Raman-induced optical shocks in nonlinear fibers

It is demonstrated that the stimulated Raman scattering in optical fibers supports kink solitons (shocks) not only in the recently considered case of anomalous dispersion but also in the normal-dispersion regime. In both cases there is a family of the kinks depending on an arbitrary (positive) wave number of the carrying wave. Although all the kinks are unstable because of the inherent instability of the cw background behind them, in the normal-dispersion regime the instability, induced solely by the stimulated Raman scattering, is essentially weaker than that in the case of anomalous dispersion.