Nir Shitrit

Spin-optical metamaterial route to spin-controlled photonics.

Making Metamaterials Controlling the propagation of electromagnetic waves is a key requirement in communication technologies. The components tend to be bulky, however, which can make it difficult to integrate with microelectronics circuits. Using arrays of metallic nanoantennae patterned on a substrate surface, Shitrit et al. (p. 724) fabricated a novel class of metamaterials: anisotropic materials without inversion symmetry. The materials may pave the way to polarization-dependent nanophotonics. Designed arrays of metallic nanoantennas provide a route for the polarization-dependent propagation of light. Spin optics provides a route to control light, whereby the photon helicity (spin angular momentum) degeneracy is removed due to a geometric gradient onto a metasurface. The alliance of spin optics and metamaterials offers the dispersion engineering of a structured matter in a polarization helicity–dependent manner. We show that polarization-controlled optical modes of metamaterials arise where the spatial inversion symmetry is violated. The emerged spin-split dispersion of spontaneous emission originates from the spin-orbit interaction of light, generating a selection rule based on symmetry restrictions in a spin-optical metamaterial. The inversion asymmetric metasurface is obtained via anisotropic optical antenna patterns. This type of metamaterial provides a route for spin-controlled nanophotonic applications based on the design of the metasurface symmetry properties.

Optical spin Hall effects in plasmonic chains.

Observation of optical spin Hall effects (OSHEs) manifested by a spin-dependent momentum redirection is presented. The effect occurring solely as a result of the curvature of the coupled localized plasmonic chain is regarded as the locally isotropic OSHE, while the locally anisotropic OSHE arises from the interaction between the optical spin and the local anisotropy of the plasmonic mode rotating along the chain. A wavefront phase dislocation was observed in a circular curvature, in which the dislocation strength was enhanced by the locally anisotropic effect.

Observation of Optical Spin Symmetry Breaking in Nanoapertures

Observation of a spin symmetry breaking effect in plasmonic nanoscale structures due to spin-orbit interaction is presented. We demonstrate a nanoplasmonic structure which exhibits a crucial role of an angular momentum (AM) selection rule in a light-surface plasmon scattering process. In our experiment, the intrinsic AM (spin) of the incident radiation is coupled to the extrinsic momentum (orbital AM) of the surface plasmons via spin-orbit interaction. Due to this effect, we achieved a spin-controlled enhanced transmission through a coaxial nanoaperture.

Rashba-type plasmonic metasurface

Observation of the plasmonic Rashba effect manifested by a polarization helicity degeneracy removal in a surface wave excitation via an inversion asymmetric metamaterial is reported. By designing the metasurface symmetry using anisotropic nanoantennas with space-variant orientations, we govern the light-matter interaction via the local field distribution arising in a wavelength and a photon spin control. The broken spatial inversion symmetry is experimentally manifested by a directional excitation of surface wave jets observed via a decoupling slit as well as by the quantum dot fluorescence. Rashba-type plasmonic metasurfaces provide a route for spin-based nanoscale devices controlled by the metamaterial symmetry and usher in a new era of light manipulation.

Spin-controlled plasmonics via optical Rashba effect

Observation of the optical Rashba effect in plasmonics is reported. Polarization helicity degeneracy removal, associated with the inversion symmetry violation, is attributed to the surface symmetry design via anisotropic nanoantennas with space-variant orientations. By utilizing the Rashba-induced momentum in a nanoscale kagome metastructure, we demonstrated a spin-based surface plasmon multidirectional excitation under a normal-incidence illumination. The spin-controlled plasmonics via spinoptical metasurfaces provides a route for spin-based surface-integrated photonic nanodevices and light-matter interaction control, extending the light manipulation capabilities.

Optical Mode Control by Geometric Phase in Quasicrystal Metasurface.

We report on the observation of optical spin-controlled modes from a quasicrystalline metasurface as a result of an aperiodic geometric phase induced by anisotropic subwavelength structure. When geometric phase defects are introduced in the aperiodic structured surface, the modes exhibit polarization helicity dependence resulting in the optical spin-Hall effect. The radiative thermal dispersion bands from a quasicrystal structure are studied where the observed bands arise from the optical spin-orbit interaction induced by the aperiodic space-variant orientations of anisotropic antennas. The optical spin-flip behavior of the revealed modes that arise from the geometric phase pickup is experimentally observed within the visible spectrum by measuring the spin-projected diffraction patterns. The introduced ability to manipulate the light-matter interaction of quasicrystals in a spin-dependent manner provides the route for molding light via spin-optical aperiodic artificial planar surfaces.

Whirling Plasmons: Angular Momentum Selection Rule

P lasmonic systems have been shown to be resonantly excited when the linear momentum selection rule is fulfi lled.1 However, conservation of total angular momentum (AM) in a closed physical system results in additional selection rules. e AM of an optical beam comprises the intrinsic component—the spin, associated with the handedness of the circular polarization—and the extrinsic component— orbital AM (OAM), associated with a spiral phase front.2 Here, we demonstrate a plasmonic nanostructure that exhibits a crucial role of an AM selection rule in a lightsurface plasmon scattering process. In our experiment, the intrinsic AM of the incident radiation was coupled to the extrinsic momentum of the surface plasmons via spin-orbit interaction, which was manifested by a geometric Berry phase.3 Due to this eff ect, we achieved a symmetry breaking that resulted in a spin-dependent enhanced transmission through coaxial nanoapertures, even in rotationally symmetric structures.4 In an optical paraxial beam with a spiral phase distribution (= –l, where  is the azimuthal angle in polar coordinates, and the integer number l is the topological charge), the total AM per photon, in units of h– (normalized AM), was shown to be j=(+l), where =1 is the right-handed circular polarization and =–1 is the left-handed circular polarization.2 In accordance with fundamental physical principles, resonant excitation of the nanoaperture eigenmode requires that the exciting wave match the excited mode, both with its linear and angular momentum. is matching imposes restrictions, or selection rules, on the excitation process. e coaxial nanoaperture was milled by a focused ion beam into a 200-nmthick gold fi lm evaporated onto a glass wafer. e inner and the outer radii of the ring slit were 250 and 350 nm, respectively. e aperture was designed to be a single mode system—in other words, to possess a single allowed excitation with OAM of lGM=±1. e aperture was surrounded by an annular coupling grating with a period of 500 nm. is element was illuminated by a green laser light (532 nm) whose phase was modulated by a spatial light modulator to achieve a spiral phase corresponding to an OAM of lext=0, ±2. e incident spin (in=±1) induced a spiral phase of the excited surface plasmons via spinorbit interaction, and, therefore, was converted to the OAM.5 e surface mode then acquired OAM of lSM= in+ lext. e best overlapping of the surface mode and guided modes was obtained when lSM= lGM, i.e. (a) Mechanism of the nanoaperture’s excitation controlled by AM selection rules. Incident beam bears the intrinsic AM of in and the extrinsic AM of lext. Excited surface mode acquires the OAM of lSM as a result of spin-orbit interaction. Guided mode with lGM is excited only if selection rule is satis ed. (Inset) Scanning electron microscope image of the structure. (b) Intensity distribution cross-sections for different lext. Blue dashed lines correspond to in=1 and red solid lines to in=–1. Intensity was normalized by the transmission measured via coaxial aperture without the surrounding corrugation. (Horizontal dimension was scaled according to the optical magni cation.) (a)

Spinoptical Metamaterials: A Novel Class of Metasurfaces

Photonic metasurfaces are metamaterials with reduced dimensionality composed of engineered subwavelength-scale meta-atoms enabling a custom-tailored electromagnetic response of the medium. These 2-D metastructures are also at the forefront of the physical enigma: What is the effect of surface symmetry properties on light-matter interactions?

Optical spin-Hall effects in plasmonics

Spin-Hall effect is a basic phenomenon arising from the spin-orbit coupling of electrons. In particular, the spatial trajectory of the moving electrons is affected by their intrinsic angular momentum. The optical spin-Hall effect (OSHE) - beam deflection due to the optical spin (polarization helicity) - was recently presented. The effect was attributed to the optical spin-orbit interaction occurring when the light passes through an anisotropic and inhomogeneous medium. Here, we present and experimentally observe the OSHE in coupled localized plasmonic chains. The OSHE is due to the interaction between the optical spin and the path of the plasmonic chain with an isotropic plasmonic mode. In addition, OSHE was observed due to the interaction between the optical spin and the local anisotropy plasmonic mode, which is independent on the chain path. A spin-dependent orbital angular momentum was observed in a circular path. Moreover, a wavefront phase dislocation due to the scattering of surface plasmons from a topological defect is directly measured in the near-field by means of interference. The dislocation strength is shown to be equal to the incident optical spin and with analogy to the magnetic flux parameter in the Aharonov-Bohm effect. OSHE in spontaneous emission was also obtained in a structure consisting of a coupled thermal antenna array. The effect is due to a spin-orbit interaction resulting from the dynamics of the surface waves propagating along the structure whose local anisotropy axis is rotated in space. The OSHE in the nanoscale provides an additional degree of freedom in spin-based optics.

Molding Surface Plasmons by Spinoptical Rashba Metasurfaces

We report on a spin-based surface plasmon directional excitation by spinoptical Rashba metasurfaces. The light-matter interaction control via the geometric design of the metasurface symmetry ushers in a new era of light manipulation.