Non-Hermitian topological photonics in coupled optical fibre loops

In this thesis, the interplay between topology, disorder, and dissipation is investigated both theoretically and experimentally. Embedded into the field of non-Hermitian physics, one-dimensional lattice models are studied, which are governed by a Schrödinger equation with a non-Hermitian Hamiltonian. These models are experimentally implemented by means of classical light propagation in coupled optical fibre loops. To begin with, the impact of stochastic dissipation on the spatial spreading of the singleparticle wavefunction is studied. Besides the resulting spectral localization, a novel and unexpected spatial delocalization is predicted and measured. Afterwards, a topological funnelling mechanism for light is presented and experimentally realized. The funnelling mechanism is based on non-Hermitian topology and due to its topological origin, the desired flow of light is robust against disorder. This thesis is concluded with the prediction and observation of a topological triple phase transition in a photonic quasicrystal. The triple phase transition involves the topology, the energy eigenstate localization, and the energy exchange with the environment, indicating a potentially close relation between these properties, which are commonly viewed as independent.