Research On Signal To Noise Ratio Improvement Technology Of Resonant Fiber Optical Gyro

Resonant Fiber Optic Gyro(R-FOG)is a kind of high-precision rotation rate sensor,which is able to use much shorter fiber length to achieve the same detection accuracy comparing with traditional Interferometric Fiber Optic Gyro(I-FOG).So R-FOG has obvious advantages in miniaturization and integration.R-FOG,however,has not been fully extended to practical applications,which is mainly restricted by the low signal-to-noise ratio of the gyro's output signal.This thesis mainly focuses on the research of signal-to-noise ratio enhancement technology of Resonant Fiber Optic Gyro.Related research work can be summarized as follows:(1)The source of Rayleigh backscattering noise in R-FOG and its effect on gyro output are expounded.The suppression process of two types of Rayleigh backscattering noise are explained theoretically.By setting up a self-heterodyne optical path and adjusting the amplitude of the modulating signal loaded on the phase modulator,the half-wave voltage and the maximum optical carrier rejection ratio of the two phase modulators were accurately measured.Zero-bias test was performed based on the single-phase modulation scheme.The results of the zero-bias test show that the Rayleigh backscattering noise in the R-FOG can be effectively suppressed when both phase modulators reach the maximum optical carrier suppression ratio.Optical carrier suppression observation experiment under the bi-phase modulation scheme verifies that the carrier suppression ratios of the two individual phase modulators can be added.The experimental results show that,when the bi-phase modulation scheme reaches the same carrier rejection ratio as the single-phase modulation scheme does,the modulation voltage accuracy requirements are lower in the former scheme.Finally,according to the different loss characteristics of stimulated Brillouin backscattering and Rayleigh backscattering,by setting up the backscattering observation optical path,adjusting input optical power to observe the change in the resonance depth of the signal light,the threshold of the input power is determined.When the input power is lower than the threshold value,it can ensure that the stimulated Brillouin backscattering does not occur in the Fiber Ring Resonator(FRR),and the stimulated Brillouin backscattering noise could be suppressed.(2)The source of polarization noise in the RFOG is introduced.Based on Jonse optics matrix theory,polarization analysis model of FRR is established and the influence of polarization noise on resonance curve is simulated according to the established polarization analysis model.By solving the eigenvalues of the single-pass transmission matrix in a ring resonator,it's theoretically proved that single-point 90° fusion scheme and double-point 90° fusion scheme can both effectively improve temperature stability of FRR and reduce polarization crosstalk in FRR.A set of test system is designed,which can synchronously compare single-point 90° fusion in the FRR and double-point 90° fusion in the FRR with single-point 0° fusion in the FRR for polarization temperature stability test.The temperature test data shows that compared with single-point 0° fusion scheme,temperature stability of single-point 90° scheme is increased by 4645 times;temperature stability of double-point 90° scheme is increased by 247 times.The feasibility of two fusion schemes to suppress polarization noise in RFOGs equipped with reflective resonator is analyzed.The feasibility analysis result shows that single-point 90° fusion is a better solution.It is verified by the zero-bias test that the single-point 90° fusion scheme can effectively suppress the polarization noise in RFOG equipped with a reflective resonator.(3)Starting from increasing the effective signal of the gyro system,that is,by amplifying the signal light in the cavity to increase the resonance depth of the resonance curve.A small coil of EDF is introduced into the passive cavity to form an active one.The working principle of the active FRR is introduced and a simple mathematical model is established.Based on this model,the characteristics of the resonance curve of the active cavity output are analyzed and simulated.Then the influence of the related parameters of the coupler on the characteristics of the active cavity is analyzed,and the principle of selecting the parameters of the coupler when the active cavity is actually constructed is obtained.Finally,the manually-built active cavity was tested to achieve a continuously tunable change in the resonance depth of the FRR output resonance curve from 0.19 to 1,and the fineness was 32 when the resonance depth was 1.Based on the above research basis,a laboratory gyro prototype is built and performance tests are executed.The scale factor is 9.1732/(°/h).In the case of the integration time of 100 seconds,the zero-bias stability of the gyro prototype is 18.9°/h within one hour.