Polarization Symmetry Breaking of GHz Dissipative Solitons

Spontaneous symmetry breaking (SSB) is a significant topic in particle physics, condensed matter physics, fluid dynamics, etc. In nonlinear optics, polarization is a crucial degree of freedom that enables novel SSB dynamics in coherently pumped Kerr platforms, yet to be explored in laser systems with self-organized localized structure-dissipative soliton. In this study, a special kind of SSB-polarization symmetry breaking (PSB) of GHz dissipative solitons is demonstrated in a mini fiber laser. First, we establish a bidirectional model of the Fabry-Pérot (FP) mini fiber laser with orthogonally polarized counterpropagating light fields. This bidirectional model theoretically predicts the onset of PSB by merely increasing the soliton energy, which manifests as a Hopf bifurcation. Then, experimental validation is performed by implementing a FP mini fiber laser operating at a GHz repetition rate. An abrupt change of the polarization dynamics from the fixed-point attractor to the limit cycle is observed as the soliton energy increases. To verify these findings in real time, specialized polarization-resolved ultrafast techniques are developed for the analysis of high-repetition-rate vectorial signals. The measurements, including the full-Stokes characterization, not only confirm the presence of PSB but also elucidate the underlying physical mechanism associated with the polarization rotation of vector solitons. Our results suggest that the mini fiber laser can potentially become a promising platform for studying the physics of SSB by exploring the nonlinear dynamics of dissipative optical solitons.