▎ 摘　　要

We demonstrate an all-optical Q-switcher based on graphene saturable absorber (GSA). Due to the cross absorption modulation (XAM) effect in graphene, we can change the transmittance of signal light periodically by introducing a train of laser pulses into graphene. This allows controlling the Q-factor of the cavity. This Q-switcher has many advantages such as all-fiber structure, all-optical modulation, broadband applications. With this Q-switcher, we have successfully fabricated an actively Q-switched ytterbium-doped fiber laser. The pulse repetition rate can be tuned from 30.32 kHz to 101.29 kHz. What's more, synchronization of the Q-switched laser pulses and modulation laser pulses can be realized, which has many potential applications such as nonlinear frequency conversion, multi-color pump probe spectroscopy and Raman scattering spectroscopy. (C) 2015 Optical Society of America