▎ 摘　　要

We demonstrate an optically tunable graphene saturable absorber to manipulate the laser operation in pulsed fiber laser system. Owing to the strongly enhanced evanescent field interaction with monolayer graphene, we could realize an efficient control of modulation depth in the graphene saturable absorber by optical means through cross absorption modulation method. By integrating the tunable graphene saturable absorber into the fiber laser system, we could switch the laser operation from Q-switching through Q-switched mode-locking to continuous wave mode-locking by adjusting only the optical power of the control beam. In addition, we realized a hybrid Q-switching of fiber laser by periodical modulation of the absorption of the graphene saturable absorber, where we observed that the repetition rate of the Q-switched laser could be continuously tuned according to the modulation frequency of the applied external signal. (C) 2016 Optical Society of America