Ren Yongxiong, Dang Anhong, Liu Ling, Guo Hong
State Key Laboratory of Advanced Optical Communication Systems and Networks and Department of Electronics, School of Electronics Engineering and Computer Science, Peking University, Beijing, China.
Appl Opt. 2012 Oct 20;51(30):7246-54. doi: 10.1364/AO.51.007246.
The heterodyne efficiency of a coherent free-space optical (FSO) communication model under the effects of atmospheric turbulence and misalignment is studied in this paper. To be more general, both the transmitted beam and local oscillator beam are assumed to be partially coherent based on the Gaussian Schell model (GSM). By using the derived analytical form of the cross-spectral function of a GSM beam propagating through atmospheric turbulence, a closed-form expression of heterodyne efficiency is derived, assuming that the propagation directions for the transmitted and local oscillator beams are slightly different. Then the impacts of atmospheric turbulence, configuration of the two beams (namely, beam radius and spatial coherence width), detector radius, and misalignment angle over heterodyne efficiency are examined. Numerical results suggest that the beam radius of the two overlapping beams can be optimized to achieve a maximum heterodyne efficiency according to the turbulence conditions and the detector radius. It is also found that atmospheric turbulence conditions will significantly degrade the efficiency of heterodyne detection, and compared to fully coherent beams, partially coherent beams are less sensitive to the changes in turbulence conditions and more robust against misalignment at the receiver.
本文研究了大气湍流和失准影响下相干自由空间光（FSO）通信模型的外差效率。更一般地，基于高斯谢尔模型（GSM），假设发射光束和本地振荡光束均为部分相干。通过使用推导得到的GSM光束在大气湍流中传播的交叉谱函数的解析形式，在假设发射光束和本地振荡光束的传播方向略有不同的情况下，推导出了外差效率的闭式表达式。然后研究了大气湍流、两束光的配置（即光束半径和空间相干宽度）、探测器半径以及失准角对外差效率的影响。数值结果表明，根据湍流条件和探测器半径，可以优化两束重叠光束的光束半径以实现最大外差效率。还发现大气湍流条件会显著降低外差检测效率，并且与完全相干光束相比，部分相干光束对湍流条件变化的敏感度较低，在接收器处对失准更具鲁棒性。
