Anomalous soliton trapping in net-normal dispersion lasers

Abstract

In a nonlinear optical system with birefringence such as fiber lasers, soliton trapping can be achieved when the fast (slow) component experiences blueshift (redshift) at normal dispersion to compensate for polarization-mode dispersion (PMD). In this Letter, we demonstrate an anomalous vector soliton (VS) whose fast (slow) component shifts to the red (blue) sides, which is opposite to traditional soliton trapping. It is found that the repulsion between the two components is induced by net-normal dispersion and PMD, while the attraction is ascribed to linear mode coupling and saturable absorption. The equilibrium of attraction and repulsion permits the self-consistent evolution of VSs circulating in the cavity. Our results indicate that the stability and dynamics of VSs are worth revisiting and studying in-depth, especially in lasers with complex configurations, despite it being a well-known object in nonlinear optics.