Momentum-Space Topological Effects of Nonreciprocity

TL;DR

This paper reviews how nonreciprocity influences topological effects in photonic systems, emphasizing momentum-space topology and recent magnet-less methods for achieving topological protection.

Contribution

It provides a comprehensive overview of the role of momentum-space topology in nonreciprocal photonics, including recent advances in magnet-less approaches.

Findings

Topological properties like Chern number explain back-scattering immune edge states.

Momentum-space Berry phase and connection are key to understanding wave propagation.

Recent magnet-less methods enable topological effects without magnetic materials.

Abstract

The connection between topology and nonreciprocity in photonic systems is reviewed. Topological properties such as Chern number, and momentum-space properties such as Berry phase and Berry connection, are used to explain back-scattering immune edge states and their topological protection. We consider several examples to illustrate the role of momentum-space topology on wave propagation, and discus recent magnet-less approaches.