Multifunctional Metasurfaces for Bridging Terahertz Waves in Free Space and Waveguides

ABSTRACT Metasurfaces integrated with transmission devices like waveguides can realize versatile control of guided waves and significantly enhance the integration level of terahertz systems. Here, a multifunctional terahertz metasurface, which enables simultaneous orthogonal polarization conversion and phase modulation, is attached to dielectric slab waveguides to achieve efficient coupling from free‐space waves to guided modes. By further constructing customized phase gradients on the metasurface, the formation of a focused spot within the waveguide is successfully demonstrated. The measured focusing results are in good agreement with the simulations. This multifunctional metasurface provides a novel strategy for converting free‐space terahertz waves into guided modes, offering significant value for the development of integrated terahertz photonic devices.