Metasurfaces, composed of prearranged artificial unit cells possessing different electromagnetic (EM) responses, provide unprecedented abilities to realize versatile wave manipulations. Especially in the terahertz spectrum, metasurfaces attract broad attention by opening up further possibilities for wave regulating. Terahertz applications in various fields, for instance, spatial light modulation (SLM), radar, imaging, time-domain spectroscopy (TDS), and high-speed communication, have been

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... tated and improved. In this article, we first give a simple review on recent advances on terahertz metasurfaces, including discussion of passive metasurfaces with fixed structures and active metasurfaces integrated with tunable components. Then, we briefly review the development of coding metasurfaces and programmable metasurfaces represented by digitized bits. We mainly focus on some powerful functions, functional multiplexing, and real-time controlled applications in terahertz frequencies. Finally, we give an abbreviated overview of developing terahertz multifunctional metasurfaces and programmable metasurfaces. Keywords: terahertz metasurface, passive metasurfaces, active metasurfaces, coding and programmable metasurfaces, real-time multifunctional control FIGURE 4 | (A,B) Illustration of the metasurface to achieve OAM multiplexing and demultiplexing. (C,D) Simulation and experimental amplitude profiles of OAM multiplexing. Reproduced with permission from [20]. Frontiers in Physics | www.frontiersin.org