Synchronisation of unidirectionally coupled two-frequency chaotic lasers

The nonlinear behaviour of a pair of optically coupled semiconductor laser diodes is studied for different coefficients of optical coupling and different pump currents. As the pump current increases, the behaviour of the system undergoes several transformations from stationary behaviour to a periodic behaviour and then to chaos. Approximate formulas for the self-oscillation frequency of the system and other characteristics of the pair of lasers are derived as functions of the pump current. An analytic expression is found for the critical pump intensity above which there appears a non-zero average difference between the frequencies of the lasers. The behaviour of these regimes in the coupled lasers is characterised by the fixed phase incursion of the fields per period. The chaotic behaviour of two-section semiconductor lasers arranged in the controlling laser – slave laser configuration is studied numerically. The possibility of an almost complete synchronisation of the chaos is demonstrated in this scheme.