The magnetic field in fiber optic gyroscope (FOG) will cause Faraday effect, resulting in Faraday phase error. Experimental results show that the axial magnetic field sensitivity is more obvious than the radial magnetic field sensitivity. The clockwise (CW) and coienter-clockwise (CCW) light which propagate in the polarization maintain (PM) fiber in Fiber-optic gyro will generate a nonreciprocal phase error associated with axial magnetic field. In this paper, the geometrical axial magnetic field sensitivity caused by helically wounded optical fiber is studied; coupled-mode theory and finite element analysis are used to induce the FOG′s specific expression of Faraday nonreciprocal phase difference generated in axial magnetic field. The simulation analysis is given based on the theoretical results. Research show that circular birefringence caused by the geometrical torsion in the fiber of the fiber coil is the main causes of the geometry Faraday phase error. Furthermore, the study results show that axial magnetic field sensitivity will increase with decreasing radius.
Mode-division multiplexing communication based on few-mode fibers (FMFs) is the most competitive scheme to address the bandwidth exhaustion in single-mode fibers. The differential mode group delay (DMGD) among different modes in FMFs is an important aspect in characterizing FMFs, and the convenient, fast, and accurate measurement of DMGD in different modes of FMFs is a crucial task. This paper presents a single-ended measurement method for DMGD in FMFs based on Fresnel reflection peaks. Experimental measurements were conducted to determine the DMGD of a 3.689 km six-mode fiber and a 9.7 km three-mode fiber, and the results were compared with the traditional time-of-flight method. The findings demonstrate that our proposed method based on Fresnel reflection peaks exhibits good accuracy in measuring the DMGD of FMFs. Moreover, this method enables single-ended measurement and offers simplicity and practicality.
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