Polarization multiplexing and bifocal optical vortex metalens

In this article, we demonstrate several optical vortex metalens (OVMs) based on the Pancharatnam-Berry (PB) geometric phase concept utilizing silicon nanobricks. The nanostructured OVMs are designed via coalescing the phase profiles of metalens and vortex phase plate, which can produce and focus the vortex beam simultaneously. Through analyzing four single-focal OVMs suitable for left circularly polarized (LCP) or right circularly polarized (RCP) incident light respectively, we find that the topological sign of vortex light is strongly associated with polarization state of incident light. Through multiplexing two OVMs only suitable for one kind of circularly polarized light, we design one polarization multiplexing OVM, which can focus different circularly polarized (CP) vortex beam to the same position. We also design one longitudinal bifocal OVM, which can focus LCP vortex beam to the different positions. Thus, these OVMs have the promising applications in integrated optics, classical and quantum optics, and vortex optics.