Terahertz six-channel metasurface for dynamic modulation of OAM

Abstract Dynamic wavefront modulation enables performance enhancement of optical device. Few reports have achieved dynamic wavefront modulation of orbital angular momentum (OAM). In this work, dynamic modulation of six-channel OAMs is realized. As VO2 is metallic, metasurface realizes OAM with the mode of l = -3 in left-hand circularly polarized (LCP) co-polarized reflection channel. In right-hand circularly polarized (RCP) co-polarized reflection channel, a vortex beam is generated with the mode of l = -1. In circularly polarized (CP) cross-polarized reflection channels, OAMs are generated with the mode of l = -2. Relatively, as VO2 is insulating, OAM is presented with the mode of l = 1 in LCP co-polarized reflection channel. In RCP co-polarized reflection channel, a vortex beam is achieved with the topological charge of l = 3. In CP cross-polarized reflection channels, obtained OAMs have the mode of l = 2. As a result, our design has a flexible multi-channel characteristic. Further, it shows considerable application value in beam shaping and optical encryption.