Terahertz Wavefront Control on Both Sides of the Cascaded Metasurfaces

In this paper, two kinds of cascaded metasurfaces are proposed for the simultaneous control of the reflected and transmitted wavefronts in the terahertz (THz) frequency band. First, an array of arrow-shaped elements backed by a strip grating is investigated. When the polarization of the incidence field is parallel to the orientation of the strip grating, the reflected and transmitted waves with approximately equal amplitude will be generated and there is a constant phase difference between them when the element dimensions are varied. Proved by the simulation and measured results, the metasurface based on the proposed element can simultaneously deflect the transmitted and reflected wavefronts but only by the same angle. Second, independent control of both amplitudes and phases of the transmitting and reflecting waves is achieved by cascading four metallic layers in order, i.e., a y-oriented strip layer, a y-directed grating layer, the arrow-shaped element, and an x-directed grating, with respect to different polarizations of the incident field. The simulation and measured results show that the y-polarized incident waves can be reflected by the four-layered metasurface into a designed reflection angle, while the x-polarized incident waves can be focused on the other side of the metasurface in a transmitting manner. Compared with the reported THz metasurfaces, the proposed elements can provide more advanced wavefront-control ability and they also feature the advantages of compact size, low cost, and lightweight. Therefore, the proposed metasurfaces can be applied as beam splitters for low-cost and compact THz imaging and detection systems.