Optical metasurfaces have been extensively investigated, but most are, however, static. We suggest an approach to realize electrically tunable optical metasurfaces, based on tuning the light reflectivity near a high-fidelity Fabry-Perot resonance. This concept is implemented in dynamic Fresnel lens focusing. The active Fresnel lens (AFL) exploits the electro-optic Pockels effect in a 300 nm thick lithium niobate layer sandwiched between a continuous thick and a nanostructured gold film serving as electrodes. We fabricate and characterize the AFL, focusing 800-900 nm radiation at a distance of 40 µm with the focusing efficiency of 15%, and demonstrating the modulation depth of 1.5%, with the driving voltage of ±10 V within the bandwidth of ~6.4 MHz.
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