Polarization preservation of partially coherent Hermite-Gaussian beams   for multiple-degrees-of-freedom free-space communication
  Multiple-degrees-of-freedom free-space communication combining polarization and high-order spatial modes promises high-capacity communication channel. While high-order spatial modes have been widely exploited for dense coding and high-dimensional quantum information processing, the properties of polarization preservation of high-order spatial beams propagating in turbulent atmosphere have not been comprehensively investigated yet. Here we focus on the properties of polarization preservation of partially coherent Hermite-Gaussian beams propagating along different atmospheric turbulence paths. The analytical expressions for the polarization of partially coherent Hermite-Gaussian beams propagating through atmospheric turbulence along different paths have been derived. It is shown that the larger the coherence length is, and the larger the beam order m, n are, the less the polarization is changed. We find that the evolution properties of the polarization in slant-down paths through turbulent atmosphere are similar to the case in free space if the condition zenith angle {\xi}<{\pi}/4 is satisfied. While at a long propagation distance, evolution properties of polarization in horizontal paths of turbulent atmosphere differs much from that in free space and in slant paths. The results may allow one to choose the optimal propagation path in terms of specific applications, which is helpful for future experimental implementation of multiple-degrees-of-freedom free-space communication. 
Ling Ji, Ai-Lin Yang, Xiao-Feng Lin, Xian-Min Jin
quant-ph physics.optics