在使用前向抽运喇曼放大器的相干光正交频分复用传输系统中, 由于喇曼抽运的强度噪声和交叉相位调制之间相互作用产生相对相位噪声, 导致系统性能大幅下降。为了研究此问题, 采用数值分析方法进行了理论分析与实验验证, 分析了不同的调制格式下, 相对相位噪声对相干光正交频分复用系统的影响, 并且比较了正交频分复用多载波系统与单载波系统在相同条件下的系统性能, 取得了由相对相位噪声所导致的系统损伤程度数据。结果表明, 抽运和信号之间相对较大的离散系数有助于抑制相对相位噪声引起的损伤, 高阶调制信号比低阶信号对相对相位噪声耐受性低; 频谱相同效率时, 正交幅度调制格式比相移键控耐受性更好。

In a coherent optical orthogonal frequency-division multiplexing transmission system with forward-pumped Raman amplification, the interplay between Raman pump relative intensity noise and cross-phase modulation leads to relative phase noise inducing non-negligible performance degradation. In order to solve this problem, by numerical analysis, theoretical analysis and experimental verification, effect of relative phase noise on the performance of a coherent optical communication system under different modulation formats was analyzed. The performance of a single-carrier orthogonal frequency division multiplexed system under the same conditions was compared with that of a multi-carrier system. The extent of system damage caused by relative phase noise was gotten. The results show that the relatively larger walk-off between pump and signal helps to suppress the impairment induced by the relative phase noise. A higher-order modulated signal is less tolerant to relative phase noise than a lower-order signal. With the same spectral efficiency, the quadrature-amplitude modulation format shows better tolerance to relative phase noise than phase-shift keying.