A theory for nonreciprocal phase shift caused by cross coupling generated in a polarization maintaining (PM) fiber optic gyroscope (FOG) under the combined action of magnetic and temperature fields is proposed. The magnetic-thermal coupling in the FOG originates from the interaction of the magnetic field, fiber twist, birefringence caused by thermal stress, and the intrinsic and bending birefringence of the fiber. The cross coupling changes with temperature. When the PM fiber has a diameter of 250 μm, beat length of 3 mm, length of 500 m, twist rate of 1  rad/m, and optical source wavelength of 1310 nm, the maximum degree of magnetic-thermal coupling generated by a 1 mT radial magnetic field within the temperature range of -20°C  to 60°C is -5.47%.

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.Index Terms-Orthogonal magnetic field, nonreciprocal phase error, polarization-maintaining fiber-optic gyros, polarization state, coupling angle I.

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We investigated the nonreciprocity induced by an orthogonal magnetic field (OMF) in a single-mode fiber coil and expressions for the propagation constant of light waves in the bent fiber are deduced. Coils with different radiuses are put into depolarized interferometric fiber optic gyroscopes (D-IFOGs) for experimental verification. Theories, simulations and experimental results show that the OMF induced nonreciprocal phase error is closely related to the bending radius and the generated magnetic drift in D-IFOGs is linear to the amplitude of the OMF.