Mode Switching With Waveguide-Coupled Plasmonic Nanogratings

Active photonic elements enable a wide range of on-chip optical applications, including enhanced light emission, integrated optical sensing and spectroscopy, photonic signal routing, and optical computing. The ability to select between different optical channels forms the basis for many of these systems. Both spectral and spatial selectivity of optical modes are desirable and together offer flexibility in tailoring the optical response of the system. In this work, we experimentally demonstrate a platform for the active switching of hybrid plasmonic-photonic Fano resonances. Our structure consists of gold nanogratings sandwiched between two dielectric thin films. Diffractive coupling into each layer is modulated by varying the refractive index above the structure. By controlling the interaction of the substrate and superstrate modes through refractive index tuning, we experimentally demonstrate on/off switching of the narrow (FWHM = 30-40 nm) Fano resonance transparency windows with up to 85% resonance contrast, and tunability across a wide spectral range (600-850 nm). Full-wave electromagnetic simulations support these results and reveal that the tuning of these modes enables both spectral and spatial selectivity.