  Localized dissipative structures (LDS) have been predicted to display a rich
array of instabilities, yet systematic experimental studies have remained
scarce. We have used a synchronously-driven optical fiber ring resonator to
experimentally study LDS instabilities in the strong-driving regime of the
AC-driven nonlinear Schr\"odinger equation (also known as the Lugiato-Lefever
model). Through continuous variation of a single control parameter, we have
observed a string of theoretically predicted instability modes, including
irregular oscillations and chaotic collapses. Beyond a critical point, we
observe behaviour reminiscent of a phase transition: LDSs trigger localized
domains of spatiotemporal chaos that invade the surrounding homogeneous state.
Our findings directly confirm a number of theoretical predictions, and they
highlight that complex LDS instabilities can play a role in experimental
systems.
