Terahertz displacement sensing based on interface states of Hetero-structures

Herein, we propose a nano displacement sensor based on the interface state of a terahertz hetero-structure waveguide. The waveguide consists of two periodically corrugated metallic tubes with different duty ratios, which can result in similar forbidden bands in their frequency spectra. It was found that the topological properties of these forbidden bands are different, and the hetero-structure can be formed by connecting these two waveguides. In the hetero-structure waveguide, the interface state of an extraordinary transmission can always arise within the former forbidden bands, the peak frequency of which is highly dependent on the cavity length at the interface of the two periodic waveguides. So, by carefully designing the structure’s topological property, the hetero-structure waveguide can be efficiently used to produce a displacement sensor in the THz frequency range. The simulations show that the resolution of the displacement can be as small as 90 nm and the sensitivity can reach over 1.2 GHz/µm. Such a sensitive interface state of the proposed hetero-structure waveguide will greatly benefit THz applications of functional devices, including not only displacement sensors but also switches with high extinction ratios, tunable narrow-band filters, and frequency division multiplexers.