Reconfigurable vortex generation based on phase change material

Abstract

The development of reconfigurable optical vortex (OV) generators is of great value because dynamic switching between different orbital angular momentum (OAM) states not only enables high-density data transmission, but also significantly enhances the security of wired and wireless communication networks. However, current dynamic OV generation methods face challenges in terms of alignment conditions, fabrication robustness, device integration and miniaturization, as well as OV generation purity. Here, we theoretically propose a reconfigurable OV generation method by dynamically engineering the photonic band structures via phase change material. OVs are generated by exploiting the winding topology properties of momentum-space polarization distributions around bound states in the continuum (BICs). By switching between different states of phase change materials, the interaction between the target BIC and the incident light can be flexibly selected to achieve OV with tunable OAM. In this work, the geometric phase gradient is generated in momentum space, thereby eliminating the need of beam alignment in real space. The purity of generated OVs approaches nearly 100 % in theory and exhibits robustness against fabrication errors to a certain extent. Using low-loss phase change materials to control the topological properties of the system offers new opportunities for tunable optical devices, on-chip optical communications and other applications.