Research On Hardware Circuit Optimization And Technique To Suppress Laser's Intensity Modulation Noise For A Miniaturized RFOG

The resonator fiber optic gyroscope(RFOG)is an inertial sensor for the measurement of rotation rate,which is based on the Sagnac effect.Compared with the interferometric fiber optic gyro(IFOG),it has the potential to achieve the same high accuracy with a shorter sensing coil length,which is an advantage in terms of miniaturization and integration.At present,although the performance of RFOG has been improved,it is still in the experimental research stage.The optic and electronic devices with large volume are still discrete,which constitutes an obstacle to practical development of the RFOG system.Therefore,the research on miniaturization and integration is of great significance to the final application of RFOG.In this dissertation,the hardware circuit of the RFOG system is optimized,and the miniaturization for the hardware circuit of the RFOG system is further realized.In addition,the laser-diode(LD)is accompanied with intensity modulation noise which has a negative impact on gyro's performance especially under dynamic condition.In this dissertation,the demodulation signal compensation technique by monitoring the second-harmonic demodulated signal is described in detail.With this compensation technique,the gyro output stability is effectively improved.The main achievements of this dissertation are as follows:(1)The integration and optimization of the digital signal processing and the photoelectric conversion hardware circuit of the miniaturized RFOG system are completed,so as to realize the further miniaturization of RFOG hardware circuit.Based on the demand analysis of the circuit,the chip models such as the power chips,the amplifiers and followers are improved and the circuit structure is optimized.Thus the FPGA digital signal processing module and the driver circuit of the photodetector(PD)are integrated in a round printed circuit board(PCB)with 8cm diameter.The test result of this optimized PCB shows that it meets the requirements of RFOG system and the power consumption is decreased from previous 3W to current 1.9W.(2)The performance of the RFOG system is tested with the optimized hardware circuit.With the integration time of 1s,the bias stability of the gyro output achieves 58.1deg/h.The Allan deviation analysis shows that the bias stability of the gyro output is better than 5.0deg/h with an integration time of 248s.The dynamic range of the system is ± 100deg/s,and the nonlinearity of the scale factor is 0.317%.The rotation response for swinging amplitude as low as O.Oldeg/s can be obviously observed.(3)Through the dynamic scanning of the demodulation curve and the analysis of the fluctuation of demodulation curve's slope,the accompany intensity modulation effect induced by the LD is analyzed and verified by experiment,which has a negative impact on gyro's performance.Experiment result shows that under 0.5deg/s and 5.0deg/s rotation rates,the 1V LD's tunning voltage fluctuation will induce the gyro error of as large as about 0.175deg/s and 3.22deg/s respectively.This result verifies that the accompany intensity modulation effect will induce large error in the RFOG especially under dynamic condition.And this error increases as rotation rate increases.(4)Based on monitoring the second-harmonic demodulated signal of closed loop,a demodulation signal compensation technique is proposed to suppress the intensity modulation noise in RFOG system.Through theoretical derivation,the expression of the gyro output signal under this compensation technique is obtained.Through the design of digital signal processing algorithm,the gyro output is compensated in real time without any additional device.In order to optimize the detection accuracy for the second-harmonic demodulated signal,the optimal quantization bit of the second-harmonic demodulated signal is obtained by theoretical and experimental analysis.According to the analysis result,the optimal quantization bit increases as rotation rate increases.When the compensation algorithm module is adopted,the stability of gyro output is effectively improved by a factor of 1.88,3.19,16.89 and 26.56 under rotation rates of 0.5deg/s,1.0deg/s,2.0deg/s and 5.0deg/s,respectively.So,the effectiveness of the compensation technique is verified and the compensation effect becomes more obvious as rotation rate increases.The results of this study provide a reference for the further research of the RFOG system miniaturization and intensity modulation induced noise.