| The vortex beam is a beam that carrying Orbital Angular Momentum(OAM).Its intensity distribution presents as a hollow ring,phase distribution a special spiral.Due to OAM has theoretically infinite dimensions,and the vortex beams carrying different OAM modes have mutually orthogonal characteristics.Therefore,multiple vortex beams are superimposed and multiplexed as a carrier for information transmission for wireless optical communication systems.The usage of this beam can greatly improve the communication capacity and spectrum efficiency.However,when the vortex beam transmits in free space,it will be affected by atmospheric turbulence,which will cause phase distortion,light flicker,and beam expansion.These will further jeopardize the reliability of information transmission.Based on this background,this paper deeply studies the feasibility of wavefront sensorless correction technology based on phase diversity(PD)algorithm for vortex beam distortion wavefront correction and compensation.The main work of this thesis is as follows:1.Research on wavefront distortion of vortex beam in atmospheric turbulence.according to the basic theory of vortex beam and kolmogorov spectrum model,the intensity and phase distribution of Laguerre-Gaussian beam are simulated,the advantages and disadvantages of several commonly used simulation methods of atmospheric turbulence phase screen are compared and analyzed in detail.Based on the multi-phase screen model,the wavefront distortion and orbit angular momentum crosstalk of Laguerre Gaussian beam after atmospheric turbulence are analyzed.2.Simulation study of vortex beam correction compensation based on PD algorithm wavefront sensorless correction technology.According to the solution model of the classic Adaptive Optics(AO)correction system,the PD algorithm is adopted as the wavefront sensorless technology to study the correction and compensation effect of the distorted vortex beam.3.Experimental study of the PD correction and compensation of distorted vortex beams An experiment platform of the overall model is built based on the designed PD adaptive optical correction technology.The feasibility of the PD algorithm to correct the distortion and vortex beam is verified through a great quantity of experiments.The results show that the adaptive correction system wavefront sensorless based on PD algorithm can effectively correct the wavefront distortion of the vortex beam.In addition,the relative power of the single and superimposed vortex beams can be improved to about 0.85 and 0.8.Meanwhile,the crosstalk between modes is reduced,the convergence speed is improved The correction effect of the vortex beam increases with the reduction of the topological load The experimental and simulation results are in good consistency. |
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