三五阶非线性光纤中光脉冲的啁啾和频谱

Frequency chirps and spectra of optical pulses propagating in optical fibers with cubic-quintic nonlinearity

为了探讨光纤的五阶非线性对光脉冲传输的影响,利用同时考虑三阶和五阶非线性效应的非线性薛定谔方程,在忽略光纤色散的情况下,解析并计算研究了超高斯光脉冲的非线性相移、频率啁啾。数值模拟了光脉冲传输的功率频谱。结果表明,与只有三阶非线性折射率的情形相比,正五阶非线性折射率的存在使光脉冲在光纤中传输的非线性相移和最大频率啁啾增大,使无啁啾光脉冲的频谱宽度变宽,谱峰数目增多,高斯脉冲初始啁啾对频谱的影响与三阶非线性折射率的情形类似;负五阶非线性折射率则使光脉冲传输的非线性相移和频率啁啾呈现新的特点,并使无啁啾光脉冲的频谱宽度变窄,谱峰数目减少。

The aim of the paper is to study the effect of the quintic nonlinearity of an optical fiber on the propagation of optical pulses. Utilizing the cubic-quintic nonlinear Schroedinger equation in which the dispersion of optical fibers is neglected, the nonlinear phase shifts and frequency chirps of super-Gaussian optical pulses are calculated and investigated analytically. The power spectra of optical pulses are numerically simulated as well. The resnlts show that the positive quintic nonlinear refractive index makes the nonlinear phase shifts and the maximum frequency chirps of optical pulses larger,the spectral width of unchirped optical pulses wider and the number of spectral peaks more than those of cubic nonlinear refractive index. The influence of initial chirps of Gaussian optical pulses on the spectra is similar to that of cubic nonlinear refractive index. In case of the negative quintic nonlinear refractive index, the nonlinear phase shifts and frequency chirps take on new characteristics. The negative quintic nonlinear refractive index also makes the width of unchirped optical pulses narrower and the number of spectral peaks less.