▎ 摘　　要

The electro-optic modulator is an important component in many low cost optical applications especially the ones based on micro-ring for their micromation, low loss etc. In order to enlarge the free spectral range and extinction ratio, a U-shaped structure is introduced in the traditional micro-ring electro-optic modulator. Besides, the double-layer graphene separated by a thin insulating layer is used as the tunable material, because its conductivity can be varied upon injection of carriers at optical frequencies. Through numerical simulations, we show that when the distance between two coupling points is equal to the circumference of micro-ring, the FSR is about 130 nm which can reduce the crosstalk in signals during electro-optic modulation greatly. And at the resonance point near lambda = 1550 nm, when the chemical potential of graphene declines from 0.5 eV to 0.3 eV, the extinction ratio (ER) is about 17dB, also the modulation depth (MD) reaches 98%. In addition, the modulator can be operated with driving voltages below 1.2 V through mainly adjusting the refractive index of the insulating layer. These results promise an efficient electro-optic modulator which will contribute to the applications in large scale on-chip optical interconnects.