▎ 摘　　要

In this paper, two double-layer graphene optical modulators based on all-dielectric metasurfaces are proposed. The double-layer graphene modulators remove the requirement of doped silicon back gates which would cause excessive loss and limit the modulation speed. The first structure is based on the electromagnetically induced transparency phenomenon, and the second one is a polarization-independent modulator that is based on the Fano resonance. The structures are simulated and analyzed using the finite element method. According to the simulation results, large modulation depth of about 95% at the wavelength of 1.55 mu m can be obtained. The required voltages of 4.95 V are obtained for both of the modulators. By assuming the device of 50 x 50 unit cells, the 3 dB bandwidth of the first (second) structure is calculated as 630 MHz (482 MHz). It is estimated that by improving the quality of graphene, the 3 dB bandwidth of more than 2 GHz could be attained. The achieved modulation performances are much better than the previously reported free-space modulators with the same device area. The proposed high-performance optical modulators are promising for free-space optics technology especially free-space optical communication networks. Published under license by AIP Publishing.