Fig. 1. Schematic of experimental setup of passively mode-locked Yb-doped fiber laser with long cavity

Fig. 2. Dynamic evolution of square pulses under different pump powers

Fig. 3. Measured pulse duration and output single pulse energy versus pump power

Fig. 4. Output square pulse under pump power of 414.47 mW. (a) Single pulse profile; (b) optical spectrum; (c) RF spectrum; (d) pulse train

Fig. 5. Comparative experimental results of cavity length. (a)(c)(e) Dynamic evolutions of square pulse profile when cavity lengths are 502,1002, and 1502 m; (b)(d)(f) measured pulse duration and output single pulse energy versus pump power when cavity lengths are 502, 1002, and 1502 m

Fig. 6. Results of experiment and simulation. (a) Profiles of DSR square pulses from lasers with different cavity lengths under 181.47 mW pump power; (b) numerical simulation results