We examine the evolution of paraxial beams carrying intrinsic spin and orbital angular momenta (AM) in gradient-index media. A parabolic-type equation is derived which describes the beam diffraction in curvilinear coordinates accompanying the central ray. The center of gravity of the beam experiences transverse AM-dependent deflections -- the spin and orbital Hall effects. The spin Hall effect generates a transverse translation of the beam as a whole, in precise agreement with recent geometrical optics predictions. At the same time, the orbital Hall effect is significantly affected by the diffraction in the inhomogeneous medium and is accompanied by changes in the intrinsic orbital AM and deformations of the beam.
We study the nonlinear propagation of diffraction-free, space-time wave packets, also called time-diffracting beams because their spatiotemporal structure reproduces diffraction in time. We report on the spontaneous formation of propagation-invariant, spatiotemporally compressed pulsed beams carrying finite power from exciting time-diffracting Gaussian beams in media with cubic Kerr nonlinearity at powers below the critical power for collapse, and also with other collapse-arresting nonlinearities above the critical power. Their attraction property makes the experimental observation of the self…
We show that a high-order Bessel beam propagating in a medium with nonlinear absorption is not completely absorbed, but survives in the form of a new propagation invariant vortex beam in which the beam energy and orbital angular momentum are permanently transferred to matter and at the same time refueled by spiral inward currents of energy and angular momentum. Unlike vortex solitons and dissipative vortex solitons, these vortex beams are not supported by specific dispersive nonlinearities (self-focusing or self-defocusing) and do not require gain. Propagation invariance in presence of multipl…
We investigate on the properties of the recently introduced time-diffracting (TD) beams in free space. They are shown to be paraxial and quasi-monochromatic realizations of localized waves, spatiotemporal localized waves travelling undistorted at arbitrary speeds. The paraxial and quasi-monochromatic regime is shown to be necessary to observe what can properly be named diffraction in time. TD beams of finite energy travelling at quasi-luminal velocities are seen to form substantially longer foci or needles of light than the so-called abruptly focusing and defocusing needle of light, or limitin…
This work deals with exact solutions to the wave equations. We start by introducing the Non-Diffracting Waves (NDW), and by a definition of NDWs. Afterwards we recall -besides ordinary waves (gaussian beams, gaussian pulses)- the simplest non diffracting waves (Bessel beams, X-shaped pulses,...). In Sec.2 we show how to eliminate any backward-traveling components, first in the case of ideal NDW pulses, and then, in Sec.3, for realistic finite-energy NDW pulses. In particular, in subsec.3.1 we forward a general functional expression for any totally-forward non-diffracting pulses. Then, in Sec.4…
Matters Arising: On physical nature of the optical deDroglie-Mackinnon wave packets. ARISING FROM Layton A. Hall and Ayman F. Abouraddy Nature Physics https://doi.org/10.1038/s41567-022-01876-6 (2023)
本文针对 Hall 与 Abouraddy 关于光学 de Broglie-Mackinnon 波包的首次实验观测，指出其理论解释及图示、数学描述中仍有含混之处并主张予以澄清。
In this paper we perform a fusion between two important theoretical methodologies, one related to the Frozen Wave beams, which are non-diffracting beams whose longitudinal intensity pattern can be chosen a priori in an medium (absorbing or not), and the other related to the Airy-Type pulses, which are pulses resistant to dispersion effects in dispersive materials. As a result, a new method emerges, capable of providing vortex pulses resistant to three concomitant effects, i.e.: diffraction, dispersion and attenuation; while concurrently the spatial variation of the wave intensity along its axi…
Propagation-invariant or non-diffracting optical beams have received considerable attention during the last two decades. However, the pulsed nature of light waves and the structured property of optical media like waveguides are often overlooked. We here present a four-dimensional spatiotemporal approach that extends and unifies both concepts of conical waves and helicon beams, mainly studied in bulk media. By taking advantage of tight correlations between the spatial modes, the topological charges, and the frequencies embedded in an optical field, we reveal propagation-invariant (dispersion- a…
Coupling of electric and magnetic responses of a scatterer known as bianisotropy enables rich physics and unique optical phenomena, including asymmetric absorption or reflection, one-way transparency, and photonic topological phases. Here we demonstrate yet another feature stemming from bianisotropic response, namely, polarization-dependent scattering of light by bianisotropic dielectric meta-atom with broken mirror symmetry, which yields a photonic analogue of spin Hall effect. Based on a simple dipole model, we explain the origin of the effect confirming our conclusions by experimental obser…
Spatiotemporal solitons (STSs) are localized solitary waves in both space and time that involve complex linear and nonlinear processes. Optical STSs have been observed in various media, but they are difficult to be realized in multimode fibers due to their large modal dispersion. Here, we report STS mode-locking and spatiotemporal nonlinear dynamics in a step-index multimode fiber mediated by gain. Gain competition and energy redistribution among different spatial modes help nonlinearity effectively cancel both temporal splitting and spatial diffracting of the entire pulse (multicomponent soli…
By considering gauge transformations on the macroscopic Maxwell's equations, a two dimensional gauge field, with its pseudo magnetic field in the real space, is identified as tilted anisotropy in the constitutive parameters. We show that optical spin Hall effect and one-way edge states become possible simply by using anisotropic media with broadband response. The proposed gauge field also allows us to design an optical isolator based on the Aharonov-Bohm effect. Our approach will be useful in spoof magneto-optics with arbitrary magnetic fields mimicked by metamaterials with subwavelength unit …
The spin orbit interaction (SOI) of light has been in the focus in recent times because of fundamental consequences and potential applications in diverse systems ranging from inhomogeneous anisotropic media to engineered plasmonics and metamaterial strutures. Here we demonstrate perhaps one of the simplest means to realize SOI and the Spin Hall Shift (SHS) using a standard Gaussian TEM$_{00}$ beam in an optical trap. Our system exploits the versatility and interference generated in a stratified medium to control and manipulate SOI and transfer the resulting angular momentum to optically trappe…
The robust spin and momentum valley locking of electrons in two-dimensional semiconductors make the valley degree of freedom of great utility for functional optoelectronic devices. Owing to the difference in optical selection rules for the different valleys, these valley electrons can be addressed optically. The electrons and excitons in these materials exhibit valley Hall effect, where the carriers from specific valleys are directed to different directions under electrical or thermal bias. Here we report the optical valley Hall effect where the light emission from the valley polarized exciton…
We show that optical beams propagating in transversally disordered materials exhibit a spin Hall effect and a spin-to-orbital conversion of angular momentum as they deviate from paraxiality. We theoretically describe these phenomena on the basis of the microscopic statistical approach to light propagation in random media, and show that they can be detected via polarimetric measurements under realistic experimental conditions
In a seminal paper Haldane conjectured that topological phenomena are not particular to quantum systems, and indeed experiments realized unidirectional, backscattering-free edge modes with electromagnetic waves. This raises two immediate questions: (1) Are there other topological effects in electromagnetic media? And (2) is Haldane's Quantum Hall Effect for light really analogous to the Quantum Hall Effect? We conclusively answer both of these questions by classifying topological photonic crystals according to material (as opposed to crystallographic) symmetries. It turns out there are four to…
We study paraxial beam propagation along the wedge axis of a disclinated amorphous medium. The defect-induced inhomogeneity results in Berry phase and curvature that are affected by the induced uniaxial anisotropy. The Berry phase manifests itself as a precession of the polarization vector. The Berry curvature is responsible for the optical spin Hall effect in the disclinated medium, where beam deflection varies sinusoidally along the paraxial direction. Its application in determining the birefringence and the magnitude of the Frank vector is explained.
Geometrical optics is extended so as to provide a model for spinning light rays via the coadjoint orbits of the Euclidean group characterized by color and spin. This leads to a theory of ``geometrical spinoptics'' in refractive media. Symplectic scattering yields generalized Snell-Descartes laws that include the recently discovered optical Hall effect.
Surface polaritons, e.g., surface plasmon polaritons, are invaluable tools in nanophotonics. However, considerable plasmon loss narrows the application regime of plasmonic devices. Here we reveal some general conditions for lossless surface polaritons to emerge at the interface of a gain and a loss media. The gain medium does not only compensate the energy loss, but also modifies surface wave oscillation mechanisms. A new type of surface polaritons induced by the sign switch of the imaginary part of the permittivity across the interface is discovered. The surface polaritons exhibit spin Hall e…
We predict an anomalous thermal Hall effect (ATHE) mediated by photons in networks of Weyl semi-metals. Contrary to the photon thermal Hall effect in magneto-optical systems which requires the application of an external magnetic field the ATHE in a Weyl semi-metals network is an intrinsic property of these systems. Since the Weyl semi-metals can exhibit a strong nonreciprocal response in the infrared over a broad spectral range the magnitude of thermal Hall flux in these systems can be relatively large compared to the primary flux. This ATHE paves the way for a directional control of heat flux…
Photonic spin Hall effect is a manifestation of spin-orbit interaction of light and can be measured by a transverse shift λof photons with opposite spins. The precise measurement of transverse shifts can enable many spin-related applications, such as precise metrology and optical sensing. However, this transverse shift is generally small (i.e. δ/λ<{10}^{-1}, λis the wavelength), which impedes its precise measurement. To-date proposals to generate giant spin Hall effect (namely with δ/λ>{10}^{2}) have severe limitations, particularly its occurrence only over a narrow angular cone (with a width …
The propagation of electromagnetic waves in vacuum is often described within the geometrical optics approximation, which predicts that wave rays follow null geodesics. However, this model is valid only in the limit of infinitely high frequencies. At large but finite frequencies, diffraction can still be negligible, but the ray dynamics becomes affected by the evolution of the wave polarization. Hence, rays can deviate from null geodesics, which is known as the gravitational spin Hall effect of light. In the literature, this effect has been calculated ad hoc for a number of special cases, but n…
We show the existence of a very large spin Hall effect of light (SHEL) in single photon plasmonics based on spontaneous emission and the dipole-dipole interaction initiated energy transfer (FRET) on plasmonic platforms. The spin orbit coupling inherent in Maxwell equations is seen in the conversion of sigma + photon to sigma - photon. The FRET is mediated by the resonant surface plasmons and hence we find very large SHEL. We present explicit results for SHEL on both graphene and metal films. We also study how the splitting of the surface plasmon on a metal film affects the SHEL. In contrast to…
