Photoelectrically-excited terahertz metasurface for switchable and tunable broadband propagation and polarization manipulations

Currently, a single metasurface with actively switchable and tunable multifunctions has arisen in more and more interest. However, the existing metasurfaces suffer usually from the issues of limited functions due to a single active material used, seriously restricting their advancements and applications. Here, a photoelectrically-excited metasurface, composed of a multilayer configuration including two patterned graphenes (PGs) and a photosensitive silicon layer as well as two dielectric layers, is proposed to execute switchable and tunable propagation and polarization manipulations in a broadband terahertz range. By applying different external excitations, the proposed terahertz metasurface can realize an actively switchable tetra-functional device including broadband modulator, absorber, half-wave plate (HWP), and quarter-wave plate (QWP). Moreover, these functions can implement flexible modulation by changing the combined ways and intensities of the external excitations individually or simultaneously. In addition, field distributions are used to discover the physical natures of broadband absorption and polarization conversions. Therefore, the integration of a single terahertz metasurface with multiple functional materials provides a new design platform for actively multifunctional and multidimensional controlled devices capable of promoting the integration and miniaturization of terahertz systems.