  Collision refers to a striking nonlinear interaction in dissipative systems,
revealing the particle-like properties of solitons. In dual-wavelength
mode-locked fiber lasers, collisions are inherent and periodic. However, how
collisions influence the dynamical transitions in the dual-wavelength
mode-locked state has still not been explored. In our research, dispersion
management triggers the complex interactions between solitons in the cavity. We
reveal the smooth or reversible Hopf-type bifurcation transitions of dual-color
soliton molecules (SMs) during collision by real-time spectral measurement
technique of TS-DFT. The reversible transitions from stationary SM to vibrating
SM, revealing that cavity parameters pass through a bifurcation point in the
collision process without active external intervention. The numerical results
confirm the universality of collision-induced bifurcation behavior. These
findings provide new insights into collision dynamics in dual-wavelength
ultrafast fiber lasers. Furthermore, the study of intermolecular collisions is
of great significance for other branches of nonlinear science.
