Research On Mean Irradiance Profile Of A Gaussian Beam Under Pointing-tracking Error

With the progress of science and technology,optical communication technology is also in the rapid development of continuous innovation,which will also be used more widely.In the studies of space optical communication,the long-term mean irradiance is very important,because it is essential for calculating the mean receiving power and evaluating the performance free space optical communication(FSO).The classical long-term irradiance profile is considered as the influence of beam wander in the most of researches.However,there exists ponting and tracking error in the space optical communication link,besides the atmospheric beam wander effects,which will cause the speckle center's random motion and inevitably influence the long-term irradiance profile.Due to the closedform expression of the random field statistics equation with optical axis jitter is unavailable,seldom researches discuss this issue.Therefore,it is necessary to study the influence of beam wander and ponting and tracking error on the long-term mean irrdiance profile.Based on the ensemble average principle,this paper proposes an original modeling method,and the closed-form expressions of long-term irradiance profile under random jitter and long-term irradiance profile under tracking error are deduced.And the criterions to predict profile type are also presented.On the basis of the classical phase screen,the multi-layers random phase screens with open-loop pointing error and closed-loop tracking error are established respectively by introducing the ponting and tracking error.The above theoretical model results are compared with the simulation results of the phase screen.Finally,The communication link loss and the influence of ponting and tracking error on the received power are studied based on the closed-form expressions of long-term irradiance profile under pointing error and long-term irradiance profile under tracking error.It is shown that the simulation results of phase screens are in excellent agreement with the results of theoretical model.The long-term mean irradiance profile under tracking error or pointing error can't be simply described as gaussian profile.Because the longterm mean irradiance profile has three forms with increased of pointing error or tracking error,it varied from an approximately Gaussian profile to a flat-topped profile to a hollow profile.The conclusion is verified by phase screens simulation,the criterion is obtained for predicting profile type changes.And for different links,the closed-form expression of mean irradiance under pointing error is different form the closed-form expression of mean irradiance tracking error.Moreover,with different pointing error or tracking error,the loss of the mean irradiance and the mean receiving power are also very different.By comparing the received power under pointing error and which under tracking error,the closed-form expression under the tracking error can indeed achieve the tilt correction,and to some extent,the influence of beam wander on the long-term mean irradiance is restrained.Therefore,the closed-form expressions of mean irradiance profile under pointing error and tracking error are derived in this paper which lays a foundation for improving the analysis and design accuracy for the performance of coarse or fine tracking and communication.