Phase-modulation based transmitarray convergence lens for vortex wave carrying orbital angular momentum

Abstract

Vortex electromagnetic (EM) waves hold promise for their ability to significantly increase the transmission capacity of wireless communication systems via the torsion resistance defined by different topological charges associated with the orbital angular momentum (OAM). However, the application of vortex waves in remote distance transmission is limited by its characteristic of divergence. In this paper, a lens based on a phase-modulation metasurface (MS) is proposed that enables vortex EM waves to converge, thereby improving their propagation performance at microwave frequencies. A phase-shift distribution on the plane of the MS is obtained based on the concept of the optical converging axicon, which can convert a Laguerre-Gaussian (LG) beam to a Bessel beam based on changing the propagation direction. Simulation results verify the ability of the MS lens to achieve OAM beam focusing, which is advantageous for enhancing the propagation directivity and increasing the gain in the main lobes of vortex waves. This is of particular importance in microwave wireless communication applications.

A Review of Orbital Angular Momentum Vortex Beams Generation: From Traditional Methods to Metasurfaces

“…Afterwards, electromagnetic band-gap (EBG) superstrate was used to achieve high gain OAM vortex waves [46]. Lenses based on the use of metasurfaces [47,48] and all-dielectric materials [49,50] have further been applied to reduce beam divergence of OAM vortex waves generated by phased antenna arrays.…”

“…However, the limitation of this method is that it can only focus the beam to a point close to the metasurface rather than propagating over a long distance. In Reference [47], a flat metalens was proposed to collimate the vortex waves (Figure 14a). The converging lens system is excited by an OAM beam generator composed of a conventional circular patch antenna array source consisting of eight patches with the same phase shift between each of the neighboring elements.…”

“…The frequency bandwidth was about 8 GHz around 10 GHz operating frequency thanks to the use of all-dielectric non-resonant unit cells. [47]. (b) A collimating all-dielectric metamaterial medium [50].…”

Multifunctional Geometric Metasurfaces Based on Tri‐Spectral Meta‐Atoms with Completely Independent Phase Modulations at Three Wavelengths

“…A plethora of fascinating metadevices based on metasurfaces have been designed and demonstrated, including metasurfacebased lenses or metalenses, [5][6][7] cloaking, [8] meta-holograms, [9][10][11][12][13] and vortex beam generators. [14][15][16] However, the wavelength-dependent behavior of the metasurface is one of the main drawbacks in most reported metadevices, especially the ones depending on spatially varying phase profiles. Besides, in order to satisfy the development of multifunctional detection and multispectral analysis, [17][18][19][20] metasurfaces that could realize different functionalities at different wavelengths are highly desired.…”

Generation of E-band metasurface-based vortex beam with reduced divergence angle

“…Using the above-mentioned methods, various metasurface structures for vortex beam generation have been studied in the recent past; however, due to the unavoidable beam divergence of vortex beams with the characteristics of Laguerre-Gaussian (LG) type waves 16,[23][24][25][26] , their practical implementation in free-space wireless-communication system is limited. Recently, several studies focused on reducing the divergence angles of OAM beams by applying meta-lens structures in the radio frequency (RF) range have been reported [26][27][28][29] . To manage the explosive increase in data capacity, research has been conducted on the use of communication links based on OAM multiplexing in the millimeter E-band frequency range 30,31 , but studies on controlling the divergence angles of OAM beams in this frequency range have not been conducted yet.…”