Stability and interactions of solitons in two-component active systems

We demonstrate that solitary pulses in linearly coupled nonlinear Schrödinger equations with gain in one mode and losses in another one, which is a model of an asymmetric erbium-doped nonlinear optical coupler, exist and are stable, as was recently predicted analytically. Next, we consider interactions between the pulses. The in-phase pulses attract each other and merge into a single one. Numerical and analytical consideration of the repulsive interaction between π-out-of-phase pulses reveals the existence of their robust pseudobound state, when a final separation between them takes an almost constant minimum value, as a function of the initial separation, Tin, in a certain interval of Tin. In the case of the phase difference π/2, the interaction is also repulsive. © 1996 The American Physical Society.