Research And Implementation Of Closed-loop Modulation Signal Processing Technology For RFOG

As one of the core devices of inertial navigation equipment,the gyroscope can measure the rotation angle of the object to be measured.The measurement accuracy of the gyroscope will directly affect the accuracy of the entire inertial navigation system.The resonant optical gyroscope is based on the Sagnac effect.Compared with interferometric fiber optic gyroscopes,because they have higher theoretical accuracy at the same fiber length,they have great potential for exploration in high precision and miniaturization,which is in line with the development trend of gyro devices.The Sagnac effect serves as the common theoretical basis for all optical gyroscopes.In a resonant gyroscope system,the light emitted by the laser is divided into the same two parts,and they enter the resonant cavity along different coupler ports.When the cavity rotates at any angle,the There will be a situation where the two resonance images are separated,and the difference between the resonance images in both directions can reflect the magnitude of the rotational angular velocity.However,because the Sagnac effect itself is very small,the frequency image difference caused by rotation is also very small,so the signal detection link The accuracy is crucial.Compared with analog circuits,digital circuits are more stable,less susceptible to interference,and more efficient in processing data.Therefore,digital signal platforms are used to process the output data of resonant fiber optic gyroscopes.The entire system uses a closed-loop modulation signal processing system to detect the measurement data,amplify weak signals,and improve system stability.The main research contents and results of the paper are as follows:First,the basic principle of all optical gyroscopes,namely the optical Sagnac effect,is introduced,so that the resonant fiber-optic gyroscope is introduced and the optical path and circuit principles of the gyroscope are introduced in depth,and the performance parameters of the resonant cavity are analyzed.The resonant fiber optic gyro closed-loop modulation signal processing system is composed of the circuit part and the optical path part.The optical path signal model from the laser output to the photodetector detection is established,and the overall composition structure model of the resonant fiber optic gyro signal detection and feedback control system is proposed.Based on the analysis of the optical path,the establishment of the gyro optical path system is completed.Then,the principle of digital signal detection of resonant fiber optic gyro is analyzed,and a sine wave optical signal modulation module is designed.In the FPGA platform,a DDS integrated IP core solution is used to implement this function.A phase-locked amplifier-based signal demodulation module is designed in FPGA.The digital platform uses a mathematical operation IP core to complete the design of the module.The optical path and circuit signals are modulated and demodulated through the principle of photoelectric interaction,and the weak gyro signal is amplified and output.In view of the randomness of laser frequency,PI feedback module is used to adjust the laser frequency so that the center frequency of the laser can track the resonant frequency point in one direction of the cavity in real time,and the discrete PI control module is implemented in the FPGA digital platform.To complete the laser frequency locking.In view of the fact that lasers and other devices are more sensitive to external interference and easily cause lock-out,a pre-adjustment module is added in the control link,and a state machine is used to implement this function in the FPGA digital platform,which makes the system more stable and the anti-interference ability enhanced.Finally,the optical path part and circuit part of the resonant fiber optic gyro are assembled to complete the gyro closed-loop modulation digital signal processing system.The system's resonant cavity characteristics,digital modulation,demodulation and feedback,and pre-adjustment are tested separately.The tests show that the system Module function design is correct.Then the whole system was tested for bias stability and scale factor,which verified the feasibility and correctness of the design of the resonant fiber optic gyro system,and realized the design of the gyro system.