Generation And Transmission Characteristics Of Vortex Beams

The vortex beam is a special beam with a helical phase factore^il??l is the topological charge,also known as the orbital angular momentum of the number of quantum,?is the azimuth?.Due to the phase singularity causes its light intensity shows a dark and hollow ring distribution.It has the advantages of better confidentiality,larger transmission capacity,higher efficiency and easier coding compared with the ordinary Gaussian beam.It is precisely because of the above characteristics makes the vortex beam widely used in optical communications,biomedical,optical manipulation,nonlinear optics,optical tweezers and other fields.The mainly aspects of this paper are as followed:1.The basic characteristics of the vortex beam are studied and several methods of generating the vortex beam are analyzed.The intensity and phase distributions of two kinds of Laguerre-Gaussian beams and high-order Bessel beams are numerically simulated.The changes in the phase of the transmission process,by comparing the above results to draw the relevant conclusions.2.In this paper,the transmission characteristics of two kinds of vortex beams of LGB and high order BGB in free space are analyzed numerically.The results show that with the increase of transmission distance,the high-order BGB anti-beam expansion ability is stronger and LGB expansion is more serious.Based on the generalized Huygens-Fresnel principle,the power spectrum inversion method is used to simulate and analyze the transmission process of two vortex beams in atmospheric turbulence.The low frequency compensation method is used to simulate the random phase Atmospheric turbulence,which solves the problem of low frequency components in simulation.The results show that the turbulence is stronger under the same conditions,the annular light intensity of the different types of vortex beams is weaker and the phase distortion is more serious,the more obvious the fluctuation of light intensity will gradually degrade into the ordinary Gaussian beam;The intensity of the two vortex beams is weakened and the attenuation is more serious,and there is a tendency to gradually degrade to the ordinary Gaussian beam.The greater the topological charge of the vortex beam,the stronger the anti-degradation ability of the ordinary Gaussian beam,but the phase distortion More serious;under the same conditions,the longer the vortex beam in the transmission process has a strong ability to suppress turbulence.Compared with LGB,BGB has good beam quality under weak turbulence and short distance,but with the increase of turbulence intensity,especially when strong turbulence conditions and transmission distance are far away,BGB light intensity is seriously attenuated,dark hollow radius No,phase distortion is more serious.In conclusion,the transmission quality and the factors of the vortex beam in the free space optical communication system include the topological load,the laser wavelength and the external factors including the turbulence intensity and the transmission distance.3.Based on the principle of atmospheric laser communication system,the error rate formula of atmospheric laser communication system is deduced.In this paper,the error rate formula of the system based on OOK modulation under the condition of horizontal and skew transport is deduced by the light intensity flicker theory of plane wave.The numerical analysis shows that the longer the wavelength is,the shorter the transmission distance,the smaller the turbulence the larger the angle,the smaller the bit error rate of the system.Based on the principle of light intensity fluctuation,the bit error rate of atmospheric laser communication system based on vortex beam transmission is analyzed by using the scintillation index of Laguerre-Gaussian vortex beam.The results show that the vortex beam has a relatively lower bit error rate compared with the atmospheric laser communication system based on plane wave.The longer the transmission distance is,the higher the bit error rate is,and the saturation ratio is.The lower.When the number of topological increases to a certain extent,the system error rate tends to be stable.4.In the experiment,we first use the MATLAB software to generate the phase map needed by the experiment.Then we use the laboratory optical platform to carry the optical path of the vortex beam,and simulate the light intensity distribution of LGB and high order BGB.Finally,two vortex beams are generated.