Bound states of gain-guided solitons in a passively mode-locked fiber laser

We report on the observation of bound states of gain-guided solitary pulses (GGSPs) in a dispersion-managed erbium-doped fiber laser. Despite the fact that the GGSP is a chirped pulse and there is strong pulse stretching and compression along the cavity in the laser, the bound GGSPs observed have a fixed pulse separation, which is invariant to the pump strength change. Numerical simulation confirmed the experimental observations and further showed that not only the pulse separation but also the relative phase difference between the bound GGSPs remained fixed along the cavity.