arXiv subjects

Wanyue Xiao

Publications and source records attributed to Wanyue Xiao.

11 recordsLinked to original sources

arXiv2026

Synthetic SU(1,1) Gauge Control of Non-Hermitian Light

Synthetic gauge fields enable nontrivial light control but remain largely restricted to compact groups such as U(1) and SU(2). Here, we study paraxial light propagation under a noncompact SU(1,1) gauge field realized in a non-Hermitian medium. Under this field, light evolves pseudo-unitarily and conserves pseudo-intensity despite material gain or loss. The gauge field drives Lorentzian precession of the optical pseudospin on a Bloch hyperboloid, producing rotations, boosts, and exceptional-point critical dynamics in an internal Minkowski space. A non-Abelian Lorentz force converts these internal dynamics into real-space oscillatory, hyperbolic, and cubic pseudo-intensity centroid trajectories, even in a uniform medium, while light of opposite pseudo-intensity can drift oppositely-a non-Hermitian spin-Hall-like effect. Our results connect non-Hermitian wave physics with noncompact gauge dynamics and reveal hidden conserved quantities in non-Hermitian light transport.

physics.optics↗

arXiv2026

Spatiotemporal Vortex Rings Induced by Spatiotemporal Coupling

Vortices and vortex rings are topological structures that arise in various physical systems. However, the generation of spatiotemporal vortices (STVs) and vortex rings (STVRs) has so far relied on complex, often active wavefront modulation. We theoretically and experimentally demonstrate that spatiotemporal coupling can drive unstructured wave packets to form vortices upon scattering from simple obstacles. The resulting STVs and STVRs possess controllable topological charges and excellent propagation stability. These findings reveal a fundamental mechanism for spatiotemporal singularity formation and provide a universal route to structured-wave generation.

physics.class-ph↗

arXiv2026

Real-space Hybrid Topological Singularities in Structured Elastic Waves

Real-space singularities govern a broad spectrum of wave phenomena, yet they remain largely unexplored in elastic wave systems. Here, we report hybrid topological singularities that emerge on the surfaces of finite-sized solids due to the full vectorial character of elastic waves. These textures fuse spin-field singularities with displacement-field singularities and exhibit unique non-pairwise topological charge dynamics. Moreover, a subset of these singularities imprint dislocation lines onto the radiated acoustic field, generating robust acoustic vortices in free space from an otherwise achiral source and structure. Our results establish elastic waves as a powerful platform for engineering real-space singularities and open avenues for singular phononics and the exploration of rich topological defects in elastic media.

physics.app-ph↗

arXiv2026

Strong optical nonreciprocity in a photonic crystal composed of spinning cylinders

Moving media break time-reversal symmetry and exhibit intriguing optical nonreciprocity. This nonreciprocity is usually weak due to the much lower moving speed of media relative to the speed of light. We demonstrate that strong optical nonreciprocity can emerge in a two-dimensional photonic crystal composed of spinning dielectric cylinders. The photonic crystal supports two types of chiral modes at the Brillouin zone center: hybridized multipole modes and symmetry-protected bound states in the continuum (BICs), both of which carry intrinsic spin angular momentum. For finite wavevectors near the zone center, the BICs transform into quasi-bound states in the continuum (QBICs). Under oblique incidence of circularly polarized plane waves, the photonic crystal exhibits nonreciprocal transmission and absorption that are significantly enhanced at the frequencies of these hybridized multipole modes and QBICs. Furthermore, the high quality factors of the QBICs enable sharp transitions in nonreciprocity. Our work uncovers strong chiral light-matter interactions in periodic moving structures, with potential applications in nonreciprocal light manipulation. The mechanism may also be generalized to other classical wave systems, such as phononic crystals.

physics.optics↗

arXiv2025

Riemann-Silberstein geometric phase in 4D polarization space

Geometric phase is a far-reaching concept in quantum and classical physics. The first discovered geometric phase, the Pancharatnam-Berry (PB) phase, has profoundly shaped nanophotonics through metasurfaces. However, the PB phase arises from SU(2) polarization evolution and is constrained to a 2D polarization space, failing to capture the full polarization degrees of freedom. We generalize geometric phase to the 4D Riemann-Silberstein (RS) space that simultaneously describes electric, magnetic, and hybrid electric-magnetic polarizations. We show that SU(4) polarization evolution can generate a new geometric phase, the RS phase, alongside the PB phase. Unlike the PB phase that typically manifests in circularly polarized light, the RS phase can emerge in arbitrarily polarized light. Together, they enable a high-dimensional geometric framework for light propagation across general interfaces. We reveal that the phase shifts governed by Fresnel equations are direct manifestations of the RS-space geometric phases, integrating a century-old wave theory into this paradigm. We experimentally validate the framework using metasurfaces and achieve high-dimensional wavefront manipulation. Our work offers fundamental insights into the geometric nature of light-matter interactions, with implications for topological and non-Abelian physics in classical wave systems.

physics.optics↗

arXiv2025

Acoustic Pancharatnam-Berry Geometric Phase

Geometric phases provide a unified framework for understanding diverse phenomena in quantum and classical physics. The Pancharatnam-Berry (PB) geometric phase, arising from variation of optical transverse polarization, has transformed light manipulation. However, this phase has never been observed in sound waves due to their curl-free longitudinal nature. Here, we theoretically and experimentally demonstrate that the PB phase can emerge in general inhomogeneous sound waves with polarization evolution of velocity field. Using surface sound waves as an example, we uncover the intriguing Janus property of the PB phase arising from spin-momentum locking, and realize acoustic PB metasurfaces for versatile wavefront manipulation. We further extend the mechanism to free-space structured sound and realize acoustic $q$-plate for generating acoustic vortices through spin-orbit interaction. Our work provides new insights into sound wave properties and enables the manipulation of inhomogeneous acoustic fields via the PB phase, with potential applications in acoustic communications and imaging.

physics.class-ph↗

arXiv2025

Optical force and torque on a spinning dielectric sphere

Optical force can enable precise manipulations of small particles for various applications. It is well known that an isotropic lossless dielectric sphere is only subject to forward optical force under the illumination of an electromagnetic plane wave. By using rigorous full-wave simulations, we show that such a sphere can experience a lateral optical force and an optical torque besides the conventional longitudinal force, if it spins with a constant angular velocity. The emergence of the unusual optical force and torque is attributed to the breaking of mirror and cylindrical symmetries by the spinning motion. Using the multipole expansion in source representation, we illustrate how the spinning-induced effective bi-anisotropy generates the lateral force and torque on the sphere through the interference of electric and magnetic multipoles. We also uncover the effect of Sagnac frequency splitting on the optical force and torque. The results contribute to the understanding of the optical force and torque in moving media and can be applied to realize unconventional optical manipulations of small particles.

physics.optics↗

arXiv2024

Nonreciprocal optical metasurface based on spinning cylinders

Optical systems breaking Lorentz reciprocity have attracted broad attention due to their intriguing physics and applications. Nonreciprocal metasurfaces can enable one-way light transmission and reflection with essential applications in optical communication. Conventional nonreciprocal metasurfaces rely on using magneto-optic or nonlinear materials to induce nonreciprocal optical properties. Here, we propose and demonstrate a new mechanism for realizing nonreciprocal metasurfaces based on the relativistic effect of a moving medium. The metasurface is composed of periodic spinning dielectric cylinders located above a dielectric substrate. The spinning motion breaks the time-reversal symmetry and induces bi-anisotropic Tellegen-type response of the meta-atoms. We show that the metasurface can realize both asymmetric and nonreciprocal manipulations of the incident plane wave. The underlying mechanism is attributed to the Sagnac effect associated with the chiral multipole modes of the coupled spinning cylinders. By introducing dielectric pillars to modulate the phase profile, the metasurface can enable nonreciprocal wavefront manipulations. Our work offers a new mechanism for realizing nonreciprocal light manipulation in free space. The proposed metasurface can serve as a platform to explore the interesting physics of nonreciprocal optics, non-Hermitian optics, and topological photonics.

physics.optics↗

arXiv2024

Directional sources realised by toroidal dipoles

Directional optical sources can give rise to the directional excitation and propagation of light. The directionality of the conventional directional dipole (CDD) sources are attributed to the interference of the electric and/or magnetic dipoles, while the effect of the toroidal dipole on optical directionality remains unexplored.} Here, we numerically and analytically investigate the directional properties of the toroidal dipole. We show that the toroidal dipole can replace the electric dipole in the CDD sources to form the pseudo directional dipoles (PDDs), which can be applied to achieve analogous near-field directional coupling with a silicon waveguide. Moreover, the directionality of the PDDs can be flexibly controlled by changing the geometric parameters of the toroidal dipole, leading to tunable asymmetric coupling between the sources and the waveguide. These new types of directional sources provide more degrees of freedom for tailoring the optical directionality compared to the conventional sources. The results open new possibilities for directional light manipulation and can find applications in on-chip optical routing, waveguiding, and nanophotonic communications.

physics.optics↗

arXiv2024

On-chip optical wavefront shaping by transverse spin induced Pancharatanam-Berry phase

Pancharatnam-Berry (PB) metasurfaces can be applied to manipulate the phase and polarization of light within subwavelength thickness. The underlying mechanism is attributed to the geometric phase originating from the longitudinal spin of light. Here, we demonstrate a new type of PB geometric phase derived from the intrinsic transverse spin of guided light. Using full-wave numerical simulations, we show that the rotation of a metallic nano bar sitting on a metal substrate can induce a geometric phase covering 2$π$ full range for the surface plasmons carrying intrinsic transverse spin. Specially, the geometric phase is different for the surface plasmons propagating in opposite directions due to spin-momentum locking. We apply the geometric phase to design metasurfaces to manipulate the wavefront of surface plasmons to achieve steering and focusing. Our work provides a new mechanism for on-chip light manipulations with potential applications in designing ultra-compact optical devices for imaging and sensing.

physics.optics↗

arXiv2023

Multiplexing spectral line shape of waveguide transmission by photonic spin-orbit interaction

Manipulating the spectral line shape exhibits great potential in realizing active optical circuits with switching, sensing, and modulation capabilities. Exploring unusual line shapes, such as Fano resonance and electromagnetically induced transparency (EIT), has attracted substantial interest. Conventional methods of engineering the spectral line shape have limited tunability and face challenges in multiplexing different spectral line shapes. Here, we propose and numerically demonstrate a new mechanism to tailor the transmission line shape almost at will by exploiting the interference of frequency-dependent chiral dipolar states in two helix particles sitting above a dielectric waveguide. We show that, by tuning the polarization of the chiral dipoles and exploiting transverse spin-orbit interaction, one can control the asymmetric Pancharatnam-Berry geometric phase for the excited guided waves propagating in opposite directions. The interference of the guided waves respectively excited by the two particles can give rise to transmissions with various line shapes, including Lorentzian-like, antiresonance-like, Fano-like, and EIT-like line shapes, which carry an intriguing property of line shape-momentum locking, i.e., the transmissions in opposite directions have different line shapes. Our findings open new possibilities for multiplexed and multifunctional nanophotonic designs with unprecedented capability of spectral-line shaping. The proposed structures can be conveniently integrated with optical circuits for on-chip applications.

physics.optics↗