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Spin vector structure of the evanescent field vortex forming the Neel-type photonic skyrmion a, Intensity distribution of the evanescent field vortex with L = 1 (bottom) and the distribution of the photonic spin orientation in the centre of the vortex (top). The arrows indicate the direction of the unit spin vector σ determined by θr = arctan(Sz/Sr). b, The radial variations of the transverse (Sr) and longitudinal (Sz) spin components of the beam (bottom) and the orientation of the spin vector in the centre of the beam (top). The in-plane wavevector (kr) of the evanescent vortex for the above calculation is set to 1.05k0, where k0 = 2π/λ represents the wavevector in the free space.
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In magnetic materials, skyrmions are nanoscale regions where the orientation of the electron spin changes in a vortex-type manner1–4. Electromagnetic waves carry both spin and orbital angular momenta5,6. Here we show that spin–orbit coupling7–12 in a focused vector beam results in a skyrmion-like structure of local photonic spin. While diffraction...
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Spin-momentum locking is an intrinsic property of surface electromagnetic fields and its study has led to the discovery of photonic spin lattices and diverse applications. Previously, dispersion was ignored in the spin-momentum locking, giving rise to abnormal phenomena contradictory to the physical realities. Here, we formulate four dispersive spi...
Citations
... In recent years, skyrmions were also manifested in laser modes by considering the Stokes vector as an entity, and these laser modes are often termed optical skyrmions [15,16]. The optical skyrmions belong to the family of full Poincaré beams and can be distinguished from others of the family by their topological protection and skyrmion number [17]. ...
Optical skyrmions formed in terms of polarization are topological quasi-particles, and they have garnered much interest in the optical community owing to their unique inhomogeneous polarization structure and simplicity in their experimental realization. These structures belong to the Poincaré beams satisfying the stable topology. We theoretically investigated the non-diffracting and self-healing Poincaré beams based on the superposition of two orthogonal Bessel modes by the longitudinal mode matching technique. These Poincaré beams are topologically protected, and we suggest them as optical skyrmions in the corresponding Stokes vector fields. These optical skyrmions are quasi-skyrmions, and their range of propagation depends on the range of superposed Bessel modes. We have shown longitudinal mode matching of superposed Bessel beams is a necessary condition for the generation of propagation-invariant and non-diffracting skyrmions. The proposed longitudinal mode matching technique facilitates the generation of skyrmions with tunable position and range without any on-axis intensity modulations along the propagation axis. A suitable experimental configuration is suggested to realize variable order skyrmions in Bessel modes. The suggested experimental configuration can produce optical skyrmions even in ultra-short laser pulses with high mode conversion efficacy. This work can provide a new direction for the generation of skyrmions with completely new textures and features with reference to existing skyrmions originating from Laguerre-Gaussian modes.
... Like optical vortex beams in free space, SPPs can also carry angular momentum including spin angular momentum (SAM) and orbital angular momentum (OAM), and generate spin−orbit coupling effects in various plasmonic structures [4]. The SPPs carrying OAM are termed as the plasmonic vortices, which has been widely applied in many fields, such as optical tweezing [5,6], super-resolution imaging [7,8], and on-chip information processing [9,10]. However, most previous research on plasmonic vortices and spin−orbit coupling of SPPs only focus on the spatial properties excited by continuous-wave laser sources [11][12][13][14][15][16][17]. ...
... As shown in figures 5(a1)-(a5), before t = 0 fs the values of L z distribution are negative, and after t = 0 fs the values of L z distribution are positive. The S z distribution also shows the negative-to-positive transition, especially at the center point with S z = −1h to 1h transition as shown in figures 6(a1)-(a5), corresponding to the ultrafast transition of a centered Néel-type photonic skyrmion from downward-facing state to upward-facing state [10,41,42]. However, in most region the values of S z are very weak (close to 0), demonstrating a high efficiency of spin-to-orbital conversion in the plasmonic vortices [9,43]. ...
The vortex field of surface plasmon polariton with orbital angular momentum (OAM), called plasmonic vortex, has played an important role in various research fields. However, the spatiotemporal properties of plasmonic vortex pulses excited by ultrafast laser, especially the dynamics of spin‒orbit coupling in the ultrafast plasmonic vortex field, have yet to be investigated deeply. Here, we study the spatiotemporal modulation of ultrafast plasmonic vortices with spin‒orbit coupling, using both analytical and simulation methods. The ultrafast plasmonic vortices are excited by a ring-shaped plasmonic lens, with an incident light composed of two time-delayed femtosecond sub-pulses carrying the same OAM but orthogonal circular polarizations. The dynamics of time-varying electric field, energy flow and angular momentum distributions of the plasmonic vortices are demonstrated, revealing details of the spin‒orbit coupling in spatiotemporal domain, such as the merging of multiple phase singularities with energy flow loops, and the variation of spin/orbital angular momentum per photon over time. This work could deepen the understanding of spin‒orbit coupling in plasmonic field and provide new ideas for ultrafast on-chip optical information processing.
... [9][10][11][12][13] In recent experiments, the topological spin textures were constructed through spin-orbit coupling in electromagnetic fields with the optical spin vectors forming either an individual skyrmion or a skyrmion/meron lattice. [14][15][16][17][18][19] In the absence of spin-orbit coupling, the spin lattices degenerate into a time-dependent lattice of field-skyrmion or field-meron type. 20,21 In addition, skyrmion-like or meron-like states were also generated in diverse forms such as Stokes vectors in Poincar e beams, [22][23][24][25][26][27][28] pseudospins in photonic crystals, [29][30][31] or magnetic vectors in propagating light pulses. ...
Topological spin textures, among which skyrmions and merons are typical examples, have with their swirling vectorial structures triggered enormous interest in physical systems including elementary particles and magnetic materials. Manipulating their symmetry and topology is important for understanding the mechanisms that underlie their topological phase transformation as well as offering tunable degrees of freedom to encode information, which has already been demonstrated in magnetic materials. Recently, the photonic counterparts of skyrmions and merons were constructed in a 2D wave system with deep-subwavelength features promising for optical sensing, imaging, and information decoding. However, their experimental realization relied on stringent excitation conditions that only support a single spin texture type on a specific structure. Here, we demonstrate for the first time the transformation between photonic skyrmion and meron spin lattices on the same metallic meta-surface having a well-designed structural period. We show experimentally the wavelength-tuned symmetry transformation of the photonic spin lattices, which are also found to be robust against disorder in the structure to a certain degree. This work provides new insights into controlling the electromagnetic field symmetry and topology, as well as in developing applications in spin optics and topological photonics.
... Such particles are conventionally difficult to make in the paraxial regime where the field vectors are exclusively transverse to the propagation direction. In the highly focused case, a longitudinal field component is introduced in the field structure enabling a 3D electromagnetic vector necessary for particle-like polarization topologies [35,36]. ...
Optical bottle beams, characterized by their unique three-dimensional dark core, have garnered substantial interest due to their potential applications across multiple domains of science and technology. This paper delves into the current methods used to create these beams and provides a method to obscure their nodal planes through coaxial non-interfering orthogonally polarized beams to generate bottle beams with enhanced uniformity. Experimental and theoretical results show the enhanced vector bottle beam maintains a smaller, more spherically uniform potential well and interesting quasi-particle polarization characteristics.
... Here, we report the experimental realization of a topological Euler insulator phase in acoustic metamaterials which is featured with an unconventional meron (i.e., half-Skyrmion) configuration in the bulk Bloch states. Remarkably, the It is worth remarking that the observation of skyrmion and meron types of states (as well as their generalizations) in photonic and acoustic systems have inspired lots of research [61][62][63][64][65][66][67]. Due to the unconventional properties of these states and their potential applications into topologically robust information processing, sensing, and lasing, these states have been studied extensively recently [67]. ...
... 16,25 Optical skyrmions, which possess topologically protected (a characteristic where the topological characteristics remain invariant under propagation through turbulent media) polarization textures, are, however, rapidly finding utility in advanced applications, such as free-space communications under turbulent conditions, [26][27][28][29][30] polarization nanoscale-metrology, and super-resolution microscopy with a sub-wavelength spatial resolution. [30][31][32][33][34] Notably, there is a lack of reports detailing the interaction between optical skyrmions and materials. ...
Skyrmions, topologically stable configurations of a three-component vector field with sophisticated textures, have been considered in many contexts, including atomic physics, Bose-Einstein condensates, liquid crystals, and magnetic materials. Although optical counterparts of skyrmions have extensively been studied theoretically and recently demonstrated in the laboratory experiments, their experimental mapping is challenging due to the fine, three-dimensional, and complicated structure of their polarization distributions. Here, we propose and demonstrate a straightforward mapping of the polarization textures of optical Néel-, Bloch-, and anti-skyrmions based on the radiation pressure and direct imprinting of the skyrmion textures on azopolymers. These results not only elucidate the exotic interaction that occurs between topologically protected quasiparticles of light and matter but also provide a simple approach for generation and characterization of optical skyrmions, based on a dual-path polarization shaping configuration with a single spatial light modulator, and their measurements based on the radiation pressure.
... In two dimensions, paraxial light is vectorial, with an inhomogeneous polarization structure throughout the transverse plane. The polarization state of a non-paraxial light beam is also vectorial in three dimensions, giving rise to novel states of structured light such as optical needles [12][13][14], Möbius strips [15][16][17][18][19][20], polarization knots [21][22][23], optical skyrmions [24][25][26], and transverse spin density [27][28][29][30][31][32][33][34][35]. Due to the importance of these structured light fields, their propagation in various media has attracted much interest [36][37][38][39][40][41][42][43]. ...
Magneto-optical effects, which have been known for over a century, are among the most fundamental phenomena in physics and describe changes in the polarization state of light when it interacts with magnetic materials. When a polarized plane wave propagates in or through a homogeneous and isotropic transparent medium, it is generally accepted that its transverse polarization structure remains unchanged. However, we show that a strong radial polarization component can be generated when an azimuthally polarized sine-Gaussian plane wave is tightly focused by a high numerical aperture lens, resulting in a magneto-optical-like effect that does not require external magnetic field or magnetic medium. Calculations show that the intensity structure and polarization distribution of the highly confined electric field strongly depend on the parameters m and φ0 in the sinusoidal term, where m can be used to control the number of the multifocal spots and φ0 can be used to control the position of each focal spot. Finally, we show that this peculiar electric field distribution can be used to realize multiple particles trapping with controllable numbers and locations.
... In recent years, skyrmions were also manifested in laser modes by considering polarization as an entity and these laser modes are often termed optical skyrmions [11,12]. The optical skyrmions belong to the family of full Poincaré beams and can be distinguished from others of the family by their topological protection and skyrmion number [13,14]. The skyrmion number can be easily understood and estimated by a stereographic projection of the three-dimensional (3D) polarization distribution in the Poincaré sphere onto a 2D plane. ...
Optical skyrmions formed in terms of polarization are topological quasi-particles and have garnered much interest in the optical community owing to their unique inhomogeneous polarization structure and simplicity in their experimental realization. These structures belong to the Poincaré beams satisfying the stable topology. We theoretically investigated the non-diffracting and self-healing Poincaré beams based on the superposition of two orthogonal Bessel modes by mode matching technique. These Poincaré beams are topologically protected, and we suggest them as optical skyrmions. These optical skyrmions are quasi-skyrmions and their range of propagation depends on the range of superposed Bessel modes. The polarization structure of these optical skyrmions has no change upon the propagation. A necessary experimental configuration is suggested to realize variable order skyrmions in Bessel modes experimentally. This work can provide a new direction for the generation of skyrmions with completely new textures and features with respect to existing skyrmions originating from Laguerre-Gaussian modes.
... (e) topological BIC optical force induced by bilayer photonic crystal [146] ; (f) optical force enabled detection of Skyrmion topological state [147] 封面文章·特邀综述 第 44 卷 第 5 期/2024 年 3 月/光学学报 Fig. 7 Lightdriven metallic surface plasmonic microstructures. (a) Surface plasmonic optical motor [148] ; (b) optical transverse force induced by surface plasmonic optical motor [149] ; (c) optical microdrone [150] 封面文章·特邀综述 第 44 卷 第 5 期/2024 年 3 月/光学学报 Fig. 8 Lightdriven dielectric metamechanics. ...
Significance Optical micromanipulation utilizes optical force to dynamically control particles, which has the
characteristics of non-contact and can be operated in a vacuum environment. Since the invention of optical tweezers in the
1980s, the field has experienced rapid development and has given rise to many emerging research directions, such as
holographic optical tweezers, near-field evanescent wave optical tweezers, fiber optic tweezers, optoelectronic tweezers,
and photo-induced temperature field optical tweezers, providing rich and powerful tools for fields such as biology,
chemistry, nanoscience, and quantum technology. These methods can not only capture, separate, and transport small
objects but also allow more precise manipulation, such as the rotation of small objects. However, traditional manipulation
methods rely on tightly focused local light, greatly limiting the action range of optical force. In addition, in order to
generate a structured light field, larger optical components such as spatial light modulators are usually required, making it
difficult to miniaturize and integrate the optical manipulation system.
In recent years, metasurfaces have emerged as integrated devices composed of subwavelength nanoantennas,
promising new opportunities for optical micromanipulation. This ultra-thin artificial microstructure device can flexiblely
control multiple degrees of freedom such as amplitude, phase, and polarization of light, by specially designing the
geometric shape, size, and material of its own micro/nanostructure. Compared with traditional optical components such as
liquid crystal spatial light modulators, gratings, and lenses, metasurfaces exhibit higher operating bandwidth, structural
compactness, and integration. With the merits of miniaturization, integration, and excellent performance in light tailoring,
optical metasurfaces have been extensively incorporated into the realm of optical micromanipulation. Especially, owing to
their peculiar photomechanical properties, the metasurfaces hold the ability to be actuated by light fields, paving the way to
the next generation of light-driven artificial micro-robots. The fast development of this subject indicates that the time is
now ripe to overview recent progress in this cross-field.
Progress We summarized principles of optical micromanipulation and metasurfaces (Fig. 1) and overviewed metamanipulation
devices, including metasurface-based optical tweezers (Fig. 2), tractor beams (Fig. 5), multifunctional micromanipulation
systems (Fig. 3), and metamachines (Figs. 7 and 8). Furthermore, we provided a detailed discussion of novel
mechanical effects, such as topological light manipulation, which stems from the topological characteristics of
nanostructures (Fig. 6).
Conclusions and Prospects We review the cutting-edge developments in the field of optical micromanipulation based
on metasurfaces. The metasurface-based micromanipulation technology is expected to evolve toward higher temporal
resolution, higher spatial accuracy, and lower manipulation power. To this end, more urgent requirements have been
imposed on the underlying design scheme and experimental preparation standards of the metasurface. Although the
introduction of metasurfaces has benefited micromanipulation systems and significantly reduced their sizes, there is still
much room for further development and improvement in wide bands, multi-dimensional responses, and device
thresholds.
In terms of micromanipulation systems, the subwavelength-scale structure of metasurfaces will continue to be a key
focus of research. Especially in the field of topological light manipulation, it is expected to further expand its research
scope, combining non-Abelitan, non-Hermitian, and nonlinear effects to discover new physical phenomena. In the fields of
biology and chemistry, metasurface technology is expected to be flexibly applied on smaller scales, even achieving
manipulation of single molecule-level objects. This technology is expected to be further applied to the fields such as batteryquality inspection and targeted therapy, bringing changes to the basic research and practical applications of energy and life
sciences. Specifically, in the development of ultrafast optics, metasurfaces are gradually exhibiting unique advantages.
Nanoscale superlattice enables high-resolution spectral measurements, and the design of nonlinear superlattice surfaces can
be used to enhance nonlinear effects or generate high-order harmonics, making high time resolution transient
micromanipulation technology possible.
Overall, the technological evolution from traditional optical micromanipulation to meta-manipulation will continue to
drive the vigorous development of nanophotonics. This technological paradigm not only meets the needs of various basic
research but also arouses more innovative applications, opening up new prospects for branched sciences and technologies.
... Consequently, the generation of novel subwavelength structured light beams has attracted extensive attention in recent years. 10,11 Using high numerical aperture objectives or spatial light modulators (SLMs) 12 is the traditional method for generating subwavelength structured light beams. However, these traditional methods require optical components with a large footprint and low integration. ...
