Shaping Near Fields of Photonic Modes into Topological Textures

Abstract

Topological textures of light, such as optical vortices and skyrmions, are attractive for high-density information encoding and light-matter interactions. In the near field, topologies have primarily been realized using polaritonic platforms that inherently tie the platform to the material dispersion, limiting their footprint due to propagation losses and restricting their operating spectral region. Here, we introduce a route to shape near-field topologies through the geometric engineering of a dielectric metasurface supporting a quasi-bound state in the continuum resonance, without the need for polaritonic surface waves. In-plane deformation of our metasurface bars conserves their resonance-driven near-fields locally, so that the metasurface geometry and the polarization of the illuminating light dictate the generated topology. By shaping silicon unit cells into geometries with rotational symmetry, we create optical topologies with controllable topological charge. Using phase-resolved scattering-type near-field optical microscopy, we experimentally characterize high-purity resonance-locked topologies such as vortices in concentric rings and topological charge doublets in Archimedean spirals. In contrast to conventional topological textures, our purely photonic mode-based field textures are stationary standing waves in the radial direction, without relying on surface-wave propagation or polaritonic dispersion, establishing a spectrally and spatially scalable platform for near-field topological photonics.