Nonlinear Dynamics of Mutually Coupled Semiconductor Lasers

We theoretically investigate the nonlinear dynamics and synchronization
properties of two self-oscillating semiconductor lasers due to feedback.
The model is based on modified single-mode rate equations for the
intracavity photon and carrier densities. We provide a detailed
stability and bifurcation analysis of the fixed points upon variation of
the coupling and feedback strengths as well as the associated delay
times. This allows us to predict a new scenario for the ``death by
delay\\\\\\\'\\\\\\\' phenomenon where the delay time in the interaction between the
physical units is not essential. We consider both oscillatory and
chaotic behavior of the solitary lasers by changing the feedback
conditions. We observe different types of synchronization including
identical, anti-phase, and out of phase, as well as several
symmetry-breaking bifurcations. When the lasers operate as two chaotic
oscillators, we find that the isochronal (zero-lagged) state is stable
within a large region in the parameter space. We also found that the
width of the frequency lockbands (Arnold tongues) of two slightly
mismatched lasers shows an interesting dependence with the coupling
delay time.