Expanded polarization tunable structural colors with two-way transmission and reflection enabled by Al-HfO₂ bilayer structure

In this study, we introduce elliptical nanopillar structures on metasurfaces, which have been theoretically validated to exhibit both transmitted and reflected colors that can be dynamically adjusted by changing the polarization of incident light. The interaction between electric quadrupole resonance and magnetic dipole resonance within the bilayer Al-HfO₂ nanopillars produces pronounced monochromatic transmission peaks and maintains vibrant reflective colors due to minimal losses. By altering the duty cycle and period of the structure, a diverse range of colors is achievable. Furthermore, we developed polarization-tunable pixels that can be adjusted from 0° to 180° using a modular design. These features make our proposed structures ideal for applications in anti-counterfeit measures, optical information encryption, and dual-sided displays.