  Dissipative solitons are self-localised structures that can persist
indefinitely in "open" systems characterised by continual exchange of energy
and/or matter with the environment. They play a key role in photonics,
underpinning technologies from mode-locked lasers to microresonator optical
frequency combs. Here we report on the first experimental observations of
spontaneous symmetry breaking of dissipative optical solitons. Our experiments
are performed in a passive, coherently driven nonlinear optical ring resonator,
where dissipative solitons arise in the form of persisting pulses of light
known as Kerr cavity solitons. We engineer balance between two orthogonal
polarization modes of the resonator, and show that despite perfectly symmetric
operating conditions, the solitons supported by the system can spontaneously
break their symmetry, giving rise to two distinct but co-existing vectorial
solitons with mirror-like, asymmetric polarization states. We also show that
judiciously applied perturbations allow for deterministic switching between the
two symmetry-broken dissipative soliton states, thus enabling all-optical
manipulation of topological bit sequences. Our experimental observations are in
excellent agreement with numerical simulations and theoretical analyses.
Besides delivering fundamental insights at the intersection of multi-mode
nonlinear optical resonators, dissipative structures, and spontaneous symmetry
breaking, our work provides new avenues for the storage, coding, and
manipulation of light.
