Generation of various vortex beams based on transformation materials

A flexible vortex beam generator (VBG) is proposed based on transformation optics (TO) to convert input plane waves to various output vortex beams. The methodology is a geometrical one based on the topological equivalence between the vortex beam cross section disc and a belt, turning the in-plane curvilinear distributed phase or polarization structures in the disc to be redistributed around the belt. Consequently, abundant vortex beams can be exported by simply configuring the incidence angles and polarization directions of the plane waves. The topology and wave propagation characteristics behind the system are investigated, and TO is used to obtain the desired materials by adopting a specific space mapping. Some sample numerical simulations are described to verify the feasibility of the proposed design, including several complex orbital angular momentum and cylindrical vector beams. Due to its flexibility and simplicity, the proposed VBG is likely to have extensive application prospects.