Broadband Graphene Based Reflective Cross Polarization Converter Metasurface Design with Unity Efficiency in the Lower Terahertz Gap

This paper deals with a monolayer graphene based wideband reflective cross polarization converter metasurface structure effective over a wide range of incident angles in the lower terahertz gap of the electromagnetic spectrum. The unit cell of the metasurface comprises a modified split ring-shaped graphene pattern deposited over a gold backed silicon dioxide (SiO2) substrate. The proposed geometry converts incident linearly polarized (LP) wave to its cross polarized form with a near unity cross polarization conversion (CPC) ratio over a bandwidth of 2.53 THz in the lower terahertz gap ranging from 1.78 THz to 4.31 THz in which a near unity polarization conversion ratio (PCR) has been achieved. The PCR is greater than 0.9 over the band 2.5 THz to 4 THz while full width at half maxima (FWHM) fractional bandwidth of 92.89% with respect to center frequency of 3.05 THz has been realized. The wide bandwidth of CPC of the incident electromagnetic wave (EM) occurs till 40º incident angles under both TE and TM polarizations of the EM wave. The proposed CPC is ultrathin in nature by having a periodicity of λ/24 and thickness of λ/18.7 with respect to minimum frequency of the CPC bandwidth.