Topological optical state integration and dynamic switching of multifunctional terahertz metasurfaces driven by phase transition

The multi-dimensional dynamic manipulation and integration of topological optical fields are crucial for advancing the application of terahertz (THz) metasurfaces in high-dimensional information processing and on-chip photonics. However, current THz metasurfaces face challenges such as insufficient reconfigurability and limited mode manipulation freedom. These hinder the dynamic generation and switching of complex topological modes. In this paper, we present a dynamically reconfigurable THz metasurface device based on vanadium dioxide (VO₂) phase-change material, achieving the integration and switching of multiple topological optical field states within the same structure for the first time. In the VO₂ insulating state (T < 68°C), we use symmetry-protected bound states in the continuum (BIC) to excite spatial vortex light and second-order Meron spin textures in transmission. This establishes a topological mapping between real space and momentum space. The reflection channel exhibits a spin-Hall shift with adjustable incident chirality. Upon the phase transition of VO₂ to the high-temperature metallic state, the BIC evolves into a quasi-BIC state, leading to the realization of radiation output of spatiotemporal vortex light. Simulations show the device maintains stable singular optical fields over a broad frequency band. This enables all-optical dynamic switching via thermal control and incident polarization. This research offers novel insights into topological multiplexing in the THz band, spatiotemporal dimension information coding, and the design of high-dimensional quantum optical devices.