Bi-directional multi-function terahertz metasurface

We propose a bi-directional multi-function terahertz metasurface, which consists of photosensitive silicon and metal composite pattern, F4B-metal layer-Si3N4, photosensitive silicon and split metal ring composite pattern from top to bottom layer. When terahertz wave is incident along +Z direction and the conductivity of the photosensitive silicon is 0 S/m, the metasurface behaves as y-polarization wave to x-polarization wave converter with a bandwidth of 3.82 THz. As the conductivity of the photosensitive silicon changes as 1 x 105 S/m, the proposed structure achieves linear-to-circular polarization converter. When terahertz wave is incident along -Z direction and the conductivity of the photosensitive silicon is 0 S/m, the structure exhibits as a band-stop filter with a stopband bandwidth of 20 GHz. Furthermore, the metasurface becomes a broadband tunable terahertz absorber when the conductivity of the photosensitive silicon changes as 1 x 105 S/m. Our proposed structure behaves bidirectional, switchable and multi-functional terahertz manipulation characteristics, providing a new perspective for multi-function terahertz device design.