  Topological photonics provides a robust framework for strategically
controlling light confinement and propagation dynamics. By exploiting the
marriage between this notion and symmetry-constrained mode competition in an
active setting, we experimentally demonstrate, for the first time, a hybrid
silicon microlaser structure supporting a topologically protected zero-mode
lasing. This mode is distributed over an integrated array of optical
microrings, each supporting multiple modes that compete for gain. However, the
mode competition is diminished in favor of a pre-defined topological state,
which reflects the charge conjugation symmetry induced by the gain profile.
Robust single-mode operation in the desired state prevails even with
intentionally introduced perturbations. The demonstrated microlaser is
hybrid-implemented on a silicon-on-insulator substrate, thereby readily
suitable for integrated silicon photonics with potential applications in
optical communication and computing.
