基于光纤拉曼放大器(FRA)的非线性耦合方程，采用数值计算的方法首次系统分析了双向多泵浦FRA系统中的偏振相关增益(PDG)特性。根据4个泵浦光源配置的不同，FRA有14种结构。首先整体分析了这14种不同FRA结构中PDG的特点；然后对其中一种结构FRA系统中PDG的特性进行了更具体的分析，包括泵浦-信号、泵浦-泵浦以及信号-信号拉曼相互作用所产生的PDG。研究结果表明，当泵浦总数目一定时，反向泵浦数目越多，其PDG均值越小；当泵浦总数目和反向泵浦数目都一定时，PDG的大小与反向泵浦光波长关系不大；双向多泵浦FRA系统中的PDG主要由泵浦-信号拉曼相互作用所产生的PDG决定。以上结果对有效降低双向多泵浦FRA系统中的PDG有重要的参考价值。

The polarization dependent gain(PDG) of fiber Raman amplifiers(FRAs) with bidirectional pumps was investigated systematically for the first time, by numerical method based on the nonlinear coupled equations describing the properties of fiber Raman amplifiers. The FRA with four pumps has 14 structures. First of all, the general PDG characteristics of the 14 different FRAs were investigated, and then the PDG characteristics of a specific structure were analyzed in detail, including the PDG induced by pump-signal Raman interaction, by pump-pump Raman interaction and by signal-signal Raman interaction. The results show that(1) the more backward pumps generates the smaller mean PDG values under constant number of pumps,(2) when the total number of pumps and the number of backward pumps are both constant, the backward pump wavelength has little effect on the PDG, and (3) the PDG of a bidirectionally pumped FRA is mainly determined by pump-signal Raman interaction. These results are useful and important for reducing the PDG of an FRA.