Polarization control of terahertz waves based on metallic parallel-plate waveguides

Terahertz (THz) communication and sensing technology has recently gained increasing attention. Metallic parallel-plate waveguides (PPWG) have been researched since they were proven to be the carrier of lossless transmission of THz waves. However, previous reports have focused on the transmission and phase properties of single-polarized THz waves in PPWGs and have barely investigated the polarization properties. To reconstruct the polarization of the output THz wave in a PPWG, we study the transmission and phase properties of both TE and TM modes in detail. The phase difference of the TE and TM modes can be continuously adjusted by varying the propagation length and the gap of the two plates in PPWG due to the different dispersion of the two modes. The polarization ellipticity and rotation angle can be modulated in the range of ±45°. When a photonic cavity structure is applied to a PPWG, the output wave will be converted to 90 ° linear polarization at the frequency located in the cavity mode. All the proposed polarization control can be tuned by changing the structural parameters forming the PPWGs, making this approach attractive for integrating the function of the THz waveguides, which has significance for THz communication and sensing.