Band relaxation triggered by modulational instability in topological photonic lattices

Modulational instability in topological photonic lattices enables the selective population of energy bands and generation of steady-state wavefields with well-defined topological invariants. This provides a way to measure bulk topological invariants, which determine the number of robust edge modes appearing at the lattice edges via the bulk-edge correspondence. Here we study numerically the process of wave thermalization arising from modulational instability in topological bands. We apply a grand canonical approach to compute the effective temperature β and chemical potential μ of the steady-state wavefields. The steady-state wavefields exhibit a strong wavevector k -dependence of β and μ throughout the Brillouin zone, suggesting the existence of a long-lived pre-thermal phase and the absence of thermalization for the moderate propagation times accessible using topological photonic lattices.