Plasmonic Nano-Gap Tilings: Light-Concentrating Surfaces for Low-Loss Photonic Integration

Owing to their ability to concentrate light on nanometer scales, plasmonic surface structures are ideally suited for on-chip functionalization with nonlinear or gain materials. However, achieving a high effective quantum yield across a surface not only requires strong light localization but also control over losses. Here, we report on a particular class of tunable low-loss metasurfaces featuring dense arrangements of nanometer sized focal points on a photonic chip with an underlying waveguide channel. Guided within the plane, the photonic wave evanescently couples to the nano-gaps, concentrating light in a lattice of hot-spots. In studying the energy transfer between photonic and plasmonic channels of single trimer molecules and triangular nano-gap tilings in dependence on element size, we identify different regimes of operation. We show that the product of field enhancement, propagation length and element size is close-to-constant in both the radiative and subwavelength regimes, opening pathways for device designs that combine high field enhancements with large propagation lengths.