Analysis of OAM Performance Using Metalenses of Different Resolutions

Yin Li,Baiyang Liu,Sirong Li,Sai-Wai Wong

doi:10.1109/access.2021.3076776

Yin Li, Baiyang Liu + Show 2 more

Open Access

https://doi.org/10.1109/access.2021.3076776

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Abstract

Recently, metasurfaces have been extensively studied, especially in connection with the construction of orbital angular momentum (OAM)-carrying beams. However, the dependence of OAM performance on the resolution of unit cells remains to be investigated. In this paper, 27 types of metalenses of varying phase resolutions (1-bit, 2-bit, and 3-bit) and with unit cells of varying width resolutions ( $1\lambda _{0}$ , (1/2) $\lambda _{0}$ , and (1/3) $\lambda _{0}$ ) were designed to analyze this dependence via simulation. A thorough analysis of the simulated results, including the radiation pattern, the near-field amplitude, the near-field phase, and the OAM mode purity, revealed that the OAM performance of a metalens improves with an increase in resolution. In addition, even metalenses of 1-bit phase resolution and $1\lambda _{0}$ width resolution were observed to exhibit OAM mode purities higher than 88%. We expect the conclusions of this study to be useful as guidelines during the future design of OAM metalenses or metasurfaces.

Highlights

Electromagnetic (EM) beams conduct both momentum and angular momentum
Various metalenses of different resolutions, constructed using cuboid media, were analyzed in this paper to determine the dependence of the performance of orbital angular momentum (OAM) waves on the phase resolution (1-bit, 2-bit, and 3-bit) and width resolution (1λ0, (1/2)λ0, (1/3)λ0) of the unit cell
It is evident from the simulated results that an increase in the resolution of the metasurface increases the mode purity of the generated OAM wave

Summary

INTRODUCTION

Electromagnetic (EM) beams conduct both momentum and angular momentum. The angular momentum of an EM comprises two components—spin angular momentum (SAM) and orbital angular momentum (OAM). In [31], two rhombic patches placed on two layers were used to design a reflect array capable of generating wideband circularly polarized OAM vortex waves in the X-band. To overcome the inefficiency and narrow bandwidth of the vortex beam generator, the authors in [33] used the Pancharatnam-Berry metasurface to generate wideband OAM waves over the 6.95 −18 GHz range (>82%). To this end, a ring-surrounded bowtie patch, which served as the unit cell of the metasurface, was designed to control the phases of the scattered fields and ensure the generation of multiple OAM modes, l = 0, +1, +2 [33]. The conclusions of this study are expected to simplify the design methodology of OAM metasurfaces in the future

THEORETICAL DESIGN

OAM METALENSE WITH DIFFERENT RESOLUTIONS

Findings

CONCLUSION