Three-dimensional nonlinear plasmonic metamaterials

Three-dimensional (3D) metamaterials show the potential for realizing efficient nonlinear nanoscale devices. Despite the recent progress, the nonlinear metamaterials lack in terms of conversion efficiencies when compared against conventional nonlinear materials that rely on phase-matching techniques. Here, we demonstrate how the nonlinear responses of 3D metamaterials can be improved by stacking metasurfaces on top of each other and by applying phase-matching techniques. We demonstrate this by successfully fabricating phase-matched metamaterials consisting of stacked metasurfaces. Especially, we observe a 25-fold enhancement of second harmonic generation emission from a device consisting of five metasurfaces.