  Topological photonics has recently emerged as a route to realize robust
optical circuitry, and nonlinear effects are expected to enable tunability of
topological states with the light intensity. Here we realize experimentally
nonlinear self-induced spectral tuning of the electromagnetic topological edge
states in an array of coupled nonlinear resonators in a pump-probe experiment.
In a weakly nonlinear regime, we observe that resonators frequencies exhibit
spectral shifts, that are concentrated mainly at the edge mode affecting only
weakly the bulk modes. For a strong pumping, we describe several scenarios of
the transformation of the edge states and their hybridization with bulk modes,
and also predict a parametrically driven transition from topological to
unstable regimes.
