(a) Schematic diagram of double-layer graphene-based THz modulator. (b) Measured transmission of the peak THz field as a function of gate voltage under different photoexcitation powers (continuous wave laser at 532 nm). Measured (c)–(e) and simulated (f)–(h) transmission with different gate voltages under photoexcitation power of 140, 280, and 420 mW, respectively.^[62] Figure reprinted with permission: Ref. [62], ©2015 by Springer Nature.