Ling-Jun Yang

A new method is proposed for detecting orbital angular momentum (OAM) in the microwave frequency band to address current detection challenges. Based on the principles of geometric coordinate transformation, this approach employs an azimuthal-quadratic phase reflective surface to achieve the conversion between OAM and focused electric field patterns at different azimuth coordinates on the receiving plane. This is the first application of an azimuthal-quadratic phase reflective surface in the detection of OAM in the microwave frequency band. To validate the proposed method, an azimuthal-quadratic phase reflective surface was designed, followed by a detailed analysis of its various parameters. Finally, the proposed method is verified through experiments. The results demonstrate good consistency between the simulated and measured outcomes.

This letter proposes a new method for controlling the divergence angles of multi-mode orbital angular momentum (OAM) vortex beams. A geometric framework is established that allows for the same divergence angle across different OAM modes, which addresses a significant challenge in multi-mode systems. Proposed method combines one-dimensional linear array theory and the design of OAM beams with an equal divergence angle. By adjusting element phases, precise divergence control is achieved without altering the metasurface structure. The method's effectiveness is verified through theoretical synthesis, full-wave simulations, and experimental validation. This approach offers accurate control over a wide range of angles, demonstrating potential applications in communication systems.

Multimode vortex beams, especially if carrying modes are tailorable without crosstalk, possess ubiquitous applications from optical to radio fields. However, most of the metasurfaces demonstrated so far, for example phase-only ones, only provide phase manipulation to generate multimode vortex waves, leading to unexpected crosstalk modes. In this paper, we propose a reflection-type broadband amplitude-phase metasurface to generate broadband and crosstalk-free multimode vortex beams, which have also been theoretically verified. Specifically, the dipole-loaded quasi-I-shaped meta-atoms are applied to achieve broadband-independent controls of reflection amplitudes within a range of [0, 0.95] and a 360° phase coverage from 8.6 to 17.8 GHz. Inspired by the amplitude-modulated (AM) technology in the time domain, we mainly investigate the AM vortex beams in the space domain, which belong to multimode vortex beams that have spatially varying amplitude along the azimuth. Finally, two broadband amplitude-phase metasurfaces are devised to generate crosstalk-free AM vortex beams in both simulation and experiment. Those AM vortex beams have spatially tailored amplitude and phase patterns, which can promote the development of multimode communication and other beam-control applications.

This article presents a novel continuous meta-grating array (MGA) for the generation of ultra-wideband, near-perfect orbital angular momentum (OAM) beams with extremely high mode purity. First, a novel dielectric-doping strategy is proposed to overcome the inherent narrowband characteristics of conventional grating atoms, resulting in an ultra-wideband dielectric-doping meta-grating atom (DDGA). By establishing an equivalent circuit model (ECM), the operational mechanism is analyzed. The design method is provided to establish clear DDGA design guidelines to follow. Simulation and ECM calculations reveal that within the 9.06–19.88 GHz (74.7%), the circularly co-polarized reflection coefficient and polarization conversion ratio exceed 99.7% and 98.7%, respectively. Subsequently, a space-variant sub wavelength MGA is generated using grating functions. The continuous grating array ensures the continuity of the reflected field, thereby avoiding beam distortions and low mode purity that may result from potential mutual coupling and diffraction effects caused by discontinuities in traditional metasurfaces. In the 9.0–21.0 GHz (80.0%), the MGA is capable of generating near-perfect vortex beams, ranging from low-orders to high-orders, with extremely high purity and very low mode crosstalk. In addition, it demonstrates frequency-aperture size insensitivity and dual-wideband properties, facilitating miniaturization and size customization while delivering high-performance OAM in the high-frequency 37–50 GHz. Finally, experimental validation confirms the effectiveness.

The wavefront control of spin or orbital angular momentum (OAM) is widely applied in the optical and radio fields. However, most passive metasurfaces provi

Conical beam antenna plays a significant role in providing stable access to satellite signals for moving communication terminals. Although metasurfaces have been used to generate conical beams, most of them can only reflect conical beams with identically distributed and mirror-symmetric phase responses for left-hand circular polarization and right-hand circular polarization, which can hinder the dual-polarization applications of metasurfaces. In this study, a metasurface is designed to independently manipulate dual-polarized excitations in broadband. To achieve the broadband control of conical beams, broadband conditions for both geometric and propagation phases are developed. Differently, metasurface designed in this study consists of three types of distinguishingly shaped elements, which can provide more degree of freedom in dual-polarization broadband design. In addition, a design method is developed for metasurface to generate the cone angle tailorable conical beams. Via fabricating a metasurface following the proposed method, the designed metasurface is verified in theorem, simulation, and experiment that it can generate desired conical beams with tailored divergent angles and phase responses covering a bandwidth from 12.5 GHz to 17 GHz.

This article presents a deep-learning-based approach to quantitatively extract misalignment information in the orbital angular momentum (OAM) radio communication systems. It is shown that the misaligned field exhibits unique sequence-based features for different misalignment information. Consequently, recurrent neural network, as a powerful method to deal with sequential data, is introduced to extract its intrinsic features and estimate the misalignment values. To further reduce the total number of parameters as well as improve the performance, a gated recurrent unit is employed to construct the recurrent layer. As far as we know, this is the first use of deep learning for the estimation of the OAM misalignment information in radio frequency. The setup of the training data and the performance of the proposed model under four different misalignment cases are demonstrated. To further validate the reliability of the proposed models, the trained model is evaluated on the sample carrying 20% Gaussian noise. Further, the effects of the position deviation and the number of samples are also investigated. Besides, the comparison with other methods are presented. It is illustrated that the tailored model can reach the same measurement resolution as the previous literatures while requiring only one-eighth of the sampling points.

Achieving 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.

Vortex beams carrying orbital angular momentum (OAM) are widely applied in various electromagnetic, optical, and quantum systems. A tailored OAM spectrum composed of several specific modes as expected holds a promise for expanding the degrees of freedom of the systems. However, such a broadband high‐purity tailored spectrum is difficult to be achieved by the present devices, where the broadband amplitude manipulation is not explored yet. In this work, inspired by the envelope‐modulation theory, an elegant and universal way to manipulate the OAM spectrum in wide bandwidth is proposed by using a shape‐tailored metasurface. First, the rotating meta‐atoms on a triangular lattice are proved to have smaller coupling distortion than that on a square lattice, and this behavior is critical for high‐purity vortex spectrum generation by the Pancharatnam–Berry‐based metasurfaces. Second, a universal modulation relation is established between the spatial arrangement of metasurfaces and the generated vortex beams. Finally, the broadband‐modulated OAM spectra and the comb‐like OAM spectra are theoretically and experimentally demonstrated by the shape‐tailored metasurfaces. The proposed amplitude‐modulation scheme offers a novel concept and engineering route to manipulate the OAM spectrum in wide bandwidth, which can promote the development of OAM‐based applications.