Research On The Non-reciprocity Error Analysis And Suppression Technology Of Fiber Optical Gyro With Double Optical Length

Fiber optic gyroscopes are widely used in navigation systems due to its high precision,high reliability and good stability.With the widespread application of miniaturized UAV platforms,there are higher requirements for its size,accuracy and environmental adaptability（magnetic field,temperature field,etc.）,which also makes the contradiction between the size,accuracy and environmental adaptability increasingly prominent.Compared with the traditional polarization-maintaining fiber optical gyro with single optical length,the polarization-maintaining fiber optical gyro（PMFOG）with double optical length could double the sensitivity of gyro under the same polarization-maintaining fiber ring（PMFC）,which is very important to improve the accuracy of gyro under the limited length of PMFC.However,the analysis of the non-reciprocal error induced in the PMFOG with double optical length under the magnetic field and time-varying temperature field is not perfect,and the analysis is not systematic enough at present.So,this paper mainly researches the nonreciprocal errors introduced in the PMFOG with double optical length and its suppression technology under the magnetic field and temperature field.The details are as follows:Firstly,theoretical derivation of the mechanism of the principle of achieving the double sensitivity in the PMFOG with double optical length and the modulation and demodulation technology based on sine wave is mainly researched.After that,the PMFOG with single and double optical length were built respectively,and the ground speed was tested and calibrated at the same location for 1 h.The zero-bias stability of the PMFOG with single and double optical length are 0.0203°/h and 0.0054°/h,respectively,and the noise width after 1s smoothing is reduced from 1.4°/h to 0.7°/h,which verified that under the premise of the same length of PMFC,the PMFOG with double optical length could double the sensitivity and improve the zero-bias stability.Secondly,the environmental adaptability of the PMFOG with double optical length under the magnetic field is researched.The theoretical models of non-reciprocity error induced by radial magnetic and axial magnetic in the system were established respectively by using Jones matrix,and the suppression process of radial magneto-induced error in this system is analyzed visually by using the Poincare sphere model.After that,the experimental systems of the nonreciprocity error induced by magnetic field in the gyro with single and double optical length were built to verify the suppression effect.The maximum of the non-reciprocity error induced by radial magnetic field is suppressed from 0.112 °/h/Gs to 0.011°/h/Gs,the suppression effect reaches 10.07 d B,and the non-reciprocity error induced by radial magnetic field is suppressed from 0.183 °/h/Gs to 0.092 °/h/ Gs,the suppression effect of 2.9d B is achieved.Finally,the environmental adaptability of the PMFOG with double optical length under the temperature field is researched.The theoretical model of the non-reciprocity error induced by time-varying temperature field in the PMFOG with double optical length is established,and the experimental test system for the non-reciprocity errors induced in the PMFOG with single and double optical length under time-varying temperature field were built respectively.Theoretical analysis and experiments verified that the non-reciprocity errors of the PMFOG with double optical length under time-varying temperature field was about 5.07 times that of the system with single-optical length.Therefore,we propose a method of adding two 90°polarization state conversion points in the PMFC,which enhances the symmetry of optical path of the system,so that the errors introduced by the time-varying temperature in the system are almost completely suppressed,and the environmental adaptability of the fiber-optic gyroscope under the time-varying temperature field is effectively improved.