Physical insight into the terahertz polarization modulator by using Smith chart

Abstract

Polarization modulation (PoM) provides an additional degree of freedom for the modulation of carrier waves and may be an alternative to conventional wireless communication techniques that use amplitude, frequency, and phase modulations. In this study, we proposed a metasurface-based modulator that transforms a linearly polarized wave into a circularly polarized wave in the terahertz range of 1.53 THz–1.57 THz. The polarization manipulation of the metasurface is analyzed using the Smith chart method, which builds a bridge between the metasurface pattern and its equivalent circuit impedance. We show the reflection/transmission coefficient and impedance of the metasurface in the Smith chart, providing clear physical images for the designers. According to the Smith chart analysis, we obtained a two-layer metasurface modulator with 90% efficiency for the transmitted field. All the results are validated from the simulation. The proposed Smith chart method opens a new design methodology of metasurface-based devices.