Electrical Tuning of Fresnel Lens in Reflection

Optical metasurfaces have been extensively investigated, demonstrating diverse and multiple functionalities with complete control over the transmitted reflected fields. Most optical are however static, only a few configurations offering (rather limited) electrical control, thereby jeopardizing their application prospects in emerging flat optics technologies. Here, we suggest an approach to realize electrically tunable metasurfaces, dynamic Fresnel lens focusing. The active (AFL) exploits electro-optic Pockels effect 300-nm-thick lithium niobate layer sandwiched between continuous thick nanostructured gold film serving as electrodes. We fabricate characterize AFL, focusing 800-900 nm radiation at distance of 40 $\mathrm{\mu}$m efficiency 15 % modulation depth 1.5 driving voltage $\pm 10$ V within bandwidth $\sim\! 4$ MHz. believe that metasurface concept introduced is useful for designing components.