We experimentally observe the formation of Polarization-Locked Vector Solitons in a modelocked fiber laser. These vector solitons have a fixed polarization state, despite the presence of birefringence. They maintain this fixed polarization by balancing nonlinearity against the birefringence, in a manner analogous to the balance between nonlinearity and dispersion that allows an ordinary soliton to maintain its pulse shape.
Theoretical results provide excellent agreement with the experiment.
In the same laser, we also observe the nonlinear instability of the fast axis.