An efficient planar meta-lens as converged vortex beam generator in microwave region

In this paper, single-layer transmission-type metalens is proposed to generate a converged vortex beam. A new meta-lens design is used to generate the vortex beam, in which the required accumulated phase difference along the propagation path is realized by designing and arranging artificial single-layer unit cells. Furthermore, the converged vortex beam is generated theoretically and experimentally by metasurface that superimposes the phase distribution for the vortex beam and converged beam. The transmitted efficiency of the meta-lens can reach 20% as designed, which approaches to the efficiency limit of this type of metasurface.