Fig. 1. Different application scenarios and control methods of terahertz wavefront control with metasurface

Fig. 2. Terahertz metasurface deflectors and lenses. (a) Terahertz metasurface deflector^[8]; (b)(c) terahertz metal metasurface lens^[10,12]; (d) terahertz Huygens metasurface lens^[25]; (e) terahertz achromatic metasurface lens^[32]

Fig. 3. Terahertz holographic metasurfaces. (a) Terahertz holographic metasurface with simultaneously modulated amplitude and phase^[40]; (b) longitudinal movement of holographic pattern from terahertz metasurface^[41]; (c) terahertz holographic metasurface with full-parameter control^[42]; (d) terahertz chiral holographic metasurfaces^[43]

Fig. 4. Terahertz multiplexing devices. (a) Terahertz polarization multiplexing active multifunctional device^[47]; (b) terahertz polarization multiplexing metasurface^[48]; (c) terahertz mode division multiplexing device^[54]; (d) terahertz OAM multiplexing device^[55]

Fig. 5. Terahertz special beams. (a) Terahertz Bessel beam^[25]; (b) terahertz Airy beam^[62]; (c) terahertz vortex beam^[65]; (d) terahertz Lorentz beam^[67]

Fig. 6. Nonlinear terahertz wavefront control. (a) Control of wavefronts with nonlinear terahertz photonic crystals^[74]; (b) nonlinear terahertz optical beam splitting and vortex beam generation^[76]; (c) nonlinear terahertz Fresnel bands sheet^[77]; (d) nonlinear terahertz chirality and nonlinear metasurfaces^[79]

Fig. 7. Terahertz surface plasmon polariton couplers. (a) Surface plasmon excitation unit^[100]; (b) polarization dependent coupler (the wavefronts are different under normal incidences of circular polarization with different directions of the rotation)^[100]; (c) surface plasmon lenses based on slit-pair column^[101]; (d) complex surface plasmon holography imaging^[102]; (e)(f) surface plasmon polariton coupler consisting of C-shape slit resonators^[103]

Fig. 8. Terahertz surface plasmon polariton couplers. (a) A coupled resonator pair composed of a slit resonator and a split-ring shaped resonator can realize asymmetric excitation^[104]; (b) surface plasmon polariton focusing structure using resonant coupler as the basic unit^[104]; (c) split-ring shaped resonator with mirror distribution^[105]; (d) asymmetric excitation under different polarized light incidence^[105]

Fig. 9. Plasmonic vortex. (a) Plasmonic vortex generated by circular-shaped slit arrays and Archimedes spiral-shaped slit arrays^[111]; (b) two plasmonic vortices generated by controlling geometric phase^[112]; (c) two plasmonic vortex couplers generated from two circular-shaped slit arrays with different radius^[113]; (d) arbitrary topological charge resulted from the interference between plasmonic vortices came from two couplers^[113]; (e)(f) temporal evolution progress of plasmonic vortices controlled by couplers with different structures^[114]

Fig. 10. Spoof surface plasmon polariton functional devices. (a) A series of waveguides based on spoof surface plasmon polaritons: straight waveguide, S-bend waveguide, Y-splitter and directional coupler^[123]; (b) logic gate^[125]; (c) wavelength diplexer^[96]; (d) 1×2 splitter with controlled splitting ratio^[126]; (e) (f) spoof surface plasmon polariton lenses based on gradient index^[127-128]