▎ 摘　　要

We propose and demonstrate a saturable absorber based on a slightly tapered graded-index multimode fiber covered with graphene for passively mode-locked fiber laser pulse generation. Compared with the slightly tapered graded-index multimode fiber device without graphene covering, the modulation depth of the proposed SA is increased by 5.6%, the pulse duration is shortened by 341 fs, and the signal-to-noise ratio is increased by 5 dB and as a result, an ultrashort mode-locked pulses with a center wavelength of 1567.09 nm, a 3 dB bandwidth of 4.43 nm, a signal-to-noise ratio of 80 dB, and a pulse duration of 709 fs are obtained. The combining of two types of SAs, graphene and graded-index multimode fiber, provides an effective way for obtaining stable ultrashort pulses with improved performance.