Compact phase-change multilayer architecture for dynamically tunable ultrabroadband near-perfect absorption

Conventional Fabry-Pérot absorbers are limited by an intrinsic trade-off among bandwidth, efficiency, and tunability, precluding devices that are simultaneously broadband, high-efficiency, and reconfigurable. We report an asymmetric, high-loss, cascaded Fabry-Pérot ultracompact cavity. The device is realized as a single planar, lithography-free stack. It achieves ultrabroad spectral coverage (380-2500 nm), ∼97% band-averaged absorptance (147% relative bandwidth), and dynamic tunability. The engineered, multi-material stack supports strongly overlapped optical resonances that, together with a graded-index antireflection scheme, maintain polarization-independent absorption for incidence angles up to 70°. Reversible crystalization of the AIST layers modulates their complex refractive index, providing a maximum absorption-contrast modulation of ∼30% in the short-wave infrared band. This manufacturable platform offers a versatile and scalable route toward multispectral camouflage, adaptive thermal control, energy-conversion technologies and multispectral stealth technologies.