Janus Structural Color from a 2D Photonic Crystal Hybrid with a Fabry-Perot Cavity

Structural colors are widely applied for their stability and their sophisticated optical responses. However, these colors always appear washed-out or pale assigning to the defect hardly avoided in the manufacturing procedures. It is still a challenge to bring multifunctional vivid color via a facile method. A composite structure combining 2D photonic crystal and Fabry-Perot cavity by a simple and convenient method is constructed here. Various metallic colors with tunable hue and high saturation are produced by the composite structure. What is more, an obvious optical Janus effect is created by the composite structure. Iridescent colors can be observed when viewing from the same side of incident light but only pale colors can be seen from the opposite side. The hues and saturation of the colors can be adjusted by the parameters of the composite structure. The experimental results indicate that the color is derived from the synergistic effect of the interference, the diffraction, and the Rayleigh scattering of the composite structure. The facile composite photonic structure pioneers a new way for art, architecture, and security features in anticounterfeiting materials.