Da instabilidade modulacional em fibras sem perdas com resposta não-linear

Abstract

In this work we analyze the problem of Modulational Instability which is associated with the early stage of development of soliton-like pulses in optical fibers. This phenomenon was investigated in pulses propagating in optical lossless fibers, taking into account the influence of relaxation effects (delay) in the nonl=-linear response and saturation of the nonlinearity. The saturation of the nonlinearity was incorporated in the dynamics of relaxation of the Kerr response. We calculate the dispersion relation through the analytical solution of the steady state. Considering the case of anomalous dispersion, the gain spectrum displays two bands in the regime of fast relaxation. In the regime of slow relaxation, the two bands tend to coalesce. One of the bands, the one with higher energy, is coming from Raman effects, while the other is of instantaneous nature. Considering the case of normal dispersion, we verify the existence of a modulational instability which is not present in media with instantaneous non-linear reesponse. In this case, we observed the existence of a single band associated with the finite response time of the nonlinearity, with different behaviors for slow and fast relaxation.