# Achromatic varifocal metalens for the visible spectrum

## TL;DR

This paper presents a novel achromatic varifocal metalens that uses polarization-dependent nanostructures to achieve tunable focus and color imaging across the visible spectrum, promising advancements in compact optical devices.

## Contribution

The authors design and demonstrate a polarization-controlled, achromatic metalens with tunable focal length and color imaging capabilities in the visible range.

## Key findings

- Focal length can be tuned from 220 to 550 micrometers by polarization rotation.
- Achromatic focusing achieved over 483-620 nm wavelength range.
- Demonstrated varifocal color imaging with white light source.

## Abstract

Metasurface optics provide an ultra-thin alternative to conventional refractive lenses. A present challenge is in realizing metasurfaces that exhibit tunable optical properties and achromatic behavior across the visible spectrum. Here, we report the design, fabrication, and characterization of metasurface lenses ("metalenses") that use asymmetric TiO2 nanostructures to induce a polarization-dependent optical response. By rotating the polarization of linearly-polarized input light, the focal length of a 40 micrometer-diameter metalens is tuned from 220-550 micrometers with nearly diffraction-limited performance. We show that imparting a wavelength-dependent polarization rotation on incident light enables achromatic focusing over a wide band of the visible spectrum, 483-620 nm. We use this property to demonstrate varifocal color imaging with white light from a halogen source. Tunable achromatic metalenses may be useful for applications in imaging and display.