Giant and reconfigurable vortical dichroism with multi-layer spiral metamaterials

In the photonics orbital angular momentum dimension, the vortical dichroism (VD) of artificial metamaterials at fixed wavelengths has been extensively investigated. However, the challenges of weak and unregulated VD magnitude still limit the development of chiral optics. Herein, we propose multi-layer spiral metamaterials with phase change material Ge₂Sb₂Te₅ (GST), which support giant VD magnitude of −176% in the optical communication band around 1550 nm. Meanwhile, by changing the temperature to control the GST from crystalline to amorphous states, the VD magnitude rapidly decreases to −1%. This large change from extremely giant magnitude to weak magnitude indicates the advantages of reconfigurable VD response. The maximum modulation depth reaches almost 100%. The GST based metamaterials possess excellent switchable capability for VD magnitude without refabricating structures, which is promising in applications for the next generation of chiral optical communication devices.