Theoretical Analyses of Pulse Evolution in a Passively Mode-Locked Laser

In passively mode-locking fiber lasers, bismuthene used as the saturable absorber (SA) paves a brand-new way for the ultra-short pulses’ generation. Based on the coupled nonlinear Schrödinger equation (CNLSE), the generation and transmitting characteristics of ultrafast pulse are studied in details, especially, the influence of the second-order dispersion on the pulse width, energy and spectrum. In this work, through changing the group velocity dispersion (from 0.03 $\mathrm{p}\mathrm{s}^{2}/\mathrm{k}\mathrm{m}$ to $0.09\mathrm{p}\mathrm{s}^{2}/\mathrm{k}\mathrm{m})$, the pulse width and energy increase with the increase of the dispersion. The results from this work can be regarded as guidance when designing a wave-breaking-free fiber laser and also provide a theoretical basis for the experimental control of pulse width and energy.