Classical-to-Topological Transmission Line Couplers

TL;DR

This paper introduces a compact, efficient transition device that connects classical transmission lines to topologically nontrivial waveguides, enabling integration of topological photonics with conventional systems and demonstrating low-loss conversion.

Contribution

It presents a novel design for a classical-to-topological transmission line coupler with minimal loss and improved interface modifications, facilitating practical integration of topological waveguides.

Findings

Loss contribution of only 2.1% per conversion

Enhanced transmission through interface modifications

Foundation for integrating topological lines with classical systems

Abstract

Recent advances in topologically robust waveguiding for electromagnetic systems have presented opportunities for improving practical photonic and microwave devices. To bring this rich area of physics within the reach of application, it is critical for such systems to be interfaced with classical, continuous waveguiding and transmission line technology. This Letter presents a compact, highly efficient transition from a classical metallic transmission line to a topologically nontrivial line wave emulating the quantum spin Hall effect. A zero-gap antipodal slot line is used as the starting transmission line, which is then coupled to the topological metasurface via a field matching procedure. Additional modifications to the interface between the two structures to eliminate unwanted edge coupling improves transmission further. A simulated loss analysis isolates the effect of the transitions from the rest of the structure, showing a loss contribution of only 2.1% per classical-to-topological conversion. Using the transition, a quantitative characterization of the robustness of common topologically protected devices is presented. This design lays the foundation to integrate topologically robust metasurface transmission lines to traditional systems, opening the door to future uses of such structures in systems.