| Atmospheric laser communication is based on the atmosphere as the transmission medium,the laser beam as the carrier.Comparing to the traditional communications,atmospheric laser communication has a lot of advantages,such as potential large data capacity,high-rate transfer rate,small volume,high security,high bandwidth,high ability of resistant to electromagnetic interference,and low power requirements.Atmospheric laser communication technology has broad application prospects in the fields of aerospace,military communications,deep space communications,satellite communications and other fields for its advantages,and also becomes one of the most concerned research.However,due to the presence of atmospheric turbulence,it will generate a wave front distortion and amplitude fluctuation when laser beam propagating through atmospheric turbulence.It can cause spatial intensity fluctuations,angle of arrival fluctuations,beam wandering,beam spreading and spatial coherence reducing,which can affect the quality of the transmission beam,increase the bit error rate and reduce the communication system performance.A laser beam with orbital angular momentum(OAM)is a vortex beam whose shape is determined by its topological charge,and the laser beam with different topological charges can be multiplexed.Because of the number of topological charge can achieve the infinite and the electromagnetic vortex wireless transmission technology can provide infinite channel number in theory.Therefore,it can greatly improve the communication transmission capacity,which makes vortex beams drawn considerable attention.In this paper,atmospheric laser communication has been studied in details,and the domestic and foreign research status is summarized.The research content of this paper is as follows:Firstly,the atmospheric turbulence model is determined as Kolmogorov turbulence and be described by statistical description.This model hypothesizes that the small-scale structure of turbulence is statistically homogeneous,isotropic,and independent of the large-scale structure.Then,the theory of laser beam propagation in random media is described,according to Born approximation theory and Rytov approximation theory.Secondly,the physical basis of the orbital angular momentum of optical field and the vortex beams are illustrated.Some methods for generating vortex beams and measuring orbital angular momentum are listed.Thirdly,the key research of this paper is the beam wander of random electromagnetic Gaussian-Shell model vortex beam and partially coherent Laguerre-Gaussian-Shell model beam propagating through a Kolmogorov turbulence.The result shows that the beam with larger topological charge,smaller coherent length,smaller wavelength,larger transverse beam width,larger degree of polarization,and weaker turbulence has less beam wander. |
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