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：相干双偏振光传输系统利用光场中四个可用自由度（两个偏振态及其各自的正交分量）来编码信息。此类系统自然基于四维信号空间运行。建立普适的解析模型以精确估计非线性干扰，对于分析此类传输系统及研究不同双偏振四维格式受非线性干扰的影响至关重要。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所有双偏振四维格式，要么未考虑全部非线性干扰贡献。本文针对整个双偏振四维调制格式类别开发了一个模型。该模型综合考虑了自信道干扰、交叉信道干扰及多信道干扰效应。作为模型应用，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。与文献先前结果相比，本模型在预测单信道及多信道传输系统中低色散与高色散光纤的非线性干扰贡献时均具有更高精度。针对非线性干扰，我们从分步傅里叶仿真结果中获得的平均偏差低于0.15分贝。仿真结果进一步表明，通过考虑信号-噪声相互作用，所提模型在长距离传输中对非线性干扰功率的预测精度最高可提升8.5%。