Experimental Realization of a Reflections-Free Compact Delay Line Based on a Photonic Topological Insulator

TL;DR

This paper demonstrates a novel, compact photonic delay line using topologically protected surface waves, enabling reflection-free, multi-wavelength delays around sharp bends, advancing photonic device design.

Contribution

First experimental realization of a topologically protected photonic delay line, overcoming scattering limitations in inhomogeneous media.

Findings

TPSWs experience reflection-free delays around sharp curves

The device operates across multiple wavelengths

It enables ultra-compact, efficient photonic buffers

Abstract

Electromagnetic (EM) waves propagating through an inhomogeneous medium inevitably scatter whenever electromagnetic properties of the medium change on the scale of a single wavelength. This fundamental phenomenon constrains how optical structures are designed and interfaced with each other. Recent theoretical work indicates that electromagnetic structures collectively known as photonic topological insulators (PTIs) can be employed to overcome this fundamental limitation, thereby paving the way for ultra-compact photonic structures that no longer have to be wavelength-scale smooth. Here we present the first experimental demonstration of a photonic delay line based on topologically protected surface electromagnetic waves (TPSWs) between two PTIs which are the EM counterparts of the quantum spin-Hall topological insulators in condensed matter. Unlike conventional guided EM waves that do not benefit from topological protection, TPSWs are shown to experience multi-wavelength reflection-free time delays when detoured around sharply-curved paths, thus offering a unique paradigm for compact and efficient wave buffers and other devices.