▎ 摘　　要

Graphene is a superb material with significant potential in broadband all-optical modulation. However, the mechanism of the all-optical modulation in graphene dispersion is still under debate. Here, we report on a pump power-dependent spatial light modulation by using the 780 nm CW laser as the pump and signal beams via graphene dispersion. The results indicate that graphene is able to convert the Gaussian signal beam into a hollow beam with a ring pattern. Examining the temporal evolution of the ring pattern, we found that spatial cross-phase modulation (SXPM) plays the dominant role at low pump power, while nonlinear scattering (NLS) becomes dominant when the pump power is high. Furthermore, the dependence of the size and intensity of the signal ring pattern on the pump power is investigated. The results can be well explained by SXPM, NLS, and saturation absorption (SA) effects. Finally, an all-optical switch is developed based on the dependence of the signal intensity on the pump power. It is demonstrated that both in-phase and out-phase modulation can be realized in one system. This work not only provides useful information in understanding the mechanism of graphene in interacting with the light, but also suggests a new way to produce hollow beam with tunable size and achieve an all-optical switch with both inphase and out-phase modulation.