Font Size: a A A

Properties Of Votex Beams In Turbulence

Posted on:2020-01-18Degree:MasterType:Thesis
Country:ChinaCandidate:J ZhouFull Text:PDF
GTID:2428330602952328Subject:Radio Physics
Abstract/Summary:PDF Full Text Request
Since the vortex beam can significantly increase the information capacity of the channel without increasing the spectral bandwidth,and can better alleviate the negative effects of turbulence on the beam transmission,the application of the vortex beam carrying orbital angular momentum?OAM?to the free-space optical?FSO?communication system has received more and more attention and research.In this paper,the received power and crosstalk power of Lommel beams carrying orbital angular momentum in anisotropic non-Kolmogorov atmospheric turbulence,anisotropic sea surface atmospheric turbulence and ocean turbulence are studied,and establishes the Lommel-Gaussian Shell beam model and analyzes the bit error rate and channel capacity of the multiplexed beam.Main research contents:1.In order to clarify orbital angular momentum,the Lommel vortex beam is decomposed into helical harmonic superposition in cylindrical coordinates.Based on the Markov and Rytov approximations theory of optical propagation in atmospheric turbulence,the received power and crosstalk power models of Lommel beams in the anisotropic non-Kolmogorov atmospheric turbulence,the anisotropic sea surface turbulence and the ocean turbulence are derived.The effects of turbulence parameters?turbulence intensity,turbulent internal and external scale,turbulence power index,anisotropy coefficient,etc.?and beam parameters?asymmetry parameters,orbital angular momentum,wavelength,etc.?on the transmission characteristics are analyzed.By comparing the received and crosstalk power of Lommel beam and multiple-Hankel Bessel beam in atmospheric turbulence,it is found that the Lommel beam is better than the multiple-Hankel Bessel?MHB?beam.Compared the Lommel beam and the multi-modified Bessel Gaussian beam when transmitting in ocean turbulence,it is found that the received power of the Lommel beam is also larger than the multi-modified Bessel Gaussian beam?MMBGS?,and the crosstalk power is smaller than the multi-modified Bessel Gaussian beam.2.Since the Lommel beam is better than LG,MHB and MMBGS when transmitting in turbulence,we have established the Lommel-Gaussian Shell beam model to discuss the received power and crosstalk power of Lommel-Gaussian beam and Lommel-Gaussian Shell beam in sea surface atmospheric turbulence.It is found that the greater the anisotropic coefficient of turbulence,the greater the intensity of turbulence?the larger the refractive index structure constant of turbulence?,the smaller the receiving power of the beam,and the larger the crosstalk.And the shorter the wavelength of the beam and the spatial coherence of the source beam will increase the effect of sea surface atmospheric turbulence on the Lommel-Gaussian Shell beam.The larger the receiving aperture,the smaller the received power of the beam and the greater the crosstalk.By comparing the receiving and crosstalk power of Lommel-Gaussian beam and Lommel-Gaussian Shell and Lommel beams in atmospheric turbulence over the sea,the negative effects of Lommel beams on turbulence mitigation are better than those of Lommel-Gaussian beams and Lommel-Gaussian Shell beams under the same turbulence conditions.3.In order to better observe the characteristics of orbital angular momentum multiplexing,we used MATLAB to plot the field strength and phase distribution of the multiplexed Lommel beam.When l1·l2?0,the number of bright spots in the intensity center of the multiplexed beam is ?l1-l 2?.The number of isophase lines in the near field is determined by the path with smaller orbital angular momentum,while in the far field the number of isophase lines is determined by the path with larger orbital angular momentum.However,when l1·l2?0 the number of bright spots in the center of the intensity map is ?l1?+?l 2?,the phase is also divided into ?l1?+?l 2? parts.Secondly,the bit error rate and channel capacity of orbital angular momentum multiplexing system in atmospheric turbulence,atmospheric turbulence over the sea and oceanic turbulence are studied.The results show that the stronger the turbulence intensity is,the greater the value of anisotropy coefficient is,the smaller the bit error rate is,and the faster the channel capacity reaches the saturation value.When beams propagate in oceanic turbulence,the smaller the dissipation rate of temperature difference,the larger the dissipation rate of kinetic energy,the smaller the ratio of temperature-induced to salinity-induced,the lower the BER of beams and the larger the channel capacity.
Keywords/Search Tags:Vortex beam, Orbital angular momentum, Anisotropy, Atmospheric turbulence, Atmospheric turbulence over the sea, Oceanic turbulence, Multiplexing
PDF Full Text Request
Related items