色散磁导率对异向介质中的调制不稳定性的影响

基于Drude模型研究了异向介质的色散磁导率对调制不稳定性的影响. 结果表明，在反常色散情形，赝五阶非线性在异向介质的负折射区中增大了调制频谱的范围及增益值，这与常规正折射介质中出现的现象正好相反；自陡峭效应在异向介质中有可能为负值，但无论正负，也无论在正折射区还是负折射区，它都抑制调制不稳定性的产生；二阶非线性色散效应在正、负折射区中分别促进和抑制调制不稳定性的产生. 在正常色散情形，由于二阶非线性色散效应的作用，使本来在常规正折射介质中不可能出现的调制不稳定性现象也能出现，这一特性为在正常色散区形成孤 关键词： 异向介质 调制不稳定性 色散磁导率 二阶非线性色散

Influence of dispersive magnetic permeability on modulation instability in metamaterials

The influence of dispersive magnetic permeability on propagation of untrashort pulses in metamaterials is mainly in that it leads to the appearance of the pseudo-χ⁽⁵⁾, self-steepening (SS) and second-order nonlinear dispersion terms in the propagation equations. In this paper, the role of dispersive magnetic permeability in modulation instability (MI) in metamaterials is identified based on the Drude model. It is found that in the anomalous dispersion regime, the pseudo-χ⁽⁵⁾ nonlinear parameter, which is always negative, increases the MI frequency and growth rate, which is opposite to that in ordinary positive-index materials; the SS tends to suppress MI regardless of its sign, while the second-order nonlinear dispersion effect tends to stimulate MI in the positive-index region and suppress MI in the negative-index region. In the normal dispersion regime, in which MI cannot occur in the ordinary materials, MI can occur due to the role of the second-order nonlinear dispersion, suggesting a new way of generating solitons or ultrashort pulse trains in the normal dispersion regime.