Interaction and hound states of pulses in the Ginzburg-Landau equations

The soliton propagation and interaction characteristics in the presence of spectral filtering, linear and nonlinear gain are investigated. Using a perturbation approach, it is shown that the nonlinear gain has a significant impact on the soliton interaction when the adjacent solitons have different phases or amplitudes. In a system with purely nonlinear gain, for which arbitrary amplitude solitons can propagate, we find that the phase difference varies continuously and the solitons oscillate only slightly around their initial time separation. Concerning the quintic Ginzburg-Laudau equation and taking into account the soliton chirping, we find the existence of two types of bound states. One of them is unstable, while the other corresponds to practically stable stationary points of the dynamical system governing the interaction. These findings are in accordance with the numerical results obtained by ourselves as well as by other authors.