Time-Modulated Conducting Oxide Metasurfaces for Adaptive Multiple Access Optical Communication

We demonstrate realization of a time-modulated metasurface in near-infrared frequency regime via integration of conducting oxide layers into plasmonic stripe nanoantennas arranged in a reflectarray configuration. The permittivity of conducting oxide layers is modulated in time through modulation of carrier concentration by applying radio frequency biasing signals which leads to generation of higher order frequency harmonics. We rigorously characterize the electro-optical frequency conversion performance of the metasurface. We then exploit the dispersionless angle-independent phase discontinuities on the wavefront of higher order frequency harmonics to achieve dynamic multi-wavelength multi-beam scanning across S, C, and L telecommunication bands via pixelated control over the modulation phase delay. It is established that such time-modulated metasurfaces can be utilized as reflectarray antennas for active multicasting as well as wavelength and angle multiplexing, thus improving optical communication capacity by providing multiple access and integrating several communication channels into a single antenna platform. The role of modulation waveform in the spectral diversity of harmonics is also explored. Specifically, modulation waveform is optimized to realize unicast and broadcast links. Finally, active beam-scanning performance of the time-modulated conducting oxide metasurface is compared with that of its quasi-static counterpart verifying the enhanced bandwidth as well as suppressed side lobes in the time-modulated platform.