(a) Schematic diagram of the ion gel gated graphene THz modulator. (b) Positive square-wave voltage applied to the graphene (top panel) and time response of the modulator under 1-, 0-, and 0.5-V gate voltages (low panel). Red lines show the results of fitting. (c) Negative square-wave voltage applied to the graphene (top panel) and the time response of the modulator under –1.0-V, –0.5-V, and –0.2-V gate voltages (low panel), respectively.^[59] Figure reprinted with permission: Ref. [59], ©2019 by the Elsevier Publisher.