Terahertz 3D bulk metamaterials with randomly dispersed split-ring resonators

Taiyu Okatani,Yoshiaki Kanamori,Yuto Sunada,Kazuhiro Hane

doi:10.1515/nanoph-2021-0703

Abstract

Abstract While optical systems using terahertz wave are expected to achieve beneficial applications, at present, the materials of the optical elements that compose them must be selected from limited choices. In this study, we propose a three-dimensional bulk metamaterial in which metal microstructures are dispersed in the bulk resin randomly. A bulk metamaterial was designed and fabricated, in which split-ring resonators known as typical metamaterials were dispersed in cyclo-olefin polymer. In the fabrication method, a resin sheet containing split-ring resonators was first prepared and then diced into resin grains containing a single split-ring resonator. Finally, they were filled in a mold and solidified with a resin solution to obtain the target bulk metamaterial. The optical properties of the fabricated bulk metamaterial were measured by terahertz time-domain spectroscopy. The measurement results confirmed that the refractive index deviated from the original refractive index of the cyclo-olefin polymer due to the resonance of split-ring resonators, suggesting that the proposed bulk metamaterials could be used as a new optical material in the terahertz band.

Highlights

Terahertz wave is an electromagnetic wave at a frequency of approximately 0.1–10 THz
The measurement results confirmed that the refractive index deviated from the original refractive index of the cyclo-olefin polymer due to the resonance of split-ring resonators, suggesting that the proposed bulk metamaterials could be used as a new optical material in the terahertz band
Metamaterials may provide design freedom for refractive index and solve the shortage of optical materials in the terahertz band, many of them reported far are not bulk materials like natural materials that make up ordinary lenses and prisms but two-dimensional (2D) materials like thin films, in which the microstructures are periodically arranged on the surface of the substrate

Summary

Introduction

Terahertz wave is an electromagnetic wave at a frequency of approximately 0.1–10 THz. Depending on the design of the microstructure, the effective permittivity of the medium containing the structure, as well as the magnetic permeability, which should normally be 1 in the light region, can be controlled to the desired value [18] Taking advantage of this feature, various metamaterial-based applications such as sensors [19–25], modulators for phase, amplitude, frequency, or polarization [26–31], absorbers [32, 33], wavelength-selective filters [34, 35], quarter-wave plate [36], and light emitting elements [37] have been shown. Metamaterials may provide design freedom for refractive index and solve the shortage of optical materials in the terahertz band, many of them reported far are not bulk materials like natural materials that make up ordinary lenses and prisms but two-dimensional (2D) materials like thin films, in which the microstructures are periodically arranged on the surface of the substrate. After fabricating the prototype of the bulk metamaterial, the optical properties are measured to verify that the anisotropy seen in the metasurface is eliminated in the 3D bulk metamaterial

Design and simulation

Fabrication

Optical properties

Conclusions