Work

Hollow-core antiresonant THz waveguides based on polymer- and metal-coated sapphire tube

Year: 2026

Type: article

Abstract: While the existing terahertz (THz) fiber optics components suffer from high loss and dispersion, low technological reliability, poor environmental resistance and radiation strength, as well as large cross-section, THz applications in different fields still require hardware for the sensing and exposure of hard-to-access objects. To mitigate this difficulty, we develop the two variants of hollow-core THz waveguides, those exploit the antiresonant reflecting optical waveguiding (ARROW) mechanism and use (as a key element) a few-millimeter-diameter sapphire tube produced by the edge-defined film-fed growth (EFG) technique. In the all-dielectric arrangement, the outer surface of this tube is coated by a sub-millimeter-thick polytetrafluoroethylene (PTFE) film, while in the metal-coated one-by a sub-micrometer-thick reflecting copper layer. These coatings increase the guiding efficiency and underlie different performance of the two geometries. Both waveguides are studied numerically and experimentally in the 0.56-0.7 THz frequency range. The observed discrepancies between the theoretical and measured propagation loss are attributed to fluctuation of the cross-section geometry over the waveguide length. In narrow frequency bands, the metal-coated waveguide offers the propagation loss as small as 5.0 dB/m, which is significantly lower than that of the all-dielectric one. Furthermore, the outer metal coating completely prevents mode leakage, whereas in an all-dielectric waveguide, some of the evanescent field extends into the surrounding space and still can be de-coupled. Our findings highlight that the ARROW sapphire THz waveguides provide a reasonable compromise between the guiding efficiency and the cross-section dimensions, thus, forming a favorable platform for the THz sensing and exposure.

Source: Scientific Reports

DOI: 10.1038/s41598-026-50305-8