Orbital Angular Momentum Vortex Research Articles

Radiation Performance Synthesis for OAM Vortex Wave Generated by Reflective Metasurface

The radiation performance of orbital angular momentum (OAM) vortex waves (OAMVWs) generated by reflective metasurface is comprehensively investigated. According to different incident sources, the issue is classified into two cases, namely, the plane-wave incidence and the focused incidence. In both cases, the radiation performance deteriorates with the increasing of topological charge $l$ . Moreover, the largest $l$ that can be generated is limited by the scale of the metasurface. In addition, a detailed analysis reveals that phase quantization affects the lobe levels of OAMVWs but has no influence on the divergence angle of the main lobe. Nevertheless, for the case of plane-wave incidence, 1-bit phase quantization method is not able to generate OAMVWs in normal direction and will cause grating lobe when the beam scans. Meanwhile, the grating lobe carries OAM with opposite $l$ against the main lobe. Finally, a focused-feed metasurface based on 1-bit phase quantization is simulated and measured. The simulation and measurement results show that OAMVW with topological charge $l=1$ is successfully generated and detected, validating the effectiveness of phase quantization method in OAMVW generation. It is worth to point out that phase quantization is highly promising in electronic-controlled reconfigurable OAMVW generation.

Generation and Analysis of High-Gain Orbital Angular Momentum Vortex Wave Using Circular Array and Parasitic EBG with oblique incidence

This paper presents an effective method for high-gain orbital angular momentum (OAM) vortex wave generation based on the integration of a circular antenna array (CAA) with a parasitic electromagnetic band gap (EBG) structure, which is referred to as the EP-CAA. The resonant height of the EBG structure at different oblique incidences is analyzed parametrically based on the defect mode transmission mechanism to achieve reasonable predictions of a consistent 3-dB gain bandwidth with optimal gain enhancement for different OAM modes. The effective radiation aperture of the EP-CAA at oblique incidence is proposed for analytical calculation of the aperture efficiency of the OAM beams (OAM-AE). A Wilkinson power divider (W-PD) is designed to extend the operating bandwidth of the EP-CAA, and the proposed W-PD arrangement is applicable for feasible OAM modes. Fabricated prototypes of the EP-CAA carrying four OAM modes operating at 10 GHz are measured to verify the effectiveness of the theoretical analysis, the maximum realized gain for different OAM modes are confirmed to be enhanced by at least 6 dB in 5% 3-dB gain bandwidth. The divergence angles of different OAM modes can be effectively concentrated using the proposed EP-CAA.

Generation, reception and separation of mixed-state orbital angular momentum vortex beams using metasurfaces

In this paper, metasurfaces are designed, fabricated and experimentally demonstrated to transmit and receive a mixed-mode orbital angular momentum (OAM) vortex wave. Firstly, the theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce the mixed-state vortex wave. Then, simulations and near-field scanning experiments are performed to verify that mixed-state vortex waves can be generated and received by using metasurfaces. The receiving experiments for mixed-mode OAM beam are conducted in the near-field zone, covered frequency band from 4.5 GHz to 7.0 GHz. In transceiving experiments, the TX is the proposed reflective metasurface generating the mixed-state OAM wave (P = 2, l1 = 1, l2 = 2), which is composed of square loop elements. The RX is an OAM receiving metasurface composed by crossed dipole elements, which can receive OAM mode l = 1 in vertical polarization but OAM mode l = 2 in horizontal polarization. Experimental results show that mixed-state vortex waves can be detected, received and separated by pure OAM-mode transmitting and receiving reciprocal metasurfaces. The proposed method paves an effective way to generate and detect the OAM vortex wave of mixed modes for microwave wireless communication and detection applications.

High-efficiency measurement of all orbital angular momentum modes in a light beam

We present an experimental demonstration of a Laguerre–Gauss (LG) spectrum measurement technique using variable focus lenses that is able to measure the strengths of the constituent modes in an unknown incoming light beam with the highest possible efficiency. The experiment modifies the classical projective, phase flattening technique by including a variable-sized pinhole and a two-electronic-lens variable imaging system that is tuned for each mode to give the highest possible detection efficiency irrespective of the beam waist of the LG mode chosen for the projection/decomposition. The modified experiment preserves the orthogonality between the modes with only a 4% cross talk so that superposition states may also be detected efficiently. Our experiment results show efficient detection of orbital angular momentum vortex beams with topological charge l values ranging from 0 to 4, with various beam waists chosen for the decomposition.

Dual-polarization and dual-mode orbital angular momentum radio vortex beam generated by using reflective metasurface

A metasurface, which is composed of printed cross-dipole elements with different arm lengths, is designed, fabricated, and experimentally demonstrated to generate orbital angular momentum (OAM) vortex waves of dual polarizations and dual modes in the radio frequency domain simultaneously. The prototype of a practical metasurface is fabricated and measured to validate the results of theoretical analysis and design at 5.8 GHz. Numerical and experimental results verify that vortex waves with dual OAM modes and dual polarizations can be flexibly generated by using a reflective metasurface. The proposed method paves a way to generate diverse OAM vortex waves for radio frequency and microwave wireless communication applications.

Generating multiple orbital angular momentum vortex beams using a metasurface in radio frequency domain

In this paper, an electromagnetic metasurface is designed, fabricated, and experimentally demonstrated to generate multiple orbital angular momentum (OAM) vortex beams in radio frequency domain. Theoretical formula of compensated phase-shift distribution is deduced and used to design the metasurface to produce multiple vortex radio waves in different directions with different OAM modes. The prototype of a practical configuration of square-patch metasurface is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that multiple OAM vortex waves can be simultaneously generated by using a single electromagnetic metasurface. The proposed method paves an effective way to generate multiple OAM vortex waves in radio and microwave wireless communication applications.

Design, fabrication, and measurement of reflective metasurface for orbital angular momentum vortex wave in radio frequency domain

In this paper, a reflective metasurface is designed, fabricated, and experimentally demonstrated to generate an orbital angular momentum (OAM) vortex wave in radio frequency domain. Theoretical formula of phase-shift distribution is deduced and used to design the metasurface producing vortex radio waves. The prototype of a practical configuration is designed, fabricated, and measured to validate the theoretical analysis at 5.8 GHz. The simulated and experimental results verify that the vortex waves with different OAM mode numbers can be flexibly generated by using sub-wavelength reflective metasurfaces. The proposed method and metasurface pave a way to generate the OAM vortex waves for radio and microwave wireless communication applications.