Tunable topological polaritons by dispersion tailoring of an active metasurface

Hyperbolic polaritons are known to exist in materials with extreme anisotropy, exhibiting exotic optical properties that enable a plethora of unusual phenomena in the fields of polaritonics and photonics. However, achieving simultaneous low-dimensionality, high-speed controllability, and on-demand reconfigurability of the polaritons remains unexplored despite their excellent potential in light–matter interactions, photonic integrated circuits, and optoelectronic devices. Here, we propose a metasurface approach to integrating artificially engineered electromagnetic anisotropy with fast-controllable electronic elements, offering a new route to realize active topological polaritons. Experiments showcase the proposed reconfigurable metasurface can support real-time transitions of designer polaritons from elliptical to flat, and then to hyperbolic and circular isofrequency contours. Correspondingly, the in-plane surface wavefront undergoes the transitions from convex to collimating, concave, and eventually back to convex. By exploiting the topological variations in polariton dispersions, we observe intriguing phenomena of controllable field canalization and tunable planar focusing. Furthermore, we report the concept of a planar reconfigurable integrated polariton circuit by spatially tailoring the distributions of polariton isofrequency contours, unveiling rich dispersion engineering possibilities and active control capabilities. We may provide an inspiring platform for developing planar active plasmonic devices with potential applications in subdiffraction-resolution imaging, sensing, and information processing.