Delay-coupled semiconductor lasers near locking: a bifurcation study

We consider a system of two identical, but possibly detuned, spatially separated semiconductor lasers that are mutually coupled via their optical fields. In a rate equation approach this system can be modeled by a set of delay differential equations, where the delay takes into account the propagation time of the light from one laser to the other. The delay introduces a complicated structure the compound laser modes (CLMs) whose interaction may lead to complicated dynamics. In this paper we present a bifurcation study of the CLM structure for the relevant system parameters, including the pump current and the detuning. Initially stable CLMs can destabilizes in Hopf bifurcations that lead to complicated dynamics on different time scales. In particular, we concentrate on the dynamics near the boundary of locked dynamics of the two lasers. Depending on the pump current we find different scenarios for the route to locking as a function of the detuning between the two lasers.