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To overcome the limitation of low spectral broadening efficiency in the normal group-velocity dispersion (GVD) regime, utilizing a multi-pulse pump source induces nonlinear effects between pulses, leading to the generation of new frequency components at extended wavelength, thus expanding the spectral range. In the process of single-pulse pumped supercontinuum generating, the evolution of non-frequency shift components of pulse tail plays a crucial role. In the case of multi-pulse pumping, the overlap of pulses makes the interaction between non-frequency shift and frequency shift components more complex. In this work, a numerical model for multi-pulse pump supercontinuum generation based on the generalized nonlinear Schrödinger equation (GNLSE) is established. The fourth-order Runge-Kutta in the interaction picture method (RK4IP) is employed to analyze the evolution of inter-pulse non-frequency shift components of multiple pulses during their transmission in the normal GVD regime. The results demonstrate that as the transmission distance increases, the non-frequency shift components at the edges of the pulse group exhibit an asymmetric evolution trend; the ones between the pulses undergo a transition from asymmetric to symmetric evolution, and this transition is significantly accelerated when the time interval between incident pulses shortens. The frequency components at the front and rear edges of the pulse group are primarily influenced by Cross-Phase Modulation (XPM) and Stimulated Raman Scattering (SRS), but the asymmetric evolution is mainly caused by SRS. While third-order dispersion (TOD) can lead to asymmetrical spectral broadening, its impact on the tail non-frequency shift components is relatively minor.
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