通过合理分析提出了便于计算多波长双向抽运光纤拉曼放大器信号及噪声功率的实用数值模型,给出求解信号和噪声功率的快速算法。在定义抽运方向度为前向抽运功率与总抽运功率值的比值后,通过对计算结果的分析发现信道平均放大自发辐射噪声功率随着抽运方向度的提高而单调递减;而信道平均双重瑞利散射噪声功率相对抽运方向度的变化曲线始终成U字形。不同的增益下存在对应的最优抽运方向度,在此抽运方向度下放大器总噪声最低。进而考虑在信号非线性失真的条件下提出了抽运方向度优化的衡量指标。优化后的多波长双向抽运方式不仅能保证对所有信道的平坦放大,而且其综合性能明显高于后向抽运方式。

A novel numerical model and an efficient algorithm are developed to calculate the powers of signal and noise light waves in multiple wavelengths bidirectionally pumping fiber Raman amplifiers. The relationship between the noises, including the amplified spontaneous emission noise and the double Rayleigh backscattering noise, and the degree of pumping directionality is studied. According to the simulation results there exists an optimal degree of pumping directionality, at which the total noise power drops to its lowest value. Furthermore, an optimization of evaluating factor considering both the optical signal to noise ratio and nonlinear distortion impact is put forward. After optimization, fiber Raman amplifiers can achieve not only flat gain spectrum but also the best balance between optical signal to noise ratio and nonlinear distortion impact.