Tunable topologically protected transmissive structural colors in layered film structures with high purity and brightness.

Structural colors from the interaction of light with well-designed nanostructures are highly promising for achieving long-term colors with high purity and brightness compared with traditional dyes and pigments. However, further improvement of the brightness and purity of colors originating from optical interference or nanophotonic resonances remains challenging due to inevitable losses and sidebands in such a design. Here, we show that in-band gap topologically protected state colors (TPSCs) that reside at the interface between layered thin films in the extended model with different Zak phases are ideal candidates for high-brightness transmissive colors due to the low loss characteristic from topology. At the same time, by applying several degrees of freedom to tune the narrow resonant linewidths (FWHM down to ∼12 nm in simulation, with further improvement possibility) of TPSCs within the band gap, we can realize a color gamut of 156% sRGB color space. The design is verified by sputtering TiO/SiO layers on a glass substrate, with FWHM ∼20 nm and a transmission above 94.5% realized. The exact TPSCs resonance at the physical interface of different units presented here may guarantee further color brightness and purity improvement with the cooperation of active materials in layered thin film structures, which are highly promising for large-scale and high-performance transmissive structural colors.