Optical mode enabled manipulation of topological phase in waveguide-based scattering networks

In a topological system with an edge, the number of edge states is typically determined by the bulk topological invariant, as per the well-established bulk-boundary correspondence. However, anomalous topological edge states can arise in periodically driven Floquet systems even when the bulk Chern number is zero. A topological invariant (winding number) has been introduced to establish the appropriate bulk-boundary correspondence in such systems. Nevertheless, manipulating the topological properties of systems, whether static or driven, remains a significant challenge. In photonic systems, optical fields with diverse inherent dimensions such as frequency and polarization offer a natural avenue for topological-phase manipulation. In this paper, we present an alternative scheme for switching the topological invariant (winding number) of the system by changing the optical-waveguide mode within an integrated waveguide-based scattering network. With creating a bonding interface, this topological-phase switching facilitates the transmissions of the interface state in different directions. Experimental validation of this concept is demonstrated using a ring-optical-waveguide device. In this paper, we introduce an alternative strategy for tailoring the topological properties of optical systems.