Fig. 1. Experimental setup of ytterbium-doped NPR mode-locked fiber laser (seed pulse part)

Fig. 2. Experimental setup of nonlinear ytterbium-doped fiber amplifier (amplification part)

Fig. 3. Seed pulse spectra of DSs at different polarization states with center wavelengths from 1027 to 1041 nm.(a) 1027 nm; (b) 1030 nm; (c) 1033 nm; (d) 1036 nm; (e) 1039 nm; (f) 1041 nm

Fig. 4. Radio frequency spectrum of seed pulse

Fig. 5. Auto-correlation curves of DSs seed pulse

Fig. 6. Output spectra of YDFA with seed pulse central wavelength from 1027 to 1041 nm (dB spectrum). Inset is local enlarged drawing from 1050 to 1250 nm

Fig. 7. Output spectra (dB spectra) with different length of DCYDFs when center wavelength of seed pulse is 1041 nm

Fig. 8. Output spectra of YDFA versus pump power when center wavelength of NPR seed pulse is 1041 nm and length of DCYDF is 8 m. Inset is the widest output spectrum of YDFA with pump power of 14 W