Characterization of terahertz propagation properties on subwavelength dielectric ribbon waveguides

Various subwavelength dielectric waveguides have been developed for imaging, sensing, and communication applications because of low-loss propagation and tailorable evanescent power distribution. Dielectric ribbon waveguides with high aspect ratio cores have lower attenuation and geometry-insensitive radiation loss compared with wire waveguides in a cylindrical core structure. This study experimentally characterizes the transmitted spectral properties of air-cladded polymer ribbons for waveguiding terahertz (THz) radiation and with aspect ratios above 200 under two orthogonally polarized wave excitations. The spectral dependence on the geometrical parameters of solid- and porous-core ribbon waveguides were completely investigated via THz time domain spectroscopy. For the first time, it is found that the measured spectral features of transverse electric (TE)-like modes, including the attenuation constant, effective refractive index, and transmission bandwidth, correlate to both the thickness and refractive index of a waveguide core, but those of transverse magnetic (TM)-like modes relate only to core thickness. The birefringence of the ribbon waveguide increases with the THz wave frequency and is large for thick or high-index ribbon cores because of the increased power ratio in the core for TE-like modes. For the dominant ribbon waveguide modes of TM-like modes, the average attenuation and delivered bandwidth at different ribbon thicknesses are successfully measured at ranges of 0.04–0.13 cm⁻¹ and 700–350 GHz, respectively, both of which are superior to those of TE-like mode and hybrid HE₁₁ mode for the polyethylene wire waveguide. Experimental results show that the polymer ribbon waveguide has potential for use in the building blocks of THz integrated circuits, THz wire communication, waveguide-based spectroscopy, and biochemical sensing applications.