Dynamical scenarios of mutually delay-coupled semiconductor lasers in the short coupling regime

We present experimental and numerical studies of the dynamics of two delay-coupled device-identical semiconductor lasers. We concentrate on the regime of short delay times where the coupling delay is comparable to the period of the relaxation oscillation frequency. We find characteristic scenarios in the intensity dynamics depending on the spectral detuning and the coupling phase. For small spectral detuning, the coupled lasers lock to the same frequency and exhibit stable emission. For larger detuning, we find pronounced oscillations of the output intensity. The frequency of oscillation shows a stair-like behavior which depends on the detuning frequency, the coupling time and the coupling phase. In addition, the coupling phase also affects the oscillation frequency and the phase relation between the two oscillating lasers.