Active Dielectric Metasurfaces for Switchable Terahertz Beam Steering and Focusing

Kaiji Chen,Weili Zhang,Quan Xu,Qingwei Wang,Xueqian Zhang,Xieyu Chen,Jiaguang Han,Ziying Zhang,Tong Wu

doi:10.1109/jphot.2021.3054861

Kaiji Chen, Weili Zhang + Show 7 more

Open Access

https://doi.org/10.1109/jphot.2021.3054861

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Abstract

Conventional metasurfaces often manipulate light propagation in a passive way, which cannot satisfy the dynamic operation requirements of many practical applications. Integrating functional materials or components into the structure design is one effective method, which, however, often introduces additional loss to the resonances, thus greatly affecting the efficiency of modulation. Here, we numerically propose a reflection-type dielectric metasurface design that could allow switchable and efficient wavefront control in the terahertz regime. The metasurfaces are composed of dielectric structures suspended on a ground metallic film, which can exhibit different phase responses at different gap distances between them owing to the variation of the Fabre-Pérot (FP) resonance. Two metasurfaces are designed and numerically demonstrated, which can achieve mechanically switchable beam steering and wave focusing responses, respectively, by only changing the gap distance by a small range of 1/3 working wavelength. The maximum efficiency can reach around 89%. The proposed method provides a new avenue towards efficient and active terahertz wavefront control.

Highlights

Benefitting from the local engineering abilities of 2D subwavelength structures in manipulating the abrupt changes of the light’s amplitude, phase, and polarization state, metasurfaces have kept arousing tremendous interest over the past decade owing to their flexibility in controlling the output wavefronts in a desirable manner [1], [2]
The metasurfaces are composed of dielectric structures suspended on a ground metallic film, which can exhibit different phase responses at different gap distances between them owing to the variation of the Fabre-Pérot (FP) resonance
We have identified that the intrinsic physical mechanism of this modulation ability is the interplay between the Mie resonance in the silicon pillar and the FP resonance in the cavity between the pillar and the metallic film, where we prove it by an interference model

Summary

Introduction

Benefitting from the local engineering abilities of 2D subwavelength structures in manipulating the abrupt changes of the light’s amplitude, phase, and polarization state, metasurfaces have kept arousing tremendous interest over the past decade owing to their flexibility in controlling the output wavefronts in a desirable manner [1], [2]. Limited by the modulation range of the functional materials, the devices are often working in a low efficiency state, such as around the perfect absorption phase of the reflection-type metasurfaces [33], [34]. A novel type of electrical-controlled phase coding metasurfaces are proposed based on reflective-type plasmonic structures by integrating functional components, diodes, into the structure design in the microwave regime, which allows for freely wavefront control while being highly efficient [37], [38]. Such diodes can hardly be achieved for the higher frequency ranges

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