Nonlinear Fano-Resonant Dielectric Metasurfaces
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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<sup>5</sup> with respect to an unpatterned silicon film and an absolute conversion
efficiency of 1.2 × 10<sup>–6</sup> with a peak pump intensity
of 3.2 GW cm<sup>–2</sup>. 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