Electrical Tuning of Fresnel Lens in Reflection

TL;DR

This paper demonstrates an electrically tunable Fresnel lens using an electro-optic metasurface with lithium niobate, enabling dynamic focusing with voltage control, which advances the development of reconfigurable flat optical devices.

Contribution

It introduces a novel electrically tunable metasurface lens based on the Pockels effect in lithium niobate, enabling dynamic control of optical focusing.

Findings

Achieved dynamic focusing at 800-900 nm with 15% efficiency.

Demonstrated modulation depth of 1.5% with ±10 V voltage.

Operates within a bandwidth of approximately 4 MHz.

Abstract

Optical metasurfaces have been extensively investigated, demonstrating diverse and multiple functionalities with complete control over the transmitted and reflected fields. Most optical metasurfaces are however static, with 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 optical metasurfaces, demonstrating 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 nanostructured gold film serving as electrodes. We fabricate and characterize the AFL, focusing 800-900 nm radiation at the distance of 40 $\mathrm{\mu}$m with the focusing efficiency of 15 % and demonstrating the modulation depth of 1.5 % with the driving voltage of $\pm 10$ V within the bandwidth of $\sim\! 4$ MHz. We believe that the electro-optic metasurface concept introduced is useful for designing dynamic flat optics components.