On‐Chip Metasurface‐on‐Facets for Ultra‐High Transmission through Waveguides in Near‐Infrared

Abstract Nature has long inspired scientists and engineers to develop transparent surfaces via constructing anti‐reflective surfaces. In absence of anti‐reflection (AR) coating, silicon reflects about 35% of light for a single interface air−silicon. Here, inspired by jellyfish anti‐reflective eyes, a man‐made anti‐reflective surface on the facet of the waveguide is proposed and demonstrated for waveguides transparency in near‐infrared. The optimized metamaterial with unit cells of 560 × 560 nm shows transparency of 2.6 times better as compared to the waveguide with blank facet. Metasurfaces are milled on the waveguides facets with a focused ion beam. Silicon‐on‐insulator waveguides are tested with an inline set‐up. Far‐field scattering diagrams reveal that it is the special geometry of the unit cells of the engraved metamaterial, which can be associated with the directional scattering resulting in combined effect: on one hand the ultra‐high transparency of the device and on the other hand the efficient coupling to the low‐order modes due to the focusing dielectric nano‐antennas effect. Reported here waveguide facets as AR metamaterials on a chip, opens up opportunities to engineer transparent on‐chip devices with high coupling efficiency for diverse applications from sensing to quantum technologies.