Reconfigurable narrowband-to-broadband absorber featuring GeTe’s phase change planar structures

Phase change materials (PCMs) like GeTe have become essential in reconfigurable nanophotonic devices due to their ability to undergo reversible structural transitions between amorphous and crystalline states, which lead to significant, tunable changes in optical properties. This tunability allows for dynamic control over light-matter interactions, making PCMs ideal for optical switches, modulators, and adaptive photonic systems. In this study, we propose a reconfigurable narrowband-to-broadband absorber based on planar GeTe structures integrated with GaAs layers and a Silicon and a gold thin-film substrate, which we designed and analyzed numerically by the Finite Element Method (FEM). Our design leverages the contrasting behaviors of GeTe: the amorphous phase enables narrowband absorption, while the crystalline phase broadens the absorption spectrum to cover the range from 1150 to 1750 nm. The influence of material thickness was also assessed to evaluate manufacturing error tolerances, allowing for a more precise selection of the desired configuration. The effects of oblique incidence angles on Transversal Electric (TE) and Transversal Magnetic (TM) polarized waves were analyzed for both cases. Additionally, the physical mechanisms of field coupling were investigated.