Coupling between two fibre lasers with a common saturable absorber

Two independent fiber lasers coupled with a common fast saturable absorber are considered theoretically. It is shown that in the instability regime where the isolated lasers are self-pulsing, the coupling results in in-phase low frequency oscillations. In the stable regime, the relaxation oscillations exhibit a low frequency component. In addition, a large domain of bistability is found between the continuous behaviour and the self-pulsing regime.