Fig. 1. Schematic of the Yb-doped fiber laser in this experiment.

Fig. 2. Single-wavelength mode-locking operation. (a) Spectrum; (b) pulse train, inset: autocorrelation trace; (c) RF spectrum; (d) shot-to-shot spectra with 1000 round-trips.

Fig. 3. Dual-wavelength mode-locking operation. (a) Spectrum; (b) pulse train; (c) RF spectrum; (d) pulse evolution before the DFT process (see Visualization 1); (e) stretched pulse evolution after the DFT process (see Visualization 2), inset: pulse energy.

Fig. 4. Pulses (a) before and (b) after the DFT process of several typical round-trips during the soliton collision process.

Fig. 5. (a) Pulse train after the DFT process with a large time range; (b), (c) two other soliton collision processes.

Fig. 6. Intensity histogram on log scale of dual-wavelength state. SWH is ∼0.219  V.