A Polarization-Insensitive Terahertz Flat Lens Based on High Transmission Dielectric Metasurface

Flat lenses or metasurface lenses (metalenses) arranged by planar phase gradient index plasmonic or dielectric meta-atoms have attracted many attention and great efforts in Terahertz (THz) spectrum owing to its many promising applications. However, the limited focusing performances such as low conversion efficiency or small numerical aperture (NA) in the far field especially for polarization-sensitive incident are still great challenges. In this paper, we design and present a sub-wavelength thickness THz flat lens by using high transmission all-dielectric metasurface without polarization-sensitivity. The dielectric metasurface is constructed by a periodical rectangular high contrast medium deposited on a substrate film. Its transmission properties and electric field distributions of unit cell are investigated and analyzed for both transverse electric (TE) and transverse magnetic (TM) mode around the target frequency. By varying its width of dielectric metasurface based on hyperbolic phase profile on the planar geometry, a flat THz metalens is formed and its focusing patterns are obtained by using a full-wave simulation studio. The obtained focal spot size is about 0.94λ which is diffraction-limited focusing. The presented studies can provide a good candidate to develop high-efficiency and dual-polarization flat metalenses based on dielectric metasurfaces in THz band.