  Black phosphorus (BP) with its enticing electric and optical properties is
intensely researched in the field of optoelectronics. In this paper, Q-switched
pulses at 1550 nm and 2 um wavelengths are obtained by inserting
bulk-structured BP based saturable absorber (SA) into an erbium-doped fiber
laser (EDFL) and an thulium/holmium-doped fiber laser (THDFL), respectively.
The BP-SA was prepared by depositing powered BP material on to the flat side of
a side-polished single mode fiber. Q-switched 1550 nm pulses with width tuned
from 9.35 to 31 us were obtained for the EDFL. For the THDFL, over 100 nm
wavelength range could be achieved from 1832 to 1935 nm by adjusting the pump
power. To the best of our knowledge, these results demonstrated the broadband
saturable absorption property of BP and for the first time verified that BP as
a new two-dimensional material for applications in saturable absorption
devices.
