Research On Multi-phase Modulation And Error Of Dual-polarization Interferometric Fiber Optic Gyroscope

As a key component of inertial sensor,fiber optic gyroscope has become the most widely used fiber optic sensor in navigation and guidance system.Among them,interferometric fiber optic gyro（IFOG）,with its advantages of anti-electromagnetic interference,small size,high precision,low noise and high stability,has a broad application prospect in inertial navigation system.At present,as a new type of angular velocity sensing instrument,dual-polarization interferometric fiber optic gyroscope has attracted the attention of researchers at home and abroad.However,because the open-loop dual-polarization IFOG is susceptible to environmental fluctuations,polarization cross coupling will occur under traditional square wave modulation.And the error study of environmental adaptability under magnetic-temperature field is not perfect.Therefore,it is necessary to design a new modulation technology and study the nonreciprocal error of multi-physical field.The main researches are as follows:（1）The cross coupling between orthogonal polarization states of the dual-polarization system will be caused by the change of ambient temperature and stress,which will reduce the stability of the dual-polarization system.In order to solve the problem of polarization cross-coupling nonreciprocal error in the traditional square wave modulation and demodulation technique,a multi-phase modulation scheme is proposed,including four-state square wave phase modulation and six-state square wave phase modulation.Four-state square wave phase modulation technique uses two modulation phases but arithmetic and close toπ,which greatly increases the precision of signal calculation and reduces the polarization cross coupling error.Based on the four-state square wave,the six-state square wave modulation of dual-polarization system is proposed,which demodulated gyroscope signal twice in one modulation period and improved signal to noise ratio.（2）The static output of dual-polarization system under different modulation and demodulation techniques is tested.On the basis of dual light source inverting modulation,the standard deviation of four-state square wave modulation is 1.07 times lower than square wave modulation,and the bias instability is 3.3 times lower than square wave phase modulation.The standard deviation of six-state square wave modulation is 1.24 times lower than square wave modulation,and the bias instability is 9.9 times lower than square wave phase modulation,reaching 9.85×10^-4°/h.Through the above research,the multi-phase modulation and demodulation technology is better used in the dual-polarization IFOG system,which solves the problem caused by the polarization cross coupling error,and significantly improves the solution accuracy and long-term bias instability of the gyroscope.（3）In order to study the environmental adaptability of dual-polarization IFOG under the magnetic field-variable temperature field,the error mechanism of dual-polarization system under magnetic-temperature field is analyzed.Considering that the temperature of IFOG varies with time in practical application,the linear birefringence and Verdet constant of polarization-maintaining fiber coil are affected.The nonreciprocal error model under magnetic-temperature field is established by infinitesimal method and Jones matrix.According to the theoretical model,the numerical simulation of dual-polarization IFOG under single magnetic field,single temperature field and the magnetic field-variable temperature field is carried out.Finally,the experimental test is carried out.The variation trend and peak-to-peak values of the errors between the experimental results and the simulation results are basically consistent,which verifies the correctness of the nonreciprocal error model under the magnetic field-variable temperature field.The error model is used to compensate the nonreciprocal errors in the dual-polarization system,and the bias instability of the IFOG is improved 32 times,which provides a theoretical and experimental basis for further improving the environmental adaptability of the dual-polarization IFOG.