Transverse spin dynamics in structured electromagnetic guided waves

Abstract

Spin–momentum locking, a manifestation of topological properties that governs the behavior of surface states, was studied intensively in condensed-matter physics and optics, resulting in the discovery of topological insulators and related effects and their photonic counterparts. In addition to spin, optical waves may have complex structure of vector fields associated with orbital angular momentum or nonuniform intensity variations. Here, we derive a set of spin–momentum equations which describes the relationship between the spin and orbital properties of arbitrary complex electromagnetic guided modes. The predicted photonic spin dynamics is experimentally verified with four kinds of nondiffracting surface structured waves. In contrast to the one-dimensional uniform spin of a guided plane wave, a two-dimensional chiral spin swirl is observed for structured guided modes. The proposed framework opens up opportunities for designing the spin structure and topological properties of electromagnetic waves with practical importance in spin optics, topological photonics, metrology and quantum technologies and may be used to extend the spin-dynamics concepts to fluid, acoustic, and gravitational waves.

Anomalous unidirectional excitation of high-k hyperbolic modes using all-electric metasources

“…This optical spin-orbit locking phenomenon comes from the transverse spin property of evanescent waves. [24][25][26][27][28][29][30][31] Unlike with the PSHE in surface plasmon polaritons at a metal-dielectric interface, [32][33][34] the directional excitation of spin dipoles in HMMs occurs inside the bulk of the structure. This greatly broadens the near-field coupling control scope.…”

Symmetry‐Protected Photonic Chiral Spin Textures by Spin–Orbit Coupling

“…The photonic chiral spin texture, which is an optical counterpart of topological defects in condensed matter systems, can be constructed using p ‐polarized or s ‐polarized surface EM waves, such as evanescent waves, [ 50 ] Bloch surface waves, [ 51 ] and surface plasmon polaritons (SPPs), [ 11 ] at a vacuum/isotropic material interface with broken inversion symmetry. [ 31 ] Most structures sustaining surface waves are lossless. Even for the SPP configuration, the loss mechanism does not affect the symmetry of the optical system, and it can be ignored by only considering the probability distribution of a single EM wave packet at the interface.…”

“…Optical spin–orbit interactions play a significant role in the formation of photonic chiral spin textures. [ 31,32 ] Light has two fundamental dynamical properties: momentum and angular momentum (AM). [ 31–34 ] The spin angular momentum (SAM) is associated with the polarization ellipticity and the orbital angular momentum is determined by either the vortex phase or the optical beam trajectory.…”

“…[ 31,32 ] Light has two fundamental dynamical properties: momentum and angular momentum (AM). [ 31–34 ] The spin angular momentum (SAM) is associated with the polarization ellipticity and the orbital angular momentum is determined by either the vortex phase or the optical beam trajectory. [ 33 ] The interplay between these two angular momenta has been studied extensively over the past few years and has been shown to result in many fascinating phenomena.…”

“…[ 40 ] The evanescent plane wave is topologically nontrivial ( invariant) and possesses the feature of spin‐momentum locking. [ 31,41,42 ] However, compared with the scalar electronic wave function, [ 43 ] the vector feature of the photon wave function gives rise to chiral spin textures that are analogous to the textures of topological defects. [ 20–22,44 ] Till date, this resemblance has been noted only in phenomenological terms and most of the relevant research has focused on the experimental characterization and applications of the photonic chiral spin textures.…”