The Aberration Of Oam Beams In Atmosphere Turbulence And Compensation Methods Research

Orbital angular momenment beam,also called the OAM(Orbital Angular Momenment)beam,has a unique annular light intensity distribution and a unique spiral phase wavefront due to it brings orbital angular momentum characteristics.In recent years,OAM beams have attracted many scholars because of their potential to increase the transmission capacity and spectral efficiency of communication systems.However,for the free space optical(FSO)communication link based on OAM beam,a key problem need to be overcomed in long-distance transmission information is that atmospheric turbulence will distort the helical phase wavefront of the OAM beam,lead to generate channel crosstalk at the receiver,reduce receive power and reduces communication performance.Based on this background,the influence of aberrations of OAM beam is studied first,then the transmission characteristics of OAM beam are simulated and analyzed under weak,medium and strong atmospheric turbulence conditions.Finally,the OAM optical wavefront distortion caused by atmospheric turbulence is analyzed,using optical adaptive compensation technology to compensate.The main work of this paper is as follows:(1)In this paper,the basic study of primary aberrations is first performed.In order to compare the effects of aberrations with Gaussian beams,the effect of five classical primary aberrations on a Gaussian beam is first simulated,and then the Gaussian beam is replaced with an OAM beam,analysising the effects of the five aberrations on the OAM beam.Finally,the coma and astigmatism that had a significant effect on the OAM beam were singled out for further detailed analysis.(2)To verify the compensation effect of the adaptive compensation scheme,the OAM beam must first pass through atmospheric turbulent transmission.Therefore,based on Kolmogorov's theory of atmospheric turbulence and its statistical properties,Zernike polynomial was used to establish a random phasing screen for atmospheric turbulence.The propagation characteristics of OAM beam in a horizontal atmosphere were simulated based on the multi-phase screen method.Finally,introducing a spiral spectrum to evaluate the OAM beam mode purity.(3)The two-dimensional multiplexing of the OAM beam with the topological charge of +1~+5 mode is simulated,and it is found that the multiplexed intensity “sidelobe” satisfies: “sidelobe” number = topological charge difference.(4)A self-adaptive compensation scheme based on pre-compensation method and GS phase recovery algorithm is designed,Zernike polynomial was used to establish a random phasing screen of atmospheric turbulence,and simulation analysis of single mode and double OAM multiplexing mode is performed during atmospheric transmission.The results show that this method improves the purity of the receiver mode.