Fig. 1. （a） Schematic diagram of our proposed device，（b） schematic diagram of mode conversion structure，（c） cross-sectional schematic diagram of the graphene modulator

Fig. 2. （a） Under the wavelength of 2.95 μm， 3 μm， 3.05 μm， the in-plane dielectric constant changes with the applied voltage，（b） the variation of the absorption coefficient for both TE₀ and TM₀ mode of graphene modulator under different chemical potential

Fig. 3. （a） The variation of effective refractive index for the first five modes in the width range from 1.4 μm to 3.4 μm，（b） analyzing the influence on coupling efficiency by sweeping the coupling length，（c） analyzing the influence on conversion efficiency by sweeping the length of three parts

Fig. 4. （a） The variation of insertion loss of various parts for the device under the wavelength from 2.95 μm to 3.05 μm，（b） the normalized transmission of the device under the wavelength from 2.95 μm to 3.05 μm