High Orbital Angular Momentum Research Articles

Atmospheric turbulence-distorted OAM mode recognition via multi-scale dilated convolution with multi-level feature fusion

Vortex beams with orbital angular momentum (OAM) significantly enhance system capacity, and high-precision recognition of OAM mode through atmospheric turbulence (AT) channels can markedly improve the information transmission capability of free-space optical communication systems. In this paper, with a cylindrical lens-assisted distinguish between positive and negative OAM, a reliable neural network combining multi-scale dilated convolution (MSDC) unit and multi-level feature fusion (MLFF) module is proposed to detect high order AT-distorted OAM modes. The network fully exploits the features in light-intensity images to achieve a highest recognition accuracy of 99.4% for mode-orders from -20 to +20 in a hybrid ATs dataset (C n 2 = 5×10−16, 5×10−14, 5×10−12 m-2/3), and almost 96% even in strong turbulence. Experimental results on accuracy, efficiency, reliability, and robustness demonstrate that the proposed method excels and provides a trustworthy solution for complex AT-distorted OAM mode recognition.

The synthetic gauge field and exotic vortex phase with spin-orbital-angular-momentum coupling

Ultracold atoms endowed with tunable spin-orbital-angular-momentum coupling (SOAMC) represent a promising avenue for delving into exotic quantum phenomena. Building on recent experimental advancements, we propose the generation of synthetic gauge fields, and by including exotic vortex phases within spinor Bose–Einstein condensates, employing a combination of a running wave and Laguerre–Gaussian laser fields. We investigate the ground-state characteristics of the SOAMC condensate, revealing the emergence of exotic vortex states with controllable orbital angular momenta. It is shown that the interplay of the SOAMC and conventional spin-linear-momentum coupling induced by the running wave beam leads to the formation of a vortex state exhibiting a phase stripe hosting single multiply quantized singularity. The phase of the ground state will undergo the phase transition corresponding to the breaking of rotational symmetry while preserving the mirror symmetry. Importantly, the observed density distribution of the ground-state wavefunction, exhibiting broken rotational symmetry, can be well characterized by the synthetic magnetic field generated through light interaction with the dressed spin state. Our findings pave the way for further exploration into the rotational properties of stable exotic vortices with higher orbital angular momenta against splitting in the presence of synthetic gauge fields in ultracold quantum gases.

Propagation of twisted laser carrying orbital angular momentum in magnetized plasma

The propagation of electromagnetic beams carrying orbital angular momentum l is investigated in a cold collisionless plasma where a static magnetic field is applied in the axial direction. The relativistic and ponderomotive nonlinearities are taken into consideration simultaneously. A stationary nonlinear Schrödinger equation is derived using the Wentzel–Kramers–Brillouin method and the slowly varying envelope approximation. The critical condition for the self-trapped mode is achieved as a function of orbital angular momentum (OAM), magnetic field, and initial laser intensity of the beam. The response of the medium to the two types of polarizations, i.e., left circular polarization (LCP) and right circular polarization (RCP), is compared, and it is observed that the RCP laser shows better focusing than the LCP laser and also requires a smaller beam radius for achieving the self-trapped mode. The effect of applied magnetic field and OAM of the laser is also studied on the beam width evolution. The laser is found to be focused earlier in the cases of a larger applied magnetic field. A Laguerre–Gaussian laser with higher OAM is observed to show efficient self-focusing. This study enables exploration in the fields of particle acceleration, electron bunch generation, x-ray sources, and more.

Effective gyration of polar vortex arrays controlled by high orbital angular momentum of light

Effective gyration of polar vortex arrays controlled by high orbital angular momentum of light

High efficiency holographic impedance metasurface for dual circular polarized OAM waves

AbstractThis paper proposes a high aperture efficiency (AE) small size tensor holographic impedance metasurface (THIMS), which has the ability to create circular polarized (CP) high purity orbital angular momentum (OAM) multi‐beams with flexibly independent control of the individual beam direction, polarization and OAM mode. The tensor unit cell is a cross‐slotted circular patch. We design a THIMS at 14.6 GHz for dual CP OAM beams: Beam‐I (LHCP, l = 1, θ1 = 30°, φ1 = 0°), Beam‐II (RHCP, l = −1, θ2 = 30°, φ2 = 180°). The developed tensor dual CP THIMS has the following advantages: high purity in xoy plane at z = 9.73 λ (λ wavelength, measured purity 88.4% for Beam‐I, and 93.5% for Beam‐II), high AE 25.1%, and small size 5.986 λ × 5.986 λ × 0.0618 λ. The calculated, simulated and measured results agree well. The generated dual CP OAM beams have potential applications for high‐capacity wireless communication, radar high resolution imaging, and rotation velocity measurement.

Superposing and modulating heterogeneous optical vortices of high-order orbital angular momentum

This article reports the preparation of high orbital angular momentum (OAM) using non-uniform beam interference both theoretically and experimentally. This study commences with the reconstruction of Bessel–Gaussian vortex beams utilizing power-exponential-phase vortices. Subsequently, two reconstructed beams are used for interfere, followed by the application of the phase multiplication technique. This methodology enables higher-order operations on the interfered beams, thereby escalating their topological charges and facilitating the attainment of high-orbit angular momentum. The implementation of these methods is especially relevant in the realms of optical manipulation and remote sensing. Lastly, the high OAM optical vortex is subjected to rotation at any controllable angle. This manipulation introduces an additional degree of freedom for particle operations, thereby expanding their application prospects.

Optical Metasurfaces for Tunable Vortex Beams

AbstractThe pursuit of device miniaturization and the generation of complex output responses has driven the development of optically tunable metasurfaces. Among these advancements, metasurface‐based vortex beams (VBs) have emerged as promising optically tunable knob technology due to their infinite output states through various orbital angular momentum (OAM) modes. In this study, the metasurface‐based VBs are successfully fabricated with exceptionally high OAM modes of 32 and 16, carefully examined using the Mach‐Zehnder interferometer. Throughout this study, these devices are referred to as infinite‐OAM meta‐knobs (IOMKs). The optical tunability of IOMKs is demonstrated by illuminating them with incident light possessing diverse degrees of freedom, including different polarizations and wavelengths. Furthermore, the interference nature of the IOMKs is experimentally explored by incorporating them into interference eraser measurements, providing an additional degree of freedom to the optical knob. In the interference eraser experiment, the broadband capability and the high reproducibility of the IOMKs with the OAM modes of 32 and 16 at three distinct wavelengths of 450, 530, and 610 nm is demonstrated. These findings represent a significant step toward understanding the potential applications of IOMKs in quantum optics and their promising role in the generation of complex output states.

Generation and Talbot Effect of Optical Vortex Lattices with High Orbital Angular Momenta

AbstractOptical vortex lattices (OVLs) are gaining increased research attention owing to their unique features related to intensity and phase structure. Interference is a common method for generating an OVL. However, the topological charge (TC) of a single building block in an OVL is fixed and cannot be modulated, thereby limiting its applicability. This study entailed the use of phase multiplication to generate a high‐order OVL to facilitate the arbitrary modulation of its TC. The generated high‐order OVL exhibited the Talbot effect during transmission, and it transformed into a super‐honeycomb lattice at specific fractional Talbot lengths. In addition, an orbital angular momentum developed in the OVL; this has broad application prospects in optical micromanipulation. Further, a method for generating super‐honeycomb lattices is devised. The findings of this study enhances understanding of the Talbot effect and broaden the practical applicability of OVLs.

Design of New Photonic Crystal Fiber for Orbital Angular Momentum Modes Transmission

In order to achieve the flexibility and miniaturization of orbital angular momentum (OAM) fiber coupler, it is necessary to continuously design and optimize the base fiber to cooperate with the efficient transmission of multiplexed beam. It is more advantageous to use the photonic crystal fiber (PCF) instead of ring fiber in the coupler design. We have proposed a new fiber based on circular PCF structure to support high performance OAM modes transmission. The optimal parameters are selected to realize the stable transmission of 4 OAM mode groups with high mode quality. In the wavelength range of 1.2 μm∼2.0 μm, the confinement loss of low order mode is less than 10−8 dB/m, and the mode purity is more than 81.7%. Because of its flexible structure and low loss characteristics, the proposed OAM fiber can be widely used in the design of optical fiber devices in modular division multiplexing (MDM) communication systems.

High orbital angular momentum lasing with tunable degree of chirality in a symmetry-broken microcavity

Chiral lasers with orbital angular momenta (OAM) are building blocks in developing high-dimensional integrated photonic devices. However, it remains demanding to arbitrarily manipulate the precise degree of chirality (DOC) and quantum numbers of OAM in microscale lasers. This study reports a strategy to generate OAM microlasers with tunable DOCs and large quantum numbers through a ring-structured Fabry–Perot microcavity with nanoscale symmetry-broken geometry. By exploiting the uneven potential of photons distributed in a microcavity, the dissymmetry factor of OAM laser can be continuously tuned from −1 to +1 by manipulating optical pump positions. High-order OAM with tunable quantum numbers were also demonstrated, in which the largest quantum number reached up to 352. Finally, multivortex laser generation on-chip in spatial and temporal domains was accomplished. This study reveals the fundamental physics of symmetry-broken cavity and provides a simple yet scalable approach for manipulating the chirality of OAM microlasers, offering insights for high-dimensional information processing and optical communications.

Generation of Terahertz OAM Waves with Six Modes Based on Three-Layer Z-Shaped Reflective Metasurface

In this paper, a broadband and efficient three-layer Z-shaped reflective metasurface for linear polarization conversion is designed and six different modes of orbital angular momentum (OAM) waves are generated in the terahertz band. The designed metasurface consisted of several units, and it is divided into twelve regions. The phase difference is achieved by changing the structural parameters of the units, and then different modes of OAM waves are generated. The terahertz OAM waves with the modes of ±1, ±2, and ±3 are generated by metasurface with high efficiency and wide bandwidth. The results show that the designed metasurface could produce high purity terahertz OAM waves with six different modes, and the reflection amplitude of the metasurface unit is more than 0.9 in the frequency range of 1.0 THz to 1.8 THz. The generated OAM waves with the modes of ±1 and ±2 have a mode purity more than 90%. The designed metasurface has good wavefront control ability, which provides an effective method to generate multimode OAM waves.

Recognition of orbital angular momentum modes based on deep learning and multiaperture speckle

We propose a method for orbital angular momentum (OAM) mode recognition based on deep learning (DL) and multiaperture speckle (MS). This method works robustly in complex environments, such as angular disturbances and random obstacles. It also has a high OAM mode recognition accuracy (RA) at 99.5 %. RA remains high even at various propagation distances. Results show that the combination of the photon OAM and the number of the apertures can be used as a new dimension for structured light information transmission. The multiaperture optical beams can be used to construct a transmission channel with multiplexed information. As an example, an image has been transmitted in an experiment utilizing the multiaperture dimension of light. The bit error rate (BER) for image transmission is as low as 0.065 %. This work provides a new application scheme for free space optical communication.

OAM mode generation in helically twisted hollow-core antiresonant fiber.

We investigate the orbital angular momentum (OAM) mode-generating process of a long-period onefold chiral fiber grating (L-1-CFG) based on a helically twisted hollow-core antiresonant fiber (HC-ARF). Taking the right-handed L-1-CFG for an example, we theoretically and experimentally prove that the first-order OAM+1 mode can be generated by only inputting a Gaussian beam. We fabricated three right-handed L-1-CFG samples based on the helically twisted HC-ARF with twist rates (α) of -0.42, -0.50, and -0.60 rad/mm, where the twisted HC-ARF with α of -0.42 rad/mm can achieve high OAM+1 mode purity of 94%. Subsequently, we present simulated and experimental transmission spectra at the C-band, and sufficient modulation depths were obtained at wavelengths of 1550 nm and 1561.5 nm in the experiment.

Orbital-angular-momentum-based optical clustering via nonlinear optics

Machine learning offers a convenient and intelligent tool for a variety of applications in the fields ranging from fundamental research to financial analysis. With the explosive growth of data streams, i.e., “big data,” optical machine learning with the inherent capacity for massive parallel processing is gradually attracting attention. Despite significant experimental and theoretical progress in this area, limited by the coherent manipulation of multibeams, high dimensional optical vector or matrix operation is still challenging. Here, by using the second harmonic generation of high dimensional orbital angular momentum superposition states, we present a compact and robust optical clustering machine, which is the crucial component in machine learning. In experiment, we conduct supervised clustering for classification of three- and eight-dimensional vectors and unsupervised clustering for text mining of 14-dimensional texts both with high accuracies. The presented optical clustering scheme could offer a pathway for constructing high speed and low energy consumption machine learning architectures.

Reflective Metasurface With Steered OAM Beams for THz Communications

The abundant spectrum resources and low beam divergence of the terahertz (THz) band, can be combined with the orthogonal propagation property of orbital angular momentum (OAM) beams to multi-fold the capacity of wireless communication systems. Here, a reflective metasurface (RMTS) is utilized to enhance the coverage of the high gain THz OAM beams by enabling the non-line-of-sight (NLoS) component by reshaping the planar wavefront of the incident wave into the helical wavefront, so that it is re-directed towards the direction of interest. This can contribute to alleviating the concern of the small aperture size, since improving the channel capacity can be achieved at the low spectrum blocks of the THz band (larger aperture size). For validation, three <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90 \times 90$ </tex-math></inline-formula> mm RMTSs are simulated, fabricated, and tested in the frequency range 90–110 GHz, to re-direct single and dual OAM beams towards the desired location.

Cooperative NOMA Based on OAM Transmission for Beyond 5G Applications

Cooperative non-orthogonal multiple access (NOMA) is heavily studied in the literature as a solution for 5G and beyond 5G applications. Cooperative NOMA transmits a superimposed version of all users’ messages simultaneously with the aid of a relay, after that, each user decodes its own message. Accordingly, NOMA is deemed as a spectral efficient technique. Another emerging technique exploits orbital angular momentum (OAM), where OAM is an attractive character of electromagnetic waves. OAM gathered a great deal of attention in recent years (similar to the case with NOMA) due to its ability to enhance electromagnetic spectrum exploitation, hence increasing the achieved transmission throughput. However, OAM-based transmission suffers from wave divergence, especially at high OAM orders. This OAM limitation reduces the transmission distance. The distance can be extended via cooperative relays (part of cooperative NOMA). Relay helps the source to transmit packets to the destination by providing an additional connection to handle the transmission and provide a shorter distance between source and destination. In this paper, we propose employing OAM transmission in the cooperative NOMA network. Simulation experiments show that OAM transmission helps cooperative NOMA in achieving higher throughput compared to the conventional cooperative NOMA. Concurrently, the cooperation part of cooperative NOMA eases the divergence problem of OAM. In addition, the proposed system outperforms the standalone cooperative OAM-based solution.

High purity orbital angular momentum of light.

We present a novel technique for generating beams of light carrying orbital angular momentum (OAM) that increases mode purity and decreases singularity splitting by orders of magnitude. This technique also works to control and mitigate beam divergence within propagation distances less than the Rayleigh length. Additionally, we analyze a tunable parameter of this technique that can change the ratio of beam purity to power to fit desired specifications. Beam generation via this technique is achievable using only phase-modulating optical elements, which reduces experimental complexity and beam energy loss.

Continuously tuneable acoustic metasurface for high order transmitted acoustic vortices

Existed tuneable acoustic metasurfaces (AMSs) can only transfer high order orbital angular momentum by converting the incident wave into reflected acoustic vortices (AVs). Here, a continuously tuneable AMS is designed and fabricated to produce transmitted AVs with multiple orders. The proposed AMS is composed of multiple layers of reconfigurable sector-shaped resonator-based units. A new design mechanism of the tuneable AMS is proposed to ensure that the discrete precision of the phase shift is not affected by the number of the layer. The theoretical, numerical and experimental results prove that the proposed AMS is able to continuously generate high-order transmitted AVs, which is promising in applications of real-time acoustic rotational manipulations such as acoustic microfluidics, cell manipulation, acoustic tweezers and acoustic communication.

Terahertz vortex beam generator carrying orbital angular momentum in both transmission and reflection spaces.

Vortex beam generators carrying orbital angular momentum (OAM) with both transmission and reflection modes has broad application prospects in full-space high data capacity communication and orbital angular momentum multiplexing systems. In this work, we proposed a vanadium dioxide (VO2) assisted metasurface to independently produce and manipulate focused vortex transmission-reflection modes with different number of beams and focal lengths under right-handed circular polarized (RCP) wave incidence. The proposed metasurface generates the diagonal vortex beams, four vortex beams, and focused vortex beam for transmission mode at 1.26THz and reflection mode at 1.06THz by changing phase state of the VO2. Our work may find many potential applications in future high data capacity information multiplexing communication systems.

Numerical analysis of a photonic crystal fiber with elliptical air hole for supporting 80 orbital angular momentum modes

• We design photonic crystal fiber with elliptical air holes, which has good orbital angular momentum transmission performance. • The influence of elliptic air hole eccentricity on photonic crystal fiber transmission performance is analyzed. • This paper provides some ideas for new photonic crystal fiber design and air hole shape error analysis. In this paper, a new photonic crystal fiber with elliptical air hole (EAH-PCF) is designed, which can support stable transmission of 80 orbital angular momentum (OAM) modes at 1550 nm. The effective refractive index differences between vector modes are all above 0.002. Most of the modes have a confinement loss between 10 −10 dB/m and 10 −8 dB/m. The effective mode area of the vector modes are all greater than 70 μm 2 and the nonlinear coefficients are all less than 1.8 W −1 /km. These properties guarantee high quality OAM. Finally, we discuss the effect of EAH’s eccentricity on the PCF. Simulations show that increasing the EAH’s eccentricity will increase the degree of separation between the vector modes, but causes a slight decrease in the quality of OAM.