Stability and interactions of solitons in two-component active systems

We demonstrate that solitary pulses in linearly coupled nonlinear Schrodinger 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 pi-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, Ti-in in a certain interval of Ti-in. In the case of the phase difference pi/2, the interaction is also repulsive.