▎ 摘　　要

In this paper, two graphene-based all-optical terahertz (THz) modulators are proposed. The operations of the structures are based on high quality factor (Q-factor) resonances in graphene-dielectric metasurfaces. The first modulator is a polarization-dependent metasurface where a sharp resonance is originated from the effect of electromagnetically induced transparency. The structure is analyzed using the finite element method. The modulation is performed by photoexcitation of carriers in graphene by infrared optical pumping. Interestingly, owing to the stimulated emission of THz photons, a high transmission change of more than 120% and a high modulation depth of 93% at the frequency of 5THz are obtained. The second structure is a polarization-independent modulator that operates based on a high Q-factor Fano resonance in asymmetric dielectric disks. It is presented that a high modulation depth of 98% is achieved. The required optical intensity for both structures is calculated to be as low as 7.35W/cm(2). As the proposed graphene-based metasurfaces are optically tunable, they are promising for the realization of fast and efficient spatial THz modulation.