Multi-mode Vortex Research Articles

A reconfigurable ultra-wideband high-purity multimode terahertz OAM antenna array based on graphene and vanadium dioxide

A reconfigurable ultra-wideband multimode terahertz OAM antenna array based on graphene and vanadium dioxide (VO2) is presented in this paper. The uniform circular array (UCA) composed of circularly polarized (CP) antennas, which include a ring radiation patch, a parasitic patch, a perovskite substrate and an irregular VO2 ground plane. The radiation patch is covered with a layer of graphene, by changing the chemical potential of graphene, the working bandwidth and axial ratio bandwidth of the antenna can be changed. By changing the phase state of VO2 (metal state / insulation state) to control the working state of the antenna. The impedance bandwidth (IBW) of the CP antenna proposed is 115.09% (1.73–6.42 THz), the axial ratio bandwidth (ARBW) is 43.97% (2.36–3.69 THz). Using the CP antenna unit can simplify the complex feed network, and only feeding the equal amplitude and equal phase excitation can realize the vortex wave. Changing the number and rotation angle of the antenna unit can realize multimode vortex waves with the l= 0, ±1, ±2, ±3, the purity is approximately 1, respectively. The proposed UCA has excellent application prospect in the 6G communication.

Identification of multimodal vortex optical orbital angular momentum in multimode fiber speckle patterns

Orbital angular momentum (OAM) multiplexing technology is a highly promising approach that can significantly increase the data capacity of optical communication systems. However, traditional optical communication systems are prone to atmospheric disturbances such as turbulence, which can degrade transmission quality. To mitigate this issue, multimode fibers (MMFs) have been introduced to reduce the impact of turbulence on signals. Moreover, previous studies have primarily focused on the identification of single vortex beams, facing challenges in accurately recognizing multiplexed modes. To address this challenge, this chapter proposes a multi-label image classification optimization algorithm based on transfer learning. By utilizing the pre-trained MobileNet V2 model as a feature extractor, this network structure can accurately identify 8-bit, 16-bit, and 24-bit multiplexed OAM from speckle patterns in multimode fibers, even with small sample datasets, achieving classification accuracies exceeding 95%. This method overcomes the limitations of traditional optical communication systems that are susceptible to atmospheric disturbances, providing new possibilities for long-distance transmission and increased data capacity in optical communication systems.

High-speed terahertz communication with graphene-based time-modulated low-bit phase coding metasurfaces: A novel architecture for enhanced performance

Coding metasurfaces have revolutionized electromagnetic device development by enabling precise electromagnetic wave manipulation. While spatial phase modulation alone offers significant capabilities, its limitations to comprehensive control and optimal functionality are evident. As a result of recent advancements, joint amplitude-phase coding approaches have been explored using different techniques in order to enhance performance. However, such methods often result in complex structures due to the combining of various modulation techniques within meta-atoms. Addressing this challenge, this paper proposes a novel architecture for terahertz (THz) communication utilizing low-bit coding metasurfaces featuring simplified meta-atoms. Our approach introduces a coding unit cell based on graphene, combined with time-modulated coding, to enable phase and amplitude control for different harmonics. As a proof-of-concept application, we demonstrate the effectiveness of our technique in multimode vortex communication. Moreover, we show secure hologram communication by using our proposed design within the THz frequency regime. By enhancing wavefront shaping flexibility through a straightforward approach, this work lays the foundation for next-generation devices, particularly in high-speed macroscale and nanoscale communication networks.

Dual-channel polarization-modulated metasurface

Metasurfaces provide excellent design flexibility, allowing for the creation of versatile integrated designs with significant potential for practical applications. This paper proposes a dual-channel polarization-modulated metasurface, which realizes the modulation of line-polarized light (LP) to circularly polarized light (CP) with opposite rotation. The polarization state of the dual channels can be changed by adjusting the polarization angle of the line-polarized light. Through the reasonable selection of element atoms, the function of the quarter waveplate is combined with the wavefront control of the general metalens, and the spiral phase can be arbitrarily added to the two channels to realize the simultaneous generation of multi-mode vortex beams. This work achieves functional integration on a single-layer metasurface, enabling its application in polarization imaging and other areas. This work achieves functional integration on a single-layer metasurface, enabling its application in polarization imaging and other areas.

Generation of Multi-Frequency Multi-Mode Vortex Waves with Multi-Ring Nested Microstrip Patch

Generation of Multi-Frequency Multi-Mode Vortex Waves with Multi-Ring Nested Microstrip Patch

Application of pipeline leakage detection based on distributed optical fiber acoustic sensor system and convolutional neural network

Underwater pipelines are exposed to harsh environments, including high salinity, multi-modal vortex corrosion, and severe wave interference. Their safety is essential for the development and transportation of marine energy. Therefore, real-time safety monitoring of long-distance energy pipelines is of great strategic importance for ensuring the safety of life and property and energy security. With the rapid development of energy development, the corrosion and leakage mechanisms of natural gas pipelines, as well as their identification and early warning, have become the focus of attention. Optical fiber sensing technology has been applied to various energy safety monitoring fields. However, the mechanism of sound source fluctuations in pipeline leakage and the mutual coupling mechanism between distributed optical fiber sensing technology and leakage sound waves are not yet clear. This paper establishes a model based on sound wave propagation and leakage noise response, derives a quadratic fitting relationship between pipeline pressure fluctuations and leakage orifices and a relationship between leakage noise source standard deviation and orifices, and proposes a complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) permutation entropy underwater natural gas pipeline leakage signal recognition method based on distributed optical fiber acoustic sensing technology. The results of theoretical analysis are verified by experiments. It shows that the signal processing method of CEEMDAN permutation entropy is superior to traditional noise reduction methods, which can better preserve the features of the original signal; the radial basis function (RBF) neural network model can accurately identify four different leakage features with an accuracy of 88.15%, and its recognition stability and generalization ability are superior to convolutional neural network, backpropagation, and random forest. Therefore, the research results of this paper provide a new method for safety monitoring in the application of energy pipeline transportation engineering, and expand the potential application scenarios of distributed acoustic sensing sensor systems and RBF neural networks.

Multi-mode vortex beams generation with single-layer transmissive metasurface

Orbital angular momentum (OAM) is a phenomenon of vortex phase distribution in free space, the infinity of whose modes and the orthogonality between modes allow it to possess great potential in enhancing channel capacity. A transmissive metasurface consisting of a single-layer substrate and a two-layer metallic structure is proposed to enable vortex beam generation based on the concept of the Pancharatnam-Berry (PB) phase. The phase response is achieved by continuous phase modulation under circularly polarised (CP) wave incidence due to the simultaneous rotation of the upper and lower metal structures. Besides, through the introduction of both phase compensation on the metasurface and phase superposition of the beams to the array design, multi-beam generation is expected to be realized. A metasurface sample composed of 30 30 elements (450 mm 450 mm) is fabricated and measured in a microwave darkroom on the basis of the simulation results. Both the simulation and measurement results provide firm demonstration that the designed metasurface is capable of simultaneously generating four beams carrying OAM mode numbers of and different beam directions at the same aperture. The designed metasurface in this paper utilized for generating multi-mode vortex multi-beams will be of wide application in multi-channel transmission in wireless communication systems.

Dual-mode vortex beam transmission metasurface antenna based on linear-to-circular polarization converter.

The generation of multi-mode vortex beams at the same aperture is currently emerging as a research hotspot. In this paper, a method based on a linearly polarized-circularly polarized translational transmission metasurface (TM) is proposed to enable a dual-circularly polarized dual-mode vortex beam generation. Through the judicious implementation of an additional rotational phase and the combination of the initial transmission phase, the phases of the left-hand circularly polarized (LHCP) and right-hand circularly polarized (RHCP) waves can be manipulated arbitrarily and independently. Meanwhile, the design of the array phase is utilized for the dual-mode dual-circularly polarized beam generation. Simulation and sample measurements provide validation data for the feasibility of this method, in which the measurement results are in excellent consistency with the simulation ones. This proposed method paves the way toward the enhancement of the channel capacity of mobile communication.

Multimode Vortex Lasing from Dye–TiO2 Lattices via Bound States in the Continuum

Spatially extended bound states in the continuum (BICs) can provide high-quality optical feedback for vortex lasing. This work reports that three out of the four supported BIC modes in 2D square lattices of dye-covered TiO2 nanoparticles can lase simultaneously under pulsed pumping, while the remaining one can be tuned into the gain bandwidth by adjusting the nanoparticle size. All the BIC modes in the in-plane symmetric lattices exhibited doughnut-shaped lasing patterns, regardless of the pump polarization, but with a polarization-dependent threshold. Multiple vortex beams can be generated by illuminating with multiple pump spots. When changing the nanoparticle shape from square to trapezoidal, the symmetry breaking resulted in predominantly single-lobed lasing at symmetry-breaking-induced band edges and dramatically suppressed two-lobe lasing at BIC modes. Such on-chip multimode lasing with different polarization patterns thus enables multiplexing in not only wavelength, but also polarization.

High-Purity Multi-Mode Vortex Beam Generation With Full Complex-Amplitude-Controllable Metasurface

Vortex beam with inherent orbital angular momentum (OAM) is promising in high-capacity communication. On multimode vortex beam generation, metasurface has shown exceptional advantages of integration and miniaturization. For the current widely used phase-only methods on multimode vortex beam generation by metasurface, the purity of the OAM-mode spectrum is severely affected. A new method for generation of multimode vortex beam with high mode purity is proposed in this article by reconstructing the complete complex amplitude information on the meta-device aperture. A 20 dB suppression of the crosstalk modes is experimentally observed for the co-directional multimode vortex beam generation, which is much improved compared to the traditional phase-only scheme. In addition, the proposed scheme also provides the capability of generating high-purity multimode vortex beams with arbitrary preset propagation directions and power allocations. This study provides a platform for high-performance vortex beam communication by increasing the signal-to-noise ratio and enabling the multicasting scenarios with customized capacity requirements.

Bifunctional Integration Performed by a Broadband High‐Efficiency Spin‐Decoupled Metasurface

AbstractAchieving broadband multitasked integration on an ultrathin interface is pivotal to increasing data capacity. However, broadband bifunctional metasurfaces exhibiting high‐efficiency and crosstalk‐free characteristics are rarely seen. Here, three broadband spin‐decoupled criteria are developed to design the meta‐atoms of high‐efficiency bifunctional metasurfaces. Specifically, six dipole‐loaded quasi‐I‐shaped meta‐atoms are proposed to satisfy the broadband spin‐decoupled criteria in radio band from 8.6 to 17.8 GHz (about 70% bandwidth) with more than 90% efficiency. The metasurface equipped with the proposed meta‐atoms can keep dispersionless phase gradients and crosstalk‐free characteristics in two orthogonal circular polarizations. This work demonstrates the broadband scheme with spin‐decoupled bifunctional metasurface, yielding two independent broadband multimode vortex beams in two completely decoupled helicities. Besides, other possible applications of the proposed meta‐atoms are illustrated from the perspective of the half‐wave plant (polarization control). Accordingly, the other multitasked‐type bifunctional metasurface is fabricated to achieve the broadband integration of two different functionalities: polarization conversion and full‐polarization anomalous refraction. The proposed schemes offer broadband, polarization‐multiplexing, and multitasked‐integration routes for complex electromagnetic wave manipulations within a subwavelength thickness, which can stimulate the development of electromagnetic/optical integration devices with broadband multiplexing techniques.

Dynamically tunable multimodal vortex beam generator based on reflective metasurface

How efficiently generating a multi-mode vortex beam is the key to the new system of wireless communication technology based on orbital angular momentum. Due to the advantages of simple structure and flexible tunability of the metasurface, in recent years, people have been devoted to generating dynamic orbital angular momentum more simply and efficiently using programmable metasurfaces. To address the current problem of a single number of modes for generating orbital angular momentum vortex beams from metasurface, the programmable reflective metasurface structure has been designed to realize the function of dynamically tunable multi-mode of vortex beams. By loading two varactor diodes inside each metal patch to construct eight digital coding units, and using the programmable bias circuit to modulate the coding distribution and resonance characteristics on the metasurface in real-time, the metasurface obtains low reflection loss and stable reflection phase, and finally obtains vortex beams with mode numbers of ℓ = ±1, ℓ = ±2, and ℓ = ±3, respectively. The designed metasurface also has the advantages of a simple structure, small electrical size, and low profile, which has a large potential value in the communication of vortex beams and a perfect application in wireless transmission.

On-chip ultracompact multimode vortex beam emitter based on vertical modes.

Free-space orbital angular momentum (OAM) communication is considered as one of the potential alternative on-chip optical interconnect solutions. The number of OAM modes determines the capacity of high-speed communication. However, existing integrated vortex beam emitters have a constraint relationship between the number of OAM modes and the emitter size, rendering it difficult to emit more OAM modes with a small-sized emitter. In view of the above, this study proposes an on-chip ultracompact multimode vortex beam emitter based on vertical modes, which permits more OAM modes without requiring an increase in the size of the emitter. Vertical modes in large-aspect-ratio waveguides are pointed out to enable multimode microrings with small radii because high-order vertical modes can maintain almost the same horizontal wave vector as that of the fundamental mode. Four-mode and five-mode vortex beam emitters with the same radius of 1.5 µm are designed and the effectiveness of these emitters is verified through simulation. Furthermore, a high-efficiency and low-crosstalk approach for high-order vertical mode coupling by varying the waveguide height is presented. This research not only promotes further integration of on-chip optical interconnection, but also provides a new strategy for optical waveguide mode selection in photonic integrated circuits design.

Generating a multi-mode vortex beam based on spoof surface plasmon polaritons.

The vortex beam provides a promising alternative for next-generation wireless communication, but it is a long-standing challenge to generate a multi-mode and robust vortex beam. In this Letter, a multi-mode vortex beam emitter is introduced and experimentally verified based on spoof surface plasmon polaritons (SSPP). The SSPP on a helical grating carries multi-mode orbital angular momentum and can be converted into a high-purity vortex beam via the diffraction of a ring array. The operation frequency and topological charge are determined by that of the SSPP. This emitter can achieve the function of beam-scanning in each radiation band. The beam-scanning and vortex characteristics are experimentally verified. The designed emitter is compact and robust, and we are confident that this work will have great application prospects in communication systems.

Imaging through diffuse media using multi-mode vortex beams and deep learning

Optical imaging through diffuse media is a challenging issue and has attracted applications in many fields such as biomedical imaging, non-destructive testing, and computer-assisted surgery. However, light interaction with diffuse media leads to multiple scattering of the photons in the angular and spatial domain, severely degrading the image reconstruction process. In this article, a novel method to image through diffuse media using multiple modes of vortex beams and a new deep learning network named “LGDiffNet” is derived. A proof-of-concept numerical simulation is conducted using this method, and the results are experimentally verified. In this technique, the multiple modes of Gaussian and Laguerre-Gaussian beams illuminate the displayed digits dataset number, and the beams are then propagated through the diffuser before being captured on the beam profiler. Furthermore, we investigated whether imaging through diffuse media using multiple modes of vortex beams instead of Gaussian beams improves the imaging system's imaging capability and enhances the network's reconstruction ability. Our results show that illuminating the diffuser using vortex beams and employing the “LGDiffNet” network provides enhanced image reconstruction compared to existing modalities. When employing vortex beams for image reconstruction, the best NPCC is − 0.9850. However, when using Gaussian beams for imaging acquisition, the best NPCC is − 0.9837. An enhancement of 0.62 dB, in terms of PSNR, is achieved using this method when a highly scattering diffuser of grit 220 and width 2 mm (7.11 times the mean free path) is used. No additional optimizations or reference beams were used in the imaging system, revealing the robustness of the “LGDiffNet” network and the adaptability of the imaging system for practical applications in medical imaging.

Smith-Purcell radiation from helical grating to generate wideband vortex beams.

A broadband vortex beam generator provides a promising solution for various applications. Since the space-charge wave of the free-electron bunch inherently covers a wide frequency range, the free-electron-driven devices can be utilized to generate broadband radiation. This work presents a wideband tunable multi-mode vortex beam generator based on the Smith-Purcell radiation (SPR) from a helical grating. The generated broadband vortex radiation presents prominent flexibility in the manipulation of frequency, topological charge, and radiation direction. The frequency range and the topological charge depend on the operating harmonic order, operating voltage, and structural parameters. The radiation direction varies with the operating frequency and covers a wide range in each band. Moreover, the proposed principle can be scaled to the terahertz frequency band. This work advances the application of the vortex beam in the millimeter wave-terahertz communication system.

Multi-beam multi-mode vortex beams generation based on metasurface in terahertz band

The generating of vortex beams in the terahertz (THz) band attracts significant attention due to their applications in high-speed communication and high-resolution imaging. In this article, a novel reflective metasurface working in the THz band is designed to generate four vortex beams with different topological charges in different directions. The unit cell is designed based on the geometric phase, and it consists of two metallic (gold) layers and one dielectric layer in between. The top layer of the unit cell includes an elliptic patch and a circular ring, and the bottom layer of the unit cell is a metallic ground. The reflection efficiency of the unit cell is very high due to the presence of metallic ground. To break through the limitations of traditional methods, the metasurface is a good choice to generate beams that carry orbital angular momentum (OAM). Using the concept of geometric phase, the reflection phase of reflective circular polarization (CP) electromagnetic waves can be controlled in an ingenious way. Owing to the property of the geometric phase, inverse phase shift can be achieved for left-handed circular polarization and right-handed circular polarization waves. By utilizing this trait of geometric phase, one can decompose a linear polarization wave into two orthogonal circular polarization waves and control their properties respectively. By rotating the top layer of the unit cell, 360-degree phase shift and the phase distribution satisfying the requirement for generating the multi-beam multi-mode vortex beam can be achieved. In order to control the direction and the topological charge of each beam, based on the geometric phase, the theory of reflectarray and the phase composition principle, the phase distribution of the reflective metasurface is calculated to provide the phase compensation to make the vortex beams point to certain directions. It is worthwhile to point out that the method presented in this paper provides a way to generate complex multi-mode vortex beams in the THz band. The simulations and measurements show that the metasurface can generate four vortex beams with topological charges <i>l</i> = ± 1 and ± 2 in different directions in the THz band. These results also indicate that our design has great potential applications in wireless communication and high-resolution imaging.

Assembled medium: A route to the generation of vortex waves carrying orbital angular momentum with different modes

In this letter, a method for the generation of multimodal vortex waves carrying orbital angular momentum (OAM) is proposed based on the transformation optics concept. The device is equally divided into eight sectors assigned by transformed material parameters, which are determined by solving Laplace’s equation. Sectors with different phase variations from 0 to 2π can be judiciously shuffled to generate vortex beams with different modes. Full wave numerical simulations are performed to validate multimodal OAM beam generation functionality and broadband performance of the proposed device. Such an implementation method opens the door to the application of vortex waves carrying OAM in communication systems.

In brief

PAGE 476 Chinese researchers present an irregular pentagonal patch array antenna, featuring a multilayer structure to enable dual-band and multi-mode orbital angular momentum (OAM) generation. The proposed array has the potential generate 6 different OAMs in 3 frequency bands and may provide new ideas for generating multi-mode vortex electromagnetic waves. PAGE 482 A multiplier design technique for stochastic computing is presented. The proposed design offers exact output and latency in the order of 2N, where N = the input precision. Compared to state of the art deterministic methods, the proposed design is faster by a factor of 2N. The technique is verified by mathematical analysis and simulation. Schematic diagram of proposed antenna array's element PAGE 501 Researchers from the Republic of Korea demonstrate integrated one-dimensional optical phase arrays (OPAs) for wide-angle, two-dimensional beam-steering in a 26.5 mm2 area. The 2-D OPA consists of 16 1-D transversal steering OPAs, whose radiators have different grating periods – allowing assignment of different longitudinal angles. Carry save adder in proposed design for N = 3. Full adder and half adder are denoted by fa and ha respectively. PAGE 510 Chinese researchers present an edge-attention-based geodesic distance which can be applied to the simple linear iterative clustering (SLIC) framework for PolSAR image superpixel segmentation, improving performance without an increase in computational expense. Experiments show the superiority of the proposed distance both qualitatively and quantitatively. Structure and design parameters of the grating radiator. PAGE 490 A collaboration of Chinese researchers propose two schemes to help prevent unwanted sideslip by wheeled mobile robots when turning. A controller is proposed combining robust control and model predictive control. Together the longitudinal velocity can be adjusted according to the state of the robot, whilst the model predictive control is used to achieve path tracking. Superpixel segmentation on PolSAR images over Changle using SLIC with the proposed distance. Fuzzy-NMPC system structure.

Generating the dual‐band and multimode OAM by irregular pentagonal patch antenna array

This Letter presents an irregular pentagonal patch array antenna with a multilayer structure for dual-band and multimode orbital angular momentum (OAM) generation. An irregular pentagonal patch antenna with U-shaped slots resonating at different frequencies is designed as the array's element. The proposed antenna array consists of two uniform circular microstrip antenna arrays and two phase-shifting feeding networks. It can be used to generate OAM mode l = − 1, 1 at 3 GHz and OAM mode l = −2, 2 at 6 GHz. The simulated near-field phase distributions images of different OAM modes are obtained, which have verified the OAM generation. This proposed array antenna has the possibility to generate a total of six different OAMs in three frequency bands, by changing the number of array elements and optimising the irregular pentagonal patch antenna. This design may provide a new idea for the generation multimode vortex electromagnetic wave.