Experimental demonstration of topological slow light waveguides in valley photonic crystals

TL;DR

This paper experimentally demonstrates topological slow light waveguides in valley photonic crystals, showing efficient, robust light transmission with high group index and protection against bends, advancing topological photonics applications.

Contribution

It provides the first experimental realization of topological slow light waveguides in valley photonic crystals with demonstrated robustness and high group index.

Findings

Topological mode achieved group index over 30.

Light transmission maintained through sharp bends.

Topological mode outperforms non-topological mode in waveguiding efficiency.

Abstract

We experimentally demonstrate topological slow light waveguides in valley photonic crystals (VPhCs). We employed a bearded interface formed between two topologically-distinct VPhCs patterned in an air-bridged silicon slab. The interface supports both topological and non-topological slow light modes below the light line. By means of optical microscopy, we observed light propagation in the topological mode in the slow light regime with a group index $n_{\rm g}$ over $30$. Furthermore, we confirmed light transmission via the slow light mode even under the presence of sharp waveguide bends. In comparison between the topological and non-topological modes, we found that the topological mode exhibits much more efficient waveguiding than the trivial one, elucidating topological protection in the slow light regime. This work paves the way for exploring topological slow-light devices compatible with existing photonics technologies.