Design Of Dual Laser Resonant Fiber Optic Gyro Signal Detection System Based On FPGA

As an angular velocity sensing instrument,gyroscope is widely used in civil and military fields,ranging from mobile phones and automobiles to rockets and satellites.The resonant fiber-optic gyroscope uses the Sagnac effect combined with the resonance phenomenon generated by the multi-beam interference formed by the cavity,and obtains the angular velocity information by detecting the difference between the two-way optical resonance point frequencies.However,the Sagnac effect is very weak and requires weak signal processing.The method is used to detect the signal and extract the angular velocity information from a large number of noises.For resonant fiber optic gyro,Rayleigh backscattering noise is one of the most important noises.For the first type of backscattering noise,there is now a mature scheme to suppress.The mainstream suppression method for the second type of backscattering noise is still Carrier suppression,but this method has two major drawbacks,one of which is susceptible to external temperature changes,and the other is that it is difficult to accurately control the modulation voltage.Based on the above research status,this paper starts from the purpose of suppressing the second type of backscattering,and uses two lasers to build a resonant fiber-optic gyro system.Combined with the optical phase-locked loop,the tracking and locking of the main laser frequency from the laser is established.The signal detection system of the laser resonant fiber optic gyroscope has carried out the following research work:(1)Aiming at the problem that the second type of backscattering noise of the resonant fiber optic gyro is difficult to suppress for a single laser source,the overall scheme of the dual laser system is proposed and designed,and the signal detection principle is analyzed.Then the optical path of the scheme is designed.Some important devices were analyzed and selected.(2)Aiming at the optical phase-locked loop technology applied to the resonant fiber optic gyroscope,this paper establishes the mathematical model of the optical phase-locked loop part of the system based on the principle of the dual-laser fiber optic gyroscope.For the implementation of the optical phase-locked loop,the beat frequency detection is obtained by using the 180° optical mixer and the balanced photodetector,combined with the high stable frequency difference signal generated by the DDS chip,and the beat frequency signal is realized by the phase frequency detector.The secondary mixing of the reference frequency difference signal,the combination of the ultra low voltage and current noise op amp and the traditional PID control method to achieve the role of the loop filter.(3)Based on the sinusoidal modulation wave generated by Cordic algorithm,a lock-in amplification demodulation method composed of full parallel multiplier and FIR filter is designed.The high-performance processing of digital signal is realized by the high performance of the internal IP core of FPGA chip..On the basis of the above work,a lock-frequency algorithm for parallel incremental PI control is established,and various parameters are adjusted in combination with simulation.With FPGA as the core device,the appropriate analog-to-digital and digital-to-analog conversion chips are selected to enhance the reliability of the system.(4)Finally,this thesis tests the dual laser resonant fiber optic gyroscope system and completes the testing and verification of each module of signal detection.The design and implementation of the dual-laser resonant gyro is of great significance for suppressing the second type of backscattering and improving the accuracy of the system.