Observation of Spectral Instability in Fiber Laser with Photonic Time Stretch

We demonstrate the observation of shot-to-shot spectral instability in a mode-locked fiber laser with the successive single-shot spectrum measurement. Using time stretch to capture 8000 consecutive single-shot spectra during 100 μs in real-time, instability of individual pulse spectrum structure, noise-like pulse (NLP), could be detected. With an excessive intra-cavity power, NLP is formed by a nonlinear polarization rotation. The behavior of spectral instability opens for new opportunities to understand the complex ultrafast phenomena.