Passively Q-Switched Yb-Doped All-Fiber Laser With a Black Phosphorus Saturable Absorber

We report two kinds of Q-switched Yb-doped fiber lasers based on a black phosphorus saturable absorber (BP-SA). The BP-SAs are prepared by two different methods, one of which is the mechanical exfoliation method and the other is the liquid-phase exfoliation method. The BP-SAs are inserted into the all-fiber Yb-doped oscillation cavity in different forms. We have experimentally shown that the passively Q-switched pulse trains could be obtained by the two methods. First, we achieve the Q-switched pulse in 1029.63 nm by using a few-layer black phosphorus sheet. The fiber laser was capable of generating pulses with a maximum average output power of 13.12 mW and a repetition rate of 79.46 kHz, corresponding to the maximum single-pulse energy of 165.11 nJ and the shortest single-pulse width of 1.55 μs. In addition, we obtain narrower pulsewidth by dropping the black phosphorus solution onto the tapered fiber. The maximum single pulse energy of 114.72 nJ and the minimum pulsewidth of 1.09 μs were obtained. The repetition rate ranges from 49.13 to 101.3 kHz.