Quad-color dark-bright pulse trapping in a fiber laser

Quad-color dark-bright pulse trapping is reported, for the first time to our knowledge, in a fiber laser, where degeneracy and interdependency behaviors are observed. In the temporal domain, the pulses at quad colors are mutually trapped with double M-shape spectra, each of which operates at a dark or bright state, and all of which degenerate spontaneously into one dark-bright pulse pair (DBPP). In the frequency domain, the DBPPs show a switchable mirror-symmetry feature of dark and bright states: bright-dark-dark-bright or dark-bright-bright-dark state, indicating an interesting interdependency between the state and color. Such degeneracy and interdependency behaviors are attributed to the cross-phase modulation (XPM) of the dark and bright pulses at different colors, not only in but also between the bands and also between the orthogonally-polarized components. This work reveals that the DBPPs at different bands can further self-assemble into one DBPP through the XPM, showcasing the evidence and possibility of undiscovered multi-color bright-dark patterns in laser cavities, such as bound state of bright-dark pulses and their complexes.