Abstract-Dynamic Terahertz Plasmonics Enabled by Phase‐Change Materials

Young‐Gyun Jeong, Young‐Mi Bahk,  Dai‐Sik Kim,

https://onlinelibrary.wiley.com/doi/10.1002/adom.201900548

Phase‐change phenomena have been an attractive research theme for decades due to the dynamic transition of material properties providing extraordinary capabilities for versatile optical device applications. Even at the terahertz (THz) frequency regime, phase‐change materials (PCMs) promote the development of dynamic devices, especially when combined with a plasmonic approach delivering strong field enhancement and localization. According to the design of plasmonic metamaterials or hybrid composites, PCMs can actively modulate the electromagnetic properties of THz waves through thermal, electrical, and optical means. In turn, THz waves can affect the PCM properties in the nonlinear regime due to the intense field strength enhancement by plasmonic structures. Here, a few types of PCMs demonstrating promising potential in THz plasmonic applications are introduced. Starting from the best‐known transition metal oxide, vanadium dioxide (VO2), which possesses an insulator‐to‐metal phase transition near room temperature, superconductors, chalcogenides, ferroelectrics, liquid crystals, and liquid metals are covered along with their phase‐change properties and the control mechanisms infused with THz plasmonic applications. The corresponding recent progress presenting how PCMs combined with plasmonic structures can demonstrate effective THz modulation is reviewed. This general overview may provide a better understanding of dynamic THz plasmonics and new ideas for future THz technology.

Abstract-Active Thermal Control of 5 nm Gap Terahertz Antennas

Hyeong Seok Yun  Jeeyoon Jeong,   Dasom Kim,   Dai‐Sik Kim,

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/adom.201800856

Metallic nanostructures are combined with various active materials for electrical, optical, and thermal modulations of their optical properties. In particular, for the thermal modulation, deformation of metallic nanostructures at high temperatures limits the applications to relatively low temperatures, where thermal expansion of metals is negligible. Here, a unique regime is reported where terahertz (THz) waves transmitting through 5 nm wide slot antennas can be significantly modulated via controlled thermal expansion of metals without active materials. The normalized amplitude is modulated by 20% and the resonant frequency by 22% at an elevated temperature of 150 °C, indicating a decrease in the gap width by 50%. The extreme width‐to‐length ratio of the THz slot antennas compensates the small thermal expansion coefficient of metals, enabling the gap width to be considerably changed. COMSOL simulation and coupled‐mode method (CMM) calculation quantitatively support the experimental data. This works suggests a new possibility of thermally active metallic nanostructures.