Orbital Angular Momentum Vortex Research Articles

Converged OAM vortex wave generation using EBG‐loaded patch array antenna

In this article, an orbital angular momentum (OAM) patch array antenna with converged beam is proposed. The electromagnetic band gap (EBG) structure is applied to a patch array antenna with 2 × 2 elements. The array antenna is excited by a carefully designed feeding phase shift network with equal output energy for four output ports. Thus, the OAM vortex wave with topological charge l = 1 is generated. By using EBG structure around the radiating patches, the surface wave of the array antenna is suppressed. As a result, the radiation pattern is improved significantly, including the enhanced gain and reduced divergence angle. A prototype was fabricated and measured. The measurement results agree well with the simulations. Compared with the other approaches, the proposed antenna is much more compact in structure and ease of fabrication.

Recognition of orbital angular momentum vortex beam based on convolutional neural network

AbstractTo identify different modes of orbital angular momentum (OAM) vortex beams after demultiplexing, deep learning technology is introduced, and a convolutional neural network (CNN) model is designed to detect OAM beams. The light intensity distribution maps of the Laguerre Gaussian beam with the topological charge from 1 to 20 through experiments are collected, the random phase screens are generated by using the power spectrum inversion method, to simulate the transmission of Laguerre Gaussian beams in the different atmospheric turbulence channels. The recognition accuracy is studied by the conditions of different CNN model iteration times, beam wavelengths, and data sets. The images are classified and processed to make different data sets, and the random vortex beam training sets are tested. Experimental results show that this method with about 98% accuracy for the conditions of long‐wavelength beams and medium or weak turbulence. The training on complex training sets can improve the effect.

A metamaterial lens based on transformation optics for horizontal radiation of OAM vortex waves

Vortex electromagnetic waves carrying orbital angular momentum (OAM) have been widely discussed for potential applications in wireless communications. Belonging to the Laguerre–Gaussian beams family, such type of waves present a hollow conical shape and divergence characteristics along with a directional radiation. In this paper, an innovative method to produce omnidirectional OAM beams based on spatial transformation is proposed at microwave frequencies. As a proof-of-concept demonstration, a lens with omnidirectional radiation in the horizontal plane is designed and simulated with an incident vortex beam carrying the OAM mode l = +2. The designed lens can be potentially implemented with an all-dielectric medium showing a gradient permittivity distribution. Furthermore, the proposed lens presents good performances over a wide operational bandwidth spanning from 8 to 17 GHz. By converting the directional beam to an omnidirectional one, the proposed method opens the door to the potential development of microwave vortex antenna systems.

Beam steering of orbital angular momentum vortex wave based on planar phased array

Orbital angular momentum (OAM) vortex electromagnetic waves can provide a new degree of freedom for information modulation at a physical level, which has great prospects of applications in the fields of wireless communication and radar imaging. The application of beam scanning techniques of phased array to OAM vortex electromagnetic wave can increase its communication coverage and expand the detection coverage of vortex radars. Firstly, in this paper, the principle of generating the beam steering vortex electromagnetic beam is discussed and the compensated phase formula for generating beam steering OAM beams is given by planar phased array. Secondly, considering the advantages of phased array antennas in beam scanning and OAM reconfigurability, a planar phased array with 8 × 8 antenna elements at 10 GHz is designed and fabricated. The performances of OAM beam steering and mode reconfigurability are verified. Finally, the performance changes of the deflecting OAM vortex beam at different scanning angles are discussed and analyzed. Simulations and measurements both show that there exist pattern distortion problems when steering angle of OAM beam becomes large. In this paper, the variation of the OAM mode purity is also studied when the scanning angle and the OAM mode number change. The results show that the planar phased array antennas can effectively generate the beam steering OAM vortex beams in a certain angle range. Hence, this paper can provide a reference for the OAM vortex electromagnetic wave communication and the vortex radar in the future.

Generation and Focusing of Orbital Angular Momentum Based on Polarized Reflectarray at Microwave Frequency

A novel polarized reflectarray is designed, fabricated, and experimentally characterized to show its flexibility and efficiency to control wave generation and focusing of orbital angular momentum (OAM) vortices with desirable OAM modes in the microwave frequency regime. In order to rigorously study the generation and focusing of OAM, a versatile analytical theory is proposed to theoretically study the compensation phase of reflectarray. Two prototypes of microwave reflectarrays are fabricated and experimentally characterized at 12 GHz: one for generation and one for focusing of OAM-carrying beams. Compared with the OAM-generating reflectarray, the reflectarray for focusing OAM vortex can significantly reduce the beam diameter, and this can further improve the transmission efficiency of the OAM vortex beams. We also show that the numerical and experimental results agree very well. The proposed design method and reflectarrays may spur the development of new efficient approaches to generate and focus OAM vortex waves for applications to microwave wireless communications.

Simple terahertz vortex beam generator based on reflective metasurfaces.

Orbital angular momentum (OAM) is an effective way to increase wireless communication capacity. The existing OAM mainly focuses on the optical and microwave frequency domain. In this letter, a reflective metasurface is proposed to generate an OAM vortex wave beam in the terahertz region with different topological charges. Under illumination of a circular polarized wave, the proposed metasurface generates the deflected OAM vortex wave beam with topological charges of l=±1 and l=±2 at a wide terahertz band from 0.3THz to 0.45THz. The OAM beam has a high mode purity that is larger than 90% at 0.4THz. Both theoretical prediction and simulated results verify that the designed metasurface can achieve a terahertz vortex wave beam with different OAM topological charges.

Generating high-purity orbital angular momentum vortex waves from Cassegrain meta-mirrors

Cassegrain meta-mirrors are proposed to generate the orbital angular momentum (OAM) vortex waves through dual-reflecting system with two-planar grounded meta-surfaces of properly devised sub-wavelength ring patches. More specifically, electromagnetic fields reflected by the secondary meta-mirror would subsequently be collimated by the primary meta-mirror and transformed into the well-converged OAM vortex waves possessing the merits of high directivities with clear helix wave-fronts. We extend such a design into conformal Cassegrain systems having the primary meta-mirrors of concave and convex profiles, respectively, and also demonstrate excellent syntheses of OAM vortex beams. Our design, using the dual-reflecting meta-mirrors to generate high-purity OAM vortex waves, can obtain the radiations with more stable angular momentum numbers in the long-distance propagation for the OAM wireless communications.

Extended aperture sample reception method for high-order orbital angular momentum vortex beam mode number measurement.

The traditional phase gradient method can effectively measure the orbital angular momentum (OAM) number of the vortex beam. However, its spatial sampling phase aperture span is strictly restricted within only π radian. In this paper, we presented a more flexible extended aperture sampling reception (EASR) method for the radio frequency (RF) applications, which can break through this restriction condition. It could make the reception and measurement methods about the OAM mode number become more complete and versatile. By converting the higher-order OAM mode to a lower-order OAM mode, the spatial phase aperture span between the adjacent receiving sampling points can realize extensions. We have conducted a comprehensive theoretical analysis and summarized the general guidelines of this EASR method in the main body of the paper. Subsequently, we perform the related numerical simulation calculations to receive and measure the OAM mode number of a high-order mode vortex beam using the EASR method. Simulation results and theoretical analysis are in good agreement.

Throughput Performance of Wireless Multiple-Input Multiple-Output Systems Using OAM Antennas

This letter experimentally demonstrated the performance improvement of orbital-angular-momentum (OAM) based 2 $\times $ 2 MIMO communication by using the diversity of different OAM modes. The OAM antenna we used is an eight-arm Archimedean spiral antenna (ASA) capable of generating multiple high-quality OAM vortex waves individually or two types of two-mode mixed vortex waves simultaneously. Both of the two cases are investigated for MIMO communication by evaluating the throughput performance. For MIMO with two OAM modes (generated by two ASAs separately), the throughput improves upon traditional MIMO by up to 30.50%, while for MIMO with two-mode mixed vortex waves (generated by one ASA), 6.59% throughput improvement is obtained.

A Reconfigurable Second-Order OAM Patch Antenna With Simple Structure

Using a single patch antenna to generate a vortex electromagnetic wave greatly simplifies the application systems of orbital angular momentum (OAM) modes. OAM modes can be synthesized from degenerate modes, and thus, characteristic mode theory is a helpful tool to guide the construction of OAM antennas. Based on this idea, a single-fed circular patch with an arc segment as a symmetrical perturbation element is proposed to radiate a second-order OAM wave. Since the arc segment is independent of the radiation element, it is easy to reconstruct the OAM mode order or vortex direction by adjusting it. In this regard, two symmetrical arc segments switched on and off using p-i-n diodes are applied to implement the reconfiguration of the second-order OAM mode. The structure effect on the vortex wave is discussed by using modal weighting coefficients.

Double-deflection vortex beam generation using a single elliptical patch with the theory of characteristic modes.

In this paper, a single elliptical patch antenna is proposed to generate double-deflection orbital angular momentum (OAM) vortex beams. The physical mechanism of an equivalent uniform elliptical array (UEA) is constructed and analyzed by using the theory of characteristic modes. The elliptical patch antenna can be fed with a 3dB directional coupler to generate the double-deflection vortex beams with single OAM mode or mixed OAM modes. The simulation and measurement results verify that the proposed single elliptical patch antenna is a simple, miniaturized, and multifunctional generator for OAM vortex beams.

Low-Profile Transmitting Metasurface Using Single Dielectric Substrate for OAM Generation

In this letter, transmitting metasurface using single dielectric substrate for orbital angular momentum (OAM) generation is presented in Ku-band. A dimension extension method is introduced in designing the unit cell of the proposed transmitting metasurface to achieve required phase shift and transmission magnitude for generating OAM. A prototype of the proposed transmitting metasurface is fabricated and measured. Measured results suggest that the proposed transmitting metasurface can generate OAM vortex wave at 18 GHz. The proposed method can be applied in wireless communication systems requiring low-profile transmitted OAM generator.

A Review of Orbital Angular Momentum Vortex Beams Generation: From Traditional Methods to Metasurfaces

In this paper, we review the generation of vortex beams carrying orbital angular momentum in the microwave domain. We firstly present the theory of Laguerre–Gaussian beams where it is demonstrated that they carry such type of momentum. We further provide an overview of the classical methods used to generate orbital angular momentum vortex beams, which rely on two main methods; plane wave to vortex wave conversion and direct generation using radiating antennas. Then, we present recent progress in the physics of metasurfaces devoted to the generation of vortex beams with a discussion about reflective and transmissive metasurfaces for plane wave to vortex wave conversion as well as methods to reduce the intrinsic divergence characteristics of vortex beams. Finally, we conclude on this rapidly developing research field.

Generation of High-Order Bessel Orbital Angular Momentum Vortex Beam Using a Single-Layer Reflective Metasurface

In this paper, we propose a method to generate a high-order Bessel orbital angular momentum (OAM) vortex beam by using a single-layer reflective metasurface, which integrates the advantages of small size, high efficiency, insensitive polarization and stable incident angles. An offset-fed horn configuration is adopted to overcome the feed-blockage effect, and a subwavelength unit cell with rotational symmetry is designed to cover the reflection phase variation range of 360° in different incident angles. The metasurface is simulated, fabricated and measured at the center frequency of 10 GHz, and the results validate that a second-order Bessel OAM vortex beam can be generated effectively. By comparing the field distributions between the Bessel OAM vortex beam and the conventional OAM vortex beam, we find that the generated Bessel OAM vortex beam is obviously more convergent and has more stable field distributions. The single-layer reflective metasurface is simple and flexible to shape the wavefront to be a Bessel OAM vortex wave, which has the potential to be used in a wide range of applications.

直接输出的超短脉冲轨道角动量涡旋光产生技术研究进展（特邀）

Orbital angular momentum (OAM) vortex beam has a phase singularity with a twisted wave-front, whose complex amplitude comprises the helical term exp (ilθ). OAM vortex beam has been widely used in optical manipulation, imaging, optical communication, sensing and so on. Ultra-short pulse OAM vortex beams have the advantages of both vortex beams and ultra-short pulses, and can be applied to chiral material processing, long distance transmission, strong field physics and nonlinear frequency conversion. Direct generation of ultra-short OAM vortex beams has the advantages of compact and simple system and good beam quality. The research progress on direct generation of ultra-short OAM vortex beams was summarized. At present, the pulse width of the ultra-short OAM vortex beam generated by the active method is still limited to a few hundred femtoseconds. How to obtain the pulsed vortex beam output within 100 femtoseconds or even with a few cycles through the direct output method will be an important future development direction.

Multifunctional Scattering Antenna Array Design for Orbital Angular Momentum Vortex Wave and RCS Reduction

In this paper, a multifunctional scattering antenna array has been proposed to generate orbital angular momentum (OAM) vortex scattering wave and meanwhile reduce antenna radar cross section (RCS). Theoretical analysis for integration of the RCS reduction and the OAM wave is given, and a circular antenna array composed of a dual polarized microstrip antenna and a tunable connection line network is designed. By adjusting the ON/OFF state of the PIN diodes embedded in the connection line network, the OAM scattering waves with the modes of $l=1$ and $l=2$ are independently generated, and accordingly in-band RCS reduction of a circular patch antenna with an increase of the antenna gain over 2 dB is achieved. A multifunctional prototype antenna array is fabricated and measured. Simulated and measured results demonstrate -10dB RCS reduction and the OAM scattering waves with the tunable modes in the frequency band of 9.37~9.8 GHz.

Synthesis and Measurement of a Circular-Polarized Deflection OAM Vortex Beam With Sidelobe Suppression Array

In this paper, a chamfer distribution antenna array is designed to generate a deflecting circular-polarized vortex beam carrying orbital angular momentum (OAM) mode. When the vortex beam is designed with a deflection angle, the sidelobe of the vortex beam will deteriorate. In order to solve this problem, an optimized array design is presented in this paper. Inspired by the Chebyshev distribution array synthesis method, the antenna elements in the four corners of the antenna array are cut out to realize the chamfer distribution array. Therefore, the sidelobe level of the deflected vortex beam can be effectively suppressed. Moreover, a simplified feeding network is designed to reduce the feeding network complexity by using circularly polarized structural center antenna element. The designed antenna array is simulated, fabricated, and measured at center frequency of 4.25 GHz in C-band. The far-field radiation pattern of the deflected vortex beam and the near E-field OAM vortex beam distribution are simulated and measured to verify the effectiveness of the proposed design method for sidelobe suppression array.

Full controls of OAM vortex beam and realization of retro and negative reflections at oblique incidence using dual-band 2-bit coding metasurface

This paper addresses a reflection-type dual-band 2-bit coding metasurface (CM) design to achieve the dual-band functionalities in two different operating bands, independently. We are particularly interested to control linearly polarized incident waves by encoding the propagation or dynamic phase in order to realize and fully control the orbital angular momentum (OAM) vortex beam (VB) for dual bands. In this regard, we perform digital addition operations to combine the coding sequences of traditional OAM (OAM that propagates in the normal direction) and phase-gradient to construct the proposed CM, which generates and steers OAM-VBs with different topological charges () in both lower () and higher () bands. The proposed concept is further extended to realize multiple OAM-VB with various beam shaping by combining the coding sequence that generates OAM in the normal direction and the coding sequence of beam shaping, and we discuss three different scenarios. Firstly, split OAM-VB is generated in both lower and higher bands. Secondly, quad OAM-VB is realized to verify the proposed concept. Finally, yet importantly, we show that the reflected beam directions can be further independently controlled to achieve anomalous, negative and retro reflections at the two bands. Two CM samples are fabricated to experimentally validate the proposed OAM-VB generation with steering features and retro or negative reflections at oblique incidences, which are in good agreement with the simulation results. The proposed concept will open up possibilities of multifunctional meta-devices and will be useful in many applications such as optical spanners, quantum optics, spatial mode multiplexing for telecommunications, and astronomy etc.

Broadband vortex beam generating for multi‐polarisations based on a single‐layer quasi‐spiral metasurface

A reflective metasurface based on the quasi-spiral element is proposed to achieve broadband orbital angular momentum vortex beams for multi-polarisations. The quasi-spiral element can provide linear and smooth phase responses covering about 360° from 10 to 15 GHz with a relative bandwidth about 40% by adjusting the length of four phase delay lines. Additionally, the metasurface can generate vortex beams with optional charges in vertical, horizontal and circular polarisations which are determined by the polarisation of feed antenna. Finally,we have designed and fabricated a 24 × 24 cm2 metasurface prototype. The simulated and measured results show that the reflective metasurface can generate broadband vortex beams with orbital angular momentum effectively. As the structure is simple, lightweight and easy to fabricate, the proposed method is applicable to generate broadband vortex beams for multi-polarisations.

Graphene-based metamaterial transmitarray antenna design for the generation of tunable orbital angular momentum vortex electromagnetic waves

A graphene-based metamaterial transmitarray antenna is proposed to generate tunable orbital angular momentum (OAM) vortex waves in terahertz. Theoretical design of the transmitarray antenna has been developed by using the transmission line network model, and a multilayer graphene-based metamaterial element has been designed. By changing the chemical potentials of the graphene sheets, the 360° transmission phase range of the element is achieved in a broad band from 4.2 THz to 5.6 THz. By arranging the metamaterial element into a transmitarray, the OAM waves with tunable modes including l = 0, ±1, ±2 and the mode purity greater than 0.96 are generated. Simulation results are given to demonstrate good performance of the proposed design, which provides a feasible way to the efficient generation and manipulation of the OAM vortex waves in terahertz.