Graphene and liquid crystals (LC) as emerging materials for the THz region are reviewed together with whispering gallery mode (WGM) resonators as fundamental building blocks for future THz applications.
Whispering gallery mode resonators can confine optical as well as THz radiation. The fundamental properties of resonators and, in particular, WGM resonators are discussed and applied to different experimental realizations of coupled resonators. Furthermore, an outlook on the very promising task of nonlinear frequency conversion between THz and optical light is given.
Liquid crystals are promising tunable materials for THz applications. The fundamental physical and electrical properties of nematic LCs in terms of molecule interaction, alignment, and tuning techniques are presented. Then, different characterization methods for the broad region of microwave to THz frequencies are reviewed for this emerging material class. Finally, possible applications based on LC material are described.
Graphene is another very promising material for THz applications. Its properties are introduced theoretically, highlighting exceptional effects such as Dirac‐like behavior of the charge carriers, extremely high carrier mobility, and carrier‐density‐dependent THz transmission properties. Several examples of promising applications, such as graphene‐based field effect transistors, switchable THz filters, and modulators are discussed.