Fano resonant optical coatings platform for full gamut and high purity structural colors

Abstract

Structural coloring is a photostable and environmentally friendly coloring approach that harnesses optical interference and nanophotonic resonances to obtain colors with a range of applications including display technologies, colorful solar panels, steganography, décor, data storage, and anticounterfeiting measures. We show that optical coatings exhibiting the photonic Fano Resonance present an ideal platform for structural coloring; they provide full color access, high color purity, high brightness, controlled iridescence, and scalable manufacturing. We show that an additional oxide film deposited on Fano resonant optical coatings (FROCs) increases the color purity (up to 99%) and color gamut coverage range of FROCs to 61% of the CIE color space. For wide-area structural coloring applications, FROCs have a significant advantage over existing structural coloring schemes.

Recent progress on structural coloration

“…Recently, Mohamed et al designed a structure called Fabry-Perot resonance optical coatings (FROCs) [110] . They deposited a layer of absorbing dielectric material on an FP cavity, where the absorbing medium forms a broadband absorbing cavity with the first metal layer, and the lower three layers form an FP resonance serving as a narrowband absorbing cavity.…”

“…(a) Integration of Si nanostructures into FP cavity for uniform cavity length structural color display (1), color tuning through the mixture of different nanostructures on a high-color-saturation display foundation (2), and easy achievement of polarization response by controlling the symmetry of nanostructures (3)[109] . (b) Schematic structure of FROCs formed by two coupled light absorbers (1), deposition of an absorbing medium on the FP cavity, coupling of the upper broadband mode with the lower FP resonance to form Fano resonance, resulting in vivid structural colors (2), (4), and exhibiting over 50°observation angle (3)[110] .…”

Aperiodic Bragg Reflectors for Tunable High-Purity Structural Color Based on Phase Change Material

“…In general, typical thin-film coatings are composed of metal–dielectric–metal (MDM) cavities and produce colors through selective absorption of light. , Nevertheless, the main drawbacks associated with these MDM thin film coatings are of poor color purity and generate iridescent and distinct colors in the reflection and transmission modes. Lately, ElKabbash et al adeptly tackled these issues by introducing a novel type of thin-film coating consisting of a broadband and a narrowband absorber, which produces colors due to the generation of the asymmetric Fano resonance. − In a brief span, this color scheme has gained significant attention among researchers because of its numerous distinctive attributes, such as the ability to produce the same iridescence-free colors in both reflection and transmission modes, along with high resolution and purity. , Recently, dynamically tunable structural coloring was demonstrated by incorporating nonvolatile phase change materials (PCMs) into FROC, − as PCMs have received great attention due to their rapid switching speed, stable memory beyond the transition temperature, large refractive index contrast, and tunable optical responses across a wide range of wavelengths from ultraviolet to terahertz. ,− Although this discovery would bring many opportunities in the field of nanophotonics − including structural coloring, there are certain drawbacks associated with reflective tunable FROC-based color filters that require further research. The main shortcomings are (i) a broad and asymmetric Fano resonance spectrum hinders achieving a selective narrow reflection band in the visible spectrum, (ii) the presence of off-resonance reflections impacts the color purity, and (iii) absorption loss due to metal and lossy dielectric material hinders the attainment of highly reflective Fano resonance with narrow line width.…”