Bowtie Nanoantenna Array Integrated With Artificial Impedance Surfaces for Realizing High Field Enhancement and Perfect Absorption Simultaneously

Mohamad Khoirul Anam,Sangjo Choi

doi:10.1109/access.2020.2997680

Mohamad Khoirul Anam, Sangjo Choi

Open Access

https://doi.org/10.1109/access.2020.2997680

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Abstract

High field enhancement and near-perfect absorption in nanoantennas were realized by using in-plane (between nanoantenna arms), out-of-plane (between nanoantenna and reflector), and array coupling (between nanoantennas in an array); however, it was challenging to satisfy both conditions at the same time. In this paper, we show that a bowtie nanoantenna array integrated with an artificial impedance surface can simultaneously satisfy both high field enhancement and perfect absorption. The artificial impedance surface is implemented as a metallic patch array on a grounded 50 nm-thick SiO2 substrate with reactive impedance surface (RIS) or high impedance surface (HIS) characteristic. Through the proposed design methodology, we designed a bowtie nanoantenna array on an optimum RIS patch array and achieved a high field enhancement factor (E/E0) of 228 and a nearly perfect absorption rate of 98% at 230 THz. This novel design outperforms the previously reported nanoantenna structures and the same bowtie nanoantenna array designed using a conventional grounded SiO2. We also show that the HIS-integrated bowtie antenna array cannot realize both goals at the same time because the highly reflective HIS cannot guarantee perfect absorption. The proposed RIS-combined nanoantenna array with high field enhancement and near-perfect absorption can be used for efficient infrared (IR) and optical detectors, sensors, and energy harvesting devices.

Highlights

Nanoantennas have been attracting attention as devices capable of concentrating and enhancing diffraction-limited light within subwavelength sizes and absorbing incident light efficiently [1]–[3]
To improve the field enhancement of the nanoantennas, researchers have been actively utilizing three methods: 1) in-plane coupling between two metallic arms of the nanoantenna [15], [16], 2) out-of-plane coupling between the nanoantenna and its image using a dielectric spacer with a metallic reflector or film [17], and 3) coupling between nanoantenna elements using nanoantenna array structures [18]–[20]
It is important to note that the thickness (80 nm) of SiO2 for achieving the maximum field enhancement lies between a quarter-wavelength inside SiO2 (225 nm) and an ultra-thin thickness such as 40 nm, which indicates that the radiation and absorption are balanced

Summary

INTRODUCTION

Nanoantennas have been attracting attention as devices capable of concentrating and enhancing diffraction-limited light within subwavelength sizes and absorbing incident light efficiently [1]–[3]. Instead of using an ultra-thin substrate with a metallic reflector, we utilized an artificial impedance surface to simultaneously fulfill the high field enhancement (> 200) and perfect absorption (> 98%) of a bowtie nanoantenna array in the IR range. The final bowtie nanoantenna array integrated with the optimum artificial impedance surface showed an almost perfect absorption of 98% at 230 THz λ = 1.3 μm) with a superior field enhancement factor (E/E0) of 228. This field enhancement is ∼1.4 times higher than the maximum value of 160 from similar nanoantenna array structures [23]–[28]. That realizes the maximum field enhancement and perfect absorption at the desired wavelength and analyzed the coupling phenomena between the artificial impedance surface and the nanoantenna structure

NUMERICAL SIMULATION

METALLIC PATCH ARRAY DESIGN FOR HIS AND RIS

Findings

VIII. CONCLUSION