Fig. 1. Schematic of experimental setup

Fig. 2. Performance characterization of modulated pump. (a) Input pump pulse waveforms and carrier signal waveforms at modulation frequencies of 2 kHz, 5 kHz, and 10 kHz; (b) relationship between modulation level and pump power

Fig. 3. Performance characterization of mode-locked and Q-switched pulses. (a) Mode-locked pulse spectrum; (b) radio frequency spectrum in the mode-locked state; (c) autocorrelation trace of mode-locked pulse; (d) Q-switched pulse spectrum; (e) radio frequency spectrum in the Q-switched state; (f) single Q-switched pulse

Fig. 4. TS-DFT accuracy verification and pulse trains during pulse state switching process. (a) Spectra recorded by OSA and single spectra extracted from TS-DFT measurements; (b) output mode-locked pulse train; (c) switching process using PD and OSC for direct detection; (d) real-time spectral data after 8 km DCF stretching

Fig. 5. Experimental real-time data for Q-switched and mode-locked pulse switching process. (a) TS-DFT spectral evolution; (b) record of switching process from Q-tuning state to mode-locked state; (c) process switching from mode-locked state to Q-switched state; (d) output Q-switched pulse train; (e) pulse energy evolution during the switching process

Fig. 6. Switching process at different pump modulation frequencies. (a) TS-DFT spectral evolution at 5 kHz; (b) TS-DFT spectral evolution at 10 kHz; (c) Q-switched pulses at 5 kHz (top part) and 10 kHz ( bottom part); (d) mode-locked pulses at 5 kHz (top part) and 10 kHz ( bottom part); (e) single-shot spectrum of TS-DFT during stable mode locking; (f) single spectrum of TS-DFT in unstable mode-locked state (inset shows extracted autocorrelation traces)