Analysis of orbital angular momentum spectra of Hankel-Bessel beams in channels with oceanic turbulence
Analysis of orbital angular momentum spectra of Hankel-Bessel beams in channels with oceanic turbulence
复制标题
海洋湍流通道中汉克尔-贝塞尔光束的轨道角动量谱分析
DOI：
10.7498/aps.67.20180155
复制
发表时间：
2018-06
影响因子：
1
通讯作者：
Guo-hua Wu
中科院分区：
文献类型：
--
作者：
Yin Xiao-Li;Guo Yi-Lin;Yan Hao;Cui Xiao-Zhou;Tian Qing-Hua;Chang Huan;Guo-hua Wu
具有不同模式数（l）的轨道角动量（OAM）的光束彼此正交，这使得在OAM复用水下光通信（UOC）系统中增大信道容量成为可能。然而，这一战略的实施受到海洋湍流的限制。携带OAM的Hankel-Bessel（HB）涡旋光束由于其在不改变强度分布的情况下传输的能力（非衍射性质）和在遇到障碍物后的显著重构能力（自修复机制）而相对较少地受大气湍流的影响。因此，HB涡旋光束可以作为提高信息传输信道容量的载体。本文基于Rytov近似理论，推导了弱水平海洋湍流信道下HB涡旋光束的OAM谱的解析表达式。通过数值计算研究了海洋湍流参数对HB涡旋光束OAM谱的影响。结果表明，海洋湍流导致传输OAM模式的检测概率下降，OAM谱变宽。海洋湍流中的空间相干长度随着传输距离的增大、均方温度耗散率的增大以及湍流动能耗散率的减小而减小，从而导致了HB涡旋光束透射OAM模式的探测概率下降。另一方面，具有较大OAM模式数的光束在湍流中传输后具有较宽的光束扩展，这导致HB涡旋光束的透射OAM模式的检测概率降低。盐度涨落对HB涡束的影响大于温度涨落，说明盐度涨落比温度涨落更能决定海洋湍流的影响。此外，在弱湍流和几十米距离下，HB涡旋光束的传输性能比最佳束腰的拉盖尔-高斯涡旋光束的传输性能差。这些结果为海洋环境下光通信链路的实现提供了参考。
Beams with different-mode-number (l) orbital angular momenta (OAMs) are mutually orthogonal to each other, which makes it possible to enlarge the channel capacity in an OAM multiplexed underwater optical communication (UOC) system. Nevertheless, the implementation of this strategy is limited by oceanic turbulence. Hankel-Bessel (HB) vortex beams carrying OAM are relatively less affected by atmospheric turbulence due to their ability to propagate without changing the intensity profile (non-diffraction nature) and remarkable ability to be reconstructed after encountering an obstacle (self-healing mechanism). Consequently, HB vortex beams can be used as the carriers to increase the channel capacity of information transmission. In this paper, based on the Rytov approximation theory, the analytical expressions of OAM spectra for HB vortex beams under weak horizontal oceanic turbulent channels are derived. The influences of oceanic turbulence parameters on the OAM spectra of HB vortex beams are investigated via numerical calculations. The results indicate that oceanic turbulence leads to the decline of detection probability of transmitted OAM mode and the broadening of OAM spectra as well. Similarly, the spatial coherence length in oceanic turbulence decreases with increasing propagation distance and the dissipation rate of mean-squared temperature and with decreasing the dissipation rate of turbulent kinetic energy, which lead to the decline of detection probability of transmitted OAM mode for HB vortex beams. On the other hand, beams with larger OAM mode numbers each have a wider beam spreading after propagating in the turbulence, which results in the decrease of the detection probability for transmitted OAM modes of HB vortex beams. And the HB vortex beams are more affected by salinity fluctuation than by temperature fluctuations, which indicates that salinity fluctuations are much more effective than temperature fluctuations in determinating the effect of oceanic turbulence. In addition, for weak turbulence and a distance of several tens of meters, the transmission performance of HB vortex beams is worse than that of Laguerre-Gaussian vortex beams with the optimal waist setting. These results provide references for the realization of optical communication links in the marine environment.