Figure 1. Principle of the dispersion engineering for polarization conversion.

(a) Concept diagram of proposed metamirror, which is composed of a metasurface, dielectric spacer and metallic ground plane. To make the analysis as general as possible and suitable for both isotropic and anisotropic metamaterials, we take the metasurface as a thin impedance sheet without special structure, which is normally illuminated with a linear polarization. The amplitude of incident E field is denoted as A while the total reflection coefficient of the metamirror is denoted as S_ii. J is the current flowing in the metasurface. (b) Unit cell of adopted metasurface, which is constructed by two split ring resonators sitting back to back positioned on a thin substrate. (c) Perspective view of proposed metamirror, which is able to convert the LCP waves achromatically to the RCP after reflection.