Enhanced four-wave mixing from multi-resonant silicon dimer-hole membrane metasurfaces

Tailoring optically resonant features in dielectric metasurfaces unveils a robust scheme to control electromagnetic near fields of light and thus to boost the nanoscale nonlinear light-matter interactions. Membrane metasurfaces offer unique possibilities for supporting multipolar resonances and meanwhile maintaining high mode volume for enhancing nonlinear frequency conversion. Here we design a silicon membrane metasurface consisting of dimer airy holes, as a versatile platform for generating four-wave mixing (FWM). We show that such a metasurface exhibits a multi-resonant feature, including a quasi bound state in the continuum (BIC) generated by the collective toroidal dipole mode excited in the designed subdiffractive periodic system. We show that via employing the BIC mode in the short-wave infrared (SWIR), together with other resonant enhanced electric near fields in the near-infrared (NIR) region, simultaneously, one can convert invisible SWIR light to visible light radiation with high efficiency, via FWM. We experimentally demonstrated a significant FWM emission enhancement from our metasurface, which leads to a conversion efficiency of 0.76 × 10-6 using pump and signal beam peak intensities as low as 0.33 GW cm-2 and 0.17 GW cm-2, respectively. Our results open new routes for enhancing nonlinear efficiencies for up-conversion processes.