LAUSR

A systematic study is carried out on the interaction of electromagnetic waves with a nonsymmetric all-dielectric C-shaped nanoantenna to achieve an ultimate control over the independent and relative spectral positions of the excited magnetic and electric dipolar modes. By properly determining the structural parameters (inner and outer radii and the opening angle) and tailoring the interference of geometrical resonances, an ultrathin C-element metasurface is designed, which can highly transmit the linearly polarized incident beam (>80%) with full phase-agility (2π) in the red light of visible regime. The investigation on the physical mechanism behind this nanoantenna reveals the confinement of magnetic and electric fields corresponding to the magnetic and electric dipolar modes mainly inside the hollow and opening angle, i.e., outside the constituent high-index material of C-element. This feature allows making building blocks less dependent on the material loss and dispersion. Three different approaches based on only varying the inner/outer radius or the opening angle are proposed which can facilitate the design complexity, the encoding of the desired phase distribution for specific functionality, and easing the fabrication procedure. The proposed approaches are leveraged to design several highly transparent graded-pattern metasurfaces with the capability of beam steering, focusing, flat-top generation, and holography.