Hi Abu Bakar
In principle, multiple pulses are generated as a result of accumulated nonlinear phase shift (phi_NL). if the value of Phi_NL exceeds certain value based on the system design, multipulsing start to appear instead of single pulse. you can see that in simple simulation using OptiSystem. just put the input as a soliton pulse then design the optical fiber as a medium of propagation with certain length and nonlinear coefficient so that you can see the pulse splitting in the output port of the fiber.
thanks
Mohamed Abouseif