Enhancing Nonlinear Interactions by the Superposition of Plasmonic Lattices on χ(2)-Nonlinear Photonic Crystals

Plasmonic structures have been revealed as efficient units to enhance localized nonlinear phenomena generated at dielectric–metal interfaces. However, their effect on the nonlinear interactions provided by quasi-phase matching processes in χ(2) modulated dielectric crystals have been scarcely addressed, mainly due to the complexity in manufacturing appropriate periodic plasmonic structures overlying the χ(2) dielectric structure. Here, by a simple method we have fabricated a periodic structure based on the combination of two commensurate lattices: a periodic lattice of chains of Ag nanoparticles and a periodic lattice of χ(2)-modulation based on a ferroelectric domains structure. The hybrid system supports multiple surface plasmon lattice resonances (SLRs) at the technologically relevant NIR spectral region, which yield the enhancement of the nonlinear diffraction pattern generated by the χ(2) structure. The superposition of the plasmonic and the χ(2)-modulation lattice results in a 20-fold enhancement of the directional SHG due to the excitation of SLRs by the interacting waves involved in the nonlinear process. The results are obtained in lithium niobate, a widely used crystal in optoelectronics, and demonstrate the potential of the approach to design integrated solid-state platforms for on-chip optical steering, multiplexing or quantum technologies.