Polarization Effects in Long-Haul Terrestrial Optical Communication Systems

全球通信的快速扩张对光纤基础设施提出了更高的要求，并刺激了对增加系统容量的需求。因此，高数据速率、密集波分复用(WDM)系统正被广泛地部署在长途陆地和跨洋链路中。在这些系统中，极化效应会严重限制系统的性能。系统设计者通常将规定的功率惩罚裕度分配给极化效应，比如2分贝。当超过此裕度时，就会发生中断。一个常见的约束是将停机概率限制在10-6。由于停机是罕见事件，因此无论从理论上还是从实验上都很难量化其发生的概率。在过去的一年里，我们利用重要性抽样实现了理论上的突破，这让我们能够准确地量化罕见事件。我们都从理论上扩展了这一技术，并首次在实验上应用它。我们的重点是确定停电的原因，并从中找到有效的缓解技术。这项研究是基于密切的实验和理论合作来研究长距离、高数据速率、地面WDM传输系统中由于极化效应导致的信道中断问题。将进行一系列实验并进行理论建模，以研究极化效应与非线性、色散和放大的自发辐射噪声的相互作用，并评估这些组合效应对RZ和NRZ格式数据的信道中断的影响。我们将在实验中确定简化模型的有效范围，该简化模型只遵循WDM系统中的斯托克斯参数，而不是完整的时域行为。我们已经在仿真中对该模型进行了验证。将根据需要开发和验证其他建模工具，以准确和高效地计算由于极化效应而导致的信道中断概率。

The rapid expansion of global communications has placed increased requirements on optical fiber infrastructure and has stimulated the demand for increased system capacity. As a result, high data rate, dense wavelength-division-multiplexed (WDM) systems are being widely deployed in long-haul terrestrial and trans-oceanic links. In these systems, polarization effects can severely limit the performance of the system. System designers commonly allocate a prescribed power penalty margin to polarization effects say 2 dB. An outage is said to occur when this margin is exceeded. A common constraint is to limit outage to a probability of 10-6. Because outages are rare events, it is difficult to quantify their probability of occurrence either theoretically or experimentally. In the past year, we have achieved a theoretical breakthrough by the use of importance sampling, which allows us to accurately quantify rare events. We both extend this technique theoretically and apply it for the first time experimentally. Our focus is on determining the causes of outage and, from that, effective mitigation techniques. The proposed research is based on a close experimental and theoretical cooperation to study the issue of channel outage due to polarization effects in long haul, high data-rate, terrestrial WDM transmission systems. A series of experiments will be carried out and theoretically modeled to study the interactions of polarization effects with nonlinearity, chromatic dispersion, and amplified spontaneous emission noise, and to assess the impact these combined effects have on channel outage for both RZ and NRZ formatted data. We will experimentally determine the region of validity of a reduced model that only follows the Stokes parameters in a WDM system, rather than the full time-domain behavior. We have already validated this model in simulations. Other modeling tools will be developed and validated as needed to accurately and efficiently calculate the channel outage probability due to polarization effects.