Fig. 1. Experimental setup for kilowatt-level narrow-linewidth thulium doped fiber amplifier

Fig. 2. Time domain and frequency domain of PRBS signal when n=7. (a) Time domain; (b) frequency domain

Fig. 3. Kilowatt narrow-linewidth thulium-doped fiber laser performances. (a) Laser output and backward powers of thulium doped fiber amplifier versus pump power at seed source linewidth of 480 MHz; (b) forward and backward laser spectra at maximum output power; (c) wide-band laser spectrum at maximum output power

Fig. 4. Relationship between SBS threshold enhancement factor and PRBS7 signal modulation parameters. (a) SBS threshold enhancement factor versus PRBS7 signal modulation frequency under different filter bandwidths; (b) theoretical and experimental SBS threshold enhancement factors versus seed source laser linewidth when modulation frequency is 1 GHz