模分复用系统中模式耦合与模式色散的统计特性研究

Study on Statistical Properties of Mode Coupling and Dispersion in Mode-Division Multiplexing Systems

对模分复用系统中模式耦合和模式色散的统计规律及特性进行了研究。利用基于密度矩阵理论的模式色散统计模型,借助数值模拟分析得到了六模光纤中模式耦合引起的光场能量分布和相干性变化的规律以及与模式色散相关的各物理量的统计分布。结果表明,光纤的随机扰动会造成光场在不同模式之间的相干性于很短的传输距离内迅速衰减为零,因此在相干光通信系统中对模式信号进行处理时,不仅根据能量耦合强度进行分组,需要同时考虑模式间的能量耦合与相干性变化以作全局处理。同时发现,六模光纤中一阶、二阶模式色散的统计分布能够用修正的偏振模色散公式加以描述。以上结论将为模分复用光信号的性能恢复提供理论依据,并有效推动模分复用技术的实用化进程。

In this paper,the statistical properties of mode coupling and modal dispersion in mode-division multiplexing systems are studied.Employing a statistical modal-dispersion model based on the density-matrix formalism,the mode-coupling induced variations of optical-field energy distribution and coherence,and the statistical distributions of various physical quantities concerning the modal dispersion in a six-mode fiber are numerically simulated.The results show that random perturbations of the fiber cause the coherence among different modes to decay rapidly to zero within a short propagation distance,therefore,when processing mode signals in coherent optical communication systems,it is important to consider both the energy coupling and coherence variation among the modes.It is also found that the statistical distributions of the first and second-order modal dispersion in the six-mode fiber can be described by a modified set of formulas originally derived for polarization mode dispersion.Our work can provide a theoretical guidance for performance recovery of optical signals in mode-division multiplexing systems and promote the practical applications of mode-division multiplexing technology.