We have investigated the broadband saturable absorption property of graphene– heterostructures and demonstrated their applications for stable harmonic mode-locking operation in a Yb-doped fiber laser and wavelength-tunable Q-switching operation in an Er-doped fiber laser. The modulation depth of a graphene– heterostructure saturable absorber () is dependent on the coverage of on the graphene. By using -covered with a modulation depth of 23.28% and saturable intensity of , the harmonic mode-locked Yb-doped fiber laser outputs the mode-locked pulses with a pulse duration down to 189.94 ps, spectral bandwidth of 3.5 nm, and repetition rate of 79.13 MHz (21st order of the fundamental frequency). After inserting the with 85% coverage of on graphene into Er-doped fiber laser cavity, whose modulation depth and saturable intensity are about 40.79% and , respectively, the wavelength-tunable Q-switched pulse with tunable wavelength range over 13.2 nm has been obtained by adjusting the intracavity fiber filter. These results suggest that the graphene– heterostructure could serve as a high nonlinear photonic device for practical applications.