Solitons in Laser Systems with Saturable Absorption

Abstract

A review is presented of the main features of localized structures - dissipative solitons - in optical systems with nonlinear amplification and absorption, without driving (holding) radiation, including cases with and without feedback. The focus is on two-dimensional laser solitons. For the case of cylindrically- symmetric intensity distributions, there is a discrete set of such solitons with different values of topological charge and different numbers of oscillations in the radial profiles of their amplitude and phase, within certain intervals of the system parameters. Even these simplest dissipative solitons have certain internal structures that become apparent in the distribution of the radiation energy flows. For weakly-coupled solitons whose tail overlap is only small, the distribution of energy flows in the vicinity of each constituent soliton is topologically similar to the distribution for individual solitons. In addition to weakly-coupled solitons, strongly coupled states exist in parameter domains overlapping with those for symmetric solitons. Symmetric structures are motionless, while asymmetric structures move and rotate. Strongly-coupled soliton states are characterized by asymmetric multi-humped intensity distributions. Rotation occurs even in the absence of radiation wavefront dislocations. We present examples of bifurcations of the phase portrait of energy flows during the transient process of the rotating structure formation, as well as different rotating chains of localized strongly-coupled laser vortices. Under conditions of modulation instability of homogeneous field distributions, new regimes arise, including localized structures with simultaneous rotation and pulsation, and “bio-solitons” with initial growth of structure like a labyrinth, with periodic separation of the fragments; then the fragments repeat the stages of growth and separation of new generations of fragments.