Research On The High Frequency Synchronous Drive And The Bias Compensation Of Electro-optical Modulation In The Phase Shift Laser Rang Finder

With the development of large precision machinery,Marine industry,aerospace and other fields,higher requirements are put forward for industrial measuring instruments.For example,in the process of space exploration,phase laser ranging method is widely used in the measurement and control of formation flying satellite.As a precise measurement method,it is often combined with GPS relative ranging technology and radio frequency ranging technology to achieve ranging accuracy of millimeter or submillimeter level.In the phase laser ranging technology,the ranging accuracy is related to the frequency and frequency stability of the ruler signal,while the bandwidth of photoelectric detection limits the improvement of frequency.In this case,the frequency stability of the ruler signal determines the ranging accuracy.Therefore,designing a precision measuring scale generation unit with high frequency stability is one of the key technologies to improve the ranging accuracy.The using of Mach-Zehnder(MZ)electro-optical intensity modulation in the phase laser ranging system has a large bandwidth and is suitable for high frequency precision measuring scale signals for ranging.However,the transmission function of Mach-Zeinder electro-optical intensity modulation will drift with the change of temperature and other factors,resulting in the instability of the intensity amplitude of the output optical signal and the modulation distortion in the long-term measurement,resulting in the drift of the measurement results of the ranging system.In the current phase laser ranging system existing in the above problems,the main research content of this subject is as follows:(1)For the ranging precision of phase laser ranging system for measuring ruler signal frequency and the stability of the requirements,I design the signal source in the precision measuring scale generation unit,which produces double sine wave signals,one for generating measuring ruler used for modulation,another for mixing the vibration signal of phase measurement unit,the frequency difference of these signals is small,and has good frequency stability.The signal source module adopts the combination of PLL and DDS to ensure the frequency stability of the output signals.Its frequency stability can reach 0.4 ppm.Secondly,the shift of the phase value of the ruler signal relative to the phase value of the local oscillator signal of mixer will bring additional ranging error,so the phase difference between the two output signals by the signal source should be stable.The synchronization circuit between multiple DDS modules is designed to suppress the drift of phase difference between the two signals and achieves the stability of phase difference within 0.025~°.(2)In view of the Mach-Zehnder optical modulator transfer function drift on the ranging accuracy and stability,Bias voltage feedback controling module is designed,which samples the modulator output optical signal to get the change of the intensity of the signal amplitude,and controls the bias voltage.The module realizes the automatic setting of appropriate bias voltage with the drift of the transmission function,so that the intensity stability of the modulator output signal is±2%,avoiding the influence on the ranging accuracy and stability.The module uses low-frequency small signals instead of high-frequency signals for detection and analysis.Detection of modulated low-frequency small signals will reduce the difficulty of circuit design and improve the control accuracy.In this paper,the high frequency signal source and bias feedback controling module are applied to the phase laser ranging system based on MZ optical stress system,which can further improve its accuracy and improve its ranging stability.