Two types of ultrafast mode-locking operations generation from an Er-doped fiber laser based on germanene nanosheets

Saturable absorbers as passive modulators in passively mode-locked fiber lasers play a crucial role in the generation of ultrashort pulses. Germanene, a graphene-like two-dimensional material with fast carrier relaxation time and large nonlinear absorption coefficient comparable to that of graphene, is a saturable absorber material with very fast response.