Wave interference is a fundamental manifestation of the superposition principle with numerous applications. While in conventional optics interference occurs between waves undergoing different phase advances during propagation, we show that the vectorial structure of the near-field of an emitter is essential for controlling its radiation as it interferes with itself on interaction with a mediating object. We demonstrate that the near field interference of a circularly polarized dipole results in the unidirectional excitation of guided electromagnetic modes in the near-field, with no preferred far-field radiation direction. By mimicking the dipole with a single illuminated slit in a gold film, we measured unidirectional surface-plasmon excitation in a spatially symmetric structure. The surface wave direction is switchable with the polarization.Interference is the cornerstone of various phenomena in nature enabling numerous applications. In optics, it is intensively used in microscopy, stellar measurements, spectroscopy, and communication technologies, among many others, and is the basis behind the concepts of reflection, refraction and light bending (1, 2). Typically, interference occurs due to the relative phase lag of different propagating waves. On the other hand, nanophotonics -the branch of optics studying the interaction of light with subwavelength nanoscale structures-deals inherently with phenomena that occur via near-field interactions before appreciable phase lags can be accumulated (3). A radiationless form of interference in the near field (4) is behind new exciting applications such as the focusing of evanescent components to achieve subwavelength resolution in imaging (5-8). Near field interference achieved through the full coherent control of the phase and amplitude of excitation light allows asymmetric spatial field localization (9, 10) and selection of propagation paths at intersections of waveguides (11).We demonstrate near field interference by considering a single source of radiation coupled to a mode with a vectorial structure of electromagnetic field. Using an additional degree of freedom provided by the vectorial character of the field, control over the near-field interference can be achieved. We show that an elliptically polarized dipole can produce destructive or constructive interference of different evanescent components in its near field, and as a result, excite electromagnetic modes in neighbouring material structures, such as dielectric and plasmonic waveguides and diffraction gratings, with a controlled directionality of propagation.

The spin Hall effect leads to the separation of electrons with opposite spins in different directions perpendicular to the electric current flow because of interaction between spin and orbital angular momenta. Similarly, photons with opposite spins (different handedness of circular light polarization) may take different trajectories when interacting with metasurfaces that break spatial inversion symmetry or when the inversion symmetry is broken by the radiation of a dipole near an interface. Here we demonstrate a reciprocal effect of spin-orbit coupling when the direction of propagation of a surface plasmon wave, which intrinsically has unusual transverse spin, determines a scattering direction of spin-carrying photons. This spin-orbit coupling effect is an optical analogue of the spin injection in solid-state spintronic devices (inverse spin Hall effect) and may be important for optical information processing, quantum optical technology and topological surface metrology.

The routing of light in a deep subwavelength regime enables a variety of important applications in photonics, quantum information technologies, imaging and biosensing. Here we describe and experimentally demonstrate the selective excitation of spatially confined, subwavelength electromagnetic modes in anisotropic metamaterials with hyperbolic dispersion. A localized, circularly polarized emitter placed at the boundary of a hyperbolic metamaterial is shown to excite extraordinary waves propagating in a prescribed direction controlled by the polarization handedness. Thus, a metamaterial slab acts as an extremely broadband, nearly ideal polarization beam splitter for circularly polarized light. We perform a proof of concept experiment with a uniaxial hyperbolic metamaterial at radio-frequencies revealing the directional routing effect and strong subwavelength l/300 confinement. The proposed concept of metamaterial-based subwavelength interconnection and polarizationcontrolled signal routing is based on the photonic spin Hall effect and may serve as an ultimate platform for either conventional or quantum electromagnetic signal processing.

Light–matter interactions can be strongly modified by the surrounding environment. Here, we report on the first experimental observation of molecular spontaneous emission inside a highly non-local metamaterial based on a plasmonic nanorod assembly. We show that the emission process is dominated not only by the topology of its local effective medium dispersion, but also by the non-local response of the composite, so that metamaterials with different geometric parameters but the same local effective medium properties exhibit different Purcell factors. A record-high enhancement of a decay rate is observed, in agreement with the developed quantitative description of the Purcell effect in a non-local medium. An engineered material non-locality introduces an additional degree of freedom into quantum electrodynamics, enabling new applications in quantum information processing, photochemistry, imaging and sensing with macroscopic composites.