高阶色散下随入纤功率变化的不稳定性增益谱

Modulation instability gain spectrum varying with the incident optical power in case of high-order dispersion

为了探讨不同入纤功率下高阶色散对交叉相位调制不稳定性增益谱的影响,从光纤中包含高阶色散的耦合非线性薛定谔方程出发,采用线性稳定性分析法,分二阶、四阶色散系数同号、异号和二阶色散系数为0等几种情形,计算了双光束的交叉相位调制不稳定性增益谱随入纤光功率的变化规律,并对各种谱特性的产生机制作了分析。结果表明,当二阶、四阶色散系数同号时,随着入纤功率的增大,增益谱由开始的两个分离谱区逐渐变宽并合成1个谱区;当二阶、四阶色散系数异号和二阶色散系数为0时,增益谱只有靠近零点的第1谱区,且谱宽和谱峰随着入纤功率的增大而增大。此研究对高重复率的超短光脉冲串的产生有一定的理论指导意义。

In order to investigate the effect of the high-order dispersion on the gain spectra of cross-phase modulation （XPM） instability under different incident optical power, starting from the coupled nonlinear Schrodinger equations of two optical waves in an optical fiber and utilizing the linear-order stability analysis, the gain spectra of cross-phase modulation instability varying with the incident optical power was calculated when the second-order and the fourth-order dispersion coefficients have the same, opposite signs and when the second-order dispersion coefficients was equal to zero, respectively. The mechanism behind these diverse spectra was analyzed in detail. The results show that, when the second-order and the fourth-order dispersion coefficients have the same sign, with the increase of the incident optical power, the gain spectrum which consists of two separated regions first, will broaden and combine to one region. When the second-order and the fourth-order dispersion coefficients have the opposite signs and the second-order dispersions are equal to zero ,the gain spectrum consists of only the first spectral region near the zero point. Moreover, the width and the peak value of the gain spectrum will increase with the incident optical power. The investigation can be a theory guidance to generate ultrashort optical pulse chains with high repetition rate to some extent.