Construction Of Multi-Gaussian Correlated Twisted Beams And Orbital Angular Momentum Transmission Characteristics

In recent years,orbital angular momentum(OAM)beam has been widely used in optical communication and particle capture due to its unique properties.In the field of optical communication,studies have shown that OAM has infinite orthogonal modes,which can make the transmitted information multiplexed,thus improving the channel capacity and communication rate of the communication system.The partially coherent beam carrying twisted phase has OAM,which shows promising applications in both fiber optic communication and atmospheric optical communication.In the field of fiber optic communication,gradient index(GRIN)fibers also have extraordinary application prospects in optical imaging and advanced manufacturing.In the field of atmospheric optical communication,the laser will be affected by atmospheric turbulence during transmission,which will lead to random fluctuations in the refractive index of the atmosphere,causing a series of negative effects such as beam expansion and drift,which seriously affects the further application of lasers in atmospheric optical communication.The partially coherent twisted beam can well suppress such negative effects.Therefore,it is of great significance to investigate the transmission of partially coherent twisted beams carrying OAM in gradient refractive index fibers and atmospheric turbulence.The specific research work in this paper is as follows.Based on the partial coherent mode expansion theory and the non-negative deterministic condition of the cross-spectral density function,it is demonstrated that the multi-Gaussian Schell mode correlation structure can carry the twisted phase,and the multi-Gaussian correlation twisted beam is obtained,and its transmission through the GRIN fiber is investigated.The results show that the intensity,coherence,orbital angular momentum flux density,and normalized orbital angular momentum flux density distribution of the beam in the GRIN fiber all show a period L variation;the intensity of the beam shows a flat-top distribution at the focal plane;due to the presence of the twisted phase,the intensity,coherence,orbital angular momentum flux density,and normalized orbital angular momentum flux density distribution all rotate during the transmission process,and the rotation The angle is limited at the focal plane to π/2.By changing the parameters such as modulus,twist factor,the orbital angular momentum appears to have different magnitudes and distributions.The evolutionary properties of the intensity and orbital angular momentum of a multi-Gaussian correlated twisted beam passing through non-Kolmogorov anisotropic atmospheric turbulence are investigated.The results show that the light intensity distribution rotates with increasing transmission distance as the beam is transmitted in anisotropic turbulence.When transmitted to the far-field,the anisotropy of the turbulence causes anisotropic distribution of the intensity in the horizontal and vertical directions.Increasing the twist factor and multi-Gaussian modulus can suppress the diffraction effect caused by anisotropic turbulence to some extent.During atmospheric turbulent transport,the total orbital angular momentum of the beam is conserved,but the magnitude of the orbital angular momentum can be influenced by the modulation of the twist phase.The propagation of array multi-Gaussian correlated beams in non-Kolmogorov anisotropic turbulence is simulated,and the evolution of their light intensity and orbital angular momentum characteristics in turbulence is analyzed.The results show that the orbital angular momentum flux density of the beam presents a circular distribution with a central singularity on the source plane.Transmission in turbulent flow,the beam at the same time with the rotation of the twisted beam features with the features of array beam from the division and short in turbulent transport are well kept,when the transmission distance is far away,the anisotropy of turbulence will destroy the beam array distribution,cumulative effect and increase the distortion factor can inhibit the anisotropy of turbulence to some extent.The magnitude and distribution of orbital angular momentum can be influenced by adjusting the twisted phase and correlation structure.