Virtually all practical femtosecond-pulse generation has been based on soliton formation, which is the compensation of a self-focusing nonlinear phase by anomalous dispersion. Although it has many advantageous properties, soliton-like pulse-shaping also limits the stable pulse energy, and this limit is severe in fiber lasers. Recent research has shown that it is possible to generate ultrashort pulses by a completely different mechanism: in a cavity with only normal-dispersion components, a stable highly-chirped pulse can be produced by the balance of spectral broadening and spectral filtering. Such a pulse balances amplitude modulations (gain and loss) as well as the phase modulations, and is referred to as a dissipative soliton. The pulse can be dechirped to the Fourier transform limit outside the cavity. This approach allows the generation of ultrashort pulses from fiber lasers with much higher energies than was possible previously. In particular, lasers based on ordinary single-mode fiber generate 100-fs and 30-nJ pulses, for average powers well above 1 W. These are the first fiber lasers to compete directly with the performance of solid-state lasers. Elimination of segments or components with anomalous dispersion produces simple and practical designs. Dissipative-soliton lasers can also be designed to generate high-energy pulses chirped to ~1000 times the transform-limited duration, which should be valuable for chirped-pulse amplifiers. In addition to their potential for applications, normal-dispersion lasers provide a convenient setting for the study of dissipative solitons, which are of much current interest in the nonlinear-waves community. Theoretical and experimental results will be reviewed.

© 2010 Optical Society of America

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