Ultrathin wave plates based on bi-resonant silicon Huygens' metasurfaces

An all-dielectric Huygens metasurface supporting electric and magnetic resonances is a promising platform for a variety of optical applications that require a combination of extremely high transmission and broad-range control of the phase of the transmitted light. A highly efficient wave plate is one example of such an application. In combination with high spectral selectivity and strong optical energy concentration, such phase plates are desirable for precision sensing and high efficiency nonlinear optics. We propose a novel approach to realizing such ultra-thin optical plates: an anisotropic Fano-resonant optical metasurface (AFROM) employing the combination of a spectrally sharp electric and a relatively broadband magnetic resonance. The phase shift coverage approaching 2{\pi} is achieved through judicious choice of the geometric parameters of a complex unit cell. A new methodology based on eigenvalue simulations of leaky magnetic/electric resonances enables rapid computational design of such metasurfaces.