MEMS-actuated Metasurface Alvarez Lens.

Miniature lenses with 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 still face challenges in 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 optical power - to construct a miniature, MEMS-actuated metasurface Alvarez lens. The implementation based on electrostatic microelectromechanical systems (MEMS) generates fast and controllable actuation with low power consumption. The utilization of metasurfaces, ultrathin and subwavelength-patterned diffractive optics, as the 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 to operate at 1550 nm wavelength, a total uniaxial displacement of 6.3 um is achieved in the Alvarez metalens with direct-current (DC) voltage application up to 20 V, modulating the focal position within a total tuning range of 68 um, producing more than an order of magnitude change in focal length and 1460 diopters change in optical power. The MEMS Alvarez metalens has a robust design that can potentially generate a much larger tuning range without substantially increasing device volume or energy consumption, making it desirable for a wide range of imaging and display applications.