Quasi-optical polarization beam splitters are important components of terahertz instrumentation widely used in interferometric and polarimetric measurements. Recently metasurfaces, i.e. two-dimensional periodic or quasi-periodic optically dense structures composed of unit cells with subwavelength dimensions, have been shown to operate as compact and efficient beam splitters. Typically, their design was based on careful optimization of anisotropic metal or dielectric resonant scatterers confined in each unit cell. In this work, we propose and experimentally demonstrate a simple and useful approach to designing circular-polarization beam splitters taking advantage of intrinsically frequency-independent properties of single-layer self-complementary metasurfaces (SCMSs). Theoretically, when illuminated with a circularly polarized beam, any SCMS at any frequency transmits a co-polarized beam with a complex transmission coefficient of 1/2. At the same time, a cross-polarized beam of the same magnitude is produced, which transmission phase can be controlled at every point of a metasurface aperture. In this work, to split the co- and cross-polarized transmitted beams, we spatially modulate this phase by constructing a spatially-nonuniform metasurface of self-complementary unit cells. With this approach we experimentally demonstrate a focusing circular-polarization beam splitter operating near 0.345 THz.
|Журнал||IEEE Transactions on Terahertz Science and Technology|
|Состояние||Опубликовано - 6 ноя 2020|