The evolution of dissipative soliton resonance from noise-like pulse via the saturable absorption to reverse saturable absorption transition within covalent organic framework saturable absorbers

In this study, for the first time, the dynamic evolution from noise-like pulses (NLPs) to dissipative soliton resonance (DSR) in an erbium-doped fiber laser system was observed and investigated by using a porphyrin/pyrene-linked covalent organic framework (COF) saturable absorber. Experimentally, by adjusting the pump power, the laser operation state was observed to be with a transition from NLPs to DSR. In addition, the correlation between the transition from NLPs to DSR and the variation from saturable absorption to reverse saturable absorption (RSA) within the COF material was analyzed, leading to the variation of absorption with increasing pump power playing a key role in this process. The competition mechanism between the spectral filtering effect and RSA was proposed, and the results observed agree quite well with the proposed model. This research not only reveals new features of pulse dynamics in fiber lasers but also highlights the potential of crystalline porous materials in nonlinear optical applications. It provides an important experimental foundation for further exploration of novel two-dimensional materials in the field of ultrafast optics.