Robust Integrated Ag/PP-PP/Ag Hollow Waveguide for Low-Loss and Low-Dispersion Transmission of Low-Frequency Terahertz Waves: Design, Fabrication and Performances

An integrated Ag/PP (polypropylene)-PP/Ag hollow waveguide (HWG) structure with low loss and dispersion was proposed based on analyses of the dispersion compensation and transmission loss of the Ag/PP HWG and PP/Ag HWG in low-frequency terahertz (THz) band. Theoretical simulations indicate that integration of a 5 mm bore Ag/PP HWG and a PP/Ag HWG with a 360 μm PP tube wall thickness by a length ratio of 2.87:10 could build up a HWG with near-zero dispersion and a low loss of 0.51–0.63 dB/m in 90-110 GHz band. A 91-cm-long flexible integrated Ag/PP-PP/Ag HWG sample was fabricated by plasma-aided chemical liquid phase deposition approach. The measured transmission loss of the HWG sample at 100 GHz changed from 2.02 to 3.35 dB/m when bent with a 15 cm radius from 0 to 150°. Terahertz time-domain spectroscopy (THz-TDS) analysis revealed that the dispersion of the integrated HWG was as low as 0.566 ps·GHz<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup>·m<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> at 100 GHz. After 10 cycles of anti-vibration test (scanning frequency range is 10-500 Hz), the integrated HWG sample showed almost unchanged dispersion and transmission loss. It could stably deliver THz wave under low (−78.5 °C) and high (65 °C) temperature conditions (output THz power fluctuation < 1.5%). The as-integrated Ag/PP-PP/Ag HWG has low dispersion, low loss, bendability and durability for transmitting low-frequency THz waves, which enables it to be a potential candidate for applications such as 6G communication, THz imaging, sensing, etc.