Route to Larger Pulse Energy in Ultrafast Fiber Lasers

Principles of pulse shaping aiming larger pulse energy in fiber lasers are reviewed. From conventional solitons generated in the anomalous dispersion regime, stretched pulses in dispersion-managed fiber lasers, similaritons in normal dispersion regime, dissipative solitons in large normal dispersion regime, and amplifier similaritons in fiber lasers with narrow bandwidth filtering to dissipative-soliton-resonance (DSR) pulses in fiber lasers, scaling of pulse energy from picojoule level to microjoule is successfully achieved. DSR is a possible way to achieve endless pulse energy, which is limited by the available pump power and material damage threshold. Properties of DSR pulses are reviewed. Specifically, we experimentally and numerically demonstrate tilt-top DSR pulses in a normal dispersion mode-locked fiber laser. Two fronts of the tilt-top pulses exhibit different intensity, and the intensity disparity maintains while the pulses extend with increasing gain. The tilt-top DSR pulses have rectangular spectral pedestal and a peak. The spectral peak deviates from the center of the rectangle spectral pedestal. Further results show that the asymmetry of two fronts is closely related to the wavelength deviation of spectral peak. Numerical simulations reveal the importance of the saddle-type spectral filtering on asymmetric DSR pulse generation.