  Optically-coupled semiconductor laser arrays are described by coupled rate
equations. The coupled mode equations and carrier densities are included in the
analysis, which inherently incorporate the carrier-induced nonlinearities
including spatial hole burning and amplitude-phase coupling. We solve the
steady-state coupled rate equations and consider the cavity frequency detuning
and the individual laser pump rates as the experimentally controlled variables.
We show that the carrier-induced nonlinearities play a critical role in the
mode control, and we identify gain contrast induced by cavity frequency
detuning as a unique mechanism for mode control. Photon-mediated energy
transfer between cavities is also discussed. Parity-time symmetry and
exceptional points in this system are studied. Unbroken parity-time symmetry
can be achieved by judiciously combining cavity detuning and unequal pump
rates, while broken symmetry lies on the boundary of the optical locking
region. Exceptional points are identified at the intersection between broken
and unbroken parity-time symmetry.

Optics