Orbital Angular Momentum Generation Research Articles

Orbital angular momentum modes in dielectrically chiral-core fibers

In this paper, we investigate a dielectrically chiral-core fiber for the generation of orbital angular momentum (OAM) modes. We observe that the presence of chirality induces a modal index split between the same order OAM modes with opposite topological charges and arbitrary phase front rotation directions, which are originally degenerate in achiral fibers. This split indicates the existence of circular birefringence (CB) associated with a dielectric chirality. The modal cutoff splitting results in a single polarization property without the possibility of coupling between the same order modes that correspond to a single +l or −l OAM mode guiding. However, neither of the two fundamental modes guided by the chiral fiber exhibits a cutoff, despite having different modal indices due to chirality. Upon fraction of modal power cutoff, the high-order modes in the core region display different cutoff fractions of modal power between the same order modes, while the fundamental mode has no cutoff fraction of modal power. Due to CB and different fractions of modal power in the core for different handed OAM modes, dielectrically chiral fibers have potential applications in chiral sensing, circular polarization-dependent OAM mode filters, and new kinds of OAM mode generators.

Single-frequency orbital angular momentum switchable modes from a microchip laser.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO4 microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO4 microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

Generation of multiple orbital angular momentum and on-demand single photons by combining quantum dot to metalens

Generation of multiple orbital angular momentum and on-demand single photons by combining quantum dot to metalens

Метаповерхности Патчаратнама-Берри с генерацией углового орбитального момента и комбинированным фазовым кодированием для широкополосного широкоугольного снижения ЭПР

The phase mechanism of a broadband wide-angle radar cross-section (RCS) reduction is examined, based on the use of non-absorbing Patcharatnam-Berry (PB) metasurfaces (MSs) with the generation of orbital angular momentum (OAM) and a combination of different phase profiles. MS unit cells contain a thin shielded single-layer substrate and meta-particles in the form of perforated rectangular patches with a coded rotation angle. The purpose of the work is to compare the scattering characteristics and scattered field cancelation efficiency for structural elements (modules) of a MS, consisting of the same number of meta-particles, but having different PB-phase profiles. A profile with an azimuthal gradient, which forms broadband scattering of vortex waves with OAM, profiles with radial and linear gradients and anomalous scattering, parabolic profiles with wide-angle scattering, and various combined phase profiles are analyzed. The purpose of the work is comparing the scattering characteristics. The MS modules scattering characteristics are studied using the HFSS (finite element method) for co-polarization and cross-polarization in the case of irradiation with a normally incident plane circular polarized wave. The simulation showed that the scattering diagrams of the co-polarized MS field in these cases have a funnel-shaped vortex character with an intense OAM minus the first order (the order of the OAM remains the same as for an MS with an azimuthal phase gradient). OAM generation significantly suppresses backscattering by co-polarization. The far-field phase in the vortex region depends not only on the azimuthal, but also on the meridional observation angles. The combination of OAM and parabolic profile increases the diffusion of broadband scattering, realizes a wider-angle scattering of the resulting field with a vortex opening angle of about 100° (at an average frequency of 14 GHz), which is important for RCS reduction.

Controlled generation of OAM-switchable vortex beams at 639 nm from a Pr3+: YLF laser

In this paper, we reported and demonstrated a blue LD-pumped Pr3+: YLF laser for the controlled generation of orbital angular momentum (OAM) switchable vortex beams at 639 nm. To begin with, the quantitative tilt imbalance of the resonator was introduced to select the higher-order Hermite-Gaussian (HG) modes by utilizing the eigenvector method and introducing the concept of mode discriminant factor. Moreover, the mode converter, composed of two cylindrical mirrors, was applied to convert the Hermite- Gaussian (HG) modes into the Laguerre-Gaussian (LG) modes with the OAM. Then, the experiment setup was built to validate the correctness and effectiveness of the quantitative tilt imbalance. The results showed that the vortex beams with OAM of 0 to ±14 at 639 nm can be obtained by adjusting the tilted angle of the output mirror, which agreed well with the simulation results, and the slope efficiencies of the vortex beams with OAM = 1, 2, and 3 are 11.64%, 8.01%, and 6.05%, respectively. The method provided a viable solution for the generation of visible vortex beams with switchable OAM from the Pr3+: YLF laser.

Generation of OAM beams with quasi omnidirectional pattern using simple slotted waveguide array

Theory and design aspects of the Slotted Waveguide Antenna (SWA) array for the simultaneous generation of Orbital Angular Momentum (OAM) modes are proposed in this paper. The proposed method is a novel approach to OAM generation that uses a simple feeding scheme and has better performance, especially in terms of mode purity. Due to its all-metallic structure, the high-power OAM beams with first-order modes (+1&-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ +1 \\, \\& \\,-1$$\\end{document}) can be generated simultaneously along the propagation axis but in opposite directions, which improves the coverage and makes the proposed SWA be used in applications like radar target detection by mounting it on a mechanically rotating platform. The proposed theory is verified by the electromagnetic (EM) simulations, followed by the experimental verification done on the laboratory prototype. The near-field characteristics of the proposed antenna confirm the generation of first-order OAM beams with high mode purity. The far-field characteristics show the high gain and quasi-omnidirectional radiation pattern. Transmission of high-power OAM beams with good far-field characteristics makes the proposed antenna mitigate the issues of long-range OAM communication to a certain extent. However, the proposed antenna can be served well in strategic applications where the mostly high-power microwave is involved.

Controlled Generation of High‐Purity Scalar Orbital Angular Momentum States from a High‐Power Single‐Crystal Fiber Laser

AbstractThe orbital angular momentum (OAM) of light, which is associated with the rotation of the phase structure, gives rise to numerous novel physical phenomena inlight–matter interactions. However, the direct generation of scalar OAM lasers with power‐handling capability and controllable states at the source remains challenging owing to mode degeneracy, handedness selection, and nonlinear thermal effects, which can even lead to topological charge splitting. This paper proposes a novel approach that allows spatial mode‐conversion‐controlled laser oscillation in a high‐gain OAM laser cavity with an integrated spiral‐face output coupler (SFOC). By adapting position‐dependent resonant modes, scalar optical vortices with a record power level (>60 W), high purity (>90%), and controllable OAM states (ħ or −8ħ) are demonstrated. Further, the dynamic process of OAM generation and evolution in the cavity is revealed. The concept presented herein opens a new route for the generation of OAM laser sources toward high power levels and holds promise for advancing classical and quantum optics, particularly in the area of light–matter interactions.

Soft Mesocrystal Enabled Multi‐Degree Light Modulation

AbstractMesocrystals introduce high‐level orders, such as chirality, topology, and hierarchy to the crystallography, and thus bring collective and emergent properties beyond traditional crystals. Orthogonally modulating the multiple degrees of light is highly pursued to fully explore the intrinsic multidimensional and large‐scale parallel processing capability of photon informatics. Unfortunately, it is unachievable with traditional light–matter interaction systems. Here, the multi‐degree light modulation is realized based on the hierarchical architecture of a soft mesocrystal. High‐quality monodomains of both blue phase I and blue phase II are formed via regulating the assembly of liquid crystals by photoalignment anchoring and electricity. The mapping relationship between optical freedoms (the spin, wavelength, and geometric phase of light) and hierarchical structures (the chirality of helix, lattice constant, and the azimuthal orientation of cubic lattices) is established. Omnidirectional spatial phase modulation with spin and full color selectivity is demonstrated. Based on the multi‐degree light modulation, 3D and wavelength‐selective orbital angular momentum generation as well as multichannel color holographic display are presented. This work extends the fundamental understanding of blue phase mesocrystals and provides a promising strategy for large‐scale parallel and multi‐degree light modulation that may be utilized in vital fields, such as supercomputing, optical communications, and virtual/augmented realities.

Multimode Orbital Angular Momentum Generation Based on Spoof Surface Plasmon Polaritons With Multiple Mode Regulation Mechanisms

Multimode Orbital Angular Momentum Generation Based on Spoof Surface Plasmon Polaritons With Multiple Mode Regulation Mechanisms

Switchable and multifunctional terahertz photonic devices based on VO2-assisted phase encoded metasurfaces

Metasurfaces, especially coded ones, have gained significant attention for their excellent ability to control electromagnetic (EM) waves, opening up possibilities for a new generation of miniaturized devices. However, integrating multiple functionalities into a single metasurface while endowing tunable performance remains a challenge. In this study, we propose a strategy to design switchable and multifunctional terahertz (THz) photonic devices using complementary Gold-VO2 split resonant ring (GV-SRR) and complementary Gold-VO2 split resonant oblong (GV-SRO) structures. The designed devices can convert right-handed circularly polarized (RCP) light into left-handed circularly polarized (LCP) light in three frequency bands, corresponding to center frequencies fre.1 = 0.34 THz (narrowband), fre.2 = 0.50 THz (narrowband), and fre.3 = 0.80 THz (broadband). The phases of the reflected LCP wave can be independently modulated across different frequency bands by rotating the in-plane orientation of GV-SRR and GV-SRO separately. In addition, the overall phase reconstruction can be achieved through the state change of VO2. By arranging GV-SRR and GV-SRO in a defined encoding form, the engineered photonic devices can exhibit distinct and switchable capabilities in modulating EM wavefronts across various frequency ranges. As proof-of-concept examples, we have designed three encoded photonic devices, namely, a dynamic beam splitter (DBS), an achromatic and zoom metalens (AZM), and a switchable device between metalens and focusing orbital angular momentum (OAM) generator (MFOAM). These devices have potential applications in wireless communication, AR holographic displays, and information processing.

Design of a new Monopulse Horn Antenna by Orbital Angular Momentum Generation

Design of a new Monopulse Horn Antenna by Orbital Angular Momentum Generation

Deep Learning Design of Orbital Angular Momentum Generators by Leaky-Wave Holograms

Deep Learning Design of Orbital Angular Momentum Generators by Leaky-Wave Holograms

Multifunctional metasurface for Terahertz wavefront manipulation based on the combination of vanadium dioxide and graphene

In this paper, we propose a multifunctional wavefront control metasurface based on vanadium dioxide (VO2) and graphene. The unit cell structure contains a VO2 substrate, three rectangular metal strips as the bottom layer, orthogonal graphene strips as the top layer, and an intermediate layer consisting of a split ring resonator and circular metal patches. The desired performances can be achieved by changing the parameters of the split ring resonator in the middle layer, as well as controlling the phase transition state of VO2 and the Fermi level of graphene. When VO2 is in the insulating phase and the Fermi level of graphene is 1 eV, a transmissive metasurface is established, which realizes cross-polarization conversion, anomalous refraction, focusing lens, and orbital angular momentum generation at the frequency of 0.63 THz by changing the geometric sizes of the unit cell. When VO2 is in the metal phase and the Fermi level of graphene is 0.01 eV, a reflective metasurface can be achieved, which realizes terahertz beam splitting, radar cross section, and anomalous reflection of a single beam at the frequency of 0.63 THz. This multifunctional wavefront control metasurface treating the combination of VO2 and graphene exhibits significant application prospects in terahertz transmission, imaging, and communication.

All-fiber function devices for twisted lights.

Lights carrying orbital angular momentum (OAM), also called twisted lights, have been applied in fields of optical manipulation, imaging, quantum communication, and mode-division-multiplexing (MDM) optical communication systems. Traditional approaches for manipulating twisted lights carrying OAM in free space paths such as Q-plates, spiral phase plates (SPPs), and spatial light modulators (SLMs) that are usually affected by diffraction effect and imperfect alignment between different optical components, limiting the practical applications of twisted lights. Here we design, fabricated, and package all-fiber function devices for twisted light carrying OAM such as all-fiber broadband OAM generator, all-fiber OAM (de)multiplexer, all-fiber OAM & WDM coupler, and all-fiber OAM 1 × 2 coupler. Base on coupled mode theory and phase-matching condition, twisted light can be generated and detected by pre-tapered single mode fiber (SMF) fusing with multi-mode fiber (MMF). The results show that the proposed all-fiber function devices for twist light have large working broadband (at least C band), high purity (above 95%), and low insert loss (less than 3 dB). The proposed devices will open a reliable way for twisted light applied in optical fiber communications and optical interconnections.

Synthetic Multimode Orbital Angular Momentum Generation and Its Object Detection Application

Synthetic Multimode Orbital Angular Momentum Generation and Its Object Detection Application

Loss-induced multiple modal coalescences in an acoustic ring cavity

Chiral exceptional points refer to a class of non-Hermitian degeneracies where two counter-propagating whispering-gallery-like eigenmodes coalesce into one travelling eigenmode, which have been utilized to create orbital angular momentum in various wave systems. However, most studies in this field have so far focused on the modal coalescence for a specific azimuthal order. In this work, we investigate the eigenmodes evolution of an acoustic ring cavity under complex spatial modulation of refractive index along the azimuthal direction. We show that a careful engineering of the complex modulation, possibly realized with acoustic metamaterials, can lead to multiple modal coalescences to produce a series of travelling eigenmodes with different orbital angular momentum orders. These coalesced eigenmodes can be directly excited by a simple source at their resonant frequencies. Our work provides a straightforward approach to the generation and manipulation of acoustic orbital angular momentum.

Dense Space-Division Multiplexing Exploiting Multi-Ring Perfect Vortex

Vortex beams carrying orbital angular momentum (OAM) have gained much interest in optical communications because they can be used to expand the number of multiplexing channels and greatly improve the transmission capacity. However, the number of states used for OAM-based communication is generally limited by the imperfect OAM generation, transmission, and demultiplexing methods. In this work, we proposed a dense space-division multiplexing (DSDM) scheme to further increase the transmission capacity and transmission capacity density of free space optical communications with a small range of OAM modes exploiting a multi-ring perfect vortex (MRPV). The proposed MRPV is generated using a pixel checkerboard complex amplitude modulation method that simultaneously encodes amplitude and phase information in a phase-only hologram. The four rings of the MRPV are mutually independent channels that transmit OAM beams under the condition of occupying only one spatial position, and the OAM mode transmitted in these spatial channels can be efficiently demodulated using a multilayer annular aperture. The effect of atmospheric turbulence on the MRPV was also analyzed, and the results showed that the four channels of the MRPV can be effectively separated under weak turbulence conditions. Under the condition of limited available space and OAM states, the proposed DSDM strategy exploiting MRPV might inspire wide optical communication applications exploiting the space dimension of light beams.

Current-Induced Magnetization Switching in Light-Metal-Oxide/Ferromagnetic-Metal Bilayers via Orbital Rashba Effect.

The orbital angular momentum (OAM) generation as well as its associated orbital torque is currently a matter of great interest in spin-orbitronics and is receiving increasing attention. In particular, recent theoretical work predicts that the oxidized light metal Cu can serve as an efficient OAM generator through its surface orbital Rashba effect. Here, for the first time, the crucial current-induced magnetic-field-free in-plane magnetization reversal is experimentally demonstrated in CoFeB/CuOx bilayers without any heavy elements. We show that the critical current density can be comparable to that of strong spin-orbit coupling systems with heavy metals (Pt and Ta) and that the magnetization reversal mechanism is governed by coherent rotation in the grains through the second-harmonic and magneto-optical Kerr effect measurements. Our results indicate that light metal oxides can play an equally important role as heavy metals in magnetization reversal, broadening the choice of materials for engineering spintronic devices.

Frequency conversion of orbital angular momentum with optimized efficiency and modal purity

The use of nonlinear optics for the creation, control, and detection of structured light has gained prominence of late, but it is plagued by low efficiency and variable modal purity. Here, we show how to optimize the efficiency and modal purity in the nonlinear conversion of structured light modes. Using difference frequency generation of orbital angular momentum carrying Laguerre–Gaussian modes as an example, we achieved more than a 40% rise in efficiency while maintaining the modal purity above 90% compared to conventional methods. To demonstrate the versatility of our approach, we show the frequency conversion of perfect vortex beams up to ℓ=40 in a topological charge, achieving a new state of the art. We believe this theoretical treatment will facilitate our work’s translation to other modal forms and nonlinear processes.

Simultaneous Efficient Excitation of Multiple Higher-Order OAM Modes Using a Single Long-Period Fiber Grating

In this paper, a method for the simultaneous generation of multiple higher-order orbital angular momentum (OAM) modes in a few-mode fiber (FMF) using a single long-period fiber grating (LPFG) is proposed and demonstrated. The high diffraction order of the grating is used to achieve the resonant coupling of multiple modes, and the coupling coefficients of different order modes are balanced by a preset-twist method. This solves the two coupling problems of over-coupling for lower-order modes and difficult excitation of higher-order modes faced by multi-order mode generation, and overcomes the challenge of balanced excitation of multiple modes with high coupling efficiency. In the experiment, the simultaneous generation and flexible combination of first-order, second-order and third-order OAM modes are successfully achieved in a six-mode fiber, in which the mode order, resonant wavelength and wavelength interval can be flexibly controlled. By fabricating with grating periods of 2300 μm, 782 μm and 990 μm, respectively, high conversion efficiency of first-order and second-order modes, first-order and third-order modes, second-order and third-order modes can be generated simultaneously. In addition, for the first time, the first-order, second-order and third-order modes are generated simultaneously at a grating period of 1630 μm with conversion efficiencies of 98.61%, 99.11% and 98.89%, respectively. The mode profiles and interference patterns of different order modes show that multiple higher-order OAM modes with insertion loss less than 1 dB and mode purity over 95% are successfully generated.