Strong second-harmonic generation in dielectric optical nanoantennas resulting from the hybridization of magnetic dipoles and lattice resonances
Arranging high-index dielectric nanoparticles in a periodic array boost their second-harmonic generation when local and collective resonances play together. In this article, H. Jiang and coauthors present numerical results for an array of AlGaAs nanocylinders, a semiconductor with a refractive index >3 in the VIS-NIR range and a marked second-order nonlinearity. Single AlGaAs nanocylinders are efficient generators of second-harmonic light, thanks to the tight confinement of the pump light at the Mie resonances. In particular, the magnetic dipole (MD) resonance is frequently used to boost their nonlinear response. Borrowing a strategy developed for plasmonic systems, the authors show that arranging many identical AlGaAs nanocylinders in a periodic array strongly reinforces the MD resonance of the single element, with a dramatic effect on the second-harmonic generation. They performed simulations for an extensive set of values of the array parameters. When the pitch gets comparable to the pump wavelength, the array supports a collective, extended mode known as a surface lattice resonance. They managed coupling the collective resonance to the local MD resonance and produced a hybridized MD-surface lattice resonance. Remarkably, the stronger circulation of the electric field of the hybridized mode enhances the second-harmonic generation by two orders of magnitude, compared to the case of an isolated nanocylinder. These numerical results confirm the efficacy of all-dielectric photonic platforms to support nonlinear effects and call for experiments soon.