Abstract
The subject of this article is divided into two parts. Part 1: By measuring the spectral loss characteristics of subwavelength-diameter THz fibers, our study support the recent theory proposed by M. Sumetsky (Opt. Lett. 31, 870, 2006) that diameter-variation-induced-radiation is a dominant loss mechanism for subwavelength fibers in the low (＜1%) core-fraction-power regime. This physical mechanism limits the lowest guidable frequency in a subwavelength fiber. Part 2: Furthermore, we demonstrated a THz directional coupler for future millimeter wave communication systems. By using subwavelength polyethylene fibers, we successfully established a single-mode fiber-based THz directional coupler. Unlike traditional directional couplers, the coupling ratio of our demonstrated sub-wavelength directional fiber coupler is independent of the length of the coupling region because of the anti-symmetric mode cutoff.