Topological one-way fiber of second Chern number

TL;DR

This paper introduces topological one-way optical fibers based on second Chern number physics, enabling scattering-immune, reflection-free light propagation with potential applications in communications and sensing.

Contribution

It proposes a novel design of 3D photonic crystal fibers that utilize second Chern number topological protection for unidirectional light transmission.

Findings

Fibers are immune to Rayleigh and Mie scattering.

Fresnel reflection is eliminated, removing the need for isolators.

Modes are topologically protected by second Chern number in 4D parameter space.

Abstract

Optical fiber is a ubiquitous and indispensable component in communications, sensing, biomedicine and many other lightwave technologies and applications. Here we propose topological one-way fibers to remove two fundamental mechanisms that limit fiber performance: scattering and reflection. We design three-dimensional~(3D) photonic crystal fibers, inside which photons propagate only in one direction, that are completely immune to Rayleigh and Mie scatterings and significantly suppress the nonlinear Brillouin and Raman scatterings. A one-way fiber is also free from Fresnel reflection, naturally eliminating the needs for fiber isolators. Our finding is enabled by the recently discovered Weyl points in a double-gyroid~(DG) photonic crystal. By annihilating two Weyl points by supercell modulation in a magnetic DG, we obtain the photonic analogue of the 3D quantum Hall phase with a non-zero first Chern number~($C_1$). When the modulation becomes helixes, one-way fiber modes develop along the winding axis, with the number of modes determined by the spatial frequency of the helix. These single-polarization single-mode and multi-mode one-way fibers, having nearly identical group and phase velocities, are topologically-protected by the second Chern number~($C_2$) in the 4D parameter space of the 3D wavevectors plus the winding angle of the helixes. This work suggests a unique way to utilize higher-dimensional topological physics without resorting to artificial dimensions.