# MEMS-actuated metasurface Alvarez lens

## TL;DR

Researchers developed a tiny, tunable lens using MEMS and metasurfaces that changes focus quickly and with low power, suitable for compact optical devices.

## Contribution

A MEMS-actuated metasurface Alvarez lens that enables large optical power changes in a compact, low-power design.

## Key findings

- The MEMS Alvarez metalens achieved a 1460-diopter change in optical power with under 20V.
- The device demonstrated a 68 µm focal position tuning range at a 1550 nm wavelength.
- The design is scalable and compatible with semiconductor fabrication for mass production.

## Abstract

Miniature lenses with a tunable focus are essential components for many modern applications involving compact optical systems. While several tunable lenses have been reported with various tuning mechanisms, they often face challenges with respect to power consumption, tuning speed, fabrication cost, or production scalability. In this work, we have adapted the mechanism of an Alvarez lens – a varifocal composite lens in which lateral shifts of two optical elements with cubic phase surfaces give rise to a change in the optical power – to construct a miniature, microelectromechanical system (MEMS)-actuated metasurface Alvarez lens. Implementation based on an electrostatic MEMS generates fast and controllable actuation with low power consumption. The utilization of metasurfaces – ultrathin and subwavelength-patterned diffractive optics – as optical elements greatly reduces the device volume compared to systems using conventional freeform lenses. The entire MEMS Alvarez metalens is fully compatible with modern semiconductor fabrication technologies, granting it the potential to be mass-produced at a low unit cost. In the reported prototype operating at 1550 nm wavelength, a total uniaxial displacement of 6.3 µm was achieved in the Alvarez metalens with a direct-current (DC) voltage application up to 20 V, which modulated the focal position within a total tuning range of 68 µm, producing more than an order of magnitude change in the focal length and a 1460-diopter change in the optical power. The MEMS Alvarez metalens has a robust design that can potentially generate a much larger tuning range without substantially increasing the device volume or energy consumption, making it desirable for a wide range of imaging and display applications.

Researchers in the United States have developed a miniature lens which can change focal length quickly and with low power usage. The device is based on the Alvarez lens design in which the movement of two optical elements changes the optical power. A normal Alvarez lens uses elements with matching curved surfaces, but Zheyi Han and her co-authors at the University of Washington adjusted the design to use metasurface optics instead. Metasurfaces provide the same effect as normal lens elements but are flat and thin, making it easier to incorporate them in miniature devices. The team used a MEMS system to move the metasurface elements, enabling them to achieve a 1460-diopter change with the application of under 20V. This approach will be useful in fabricating tunable lenses for ultra-compact uses, such as endoscopy and mobile devices.