Vector bright soliton interactions of the coupled Sasa-Satsuma equations in the birefringent or two-mode fiber

Investigated in this paper are the vector bright soliton interactions of the coupled Sasa-Satsuma equations, which describe the simultaneous propagation of two ultrashort pulses in the birefringent or two-mode fiber. Lax pair and the corresponding Darboux-dressing transformation are constructed. Performing the iterative formula, analytic bright one-, two- and even N-soliton solutions can be obtained. Through classifying different parameter conditions, we present six cases of the interactions between the vector two solitons via the graphic analysis. During the interaction between the two solitons, in addition to the energy exchanges, the singular-I soliton always keeps its sech-type profile, while the singular-II and nonsingular solitons may be converted to each other.