The effect of dielectric absorption on the transmission characteristics of terahertz hollow fibers

Hollow fiber with internal metal and dielectric coating films is one of the promising media for THz transmission. Although the dielectric layer can effectively reduce the transmission loss, it brings additional loss due to its absorption. It has been shown in mid-infrared region that the optimum thickness of the dielectric layer becomes smaller due to absorption. For terahertz hollow fibers, the film thickness of the dielectric layer become much larger and the transmission characteristics are more dependent on the dielectric absorption. The influences of dielectric absorption on the structure parameters of the dielectric-coated metallic hollow fibers are discussed. Calculation results show that the optimum refractive index of the dielectric layer, which is 1.41 for perfect transparent dielectrics, turns out to be greater. The absorption tolerance is also investigated considering the factors of inner diameter, the refractive index, and the transmission wavelength. It is shown that absorption tolerance decreases when the inner diameter becomes smaller or when the transmission wavelength becomes larger. In extreme cases of small inner-diameter or large transmission wavelength, the absorption tolerance is not existent. Because the loss of the dielectric-coated metallic hollow fiber is larger than that of metallic hollow fiber even the dielectric layer has no absorption. The calculation results are helpful to the structure design and material selection in the fabrication of terahertz hollow fibers.