Multipole lattice effects in high refractive index metasurfaces

In this Perspective, we outline the recent progress, primary achievements, and further directions in the development of high refractive index nanostructures and metasurfaces. In particular, we review the role of multipole lattice effects in resonant properties of underlying nanostructures and nanophotonic elements in detail. Planar optical designs with efficient light control at the nanoscale can be engineered based on photonic lattices that operate in the translational regime between two and three dimensions. Such transdimensional lattices include 3D-engineered nanoantennas supporting multipole Mie resonances and arranged in the 2D arrays to harness collective effects in the nanostructure. Lattice effects in the periodic nanoparticle arrays have recently attracted a lot of attention as they enable not only spectrally narrow resonant features but also resonance position tuning over a broad range. The recent results indicate that different nanoparticle multipoles not only produce resonant spectral features but are also involved in the cross-multipole coupling, and these effects need to be accounted for in photonic designs. Multipole lattice phenomena provide an effective way to control nanoparticle resonances, facilitate excitation of additional multipoles through a cross-multipole coupling, and enable light localization in planar photonic elements. We review different effects related to the same- and cross-multipole interactions in the arrays. Both infinite and finite arrays, as well as lattices of complex-shape nanoparticles, which allow out-of-plane multipole excitations, are considered.