Photonic topological phase transition on demand

On-demand, switchable phase transitions between topologically nontrivial and trivial photonic states are demonstrated. Specifically, it is shown that the integration of a two-dimensional array of coupled ring resonators within a thermal heater array enables unparalleled control over topological protection of photonic modes. Importantly, auxiliary control over a spatial phase modulation opens up a way to guide topologically protected edge modes along generated virtual boundaries. The proposed approach can lead to practical realizations of topological phase transitions in many photonic applications, including topologically protected photonic memory/logic devices, robust optical modulators, and switches.