Photonic topological insulators in femtosecond laser direct-written waveguides

Topological photonics attract significant interests due to their intriguing fundamental physics and potential applications. Researchers are actively exploring various artificial platforms to realize novel topological phenomena, which provides promising pathways for the development of robust photonic devices. Among these platforms, femtosecond laser direct-written photonic waveguides show unique ability to visualize intricate light dynamics in 2 + 1 dimensions, which rendering them ideal tools for investigating topological photonics. By integrating topological concepts into these waveguides, researchers not only deepen their understanding of topological physics but also provide potential methodology for developing advanced topological photonic integrated devices. In this review, we discuss recent experimental implementations of different topological phases within femtosecond laser direct-written photonic waveguides, as well as the fascinating physical phenomena induced by the interplay of topology with non-Hermiticity, nonlinearity and quantum physics are also introduced. The exploration of topological waveguide arrays shows great promise in advancing the field of topological photonics, providing a solid foundation for further research and innovation in this rapidly developing domain.