Direction‐Dependent Janus Metasurface Supported by Waveguide Structure with Spoof Surface Plasmon Polariton Modes

Abstract In this work, a novel direction‐dependent Janus metasurface (DDJM) supported by waveguide structure (WGS) with surface plasmon polariton (SSPP) modes is proposed. In −z‐direction, linear‐to‐linear (LTL) polarization conversion (PC) can be implemented at the low frequencies by the reflection characteristics of the WGS. And in the +z‐direction, the ultrawideband absorption takes shape due to the SSPP modes, in which strongly localized oscillation of free electrons are confined to the metal–dielectric interface assisted by the WGS. The combination of the WGS and the PC structure finally enables the low‐frequency LTL PC with the high polarization conversion ratio (over 0.9) at 0.87–1.35 THz in −z‐direction, corresponding to the relative bandwidth of 43.24%, as well as the absorption in +z‐direction with an efficiency of over 0.9 in the frequency range of 0.8–1.2 THz. Also the fixed direction‐independent transparent window brought by WGS runs from 1.57 to 1.90 THz when the co‐polarized transmission coefficient exceeds 0.85, occupying a staggered band compared to that of PC or absorption. The favorable properties of the DDJM promise a potential practical application in full‐space electromagnetic wave control and radar stealth technology fields.