Orbital Angular Momentum Multiplexing And Crosstalk Analysis Under Atmospheric Turbulence

With,the rapid development of the inforamation industry,the previous modulation and multiplexing technologies have been unable to meet the future largewcapacity,high-speed communications requorements.In order to furtlier meet the requirements for communication chainel capacity and spectrum utilization,it has been proposed to use the vortex beam with orbital angular momentum(OAM)for multiplexing communication.Since the nature of OAM is a spatial distribution function,a multiplexing communication based on OAM beams is inevitably affected by atmospheric turbulence.In this paper,we study the OAM beams and its transmission in atmospheric turbulence.The main works are as follows:1.The multiplexing characteristic of OAM beans are investigated.Taking two OAM beams as an example,the intensity and phase distribution characteristies of OAM multiplexing beams under different topological charges are bnvestigated,the simulation results are verified by expeuments.2.Influence of atmospheric turbulence on the intensity and phase of OAM nmultiplexing beams was investigated.Based on the Von Karman spectral model,the effects of different transmission conditions on the intensity and phase distribution of OAM multiplexing beams are investigeated.The simulation results are verified by experiments.3.Numerical analysis the crosstalk of OAM multiplexing beams under atmospheric turbulence.Spiral spectrum is used to quantitatively analyze the degree of dispersion between the beams of the OAM multiplexing beams under different transxission conditions.Considering the mixed noise under the actual attospletic channel,the change of the system BER under diflferent turbulence intensity is investigated.The results show:the number of intensity spots and phase lines of the positive number OAM multiplexing beams is determined by the beams with the largest number of topological charge in the multiplexing beams,The number of intensity spots and phase lines of the different number OAM multiplexing beams is determined by the sum of the topological charges of the multiplexing beams,the intensity distribution of OAM multiplexing beams in different multiplexing modes is regularly distributed,and the pattern of OAM multiplexing beams can be detected according to the obtained rules;The higher the turbulence intensity and the longer the transmission distance,the more obvious the intensity scintillation of the OAM multiplexing beam is,and the more serious the phase lines distortion of the multiplexing phase is,in strong turbulence and long-distance transmission conditions,the flare and phase distortion of the OAM multiplexed beam spot are more serious,which will directly lead to a decline in the communication quality of the optical communication system or even the interruption of communication;The degree of dispersion between OAM multiplexing beams increases with the increase of turbulence intensity,and strong turbulence leads to distortion of OAM multiplexing beams;Under the same turbulence intensity and the same transmission distance,the larger the topological charges of OAM beams,the greater the BER.At the same turbulence intensity,the BER of OAM multiplexing beams increases with the increase of transmission distance.