Abstract
This study investigates the effects of asymmetric coupling strength on nonlinear dynamics of two mutually long-delay-coupled semiconductor lasers through both experimental and numerical efforts. Dynamical maps and spectral features of dynamical states are analyzed as a function of the coupling strength and detuning frequency for a fixed coupling delay time. Symmetry in the coupling strength of the two lasers, in general, symmetrizes their dynamical behaviors and the corresponding spectral features. Slight to moderate asymmetry in the coupling strength moderately changes their dynamical behaviors from the ones when the coupling strength is symmetric, but does not break the symmetry of their dynamical behaviors and the corresponding spectral features. High asymmetry in the coupling strength not only strongly changes their dynamical behaviors from the ones when the coupling strength is symmetric, but also breaks the symmetry of their dynamical behaviors and the corresponding spectral features. Evolution of the dynamical behaviors from symmetry to asymmetry between the two lasers is identified. Experimental observations and numerical predictions agree not only qualitatively to a high extent but also quantitatively to a moderate extent.
Highlights
Nonlinear dynamics of two mutually delay-coupled semiconductor lasers has attracted much research interest due to its profound physics and promising applications
This suggests that if a specific dynamical behavior is used for applications where a difference in the coupling strength between the two lasers is likely to happen in order to achieve certain features or functionalities, care must be taken so that the laser system is operated at the same dynamical behavior even when the coupling strength becomes asymmetric during operation
The results demonstrate that the dynamical behaviors of the two lasers could become asymmetric when the coupling strength becomes highly asymmetric. This suggests that if both lasers are expected to simultaneously operate at a specific dynamical behavior all the time for applications, care must be taken either to avoid the operation of the laser system with highly asymmetric coupling strength, or to avoid the operation of the laser system over regions where symmetry breaking in the dynamical behavior happens
Summary
Nonlinear dynamics of two mutually delay-coupled semiconductor lasers has attracted much research interest due to its profound physics and promising applications. The answer to this question is important for fundamental understandings about how and to what extent such a laser system responds to asymmetric coupling strength, and for technological applications where such a laser system is expected to operate at a specific dynamical behavior all the time even when the coupling strength becomes asymmetric This issue has not been much emphasized yet, and is numerically and experimentally investigated in this study using two mutually coupled lasers with a delay time longer than the relaxation resonance period of the lasers at free running.
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