Hybrid metal wire-dielectric terahertz waveguides: challenges and opportunities [Invited]

In this review we evaluate recent experimental and theoretical progress in the development of wire-based waveguides used for practical low-loss and low-dispersion delivery of terahertz radiation. Waveguides considered in this review utilize plasmonic modes guided in the air gap between two parallel wires. The two parallel wires are, in turn, encapsulated inside of a low-loss, low-refractive-index micro- or nano-structured cladding that provides mechanical stability and isolation from the environment. We describe two alternative techniques that may be used to encapsulate the two-wire waveguides while minimizing the negative impact of dielectric cladding on the optical properties of the waveguide. The first technique uses low-density foam as a cladding material, while the other uses air-filled microstructured plastic claddings to support metallic wires. Additionally, we offer a detailed analysis of the modal properties of wire-based waveguides, compare them with the properties of a classic two-wire waveguide, and present several strategies for the improvement of hybrid waveguide performance. Using the resonant dependence of the confinement properties of some hybrid plasmonic modes also allows us to propose their use in terahertz refractometry. Finally, we demonstrate that wire-based porous waveguides can have a very large operational bandwidth while supporting tightly confined, air-bound modes at both high and low frequencies. This is possible as, at higher frequencies, hybrid fibers can support ARROW-like low-loss air-bound modes while changing their guidance mechanism to plasmonic confinement in the inter-wire air gap at lower frequencies. (C) 2014 Optical Society of America