Helicity-dependent orbital angular momentum metalens for varifocal and polarization-multiplexing applications

Optical vortex beams serve as ideal carriers for optical communication. However, existing metasurfaces have limitations in dynamic and multi-dimensional control, restricting their synergistic application in polarization multiplexing and dynamic focusing. To address this, this paper designs a dual-layer helicity-dependent tunable orbital angular momentum dielectric metalens operating at a wavelength of 1550 nm. This structure comprises a lower layer of silicon nanopillars (combining propagation and geometric phases) and an upper layer of Sb₂S₃ phase-change material nanopillars (providing tunable propagation phase). It achieves continuous adjustment of focal length through material phase transition without altering the physical structure. Upon incidence of linearly polarized (LP) light, two sets of focused spots with topological charges of ±1 can be simultaneously generated. For right-handed circularly polarized light incidence, a focal spot with a topological charge of -1 is generated, with a focal tuning range of 16.4 -20.0μm. For left-handed circularly polarized light incidence, a focal spot with a topological charge of +1 is generated, with a focusing range of 32.5-43.0μm. Simulations show that the focusing efficiencies for circularly and LP light are higher than 56.7% and 39%, respectively. This metalens possesses both polarization multiplexing and continuous focusing capabilities, holding potential applications in integrated optical vortex devices and quantum information processing, and is expected to drive the development of low-cost, large-scale optical vortex chips.