Soliton formation from dispersive waves in a passively mode-locked fiber soliton ring laser

Due to its potential as a compact, stable light source of ultrashort pulses, passively mode locked fibre soliton lasers have been intensively investigated recently. An important issue of the studies has been how to efficiently utilize the gain bandwidth to produce shortest pulses. There are two mechanisms that prevent the pulse shortening in the laser. One is the pulse splitting, which is due to the fact that the total loss from the saturable absorber and the cut-off of the gain bandwidth is smaller for two broader pulses than for one sharp pulse, provided that they have the same total energy. The other one is the resonant sideband formation in the laser. When there is discrete perturbation in the cavity, a soliton circulating in the cavity will reshape its form and shed the excess energy into dispersive waves. A resonant energy transfer occurs between the soliton and those dispersive waves whose phase is matched to the soliton. The energy transfer rate depends on the overlapping between the resonant sidebands and the soliton spectrum. With the same sidebands a shorter soliton pulse will have higher energy transfer rate and will therefore stop shortening when all energy injected into the soliton pulse is transferred to the dispersive waves. In this paper we study further the dynamics of a passively mode locked fibre soliton laser as the laser gain is increased. We show experimentally that under a resonant soliton energy transfer to the dispersive waves, new soliton pulses can be formed through soliton shaping of dispersive waves in the laser.