Flexible Bandwidth Broadening in Topological Waveguides

Topological photonic insulators, allowing wave propagating immune to disorders at the boundary, are promisingly applicable in photonic devices called topological waveguides. However, broadband topological waveguides designs are now lacked, which limits further applications of topological waveguides. Here, we propose and experimentally demonstrate a practical method on flexible bandwidth broadening in topological waveguides, by altering structure parameters while keeping materials unchanged. Inspired by bilayer graphene model, we construct a topological waveguide where transmission bandwidth can be broadened flexibly by adjustable interlayer couplings, while the interlayer coupling can be altered by interlayer distance. Experimental results validate the theoretical model, displaying that the relative bandwidth broadened from 7.3% to 16%. Our work focusing on bandwidth broadening will pave the way for further practical application such as perfect filters, splitters, and reflection-free delay-lines.