Second-harmonic generation in subwavelength graphene waveguides

We suggest a novel approach for generating second-harmonic radiation in subwavelength graphene waveguides. We demonstrate that quadratic phase matching between the plasmonic guided modes of different symmetries can be achieved in a planar double-layer geometry when conductivity of one of the layers becomes spatially modulated. We predict theoretically that, owing to graphene nonlocal conductivity, the second-order nonlinear processes can be actualized for interacting plasmonic modes with an effective grating coupler to allow external pumping of the structure and output of the radiation at the double frequency.Comment: 5 pages, 3 figure

Quantum spin Hall effect of light

Maxwell's equations, formulated 150 years ago, ultimately describe properties of light, from classical electromagnetism to quantum and relativistic aspects. The latter ones result in remarkable geometric and topological phenomena related to the spin-1 massless nature of photons. By analyzing fundamental spin properties of Maxwell waves, we show that free-space light exhibits an intrinsic quantum spin Hall effect, i.e., surface modes with strong spin-momentum locking. These modes are evanescent waves that form, e.g., surface plasmon-polaritons at vacuum-metal interfaces. Our findings illuminate the unusual transverse spin in evanescent waves and explain recent experiments demonstrating the transverse spin-direction locking in the excitation of surface optical modes. This deepens our understanding of Maxwell's theory, reveals analogies with topological insulators for electrons, and offers applications for robust spin-directional optical interfaces.Comment: 8 pages, 4 figures, Supplementary Material

Optical anapoles in nanophotonics and meta-optics

Interference of electromagnetic modes supported by subwavelength photonic structures is one of the key concepts that underpins the subwavelength control of light in meta-optics. It drives the whole realm of all-dielectric Mie-resonant nanophotonics with many applications for low-loss nanoscale optical antennas, metasurfaces, and metadevices. Specifically, interference of the electric and toroidal dipole moments results in a very peculiar, low-radiating optical state associated with the concept of optical anapole. Here, we uncover the physics of multimode interferences and multipolar interplay in nanostructures with an intriguing example of the optical anapole. We review the recently emerged field of anapole electrodynamics explicating its relevance to multipolar nanophotonics, including direct experimental observations, manifestations in nonlinear optics, and rapidly expanding applications in nanoantennas, active photonics, and metamaterials.Comment: 14 pages, 6 figure

Ring Dirac solitons in nonlinear topological systems

We study solitons of the two-dimensional nonlinear Dirac equation with asymmetric cubic nonlinearity. We show that with the nonlinearity parameters specifically tuned, a high degree of localization of both spinor components is enabled on a ring of certain radius. Such ring Dirac soliton can be viewed as a self-induced nonlinear domain wall and can be implemented in nonlinear photonic graphene lattice with Kerr-like nonlinearities. Our model could be instructive for understanding localization mechanisms in nonlinear topological systems.A.N.P. acknowledges the support of the Australian Research Council and of the “Basis” Foundation. D.A.S. acknowledges the support of the Russian Foundation for Basic Research (Grant No. 18-02-00381)