Coupling‐Mediated Selective Spin‐to‐Plasmonic‐Orbital Angular Momentum Conversion

Abstract

their axis of propagation like a corkscrew, and possess a "doughnut" intensity profile. [3] In the past few decades, many demonstrations and applications of vortex beams have been reported, including optical data storage, [4,5] optical tweezers, [6] quantum cryptography, [7] communications, [8,9] etc. Particularly, geometric phase devices composed of basic elements with a spatially varying orientation could perform spin-to-orbital angular momentum conversion, [10][11][12][13][14] providing a direct connection between optical SAM and OAM. [15] Recently, plasmonic vortices generated through excitation of surface plasmons (SPs) with azimuthal-dependent phase profiles e ilθ at a metal-dielectric interface have attracted considerable attention [16][17][18][19][20][21][22] due to their strong OAM in the evanescent field region. In particular, Archimedean spirals [16][17][18]22] and well-arranged subwavelength resonators [19][20][21] have been employed to achieve spin-toplasmonic-orbital angular momentum conversion, providing useful insights into the nature of OAM and opening the door toward a number of exciting on-chip applications. [17,23] In most of these works, the incident LCP and RCP waves were transformed to plasmonic vortices of different topological charges, and the associated spin-dependent phenomena can be regarded as the photonic spin-Hall effect. [24][25][26] In direct analogy with the Orbital angular momentum (OAM) has been recently introduced to plasmonics for generating plasmonic vortices with a helical wavefront, opening avenues for exotic on-chip applications such as quantum information processing and communications. In previous demonstrations, carefully designed optical elements are used to convert left-and right-circular polarizations into plasmonic vortices with different topological charges, resulting in conversion from optical spin angular momentum (SAM) to plasmonic OAM. Here, it is demonstrated theoretically and experimentally that by utilizing the near-field coupling between paired resonators in a metasurface, selective conversion from optical SAM to plasmonic OAM is realized, where generation of plasmonic vortices can be achieved for incident light of one circular polarization while significantly suppressed for the other circular polarization. The proposed design scheme may motivate the design and fabrication of future practical plasmonic devices. PlasmonicsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.Light carries coordinate-independent spin angular momentum (SAM) [1] of ±ħ per photon, corresponding to left-and rightcircular polarizations (LCP and RCP), where ħ is the reduced Planck's constant. In the pioneering work by Allen et al., [2] it was shown that electromagnetic fields with a phase profile e ilθ could also carry orbital angular momentum (OAM), where l and θ are the topological charge and azimuth angle, respectively. Such beams, known as optical vortices, rotate around

Topology‐Induced Phase Transitions in Spin‐Orbit Photonics

“…Our findings provide a unified picture to understand two previously discovered effects on the same foot, and can be extended to study other SOI-induced effects in light (e.g., spin-controlled vortex generation [1,[9][10][11][12] and spin-Hall momentum shift [35][36][37][38][39] in inhomogeneous anisotropic media) and other waves (e.g., vortexbearing electron beams). [40,41] More importantly, as the SOI of light plays an increasingly important role in nanophotonics, [42][43][44][45][46][47][48] plasmonics, [49][50][51] and topological photonics, [52][53][54][55] our results…”

“…Our findings provide a unified picture to understand two previously discovered effects on the same foot, and can be extended to study other SOI‐induced effects in light (e.g., spin‐controlled vortex generation [ 1,9–12 ] and spin‐Hall momentum shift [ 35–39 ] in inhomogeneous anisotropic media) and other waves (e.g., vortex‐bearing electron beams). [ 40,41 ] More importantly, as the SOI of light plays an increasingly important role in nanophotonics, [ 42–48 ] plasmonics, [ 49–51 ] and topological photonics, [ 52–55 ] our results may pave the way for a variety of applications, such as precision metrology, [ 56,57 ] edge detection, [ 58,59 ] particle manipulation, [ 60,61 ] and various spin‐photonic components. [ 42–45,62,63 ]…”

Terahertz surface plasmonic waves: a review

“…4(m). Recently, Xu et al 147 further utilized this SSR pair for selective spin-to-plasmonic-orbital angular momentum conversion, where the generation of plasmonic vortices can be achieved for the incident light of one circular polarization while significantly suppressed for the other circular polarization.…”

Optical Singularity Built on Tiny Holes

“…Plasmonic vortex generators built on a) parallel rectangular holes on one circle under the linear polarization illumination, [ 74 ] b) two sets of rectangular holes on one circle under the linear polarization illumination, [ 76 ] c) orthogonal U‐shaped holes on two concentric circles under the RCP illumination, [ 77 ] d) orthogonal rectangular holes on two concentric circles under the LCP illumination, [ 75 ] e) parallel cross holes on a spiral trajectory under the linear polarization illumination, [ 81 ] and f) orthogonal rectangular holes on two parallel spiral trajectory under the LCP illumination. [ 75 ] a) Reproduced with permission.…”

“…c) Reproduced with permission. [ 77 ] Copyright 2019, John Wiley & Sons. d,f) Reproduced with permission.…”