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Higher-order orbital angular momentum (OAM) mode guiding in a waveguide which is suitable for on-chip integration has been investigated. Based on the relation between the Laguerre-Gaussian mode and the Hermite-Gaussian mode, it has been shown that two degenerate guided modes of π/2l-rotation symmetry can support the l-th order OAM mode. In order to mimic the rotational symmetry, we have proposed the waveguide structure of a cross-shaped core and designed a waveguide that can support OAM modes of ±1 and ±2 topological charges simultaneously at a wavelength of 1550 nm. Purity of the OAM modes guided in the designed waveguide has been assessed by numerically calculating their topological charges from the field distribution, which were close to the theoretical values. We also investigated the guiding of OAM modes of ±3 and ±4 topological charges in our proposed waveguide structure, which revealed the possibility of the separate guiding of those OAM modes with relatively lower purity.

The orbital angular momentum (OAM) of beams provides a new dimension, and have already found lots of applications in various domains. Among such applications, the precisely and quantitatively diagnostic of intensity distributions among different OAM modes, namely the OAM spectrum of a beam, is of great significance. In this paper we propose and experimentally validate a simple interferential method to achieve this goal. By analyzing the interference pattern formed by the beam and a reference field, the OAM spectrum can be obtained instantaneously. Furthermore, the proposed method is also available for more complex light fields, for instance, the multi-ring optical vortices. In the proof-of-concept experiment, the OAM spectra of both single-mode and N-fold multiplexed OAM modes with various intensity distributions are well detected. Our work offers a new way to precisely measure the OAM spectra of beams and will advance the development of many applications ranging from classical to quantum physics as the OAM based large-capacity data transmissions, rotation detection, quantum manipulation and so on.

The paper presents a comprehensive description of a new setup implemented and commissioned at the SEXTANTS beamline of Synchrotron SOLEIL for absorption and scattering experiments with X‐ray beams carrying an orbital angular momentum, also known as twisted X‐ray beams. Two alternative methods have been implemented, based on the use of either spiral zone plates or fork grating devices, and we show how they can be used for both defining and assessing the orbital angular momentum of an X‐ray beam. We also demonstrate that cascading multiple devices enables integer operations on the orbital angular momentum of the resulting X‐ray beam. Finally, we report the results of the first resonant scattering pilot experiments in transmission and reflection mode, intended to assess the feasibility of future users' measurements. The availability of twisted soft X‐rays complements the range of experimental techniques in elastic, resonant and coherent scattering available at the SEXTANTS beamline. Characterization and testing of a new setup for absorption and scattering experiments with soft X‐rays carrying an orbital angular momentum at the SEXTANTS beamline of Synchrotron SOLEIL are presented.

The existence and dynamics of stable quantized vortices is an important subject of quantum many-body physics. Spin–orbital-angular-momentum coupling (SOAMC), a special type of spin–orbit coupling, has been experimentally achieved to create vortices in atomic Bose–Einstein condensates (BEC). Here, we generalize the concept of SOAMC to a two-component polariton BEC and analyze the emergence and configuration of vortices under a finite-size circular pumping beam. We find that the regular configuration of vortex lattices induced by a finite-size circular pump is significantly distorted by the spatially dependent Raman coupling of SOAMC, even in the presence of a repulsive polariton interaction which can assist the forming of stable vortex configuration. Meanwhile, a pair of vortices induced by SOAMC located at the center of polariton cloud remains stable. When the Raman coupling is sufficiently strong and interaction is weak, the vortices spiraling in from the edge of polariton cloud will disrupt the polariton BEC.

Structured light with inhomogeneous phase, amplitude, and polarization spatial distributions that represent an infinite-dimensional space of eigenstates for light as the ideal carrier can provide a structured combination of photonic spin and orbital angular momentum (OAM). Photonic spin angular momentum (SAM) interactions with matter have long been studied, whereas the photonic OAM has only recently been discovered, receiving attention in the past three decades. Although controlling polarization (i.e., SAM) alone can provide useful information about the media with which the light interacts, light fields carrying both OAM and SAM may provide additional information, permitting new sensing mechanisms and light–matter interactions. We summarize recent developments in controlling photonic angular momentum (AM) using complex structured optical fields. Arbitrarily oriented photonic SAM and OAM states may be generated through careful engineering of the spatial and temporal structures of optical fields. Moreover, we discuss potential applications of specifically engineered photonic AM states in optical tweezers, directional coupling, and optical information transmission and processing.

Diverse spatial mode bases can be exploited in mode-division multiplexing (MDM) to sustain the capacity growth in fiber-optic communications, such as linearly polarized (LP) modes, vector modes, LP orbital angular momentum (LP-OAM) modes, and circularly polarized OAM (CP-OAM) modes. Nevertheless, which kind of mode bases is more appropriate to be utilized in fiber still remains unclear. Here, we aim to find the superior mode basis in MDM fiber-optic communications via a system-level comparison in air-core fiber (ACF). We first investigate the walk-off effect of four spatial mode bases over 1-km ACF, where LP and LP-OAM modes show intrinsic mode walk-off, while it is negligible for vector and CP-OAM modes. We then study the mode coupling effect of degenerate vector and CP-OAM modes over 1-km ACF under fiber perturbations, where degenerate even and odd vector modes suffer severe mode cross talk, while negligible for high-order degenerate CP-OAM modes based on the laws of angular momentum conservation. Moreover, we comprehensively evaluate the system-level performance for data-carrying single-channel and two-channel MDM transmission with different spatial mode bases under various kinds of fiber perturbations (bending, twisting, pressing, winding, and out-of-plane moving). The obtained results indicate that the CP-OAM mode basis shows superiority compared to other mode bases in MDM fiber-optic communications without using multiple-input multiple-output digital signal processing. Our findings may pave the way for robust short-reach MDM optical interconnects for data centers and high-performance computing.

The discovery of orbital angular momentum (OAM) for the last three decades has made it very versatile for an extensive range of applications. It is an imperative tool for optical research community. So, in this study, we investigated the interaction of vortex electromagnetic (VEM) wave with a perfect electromagnetic conductor (PEMC) sphere. The PEMC is regarded as an extension of the perfect electric and the perfect magnetic conductors. The incident VEM wave fields are expanded by taking into account features of OAM and using spherical vector wave functions (SVWFs). The incident expansion coefficients for VEM wave are derived by means of the definite integrals. Various factors such as normalized differential scattering cross section (DSCS), OAM density, total time-averaged intensity and total field intensity in the context of the electric field amplitudes for scattered fields are computed and investigated. It is expected that findings of the study would be beneficial regarding interaction between the VEM waves and metamaterials in terms of optical diagnostics, optical tweezers and manipulation of spherical particles/surfaces. Findings from this study have applications in electromagnetic scattering and propagation, OAM imaging, particle characterization, measuring optical radiation force, radiative transfer processes, scattering asymmetry factor, remote sensing, radar technology, telecommunications systems and other domains. OAM density (linear + circular), total time-averaged intensity, total scattered electric field intensity and normalized DSCS have also been analyzed numerically. The influence of sphere size, beam waist radius and electromagnetic admittance is examined and discussed.

Orbital angular momentum (OAM) from lasers holds promise for compact, at-source solutions for applications ranging from imaging to communications. However, conjugate symmetry between circular spin and opposite helicity OAM states (±ℓ) from conventional spin–orbit approaches has meant that complete control of light’s angular momentum from lasers has remained elusive. Here, we report a metasurface-enhanced laser that overcomes this limitation. We demonstrate new high-purity OAM states with quantum numbers reaching ℓ = 100 and non-symmetric vector vortex beams that lase simultaneously on independent OAM states as much as Δℓ = 90 apart, an extreme violation of previous symmetric spin–orbit lasing devices. Our laser conveniently outputs in the visible, producing new OAM states of light as well as all previously reported OAM modes from lasers, offering a compact and power-scalable source that harnesses intracavity structured matter for the creation of arbitrary chiral states of structured light.A metasurface laser generates orbital angular momentum states with quantum numbers reaching ℓ = 100. Simultaneous output vortex beams, with Δℓ as great as 90, are demonstrated in the visible regime.

We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next. This article is part of the themed issue ‘Optical orbital angular momentum’.

Spin angular momentum of light is vital to investigate enantiomers characterized by circular dichroism (CD), widely adopted in biology, chemistry, and material science. However, to discriminate chiral materials with multiscale features, CD spectroscopy normally requires wavelength-swept laser sources aswell aswavelength-specific optical accessories. Here, we experimentally demonstrate an orbital-angular-momentum-assisted approach to yield chiroptical signals with monochromatic light. The gigantic vortical differential scattering (VDS) of ∼120% is achieved on intrinsically chiral microstructures fabricated by femtosecond laser. The VDS measurements can robustly generate chiroptical properties on microstructures with varying geometric features (e.g., diameters and helical pitches) and detect chiral molecules with high sensitivity. This VDS scheme lays a paradigm-shift pavement toward efficiently chiroptical discrimination of multiscale chiral structures with photonic orbital angular momentum. It simplifies and complements the conventional CD spectroscopy, opening possibilities for measuring weak optical chirality, especially on mesoscale chiral architectures and macromolecules.