Disordered Near-Field Metasurfaces for On-Chip Wavelength Demultiplexing

Plasmonic and dielectric building blocks shape the flow of light at boundaries and interfaces. While metasurfaces that consist of plasmonic or dielectric nanophotonic elements have established a framework for shaping the far field, control over near fields remains largely unexplored. Here, we introduce disordered metasurfaces for near-field light shaping. Near-field distributions are created by engineering the interference of surface plasmons launched from scatterers on metallic surfaces. We demonstrate near-field metasurfaces to direct, focus, and demultiplex light. These structures use a strip-off process, resulting in ultrasmooth metallic surfaces suitable for efficient surface plasmon propagation. An optical imaging setup enables retrieval of the local near-field by mapping it into the far-field. Our concept can be generalized to arbitrary near-field distributions, permitting nanoscale routing and sorting of light based on polarization and orbital angular momentum, as well as coupling schemes to emitters and nanoscale systems in ultracompact integrated photonic receivers and demultiplexers.