研究了色散缓变光纤中飞秒光脉冲的调制不稳定性，发现当色散缓变光纤的色散参量满足一定关系式时，增益谱的谱宽最宽，获得了增益谱的表达式；三阶色散对调制不稳定性不起作用；自变陡效应使增益谱的谱宽变窄，振幅的增长速度减漫；拉曼效应改变了调制不稳定性的产生区域。

Modulation instability of femtosecond optical pulses in decreasing dispersion fibers is investigated. The expression of gain spectrum is obtained. It is found that the broadest spectral width of the gain spectrum can be obtained when the dispersion parameter of the decreasing dispersion fibers fits to a certain equation, and the third order dispersion does not contribute to modulation instability, the range of gain spectrum is narrowed and the growth rate of amplitude is slowed down by self-steepening, and the Raman effect alters the range of modulation instability.