Terahertz Metamaterials for Free-Space and on-Chip Applications: From Active Metadevices to Topological Photonic Crystals

Abstract

Terahertz (THz) waves have exhibited promising applications in imaging, sensing, and communications, especially for the next-generation wireless communications due to the large bandwidth and abundant spectral resources. Modulators and waveguides to manipulate THz waves are becoming key components to develop the relevant technologies where metamaterials have exhibited extraordinary performance to control free-space and on-chip propagation, respectively. In this review, we will give a brief overview of the current progress in active metadevices and topological photonic crystals, for applications of terahertz free-space modulators and on-chip waveguides. In the first part, the most recent research progress of active terahertz metadevices will be discussed by combining metamaterials with various active media. In the second part, fundamentals of photonic topological insulations will be introduced where the topological photonic crystals are an emerging research area that would boost the development of on-chip terahertz communications. It is envisioned that the combination of them would find great potential in more advanced terahertz applications, such as reconfigurable topological waveguides and topologically-protected metadevices.

Emerging Trends, Applications, and Fabrication Techniques in Photonic Crystal Technology

“…In traditional photonic crystals, light propagation is governed by the bandgap, a frequency range where certain wavelengths of light cannot propagate through the crystal. However, in topological photonic crystals, protected edge or surface states exist within the bandgap due to the nontrivial topology of the crystal's structure [25,26].…”

“…One of the significant advantages of topological photonic crystals is their potential for creating low-loss waveguides and on-chip optical circuits. By exploiting the topological edge states, light can be guided along specific paths without suffering significant losses due to scattering or other forms of energy dissipation [25,28].…”

Literature Review on Recent Advances on Terahertz Antenna Design

“…THz metamaterial-based sensors utilize pseudo-surface plasma effects to amplify incident THz waves, improving signal quality. By incorporating semiconductors in multilayer structures, design flexibility is increased while maintaining negative permittivity for metamaterial integrity [21]. Active meta devices and topological photonic crystals are advancing THz applications, enabling control over free-space propagation and on-chip waveguides.…”

Recent Advances in Terahertz Manipulations Using C‐Shape‐Split‐Ring‐Resonator Metasurfaces (Review)

“…[55,56] Researchers have proposed various THz metasurfaces utilizing different elements such as metal rods, [57,58] grids, and patches, [59] C-shape-split-ring resonators (CSRRs), [60] V-shape resonators, [61] all-dielectric structures, [62,63] and photonic crystals. [64] Among these, metasurfaces based on CSRRs have gained particular popularity and widespread adoption in the THz frequency range. Compared to other structures, CSRRs offer several primary advantages.…”