▎ 摘　　要

Based on nonlinear optical measurement on graphene sheet stacks, we find that graphene sheet stacks exhibit low reflectivity, which increases with an increase of incident laser intensity as a consequence of saturable absorption. By virtue of this nonlinear optical property, graphene sheet stacks are further employed to passively Q-switch an erbium-doped fiber laser, wherein stable Q-switched laser operation with a single pulse width of 10.4 mu s, pulse repetition rate of 13.8 kHz and central wavelength of 1530 nm was finally achieved. This constitutes the first application of the nonlinear reflectivity property of graphene sheet stacks.