Metasurfaces with continuous ridges for inverse energy flux generation

In this study, we propose a new approach to construct metasurfaces for the generation of inverse energy flux near the optical axis. We derive new equations intended to create continuous subwavelength relief for transformation of a linearly polarized input field into a radially polarized beam with an arbitrary order. Proposed metasurfaces combine the polarization converter as subwavelength gratings with a varying period and the focusing element as additional structure. Such a combination increases polarization conversion efficiency and decreases the number of optical elements in an arrangement. Numerical simulations of the proposed metasurfaces, based on the finite element method, show that the higher-order polarization conversion provides the greater integrated inverse energy flux. Moreover, the shape of the inverse flux area achieved with the higher-order metasurface is annular and has bigger force area.