Fabrication of terahertz hollow-glass metallic waveguides with inner dielectric coatings

Abstract

Hollow-core glass waveguides (HCWs) with inner coatings of silver and polystyrene (PS) have been fabricated for transmission of terahertz radiation. A liquid-phase chemical deposition process was used to deposit silver and PS thin film coatings inside glass tubing. The PS dielectric layer can substantially lower the loss of the HCW compared to the metal-only waveguide. A polymer coating was chosen because it is possible to deposit the dielectric film thickness required for operation in the terahertz regime. Specifically, the dielectric film thickness is proportional to the wavelength so the PS coatings need to be on the order of 10 to 15 μm to minimize transmission losses at terahertz frequencies. This is much thicker than the submicron thick dielectric coatings needed in the IR region. The thickness of the PS film depends on the concentration of PS in the coating solution and the coating rate. Both of these parameters are studied and related to the losses in the waveguides. The lowest loss of 0.95 dB/m at 119 μm (2.5 THz) was obtained for hybrid HE mode propagation in a waveguide with a 8.2 μm thick PS film deposited inside a 2.2 mm bore, 90 cm long glass tube.