光子晶体光纤中频率啁啾对超连续谱的影响

基于光子晶体光纤(PCF)中脉冲演变遵循的非线性演化方程,用数值方法研究了反常色散情形下PCF中脉冲初始啁啾对超连续谱产生的影响,探讨了利用脉冲啁啾控制超连续谱产生的方法。结果表明：正、负啁啾均使谱展宽的速率变小,尤其是负啁啾情形,展宽速率更小,说明啁啾对谱展宽是不利的;在一定的初始条件下,光谱展宽存在一个最佳光纤长度,在这个长度处,光谱展宽最大,进一步增加光纤长度,谱宽基本保持不变;相对于变换极限脉冲来说,初始正、负啁啾脉冲对应的最佳光纤长度分别缩短和延长。

Influence of Frequency Chirp on Supercontinuum in Photonic Crystal Fibers

Based on the nonlinear Schroedinger equation describing pulse propagation in photonic crystal fibers(PCF),we investigate the effect of pulse chirp on supercontinuum generation in the case of anomalous dispersion by numerical simulation and discuss the way to controlling supercontinuum generation by using pulse chirp.It is shown that both the positively and negatively chirped pulses slow down the spectral broadening comparing with the chirp-free pulse,especially in the case of the negative chirp.This phenomenon indicates that the chirped pulse is a great disadvantage for us to broaden the spectrum.Furthermore,there exists an optimum propagation distance for spectral broadening at which the spectrum is widest under certain initial power.If we increase the propagation distance,the spectral width is constant on the whole.Comparing with the chirp-free pulse,the optimum propagation distance of the positively chirped pulse is shortened and that of the negatively chirped pulse is extended.