Dynamic topological charge switching in vortex beam generation using phase-change materials

This study employs the phase-change material Sb₂S₃ to design a tunable vortex beam (VB) generator based on bound states in the continuum (BICs). Sb₂S₃ exhibits a significant contrast in refractive indices between its amorphous and crystalline states, with negligible loss in the near-infrared region, rendering it an ideal phase-change material. Dynamic switching of the topological charges of BICs in the photonic crystal plate was achieved by transition of the states of Sb₂S₃, which resulted in the generation of tunable VBs at the target wavelength of 1310 nm with topological charges of -2 and +2, respectively, using the polarization topology surrounding these BICs. Meanwhile, the symmetry of the structure is changed from C_4v to C_6v, which enables the generation and dynamic modulation of high- and low-order VBs with topological charges of +4 and -2. This phase-change-based tunable VB generator opens new avenues for optical communication, optical micromanipulation, and optical microscopy research.