Germanene Nanosheets As Saturable Absorbers for Soliton Rains and Large-Energy Pulse Generation in Passively Mode-Locked Fiber Lasers

Germanene (Ge), as one kind of Xene, possesses excellent nonlinear optical and photoelectric properties. In this paper, Ge nanosheets (Ge-NSs) were prepared and utilized as saturable absorbers in an Er-doped fiber laser to successfully achieve soliton rain and large-energy pulse modulation. The operation of a soliton rain pulse was achieved at a pump power of 34 mW. The number of drifting solitons gradually increases with increasing pump power. By increasing the pump power to 90.8 mW and adjusting the polarization controller, the second and third harmonic soliton rain phenomena can also be produced. Stable large-energy pulse output was obtained at pump powers ranging from 125.3 to 585.2 mW, with a maximum pulse energy of 12.75 nJ and a maximum pulse width of 120.08 ns. The research results show that Ge-NSs can be used as excellent optical modulators for studying multiple soliton dynamics and generating large-energy pulses, which have great potential for applications in nonlinear photonics.