Fig. 1. High power mode-locked multi-mode fiber laser^[15]. (a) Schematically shows the coupling between the fundamental mode and higher order modes in the fiber core; (b) the experimental setup schematic of the high power mode-locked Tm³⁺-doped fiber laser; (c) schematically shows the simulated intensity profile of several spatial modes and the final overlapped one in this multi-mode fiber laser; (d) schematically indicates the temporal pulse

Fig. 2. Some typical reports on the output pulses width of mode-locked fiber lasers based on low-dimensional nanomaterials in recent years^[17-27]

Fig. 3. Passive mode-locked fiber laser based on BP^[17]. (a) SEM image of fiber connector with visible BP layer covering the core and clad; (b) experimental setup schematic of passive mode-locked fiber laser based on BP; (c) optical spectra of the laser (red line) together with the water absorption lines taken from the HITRAN database (blue line) and the inset is the spectrum measured in wide 60 nm span; (d) autocorrelation trace of the 739 fs pulse gene

Fig. 4. Passive mode-locked Ho-doped fiber laser based on graphene^[21]. (a) Experiment setup schematic of passive mode-lockedHo-doped fiber laser based on graphene; (b) output optical spectra evolution as a function of the net cavity dispersion

Fig. 5. Some typical reports of mode-locked fiber laser based on NPR about pulse width and energy relationship for intra-cavity net dispersion^{[5,28-31,32-33]}

Fig. 6. Schematic of NALM mode-locked Tm-fiber laser and the corresponding group dispersion delay in cavity as well as the normalized ASE spectrum^[35]. (a) Schematic of the laser; (b) group dispersion delay in cavity as well as the normalized ASE spectrum

Fig. 7. Typical spectra and the corresponding interference autocorrelation trace of the oscillator in different mode-locking regions. (a)(c)(e) Typical spectra, the orange regions are the spectra from simulation; (b)(d)(f) autocorrelation trace, the orange regions correspond to the calculated intensity autocorrelation trace of the transform-limited pulse

Fig. 8. Experiment setup schematic of mode-locked Er³⁺-doped fluoride fiber laser based on NPR and autocorrelation trace and phase^[39]. (a) Experiment setup schematic; (b) autocorrelation trace and phase

Fig. 9. Simplified energy level diagram of erbium ions under a dual wavelength pump

Fig. 10. Tunable picosecond mode-locked Dy³⁺ ZBLAN fiber laser^[55]. (a) Experiment setup schematic of mode-locked Dy³⁺-doped ZBLAN fiber laser; (b) characteristic spectra within the mode-locked FSF laser's 330 nm tuning range (arbitrarily shifted in intensity for visual clarity); (c) spectral shapes between Q-switched and mode-locked operation

Fig. 11. Schematic of chirped pulse amplification

Fig. 12. Schematic of the relationship among the repetition frequency, pulse energy, and corresponding pulse width of CPA systems reported in recent years^[57-74]

Fig. 13. High-power thulium-doped fiber chirped pulse amplification system^[58]. (a) Experimental setup schematic of the high-power thulium-doped fiber chirped pulse amplification system; (b)(c) measured intensity autocorrelation signal and frequency spectrum at 1060 W average output power after compression; (d) measured average output power at a 1960 nm center wavelength before and after Treacy compressor versus launched pump power at 793 nm; (e) M