采用线性稳定性分析法, 解析和计算了指数饱和非线性和高阶色散光纤中的调制不稳定条件和增益谱。结果表明: 当二阶和四阶色散同为负时,随着参数的不同, 增益谱可能只有一个谱区, 也可能出现两个分离的谱区；当二阶和四阶色散分别为正和负时, 无调制不稳定性；在其它色散区, 则只有一个谱区。指数饱和非线性可能使各谱区的谱宽、峰值增益随入纤功率的增大呈现出先增大后减小的特点, 即出现两个不同的输入功率对应同一个不稳定增益峰值和谱宽的情形。在其它参数相同时, 指数饱和非线性下增益谱的谱宽和峰值增益随入纤功率的变化速度将比传统饱和非线性更快。

Utilizing the linear-stability analysis, the condition and gain spectra of modulation instability in optical fibers are investigated and calculated in case of exponential saturable nonlinearity and high-order dispersion. The results show that, when the fourth-order and the second-order dispersion are both negative, depending on different parameters, modulation instability may have only one spectral region or two separated spectral regions. When the second-order and fourth-order dispersions are respectively positive and negative, no modulation instability occurs. In the other dispersion regimes, the gain spectra consist of only one regime. The existence of the exponential saturable nonlinearity may make the spectral width as well as the peak gain of every spectral region increase with the input powers before decrease. That is to say, for every spectral region, this may lead to a unique value of peak gain and spectral width for two different input powers. In comparison with the case of conventional saturable nonlinearity, when the other parameters are the same, the variation of the spectral width as well as the peak gain with the input powers will be faster in case of exponential saturable nonlinearity.