Meta Resonant Waveguide-Gratings Providing Selective Diffraction

The past decade has witnessed the development of a large variety of new flat optics referred to as metasurfaces [1]. These metasurfaces are relying on arrays of a large variety of phase shifting elements. This article aims at presenting a novel type of flat optics able to perform wavefront shaping and beam redirection with a high wavelength or angular selectivity, as well as an intrinsic polarization selectivity. These new elements are not relying on localized phase-shifting but on a distributed guided-mode, closely linked to Resonant Waveguide Gratings (RWG). These new optical elements are referred to as Meta Resonant Waveguide Gratings (MRWG). MRWGs have intrinsically rather low aspect ratios and can be produced with existing high-throughput manufacturing methods such as hot embossing and physical vapor deposition (PVD), making them industrially attractive. Multiple design options linked to their many degrees of freedom enable a wide range of optical properties, such as color-selective free-space combiners and diffractive couplers configurations. The properties of a simple MRWG are detailed, before unveiling a few variants to discuss the influence of some key design parameters, and providing a general design method for complex arrangements.