Programmable polariton canalization in reconfigurable metasurfaces.

The topological transition of polariton dispersion in twisted van der Waals layers at the photonic magic angle results in the diffraction-less and collimated propagation state, termed canalization regime. This type of robust transport of polaritons (i.e., polariton canalization) holds promise for subwavelength control of energy flows. However, the lack of in situ dynamic tunability of canalized polaritons hinders such control because the canalization direction is fixed in the fabricated device. Here, we overcome this limitation by demonstrating programmable polariton canalization in a reconfigurable single-layer metasurface. By engineering the orientation of metasurface unit cells, the direction of canalized magnetic polaritons can be programmed along any in-plane direction (i.e., dynamic all-angle tunability). On-demand steering of canalized polaritons allows customized near-field patterns to be obtained at any desired location-a proof of concept for canalization-based information display applications. These findings offer opportunities to transcend conventional diffraction constraints for integrated photonic devices, thus opening the door for photonic applications where on-demand control is crucial.