2D and 3D Terahertz Metamaterials: Design, Fabrication and Characterization

Abstract

Terahertz metamaterials become increasingly important as they can be made into various devices to manipulate terahertz waves in novel approaches, which cannot be realized by the natural materials. It is a critical problem that the metamaterials are limited in the narrow working band arising from the resonance properties. In order to cover a broadband working frequency band, this study covers the metamaterials design, fabrication, and characterization from two dimensional (2D) to three dimensional (3D) forms to achieve the resonance tunability by different means. A novel 3D `metamaterials tube? design was proposed and investigated for the first time to achieve passive broadband resonance tunability.

2D metamaterials with symmetry breaking were investigated to show the influence of structural parameters on the resonance behaviors. Laser micro-lens array lithography, which is a fast-speed fabrication means in parallel mode, was used to fabricate the terahertz metamaterials on the silicon substrates. A new characterization method, which measure polarization dependent loss, was applied to eliminate the side effect of the substrates on the detection, which can provide only the transmission properties of the metamaterials. Hybrid metamaterials, which combine several metamaterial unit cells designed with different structural parameters, were also studied to realize the broadband resonance performance.

In order to reduce the loss in the terahertz metamaterials, thin flexible multi-layer metamaterials were designed and constructed on the transparent polyethylene naphthalate (PEN) substrates. Two different 3D multi-layer metamaterials were made to achieve (1) enhanced resonance up to 10,000 times and (2) broadband resonance with the spectral bandwidth up to 0.38 THz.

3D metamaterials tubes by rolling up the 2D metamaterials into non-planar forms, were proposed to achieve a passive resonance tunability with blue-shift (a new finding) by varying the diameter of the metamaterials tube flexibly. This method can tune the resonance frequency from 0.75 to 1.13 THz, which is 2.5 times larger than the best published result so far which works in active tuning modes. This novel metamaterials tube can extend the resonance frequency range to cover the entire terahertz regime by the effective combination with conventional red-shift metamaterial devices.