An all-fiber passively Q-switched Yb-doped fiber laser with fiber saturable absorber (SA) based on a piece of Sm-doped fiber is presented. For the first time, we observe the fast stimulated Brillouin scattering Q-switched process in an Yb/Sm all-fiber laser and obtain 41 ns pulses and 1.7 kW maximum peak power. Compared with the reported traditional SA Q-switched process, the pulse energy and peak power are both improved an order of magnitude. Furthermore, a traditional SA Q-switched process with 450 ns pulsewidth and 7.5 W peak power is also obtained in the same structure by increasing the feedback of cavity's output end.
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