Square spectrum pulses observed in a mode-locked laser with anomalous dispersion

Optical spectral analysis plays a crucial role in ultrafast lasers for distinguishing pulse types within a specific dispersion regime.A square spectrum, commonly found in normal dispersion regimes, can also be detected in a net anomalous dispersion cavity centered around a wavelength of 1.78 m.The performance of these pulses has been characterized through experiments.Our simulations are able to replicate the spectra using experimental parameters that closely match those used in the experiments.It indicates that this phenomenon occurs due to changes in the gain center of the effective gain, which are influenced by saturation effects.We believe this research could offer valuable techniques for pulse control and aid in the characterization of similar pulse behaviors.