  We report the first observation of lasing in topological edge states in a 1D
Su-Schrieffer-Heeger active array of resonators. We show that in the presence
of chiral-time ($\mathcal{CT}$) symmetry, this non-Hermitian topological
structure can experience complex phase transitions that alter the emission
spectra as well as the ensued mode competition between edge and bulk states.
The onset of these phase transitions is found to occur at the boundaries
associated with the complex geometric phase- a generalized version of the Berry
phase in Hermitian settings. Our experiments and theoretical analysis
demonstrate that the topology of the system plays a key role in determining its
operation when it lases: topologically controlled lasing.
