Active modulation of terahertz vortex beams by Dirac semimetals-based space–time-coding​ metasurface

Abstract

Coding metasurfaces have developed rapidly in the last few years because of the digital thought. Recently, spatiotemporal metasurface have attracted considerable attention for the additional degrees of freedom they provide when manipulating electromagnetic waves in space and time domains. This study proposed Dirac semimetal based space–time-coding metasurfaces in the terahertz band. The conversion from a low- to high-bit programmable metasurface was achieved using a spatiotemporal metasurface, that is, 2-bit coding was equated to 3-bit coding. Space–time-coding metasurfaces facilitated the realization of the function of wide-band terahertz vortex beam generator switching according to the vortex phase arrangement, and were combined with the convolution theory for the successful realization of the modulation of terahertz vortex deflection and beam splitting under space–time coded modulation. The modulation of the equivalent 3-bit vortex beam produced under space–time coded modulation considerably reduced the gain of the side lobes and achieved precise modulation of the terahertz vortex beam. Moreover, the principle and method proposed in this study are also applicable to microwave and visible wavelengths. The results of this study are expected to result in promising applications in future terahertz high-data-capacity communication systems and multi-target precision tracking and guidance.