Solitary-pulse stabilization and shortening in actively mode-locked lasers

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Abstract
We present a theory and experiments on active mode locking in the presence of negative group-velocity dispersion (GVD) and self-phase modulation (SPM). It is shown that beyond a critical value of GVD a solitonlike pulse can be stabilized by the mode locker. The width of the soliton can be shorter than the width of the Gaussian pulse produced by the mode locker in the absence of soliton shaping. We establish analytically that the pulse shortening possible by addition of SPM and GVD is limited only by the requirement that the phase shift of the soliton per round trip be limited. Parameter ranges allowing for stable solitary-pulse formation and shortening are derived and discussed for different gain media and compared with numerical simulations and experimental results.