提出了一种改进的、可用于计算偏振相关拉曼增益的光纤拉曼放大器的非线性耦合波方程。建立了单模双折射光纤拉曼增益的数学模型,分析了线偏振抽运光以与光纤快轴成45°激励的单模双折射光纤拉曼放大器模型与实际具有随机双折射的光纤拉曼放大器的拉曼增益偏振相关特性的等价性。基于上述模型,提出了一个可定量表征单模光纤偏振模色散统计特性的拉曼增益偏振相关因子,用以替代常规的光纤拉曼放大器非线性耦合波方程中的偏振相关因子。计算结果与已报道文献的实验数据非常吻合。同时对抽运增益在同向和反向抽运方式下截然不同的增益偏振相关特性给出了合理的解释。

A set of improved nonlinear coupled-wave equations describing the properties of fiber Raman amplifiers is developed, which can be applied to calculate the polarization dependent Raman gain. The mathematical model of the Raman gain in single-mode birefringence optical fiber is presented by coupling mode theory. The equivalence between the single-mode birefringence fiber Raman amplfiers excited at 45° with the fast axis by a linearly polarized pump and the practical fiber Raman amplfiers with randomly varying birefringence is discussed. A polarization dependent factor expressing the statistical properties of the polarization mode dispersion in single mode optical fibers quantitively is developed to substitute the one employed in the normal fiber Raman amplifier coupled nonlinear equations. The results of numerical simulations are accordant with the reported experimental data. The differences of the polarization dependent gains between the copropagating and counterpropagating pump are discussed.