Physical Explanation of Fabry–Pérot Cavity for Broadband Bilayer Metamaterials Polarization Converter

We propose a wideband linear polarization converter in transmission mode by bilayer metamaterial. The polarization converter operates from 0.55 to 1.37 THz with polarization conversion ratio maintaining nearly 100%. The distribution of surface current and electrical field was numerically simulated to clarify physical mechanism of polarization conversion. Importantly, we introduced the Stokes method to assess the polarization state of transmitted converter. The Fabry-Pérot-like cavity model was established to reveal the enhancement of polarization conversion ratio. The clear expressions including ideal and approximate model were deduced to provide an excellent explanation of Fabry-Pérot cavity in subwavelength bilayer metamaterials structure.