High-Efficiency Electrically Tunable Active Metasurfaces at Telecommunication Wavelengths

We theoretically discuss different design pathways towards achieving high-efficiency active metasurfaces. We demonstrate electrically tunable active metasurfaces, which can dynamically manipulate the wavefront of the reflected light in the near-infrared wavelength range while exhibiting optical efficiencies &gt; 80%. Our active reflective metasurfaces consist of a gold (Au) back reflector, followed by a silica spacer (SiO₂) on top of each we place an array of amorphous silicon (a-Si) pillars [1]. The quality factors of the designed metasurfaces can adopt values ranging from a few 100s up to 60,000.<br/>We achieve a dynamically tunable optical response by integrating an electro-optically tunable lithium niobate layer (LNO) layer into the resonant metasurface structure and introducing indium tin oxide (ITO) interconnects. By applying electrical bias, we achieve a dynamically tunable phase shift of 236^o when the refractive index of the LNO layer varies between 2.212 and 2.208. The optical efficiency of the designed metasurface is &gt; 80 % for all the considered values of the applied bias, and the Q-factor of the considered resonance is 40,000. In alternative implementations, we use ITO or tungsten disulfide (WS₂) as dynamically tunable materials and present realistic active metasurface designs adapted to the choice of the active material. Finally, we analyze the beam steering performance of the designed metasurfaces considering the cases of both two-dimensional and one-dimensional beam steering.<br/>The designed high-efficiency metasurfaces could be useful for a number of applications such as free-space optical communications, light detection and ranging (LiDAR), and laser-based additive manufacturing.<br/><br/>[1] Ruzan Sokhoyan, Claudio U. Hail, Morgan Foley, Meir Y. Grajower, and Harry A. Atwater, “All-dielectric high-Q dynamically tunable transmissive metasurfaces”, arXiv:2309.08031v1.