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• A large bandwidth optical fiber magnetic field sensor based on Sagnac interferometer for weak alternating magnetic fields measurement is proposed. • The sensing mechanism of this magnetic field sensor under an alternating magnetic field is theoretically derived and simulated. • The experimental system is built to verify the simulation results, and the magnetic field sensitivity is optimized by increasing the length of the delayed fiber ring. • The magnetic field sensor performances, such as frequency response, linear range, and noise, are analyzed theoretically and demonstrated experimentally. In this paper, a fiber magnetic field sensor is proposed based on Terfenol-D and Sagnac interferometer. The mechanism of the sensor is deduced theoretically. As the frequency of the magnetic field increases, on the one hand, the sensitivity is enhanced because the response to the high-frequency non-reciprocal phase differences is intensified in the Sagnac interferometer. On the other hand, the sensitivity is suppressed by the eddy current effect. Then it exhibits significant linear response to alternating magnetic field in a certain frequency range. The sensor performances, such as frequency response, linear range, and noise, are analyzed theoretically and demonstrated experimentally. Experimental results show that the sensor has a 3 dB bandwidth from 100 Hz to 2500 Hz, and the excellent linearity and reversibility from 0 to 274.05 μT (rms). The high sensitivity of 1.34 mV/μT (rms) and minimum detectable magnetic field of 25 nT/√Hz (rms) are achieved at 500 Hz. The sensor with large bandwidth and wide measuring range is suitable for detecting weak alternating magnetic field. [ABSTRACT FROM AUTHOR]

• The differences in the suppression mechanisms of radial and axial magnetic errors in the PMFOG with orthogonal polarization states are analyzed theoretically, and the corresponding experimental verifications are carried out, which the suppression effect of the radial and axial magnetic errors could be achieved 10.07 dB and 2.9 dB, respectively. • The Poincare sphere model of the evolution process of the polarization state in the PMFC is established, which intuitively reflects the radial magnetic error can be effectively suppressed in the system. • The influence of different polarization state on magnetic error were compared and analyzed under the different magnetic field, and the radial and axial magnetic error achieved a different degree of suppression effect by utilizing orthogonal polarization states respectively. In this paper, a polarization-maintaining fiber optical gyro (PMFOG) based on orthogonal polarization states is constructed. The clockwise light and counterclockwise light in the PMFOG pass through the same fiber coil with X/Y polarization and Y/X polarization respectively. Theory and experiments have shown that this system not only doubles the sensitivity of the PMFOG at the same length, but also suppresses the magnetic error obviously compared with the single-polarization PMFOG. The Poincare sphere model is established in the PMFOG with orthogonal polarization states under the radial magnetic field, which intuitively shows that magnetic error is opposite in the orthogonal polarization state, and can offset through each other. The radial magnetic error is suppressed from 0.112°/h/Gs to 0.011°/h/Gs, and the suppression reaches 10.07 dB. Meanwhile, the axial magnetic error is suppressed from 0.183°/h/Gs to 0.092°/h/Gs, achieving a suppression effect of 2.9 dB. The results of this research are of great significance to the miniaturization, the improvement of signal-to-noise ratio, and the optimization of environmental adaptability in fiber optic gyroscope. [ABSTRACT FROM AUTHOR]

• The mechanism of nonreciprocal errors under the magnetic field-variable temperature field is proposed. • Based on dual-polarization interferometric fiber optic gyroscope (IFOG). • The nonreciprocal errors under the magnetic field, variable temperature field and magnetic field-variable temperature field are compared. A dual-polarization fiber optic gyroscope system is built to systematically analyze the nonreciprocal errors of the system under the magnetic field-variable temperature field. Under the magnetic field-variable temperature field, the nonreciprocal errors are caused by magnetic-thermal coupling birefringence nonreciprocal error, linear birefringence nonreciprocal error and Shupe effect error. The nonreciprocal errors of dual-polarization fiber optic gyroscope system are related to temperature and temperature gradient. In X and Y polarization states, the signs of magnetic-thermal coupling birefringence nonreciprocal error and linear birefringence nonreciprocal error are opposite, and these two errors can be suppressed in the dual-polarization system. But the Shupe effect errors are the same in X and Y polarization states, which can not be suppressed in the dual-polarization system. The experimental results are consistent with the theoretical analysis, which verifies the correctness of the nonreciprocal error model under the magnetic field-variable temperature field. The research results provide a theoretical and experimental basis for the study of the environmental adaptability of the fiber optic gyroscope and other common-path fiber sensing systems based on dual-polarization. [ABSTRACT FROM AUTHOR]