Soliton–similariton fibre laser

Rapid progress in passively mode-locked fibre lasers1,2,3,4,5,6 is currently driven by the recent discovery of new mode-locking mechanisms, namely, the self-similarly evolving pulse (similariton)7 and the all-normal-dispersion (dissipative soliton) regimes8,9. These are fundamentally different from the previously known soliton10 and dispersion-managed soliton (stretched-pulse)11 regimes. Here, we report a fibre laser in which the mode-locked pulse evolves as a similariton in the gain segment and transforms into a regular soliton in the rest of the cavity. To our knowledge, this is the first observation of similaritons in the presence of gain, that is, amplifier similaritons, within a laser cavity. The existence of solutions in a dissipative nonlinear cavity comprising a periodic combination of two distinct nonlinear waves is novel and likely to be applicable to various other nonlinear systems. For very large filter bandwidths, our laser approaches the working regime of dispersion-managed soliton lasers; for very small anomalous-dispersion segment lengths it approaches dissipative soliton lasers. Scientists report a mode-locking regime of an erbium-doped fibre laser in which the laser pulse evolves as a similariton in the gain segment of the cavity and transforms into a soliton in the rest of the cavity. The findings constitute the first observation of amplifier similaritons in a laser cavity and are likely to be applicable to various other nonlinear systems.