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In this work, we investigate the spatially dependent optical properties of quantum dot (QD) molecules interacting with optical vortex beams. By analyzing the absorption and dispersion profiles of a weak probe field, we uncover the influence of tunneling and quantum interference mechanisms on the system's response. The optical vortex beams, characterized by their orbital angular momentum (OAM), introduce azimuthal dependence in the susceptibility of the QD system. When tunneling alone is present, petal-like patterns emerge in the spatial profiles, with their symmetry determined by the OAM of the signal field. These patterns undergo rotation in the azimuthal plane as the relative phase of the applied fields varies. Similarly, when quantum interference dominates, distinct symmetry-driven features arise, demonstrating phase-sensitive spatial modulation. Notably, when both tunneling and quantum interference are present, the profiles exhibit reduced absorption and gain due to the combined effects of state delocalization and modified decay pathways. Our findings highlight the complex interplay between tunneling and quantum interference, offering pathways for controlling light-matter interactions in QD systems. These results pave the way for innovative applications in structured light technologies, optical switching, and quantum information processing. [ABSTRACT FROM AUTHOR]

Vortex dichroism in chiral metamaterials is of great significance to the study of photoelectric detection, optical communication, and the interaction between light and matter. Here we propose a compact chiral metamaterials structure composed of two elliptical SiO2 rods covered with a Au film on a substrate to achieve a significant vortex-dichroism effect. Such a structure has different responses to a Laguerre-Gaussian beam carrying opposite-orbital angular momentum, resulting in giant vortex dichroism. The influences of various structural parameters are analyzed, and the optimal parameters are obtained to realize a remarkable vortex dichroism of about 58.5%. The simplicity and giant VD effect of the proposed metamaterials make it a promising candidate for advancing chiral optical applications such as optical communication and sensing. [ABSTRACT FROM AUTHOR]

Given the burgeoning necessity for high-speed, efficient, and secure wireless communication in 6G, visible light communication (VLC) has emerged as a fervent subject of discourse within academic and industrial circles alike. Among these considerations, it is imperative to construct scalable multi-user VLC systems, meticulously addressing pivotal issues such as power dissipation, alignment errors, and the safeguarding of user privacy. However, traditional methods like multiplexing holography (MPH) and multiple focal (MF) phase plates have shown limitations in meeting these diverse requirements. Here, we propose a novel spatial multiplexing holography (SMH) theory, a comprehensive solution that overcomes existing hurdles by enabling precise power allocation, self-designed power coverage, and secure communication through orbital angular momentum (OAM). The transformative potential of SMH is demonstrated through simulations and experimental studies, showcasing its effectiveness in power distribution within systems of VR glasses users, computer users, and smartphone users; enhancing power coverage with an 11.6 dB improvement at coverage edges; and securing data transmission, evidenced by error-free 1080P video playback under correct OAM keys. Our findings illustrate the superior performance of SMH in facilitating seamless multi-user communication, thereby establishing a new benchmark for future VLC systems in the 6G landscape. [ABSTRACT FROM AUTHOR]

Spatiotemporal optical vortices with arbitrary tilt angles can be generated by adjusting spatial chirp and beam size at a phase modulation plane in a pulse shaper setup. A grating pair setup is proposed to generate variable spatial chirp independent of the beam profile. The initial dispersion of the pulse allows for the independent control of the vortex orientation. By adjusting the beam size, spatial chirp, and initial dispersion, arbitrary vortex orientation across all the possible angles can be achieved. The ability to achieve arbitrary vortex orientations at long propagation distances could offer significant advantages for long-distance communication applications. [ABSTRACT FROM AUTHOR]

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]

Orbital angular momentum (OAM) beam's spatial information captured using a camera, employs millions of single-pixel detectors arranged in a two-dimensional matrix. Poses challenges in OAM detection due to significant storage requirements, reduced speed due to low frame rate, and increased post-processing time. To address this bottleneck, a novel OAM detection technique utilizing only a diffuser and a single-pixel fast photodiode (FPD) is reported. The sixteen OAM beams, l = [ − 8 + 8 ] interact with the rotating diffuser resulting in a temporally varying speckle field. The 1D temporal speckle information (TSI) has been segregated from the temporally varying 2D speckle pattern images for each beam. The segregated 1D TSI has been classified by employing a machine learning model and achieved a classification accuracy of 97.1% and 97.3% on simulated and experimental data respectively. To further validate the proposed single-pixel OAM detection method, the 1D TSI is captured directly using a FPD. The experimentally captured 1D TSI captured via photodiode has been classified by a lightweight custom-designed 1D convolutional neural network and achieved an increased classification accuracy of 96%. This approach redefines OAM detection, operating in the temporal domain with a single-pixel FPD, thereby significantly reducing storage and computational costs while promising high-speed OAM detection. [ABSTRACT FROM AUTHOR]

Optical vortex induced forward transfer (OV-LIFT) allows the crystallization of magnetic nanoparticles enabling the fabrication of a 2-dimensional array of monocrystalline structures with a high spatial resolution. We herein investigate the optimum experimental conditions, such as the viscosity range of the donor and the energy range of the optical vortex pulse required for the crystallization of magnetic nanoparticles through a cavitation processes, including the flight dynamics of donor. [ABSTRACT FROM AUTHOR]

Optical vortex beams carrying orbit angular momentum have attracted significant attention recently. Perfect vortex beams, characterized by their topological charge-independent intensity profile, have important applications in enhancing communication capacity and optimizing particle manipulation. In this paper, metal-insulator-metal copper-coin type reflective metasurfaces are proposed to generate perfect composite vortex beams in X-band. We introduce the qualified equivalent circuit model based on the theory of transmission line to design the meta-atom of the structure. The experiments are performed to measure the far-field and near-field perfect composite vortex beams and evaluate their orbital angular momentum purity at different frequencies. The experimental results agree well with the theoretical predictions. This work provides new ideas and methods for generating high-quality metasurface-based perfect composite vortex beams in the microwave region, paving an ideal path for microwave communication systems, optical manipulation and radar detection. [ABSTRACT FROM AUTHOR]

The vortex beam carrying Orbital Angular Momentum (OAM) has infinite orthogonal characteristic states, which theoretically can infinitely increase the communication transmission capacity, thus attracting much attention in the field of optical communication. Due to the large amount of data required for training each OAM mode, the increase in channel capacity leads to an exponential growth in the required data volume. At the same time, the phase wavefront distortion caused by atmospheric turbulence (AT) further increases the difficulty of OAM pattern recognition. This article introduces transfer learning into the field of OAM modal detection and establishes an OAM modal classifier for detecting the topological charge of distorted vortex beams. The influence of different data volumes, turbulence intensities, and propagation distances on the accuracy of OAM modal detection during the transmission of Laguerre Gaussian beams in atmospheric turbulent channels is studied, and the generalization ability of the model is analyzed. The results show that compared with traditional convolutional neural networks, the modal classifier proposed in this paper reduces the dataset size to 1/10 of the original and successfully improves the OAM detection accuracy by 15.84%. It also exhibits good generalization under unknown atmospheric turbulence strengths, providing a new approach for identifying OAM modes. [ABSTRACT FROM AUTHOR]

Perfect vector vortex beams (PVVBs) possess various degrees of freedom (DoFs) for optical information applications, benefiting from increasing information capacity, processing speed, etc. During the last two decades, various methods have been proposed for generating and controlling PVVBs, but most of these methods can only manipulate two or three DoFs, greatly hindering further exploration and application of PVVBs. To overcome this problem, we propose an attenuation-controlled holographic technique based on metasurfaces, which can realize the arbitrary and independent control of 6-DoFs, greatly improving the manipulation dimension of PVVBs. The PVVBs with 6 on-demand DoFs can appear in the array forms of either concentric or matrix rings without cross-talks or number limitations, which notably enlarges the number of information channels that can be simultaneously employed. Furthermore, we introduce a multi-dimensional dynamic addressing strategy for optical encryption with the advantages of both large capacity and high security due to its theoretically infinite code space. Our findings can not only deepen the study of optical field manipulation at the nanoscale, but also expand the application of structural light, promoting their utilization across the fields of nanophotonics, integrated optics, and optical information science at the high-dimensional level. [ABSTRACT FROM AUTHOR]

In this article, a model of the astigmatic structured beam obtained by the ABCD matrix method is shown to be simpler and more visual compared to the approach of integral transforms [Volyar AV, Abramochkin EG, Bretsko MV, Khalilov SI, Akimova YE. Control of giant orbital angular momentum bursts of structured Laguerre-Gaussian beams in a medium with general astigmatism. Computer Optics 2024; 48(1): 35-46. DOI: 10.18287/2412-6179-CO-1395]. We study in detail physical mechanisms of shaping super-high orbital angular momentum (OAM) after a cylindrical lens during general astigmatic transformations. We also theoretically substantiate and experimentally confirm a new technique for measuring a total OAM in the structured beam based on a single measurement of the crossed intensity moment as a result of computer processing of the intensity pattern. It is shown that such simplified measurements are based on the degeneracy of the off-diagonal elements W and M of the submatrices, which reduces the number of additional degrees of freedom of the structured beam from ten to seven.

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.

Multiplexing multiple yet distinct functionalities in one single device is highly desired for modern integration optics, but conventional devices are usually of bulky sizes and/or low efficiencies. While recently proposed metasurfaces can be ultra-thin and highly efficient, functionalities multiplexed by metadevices so far are typically restricted to two, dictated by the number of independent polarization states of the incident light. Here, we propose a generic approach to design metadevices exhibiting wave-control functionalities far exceeding two, based on coherent wave interferences continuously tuned by varying the incident polarization. After designing a series of building-block metaatoms with optical properties experimentally characterized, we construct two metadevices based on the proposed strategy and experimentally demonstrate their polarization-tuned multifunctionalities at the wavelength of 1550 nm. Specifically, upon continuously modulating the incident polarization along different paths on the Poincare’s sphere, we show that the first device can generate two spatially non-overlapping vortex beams with strengths continuously tuned, while the second device can generate a vectorial vortex beam carrying continuously-tuned polarization distribution and/or orbital angular momentum. Our proposed strategy significantly expands the wave-control functionalities equipped with a single optical device, which may stimulate numerous applications in integration optics.

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.

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.

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.

In 1992, Allen et al. (Allen L, Beijersbergen MW, Spreeuw RJC, Woerdman JP. 1992 Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes. Phys. Rev. A45, 8185–8189. (doi:10.1103/physreva.45.8185)) published their seminal paper on the orbital angular momentum of light, drawing together seemingly unrelated themes and ideas in optics. This breakthrough initiated a new area of optical science concerning the physics and applications of structured light beams. This orbital angular momentum is an important concept for both classical and quantum science, especially where the framing in terms of angular momentum demystifies some of the quantum properties of light. Loudon's own work (Loudon R. 2003 Theory of the forces exerted by Laguerre-Gaussian light beams on dielectrics. Phys. Rev. A68, 013806. (doi:10.1103/PhysRevA.68.013806)) in this area focused on the interactions between light and matter where the orbital angular momentum extended his studies from linear impulses to rotational torques. This article is part of the theme issue 'The quantum theory of light'. [ABSTRACT FROM AUTHOR]

After years of development, holography has become an essential tool of modern optics for many applications. Among them, holographic encryption and dynamic display are the two most typical applications. So far, however, only 2D targets or 2D images of 3D targets can be encrypted with holographic technology. The 3D multiplexing holographic technology of 3D multi‐targets has not yet been realized and holographic encryption of 3D multi‐targets is still a blank. Here, the conception of 3D orbital angular momentum (OAM) multiplexing holography is proposed, and holographic encryption of 3D multi‐targets is realized for the first time. This breaks the restriction that only 2D images can be encrypted in traditional holographic encryption. Furthermore, the results also show that the 3D OAM holography can be used in the dynamic display for 3D multi‐targets. In the experiment, the metasurface is used for taking its high‐resolution advantage in light field manipulation, and verify the feasibility of 3D OAM multiplexing holographic technology, holographic encryption of 3D multi‐targets, and holographic dynamic display of 3D targets. The work creates a precedent for the 3D multiplexing holography, encryption, and dynamic display technology of 3D multi‐targets, which brings real 3D life closer to humankind. [ABSTRACT FROM AUTHOR]

Light beams possess two intrinsic quantized degrees of freedom, related to spin angular momentum (SAM) and orbital angular momentum (OAM), whose manipulation enables extensive control over the topological properties of electromagnetic fields. In this context, structured fields constructed from a non‐separable combination of SAM and OAM have recently gained sustained interest. Such states are eigenstates of the so‐called generalized angular momentum (GAM), a mixed angular momentum operator encompassing both SAM and OAM components, which can result in astonishing fractional eigenvalues. The demonstration of GAM conservation under harmonic generation has suggested a potential relevance of this new form of angular momentum as a meaningful quantum number. In the present work, the scope of evaluation is expanded by investigating its conservation law with second‐harmonic generation in an underdense isotropic inhomogeneous plasma that relies on dipole‐forbidden interaction implying spin‐orbit coupling. This study reveals that the symmetry and topological properties of the field are disrupted during the nonlinear process, the GAM charge being only conserved on average. This symmetry breaking can be exploited to provide an easily detectable signature of the driving field topology or to create a robust topological attractor. [ABSTRACT FROM AUTHOR]

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]

A new category of optical orbital angular momentum (OAM) associated with intensity singularity independent of phase singularity is predicted, and a kind of structured vortex beams (VBs) with arbitrary transverse shapes is demonstrated. A universal inverse‐designed caustic scheme is developed for generating such structured VBs which exhibit crucial intensity gradient and phase gradient. Additionally, they exhibit nonuniformly distributed phase gradients, capable of driving particles accelerately along a desired trajectory. Particle trapping experiments validate that such structured VBs without phase singularity drive the trapped particles to move along predefined trajectories. The idea not only provides an approach for generating and manipulating OAM from intensity singularity, enabling to spur further independent insights into the generation of OAM, but also paves the way for optically driving and accelerating particles along a desired trajectory. [ABSTRACT FROM AUTHOR]