Highly Precise Magnetic Field Measurement Based RF-Assisted Sagnac Interferometer With Tapered Fiber

A radio frequency (RF)-assisted Sagnac interferometer based on a dual-loop optoelectronic oscillator (OEO) is experimentally demonstrated for high-precision magnetic field measurement, in which the tapered fiber covered with the magnetic fluid (MF) as the magnetic field sensing head is embedded in the Sagnac interferometer. The evanescent field of the tapered fiber can interact with the MF under the external magnetic field to cause the birefringence variation of the fundamental mode, leading to the change in the free spectral range (FSR) of the interferometer, which can be mapped to the oscillation frequency shift of the OEO in the microwave domain. By the above converting, the magnetic field measurement with high interrogation speed and resolution can be realized. In addition, the designed device shows a certain measurement directionality of the magnetic field due to two orthogonally polarized fundamental modes asymmetric to the magnetic field, obtaining a good conformity with the constructed theoretical models. The experimental results show the maximum magnetic field sensitivities of 159.4 Hz/mT in the range of 8.48-27.83 mT, and 350.8 Hz/mT in the range of 0-5.14 mT, corresponding to the light wave vector parallel and perpendicular to the magnetic field, respectively.