| Satellite optical communication is the key technologies to realize the integration of high-efficiency real-time network in the future,which has been received a range of concerns in the world due to the advantages of large transmission capacity.The rapid establishment and stable maintenance of the laser link are the core technologies in the process of satellite laser communication and networking,and the stable maintenance is mainly achieved by beam tracking.In order to improve tracking stability of the satellite laser link,the existing satellite optical communication systems have carried out a large number of simulation and equivalent verification tests on the ground,however the current performance metrics in the on-orbit are not ideal due to the limited analysis methods,onorbit equivalence and other factors.The main processes of rapid establishment and stable maintenance of the laser link are as follows,the two terminals of satellite laser link should aim and capture each other,and then realize the laser links built in a rapid speed through the closed-loop of photoelectric.On this basis,the terminal aiming devices complete the tracking of the beam and finally ahieve stable maintenance of the link.According to the reports in the literaturess,the rapid establishment time of satellite laser link is generally between 3 and 70 s.However,in terms of laser link tracking stability,the effective data transmission time in the foreign reports only accounts for less tan 80% of the available link time,which cannot meet the requirement of effective transmission data.At present,the analyses of the tracking stability for the satellite laser link are mainly focusing on the beam near-field characteristics.Since the far-field dynamic sence is not considered in the theorical mode and the equivalence of ground experiments is poor,therefore it is difficult to effectively optimize the tracking strategy on the ground,resulting in low tracking stability of the laser link in orbit.Meanwhile,according the investigation on the existing satellite laser links tracking stability,there are also problems such as the low degree of system link tracking stability evaluation and the lack of large-system comprehensive optimization analysis methods.In view of the above technical development requirements,this dissertation is concerned with the research on the theoretical modeling of beam far-field dynamic characteristics,quantitativeanalysis of link tracking stability and ground-based equivalent verification optimization of link large systems.The specific work includes the following aspects:Firstly,considering the actual working state of the satellite optical communication system in orbit,the theoretical analysis model of beacon beam far-field dynamic characteristics for the inter-satellite laser link is established,especially for the influence of tracking angle deviation and beam wave phase difference on the beam far-field dynamic characteristics.Based on the inter-satellite laser link,for the satellite-to-ground laser link,the influence conditions of atmospheric turbulence disturbance are added,and the far-field dynamic characteristic analysis model of the satellite-to-ground beacon is established.The focus is on beam drift,beam expansion and arrival angle fluctuation.The impact of field dynamics,especially for considering the influence of the space transmission medium,the impact of the beam drift,beam spread and arrival angle fluctuation on beam far-field dynamic characteristics.Secondly,in order to the quantitative analysis of tracking stability,the tracking correlation equation of the far-field dynamic characteristics on the link tracking stability is established.The beam-field far-field dynamic characteristic correlation factor variance is proposed to provide a quantitative analysis method for the evaluation and estimation of the link tracking stability comprehensive performance.The influence model of beam divergence angle,wave aberration distortion degree,detector accuracy and atmospheric turbulence disturbance on the laser link beacon far-field dynamic characteristic correlation factor variance is established.Under the requirement of link tracking accuracy,link tracking stability is proposed to provide an effective solution for improving the tracking stability of the laser link.Thirdly,a ground equivalence analysis method of the influence of the satellite link beacon beams far-field dynamic characteristics on link tracking stability is proposed to solve the problems of the parameter optimization design of tracking optoelectronic large system.In order to compensate the influence of the beam far-field dynamic characteristics,a regenerative time-domain equalization compensation algorithm is proposed.In order to improve the dynamic coupling efficiency of single-mode fiber in the tracking process,an optimization analysis method for the coupling efficiency of the fiber on beam far-field dynamic characteristics is proposed,which provides a technical method for improving the comprehensive communication performance of the large system.Finally,the experimental verification work was performerd based on the above theories and methods.Through the ground equivalent and semi-physical simulation,the influence of the beam far-field dynamic characteristics is carried out,and the proposed optimization method o tracking stabilityis verified.By combining with he tracking correlation equation,link tracking stability optimization algorithm and regenerative time domain equalization compensation algorithm,the evaluation,estimation and optimization of typical laser link tracking stability have been completed.t.The ground equivalent simulation test and the on-orbit test comparison results show that the proposed optimization method in this paper can effectively improve the overall performance of the satellite laser tracking link.The research results in this paper can provide a new theoretical and technical analysis method for laser link tracking stability optimization design and effectively improve the operational stability of satellite optical communication link in large closed-loop tracking system.It is great significance to the application of future satellite optical communication network and the space-ground integrated information network. |
PDF Full Text Request