Composite solitons and two-pulse generation in passively mode-locked lasers modeled by the complex quintic Swift-Hohenberg equation.

The complex quintic Swift-Hohenberg equation (CSHE) is a model for describing pulse generation in mode-locked lasers with fast saturable absorbers and a complicated spectral response. Using numerical simulations, we study the single- and two-soliton solutions of the (1+1)-dimensional complex quintic Swift-Hohenberg equations. We have found that several types of stationary and moving composite solitons of this equation are generally stable and have a wider range of existence than for those of the complex quintic Ginzburg-Landau equation. We have also found that the CSHE has a wider variety of localized solutions. In particular, there are three types of stable soliton pairs with pi and pi/2 phase difference and three different fixed separations between the pulses. Different types of soliton pairs can be generated by changing the parameter corresponding to the nonlinear gain (epsilon).