Tailored Two-Wire Plasmonic Waveguides for Low-Insertion-Loss Terahertz Optical Circuits

The practical implementation of terahertz technologies is hindered by the lack of universal, low-loss waveguide platforms that deliver guided mode accessibility and multifunctional integration. The two-wire plasmonic waveguide offers a promising path toward cost-effective terahertz systems. However, waveguide circuits based on this platform still suffer from high insertion loss and limitations in coupling with other platforms. Herein, to overcome these fundamental bottlenecks, we propose novel two-wire plasmonic waveguide designs that introduce an additional degree of freedom for manipulating the guided wave. We propose waveguides with elliptical wire cross-sections and demonstrate two optimal configurations, i.e., one for minimal transmission loss (1.21 m−1) and another for a high-power coupling coefficient with rectangular waveguides at 140 GHz. Improvements in these designs over conventional cylindrical wire ones have been experimentally validated. Subsequently, we propose tapered two-wire waveguide components with gradually varying cross-sections to enable seamless integration between distinct waveguide designs, thereby permitting decoupled optimization of individual functional elements in waveguide circuits. A low-loss three-segment two-wire circuit configuration for interfacing with rectangular waveguides is demonstrated. We believe that the proposed customized wire profiles open prospects for tailoring terahertz guided waves with ease and flexibility, and their integration into plasmonic circuits facilitates global optimization of multiple functionalities, thereby offering a promising path toward practical, versatile terahertz systems, pending further optimization of coupling interfaces and fabrication processes.