Polarization-independent binary-switchable varifocal metalenses enabled by phase-change metasurfaces

Abstract Conventional varifocal lenses, though indispensable in modern optics, suffer from structural complexity and miniaturization limitations due to their reliance on mechanically tunable multi-element refractive architectures. Active metalenses have recently emerged as a promising alternative, offering compact form factors and reconfigurability; however, the longstanding challenge of simultaneously achieving dynamic focal tuning and polarization-independent operation continues to impede their widespread implementation. Herein, we present a universal design paradigm for polarization-independent binary-switchable varifocal metalenses, realized through two strategically configured sets of Ge 2 Sb 2 Se 4 Te 1 (GSST) nanofins-based anisotropic meta-atoms. By strategically engineering one nanofin set in the amorphous state and the other in the crystalline state with mutual orthogonal cross-polarization transmission, the proposed metalens configuration with carefully tailored numerical apertures facilitates exceptional phase-transition-mediated bifocal switching capability, manifesting a 158 μ m focal shift and 26.1 dB contrast ratio while consistently maintaining diffraction-limited focusing performance (with full-width at half-maximum values of 1.93 λ 0 in amorphous state and 1.41 λ 0 in crystalline state) at the operational wavelength of 7 μ m. Rigorous enforcement of polarization independence is achieved by restricting meta-atom rotations exclusively to 0° or 90° orientations, resulting in minimal focal spot variation (<3%) across all possible polarization states. We further demonstrate the versatility of this approach by successfully implementing a polarization-insensitive dual-focus binary-switching varifocal metalens prototype. This work bridges the critical gap between adaptive focal control and polarization-independent functionality, unlocking transformative applications in high-resolution bioimaging, multiplanar depth sensing, and wavelength-division-multiplexed optical communication systems.