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

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.