| The transmission capacity is rapidly approaching the basic limit as the utilization of amplitude,wavelength,phase,polarization in the filed of optical waves for optical communication.In order to develop new large capacity communication technology,the orbital angular momentum(OAM)has been widely concerned by researchers in optical communication as a new communication freedom.Communication through orbital angular momentum can greatly improve the communication capacity of the system and effectively solve the capacity crisis.At present,orbital angular momentum has been widely used in storage,optical information transmission,bio-medicine,information coding,photon capture,quantum manipulation and so on.The beam carrying the orbital angular momentum is called vortex beam and the radius of the central bright ring of the traditional vortex beam intensity distribution is directly proportional to its topological charge number.Therefore,the interference between the beams of different modes caused by different radii can make the serious loss of communication quality when the vortex beams with different topological charges are coupled or multiplexed.The appearance of perfect optical vortex beam(POV)solves the interference problem of traditional vortex beam multiplexing,which makes it become an extremely important research hotspot in the field of vortex beam in recent years.Compared with the traditional vortex beam,the perfect vortex beam has the advantage that the beam radius and ring width are completely controllable.However,as a new type of special vortex beam,the turbulence characteristics of perfect vortex beam have not been known by the public,so it can not be further applied in optical communication.Based on the above problems,in this thesis,the generation and control technology of POV beams which can stabilize the radius and width is studied by analyzing the theory of vortex beams and perfect vortex beams.At the same time,on the basis of achieving stable control to generate POV beam,the transmission characteristics of the POV beam in atmospheric turbulence are studied by analyzing the theory of atmospheric turbulence,constructing a random phase screen of atmospheric turbulence and building an atmospheric turbulence transmission link based on the POV beam.Finally,a turbulent distortion detection scheme for the POV beam is designed,which is used to reveal the unique beam-holding characteristics of the POV beam in atmospheric turbulence.The main work is as follows:(1)Research on the generation and control technology of perfect vortex beam.Firstly,the spatial light field characteristics of the vortex beam are analyzed in detail by studying the theory of vortex beam and orbital angular momentum.Then,the light field distributions of LG beams and BS were obtained by simulation,so that the light intensity and phase characteristics of these two beams in free space were studied.Finally,the principle ofgenerating perfect vortex beam is analyzed by studying the source of the definition of the POV beam.Comparing the experimental results,the factors affecting the distribution radius and ring width of the light field are gradually determined,and the radius and ring width of the perfect vortex beam are adjusted.(2)Research on propagation characteristics of POV beam in atmospheric turbulence.Depending on the theory of Kolmogorov turbulence spectrum,the random phase screen of atmospheric turbulence is designed by power spectrum inversion method and sub-harmonic method,which achieves the simulation of atmospheric turbulence.With the help of Fresnel diffraction theory,an atmospheric turbulence transmission link based on a POV beam is designed.The corresponding relationship between the POV beam and atmospheric turbulence is obtained by analyzing the light field distribution structure after the atmospheric turbulence transmission of the POV beam under various conditions.The transmission characteristics of the POV beam in atmospheric turbulence were successfully revealed by comparing and analyzing the simulation and experimental results.The transmission characteristics are as follows: without the influence of the turbulence intensity,transmission distance and topological charge number,the turbulence transmission result of the POV beam is closely related to the radius and ring width before it is generated,and these two effects are independent of each other.(3)Research on beam-holding characteristics of POV beam propagating in atmospheric turbulence.The atmospheric turbulence beam-preserving characteristics of the perfect vortex beam are revealed by analyzing the properties exhibited by the POV beam as it propagates through atmospheric turbulence.A turbulent distortion detection scheme which is suitable for POV beam based on Matlab is designed to evaluate the extent of turbulence effects of the beam.The beam-holding characteristics of a POV beam propagating in atmospheric turbulence are studied by contrasting and analyzing the difference of the distortion with different modes of beams in turbulent.A POV beam communication simulation based on QPSK modulation is realized by combing with QPSK modulation.Through numerical simulation and experimental test comparison and verification,we found that after being transmitted by atmospheric turbulence,the beam can maintain the same circular light field distribution when its radii and width are modulated to some specific values.In addition,among the mode beams that already have the ability to maintain a circular distribution,the affect on some modes by distortion are less than others. |
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