Research On The Transmission Properties Of Fractional And Petal Orbital Angular Momentum States

Free-space optical(FSO)communication employing orbital angular momentum(OAM)multiplexing can tremendously improve the transmission rate of system without an extra spectrum bandwidth.However,when the beam carrying OAM is transmitted through free space and underwater environment,it is inevitable to be disturbed by atmospheric turbulence and underwater turbulence.With the maturity of the research on integer OAM mode,the attention on the propagation of fractional OAM mode and the petal OAM mode is attracted.We do study on the propagation property of fraction OAM and petal OAM mode through free-space and underwater environment in the thesis.The main results are as follows:(1)Firstly,considering at the problem of topological charge limitation in practical optical experimental scenes,we research the transmission performance of fractional orbital angular momentum in free space and underwater environment.The topological value of the fractional orbital angular momentum can be any value,and is no longer limited to integer values.The OAM topological charge value with an interval of not integer is used as the information transmission carrier,so that the channel capacity can be effectively increased under the condition of limited topological charge.The simulation results under the environment of atmospheric turbulence show that the fractional orbital momentum states with intervals not equal to integers can be multiplexed and transmitted.The closer the interval topological value is to an integer,the smaller the interference between channel.And the interval topology value is 0.2,the crosstalk is already large,but it can effectively increase the number of multiplexing channels.The results of underwater experiments show that under the condition of topological charge value limitation(0<l<5),the topological charge value(interval topological charge value of 0.95,0.9)satisfying a certain interval can effectively increase the channel capacity,by compared with integer multiplexing communication system,the channel capacity increase by more than 50%.(2)Secondly,considering the crosstalk problem caused by the disturbance caused by atmospheric turbulence and underwater turbulence,we research the transmission performance of petal orbital angular momentum in free space and underwater environment.Because the characteristics of the beam energy of the petal orbital angular momentum are more concentrated,the different petal patterns are used to transmit against the turbulence caused by atmospheric turbulence and underwater turbulence.The simulation results of atmospheric turbulence show that the orbital angular momentum of petal can effectively resist the influence of atmospheric turbulence compared with the orbital angular momentum of single mode.The structural similarity of petal orbital angular momentum can be more than doubled compared with the single mode.When the generated topological load value is satisfied,the anti-interference performance of the petal is significantly improved,and the more the number of petals of the petal,the stronger the ability to resist turbulence.The results of underwater experiments show that it can be seen that the confidence of the petals is more than doubled compared with the single mode,and the higher the number of petals,the higher the confidence of the image,the easier to be recognized by using Baidu artificial intelligence open platform.