脉冲内拉曼散射所致啁啾的研究

A Study of Chirp Induced by Intrapulse Stimulated Raman Scattering

探究孤子自频移现象,从啁啾的角度来解释其产生的原因。运用数学求解及数值模拟方法,通过MATLAB编程画出了啁啾演变图,据此来研究自频移现象。研究结果表明,在高阶非线性效应中,脉冲内拉曼散射、色散和自相位调制共同所致的啁啾,与无拉曼散射效应时产生的啁啾相比,发生一系列新的变化:啁啾的中心发生漂移且图形的前后沿不对称,即负啁啾的峰值的绝对值大于正啁啾的峰值,这说明了脉冲频谱“红移”的谱峰变宽,或者说频谱移向了长波长方向—即人们所说的孤子自频移现象。

In order to further study the self-frequency shift of solitons this paper trys to explain this phenomenon in terms of the chirps. By means of mathematical calculation and numerical simulation, the chirp evolutions are plotted using MATLAB. hence the phenomenon of self-frequency shift can be studied. The results show that the chirps due to the effects of Raman scattering, dispersion and self-phase modulation change a great deal Compared with the chirps under the same condition but without Raman scattering effect： the centers of evolutions shift, and there is asymmetry between the leading and trailing edges in the evolutions are greater than those the absolute peak values of the negative chirps comeparing with of the positive chirps. It can be explained by the fact that the spectrum band has been broadened, or it can equally be deduced that the frequency spectrum shifts to the long wavelength side red shift. This phenomenon is what we call the self-frequency shift of solitons.