We demonstrate a modelocked ytterbium (Yb)-doped fiber laser that is designed to have strong pulse-shaping based on spectral filtering of a highly-chirped pulse in the cavity. This laser generates femtosecond pulses without a dispersive delay line or anomalous dispersion in the cavity. Pulses as short as 170 fs, with pulse energy up to 3 nJ, are produced.

Mode-locked fiber lasers in which pulse shaping is based on filtering of a frequency-chirped pulse are analyzed with the cubic-quintic Ginzburg-Landau equation. An exact analytical solution produces a variety of temporal and spectral shapes, which have not been observed in any experimental setting to our knowledge. Experiments agree with the theory over a wide range of parameters. The observed pulses balance gain and loss as well as phase modulations, and thus constitute dissipative temporal solitons. The normal-dispersion fiber laser allows systematic exploration of this class of solitons.

We report a study of the scaling and limits to pulse energy in an all-normal-dispersion femtosecond fiber laser. Theoretical calculations show that operation at large normal cavity dispersion is possible in the presence of large nonlinear phase shifts, owing to strong pulse shaping by spectral filtering of the chirped pulse in the laser. Stable pulses are possible with energies of tens of nanojoules. Experimental results from Yb-doped fiber lasers agree with the trends of numerical simulations. Stable and self-starting pulses are generated with energies above 20 nJ, and these can be dechirped to $<200\mathrm{fs}$ duration. Femtosecond pulses with peak powers near $100\mathrm{kW}$ are thus available from this simple and practical design.