Broadband Multifunctional Efficient Meta-Gratings Based on Dielectric Waveguide Phase Shifters.

Molding the wavefront of light is a basic principle of any optical design. In conventional optical components such as lenses and waveplates, the wavefront is controlled via propagation phases in a medium much thicker than the wavelength. Metasurfaces instead typically produce the required phase changes using subwavelength-sized resonators as phase shift elements patterned across a surface. This "flat optics" approach promises miniaturization and improved performance. Here we introduce metasurfaces which use dielectric ridge waveguides (DRWs) as phase shift elements in which the required phase accumulation is achieved via propagation over a subwavelength distance. By engineering the dispersive response of DRWs, we experimentally realize high resolving power meta-gratings with broadband (λ = 1.2-1.7 μm) and efficient routing (splitting and bending) into a single diffraction order, thus overcoming the limits of blazed gratings. In addition, we demonstrate polarization beam splitting capabilities with large suppression ratios.