Abstract
The transmission of the orbital angular momentum (OAM) beam has attracted a lot of attention in the field of free-space optical (FSO) communication. Usually, after transmitting in atmospheric turbulences, the helical phase-front of OAM beams will be severely distorted, and there will exist the intermode crosstalk. As a result, the performance of the communication system will degrade significantly. In this paper, we have investigated the influences of the level of the turbulence strength to the transmitting OAM beams by changing the refractive-index structural parameter of C n 2 and the number of turbulence random phase screens of N in simulation environment. Then, by adopting the Gerchberg-Saxton (GS) algorithm, which can be used to compute the pre-compensation phase and correct the distorted OAM beams, the retrieving performances of transmitting single and multiplexed OAM beams under different turbulence strengths were also investigated. The simulation results show that with increasing the atmospheric-turbulence strength levels determined by the parameters C n 2 and N, the retrieving performances decrease dramatically. When the turbulence strength level is selected within an appropriate range, the OAM beams can be effectively retrieved by adopting GS algorithm and observing the power density spectrum. Notably, the retrieving performance for the transmission of a single OAM beam is better than that of the multiplexing OAM beam.
Highlights
In 1992, Allen et al demonstrated that the Laguerre-Gaussian (LG) beam with helical wave-front carries the orbital angular momentum (OAM) [1]
OAM modes modes after after transmitting in the different turbulences with the aids of algorithm, which are described by transmitting in the different turbulences with the aids of GS algorithm, which are described by the the power density (PD) defined as the ratio of the obtained target OAM mode power on the original incident OAM mode power
We explore the effect of turbulent channel with a different refractive index structure parameter C2n and phase screen number N on the transmitted single OAM beam
Summary
In 1992, Allen et al demonstrated that the Laguerre-Gaussian (LG) beam with helical wave-front carries the orbital angular momentum (OAM) [1]. It was shown that the LG beam with helical phase term of exp(ilφ), have an OAM of l} per photon, where φ is the azimuthal angle, is the Planck’s constant divided by 2π, and l is the azimuthal index called topological charge which represents the OAM mode. A key property of the OAM beams is that beams with different topological charges are mutually orthogonal. OAM has been widely applied to many other fields, such as optical tweezers [12,13], quantum information processing [14,15,16], super high-density data storage [17], and so on. For a practical OAM-based FSO communication link, atmospheric turbulence is a serious challenge, which distorts both intensity and phase of the received light field, because it will introduce intermode
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