We investigate the three-coupled Hirota system, which is applied to model the long distance communication and ultrafast signal routing systems governing the propagation of light pulses. With the aid of the Darboux dressing transformation, composite rogue wave solutions are derived. Spatial–temporal structures, including the four-petaled structure for the three-coupled Hirota system, are exhibited. We find that the four-petaled rogue waves occur in two of the three components, whereas the eye-shaped rogue wave occurs in the other one. The composite rogue waves can split up into two or three single rogue waves. The corresponding conditions for the occurrence of such phenomena are discussed and presented. We find that the relative position of every single rogue wave is influenced by the ratios of certain parameters. Besides, the linear instability analysis is performed, and our results agree with those from the baseband modulation instability theory.
Efforts have been put into investigating a variable-coefficient coherently coupled nonlinear Schrödinger system with the alternate signs of nonlinearities, describing the propagation of the waves in the nonlinear birefringent optical fiber. Via the Lax pair, Darboux transformation for the system is derived. Then, we derive the vector one- and two-soliton solutions. Figures are displayed to help us study the properties of the vector solitons: with the strength of the four-wave mixing terms γ(t) as a constant, the vector soliton propagates with the unvarying velocity and amplitude; with γ(t) being a time-dependent function, amplitude and velocity of the vector soliton keep varying during the propagation; bell- and M-shaped solitons can both be observed in q2 mode, while we just observe the bell-shaped soliton in q1 mode, where q1 and q2 are the two slowly varying envelopes of the propagating waves; head-on and overtaking interactions between the vector two solitons are both presented.