Multiple Vortex Beams Research Articles

Heterogeneous‐Gradient Supercell Metasurfaces for Independent Complex Amplitude Control over Multiple Diffraction Channels

AbstractThe ability to achieve independent complex amplitude control across multiple channels can significantly increase the information capacity of photonic devices. Diffraction inherently holds numerous channels, which are good candidates for dense light manipulation in angular space. However, no convenient method is currently available for attaining this. Here, a flexible interference approach utilizing silicon‐based transmission‐type heterogeneous‐gradient supercell metasurfaces is proposed. By simply designing the phases of the meta‐atoms’ radiations within a supercell, the complex amplitude of each diffraction channel can be individually and analytically controlled. Crucially, the complex amplitudes of multiple diffraction channels can be simultaneously controlled in a non‐interleaved manner, where the number of channels is determined by the number of effective adjusting degrees of freedom (DoF). As a proof‐of‐concept validation, several meta‐devices are experimentally demonstrated in the terahertz regime, which can generate multiple vortex beams, focal points, and splitting beams in different desired diffraction angles. This advancement heralds a new pathway for the development of multifunctional photonic devices with enhanced channel capacity, offering significant potential for both research and practical applications in photonics.

Engineered 3D Vortex Array with Customized Energy and Topological Charges for Multi‐View Display

AbstractArrays of multiple vortex beams enhance parallel processing capabilities from particle manipulation to information communication. However, the spatial position, topological charge, and energy parameters of the vortex beams within the array have yet to be precisely controlled, posing significant challenges to the realization of multi‐view 3D Orbital Angular Momentum (OAM) display using vortex arrays as information carriers. To address this issue, a method for generating vortex arrays based on a phase‐only hologram, customizing the array by using the energy and OAM spectrum of each vortex beam as the loss function is developed. Experimental results indicate that a 2D array generates 100 vortex beams in the spatial frequency domain, while a 3D array in the Fresnel zone produces 252 vortex beams across 7 planes, each with 36 unprecedentedly controllable energy and topological charge vortex beams. Subsequently, images of 4 views using the 3D vortex arrays and decoded through coordinate transformation to achieve a multi‐view 3D OAM display are encoded. The results demonstrate imaging quality with Mean Peak Signal‐to‐Noise Ratio (MPSNR) of 12.7, 13.0, 13.4, and 12.2 dB in 4 views, respectively, offering promising opportunities for applications in 3D optical manipulation, high‐capacity communication, and 3D OAM holography.

Bidirectional multi-mode multiple vortex beams generator based on terahertz metasurface

Herein, we propose a vortex beam generator based on vanadium dioxide (VO2), which can switch between two operating modes (reflection and transmission) to generate bidirectional multi-mode multi-vortex beams across a wide frequency band range of 0.8 THz to 1.6 THz. By leveraging the transition of VO2 from the insulating state to the metallic state with temperature changes, the switching between transmission and reflection modes is achieved. Furthermore, through the application of the convolution and superposition theorem, the multiplexing of orbital angular momentum (OAM) is realized. Our work introduces a new method for multi-channel, multiplexed communication and imaging systems, and offers a novel approach to achieve powerful and flexible regulation of terahertz communication systems.

Double-slit experiment with multiple vortex beams

Double-slit experiment with multiple vortex beams

Terahertz metasurface for independent modulation of amplitude and phase in multi-channels

It is necessary to achieve simultaneous and independent modulation of the amplitude, polarization and phase of lights utilizing metasurface, which is also a great challenge. In this paper, an all-dielectric metasurface is proposed for simultaneously controlling the amplitude and phase of orthogonal linearly polarized lights in multi-channels. Three pairs of complex amplitude information are encoded in three independent channels by elaborately selecting and combining the meta-atoms. To verify the performance of proposed metasurface in the terahertz (THz) band, three examples are designed, including producing multiple vortex beams and arbitrary orbital angular momentum (OAM) superposition states, producing multiple foci with controllable intensity ratios, and producing multiple foci with controllable intensity ratios and focal lengths. The simulative results agree with experimental results. The proposed design based on single-layer structure has advantages of controllable focusing, compact structure, and simple fabrication, providing an alternative way for the preparation of integrated multifunctional and miniaturized optical devices.

Simultaneous recognition of the orbital angular momentum and phase singularity position of multiple vortex beams from speckle pattern via deep learning

The orbital angular momentum (OAM) carried by vortex beams can be used for encoding information in optical communications. The measurement of OAM is critical for these applications. However, traditional methods of measuring OAM are invalid in the presence of a scattering medium because the spiral wavefront of a vortex beam is distorted. To address this issue, we propose a deep learning-based method to simultaneously recognize the OAM and the position of the phase singularity from the speckle pattern generated by the propagation of vortex beams through a scattering medium. Our method achieves an accuracy of more than 98 % in identifying both the topological charge and singularity position information of multi-beam vortex beams with changing positions using deep learning technology. We also explore the minimum displacement accuracy that can be recognized by the neural network. When the displacement of the vortex beam with changing position is reduced to 1 pixel (12.5 µm), the information recognition accuracy remains above 95 %. Our method is a promising approach for accurate and efficient measurement of OAM and phase singularity position in the presence of scattering media.

Optical Encryption in the Photonic Orbital Angular Momentum Dimension via Direct-Laser-Writing 3D Chiral Metahelices.

Vortex beams, which intrinsically possess optical orbital angular momentum (OAM), are considered as one of the promising chiral light waves for classical optical communications and quantum information processing. For a long time, it has been an expectation to utilize artificial three-dimensional (3D) chiral metamaterials to manipulate the transmission of vortex beams for practical optical display applications. Here, we demonstrate the concept of selective transmission management of vortex beams with opposite OAM modes assisted by the designed 3D chiral metahelices. Utilizing the integrated array of the metahelices, a series of optical operations, including display, hiding, and even encryption, can be realized by the parallel processing of multiple vortex beams. The results open up an intriguing route for metamaterial-dominated optical OAM processing, which fosters the development of photonic angular momentum engineering and high-security optical encryption.

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.

Intense vortical-field generation using coherent superposition of multiple vortex beams

Coherent beam combining technology applied to multiple vortex beams is a promising method to generate high-power vortex beams. We utilize the coherent combination of multiple Laguerre-Gaussian beams at the waist plane and propose theoretically a practical generation system for a high-power beam carrying orbital angular momentum by considering oblique incidence. The results demonstrate that the orbital angular momentum distribution of the combined field is similar to that of a single Laguerre-Gaussian beam within the Rayleigh length. Moreover, the combined field has relativistic intensity local spots that exhibit stable spatial propagation. The proposed system may potentially be applied to intense vortical fields, large scale nuclear fusion device, such as suppressing stimulated Raman scattering and filamentation when a laser beam propagates in plasma.

Generating multiple vortex beams simultaneously and independently in different directions by elaborately splicing multiple transmissive metasurfaces featuring polarization isolation.

In this paper, by elaborately splicing multiple transmissive metasurfaces (MSs) featuring polarization isolation, multiple linear polarized (LP) vortex beams are generated simultaneously and independently in different directions. Specifically, by carefully optimizing the radius of the array and the distance between the MS and array, each MS generates a well-performed deflection vortex beam with a low side-lobe level and little diffraction, resulting in a minor effect on other deflection vortex beams. Subsequently, four transmissive MSs are elaborately spliced, showing the polarization isolation characteristic between the adjacent MS, and thereby each MS is only illuminated by the respective antenna array. In addition, each MS only generates the desired LP vortex beam, and the corresponding cross-polarization is suppressed. Finally, the simulation and measurement results show that multiple LP vortex beams carrying different orbital angular momentum (OAM) modes are generated simultaneously and independently in different directions, verifying the effectiveness of the proposed method.

Bifunctional Full-Space Metasurface Combining Pancharatnam–Berry and Propagation Phases

A bifunctional full-space metasurface (FS-MS) capable of generating reflective multiple vortex beams and focusing transmissive electromagnetic waves within different frequency bands is presented in this letter. The generation of vortex beams is based on the Pancharatnam–Berry (PB) phase, which exhibits the property of full phase control by rotating the orientation angle of an I-shaped patch. Meanwhile, this PB unit is backed by a metallic square loop frequency selective surface (FSS), which behaves as stopband and passband responses around 18 GHz and 12 GHz, respectively. By encoding PB phase to generate a certain phase response, four reflective vortex beams carrying orbital angular momentum (OAM) are achieved at a higher frequency band under normal incidence. On the other hand, the incident waves operating at a lower frequency band can pass through such an FSS-backed PB unit and be focused by a three-layer composite unit consisting of a polarization-conversion unit sandwiched by two orthogonal polarizers. Therefore, upon illumination of normal incident plane waves, the proposed FS-MS works as a multiple OAM beams generator and a focusing lens simultaneously. The proposed design can motivate the realizations of FS-MS and hold potential applications in intelligent housing systems.

Circularly Polarized Antenna Array with Decoupled Quad Vortex Beams.

Achieving multiple vortex beams with different modes in a planar microstrip array is pivotal, yet still extremely challenging. Here, a hybrid method combining both Pancharatnam−Berry (PB) phase that is induced by the rotation phase and excitation phase of a feeding line has been proposed for decoupling two orthogonal circularly polarized vortex beams. Theoretical analysis is derived for array design to generate quad vortex beams with different directions and an arbitrary number of topological charges. On this basis, two 8 × 8 planar arrays were theoretically designed in an X band, which are with topological charges of l1 = −1, l2 = 1, l3 = −1, and l4 = 1 in Case I and topological charges of l1 = −1, l2 = 1, l3 = −1, and l4 = 1 in Case II. To further verify the above theory, the planar array in Case I is fabricated and analyzed experimentally. Dual-LP beams are realized by using rectangular patch elements with two orthogonally distributed feeding networks on different layers based on two types of feeding: proximity coupling and aperture coupling. Both the numerical simulation and experimental measurement results are in good agreement and showcase the corresponding quad-vortex-beam characteristics within 8~12 GHz. The array achieves a measured S11 < −10 dB and S22 < −10 dB bandwidth of more than 33.4% and 29.2%, respectively. In addition, the isolation between two ports is better than −28 dB. Our strategy provides a promising way to achieve large capacity and high integration, which is of great benefit to wireless and radar communication systems.

Multichannel terahertz quasi-perfect vortex beams generation enabled by multifunctional metasurfaces

Abstract Vortex beams carrying orbital angular momentum (OAM) open a new perspective in various terahertz research. Multichannel and divergence controllable terahertz vortex beam generation holds the key to promoting the development of OAM related terahertz research. Here, we introduced and experimentally demonstrated quasi-perfect vortex beam (Q-PVB) with a controllable divergence angle independent of the topological charge and multichannel Q-PVBs generation with all-dielectric multifunctional metasurfaces. By superimposing specific phase functions together into the metasurfaces, multiple vortex beams and four-channel Q-PVBs with different topological charges are generated as well as focused at separated positions. High resolution characterization of terahertz electric field shows the good quality and broadband properties of Q-PVBs. Interestingly, compared with conventional perfect vortex beam; Q-PVB displays a smaller divergence angle and thinner ring width. The metasurfaces proposed here provide a promising avenue to realize multichannel vortex beams generation in compact terahertz systems; benefiting OAM related researches such as mode division multiplexing, vortex beam related plasmonic enhancement and spinning objective detection.

Measuring high-order multiple vortex beams with fork-shaped grating

Orbital angular momentum (OAM) is a degree of freedom independent of polarization and frequency of vortex beams. Therefore, the measurement of OAM has attracted great interest. In this paper, we propose a method to detect OAM beams utilizing far-field diffraction feature fringes caused by fork-shaped grating (FSG), which has characteristics of wide-range, high efficiency, and excellent extensibility for detection of high-order OAM beam. We give a detailed explanation of the concept and feature of FSG detection theoretically, and improve detection reliability of fringes by increasing the number of forks and setting appropriate offset. Experimentally, we achieve detection of OAM+50. Moreover, although only two OAMs were detected at the same time in our experiment, FSG can also be used in the detection of multi-OAM beams due to the excellent extensibility of this method. Our finding opens up a new method for the detection of high-order OAM and multi-OAM beams, which is of great significance to the application of FSG.

Generating Different Polarized Multiple Vortex Beams at Different Frequencies from Laminated Meta-Surface Lenses.

We demonstrate the generation of multiple orbital angular momentum (OAM) vortex beams with different radiating states at different frequencies through a laminated meta-surface lens consisting of a dual polarized meta-array interconnected with a frequency selective meta-array. The co-linearly polarized (LP) waves from the source can directly penetrate the meta-surface lens to form multiple OAM vortex beams at one frequency. On the other hand, the meta-surface lens will be capable of releasing the cross-LP counterparts at another frequency with high-efficient polarization conversions to have multiple OAM vortex radiations with different radiating directions and vortex modes. Our design, using laminated meta-surface lens to synthesize multiple OAM vortex beams with orthogonal polarizations at different frequencies, should pave the way for building up more advanced vortex beam communication system with expanded diversity of the meta-device.

Generation of Multiple High-Order Bessel Beams Carrying Different Orbital-Angular-Momentum Modes through an Anisotropic Holographic Impedance Metasurface

Conventional multiple vortex beams carrying different orbital-angular-momentum (OAM) modes propagating in different directions suffer from beam divergences along with the increasing transmission distance, which greatly limits their practical applications. This article presents a diffraction-resisting dual high-order Bessel-beam (DHOBB) generator based on an anisotropic holographic impedance metasurface (AHIM) operating at 30 and 30.5 GHz. By virtue of leaky-wave theory and the optical holographic principle, surface waves excited by a monopole antenna welded on the back of the metasurface can be modulated into nondiffractive DHOBBs. Different geometric parameters of the subwavelength meta-atoms can be mapped by the interference patterns between the reference surface waves and the desired beams. Furthermore, this designed single-layer anisotropic metasurface can be equivalent to the functionalities of spiral-phase-plate, refractive-hyperbolic, and axicon lenses synthetically utilized in the popular air-fed metasurface to generate HOBBs. Compared with the most popular air-fed metasurface, this design results in predominant performances of ultralow profile, easy fabrication, and integration with other electronic components and avoids alignment errors. Both simulated and measured results demonstrate that nondiffractive DHOBBs carrying different OAM modes can be generated by this designed AHIM. Nondiffractive DHOBBs with different Bessel orders with distinctive properties may open a window for wireless communications with multiarea coverage and multitarget radar detection.

Dual-frequency multiple compact vortex beams generation based on single-layer Bi-spectral metasurface

Vortex beams carrying orbital angular momentum (OAM) have attracted considerable attention owing to the potential to expand channel capacity of microwave and optical communication. However, the OAM generations usually suffer from divergence along propagation. In this work, we proposed a strategy to generate multiple vortex beams with compact energy distributions based on a single-layer reflective metasurface. First, the mechanism is developed for the generation of multiple compact vortex beams. Then, an advanced single-cell bi-spectral meta-atom, which is composed of a double C-shaped slot resonator and a modified double C-shaped resonator, is proposed to actualize independent geometric phase controls at two frequencies. As an illustrative example, a dual-frequency metasurface that can achieve four compact vortex beams (two beams at each frequency) with different OAM modes at 9 and 13 GHz is designed, and each OAM beam features a much more compact energy distribution compared to the conventional OAM beam. The measured results agree very well with the simulated results, which validate the proposed design methodology.

Measuring OAM by the hybrid scheme of interference and convolutional neural network

The atmospheric turbulence can cause wavefront distortion when vortex beam carrying orbital angular momentum (OAM) propagates in free space. This brings challenges to the recognition of OAM modes. To realize effective recognition of multichannel vortex beams in atmospheric turbulence, a hybrid interference-convolutional neural network (CNN) scheme is proposed. Here, we compare two different approaches to identify the topological charges under different turbulence levels: the first is based on CNN only and the second is the hybrid scheme of interference and CNN. The simulation shows that the recognition performance of multiple vortex beams under different turbulence levels is improved by our hybrid scheme. Compared with the traditional CNN-based method, the interference-CNN scheme can further identify the sign of topological charge. Moreover, we generalize its feasibility through different kinds of vortex beams with a radial index of p ≠ 0. This provides a versatile tool for large-capacity optical communication based on OAM modes.

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

Vortex beams have witnessed tremendous development in the past decade by exhibiting profound implications for both fundamental physics and a multitude of novel engineering applications. In this work, broadband high-efficiency multiple vortex beams with independent topological modes and inclination angles are generated leveraging an interleaved geometric-phase multifunctional metasurface operating in a very broadband frequency range. A set of meta-atoms are elaborately engineered to offer broadband high-efficiency complete phase control covering the entire 2π range. Multiple geometric-phase sub-arrays implemented by the designed meta-atoms are synthesized into one metasurface via a shared-aperture interleaved manner, in which each sub-array can be individually manipulated and serves as an independent channel for launching a vortex beam. According to the established design methodology, two vortex beams with topological modes of −1 and +2 and distinct inclination angles are generated by one metasurface. Experimental results are provided to corroborate the proposed mechanism for multiple vortex beams generation, which exhibit broadband and high-efficiency features. The presented multifunctional metasurface paves the way for the generation of broadband high-efficiency multiple vortex beams in the microwave, millimeter-wave and terahertz regions. This work is of significance for high-capacity wireless communication applications, high-efficiency manipulation of electromagnetic waves, and novel design of radar and imaging systems.

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface

Broadband high-efficiency multiple vortex beams generated by an interleaved geometric-phase multifunctional metasurface