Fig. 1. NPR-based Er-doped mode-locked fiber laser and the measurement system

Fig. 2. Characteristics of the stationary soliton at pump power of 40.8 mW. (a) RF spectrum, inset: pulse train; (b) Left-shown: variations of soliton energy and spectral intensity, right-shown: shot-to-shot spectral evolution; (c) Spectra and averaged spectra recorded by OSA and DFT; (d) Autocorrelation trace

Fig. 3. Characteristics of invisible soliton pulsation under pump power of 49.2 mW. (a) RF spectrum, inset: pulse train; (b) Left-shown: variations of soliton energy and spectral intensity, right-shown: shot-to-shot spectral evolution; (c) Spectra and averaged spectra recorded by OSA and DFT; (d) Autocorrelation trace; (e) Successive single-shot spectra from RT 1 to RT 4; (f) Total soliton energy, KS intensity and PS intensity versus RTN

Fig. 4. Characteristics of soliton pulsation under pump power of 41.4 mW (a)-(c), 42 mW (d)-(f), 45.4 mW (g)-(i) and 49.2 mW (j)-(l), respectively. (a), (d), (g) and (j) are RF spectra; (b), (e), (h) and (k) are real-time spectral evolutions; (c), (f), (i) and (l) are variations of spectral 3 dB bandwidth

Fig. 5. Evolution characteristics in the route from the invisible soliton pulsation generation to disappearance. (a) Soliton spectra under different pump power; (b) Variations of ∆λ_KS and ∆λ_PS versus pump power; (c) Variations of center wavelength and output power; (d) Three modulation frequencies versus pump power in the soliton pulsating evolution