Linear-coupling-induced double-period pulsating vector solitons in lasers

Pulsating solitons is a universal phenomenon originating from the Hopf-type bifurcation in dissipative systems such as lasers and microresonators. Here, we report the vector soliton in a fiber laser pulsating with two periods of different orders of magnitude. The short-period pulsation manifests as the period-tripling facilitated by the linear coupling between orthogonal polarization components, which breaks the self-consistent evolution of the vector soliton over a single round trip (RT). The long-period pulsation arises from the mode competition between the two polarization components mediated by various cavity effects. The interplay between linear coupling and mode competition gives rise to the robust double-period pulsating (DPP) vector soliton. Our results provide a clear physical mechanism for the broadly observed double-period breather, which has a significant value in exploring breathers with complex dynamics and multiple comb spectroscopy.