Torus-Projected Electromagnetic Wormholes Enabled by Anisotropic Singularity Reconstruction of Metamaterials

Abstract: Transformation optics uses coordinate mappings to emulate curved geometries and control electromagnetic fields. However, existing approaches primarily focus on geometric deformation while offering limited control over the global topology of the resulting optical space. Here we introduce a torus projection combined with a conformal mapping to construct a wormhole-like virtual optical geometry, providing a controllable route to manipulate optical-space topology within transformation optics. By tuning a single torus parameter, the virtual-space refractive index switches between isotropic and anisotropic forms, transforming point-like singularities in a disconnected geometry into extended transport channels that connect the optical space. This topology transition manifests as the opening or closure of an electromagnetic wormhole and is accompanied by pronounced changes in ray dynamics and cavity modes. Our results demonstrate how refractive-index anisotropy governs singularity structure and topology in transformation optics, providing a route to photonic systems with tunable optical geometry and connectivity.