Generation of an ultrashort soliton train by pumping two identical time-delayed pulses in a third-order nonlinear composite medium

We report the generation of an ultrashort soliton train by pumping two identical time-delayed femtosecond pulses in a third-order nonlinear composite medium with normal dispersion. The entire composite medium is composed of two segments, the first segment with self-focusing nonlinearity and the second segment with self-defocusing nonlinearity. In the self-focusing segment, a temporal pulse sequence is generated via the formation of a dark soliton train due to the nonlinearity acting on the modulation. In the self-defocusing segment, these temporal pulses can be effectively compressed into the controlled and isolated ultrashort solitons via the temporal compression method, as long as the time delay between double pulses and the ratio of the self-focusing segment are suitably set. Interestingly, when the ratio of the self-focusing segment is relatively small, a giant soliton can be produced by the combined effect of temporal compression and soliton collision, which exhibits an extremely high intensity and a significant redshift but does not need to follow the $\mathsf{L}$-shaped intensity probability distribution.