Generating high-purity orbital angular momentum vortex waves from Cassegrain meta-mirrors

Cassegrain meta-mirrors are proposed to generate the orbital angular momentum (OAM) vortex waves through dual-reflecting system with two-planar grounded meta-surfaces of properly devised sub-wavelength ring patches. More specifically, electromagnetic fields reflected by the secondary meta-mirror would subsequently be collimated by the primary meta-mirror and transformed into the well-converged OAM vortex waves possessing the merits of high directivities with clear helix wave-fronts. We extend such a design into conformal Cassegrain systems having the primary meta-mirrors of concave and convex profiles, respectively, and also demonstrate excellent syntheses of OAM vortex beams. Our design, using the dual-reflecting meta-mirrors to generate high-purity OAM vortex waves, can obtain the radiations with more stable angular momentum numbers in the long-distance propagation for the OAM wireless communications.