Phase change material-based tunable Fano resonant optical coatings and their applications

Thin-film coatings offer a scalable optical platform, as compared to nanopatterned films, for various applications including structural coloring, photovoltaics, and sensing. Recently, Fano resonant optical coatings (FROCs) have gained attention. FROCs consist of coupled thin film nanocavities composed of a broadband and a narrowband optical absorber. The optical properties of FROCs can be dynamically adjusted using chalcogenide phase change materials (PCM). Switching the structural states of PCM layers in the cavity between amorphous and crystalline states, the Fano resonance supported by FROC can be modulated in terms of resonance wavelength, intensity, and bandwidth. This review discusses the scientific and technological facets of both passive and active FROCs for applications in structural coloring and spectrum-splitting filters. We explore electrically tunable FROCs for dynamic color generation and optical steganography. Furthermore, we discuss the utilization of passive and active FROCs as spectrum-splitting filters to mitigate the drop in photovoltaic efficiency of solar cells due to heating and for hybrid thermal-electric power generation.