Microelectromechanical Systems-Tunable Reflective Metalenses for Switchable Focusing between Two Arbitrary Phase States.

Abstract

Dynamic metasurfaces (MSs) have already shown great potential for empowering ultracompact reconfigurable optics. However, existing tuning strategies, including those based on refractive-index-modulating materials or mechanical reconfiguration, face significant challenges in achieving arbitrary and continuous 2π-phase modulation for two independent states subjected to dynamic two-dimensional wavefront shaping. This restriction has hindered the realization of meta-devices capable of switching between two completely different phase profiles and thereby realizing distinct optical functions. Here, we overcome this challenge using a microelectromechanical systems (MEMS)-tunable metalens (ML) platform that integrates a bilayer MS (BMS) with a piezoelectric MEMS mirror, enabling full 360° × 360° phase coverage in two independently addressable states while maintaining uniformly high reflection amplitude (between 0.74 and 0.85) and thus ensuring efficient operation. We experimentally realize two MEMS-tunable MLs: a switchable off-axis focusing ML, capable of dynamically shifting its focal position, and a switchable vortex ML, capable of alternating between conventional and vortex focusing states. Both meta-devices exhibit high-efficiency operation (30-40<i>%</i>) at their optimal wavelength, persistent dynamic functionalities throughout the spectral range of 650-850 nm, and fast switching with rise/fall times of 0.58/0.4 ms. The developed MEMS-tunable ML platform enables truly arbitrary, dynamically controlled dual-phase-map switching and can straightforwardly be extended to feature other dynamic functionalities, thereby enriching the portfolio of already developed compact, advanced, and dynamic optical systems.