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We demonstrate that higher-order vortex solitons (with larger vortex charges m) in the nonlinear Schrödinger equation with cubic (defocusing Kerr) nonlinearity can be stabilized by the action of a flat-bottom potential. Such a model can also support the common fundamental (vorticityless) solitons, including the Gaussian-like and flat-top solitons. The effective radii of the fundamental and vortex solitons can be modified by tuning the radius of the flat-bottom part of the potential. We display the contours and phases of vortex solitons with vorticity numbers up to m = 12 . Interestingly, the central holes of vortex solitons increase with the increase of vortex charges, and the central portions of these higher-order vortices become flat. We investigate the existence and stability of both the fundamental and vortex solitons, for different values of the relevant model parameters: the radius of the flat bottom, initial beam power, propagation constant, and the strength of nonlinearity. We also consider the propagation of perturbed initial beams, as well as the propagation in longitudinally modulated flat-bottom potentials. Such a modulated propagation allows for an easy soliton management. We find that the fundamental solitons are completely stable, while the higher-order vortex solitons are prone to the modulation instability, degenerating into m simple vortices that fly away from the inside to the outside of solitons. Eventually, an initial higher-order vortex beam turns into a fundamental (chargeless) soliton. [ABSTRACT FROM AUTHOR]

Mode‐division multiplexing (MDM) techniques based on various spatial mode bases are of great significance in satisfying the demand for efficient capacity scaling. With the development of diverse MDM systems, the seamless connection and integration between them are particularly important. In this scenario, a laudable goal would be to implement flexible spatial mode bases mapping. To break the barrier between different MDM systems, a compact 3D photonic device based on diffractive neural network (DNN) is presented for mode bases mapping, transforming orbital angular momentum (OAM) modes into linearly polarized (LP) modes. Through simulations and experiments, a four‐layer optical neural network mode mapper (ONNMM) is successfully demonstrated, exhibiting its capability of mapping five orthogonal spatial modes between OAM and LP mode bases simultaneously. The ONNMM shows a vision for grooming MDM optical communications and interconnects, as well as other emerging applications enabled by intelligent 3D integrated compact devices. [ABSTRACT FROM AUTHOR]

As an important quantum resource, optical cat state is successfully prepared and applied in quantum information science. It is shown that optical quantum states carrying orbital angular momentum (OAM) have wide applications in quantum communication and quantum precision measurement. Here, optical cat states carrying OAM are experimentally prepared with topological charges ℓ$\ell$= 0, +1, +2, +4 by changing the wavefront of the photon‐subtracted squeezed vacuum state with a combination of quarter‐wave plate and q‐plate. To verify the prepared cat states, both Wigner functions and topological charges of OAM are measured. It is shown that the fidelities and amplitudes of optical cat states carrying OAM decrease slightly with the increase of topological charges of OAM, although the spatial size of the optical beam is increased. These results present a new kind of optical cat state carrying OAM, which has potential applications in quantum precision measurement. [ABSTRACT FROM AUTHOR]

Pancharatnam–Berry (PB) phase is typically employed to control circularly polarized (CP) waves, but it has spin‐locked limitations due to its conjugate phase response to different spins. Recently, by modulating both propagation and PB phases, spin‐decoupled metasurfaces have attracted much attention. Most of these spin–decoupled metasurfaces are realized by regulating co‐polarized components, which need N meta‐atoms to achieve a 360° phase coverage. However, this research on wideband high‐efficiency spin‐decoupled metasurfaces based on polarization conversion meta‐atoms by adjusting cross‐polarized components is still lacking. Compared with the regulation of co‐polarized components, only N/2 meta‐atoms are needed for the regulation of cross‐polarized components, which greatly reduces the design difficulty. Here, two spin‐decoupled metasurfaces are proposed for the generation of multiple vortex beams and pencil beams, which exhibit broadband and high‐efficiency performance at the frequency range of 9–21 GHz. This work has the potential to significantly promote the development of wideband polarization multiplexing and multichannel meta‐devices, with various applications in cyberspace security, wireless communication, imaging, and target detection. [ABSTRACT FROM AUTHOR]

Vortex air lasing opens exciting perspectives for remote generation, amplification, and control of vortex beams in ambient air. By combining the advantages of air lasing and vortex beams, it holds great potential in some specific applications such as standoff detection of chiral molecules and rotating objects. However, it remains challenging to produce high‐order vortex air lasing and flexibly control its orbital angular momentum, hindered by the inhomogeneous distribution and instability of laser‐induced plasma. Herein, vortex N2+${\mathrm{N}}_2^ + $ lasing with a tunable vortex order from the first up to the tenth order is achieved through vortex seed amplification in plasma. The helical phase structure of the seed is well conserved in the amplification process. Each order vortex air lasing shows the same topological charge as the seed and a doughnut‐shaped profile. Moreover, the amplification factor is up to 104. Generation of high‐order, high‐gain vortex air lasing is attributed to the choice of an appropriate population‐inversion system, as well as the optimal control over spatial matching of pump and seed beams, gas pressures, and focusing conditions. This work facilitates the understanding of the gain mechanism of N2+${\mathrm{N}}_2^ + $ lasing and promises to extend the application scenarios of air‐lasing‐based spectroscopy. [ABSTRACT FROM AUTHOR]

Chiral plasmonic nanomaterials have been widely utilized to study light‐matter interactions due to its capability to amplify chiroptic signals. Conventionally, chiro‐optic experiments have demonstrated interactions between circularly polarized light and materials. However, employing light with chiral phase, i.e., optical vortex, can generate a strong chiral response and holds the potential to unveil extensive material information owing to the infinite topological numbers. In this work, an array of 3D chiral nanoparticles is employed to demonstrate large helical dichroism (HD). Chiral gold nanoparticle arrays are illuminated by vortex beams of opposite helicity, which revealed the high HD value of 0.93. The chiral interaction is theoretically investigated, and enantioselective interaction can be explained by multipole analysis. It is determined that the strong HD is attributed to the interaction of higher‐order multipole moments such as electric quadrupole and magnetic quadrupole moments. This study provides deeper insight into understanding of the interaction between optical vortex and chiral plasmonic nanostructures and paves the way for next‐generation chiroptical applications ranging from ultrasensitive chiral spectroscopy to chiral quantum optics. [ABSTRACT FROM AUTHOR]

Singularity in a two-point complex coherence function, known as coherence vortices, represents zero visibility with a helical phase structure. In this paper, we introduce a novel technique to generate the coherence vortices of different topological charges by incoherent source transmittance with exotic structured binary pinholes. The binary pinhole structures have been realized by lithography, followed by wet etching methods. We control the transmittance from the incoherent source plane using these exotic apertures, which finally results in a coherence vortex spectrum that features multiple and pure orbital angular momentum modes. The generation of the coherence vortices is achieved within the two-point complex spatial coherence function. The spatial coherence function exhibits the helical phase profile in its phase part, and its absolute part shows a doughnut-shaped structure. A theoretical basis is developed and validated with simulation, and experimental results. The coherence vortex spectra with OAM modes superposed with opposite topological charges, known as photonic gears, are also generated with the proposed theory. [ABSTRACT FROM AUTHOR]

Accelerating a free electron to high‐energy forms the basis for studying particle and nuclear physics. Here it is shown that the wave function of such an energetic electron can be further manipulated with the femtosecond intense lasers. During the scattering between a high‐energy electron and a circularly polarized laser pulse, a regime is found where the enormous spin angular momenta of laser photons can be efficiently transferred to the electron orbital angular momentum (OAM). The wave function of the scattered electron is twisted from its initial plane‐wave state to the quantum vortex state. Nonlinear quantum electrodynamics (QED) theory suggests that the GeV‐level electrons acquire average intrinsic OAM beyond ⟨l⟩∼100ℏ$\langle l \rangle \sim 100\hbar $ at laser intensities of 1020 W cm−2 with linear scaling. These electrons emit γ‐photons with two‐peak spectrum, which sets them apart from the ordinary electrons. The findings demonstrate a proficient method for generating relativistic leptons with the vortex wave functions based on existing laser technology, thereby fostering a novel source for particle and nuclear physics. [ABSTRACT FROM AUTHOR]

The optomechanical motion of a gold nanoparticle (GNP) dimer—a pair of optically bound GNPs—in fluid, manipulated by a Bessel beam, is theoretically studied using the multiple multipole (MMP) method. Since a Bessel beam possesses orbital angular momentum (OAM) and spin angular momentum (SAM) simultaneously, complicated rigid-body motions of the dimer can be induced. The mechanism involves the equilibrium between the optical force with the reactive drag force exerted by the fluid. Our results demonstrate that the dimer rotates around its center of mass (COM), while the COM performs an orbital revolution around the optical axis. Additionally, each individual GNP undergoes spinning. The directions of the GNPs' spin and the orbital revolution of COM depend on the handedness and the order (topological charge) of Bessel beam, respectively. Nevertheless, the rotation direction of the dimer depends on the size of GNP. In the case of a smaller dimer, the direction of dimer's rotation with respect to the COM is consistent with the handedness of the light. Conversely, a larger dimer performs a reverse rotation, accompanied by a precession during the orbital revolution. There are multiple turning points in the radius of the GNP for the alternating rotation of the dimer caused by positive or negative optical torque. Our finding may provide an insight to the optomechanical manipulation of optical vortexes on the motions of GNP clusters. [ABSTRACT FROM AUTHOR]

Velocimetry of a motion target within 3‐D space is highly desirable in numerous applicable realms, ranging from explosion and shock wave physics, aerospace engineering to astronomical surveys. However, it is challenging to achieve synchronous, real‐time, and photon‐counting 3‐D velocimetry in modern frameworks as they either require separate multi‐directional detections, and cumbersome calculation processes or are confined to achieve in situ measurements. Here, a new conceptual paradigm is proposed to circumvent these constraints using orbital‐angular‐momentum (OAM)‐driven multi‐point Doppler effect at the photon‐counting level. This scheme, emanating from a single‐direction launch of an on‐demand engineered sequence OAM light mode onto a motion surface, enables simultaneous and independent detections of time‐varying Doppler photon‐count events from three orthogonal echo light paths. Concretely, at the range of motion velocity of 0.25–0.5 ms−1, the relative measurement errors of this proof‐of‐principle prototype are below 1.5%, thus achieving high‐accuracy 3‐D velocimetry at the photon‐counting level for the first time. The exploration of the OAM‐photon‐counting 3‐D velocimetry techniques provides unprecedented advantages in potential applications of synchronous, real‐time, high‐efficiency, and long‐range quantum lidar. [ABSTRACT FROM AUTHOR]

Janus metasurfaces, offering versatile light manipulation contingent on incident direction, are explored across microwave to mid‐infrared spectra. Nonetheless, prior designs often resort to spatial multiplexing or vertical stacking, entailing complex fabrication. Metallic Janus metasurfaces, owing to material properties, suffer notable Ohmic losses in the visible spectrum. In this study, Single‐layer TiO2‐based Janus metasurfaces with arbitrary polarization control is experimentally demonstrated, exhibiting directionally asymmetric functionalities in spin and orbital angular momentum (OAM). A novel Jones matrix formulation tailored for Janus metasurfaces is presented, enabling efficient generation of two asymmetric, high‐purity OAM states of vortex beams at wavelength of 532 nm, contingent on incidence direction. This innovation facilitates compact and versatile phase manipulation, encompassing applications such as lasers and optical combiners, thereby expanding its utility across diverse domains. [ABSTRACT FROM AUTHOR]

We theoretically studied the dynamic properties of the skyrmion driven by electromagnetic (EM) waves with spin angular momentum (SAM) and orbital angular momentum (OAM) using micromagnetic simulations. First, the guiding centers of the skyrmion driven by EM waves with SAM, i.e., left-handed and right-handed circularly polarized EM waves, present circular trajectories, while present elliptical trajectories under linear EM waves driving due to the superposition of oppositely polarized wave components. Second, the trajectories of the skyrmion driven by EM waves with OAM demonstrate similar behavior to that driven by linearly polarized EM waves. Because the wave vector intensity varies with the phase for both linearly polarized EM waves and EM waves with OAM, the angular momentum is transferred to the skyrmion non-uniformly, while the angular momentum is transferred to the skyrmion uniformly for left-handed and right-handed circularly polarized EM driving. Third, the dynamic properties of the skyrmion driven by EM waves with both SAM and OAM are investigated. It is found that the dynamic trajectories exhibit more complex behavior due to the contributions or competition of SAM and OAM. We investigate the characteristics of intrinsic gyration modes and frequency-dependent trajectories. Our research may provide insight into the dynamic properties of skyrmion manipulated by EM waves with SAM or OAM and provide a method for controlling skyrmion in spintronic devices. [ABSTRACT FROM AUTHOR]

An analogy with the polarization Stokes parameters and symplectic methods of the second-order intensity moment matrix allowed us to develop a simple technique for measuring the orbital Stokes parameters followed by mapping the structured beam states onto the orbital Poincaré sphere. The measurement process involves only two shots of the beam intensity patterns in front of a cylindrical lens and in its double focus. Such a simple measurement approach is based on the reciprocity effect between the experimentally measured cross-intensity element W x y and the orbital angular momentum of the intensity moment matrix. For experiments, we chose two types of two-parameter structured beams, namely, structured Laguerre–Gaussian beams and binomial beams. We obtained a good agreement between our theoretical background and the experiments, as well as the results of other authors. [ABSTRACT FROM AUTHOR]

In view of the recent increased interest in light-induced manipulation of magnetism in nanometric length scales this work presents metal clusters as promising elementary units for generating all-optical ultrafast magnetization. We perform a theoretical study of the opto-magnetic properties of metal clusters through ab-initio real-time (RT) simulations in real-space using time-dependent density functional theory (TDDFT). Through ab-initio calculations of plasmon excitation with circularly polarized laser pulse in atomically precise clusters of simple and noble metals, we discuss the generation of orbital magnetic moments due to the transfer of angular momentum from light field through optical absorption at resonance energies. Notably, in the near-field analysis we observe self-sustained circular motion of the induced electron density corroborating the presence of nanometric current loops which give rise to orbital magnetic moments due to the inverse Faraday effect (IFE) in the clusters. The results provide valuable insights into the quantum many-body effects that influence the IFE-mediated light-induced orbital magnetism in metal clusters depending on its geometry and chemical composition. At the same time, they explicitly demonstrate the possibility for harnessing magnetization in metal clusters, offering potential applications in the field of all-optical manipulation of magnetism. [ABSTRACT FROM AUTHOR]

Optical vortex beam has gained much attention in the field of information processing because of its inherent features, such as the infinite number of orthogonal modes. In this paper, we demonstrate optical image encryption based on the deoxyribonucleic acid (DNA) encoding rule through optical vortices. In this scheme, two levels of security are achieved; in the first level, an input image is encrypted using equal modulus decomposition as well as phase truncation and phase reservation approach. Thus, the obtained encrypted image is encoded into a DNA sequence according to the existing DNA encoding rule and then DNA exclusive-OR operation is applied with the DNA sequence of a random key image in order to obtain the ciphertext. In the second level of security, the DNA sequence of the encrypted image is encoded into vortex beams using different orthogonal modes and arranged in the form of optical lattices. This type of encoding rule overcomes the tedious task of manually encoding the vortex beam and also enhances the key space and, hence, the security. Simulation and experimental results support the efficacy of the proposed scheme.Article Highlights: The proposed scheme combines DNA encoding with optical vortices under asymmetric encryption framework. It offers an easy way of information encoding into optical vortices having different topological charges. The proposed combination has been tested as a very robust cryptosystem under statistical and specific attacks. [ABSTRACT FROM AUTHOR]

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This study is devoted to analyze the scattering from spherical homogeneous rain droplet particles illuminated by structured light beam i.e., Gaussian vortex beam (GVB) with different orbital angular momentum (OAM). The promising applications of intricate optical beam fields regarding environmental monitoring and detection have mesmerized the consideration of optical community. The optical effects i.e., absorption and scattering of the atmospheric environment cause intensity distribution of GVB which lowers quality of beam signal. GVB carries OAM and when it propagates in the atmosphere then its interaction with the environment constituents (rain, fog, snow, clouds, water vapours, atmospheric gases, and other particles) makes the problem quite interesting. Rainy medium is considered as a uniformly spherical shaped sphere. So, the interaction between a linearly polarized GVB and a rainy atmosphere is investigated using the generalized Lorenz–Mie theory (GLMT). The expressions for electromagnetic fields (incident + scattered + inside) of GVB are expanded using spherical vector wave functions (SVWFs). By implementing continuous boundary conditions (BCs) at the spherical surface of rain droplets, the scattering coefficients in context of beam shape coefficients are obtained. The efficiencies (scattering, extinction, and absorption), forward scattering, backward scattering, GVB attenuation as well as transmittance are computed and discussed. In addition to that, the influence of OAM mode number, beam waist radius, and incident beam operating wavelengths of rainy medium on the efficiencies, electromagnetic scattering, attenuation, and transmittance is analyzed. This study establishes the groundwork for examining the tuning capability of GVBs for rainy atmosphere at various parameters. [ABSTRACT FROM AUTHOR]

This letter explores the possibility of long‐distance transmission of an orbital angular momentum (OAM) beam through rectangular tunnels. Theoretical analysis reveals that the OAM beam propagating in the tunnel with square cross section fulfills the conditions for axial propagation and exhibits azimuth symmetry. In comparison with free‐space OAM generation, we draw the conclusion that long‐distance transmission of OAM beams is achievable in the tunnels with square cross section. The validity of our conclusion is further substantiated through numerical experiments. Simulation results demonstrate that the first‐order OAM beam radiated by a uniform circular antenna array exhibits favorable helical phase distribution and the circular symmetry of the amplitude distribution in the tunnel beyond the Rayleigh distance. However, these characteristics degrade with increasing mode order and propagation distance, because the increase of high‐order OAM beam divergence angle and propagation distance will exacerbate the impact of multipath effects in the tunnel environment. [ABSTRACT FROM AUTHOR]

Arrays of multiple vortex beams enhance parallel processing capabilities from particle manipulation to information communication. However, the spatial position, topological charge, and energy parameters of the vortex beams within the array have yet to be precisely controlled, posing significant challenges to the realization of multi‐view 3D Orbital Angular Momentum (OAM) display using vortex arrays as information carriers. To address this issue, a method for generating vortex arrays based on a phase‐only hologram, customizing the array by using the energy and OAM spectrum of each vortex beam as the loss function is developed. Experimental results indicate that a 2D array generates 100 vortex beams in the spatial frequency domain, while a 3D array in the Fresnel zone produces 252 vortex beams across 7 planes, each with 36 unprecedentedly controllable energy and topological charge vortex beams. Subsequently, images of 4 views using the 3D vortex arrays and decoded through coordinate transformation to achieve a multi‐view 3D OAM display are encoded. The results demonstrate imaging quality with Mean Peak Signal‐to‐Noise Ratio (MPSNR) of 12.7, 13.0, 13.4, and 12.2 dB in 4 views, respectively, offering promising opportunities for applications in 3D optical manipulation, high‐capacity communication, and 3D OAM holography. [ABSTRACT FROM AUTHOR]

Orbital angular momentums (OAMs) greatly enhance the channel capacity in free-space optical communication. However, demodulation of superposed OAM to recognize them separately is always difficult, especially upon multiplexing more OAMs. In this work, we report a directly recognition of multiplexed fractional OAM modes, without separating them, at a resolution of 0.1 with high accuracy, using a multi-task deep learning (MTDL) model, which has not been reported before. Namely, two-mode, four-mode, and eight-mode superposed OAM beams, experimentally generated with a hologram carrying both phase and amplitude information, are well recognized by the suitable MTDL model. Two applications in information transmission are presented: the first is for 256-ary OAM shift keying via multiplexed fractional OAMs; the second is for OAM division multiplexed information transmission in an eightfold speed. The encouraging results will expand the capacity in future free-space optical communication. [ABSTRACT FROM AUTHOR]

The orthogonality characteristics of orbital angular momentum (OAM) can provide a new degree of freedom for optical wireless communication (OWC) systems. By transmitting multiple different orders of OAM states within a single beam, multiple data channels can be carried to the end users simultaneously. As the value of the OAM state increases to a higher order, the conventional single OAM state beam suffers from destructive interference due to decreasing intensity and increasing divergence angle as the beam spreads out. In this paper, we propose a novel OAM beamforming technique for an indoor multiuser OWC network using weighted impulse response, based on the sum of intensity contributions of superposed multiple OAM states carrying Laguerre-Gaussian (LG) ultraviolet (UV) beams. The proposed OAM beamforming method is shown to reduce the destructive interference at the dark region of the beam and to increase the amplitude of intensity distribution of the beamformed OAM states. Consequently, the proposed method shows better performance with increasing OAM states beamformed together in the OWC channel, compared to a conventional single OAM state LG UV beam.

Abstract The optomechanical motion of a gold nanoparticle (GNP) dimer—a pair of optically bound GNPs—in fluid, manipulated by a Bessel beam, is theoretically studied using the multiple multipole (MMP) method. Since a Bessel beam possesses orbital angular momentum (OAM) and spin angular momentum (SAM) simultaneously, complicated rigid-body motions of the dimer can be induced. The mechanism involves the equilibrium between the optical force with the reactive drag force exerted by the fluid. Our results demonstrate that the dimer rotates around its center of mass (COM), while the COM performs an orbital revolution around the optical axis. Additionally, each individual GNP undergoes spinning. The directions of the GNPs’ spin and the orbital revolution of COM depend on the handedness and the order (topological charge) of Bessel beam, respectively. Nevertheless, the rotation direction of the dimer depends on the size of GNP. In the case of a smaller dimer, the direction of dimer’s rotation with respect to the COM is consistent with the handedness of the light. Conversely, a larger dimer performs a reverse rotation, accompanied by a precession during the orbital revolution. There are multiple turning points in the radius of the GNP for the alternating rotation of the dimer caused by positive or negative optical torque. Our finding may provide an insight to the optomechanical manipulation of optical vortexes on the motions of GNP clusters.

Abstract Optical vortex beam has gained much attention in the field of information processing because of its inherent features, such as the infinite number of orthogonal modes. In this paper, we demonstrate optical image encryption based on the deoxyribonucleic acid (DNA) encoding rule through optical vortices. In this scheme, two levels of security are achieved; in the first level, an input image is encrypted using equal modulus decomposition as well as phase truncation and phase reservation approach. Thus, the obtained encrypted image is encoded into a DNA sequence according to the existing DNA encoding rule and then DNA exclusive-OR operation is applied with the DNA sequence of a random key image in order to obtain the ciphertext. In the second level of security, the DNA sequence of the encrypted image is encoded into vortex beams using different orthogonal modes and arranged in the form of optical lattices. This type of encoding rule overcomes the tedious task of manually encoding the vortex beam and also enhances the key space and, hence, the security. Simulation and experimental results support the efficacy of the proposed scheme.

In free-space diffraction, the orbital angular momentum(OAM)of the vortex light field remains unchanged. However, in a turbulent layer, the symmetry of the OAM spectrum distribution will be broken, and the OAM will change due to the existence of a quasi-ordered structure in the flow field. In this paper, the mechanism of detecting the flow structure by using the symmetry breaking of OAM spectrum distribution was investigated. The feasibility of applying OAM of vortex light field to detect undersea vehicles was analyzed, and relevant test results were given. In addition, according to the characteristics that the total OAM of the light field also changes, the theoretical basis for identifying the characteristics of different flow fields based on OAM was elaborated through the cross-OAM matrix method. Lastly, the perception characteristics of the water medium of the vortex light field were studied. Combined with the results of numerical simulation, a technical concept for detecting undersea vehicles based on the characteristics of OAM propagation was proposed.

This paper introduces a novel high-speed Visible Light Communication (VLC) system capable of transmitting data rates of 120 Gbps. The system leverages the multiplexing capabilities of Dual Polarization (DP) and Orbital Angular Momentum (OAM) beams. It incorporates three Laser Diode (LD) sources operating at distinct wavelengths: red (700 nm), green (570 nm), and blue (450 nm). Each LD source generates four OAM beams operating at DP states, with each OAM beam carrying a data rate of 5 Gbps. The proposed system is designed for indoor VLC applications, considering line-of-sight (LoS) link configurations. The proposed system is evaluated for different detector surface areas, and transmission distance. The bit error rate (BER), and eye diagrams as evaluation metrics are used to characterize the performance of the system. The findings of different detection areas reveal that larger surfaces yield superior performance, with significant reductions in BER observed at the cost of collecting more ambient noise. Additionally, shorter transmission distances exhibit enhanced performance, underscoring the importance of propagation range in VLC systems. Through extensive performance analysis, our proposed DP-OAM-VLC model achieves an overall transmission capacity of 120 Gbps at a range of 1.1 m, with a BER below 10−3.

This study introduces a distinctive entwined photonic crystal fiber (PCF) featuring two distinct and independent directed mode sections, collectively supporting a total of 112 orbital angular momentum (OAM) modes, comprising 76 + 36 modes. The confinement loss (CL) ranges approximately between 2.49701 × 1 0 - 11 and 9.13425 × 1 0 - 9 dB / m , while highest attained OAM purity is 99.31969 % and 98.99258 % at H E 2 , 1 mode, respectively, for both inner and outer rings. All the modes demonstrate ERIDs exceeding 1 0 - 4 , and minimum dispersion variation observed is - 856 ps / km - nm . Additionally, we achieved an outstanding isolation performance with the highest attained ISO reaching 294 dB at HE 9 , 1 mode and observed a substantial effective mode area of 9.15 μm2 and 25.8μm2, respectively, for inner and outer rings. This research leverages COMSOL Multiphysics' finite element method (FEM) and perfectly matched layer (PML) capabilities alongside MATLAB processing to calculate all key properties of the proposed fiber. Therefore, the suggested PCF demonstrates promising prospects for extended-range, high-capacity data transmission within optical communications and applications related to OAM sensing. [ABSTRACT FROM AUTHOR]

In this work, detection probability of the orbital angular momentum (OAM) states of the Bessel-Gaussian (BG) and Laguerre-Gaussian (LG) beams passing through a plasma sheath turbulence (PST) are theoretically investigated. For this purpose, OAM-spectrum of the vortex beams (VB) is derived by using the modified von-Karman spectrum in the frame of Rytov theory, then some numerical analysis is performed to show the difference of considered VBs in the propagation through a PST. Obtained results indicate that incident beam parameters such as angular mode number, beam waist, and wavelength can easily affect the OAM-spectrum of both types of VBs. As well as, increasing the anisotropic parameters of the turbulent media can mitigate the turbulence-induced disturbance of the propagated VBs. Furthermore, it is found that diffraction-free BG beams show a better propagation performance than LG beams in the PST. This feature allows the BG beam to be a good candidate for free-space communication applications.

Abstract We explore the propagation of structured vortex laser beams-shaped light carrying orbital angular momentum (OAM)-through complex multiple scattering medium. These structured vortex beams consist of a spin component, determined by the polarization of electromagnetic fields, and an orbital component, arising from their spatial structure. Although both spin and orbital angular momenta are conserved when shaped light propagates through a homogeneous, low-scattering medium, we investigate the conservation of these angular momenta during the propagation of Laguerre–Gaussian (LG) beams with varying topological charges through a turbid multiple scattering environment. Our findings demonstrate that the OAM of the LG beam is preserved, exhibiting a distinct phase shift indicative of the ‘twist of light’ through the turbid medium. This preservation of OAM within such environments is confirmed by in-house developed Monte Carlo simulations, showing strong agreement with experimental studies. Our results suggest exciting prospects for leveraging OAM in sensing applications, opening avenues for groundbreaking fundamental research and practical applications in optical communications and remote sensing.

In recent years, acoustic metamaterials, as a sort of novel artificial composite materials, have demonstrated the ability to surpass the limitations of traditional materials through their exceptional acoustic parameter manipulation capabilities. Thus, acoustic metamaterials have shown promising applications in numerous areas such as underwater detection, underwater target identification, acoustic imaging, navigation, and underwater communication. The advancements in metamaterial-based underwater acoustic communication were reviewed, focusing primarily on multiplex communication based on acoustic orbital angular momentum, underwater acoustic communication between specific transmitter and receiver based on beam steering of acoustic metasurface, and water-air trans-medium acoustic communication. The key technologies were summarized, and the current challenges and future prospects of metamaterial-based underwater acoustic communication were outlined.

Orbital Angular Momentum (OAM) waves are characterized by helical wave fronts and orthogonality between different modes. Therefore, OAM waves have huge potential in improving wireless communications' channel capacity and radar imaging's resolution. Consequently, the generation and application of OAM waves have attracted a lot of attention. And many methods are proposed to generate OAM waves. Although antenna array is the most popular method of generating OAM waves, OAM waves generated by antenna array have redundant modes. However, all advantages of OAM waves are closely related to infinite OAM modes. Thus, to better apply OAM waves to wireless communications and radar, it is very important to reduce unnecessary OAM modes and improve the OAM mode purity. In order to improve the OAM mode purity, two combined antenna arrays composed of X direction antenna and Y direction antenna array are proposed in this paper. The X direction antenna array and the Y direction antenna array are supplied by the excitations with the same amplitude and fixed phase shift. The overall phase shift of the X direction antenna array is π/2 more or less than that of the Y direction antenna array. The results of formulas and antenna models in CST show that the combined antenna arrays can generate OAM waves with less redundant modes in x component, y component and z component. Besides, the z component carries pure OAM modes.

Enhancing rotational measurement resolution and broadening the detectable spectral range are two critical and unresolved matters within the realm of motion perception. The rotational Doppler effect (RDE) is combined with the harmonic generation process to create a rotational measurement scheme that offers flexible detection wavelength conversion, exponential improvement of measurement resolution, and real‐time display of detection results. In the experiments, a cascaded second harmonic generation process is employed to attain a fourfold enhancement in rotational resolution and demonstrate how low‐cost silicon‐based detectors can be used for real‐time detection of infrared objects. This scheme employs a Gaussian beam within the nonlinear process to achieve high conversion efficiency, thereby enabling potential for subsequent cascade amplification. Additionally, it is fully compatible with existing RDE schemes, allowing for co‐amplification of rotational resolution at both the front‐end and back‐end. This research could offer a more precise and cost‐effective method for remote sensing detection. [ABSTRACT FROM AUTHOR]

Optical skyrmions are topologically stable quasiparticles that can be constructed with electric field, spin angular momentum, polarization Stokes vector, pseudospin, etc. In this letter, both theoretical and experimental studies are carried out to reveal the role of Gouy phase in the topology transformation during the tight focusing of Stokes skyrmions. The Stokes skyrmionic beam can be constructed by superposing two orthogonally polarized components with orthogonal spatial modes. The Gouy phase produced in the focused field depends on the orbital angular momentum carried by the high order mode component of the incident Stokes skyrmionic beam. While the beam size of the focused field is diffraction limited, the variation of the Stokes vectors in the skyrmion topology is in the sub‐diffraction limited scale. The presented results shed light on the understanding of the topology transformation between the incident and the tightly focused fields, paving the way for engineering the optical skyrmions in micro‐nano scale and their applications in information processing, quantum technology, metrology, etc. [ABSTRACT FROM AUTHOR]

The optical coordinate transformation based on the ray model can flexibly and efficiently complete the manipulation of complex light fields through a pair of phase plates, and is successfully used to sort orbital angular momentum (OAM) of light. Generally, the phase modulation required by the optical coordinate transformation is derived analytically under the paraxial approximation, however, this would induce the phase modulation error, and thus worsen the quality of the transformed beam. Here, a non‐paraxial design for the spiral coordinate transformation is proposed, where the phase of the unwrapper is obtained by numerically solving the partial differential equations on the coordinate mapping and the phase corrector is obtained by the angular spectrum diffraction integral method. Due to more accurate phase modulation, the non‐paraxial spiral transformation effectively improves the beam quality, and realizes the demultiplexing of OAM modes with higher efficiency and lower cross‐talk. The proposed approach is verified with a compact metasurface‐based optical vortex mode sorter, which is extensible toward OAM‐based multi‐mode systems involving classical and quantum optical information processing. [ABSTRACT FROM AUTHOR]

Bell state measurement plays a pivotal role in the realm of quantum communication, yet a definitive solution for achieving complete Bell state measurement remains unclear. In this paper, we propose a theoretical scheme for four-dimensional orbital angular momentum Bell state measurement, harnessing the polarization and frequency degree of freedom as auxiliary tools. Within this scheme, the input state traverses a hyperentangled state analyzer comprised of quantum logic gates, ultimately enabling the realization of Bell state measurement in a four-dimensional mode. Simultaneously, serving as a novel avenue to enhance the capacity of quantum communication, this scheme has potential applications in realizing large-capacity quantum communication. [ABSTRACT FROM AUTHOR]

Light diffraction is studied numerically and experimentally on a double fork‐shaped grating representing a periodic grating containing two spaced dislocations. The spatial dynamics of the phase singularities (optical vortices) has been investigated as a function of dislocation parameters. Produced optical vortices affect each other while propagating in a free space. For dislocations of the same topological charge, the propagation trajectories and their transverse displacement coordinates depend on the dislocation spacing, and the larger the dislocation spacing, the smaller the relative displacement of the optical vortices and the smaller their trajectory curvatures. For oppositely charged dislocations, three types of spatial behavior of optical vortices are found. The numerical results agree well with the experimental data. [ABSTRACT FROM AUTHOR]

Low-intensity light beams carrying orbital angular momentum (OAM), commonly known as vortex beams, have garnered significant attention due to promising applications in areas ranging from optical trapping to communication. In recent years, there has been a surge in global research exploring the potential of high-intensity vortex laser beams and specifically their interactions with plasmas. This paper provides a comprehensive review of recent advances in this area. Compared with conventional laser beams, intense vortex beams exhibit unique properties such as twisted phase fronts, OAM delivery, hollow intensity distribution, and spatially isolated longitudinal fields. These distinct characteristics give rise to a multitude of rich phenomena, profoundly influencing laser-plasma interactions and offering diverse applications. The paper also discusses future prospects and identifies promising general research areas involving vortex beams. These areas include low-divergence particle acceleration, instability suppression, high-energy photon delivery with OAM, and the generation of strong magnetic fields. With growing scientific interest and application potential, the study of intense vortex lasers is poised for rapid development in the coming years. [ABSTRACT FROM AUTHOR]

One of the main challenges for modern information read and write technology is how to effectively and precisely modulate the interconversion between electricity and magnetism with a high data density. Herein, it is proposed that two‐dimensional magnetic sliding ferroelectrics can serve as a prototypical material platform with tunable electric current‐induced magnetization variation, a typical nonequilibrium magnetoelectric coupling process. Using a CrI3 bilayer as the exemplary material, first‐principles calculations are performed to enumerate the monopole values, toroidal vectors, and quadrupole moment tensors. Their switching is also elucidated under a short distance sliding between the two layers, which can effectively flip the electric dipole moment. In addition to spin polarization which is usually studied for magnetic systems, the orbital moment contribution to the magnetoelectric coupling is also evaluated. They are found to be comparable in their magnitude and neither should be omitted, as opposed to equilibrium states. The work helps to reveal the underlining mechanisms among electronics, spintronics, and orbitronics in low‐dimensional multiferroic materials. [ABSTRACT FROM AUTHOR]

The integration of terrestrial- and satellite-based quantum key distribution (QKD) experiments has markedly advanced global-scale quantum networks, showcasing the growing maturity of quantum technologies. Notably, the use of unmanned aerial vehicles (UAVs) as relay nodes has emerged as a promising method to overcome the inherent limitations of fiber-based and low-Earth orbit (LEO) satellite connections. This paper introduces a protocol for measurement-device-independent QKD (MDI-QKD) using photon orbital angular momentum (OAM) encoding, with UAVs as relay platforms. Leveraging UAV mobility, the protocol establishes a secure and efficient link, mitigating threats from untrusted UAVs. Photon OAM encoding addresses reference frame alignment issues exacerbated by UAV jitter. A comprehensive analysis of atmospheric turbulence, state-dependent diffraction (SDD), weather visibility, and pointing errors on free-space OAM-state transmission systems was conducted. This analysis elucidates the relationship between the key generation rate and propagation distance for the proposed protocol. Results indicate that considering SDD significantly decreases the key rate, halving previous data results. Furthermore, the study identifies a maximum channel loss capacity of 26 dB for the UAV relay platform. This result is pivotal in setting realistic parameters for the deployment of UAV-based quantum communications and lays the foundation for practical implementation strategies in the field. [ABSTRACT FROM AUTHOR]

Optical vortex lattices (OVLs) with diverse modes show potential for a wide range of applications, such as high-capacity optical communications, optical tweezers, and optical measurements. However, vortices in typical regulated OVLs often exhibit irregular shapes, such as being narrow and elongated. The resulting increase in asymmetry negatively impacts the efficiency of particle trapping. Additionally, the vortex radii expand with an increase in topological charge (TC), limiting the TC value of the vortices and hindering their ability to fully utilize orbital angular momentum (OAM). Herein, we propose an alternative approach to custom OVLs using off-axis techniques combined with amplitude modulation. Amplitude modulation enables the precise generation of an OVL with perfect vortex properties, known as a perfect off-axis OVL. Further, the number of vortices in the perfect off-axis OVL, the off-axis distances, and the TC can be freely modulated while maintaining a circular mode. This unique OVL will promote new applications, such as the complex manipulation of multi-particle systems and optical communication based on OAM. [ABSTRACT FROM AUTHOR]

Two-dimensional leaky-wave antennas (LWAs) are a class of planar, traveling-wave radiators with attractive features of a low profile, ease of feeding, frequency reconfigurability of the radiation pattern, and polarization agility. Their use in conjunction with array feeders has been the subject of various investigations in recent decades, thanks to the additional degrees of freedom provided by the presence of multiple independent sources. Here, we provide a review of some of the most recent and promising array-fed two-dimensional (2-D) LWAs, selecting a couple of the most significant structures in application, namely Fabry–Perot cavity antennas and bull's-eye antennas, and discussing some of their recently proposed advanced features. [ABSTRACT FROM AUTHOR]

Laguerre-Gaussian (LG) beam is a vortex beam, which is characterised by its helical phase, and has a number of potential applications apart from being a precursor for generation of other vortex beams. Generation of LG beams, carrying higher-order orbital angular momentum (OAM), have been demonstrated by the utilization of multiple vortex phase plates (VPPs) with capability of imparting lower topological charges (TCs). The TCs of the generated LG beams were experimentally ascertained by the analysis of fork patterns generated by interfering the generated LG beams with their corresponding reference Gaussian beams. The experimentally obtained amplitude profiles and fork patterns, exhibited a fair agreement with the results of theoretical formulations. [ABSTRACT FROM AUTHOR]

Vortex wave and plane wave, as two most fundamental forms of wave propagation, are widely applied in various research fields. However, there is currently a lack of basic mechanism to enable arbitrary conversion between them. In this paper, we propose a new paradigm of extremely anisotropic acoustic metasurface (AM) to achieve the efficient conversion from 2D vortex waves with arbitrary orbital angular momentum (OAM) to plane waves. The underlying physics of this conversion process is ensured by the symmetry shift of AM medium parameters and the directional compensation of phase. Moreover, this novel phenomenon is further verified by analytical calculations, numerical demonstrations, and acoustic experiments, and the deflection angle and direction of the converted plane waves are qualitatively and quantitatively confirmed by a simple formula. Our work provides new possibilities for arbitrary manipulation of acoustic vortex, and holds potential applications in acoustic communication and OAM-based devices. [ABSTRACT FROM AUTHOR]

Controlling light at the nanoscale by exploiting ultra‐confined polaritons—hybrid light and matter waves—in various van der Waals (vdW) materials empowers unique opportunities for many nanophotonic on‐chip technologies. So far, mainstream approaches have relied on interfacial techniques (e.g., refractive optics, meta‐optics, and moire engineering) to manipulate the polariton wavefront. Here, it is proposed that orbital angular momentum (OAM) of incident light can offer a new degree of freedom to structure vdW polaritons. With vortex excitations, a new class of accelerating polariton waves is observed—Airy‐like hyperbolic phonon polaritons (PhPs) in high‐symmetry orthorhombic vdW crystal α‐MoO3. In analogous to the well‐known Airy beams in free space, such Airy‐like PhPs also exhibit self‐accelerating, nonspreading, and self‐healing characteristics. Interestingly, the helical phase gradient of the vortex beam leads to asymmetry excitation of polaritons, as a result, the Airy‐like PhPs possess asymmetric propagation features even with a symmetric mode, analogous to the asymmetry hyperbolic shear polaritons in low‐symmetry crystals. The finding highlights the potential of OAM to manipulate polaritons in vdW materials, which can be further extended into a variety of applications such as active structured polaritonic devices. [ABSTRACT FROM AUTHOR]

The evolution of a controllable vortex anomalous hollow beam (CVAHB) in free space is studied theoretically and numerically. Based on the Collins integral, the analytical formula of its propagation under free space paraxial approximation is derived. The corresponding beams with different parameters are simulated numerically, and the influence of each beam parameter on the beam type and intensity distribution during beam propagation is studied. Through the parameter control, the CVAHB can present a variety of intensity modes, such as hollow, three-segment, boat, etc. It is obvious that the evolution of CVAHB is different from that of the controllable anomalous hollow beam (CAHB). By changing the value of the topological charge (TC), the role of the orbital angular momentum (OAM) in the transverse distribution and propagation of light intensity is studied in detail. [ABSTRACT FROM AUTHOR]

The expeditious acquisition of information pertaining to objects through the utilization of quantum technology has been a perennial issue of concern. So far, the efficient utilization of information from dynamic objects with limited resources remains a significant challenge. Here, we realize a nonlocal integrated sensing of the object’s amplitude and phase information by combining digital spiral imaging with the correlated orbital angular momentum states. The amplitude information is utilized for object identification, while the phase information enables us to determine the rotational speed. We demonstrate the nonlocal identification of a rotating object’s shape, irrespective of its rotational symmetry, and introduce the concept of the correlated rotational Doppler effect, establishing a fundamental connection between this effect and the classical rotational Doppler effect, i.e., that both rely on extracting crucial information from the spiral spectrum of objects. The present study highlights a promising pathway towards the realization of quantum remote sensing and imaging. [ABSTRACT FROM AUTHOR]

In measuring object rotational velocity using vortex beam, the incident light on a tilted object causes spectral broadening, which significantly interferes with the identification of the true rotational Doppler shift (RDS) peak. We employed a velocity decomposition method to analyze the relationship between the spectral extremum and the central frequency shift caused by the object tilt. Compared with the linear growth trend observed when calculating the object rotational velocity using the frequency peak with the maximum amplitude, the central frequency calculation method effectively reduced the deviation rate of the RDS and velocity measurement value from the true value, even at large tilt angles. This approach increased the maximum tilt angle for a 1% relative error from 0.221 to 0.287 rad, representing a 29.9% improvement. When the tilt angle was 0.7 rad, the velocity measurement deviation reduction rate can reach 5.85%. Our work provides crucial support for achieving high-precision rotational velocity measurement of tilted object. [ABSTRACT FROM AUTHOR]

Orbital angular momentum (OAM) has emerged as a revolutionary technology for communication networks due to its ability to significantly increase the channel capacity. However, traditional optical fibers present significant hurdles to harnessing OAM’s full potential, including dispersion and limited bandwidth, which facilitates investigations on supercontinuum (SC) generation for OAM beams. In this paper, an air-core Ge-doped ring fiber is proposed and designed to support high-order OAM mode up to |l| = 24. To achieve this, the fiber has a high refractive index difference between the ring core and the cladding, enabling stable transmission of high-order OAM modes. A key feature of this design is the OAM24,1 mode, which exhibits near-zero and flat dispersion. This characteristic translates into high coherence and a remarkably broad SC generation. The generated SC spans over two octaves (2336 nm) within the infrared wavelength range (764 nm to 3100 nm) at a power level of −40 dB. Furthermore, by optimizing the structural parameters, we ensure near-zero and flat dispersion characteristics for the other OAM modes (|l| < 24), along with broad SC generation exceeding two octaves. This fiber design holds significant promise for future advancements in OAM beam transmission within the infrared spectrum.

The investigation of orbital angular momentum (OAM) of delocalised Bloch electrons has advanced our understanding of magnetic, transport, and optical phenomena in crystals, drawing widespread interest across various materials science domains, from metals and semiconductors to topological and magnetic materials. Here, we review OAM dynamics in depth, focusing on key concepts and non-equilibrium systems, and laying the groundwork for the thriving field of orbitronics. We review briefly the conventional understanding of the equilibrium OAM based on the modern theory of orbital magnetisation. Following this, we explore recent theoretical and experimental developments in out-of-equilibrium systems. We focus on the generation of an OAM density via the orbital magneto-electric, or Edelstein effect, the generation of an OAM current via the orbital Hall effect, the orbital torque resulting from them, along with their reciprocal non-equilibrium counterparts – the inverse orbital Edelstein and inverse orbital Hall effects, as well as OAM conservation. We discuss the most salient achievements and the most pressing challenges in this rapidly evolving field, and in closing we highlight the future prospects of orbitronics.