Fig. 1. Schematic of the figure-eight few-mode fiber laser.

Fig. 2. Characteristics of single-wavelength NLSP: (a) spectrum (inset: the corresponding beam profile); (b) pulse-train (inset: the details of a pulse); (c) RF spectrum over a 1 MHz span (inset: the RF spectrum over a 1 GHz span); (d) pulse autocorrelation trace.

Fig. 3. Characteristics of the STML synchronous dual-wavelength NLSPs: (a) the spectra [whole represents the original spectrum of the pulse; sample 1 (S1) and sample 2 (S2) represent the spectra at different parts of the output beam; inset: the output beam profile]; (b) RF spectra of the original pulse and sampling signals; (c) autocorrelation trace of the original pulse; (d) the original spectrum (whole) and the filtered spectra; (e) RF spectra of the original pulse and the filtered signals (inset: the RF spectrum of the dual-wavelength NLSPs over a 1 GHz span); and (f) the whole and filtered pulse-train (inset: the details of a pulse).

Fig. 4. Characteristics of the STML dual-wavelength NLPs in simulations: (a) spectrum evolution; (b) pulse evolution; (c) real-time spectra of mode-resolved pulses in round-trips of 300; (d) real-time pulses of mode-resolved pulses in round-trips of 300.

Fig. 5. Characteristics of the wavelength-resolved pulses: (a)–(c) pulse evolution, fine structure of the overall pulse in 300th round-trip (inset: zoomed-in sub-pulses of the overall pulse), and mode energy evolution at 1549 nm, respectively; (d)–(f) pulse evolution, fine structure of the overall pulse in 300th round-trip (inset: zoomed-in sub-pulses of the overall pulse), and mode energy evolution at 1551.5 nm, respectively.