Study On Nonlinear Propagation Properties Of Copropagating Pulses In Metamaterial

The metamaterial is a kind of artificial synthetic material. It has a dispersive permittivity and a dispersive permeability simultaneously and its unique electromagnetic properties which can not occur in ordinary material will induce a lot of new science ideas. As metamaterial in the near IR and optical range has been experimentally demonstrated, it has important influence on the field of electromagnetics, optics, material and communication, which will expand these fields greatly. In this paper, the nonlinear propagation properties of two copropagating pulses in metamaterial are investigated by combining the basic theory of conventional nonlinear fiber optics and the novel properties of metamaterials. The main research results are listed below:Firstly, from the Maxwell equations, by combining the generalized nonlinear Schr(o|¨)dinger equation derivation methods and the properties of metamaterials, a theoretical model for two optical pulses with different central frequencies copropagation in metamaterials is built. This model discloses the influence of new nonlinear effects induced by the dispersive permeability on pulse propagation.Secondly, based on the theoretical model, the expression for the gain of modulation instability induced by cross-phase modulation (XPM) in metamaterials is obtained by a standard linear stability analysis. As an example, it is applied to the Drude model to discuss the XPM-induced modulation instability features. The respective role of group-velocity mismatch, self-steepening and second-order nonlinear dispersion effect is particularly demonstrated. The results show that XPM-induced modulation instability can occur irrespective of the sign of refractive index in metamaterials. And it can be manipulated by engineering the group-velocity mismatch, self-steepening and second-order nonlinear dispersion effect.Finally, XPM-induced modulation instability in metamaterials is proved by the split-step Fourier method and the characteristics of nonlinear evolvement are obtained. The results show that in the anomalous group-velocity dispersion (GVD) regime of negative index materials, the two pulses can both break up into a periodic ultra-short pulse train. In the normal GVD regime, because of the small gain, the two pulses can break up under the condition of long propagation distance. In the different GVD regime, only one pulse can break up into a periodic ultra-short pulse train.