Research on the dynamic characteristics of ultrafast pulse based on EDFL cavity parameter adjustment

Mode-locking is a complex transient process in fiber lasers, and the understanding of its dynamics is essential for elucidating the underlying mechanisms and optimizing laser performance. In this study, we experimentally demonstrate a mode locked erbium-doped fiber laser based on nonlinear polarization rotation, generating femtosecond pulses near 1550nm. Employing the time-stretching dispersive Fourier transform (TS-DFT) technique, we capture the real-time evolution of pulse dynamics during the transition from continuous-wave to mode-locking operation for different cavity lengths and intracavity losses, and the differences of the output characteristics are compared and discussed. The mode-locking process involves rapid spectral modulation followed by gradual stabilization, with the buildup time and spectral characteristics varying with pump power and cavity conditions are demonstrated. The results show that lower pump power leads to prolonged fluctuations before steady-state mode locking, while higher pump power accelerates stabilization but may introduce spectral noise. These results provide critical insights into the interplay between nonlinear effects, dispersion, and gain dynamics in ultrafast fiber lasers and offer practical guidance for optimizing mode locked laser design, particularly in balancing key parameters for stable femtosecond pulse generation.