Spectral splitting of vector solitons in a birefringence-managed fiber laser

Pulse splitting, which results from the excessive accumulation of nonlinear phase shifts, enables multipulse emission with an identical spectrum in mode-locked fiber lasers. However, spectral splitting was rarely observed owing to the limited gain bandwidth and gain competition effect. We demonstrate the spectral splitting of mode-locked pulses ubiquitously existed in birefringence-managed normal-dispersion fiber lasers, where a single-spectrum pulse evolves into multispectrum pulses with different group velocities by increasing the pump intensity. Theoretical analysis and numerical simulations fully reproduce the experimental observations, confirming that the periodic linear and nonlinear coupling of vector modes split the pulse in the frequency domain. This study presents a simple yet efficient method for generating controllable multispectrum mode-locked pulses without the use of spectral filters, which has significant implications for exploring multicolor pulse interactions and facilitating practical applications such as absolute distance measurement.