Si metasurface supporting multiple quasi-BICs for degenerate four-wave mixing

Abstract

Dielectric metasurfaces supporting quasi-boundstates in the continuum (qBICs) enable high field enhancementwith narrow-linewidth resonances in the visible andnear-infrared ranges. The resonance emerges when distortingthe meta-atom’s geometry away from a symmetryprotectedBIC condition and, usually, a given design cansustain one or two of these states. In thiswork, we introducea silicon-on-silica metasurface that simultaneously supportsup to four qBIC resonances in the near-infrared region.This is achieved by combining multiple symmetry-breakingdistortions on an elliptical cylinder array. By pumping twoof these resonances, the nonlinear process of degeneratefour-wave mixing is experimentally realized. By comparingthe nonlinear response with that of an unpatterned siliconfilm, the near-field enhancement inside the nanostructureddielectric is revealed. The presented results demonstrateindependent geometric control of multiple qBICs and theirinteraction through wave mixing processes, opening newresearch pathways in nanophotonics, with potential applicationsin informationmultiplexing,multi-wavelength sensingand nonlinear imaging.