Abstract

A metalens is a flat lens that can control the phase of light so that dispersed light can be reconcentrated. This study devised a tunable metalens with a switchable focal length based on the phase transition properties of vanadium dioxide (${{\rm VO}_2}$). The unit structure comprises three layers from bottom to top: gold, polyimide, and two square resonant rings. The metalens can not only transform incident x-polarized waves into y-polarized waves but also achieve beam focusing simultaneously. The designed metalens achieves polarization conversion efficiency at an operating frequency of 0.8 THz. In the insulating state of ${{\rm VO}_2}$, the beam focal point is at ${\rm L} = {1914}\;{\unicode{x00B5}{\rm m}}$; in the metallic state, the wave converges at ${\rm L} = {982}\;{\unicode{x00B5}{\rm m}}$, closely aligning with the predetermined focal length. By controlling external temperature, focal point switching can be achieved, making it highly versatile in practical applications.

© 2024 Optica Publishing Group

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