| Vortex beams are known to carry certain amount of orbital angular momentum by their special spiral phase structure.These characteristics make them widely used in information transmission,biological medicine,optical micro manipulation and in particular,in the field of free space optical communication which has more potential applications.Investigations on the transmission characteristics of vortex beam propagating in atmospheric turbulence is one of the most interesting topics about free space communication.Atmospheric turbulence has serious influence on vortex beam propagating in it,which can cause scintillation,beam drift and beam spreading.Toward these problems,we establish simulations mimicing the atmospheric channel as random phase screens based on the turbulence theory of Kolmogorov.Two methods of experimental simulations are explored.Using spatial light modulators,the light path of simulation experiment is designed to simulate the transmission of vortex beam.Gaussian vortex beam and Laguerre-Gaussian vortex beam were used as prototype fields to study the effects of turbulence strength and transmission distance on their propagation.Experimental results show obvious effect of turbulence strength through the changes of scintillation and beam drift.The larger the intensity of turbulence,the stronger the scintillation and beam drift.The transmission distance also affects the beam scintillation and drift.They increase with the propagation distance.The atmospheric turbulence will affect the polarization distribution of the vortex beam.The study also found that the number of topological charges has an influence on the transmission of vortex beam in turbulence.When the topological charge is larger,the beam transmission becomes more stable.Through our experiments,some theoretical analysis of the beam fturbulence effect were verified.Our study may have great significance and find potential applications in e.g.,optical communication,laser guidance,and laser radar. |
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