Moire Metasurface with Triple-Band Near-Perfect Chirality

Chiral metasurfaces have been proven to possess great potential in chiroptical applications. However, the multiband chiral metasurface with near-perfect circular dichroism has not been well studied. Also, the widely used bilayer metasurface usually suffers from the interlayer alignment and weak resonance. Here, we propose a twisted Moire metasurface which can support three chiral bands with near-unity circular dichroism. The Moire metasurface can remove the restriction of interlayer alignment, while maintaining a strong monolayer resonance. The two chiral bands in the forward direction can be described by two coupled-oscillator models. The third chiral band is achieved by tuning the interlayer chiral mode on resonance with the intralayer mode, to eliminate the parallel and converted components simultaneously. Finally, we study the robustness and tunability of the triple-layer Moire metasurface in momentum space. This work provides a universal method to achieve three near-unity circular dichroism bands in one metasurface, which can promote applications of chiral metasurfaces in multiband optical communication, chiral drug separation, sensing, optical encryption, chiral laser, nonlinear and quantum optics, etc.