  We report on the experimental observation of bunching dynamics with temporal
cavity solitons in a continuously-driven passive fibre resonator. Specifically,
we excite a large number of ultrafast cavity solitons with random temporal
separations, and observe in real time how the initially random sequence
self-organizes into regularly-spaced aggregates. To explain our experimental
observations, we develop a simple theoretical model that allows long-range
acoustically-induced interactions between a large number of temporal cavity
solitons to be simulated. Significantly, results from our simulations are in
excellent agreement with our experimental observations, strongly suggesting
that the soliton bunching dynamics arise from forward Brillouin scattering. In
addition to confirming prior theoretical analyses and unveiling a new cavity
soliton self-organization phenomenon, our findings elucidate the manner in
which sound interacts with large ensembles of ultrafast pulses of light.
