Pure-quartic soliton pulsating and creeping dynamics in a bidirectional mode-locked fiber laser

Pure-quartic solitons (PQSs) represent a significant advancement in the field of ultrafast optics, enabling the generation of high-energy pulses. This study presents a systematic numerical investigation of the pulsating and creeping dynamics of PQSs in a bidirectional mode-locked fiber laser, focusing on the influence of fourth-order dispersion (FOD). By carefully adjusting the FOD, distinct pulsating behaviors of PQSs are observed in both clockwise (CW) and counterclockwise (CCW) directions of propagation. However, notable differences in the pulsating amplitudes between the two propagation directions are identified, primarily attributed to the interplay between nonlinear effects and FOD within the laser cavity. Furthermore, as the FOD is increased beyond a certain threshold, PQSs begin to exhibit creeping behavior, characterized by periodic temporal shifts in their pulse dynamics. Importantly, precise control over the creeping distance can be achieved by tuning the FOD. This work also reveals intricate aspects of creeping dynamics, including phenomena such as synchronized and asynchronous creeping periods. These findings not only deepen our understanding of ultrafast optics but also provide both theoretical insights and practical guidance for the application of dual-comb light sources.