单模光纤中受激喇曼散射对调制不稳定性的影响

基于修正的非线性薛定谔方程，利用线性扰动理论和数值方法研究了单模光纤中的调制不稳定性.由于受激喇曼散射的作用，使得喇曼增益谱叠加到光纤中的调制不稳定性增益谱上.这样，原本调制稳定的光纤正常色散区也出现了调制不稳定性；而在反常色散区，随着初始功率的增加，常规的调制不稳定性增益谱的增益和频谱范围均增大，而喇曼增益谱的增益增大但其频谱范围基本不变，这样导致常规的不稳定区域逐渐侵入并最终掩盖喇曼增益区.数值模拟验证了解析结果的正确性，并证明了利用反常色散情形下的调制不稳定性可以产生超短脉冲序列，但这种脉冲序列的进一步传输将会出现喇曼孤子自频移现象.

Influence of Stimulated Raman Scattering on Modulation Instability in Single-mode Fibers

Modulation instability (MI) in single-mode optical fibers is investigated analytically and numerically using a modified nonlinear Schrdinger equation. Due to the role of stimulated Raman scattering, Raman gain spectrum is superposed over the conventional MI gain spectrum in optical fibers. As a result, MI occurs in the normal dispersion region where MI does not appear otherwise; in the anomalous dispersion region, as initial power increases, the spectral range and gain of the conventional MI gain spectrum increase, while the spectral range of the Raman gain spectrum remains unchanged even though its gain increases. Thus the conventional instability region gradually intrudes and eventually screens Raman gain region. Numerical simulations confirms the analytical results and demonstrates that ultrashort pulse trains can be generated by MI in the anomalous dispersion regime, but Raman soliton self-frequency shift appears as the pulse train propagates further.