Tunable Structural Transmissive Color in Fano-Resonant Optical Coatings Employing Phase-Change Materials

TL;DR

This paper demonstrates a novel four-layer optical coating using phase-change materials to achieve tunable, narrowband structural colors in reflection and transmission via Fano resonances, with asymmetric responses and ML-optimized designs.

Contribution

It introduces a new Fano-resonant optical coating incorporating phase-change materials for tunable structural colors in both reflection and transmission.

Findings

Achieved tunable narrowband peaks in both reflection and transmission.

Demonstrated asymmetric optical response depending on light incidence side.

Used machine learning for multi-objective inverse design of the coatings.

Abstract

Reversible, nonvolatile, and pronounced refractive index modulation is an unprecedented combination of properties enabled by chalcogenide phase-change materials (PCMs). This combination of properties makes PCMs a fast-growing platform for active, low-energy nanophotonics, including tunability to otherwise passive thin-film optical coatings. Here, we integrate the PCM Sb2Se3 into a novel four-layer thin-film optical coating that exploits photonic Fano resonances to achieve tunable structural colors in both reflection and transmission. We show, contrary to traditional coatings, that Fano-resonant optical coatings (FROCs) allow for achieving transmissive and reflective structures with narrowband peaks at the same resonant wavelength. Moreover, we demonstrate asymmetric optical response in reflection, where Fano resonance and narrow-band filtering are observed depending upon the light incidence side. Finally, we use a multi-objective inverse design via machine learning (ML) to provide a wide range of solution sets with optimized structures while providing information on the performance limitations of the PCM-based FROCs. Adding tunability to the newly introduced Fano-resonant optical coatings opens various applications in spectral and beam splitting, and simultaneous reflective and transmissive displays, diffractive objects, and holograms.