Controllable terahertz radiation from electrically tunable plasmonic metasurfaces based on multiple quantum wells

Subwavelength plasmonic metasurfaces combined with multiple quantum wells (MQWs) heterostructures have recently demonstrated highly efficient nonlinear wave generation under low power input intensities. They can pave the way for developing highly efficient, compact, tunable and room temperature terahertz (THz) wave sources through the mixing and down-conversion of optical incident pumps. In this paper, we study and analyze the electrically controllable THz radiation of a nonlinear metasurface loaded with MQW through difference frequency generation (DFG) process. An analytical formulation procedure based on the effective nonlinear susceptibility model and free-space Green's function is proposed for derivation of generated THz wave radiation pattern. Also, we demonstrate phase and amplitude variation of intrinsic second-order nonlinear susceptibility coefficient of MQW by applying different bias voltages. Far-field directivity pattern of DFG radiation from the linear array configuration of plasmonic nonlinear metacells is obtained at 5.5 THz through the proposed analytical method and is verified by full-wave analysis. Using the proposed electrical tunability of MQW nonlinear susceptibility, THz beam steering of the nonlinear metasurface is demonstrated which is rotated from -20 to 20 degree through different bias voltages. Our work proposes an effective tool for rapid and accurate design and analysis of highly efficient THz electrically tunable MQW nonlinear metasurfaces for future applications in THz wireless communications, spectroscopy and quantum imaging.