Transparent Dielectric Metasurfaces for Spatial Mode Multiplexing

Expanding the use of physical degrees of freedom to employ spatial multiplexing of data in optical communication is considered to be the most disruptive and effective solution for meeting the capacity demand of the growing information traffic. Development of space division–multiplexing methods stimulated research on spatial encoding, detection, and processing of data, attracting interest from various fields of science. Here a passive all-dielectric metasurface with near-unity transmission is demonstrated that engineers spatial mode profiles, potentially of an arbitrary complexity. The broadband response of the metasurface covers all S, C, and L bands of fiber communications. Unlike conventional phase plates, the metasurface allows for both phase and polarization conversion, providing full flexibility for the mode engineering. The dielectric metasurface is employed for mode multiplexing in a free-space optical communication system with an extinction ratio in excess of 20 dB over the whole C-band with negligible penalty even for 100 Gb s⁻¹ data transmission. These results merge two seemingly different fields, optical communication and metamaterials, and they suggest a novel approach for an ultimate miniaturization of mode multiplexers and advanced LiFi technologies.