-magnetization to a giant magnetostrictive material to improve its magnetostrictive coefficient. The FBG is mechanically bonded to this structure, forming a highly responsive magnetic field sensing unit. The OEO-based demodulating system consists of a feedback oscillation loop incorporating a broadband light source, an optical modulator, a dispersion medium, and a photodetector. It converts the wavelength shift of the FBG induced by the magnetic field into a corresponding oscillation frequency shift of the OEO, enabling precise magnetic field measurement through frequency monitoring. Experimental results demonstrate that the magnetic field responsivity of the enhanced sensor reaches 3920 Hz/mT, which is 16.3 times higher than that of the unenhanced configuration. A magnetic field resolution of 0.255 µT and an accuracy of 51 µT are achieved. The proposed magnetic field sensing system significantly enhances responsivity without increasing the complexity of the demodulation architecture. This work provides a novel, to our knowledge, and practical approach for high-accuracy magnetic field measurement in engineering applications.