(color online) Corresponding width of graphene for cavity resonance mode. (a) The calculated near-field amplitude in graphene resonator with different widths under the incident frequency of 930 cm⁻¹. The schematic of simulation model is shown in inset. We record the amplitude in the center of graphene (shown as purple area). (b) Numerically simulated amplitude in the graphene center for different widths and incident frequencies (background color). The discrete dots show the experimental W_Gra for cavity modes extracted from Fig. 2. The consistency between experimental results and numerical simulations indicate that we observe and control the cavity mode of graphene plasmons.