116 1 0.3 THz 1 2 X 2020 Si MgO 3.4 3.1 H 3 4,5 4 5 0.31 THz n eff = 6.7 + j0.12 92% 1.2% 6-9 10 V 11,12 13 14 15 16 The growth of terahertz technology has opened up the strong potential of various attractive applications in the terahertz waveband. However, conventional optical elements such as collimated lenses are too large for the wavelength, and terahertz devices demand compact and thin optical elements for industrial applications. We propose and design an ultrathin gradient lens with

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... edented high refractive indices and extremely low refl ection controlled by paired metal cut wires in the 0.3-THz band. We used a unit model with periodic boundary walls and designed a refractive index n eff = 7.06 + j0.330, refl ection power of 1.0%, and transmission power of 82.0% for the center of the lens. We also designed a refractive index of n eff = 3.55 + j0.0582, reflection power of 15.2%, and transmission power of 81.9% for the periphery. A full model analysis also verifi es a focusing effect at 4.69 mm (4.69λ 0 ) from a lens. The proposed ultrathin gradient lens with high refractive indices and extremely low refl ection will provide valuable solutions for a wide range of applications.