Visible Frequency Zero-Index Metasurfaces for 3D Augmented Reality Displays*

Arrays of gratings can be multiplexed to create multi-view backlights, where each super-pixel is composed of several angularly directive beams. However, real applications of this technology are hampered by a limited field of view. In particular, diffractive optics are incapable of efficiently radiating light perpendicular to the plane of the array. This causes a hole in the center of the field of view because the refracted beam intensity from a diffraction grating coupler at wavelengths near cut-off. The grating is unable to produce a beam at the broadside, due to a standing wave formed in the plane of the array.
To overcome this limitation, we have developed metasurface-based pixel. The design consists of an array of high-index dielectric pillars, which exhibit simultaneous electric and magnetic resonances. The resulting metasurface supports leaky waves above the light line, which efficiently radiate into the broadside at telecom and visible frequencies. The Dirac-cone metasurface can produce beams over a continuous range of angles around the broadside due to its linear dispersion at the center of the Brillouin zone. By carefully tuning the interference of multiple bound modes, we can independently control the radiative efficiency, beam width, and beam angle.