Research On High Precision Pointing Technology For Spaceborne Optical Communication Applications

Space optical communication has significant advantages such as high bandwidth.And it has great application potential in the field of satellite communication.However,the divergence angle of the laser used in space optical communication is much smaller than that of the microwave.The smaller divergence angle requires the communication terminal to perform high-precision pointing.When the beam pointing error exists,the optical power received by the receiver will decrease sharply,and the bit error rate will be severely degraded.Therefore,the beam pointing accuracy of the space optical communication system should generally reach the microradian level.This paper studies the high-precision pointing technology for spaceborne optical communication,focusing on the effects of satellite platform vibration,and its compensation for finer beam pointing.Firstly,based on the Olympus satellite platform vibration model,the harmony superposition method is used to generate the time series in order to simulate effect of satellite platform vibration.The generated time series is used as disturbance signal,and feedforward LMS algorithm,feedforward NLMS algorithm,and feedforward RLS algorithm are used to compensate the disturbance.Simulation results show that all three methods have compensation effects.The root mean square values after compensation are 0.69?rad,0.27?rad,and 2.58?rad respectively.The feedforward NLMS algorithm has the best compensation effect,and the feedforward RLS algorithm has the worst compensation effect.Secondly,the distribution of the light spot,working mode of QD,and their impact on the measurement sensitivity and detection range are studied for the four-quadrant detector(QD).The simulation results show that the measurement sensitivity at the center of the QD is the highest.Generally,the value of the spot radius ranges from d/2 < w < D/2,where d is the gap width and D is the diameter of QD.According to the simulation results of the Gaussian distribution of the cross mode,the curve fitting expressions of E?x and x?0 are obtained.Result shows the smaller the Gaussian beam waist radius,the larger the measurement error in the same measurement range.Finally,a satellite platform vibration simulation system is set up in the laboratory.The generated time series is used as disturbance signal,and PID algorithm is used to compensate it.The root mean square value is reduced from 14.67 ?rad to 1.78 ?rad,and the peak-to-peak value is reduced from 93.51 ?rad to 27.65 ?rad.It can be seen that the PID algorithm has good compensation effect on the disturbance signal.