Broadband terahertz half-wave plate based on anisotropic polarization conversion metamaterials

Abstract

We propose a half wave plate in the terahertz region to realize broadband linear polarization conversion in the reflection mode through anisotropic metamaterials. The structure of this design is composed of two pairs of patches in one unit cell that can rotate the polarization direction of a linearly polarized incident wave for an angle of 2β in a broadband frequency range. This work concentrates mainly on numerical simulations by using the standard finite difference time domain method. The efficiency of the half wave plate is higher than 50%, and PCR is higher than 85% in a broadband frequency range for cross polarization conversion. In the operating frequency band, three polarization conversion peaks can be found with the conversion efficiency nearly 100%. A more outstanding performance can be achieved by using low-loss substrate. The in-depth physical mechanism is revealed by further analysis. Besides, the expressions referring to theoretical decomposed electric field are deduced.