Turbulence Mitigation Scheme for Optical Communications using Orbital   Angular Momentum Multiplexing Based on Channel Coding and Wavefront   Correction
  The free-space optical (FSO) communication links with orbital angular momentum (OAM) multiplexing have been demonstrated that they can largely enhance the systems' capacity without a corresponding increase in spectral bandwidth, but the performance of the system is unavoidably disturbed by atmospheric turbulence (AT). Different from the existed AT disturbance, the OAM-multiplexed systems will cause both the burst and random errors for a single OAM state carrier and the `crosstalk' interference between the different OAM states carriers. In this paper, we propose a turbulence mitigation method to improve AT tolerance of OAM-multiplexed FSO communication links. In the proposed scheme, we use channel codes to correct the burst and random errors caused by AT for a single OAM state carrier; And we use wavefront correction method to correct the `crosstalk' interference between the different OAM states carriers. The improvements of AT tolerance are discussed by comparing the performance of OAM-multiplexed FSO communication links with or without channel coding or Shark-Hartmann wavefront correction method. The numerical simulation results show that the OAM-multiplexed FSO communication links have enhanced their AT tolerance. The usage of channel codes and wavefront correction methods together has improved greatly the performance of OAM-multiplexed FSO communication links over atmospheric turbulence. 
Shengmei Zhao, Bei Wang, Li Zhou, Longyan Gong, Wenwen Cheng, Yubo   Sheng and Baoyu Zheng
physics.optics