Coherent dual-polarization (DP) optical transmission systems encode information on the four available degrees of freedom of an optical field: the two polarization states, each with two quadrature components. Such systems naturally operate based on a four-dimensional (4D) signal space. Having a general analytical model to accurately estimate nonlinear interference (NLI) is key to analyze such transmission systems as well as to study how different DP-4D formats are affected by NLI. However, the available models in the literature are not completely general. They either do not apply to the entire DP-4D formats or do not consider all the NLI contributions. In this paper we develop a model that applies to the entire class of DP-4D modulation formats. Our model takes self-channel interference, cross-channel interference and multiple-channel interference effects into account. As an application of our model, we further study the effects of signal-noise interactions in long-haul transmission via the proposed model. When compared to previous results in the literature, our model is more accurate at predicting the contribution of NLI for both low and high dispersion fibers in single- and multi-channel transmission systems. For the NLI, we report an average gap from split step Fourier simulation results below 0.15dB. The simulation results further show that by considering signal-noise interactions, the proposed model in long-haul transmission improves the NLI power accuracy prediction by up to 8.5%.

翻译：相干双偏振（DP）光传输系统利用光场的四个可用自由度（两个偏振态，每个偏振态包含两个正交分量）来编码信息。此类系统天然基于四维（4D）信号空间运行。建立一个通用的解析模型以准确估计非线性干扰（NLI），对于分析此类传输系统以及研究不同DP-4D格式受NLI影响的方式至关重要。然而，现有文献中的模型并不完全通用：它们要么无法适用于全部DP-4D格式，要么未能考虑所有NLI贡献。本文开发了一个适用于整个DP-4D调制格式类别的模型。我们的模型综合考虑了自信道干扰、交叉信道干扰以及多信道干扰效应。作为模型的应用示例，我们进一步通过所提模型研究了长距离传输中信号-噪声相互作用的影响。与现有文献结果相比，我们的模型在单信道和多信道传输系统中，对低色散光纤和高色散光纤的NLI贡献预测均更为准确。对于NLI，报告显示与分步傅里叶仿真结果的平均偏差低于0.15dB。仿真结果进一步表明，在长距离传输中，通过考虑信号-噪声相互作用，所提模型对NLI功率的预测精度最高可提升8.5%。