Methodology for High Purity Broadband Near-Unity THz Linear Polarization Converter and its Switching Characteristics

Jianguo Zhang,Jinping Tian,Shuyuan Xiao,Lu Li

doi:10.1109/access.2020.2979021

Abstract

Terahertz (THz) polarization converter with high purity of linear polarization conversion, broader conversion band and near-unity conversion efficiency is one of the main research interests in the photonic field. Based on a tri-layer structure of Au, parylene-C and Au, a high purity broadband near-unity THz converter is successfully achieved, and the relative bandwidth (RBW) with polarization conversion ratio (PCR) greater than 98% (90%) can reach about 64.782% (73.094%). The ellipticity is close to zero and the polarization azimuth angle is almost equal to ±90° within the frequency range of 1.818~2.631 THz. These performances originate mainly from the hybridization of the electric excitations and strong coupling effect among the three resonant modes. Besides, the dependencies of conversion performances on the material's electromagnetic parameters and structural parameters are discussed in detail. By selecting metal material with high conductivity and dielectric material with small real and imaginary permittivities, the conversion performances of the proposed converter can be well improved. Meanwhile, the conversion performances are highly robust when the structural parameters change slightly near the optimized value. Finally, the influences of the incident angle and the polarization angle on the conversion performances are also investigated, and the results show that the proposed converter has the characteristics of wide incident angle and polarization angle dependent switching performance. The simple geometry and the better performances make the proposed linear polarization converter a potential candidate in the area of sub-wavelength scale polarization converters, filters, sensors, switches, and so on.

Highlights

Over the past decade, terahertz (THz) radiation has attracted considerable attention in areas of industrial, security, and biomedical applications [1]–[3]
The results show that the converter can realize simultaneously the performances of higher linear polarization conversion purity, broadband and near-unity polarization conversion ratio (PCR), and possesses the switching characteristics
The study results have shown that the relative bandwidth (RBW) with PCR greater than 98% (90%) can reach about 64.782% (73.094%)

Summary

Introduction

Terahertz (THz) radiation has attracted considerable attention in areas of industrial, security, and biomedical applications [1]–[3]. One of the reasons is that it can penetrate into objects while posing little destructive risk. The development of THz technology is lagging. Far behind the microwave and optical technologies. In THz science and technology, due to the lack of suitable natural materials, devices based on metamaterials (MMs) are attractive. MMs are composed of a layer of metasurface (MS), a layer of dielectric spacer, and a layer of metal substrate. The MS layer is often considered as a two dimensional structure formed by a periodically arranged metal pattern array with sub-wavelength scale, which has drawn intense interest owing to the highly controllable

Methods

Results

Conclusion