Optically controlled metasurface antennas [Invited]

Over the past decade, metasurfaces (MTSs) have emerged as a highly promising platform for the development of next-generation, miniaturized, planar devices across a wide spectrum of microwave frequencies. Among their various applications, MTS-based antennas—particularly those based on surface-wave excitation—represent a significant advancement for communication technologies. In this paper, we report an experimental demonstration of an optically controlled Ka-band metasurface antenna realized by printing subwavelength metallic elements on a high-resistivity silicon substrate. By exploiting the photoconductive properties of silicon under near-infrared illumination, the complex permittivity of the substrate is locally modified, resulting in a change of the effective surface reactance. This mechanism enables optical control of surface-wave propagation and its conversion into radiation. Experimental results demonstrate optical control of the antenna radiation characteristics, with a measured gain variation of approximately 6.7 dB, while full-wave simulations of the fully silicon-based antenna configuration predict gain variations of up to 15 dB, under low optical power densities (below 1W/cm^2 at 971 nm). Building on these results, we then propose and numerically validate a novel antenna concept in which the radiating functionality is entirely implemented in silicon, without any printed metallic elements. In this configuration, the metasurface behavior is achieved purely through spatial and temporal modulation of the substrate properties induced by optical illumination. Full-wave simulations demonstrate that this approach enables dynamic control of radiation characteristics, opening the way to fully photonic, reconfigurable microwave antennas. These results establish a new paradigm in antenna design, where optical excitation of a photosensitive substrate enables direct and efficient control of microwave radiation without the need for electronic tuning components or patterned conductive layers.