Continuously Tunable Alvarez Metalenses for Varifocal Imaging

Compact and lightweight lenses are essential for miniaturized varifocal imaging. We designed and fabricated an Alvarez metalens comprising two cascaded metalenses that enable continuously tunable focal length via lateral actuation. In order to suppress aberration, Zernike basis functions were incorporated into the phase profile of Alvarez metalenses. The focusing and imaging performance of the metalens was then experimentally validated at the design wavelength. With a 1 mm in-plane displacement, the Alvarez metalens (4 mm aperture, 0.62 g weight, λ=532 nm) enabled focal length modulation from 10 mm to 150 mm, all while achieving an average diffraction efficiency of approximately 40%. The integration of an in-plane-actuation-only varifocal mechanism with ultrathin metalenses enables a highly scalable approach to miniaturizing systems for imaging, optical communications, and biomedical applications.