  On-demand, switchable phase transitions between topologically non-trivial and
trivial photonic states are demonstrated. Specifically, it is shown that
integration of a 2D array of coupled ring resonators within a thermal heater
array enables unparalleled control over topological protection of photonic
modes. Importantly, auxiliary control over 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.
