Sub-terahertz wideband vector beam generator based on superwavelength lattice dielectric grating

Abstract

Segmented orientation of a half wave plate will convert a linear polarization into a cylindrical vector polarization. In this work, the half wave plate is achieved by 3D printed low-index dielectric grating, whose segmented rotation forms a vector beam generator. The radially and azimuthally polarized beam is experimentally measured at 140 GHz when passing through the printed sample. Further study shows that the grating lattice affects the bandwidth of the vector beam generator. The frequently used subwavelength lattice design shows narrow bandwidth due to the undesired eigenmode dispersion and interaction. In contrast, the superwavelength lattice design offers wideband and efficient vector beam generation thanks to the weak diffraction of the low-index material and the proper eigenmode dispersion. The mechanism can be applied similarly to other type of polarization control to enrich sub-terahertz elements.