Dispersion Of Orbital Angular Momentum Spectrum Of Partially Coherent Vortex Beam Propagating In Turbulent Atmosphere

Compared with conventional optical communication systems,communication systems based on orbital angular momentum modes significantly expand the channel capacity of wireless optical communication systems.However,atmospheric turbulence causes intensity fluctuations,beam wander,beam expansion,etc.,resulting in degradation of the performance of the wireless optical communication system.In addition,since the partially coherent beam can effectively mitigate the influence of atmospheric turbulence,it is a meaningful subject to study the interaction law between the partially coherent beams carrying orbital angular momentum modes and the atmospheric turbulence,and improve the transmission performance of the optical communication system signal.Based on the Huygens-Fresnel principle,this paper explores the orbital angular momentum of two partially coherent beams(multi-Gaussain-Schell Bessel beam and partially coherent Lommel beam with conventional Gaussian-Schell-model correction function)propagating in non-Kolmogorov turbulent atmosphere.The numerical results show that the cross-spectral density distribution of the multi-Gaussian-Schell Bessel beam is closely related to the initial beam parameters.The effects of diffraction during free space and atmospheric turbulence correlates to a tendency that energy of the beam migrates to the right.The spiral spectrum distribution,mode probability density and crosstalk probability density of partially coherent Lommel beams are also studied in this paper.During propagating in non-Kolmogorov turbulent atmosphere,the probability density of partially coherent Lommel beam decreases rapidly,and the crosstalk probability density increases rapidly.As the propagation distance increases,crosstalk gradually spreads from the adjacent mode to the peripheral mode.The partially coherent Lommel beam with longer wavelength and smaller asymmetric parameter is more concentrated and less susceptible to turbulent atmosphere.For these two partially coherent beams,a certain increase in the spatial coherence length means that the mode intensity of the partially coherent beam is more concentrated in the beam center,which can alleviate the effect caused by atmospheric turbulence.However,this applies only in weak turbulence or moderate-intensity turbulence.The above research results have potential application value in the field of beam shaping and optical communication.