16:30 〜 16:45
▲ [16p-C301-11] A study on the Modulational Instability in delayed Saturable Nonlinear Optical Media
キーワード：Optical fiber, Modulational Instability, noninearity
Modulation instability (MI) is a universal good old phenomenon, which is an inherent feature of most nonlinear wave systems in nature. MI is known to be the process where weak perturbations, typically the noise imposed on a CW state grow exponentially, as a result of the interplay between nonlinear and dispersive effects. Recently, much attention is devoted to the influence of the relaxation of the nonlinear response. For the case of ultrashort pulses the usual assumption of instantaneous nonlinear response fails and thus delayed contributions of the nonlinear responses has to be taken into account. The non-instantaneous nature of the nonlinear response plays crucial role in the MI dynamics, like the possibility of MI in the normal dispersion regime and the evolution of additional bands of sideband in the anomalous dispersion regime and so on. We performed the linear stability analysis of the equation governing the propagation of optical beam in the non-instantaneous with saturation of nonlinearity. We infer that the MI occurs in both the regime irrespective of the sign of the dispersion. This is interesting because of the fact that the normal dispersion regime is not subject to MI, due to the lack of phase matching between linear and nonlinear effects. However, the existence of MI band in ND regime is attributed to the fact that any finite delay in nonlinear response leads to imaginary part to the wave vector and thereby extends the MI even to the normal GVD. On the other hand, the saturation of nonlinearity suppresses the MI, due to the reduced value of the effective nonlinearity. Thus delay extends the instability window whereas the saturation suppresses the MI. Thus the two opposite physical effects, saturation and relaxation makes the study interesting the context of MI.