Nonlinear Plasmonic Meta‐Crystals with Coupling Induced Symmetry Breaking

Abstract

AbstractSymmetry plays an important role in determining the amplitude and polarizations of nonlinear optical waves occurring in conventional crystals. While the symmetry of crystals is limited by the materials’ synthesis process, it can be easily controlled in photonic meta‐crystals. Both the linear and nonlinear optical properties of the meta‐crystals can be judiciously tailored by the local symmetry of the meta‐atoms. Here, it is demonstrated that the symmetry of the nonlinear meta‐crystals can be artificially manipulated by introducing the coupling between adjacent plasmonic meta‐atoms. By assembling the two groups of plasmonic meta‐atoms with inversion symmetry into a hexagonal boron nitride‐like lattice, the global inversion symmetry of the metasurface is broken. Second harmonic generations due to the coupling‐induced symmetry breaking are experimentally observed from the meta‐crystals. It is also found that the polarization of the second harmonic waves obey certain symmetry selection rules. The proposed methodology, which takes advantage of the coupling effects and the intrinsic nonlinearity of the plasmonic meta‐atoms, can be used to develop a variety of nonlinear nanophotonic devices with multiple functionalities.