Terahertz (THz) radiation has important applications in spectroscopy, imaging, and space science. For some of these applications, in particular spectroscopy, a flexible fiber optic could potentially simplify the THz system and enable the user to transmit radiation to remote locations without excessive absorption by atmospheric moisture. To date THz fiber optics and waveguides have been limited to rigid hollow metallic waveguides, solid wires, or short lengths of solid-core transparent dielectrics such as sapphire and plastic. In this paper we report on flexible, hollow polycarbonate waveguides with interior Cu coatings for broadband THz transmission fabricated using simple liquid-phase chemistry techniques. The losses for these hollow-core guides were measured using a tunable, cw single-mode far IR laser. The losses for the best guides were found to be less than four dB/m and the single mode of the laser was preserved for the smaller bore waveguides. Loss calculations of the loss for the HE11 mode reveal that the metal-coated hollow waveguides have much higher loss than for waveguides coated with both metallic and dielectric thin films.
Hollow glass waveguides (HGWs) have been fabricated with CdS and PbS dielectric coatings deposited on Ag. HGWs were fabricated with both single layer CdS and PbS coatings on Ag and with multilayer CdS/PbS coatings on Ag. The straight and bending losses for the Ag/metal-sulfide HGWs have been measured at 10.6 μm. Single layer Ag/metal-sulfide HGWs have theoretical losses comparable to the traditional Ag/AgI fibers, but the transmission range can be extended to wavelengths as short as 500 nm for CdS films. The use of multiple metal-sulfide layers can reduce the losses substantially, with a theoretical 3-fold reduction in loss using a 3 layer CdS/PbS/CdS stack. The measured losses of metal/metal-sulfide HGWs are higher than predicted by theory. A single layer CdS HGW has a loss 3-4 times higher than Ag/AgI. A single layer Ag/PbS HGW has a loss 8 times higher than Ag/AgI. A 3-layer Ag/CdS/PbS/CdS have a loss 50% lower than single layer Ag/CdS