Polarization Independent, Broad Angle RetroReflection with an Optical Meta-Grating

Metasurfaces enable a large degree of manipulation of the impinging electromagnetic wavefront over a thin profile. As an example, retroreflective metasurfaces reflect waves in the opposite half space compared to regular mirrors, a functionality highly desirable for identification tagging, radars and street signaling. While common approaches require bulky configurations, gradient metasurfaces have been recently proposed as thin retroreflectors. However, these designs suffer from inefficiencies and sensitivity to loss. Here, we discuss the design and implementation of an ultrathin grating metasurface realizing polarization-independent retroreflection on the impinging wavefront, with a broad angular response and nearly lossless features. By judiciously engineering the metasurface in space, the incident light can be coupled back to an anomalous diffraction order aligned with the impinging direction. We optimize the surface to provide a robust response in angle and frequency, paving the way towards efficient, easy to engineer and polarization-independent retroreflection using a single, deeply subwavelength metasurface layer.