Polarization Effects in Long-Haul Terrestrial Optical Communication Systems

全球通信的迅速发展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）系统被广泛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。系统设计者通常为极化效应分配一个规定的功率惩罚余量，比如2db。当超过这个余量时，就会发生中断。常见的约束是将中断限制为10-6的概率。由于中断是罕见的事件，因此很难从理论上或实验上量化其发生的概率。在过去的一年里，我们通过使用重要性抽样实现了理论上的突破，使我们能够准确地量化罕见事件。我们在理论上扩展了这一技术，并首次在实验中应用了它。我们的重点是确定中断的原因，并从中找到有效的缓解技术。提出的研究是基于密切的实验和理论合作，研究在长距离、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。我们将进行一系列实验并建立理论模型来研究极化效应与非线性、色散和放大的自发发射噪声的相互作用，并评估这些综合效应对RZ和NRZ格式数据信道中断的影响。我们将通过实验确定仅遵循WDM系统中Stokes参数的简化模型的有效性区域，而不是整个时域行为。我们已经在模拟中验证了这个模型。其他建模工具将根据需要开发和验证，以准确有效地计算极化效应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.