THz phase modulation with broadband metasurfaces for controlling light propagation

The ultra-thin phase metasurface structures based on the complementary square split ring nanoantenna have been proposed to achieve the THz optical metalenses with multi-dimensional and multi-focusing. The Fabry–Pérot resonance mode could be usefully employed in explaining the principle of beam propagation and efficient transmission. The THz metalens can transfer the linear cross-polarization efficiently under the effect of the gratings on the incident plane. By locally tailoring edge lengths and opening angles of the split rings, full control over abrupt phase changes can be achieved. Two symmetrically distributed parallel focal spots and two vertical focal spots with arbitrary distance are obtained by arranging the SSRs units on the metalenses. Furthermore, we apply the concept of partitioned phase mode to realize the double-focusing metalens in the longitudinal direction, which provides a flexible and convenient method for focusing properties.