Design And Research Of Signal Detection System For RFOG Based On The FPGA

Resonant fiber optic gyroscope is a new type of high-precision angular velocity sensor device.Because the output signal of the resonant cavity based on the optical Sagnac effect theory is particularly weak,and it is easy to introduce various noises and interferences in the optical path and circuit,which will directly reduce the accuracy of the gyro rotation angular velocity output,the design of the gyro signal detection processing system is extremely critical.This paper mainly studies the noise processing of the gyro system signal.It improves the signal-to-noise ratio of the gyro system from several aspects such as optical backscatter noise suppression,gyro signal separation,and digital filtering,so as to improve the accuracy of the signal detection system and ultimately improve the accuracy of the gyro angular velocity measurement.This subject adopts the detection system with FPGA chip as the core to detect and process the gyro signal accordingly.The main research contents and results of the paper are as follows:Based on the Sagnac effect,the characteristics of the resonance curve and the modulation and demodulation curve generated by the light wave in the optical path transmission process are derived and explained in detail.Since light waves also generate a large amount of backscattering noise during transmission,in order to suppress the backscattering noise,a mathematical model is established,and a model of the backscattering noise is set up to conduct experiments to observe the backscattering fluctuation.Then it is suppressed by two phase modulation techniques with different frequencies.During the phase modulation process,the amplitude of the modulation signal is particularly sensitive to the gyro signal.Therefore,first,the optimal modulation voltage of the phase modulator is theoretically derived;then the self-heterodyne optical path is used to measure the corresponding relationship between the modulation voltage and the carrier rejection ratio to find the optimal modulation voltage.In order to further observe the effect of the maximum carrier rejection ratio,Based on theexperimental data,the influence of the modulation voltage on the gyro signal-to-noise ratio and the stability of the gyro bias is obtained,so as to find the optimal modulation voltage.Separate the digital signals of the modulated gyro system offline to reduce the influence of optical path noise and circuit noise on the gyro.Firstly,the frequency spectrum of the triangle wave and sine wave modulation signals in the gyro system is analyzed theoretically,and then it is verified by simulation using Matlab.The empirical modal decomposition algorithm was used to analyze and test the signal separation effect: the signal-to-noise ratios of triangle wave modulation and sine wave modulation were increased by 0.32 d B and 2.72 d B,respectively.The filtering algorithm in the signal detection and processing system is studied.The digital filter is designed in the signal detection system with FPGA as the core,and the simulation analysis and experimental process are implemented with the Verilog HDL programming language.The results show that the digital filter has a smooth denoising effect on the modulation curve and demodulation curve and improves the accuracy of the gyro.At the same time,wavelet threshold filtering is performed on the gyro output angular velocity signal.Through the Allan variance evaluation standard,it is verified that the filtering algorithm has a good effect in reducing the five major noise sources of the gyro system.