Multifunctional metalens design and optimization based on bilayer phase-change materials at near-infrared wavelength

Flat optical components capable of dynamic multifunctional control are essential for next-generation imaging, anti-counterfeiting, and communication technologies. Here, we demonstrate a reconfigurable metalens based on a bilayer Sb₂Se₃ metasurface operating at 1064 nm in the near-infrared regime. By harnessing the large refractive index contrast between amorphous and crystalline phases and employing Pancharatnam-Berry phase engineering, the device enables non-volatile switching among tunable focal lengths, variable focus intensities, and dual- or single-focus modes. Reversible phase transitions of individual Sb₂Se₃ nanofins in upper and lower layers allow arbitrary switching between <i>F₁</i>, <i>F₂</i>, and combined <i>F₁</i>+ <i>F₂</i> focusing states, with focusing efficiency exceeding 50%. Building on this, we further show programmable pattern generation across different focal planes by spatially controlling the phase states of meta-atom arrays, enabling intensity-tunable image rendering for compact, high-security optical anti-counterfeiting systems. This work advances programmable photonics through a scalable and integrable platform for adaptive flat optics.