Nonreciprocal Phase Error Caused by Orthogonal Magnetic Field in a Polarization-Maintaining Fiber-Optic Gyro

This paper aims to investigate the nonreciprocity caused by orthogonal magnetic field (OMF) vertical to the light direction propagating in a polarization-maintaining fiber-optic gyro (PM-FOG). In orthogonal magnetic field, the nonreciprocal phase error (NPE) results from the small change of the propagation constants of the two opposite light waves propagating in the fiber coil. Even using a PM fiber coil, the pressure, twist, and other imperfections will change the polarization state, which may lead to an instable drift in PM-FOGs. This phenomenon was observed in the 0°-coupling regime which is commonly used for PM-FOG systems. Theoretical analysis and experimental results show and confirm that the instability of the NPE can be evidently reduced by taking a double-45°-coupling scheme. In this case, the NPE appears to be linear to the OMF and can therefore be compensated via later processes.