Dynamics of two semiconductor lasers coupled by a passive resonator.

The stability of two semiconductor lasers that are spatially separated by a passive resonator is analyzed using the composite-cavity mode approach. We study the nonlinear interactions of three composite-cavity modes and identify regions of in-phase and out-of-phase laser locking in the parameter plane of the transmission coefficients of the coupling mirrors and the laser length difference. Bifurcation analysis shows that the structure of the locking regions strongly depends on (i) the length of the passive resonator and (ii) the amount of amplitude-phase coupling of the laser field. Specifically, we find a single locking region when the passive resonator and the lasers have comparable lengths and up to three separate locking regions when the passive resonator is much shorter than the lasers. Furthermore, we use the recently developed 0-1 test for chaos to uncover intricate regions of chaotic dynamics that shrink in size and eventually disappear as the passive resonator length becomes comparable to the laser length.

Locking behavior of three coupled laser oscillators.

Single-frequency operation or locking in a lateral array of three laser oscillators is studied within the composite-cavity-mode approach. We compute the regions of stable locking, which have a nontrivial shape in the plane of coupling strength versus frequency detuning. The locking regions depend drastically on the amount of amplitude-phase coupling of the lasing field that is quantified by the alpha parameter. For small alpha, locking is possible for arbitrary coupling, but only if the middle laser has sufficient frequency detuning from the two outer lasers. In contrast, for larger alpha, locking is only possible for weak to moderate coupling, provided that all three lasers have similar frequencies.

Dynamics of two laterally coupled semiconductor lasers: strong- and weak-coupling theory.

The stability and nonlinear dynamics of two semiconductor lasers coupled side to side via evanescent waves are investigated by using three different models. In the composite-cavity model, the coupling between the lasers is accurately taken into account by calculating electric field profiles (composite-cavity modes) of the whole coupled-laser system. A bifurcation analysis of the composite-cavity model uncovers how different types of dynamics, including stationary phase-locking, periodic, quasiperiodic, and chaotic intensity oscillations, are organized. In the individual-laser model, the coupling between individual lasers is introduced phenomenologically with ad hoc coupling terms. Comparison with the composite-cavity model reveals drastic differences in the dynamics. To identify the causes of these differences, we derive a coupled-laser model with coupling terms which are consistent with the solution of the wave equation and the relevant boundary conditions. This coupled-laser model reproduces the dynamics of the composite-cavity model under weak-coupling conditions.

Feedback phase sensitivity of a semiconductor laser subject to filtered optical feedback: experiment and theory.

We investigate experimentally and theoretically the dynamics of a semiconductor laser subject to filtered optical feedback. Depending on the feedback strength we find dynamical regimes with different dependence on the feedback phase. In particular, the influence of the feedback phase on cw emission and on frequency oscillations is characterized experimentally. We also measure the dependence of the filter mirror distance on the frequency oscillations. In general, good agreement between experiment and theory is found.

Frequency versus relaxation oscillations in a semiconductor laser with coherent filtered optical feedback.

We investigate the dynamics of a semiconductor laser subject to coherent delayed filtered optical feedback. A systematic bifurcation analysis reveals that this system supports two fundamentally different types of oscillations, namely relaxation oscillations and external roundtrip oscillations. Both occur stably in large domains under variation of the feedback conditions, where the feedback phase is identified as a key quantity for controlling this dynamical complexity. We identify two separate parameter regions of stable roundtrip oscillations, which occur throughout in the form of pure frequency oscillations.

Synchronization of delay-coupled oscillators: a study of semiconductor lasers.

Two delay-coupled semiconductor lasers are studied in the regime where the coupling delay is comparable to the time scales of the internal laser oscillations. Detuning the optical frequency between the two lasers, novel delay-induced scenarios leading from optical frequency locking to successive states of periodic intensity pulsations are observed. We demonstrate and analyze these dynamical phenomena experimentally using two distinct laser configurations. A theoretical treatment reveals the universal character of our findings for delay-coupled systems.