An optical back propagation (OBP) technique using Raman pumped dispersion compensation fibers (DCF) is investigated to compensate for nonlinear impairments in WDM systems in real time. The proposed inline OBP module consists of an optical phase conjugator, amplifiers and a Raman pumped DCF. In order to suppress the nonlinear effects of the transmission fibers exactly, the power in the backpropagation fiber should increase exponentially with distance. This can be approximately achieved by using forward/backward Raman pumping of the dispersion compensating fiber (DCF). We introduce two configurations to realize the OBP. In this paper, we show that the OBP with forward/backward pumping provides 2.45 dB Q-factor gain compared to single-channel digital back propagation (DBP) when transmission distance is 1500 km for a WDM system with QAM-64. To minimize the variation of effective gain coefficient of the Raman pumped DCF as a function of distance, bidirectional pumping scheme which can provide the signal power profile closest to that required by the ideal OBP condition is proposed. The bidirectional pumping scheme provides a superior performance over forward/backward pumping and wideband DBP (i.e., DBP is applied on the entire WDM signal). Our numerical simulation results show that the bidirectional pumping scheme provides 7.6 dB and 5 dB advantage in Q-factor as compared to single-channel DBP and wideband DBP, respectively at a transmission distance of 5000 km. The maximum achievable reach of a long haul WDM system can be enhanced by $225\%$ using bidirectional pumping scheme as compared to wideband DBP.

中文翻译：

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用于光纤通信的拉曼泵浦色散和非线性补偿光纤

研究了一种使用拉曼泵浦色散补偿光纤 (DCF) 的光学反向传播 (OBP) 技术，以实时补偿 WDM 系统中的非线性损伤。所提出的在线 OBP 模块由光学相位共轭器、放大器和拉曼泵浦 DCF 组成。为了准确抑制传输光纤的非线性效应，反向传播光纤中的功率应随距离呈指数增长。这可以通过使用色散补偿光纤 (DCF) 的正向/反向拉曼泵浦来近似实现。我们引入了两种配置来实现 OBP。在本文中，我们表明，当传输距离为 1500 公里时，使用 QAM-64 的 WDM 系统与单通道数字反向传播 (DBP) 相比，具有前向/后向泵浦的 OBP 可提供 2.45 dB 的 Q 因子增益。为了最小化拉曼泵浦 DCF 有效增益系数随距离的变化，提出了双向泵浦方案，该方案可以提供最接近理想 OBP 条件所需的信号功率分布。双向泵浦方案提供优于前向/后向泵浦和宽带 DBP（即 DBP 应用于整个 WDM 信号）的性能。我们的数值模拟结果表明，在 5000 公里的传输距离下，双向泵浦方案与单通道 DBP 和宽带 DBP 相比，在 Q 因子方面分别提供了 7.6 dB 和 5 dB 的优势。与宽带 DBP 相比，使用双向泵浦方案可以将远程 WDM 系统的最大可实现范围提高 225\%$。