Ultra-thin metalens generating coverging vortex beam in microwave region

In this paper, a planar ultra-thin metalens is proposed to generate converging vortex beam carrying orbital angular momentum (OAM) in microwave region. Phase changes are introduced to manipulate the transmitted wave front by designing rotation angles of Pancharatnam-Berry phase unit cell. Based on the superposition of phase profile of converging lens and spiral phase plate, the converging vortex beam with OAM mode can be generated by proposed metalens in microwave region. The measurement results are in good accordance with simulation results, which verify the theoretical design procedures.