Guided-Mode-Resonance Bilayer ITO Nanogratings: High-Quality Structural Colors with Multimodal Tunability for Advanced Photonic Applications

Structural color filters often face trade-offs among color purity, gamut, and dynamic functionality. This study demonstrates a reflective color filter based on nanoscale bilayer ITO-based grating that overcomes these limitations by leveraging the synergistic interplay between guided-mode resonance and index-matching-enhanced field confinement. The optimized device delivers exceptional optical performance, including high color purity, enhanced brightness, and an extended color gamut. Specifically, for a red filter, the nanoscale-tailored bilayer structure achieves 81% reflectivity at 625 nm─representing a 9-fold enhancement compared to single-layer designs─along with ultranarrowband resonance (8 nm fwhm) and a color gamut covering 132% of the standard sRGB space. Furthermore, the platform supports multimodal dynamic modulation via electrochromism, polarization, and angle control, enabling dual-information encoding within a subwavelength single pixel. These attributes, combined with CMOS compatibility, make this architecture a versatile candidate for applications in high-density optical storage, advanced displays, and anticounterfeiting.