Topological photonic crystal fibre

TL;DR

This paper introduces a novel photonic crystal fibre design utilizing topological crystalline insulator principles, enabling low-loss, bend-resistant light transmission with potential for advanced optical applications.

Contribution

The work demonstrates a new PCF design based on topological bandstructure, confirmed by theoretical analysis and experimental validation, offering improved bending resistance over conventional fibres.

Findings

Low losses of 10-20 dB/km in topological fibre

Bending losses are minimal and comparable to straight fibre

Topological modes enable new functionalities in optical fibres

Abstract

Photonic crystal fibres (PCFs) are optical fibres that guide light using a modulated dielectric medium. They provide an exceptionally versatile platform for various applications, thanks to the flexibility with which light-guiding can be customised by modifying the fibre geometry. Here, we realise a PCF with guided modes produced by photonic bandstructure topology rather than conventional mode-trapping mechanisms. The design, which is compatible with the stack-and-draw fabrication process, consists of a cross-sectional photonic topological crystalline insulator with a disclination. A bulk-defect correspondence produces degenerate topological modes, lying below the cladding light line. We use various theoretical methods to confirm their topological origins, including a spectral localiser that makes minimal assumptions about the bandstructure. Our experiments on the fabricated topological fibre show it transmitting visible to near-infrared light with low losses of 10--20 dB/km, which do not increase much when the fibre is bent. A comparable solid-core PCF of conventional design exhibits substantially higher bending losses. Optical fibres based on topological modes thus hold promise for improved performance and novel functionalities.