Breaking Bullseye’s Symmetry for Axial Field Focusing

Abstract

We propose a bullseye type device capable of coupling the incident linearly polarized THz waves and focusing the axial electric field component. In order to avoid the destructive interference of the axial field occurring at the center of classic bullseyes, we introduce a spatial π -phase shift on half part of it. The device is a simpler alternative than the use of classic bullseyes illuminated by a radially polarized incidence wave for the generation of axial field.