Transformation of a dark soliton into a bright pulse

We consider a system of cubic complex Ginzburg-Landau equations governing c opropagation of two waves with opposite signs of the dispersion in a nonlin ear optical fiber in the presence of gain and losses. The waves are coupled by cross-phase modulation and stimulated Raman scattering. A special exact solution for a bound state of bright and dark solitons is found (unlike th e well-known exact dark-soliton solution to the single complex Ginzburg-Lan dau equation, which is a sink, this compound soliton proves to be a source emitting traveling waves). Numerical simulations reveal that the compound s oliton remains stable over similar to 10 soliton periods. Next, we demonstr ate that a very weak seed noise, added to an initial state in the form of a dark soliton in the normal-dispersion mode and nothing in the anomalous-di spersion one, gives rise to a process of the generation of a bright pulse i n the latter mode, while the dark soliton gets grayer and eventually disapp ears. Thus this scheme can be used for an effective transformation of a dar k soliton into a bright one, which is of interest by itself and may also fi nd applications in photonics. (C) 2000 Optical Society of America [S0740-32 24(99)00408-7] OCIS codes: 060.5530, 190.0190, 190.5650, 060.0060.