▎ 摘　　要

Electro-optical modulators, working at near-infrared range are a key device in modern optical system. Modulation speed is an important parameter to evaluate the performance of an electro-optical modulator. However, the modulation speed which is controlled by contact resistance and quantum capacitance of a graphene-based modulator is difficult to calculate in previous numerical simulation. In this paper, we proposed a method based on a simple structure to calculate the modulation speed. The simulation results show that the modulation speed is approximate 1.2 GHz which is consistent with the experimental results. And the dependence of the modulation speed on the effective oxide thickness (EOT) and doping of graphene are investigated in our work. Meanwhile, we optimize the structure parameters of modulator to promote the modulation speed which can be increased to similar to 3.6 GHz. The proposed method to evaluate and optimize the modulation speed could have many applications potential for various graphene-based devices.