Nonlinear Fano-Resonant Dielectric Metasurfaces

TLDR

Strong nonlinear light–matter interactions are sought for lasing and all‑optical modulation, and while resonant plasmonic structures can enhance near‑field effects, their tiny mode volumes limit the exploitation of metal nonlinearities. The authors propose a Fano‑resonant silicon metasurface as an alternative platform. The metasurface delivers intense near‑field enhancement inside the silicon resonator with reduced two‑photon absorption, and pump–probe experiments elucidate its modulation mechanism. It yields a 1.5 × 10⁵‑fold third‑harmonic generation enhancement, a 1.2 × 10⁻⁶ conversion efficiency at 3.2 GW cm⁻², and a 36 % transmission modulation depth.

Abstract

Strong nonlinear light-matter interaction is highly sought-after for a variety of applications including lasing and all-optical light modulation. Recently, resonant plasmonic structures have been considered promising candidates for enhancing nonlinear optical processes due to their ability to greatly enhance the optical near-field; however, their small mode volumes prevent the inherently large nonlinear susceptibility of the metal from being efficiently exploited. Here, we present an alternative approach that utilizes a Fano-resonant silicon metasurface. The metasurface results in strong near-field enhancement within the volume of the silicon resonator while minimizing two photon absorption. We measure a third harmonic generation enhancement factor of 1.5 × 10(5) with respect to an unpatterned silicon film and an absolute conversion efficiency of 1.2 × 10(-6) with a peak pump intensity of 3.2 GW cm(-2). The enhanced nonlinearity, combined with a sharp linear transmittance spectrum, results in transmission modulation with a modulation depth of 36%. The modulation mechanism is studied by pump-probe experiments.