I. Introduction
Relying on rich physical mechanisms and complex dynamics in passively mode-locked fiber lasers, various optical pulses, as well as the related interactions, have been explored extensively in past decades. These are still among the hot topics to date, due to the further in-depth studies and the applications of some newly-emerging materials as saturable absorbers (SAs), especially the intensively investigated two-dimensional (2D) materials [1], [2]. Besides several early discovered pulse types, such as conventional solitons, dispersion-managed solitons, dissipative solitons, etc., in recent years, particular attentions have been paid to some long-duration, wave-breaking-free pulses that are formed typically in long-cavity fiber lasers, where considerable accumulatively nonlinear effects can typically be developed due to strong field-confinement of single mode fiber (SMF) and the considerable interaction length. With such a cavity, multiple solitons would be generated due to the well-known area-theorem if the net cavity dispersion falls in the anomalous dispersion regime [3]. Even for the dispersion-managed solitons or dissipative solitons, there are still some upper limits on the single pulse energy and energy quantization still exists [4]–[6].