Orbital Angular Momentum Properties Research Articles

Propagation behavior of orbital angular momentum in vector anomalous vortex beams under maritime atmospheric turbulence

This study explores the propagation properties of orbital angular momentum (OAM) carried by a vector anomalous vortex beam (VAVB) in maritime atmospheric turbulence, utilizing the Rytov approximation. A comparative analysis is conducted between the VAVB and Laguerre-Gaussian beam, revealing that the VAVB exhibits a higher detection probability under specific circumstances. This suggests that the VAVB is more suitable for scenarios where maximizing detection probability is critical. The detection probability of the signal OAM mode is affected by the characteristics of maritime atmospheric turbulence and propagation distance, but can be significantly improved by manipulating beam parameters such as wavelength, beam order, beam waist, and quantum number, while considering the characteristics of maritime atmospheric turbulence. Hence, the use of VAVB has the potential to facilitate reliable optical communication in challenging maritime environments.

Characterization parameters for antennas generating orbital angular momentum waves

As one of the pivotal candidate technologies of 6G, orbital angular momentum (OAM) carrying radio waves have attracted much attention in wireless communication and sensing technology fields owing to the particular twisted phase fronts. Various kinds of antennas have been proposed to generate this kind of wave; however, the antenna performance has not been well analyzed in terms of the OAM carrying wave’s characteristics. In this paper, some dedicated characterization parameters termed as conjugated receiving pattern, purity related bandwidth, and mode phase linearity based on well-known properties of OAM carrying electromagnetic waves are proposed for the first time. These parameters can be used to characterize the performance of OAM antennas. As an example, the performance of a fabricated helical OAM antenna with a wide bandwidth is characterized by the proposed parameters, which proves the reasonableness and necessity of the proposed characterization parameters.

Experimental generation and orbital angular momentum properties of focused field for vector vortex beams on Hybrid-order Poincaré sphere

Due to the anisotropic spatial polarization state and spiral phase distribution, the orbital angular momentum (OAM) of vector vortex beams (VVBs) has attracted increasingly attention in recent years. In this paper, the Hybrid-order Poincaré sphere VVBs are constructed by orthogonal left-handed (L-H) and right-handed (R-H) circularly polarized vortexes. The vector vortex light fields of different orders at the focal plane are collected and analyzed experimentally. Based on the vector diffraction integral theory, the effects of the topological charge and polarization order for VVBs, as well as the initial phase difference for L-H and R-H components on the OAM properties of focused field for the longitudinal component are investigated numerically. It is found that the OAM density distribution of the longitudinal component shows inner and outer two layers on the whole, and the layers mainly concentrate the corresponding L-H and R-H components respectively. Meanwhile, the signs of the topological charges for L-H and R-H components determine the positive and negative distributions of the inner and outer OAM density respectively. When the initial phase difference of L-H and R-H components ϕ0 changes in the range of 0–2π, the OAM density rotates the angle ϕ0/2 along the clockwise. However, the OAM of the longitudinal component does not change with ϕ0, and increases as the polarization order m increases when the topological charge of VVBs l>2. The results could be helpful to further explore the applications of the OAM for VVBs in the fields of optical detection and communication.

Time-varying orbital angular momentum in tight focusing of ultrafast pulses.

The orbital angular momentum (OAM) of light has important applications in a variety of fields, including optical communication, quantum information, super-resolution microscopic imaging, particle trapping, and others. However, the temporal properties of OAM in ultrafast pulses and in the evolution process of spin-orbit coupling has yet to be revealed. In this work, we theoretically studied the spatiotemporal property of time-varying OAM in the tightly focused field of ultrafast light pulses. The focusing of an incident light pulse composed of two time-delayed femtosecond sub-pulses with the same OAM but orthogonal spin states is investigated, and the ultrafast dynamicsa time delay of OAM variation during the focusing process driven by the spin-orbit coupling is visualized. Temporal properties of three typical examples, including formation, increase, and transformation of topological charge are investigated to reveal the non-uniform evolutions of phase singularities, local topological charges, self-torques, and time-varying OAM per photon. This work could deepen the understanding of spin-orbit coupling in time domain and promote many promising applications such as ultrafast OAM modulation, laser micromachining, high harmonic generation, and manipulation of molecules and nanostructures.

Real-time OAM cross-correlator based on a single-pixel detector HOBBIT system.

The creation and detection of spatial modes of light with transient orbital angular momentum (OAM) properties is of critical importance in a number of applications in sensing and light matter interactions. Most methods are limited in their frequency response as a result of their modulation techniques. In this paper, a new method is introduced for the coherent detection of transient properties of OAM using a single pixel detector system for the creation of an OAM spectrogram. This technique is based on the ideas utilized in acousto-optic based optical correlators with log-polar optical elements for the creation and detection of higher order bessel beams integrated in time (HOBBIT) at MHz data rates. Results are provided for beams with time varying OAM, coherent combinations, and transient scattering by phase objects.

Ring-based coil structure photonic crystal fiber for transmission of Orbital Angular Momentum with large bandwidth: Outline, investigation and analysis

A unique, spectacular design of Photonic Crystal Fiber (PCF) is discussed in this paper to introduce one of the highest numbers of Orbital Angular Momentum (OAM) modes for the very first time with a very large bandwidth of 1,900 nm. Three layers of convoluted coiled structure air cavities formed the cladding region. The optimal design of PCF is used to derive the OAM properties. Finite Element Method (FEM) is used to examine and calculate the fundamental optical characteristics. The result of simulation supports 56 OAM modes with flat dispersion variation. Most of the OAM modes for confinement loss are below 10−8 dB/m where the lowest value is 1.7407×10−11 dB/m at wavelength 1,100 nm for HE11,1 mode. The non-linear coefficient and numerical aperture are lower than 4 W−1km−1 and 0.17, respectively. These splendid optical characteristics ensure the addressed design as a striking competitor for OAM transmission with large bandwidth and many other relevant optical communications. It can be used in long haul communication, encoding and Mode Division Multiplexing (MDM).

Partially coherent vortex beams of arbitrary radial order and a van Cittert–Zernike theorem for vortices

The orbital angular momentum properties of beams having an arbitrary degree of coherence for any radial and azimuthal order are analyzed. A generalized analytic solution is determined and the vortex structure on propagation is found to reconstruct itself, an effect that can be considered as a vortex supplement to the van Cittert--Zernike theorem.

Photonic crystal fiber for robust orbital angular momentum transmission: design and investigation

In this paper, a novel design, photonic crystal fiber (PCF) has been reported to support more orbital angular momentum (OAM) modes for the first time. The cladding region formed by employing the three-layer chain shaped air cavities. The OAM properties and parameters are calculated by optimizing the design of the PCF. The simulation results can support 26 OAM modes with a wider bandwidth (750 nm). The confinement loss of the most OAM modes is below average 10−7 dB/m and the nonlinear coefficient is less than 4 W−1/km. Some OAM modes with comparatively flat dispersion variation (such as 3.8684 ps/km-nm) for HE2,1 are noticed from the design. Moreover, fundamental optical characteristics have been rigorously computed by utilizing the finite element method. Now, it can be anticipated that, these excellent optical characteristics confirm the introduced design as a prominent candidate for the OAM transmission and other relevant areas of optical communications.

Dirac wire: Fermionic waveguides with longitudinal spin

The interplay of photon spin and orbital angular momentum (OAM) in the optical fiber (1D waveguide) has recently risen to the forefront of quantum nanophotonics. Here, we introduce the fermionic dual of the optical fiber, the Dirac wire, which exhibits unique electronic spin and OAM properties arising from confined solutions of the Dirac equation. The Dirac wires analyzed here represent cylindrical generalizations of the Jackiw-Rebbi domain wall and the minimal topological insulator, which are of significant interest in spintronics. We show the unique longitudinal spin arising from electrons confined to propagation in a wire, an effect which is fundamentally prohibited in planar geometries. Our work sheds light on the universal spatial dynamics of electron spin in confined geometries and the duality between electronic and photonic spin.

Local property study for arbitrary polarised OAM beam

The local angular momentum (AM) properties of arbitrary polarised orbital AM (OAM) beams become important when the radio OAM properties are used for remote sensing. In this study, based on the decomposition of ϕ- directional Poynting vector, the local AM mode is decomposed into a local OAM mode, a local spin AM (SAM) mode, and a new component named local coupling AM mode (CAM), which is related to the ϕ- directional coupling Poynting vector and dependent on the polarisation state of the OAM beams. The summation of the local OAM mode and the local SAM mode is found to be equal to the local topological charge which is physically related to the flow of the local azimuthal linear momentum density. The above conclusions are theoretically analysed and simulation verified by the different polarised OAM beams generated by different directional circular antenna arrays.

Experiments of Orbital Angular Momentum Phase Properties for Long-Distance Transmission

In this paper, we propose a new method to effectively measure orbital angular momentum (OAM) properties for long-distance transmission. Properties of OAM wavefront in terms of phase and amplitude are measured by rotating the OAM wave antenna and fixing the plane wave antenna as a reference. To verify OAM phase properties for long-distance transmission, experiments are conducted in Tsingtao, China, with 3.7 km and 7.0 km across the Yellow Sea, which demonstrates that vortex phase properties of OAM keep well after long-distance transmission. Meanwhile, periodical properties of OAM waves' phase fronts are the same in different transmission distances.

Twisted vortex Gaussian Schell-model beams.

We introduce a new class of partially coherent vortex beams in which the angular momentum of the beam is provided from two different sources: the underlying vortex of the random beam and the "twist" given to the ensemble of beams. The statistical and propagation properties of such beams are investigated, and their orbital angular momentum properties are analyzed. The combination of distinct orbital angular momentum sources allows unusual behaviors that were previously unobserved.

Twisted optical communications using orbital angular momentum

Angular momentum, a fundamental physical quantity, can be divided into spin angular momentum (SAM) and orbital angular momentum (OAM) in electromagnetic waves. Helically-phased or twisted light beams carrying OAM that exploit the spatial structure physical dimension of electromagnetic waves have benefited wide applications ranging from optical manipulation to quantum information processing. Using the two distinct properties of OAM, i.e., inherent orthogonality and unbounded states in principle, one can develop OAM modulation and OAM multiplexing techniques for twisted optical communications. OAM multiplexing is an alternative space-division multiplexing approach employing an orthogonal mode basis related to the spatial phase structure. In this paper, we review the recent progress in twisted optical communications using OAM in free space and fiber. The basic concept of momentum, angular momentum, SAM, OAM and OAM-carrying twisted optical communications, key techniques and devices of OAM generation/(de)multiplexing/detection, high-capacity spectrally-efficient free-space OAM links, fiber-based OAM links, and OAM processing functions are presented. Ultra-high spectral efficiency and petabit-scale free-space data links are achieved benefiting from OAM multiplexing. The key techniques and challenges of twisted optical communications are also discussed. Twisted optical communications using OAM are compatible with other existing physical dimensions such as frequency/wavelength, amplitude, phase, polarization and time, opening a possible way to facilitate continuous increase of the aggregate transmission capacity and spectral efficiency through N -dimensional multiplexing.

Wavelength-switchable vortex beams based on a polarization-dependent microknot resonator

We experimentally demonstrated a method of generating continuously wavelength-switchable optical vortex beams (OVBs) in an all-fiber laser. A polarization-dependent microknot resonator (MKR) functions as comb filter and accounts for the narrow linewidth (0.018 nm) of multiwavelength channels. The wavelength interval corresponds to the free spectral range of the MKR. We exploit a fused SMF–FMF (single mode fiber–few mode fiber) mode coupler to obtain broadband mode conversion and successfully achieve multiwavelength switchable OVBs. As far as we know, this is the first report about identical multiwavelength vortex beams with topological charges of ±1. It has been verified that each channel of the vortex beams preserves the same orbital angular momentum (OAM) properties through their clear spiral interferograms. Multiwavelength vortex beams with identical OAM properties are desirable for multiplexing, exchanging, and routing to further improve the capacity of optical fiber transmission.

Light-quarkonium spectra and orbital-angular-momentum decomposition in a Bethe\u2013Salpeter-equation approach

We investigate the light-quarkonium spectrum using a covariant Dyson–Schwinger–Bethe–Salpeter-equation approach to QCD. We discuss splittings among as well as orbital angular momentum properties of various states in detail and analyze common features of mass splittings with regard to properties of the effective interaction. In particular, we predict the mass of bar{s}s exotic 1^{-+} states, and identify orbital angular momentum content in the excitations of the rho meson. Comparing our covariant model results, the rho and its second excitation being predominantly S-wave, the first excitation being predominantly D-wave, to corresponding conflicting lattice-QCD studies, we investigate the pion-mass dependence of the orbital-angular-momentum assignment and find a crossing at a scale of m_pi sim 1.4 GeV. If this crossing turns out to be a feature of the spectrum generated by lattice-QCD studies as well, it may reconcile the different results, since they have been obtained at different values of m_pi .

Position, spin, and orbital angular momentum of a relativistic electron

Motivated by recent interest in relativistic electron vortex states, we revisit the spin and orbital angular momentum properties of Dirac electrons. These are uniquely determined by the choice of the position operator for a relativistic electron. We overview two main approaches discussed in the literature: (i) the projection of operators onto the positive-energy subspace, which removes the zitterbewegung effects and correctly describes spin-orbit interaction effects, and (ii) the use of Newton-Wigner-Foldy-Wouthuysen operators based on the inverse Foldy-Wouthuysen transformation. We argue that the first approach [previously described in application to Dirac vortex beams in K.Y. Bliokh et al., Phys. Rev. Lett. 107, 174802 (2011)] has a more natural physical interpretation, including spin-orbit interactions and a nonsingular zero-mass limit, than the second one [S.M. Barnett, Phys. Rev. Lett. 118, 114802 (2017)].

Orbital angular momentum of the vortex beams through a tilted lens

Properties of orbital angular momentum (OAM) of a linearly polarized vortex beam traversing a tilted lens is investigated in detail, where the influences stemming from the tilted angle of the lens and the separation between the beam and the lens are mainly focused on. It was shown that such an optical system can invert the sign of the topological charge of the incident vortex beam. The possibility of reversing the sign of OAM was discussed and it was found that it only depends on the elements of the ray transfer matrix of this optical system. Finally, a simple experiment was carried out to verify the theoretical results.

Orbital angular momentum modes of high-gain parametric down-conversion

Light beams with orbital angular momentum (OAM) are convenient carriers of quantum information. They can also be used for imparting rotational motion to particles and providing high resolution in imaging. Due to the conservation of OAM in parametric down-conversion (PDC), signal and idler photons generated at low gain have perfectly anti-correlated OAM values. It is interesting to study the OAM properties of high-gain PDC, where the same OAM modes can be populated with large, but correlated, numbers of photons. Here we investigate the OAM spectrum of high-gain PDC and show that the OAM mode content can be controlled by varying the pump power and the configuration of the source. In our experiment, we use a source consisting of two nonlinear crystals separated by an air gap. We discuss the OAM properties of PDC radiation emitted by this source and suggest possible modifications.

Delay in Space: Orbital Angular Momentum Beams Transmitting and Receiving in Radio Frequency

ABSTRACTUsing an orbital angular momentum-based communication system to increase the channel capacity has recently attracted more and more attention. This article proposes a novel antenna array to transmit and receive orbital angular momentum beams at a radio frequency (3 GHz) by using delay in space. Different from the well-known uniform circular array which needs a phase-shifting network, every element in the proposed helicoidal array has the same phase. As long there are enough array elements and a power divider, arbitrary orbital angular momentum mode can be generated easily by only changing the positions of the array elements without any phase-shifting. In this experiment, l = 1 and l = 2 helicoidal arrays with eight half-wavelength dipoles are fabricated. The simulated and measured results, such as S parameters, near-field orbital angular momentum properties, far-field orbital angular momentum properties, the channel isolation between different orbital angular momentum channel, and the packet-loss-rate of an orbital angular momentum-based communication system using the helicoidal arrays, are presented, which shows that a helicoidal array can indeed generate arbitrary orbital angular momentum mode. Moreover, different kinds of antenna arrays can be constructed using delay in space and delay in phase together. The authors propose a crossed array to generate orbital angular momentum beams in four directions. The simulation and experimental results of the crossed array are demonstrated. Delay in space is another degree of freedom to generate orbital angular momentum beams in radio frequency.

Intense harmonics generation with customized photon frequency and optical vortex

An optical vortex with orbital angular momentum (OAM) enriches the light and matter interaction process, and helps reveal unexpected information in relativistic nonlinear optics. A scheme is proposed for the first time to explore the origin of photons in the generated harmonics, and produce relativistic intense harmonics with expected frequency and an optical vortex. When two counter-propagating Laguerre–Gaussian laser pulses impinge on a solid thin foil and interact with each other, the contribution of each input pulse in producing harmonics can be distinguished with the help of angular momentum conservation of photons, which is almost impossible for harmonic generation without an optical vortex. The generation of tunable, intense vortex harmonics with different photon topological charge is predicted based on the theoretical analysis and three-dimensional particle-in-cell simulations. Inheriting the properties of OAM and harmonics, the obtained intense vortex beam can be applied in a wide range of fields, including atom or molecule control and manipulation.