Energy-driven multistage evolution and reversible transitions between vector dissipative solitons and noise-like pulses in a pure-quartic fiber laser

Although pure-quartic fiber lasers exhibit diverse soliton dynamics, the multistage evolution and controllability of vector dissipative pure-quartic solitons remain underexplored. We show that increasing the saturable energy enhances the spectral group delay near the frequency edges via positive fourth-order dispersion, breaking phase equilibrium and triggering a cross-phase-modulation-induced energy imbalance between polarization components. This, combined with modulation instability, leads to spectral collapse and transition into noise-like pulses. Remarkably, precise tuning of the polarization controller enables reversible switching back to the vector dissipative pure-quartic soliton state. We further employ mutual information and Pearson correlation analysis to quantify spectral coherence and verify deterministic chaos in noise-like pulses via Poincar\'e sections and Grassberger-Procaccia dimensions. These results offer insight into nonlinear dynamics and controllable state transitions in high-order-dispersion fiber lasers.