Optical communications networks include basic components such as EDFAs and WSSs that present a polarization gain imbalance. The gain imbalance at the component output depends on the incident state-of-polarization. This well-known phenomenon called Polarization Dependent Loss (PDL) is revisited in this article and systematically analyzed within the framework of communications theory and practical achievable information rates. The rate impairment induced by PDL is discussed on an optical channel with distributed PDL and on a simplified equivalent lumped PDL channel. We have previously designed the New Spatially Balanced (NSB) signaling, an optimal 4D modulation based on this simplified model. We explore in this article its performance through numerical simulations and experimentally over a transmission in a recirculating loop with in-line PDL. Experimental measurements confirm an accurate channel modeling and significant information rate gains brought by NSB that results in SNR gains of the order of 0.4 dB at a practical transmission outage.

中文翻译：

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光链路中的 PDL：PDL 弹性调制的模型分析和演示

光通信网络包括基本组件，例如 EDFA 和 WSS，它们呈现偏振增益不平衡。组件输出的增益不平衡取决于入射极化状态。本文重新审视了这种著名的现象，称为极化相关损耗 (PDL)，并在通信理论和实际可实现的信息速率的框架内进行了系统分析。在具有分布式 PDL 的光信道和简化的等效集总 PDL 信道上讨论了由 PDL 引起的速率减损。我们之前设计了新的空间平衡 (NSB) 信号，这是一种基于此简化模型的最佳 4D 调制。我们在本文中通过数值模拟和实验探讨了其在具有串联 PDL 的再循环回路中的传输的性能。