Optical spectrum behaviour of a coupled laser system under chaotic synchronization conditions

Synchronization characteristics of two bidirectionally coupled semiconductor lasers, one operating in a chaotic regime with low-frequencyfluctuations and the other with free laser beam emission, were experimentally investigated. The chaotic synchronization regimes and opticalspectral behavior of the coupled system were analyzed with respect to the optical spectra emitted initially by the two uncoupled lasersoperated under the same feedback conditions. It was observed that the number of synchronization regimes that can be obtained and theirstability depend on the similarity of spectral structures of the uncoupled lasers emissions. The dominant active laser modes of the coupledsystem emission coincide with the laser modes of the one or both uncoupled laser emissions, depending on the operating synchronizationregime. We have associated changes in the optical spectrum of the coupled system with the synchronization regimes. The repartition ofpower between the active modes of a coupled system allows identification of the synchronization regime