Orbital Angular Momentum Vortex Wave Research Articles

Realization of Flat-Topped Electromagnetic Orbital Angular Momentum Vortex Wave With a Square Array

Realization of Flat-Topped Electromagnetic Orbital Angular Momentum Vortex Wave With a Square Array

Design of an ultra wideband THz reflectarray antenna based on orbital angular momentum

A Reflectarray antenna (RA) that can generate orbital angular momentum vortex waves in the THz band was proposed. First of all, a reflective phase-shifting element composed of a notched double-shaped ring and a single Matal structure was designed to form a radiation patch. The reflective phase-shifting element has the advantages of good linearity, high smoothness, and a large phase shift range, which is suitable for the subsequent production of reflective array antennas. Then, the phase distribution of the reflected wave of the OAM vortex wave carrying mode l=+1、+2、+3、+4 is given, and the size of each element is determined based on the reflected phase of each element. Using the proposed element, an OAM reflectarray antenna operating within the waveguide standard WR-5 (120GHz–220GHz) is designed. The optimal frequency band for antenna operation in mode l=+1 is 150GHz–190 GHz, and the maximum gain of the reflector array antenna is 19.4 dBi, and the minimum divergence angle of the antenna array is 5.2°, which has good directivity and beam radiation ability. The spiral structure of the OAM beam space generated by the RA in this paper is clearly visible, proving that the implementation of OAM vortex waves in the THz frequency band is feasible. This design also provides a new method for generating OAM vortex waves in wireless and microwave wireless communications. The proposed RA is suitable for 6G wireless communication systems.

Demodulation method of orbital angular momentum vortex wave by few fields sampled on an extremely small partial aperture in radiation region

In this paper, a demodulation method of electromagnetic wave carrying orbital angular momentum (OAM) has been developed by using few electric fields sampled on an extremely small portion of the whole circumference in the radiation region. Considering that the field of the OAM wave is naturally of the form of exp (ilφ) in the far-field region, the matrix pencil method is used to extract the magnitude terms and the exponential terms according to the real and imaginary parts of the fields sampled on a small portion of the whole circumference, and further, the mode purities corresponding to the desirable OAM modes can be easily solved. The proposed demodulation method only uses four sampling electric fields with the sampling angle ranges of 3.3° and 9° to well demodulate the mode purities of the OAM waves with the single mode and the mixed dual-mode, respectively. The prototype of a dual uniform circular array with the equal divergent angle for the OAM waves of the modes l = 1 and l = 2 is fabricated and measured. Good agreement between the simulation and the measurement is observed to verify the proposed demodulation method.

Optically transparent anisotropic holographic impedance metasurface for launching orbital angular momentum vortex wave

The visualization of electronic products is essential for the digitization and visualization of human-computer exchange in the future smart world. However, due to its large non-translucent aperture, the conventional hologram metasurface urgently needs transparency for wide scene usage. In this paper, an optically transparent holographic impedance metasurface with a low profile is investigated for generating orbital angular momentum (OAM) vortex waves in the radio-frequency domain for the first time. Indium tin oxide is applied to perform the metal functionality, which is featured by high optical transparency, and polymethyl methacrylate is proposed as the substrate material in the meta-atom design. By virtue of classic optical metasurface theory and leaky-wave principle, holographic impedance mapping is achieved, so the surface wave generated by the monopole port is effectively converted into a radiating vortex wave at 15 GHz. The prototype has been manufactured and fabricated, and the experiment results exhibit good agreements with theory and simulation analyses, showing a good prospect for OAM vortex wave launch in visualized applications.

Multiple Orbital Angular Momentum Beams with High‐Purity of Transmission‐Coding Metasurface

AbstractVortex electromagnetic wave carrying orbital angular momentum (OAM) is expected to break through the shortage of spectrum resource because of its multiple independent modes. Nowadays, there are various methods to generate OAM vortex beam. Based on the concepts of digital metasurface and propagation phase, a broadband 3‐bit coding transmission metasurface is designed and illustrated by simulation and measurement. The elements exhibit the different phase by changing the size of metal patch, and the focusing phase is introduced to reduce the divergence of OAM beams. Based on the principle of phase superposition, the wide‐band, high‐purity, and multi‐beam OAM vortex waves can be generated by the transmission‐coding metasurface (TCMS). The experimental results verify that TCMS realizes the multiple OAM beams along different directions simultaneously from 9 to 10.5 GHz, which are consistent with the theoretical results. The high purity more than 90% of OAM mode is demonstrated by both the simulated and measured results. The TCMS provides a potential and effective scheme for OAM multiplexing and multi‐target positioning in wireless systems.

A broadband vortex beam generator using graphene metasurface reflectarray in terahertz region

In this paper, a broadband vortex beam generator based on the graphene metasurface reflectarray is demonstrated in terahertz region. The designed graphene metasurface reflectarray structure realizes the generation of orbital angular momentum vortex wave with topological charges of l = ±1, l = ±2 and l = ±3 ranging from 2 to 2.4 THz by modulating the chemical potential and the radius of the graphene unit. Moreover, all of the vortex beam with topological charges of l = +1, l = +2 and l = +3 have a high purity in the range from 2 to 2.4 THz. Our finding shows that the graphene metasurface reflectarray structure might find applications in the fields of broad band vortex wave devices in THz domains and also provide new insights into innovative low-profile devices in the wireless communication.

Dual‐mode dual‐polarization orbital angular momentum metasurface antenna with in‐band radar cross‐section reduction

In this paper, an orbital angular momentum (OAM) metasurface antenna is proposed. Based on the idea of controlling the radiation and scattering simultaneously, the metasurface unit cells play two roles of radiating and scattering energy. For radiation, the metasurface unit cells are excited by two carefully designed phase shift networks (PSNs) at two orthogonal directions. Thus, OAM vortex waves with topological charge l = ±1 are generated at 7.48 GHz band. For scattering, the incident wave is deflected through the phase canceling scheme due to the anisotropy property of the metasurface unit cells. As a result, the in-band radar cross section is reduced. A prototype of the antenna was fabricated and measured. The measurement results agreed well with the simulations.

Multimodal Orbital Angular Momentum Data Model Based on Mechanically Reconfigurable Arrays and Neural Networks.

Multimodal orbital angular momentum is a research hotspot in the field of electromagnetic wave communication. How to accurately detect and identify multimodal orbital angular momentum data is a current academic problem. Based on the theory of mechanically reconfigurable arrays and neural networks, the purity, detection method, and transmission and reception of orbital angular momentum vortex waves are modeled in this paper. Through the network identification of the dynamic model of the three-degree-of-freedom reconfigurable manipulator, the paper takes the identification result and the control input of the single neuron PID as the input of the system control torque of the manipulator and realizes the reconfigurable manipulator. In the simulation process, the local approximation effect of the nonlinear control system used is very ideal. The single neuron PID controller overcomes the shortcomings of time-consuming and unsatisfactory control accuracy caused by the constant parameter of the traditional PID controller and realizes the circular loop. On the other hand, at the point of interest of the human eye, its resolution value is the largest, and its value gradually decreases as the distance from the pit increases. The experimental results show that the three-transmitting and three-receiving orbital angular momentum vortex wave transceiver system based on the mechanically reconfigurable array and neural network theory is relatively complete, and the transmission coefficient between the same modes reaches 0.827, which is much higher than that between different modes. On this basis, the modal purity, detection method, and reception of orbital angular momentum are studied accordingly. At the same time, the damage to the microscopic particles can be greatly reduced. At the same time, the information delay is reduced to 8.25%, which effectively improves the isolation characteristics of different modal orbital angular momentum channels and promotes the communication transmission of multimodal signals.

Cylindrical holographic impedance metasurface for OAM vortex wave generation

In this Letter, we present a cylindrical conformal holographic impedance metasurface for orbital angular momentum (OAM) generation. The conformal holographic metasurface is designed by establishing the element library and deducing the formula of holographic tensor impedance modulation. The feasibility of the scheme is verified by simulations and experiments. Simulated and experimental results are in good agreement with theoretical analysis. The results show that OAM vortex wave energy can be generated efficiently by a cylindrical conformal impedance metasurface, which can provide a reference for OAM communication and vortex radars with conformal devices.

An orbital angular momentum vortex wave antenna with low in‐band radar cross section and reduced divergence angle

In this article, an orbital angular momentum (OAM) vortex wave antenna with low radar cross section (RCS) and reduced divergence angle is proposed. The antenna is composed of four slot-coupled elements working from 7.5 to 8.0 GHz and fed by a phase shift network. OAM vortex wave with l = 1 is generated. In order to reduce the RCS and divergence angle simultaneously, complementary split-ring resonators (CSRRs) are designed and integrated to the antenna. The CSRRs can stop the transmission of surface wave and reflect the incident energy with phase canceling scheme. As a result, the RCS and divergence angle is reduced simultaneously.

A Review of Orbital Angular Momentum Vortex Waves for the Next Generation Wireless Communications

The next-generation wireless technology that can fulfill such a demand, namely the fifth-generation (5G) technology, should provide 1000 times larger capacity. Moreover, sixth-generation (6G) communication, which represents a significant upgrade from the fifth-generation (5G) network and is anticipated to operate from 100 GHz to 3 THz band, will be required in the years after 2030 due to newly developed data-hungry applications and the greatly expanded wireless network. To meet the ever-growing demands of wireless carriers, an efficient wireless access method that can improve wireless area throughput without expanding bandwidth or cell size is required. Radio Frequency (RF) Orbital Angular Momentum vortex waves (which is now on referred to as OAM waves) to address the concerns mentioned above have attracted much attention in recent years. Due to their orthogonality, different OAM waves of different modes can be multiplexed in the same frequency channel, which can greatly increase the channel capacity. Using the orthogonal modes, a new type of multiple access scheme known as Mode Domain Multiple Access (MDMA) can be used by multiple users using the same frequency channel without additional resources such as frequency and time. As a result, the channel capacity for the next generation wireless communication systems can be enhanced as well as the overall spectrum efficiency can be improved. This review paper begins with an overview of the next generation communication such as 5G communication technology and beyond. This paper first briefly discusses the theory of OAM waves and several methods to generate OAM waves. Various different designs have also been analyzed for their ability to generate OAM waves and discussion on several restrictions and solutions to resolve. Open concerns and development trends are discussed for possible future RF OAM antenna upgrades. This study also proposes that for next generation wireless communication employing OAM, the typically used Uniform Circular Array (UCA) could be paired with the Multiple-Input-Multiple-Output (MIMO) system to improve performance in dense or urban areas for multiusers. In addition, the purity of OAM-modes needs to be considered for efficient utilization of the OAM system for future communications at the radio domain.

Design of cylindrical conformal transmitted metasurface for orbital angular momentum vortex wave generation

We propose a cylindrical conformal transmitted metasurface for orbital angular momentum vortex wave generation. Formulas for calculating the phase distributions of cylindrical conformal transmitted metasurface is presented. A prototype of the proposed conformal transmitted metasurface is designed, fabricated and measured. Measured results shows that the proposed conformal transmitted metasurface can effectively generate vortex waves, which verifies the effectiveness of our method. The proposed method may pave the way of vortex wave generation with cylindrical conformal devices.

Beam Steering of Orbital Angular Momentum Vortex Waves With Spherical Conformal Array

In this letter, a spherical conformal antenna is designed, fabricated, and experimentally demonstrated to realize the beam steering of orbital angular momentum (OAM) vortex waves with hemisphere coverage. The theoretical formula of phase shift is deduced to design the conformal array antenna producing vortex radio waves with arbitrary beam direction. A prototype of a geodesic dome-based spherical conformal phased-array antenna is presented to validate the theoretical analysis. The experimental results verify that the hemispherical beam steering of OAM vortex waves can be effectively and flexibly generated. The proposed method can provide a reference for OAM vortex communication with full space coverage.

Polarization induced reconfigurable multiple OAM vortex waves through a composite meta-surface beam former.

We demonstrate a composite meta-surface beam former to generate reconfigurable multiple orbital angular momentum (OAM) vortex waves by integrating a polarization conversion meta-mirror with a multi-functional anisotropic meta-lens. More specifically, electromagnetic fields from the feed would be firstly reflected by the meta-mirror, and then transmit through the meta-lens to form the well converged OAM vortex waves with tailored beam numbers, radiation directions and topological charges. Especially, we show that the anisotropic characteristics of the meta-lens would create different multiple OAM vortex waves when the meta-mirror is rotated or equipped with active circuits to have different polarized illuminations on the meta-lens. Our design should pave the way for the reconfigurable design of generating multiple OAM vortex waves to further expand the communication capacity.

Compact cascaded meta-surface system for controlling the spin and orbital angular momentum of electromagnetic fields simultaneously.

We propose a compact cascaded meta-surface system (CCMS) to produce well converged orbital angular momentum (OAM) vortex waves with tailored spin angular momentum (SAM) by integrating a meta-surface lens (ML) with an assistant meta-mirror (AM). Specifically, the co-linearly polarized (LP) waves from the feed would be reflected by the ML firstly and then twisted into the cross-LP counterparts by the AM to penetrate the ML for the perfect synthesis of the OAM vortex beams while performing the linear-to-circular polarization conversion. Especially, the CCMS can pack the ML and the AM closely together with a quarter of the ML focal length when we apply proper phase distributions on the AM. In addition, the proposed CCMS can readily be extended to the generation of multiple circularly polarized OAM vortex waves with different modes. Our design should thus pave the way for building up more efficient wireless communication systems with expanded channel capacity.

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.

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.