| The resonator fiber optic gyro(RFOG)is an inertial sensor based on the optical Sagnac effect,which is used to measure the rotation rate of the objects.The theoretical study result indicates that compared with the interferometric fiber optic gyro(IFOG),the RFOG can achieve the similar theoretical precision as the IFOG with shorter fiber,which is beneficial to miniaturization and integration of the fiber optic gyroscope(FOG).Currently,the performance of RFOG has been improved;nevertheless,the research of the RFOG is still in the laboratory stage and the various system noises restrict the further accuracy improvement for the RFOG.The double closed-loop RFOG has certain advantages in the performance such as the dynamic range compared with the single closed-loop RFOG.In this thesis,the size of some key components in the double closed-loop RFOG has been optimized.The Kerr effect induced error caused by the intensity modulation induced by the laser diode(LD),which is used in this double closed-loop RFOG system,has been studied,and an error suppression algorithm is added into the system to improve the accuracy,which requires no additional device.In the meanwhile,this thesis focuses on the sme-serrodyne phase modulation technology used in the double closed-loop system,and studies the phase modulation spectrum overlapping.In addition,the noise characteristics caused by serrodyne wave's non-ideal reset is discussed.This dissertation mainly carried out the following research work:(1)A double closed-loop RFOG system is set up based on some miniaturized key components.This thesis optimizes the volume and size of some key components in the double closed-loop RFOG system.This system uses a cylindrical semiconductor laser module with diameter of 8 cm and height of 2.2 cm,a short waveguide LiNbO3 phase modulator with the size of 2.0cm×0.7cm×0.4cm,and a circular digital signal processing hardware circuit with the diameter of 8.4 cm.It provides a reference for the further miniaturization of the double closed-loop RFOG system.(2)Experimental verification of the Kerr effect induced error caused by the intensity modulation of LD has been done.In this double closed-loop RFOG system,an LD is used as the laser source.In the process of resonant frequency tracking,the intensity modulation caused by the LD would be induced,and this would lead to the Kerr effect induced error.By testing the Kerr effect induced error caused by intensity modulation,the relationship between the gyro output and the second harmonic difference is obtained,and it is verified that the Kerr effect induced error caused by the intensity modulation does have an impact on the gyro output.The research results provide a reference for the further study of Kerr effect induced error caused by intensity modulation in double closed-loop RFOG system.(3)A method of suppressing the Kerr effect induced error,based on second harmonic,is proposed.Aiming at the Kerr effect induced error,the expression of the linear relationship between the Kerr effect induced error and the normalized second harmonic difference is obtained,which could be used for gyro output signal compensation.Without adding additional device,the digital signal processing algorithm for the error suppressing is designed to realize the real-time compensation for the gyro output signal error,which improves the system stability.By comparing the gyro output with/without adding the error suppression algorithm under different optic intensity differences,the effectiveness of this algorithm is verified,and the noise suppression rate is better than 7.95%under this algorithm.This research results provide a reference for the further research on the Kerr effect induced error suppression methods in the double closed-loop RFOG systems(4)The sine-serrodyne phase modulation spectral overlapping characteristics and serrodyne wave reset characteristics are studied.By the analysis of the sine-serrodyne phase modulation spectrum overlapping characteristics of the two optical loops,the modulation frequency difference between the two loops is optimized to decrease the backscatter noise,which would be caused by the spectrum overlapping.The experimental results before and after the spectrum optimization are compared,and it is verified that the spectrum optimization is effective in improving the system accuracy.Aiming at the about 1?s reset delay of the serrodyne wave caused by the small bandwidth signal amplification circuit in the system,the characteristics of the output pulse noise caused by this reset delay is studied,and the influence of this reset pulse noise on the zero point of the demodulation curve of the double closed-loop RFOG system is preliminarily investigated.These results provide a reference for the further characteristic study of the double closed-loop system's modulation spectrum and serrodyne wave reset.The above research results provide a reference for the further research of the miniaturized double closed-loop RFOG system. |
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