Third Harmonic Generation Enhanced by Multipolar Interference in Complementary Silicon Metasurfaces

Nonlinear harmonic generation in metasurfaces has shown great promise for applications such as novel light sources, nonlinear holography, and nonlinear imaging. In particular, dielectric metasurfaces have shown multifold enhancement of the harmonic efficiency in comparison to their plasmonic counterparts due to lower optical loss and much higher damage threshold. In this work, we propose to enhance the efficiency of the third harmonic generation in a complementary silicon nonlinear metasurface, consisting of nanoapertures of cross-like shape in the silicon film. The efficiency enhancement is based on a multipolar interference between the magnetic dipole and electric quadrupole, resulting in significant near-field enhancement and a large mode volume of the nonlinear interaction. The measured efficiency of third harmonic generation from the silicon metasurface is 100× higher than that from a planar silicon film of the same thickness. Numerical analysis of the near-field resonant modes confirms the multipolar mechanism of nonlinear enhancement. Enhanced third harmonic generation by multipolar interference in complementary dielectric nanostructure opens a new route for developing high-efficiency nonlinear metasurfaces.