Entrainment of Optical Low-Frequency Fluctuations is Enhanced by Coupling

The control of the low-frequency fluctuations exhibited by two mutually coupled semi-conductor
lasers is studied experimentally and numerically. We observe that coupling
enhances the response of the system to a weak periodic modulation of the injection cur-rent
of one of the lasers, leading to a highly efficient entrainment of both laser outputs,
in the form of synchronized and periodic power dropouts. We compare the quality of the
entrainment with the one obtained in a single semiconductor laser with optical feedback,
showing the beneficial role of coupling in this pursuit. The experimental observations are
satisfactorily reproduced by numerical simulations of a set of coupled delay-differential
rate equations.