The work in this thesis is focused on the complex dynamics of semiconductor laser (SL) devices which receive time-delayed feedback from an external cavity or are delay-coupled with a second semiconductor laser. We investigate fundamental properties of the dynamics and study the utilization of transient complex dynamics of a single SL arising from delayed feedback and external signal injection for a neuro-inspired photonic data processing scheme. Based on experiments and numerical modelling, we investigate systems of two coupled SLs, gaining insights into the role of laser and coupling parameters for the synchronization characteristics of these systems. We link certain features of the synchronization dynamics, like intermittent desynchronization events, to the underlying nonlinear dynamics in the coupled laser system.
Our research thus combines both fundamental insights into delay-coupled lasers as well as novel application perspectives.
In order to explore the capabilities of a single SL with delayed feedback, we follow the concept of reservoir computing (RC) based on delay systems. In particular, we study two different tasks, which are computationally hard for traditional computing concepts. We explore several feedback configurations, data injection methods and operating regimes of the laser and identify the task-dependent optimal operating conditions. Our work demonstrates the potential of simple photonic setups and the RC concept for future computational paradigms.
Furthermore, we study the synchronization properties in systems of two delay-coupled SLs with relay. We explore the consequences of asymmetries in this basic setup for the dynamics and synchronization properties. One key question is, how synchronization decays or is lost, which is of significant importance for applications in chaotic communications schemes and key-exchange protocols. We follow an event-based approach and connect changes in the synchronization levels for varying operating parameters or varying mismatches to the onset and characteristics of desynchronization events. Our results regarding synchronization levels and synchronizability underline the significance of symmetry and matching parameters for the identical synchronization of delay-coupled oscillators.
We apply our findings regarding the possibility for identical synchronization to develop and implement an experimental method to identify determinism in the chaotic dynamics of a SL with delayed feedback. Our method is based on zero-lag synchronization of the laser with a twin system. We focus our investigation on power dropouts in the Low Frequency Fluctuations regime of a SL since they represent distinct dynamical features whose origin had been controversially discussed in the past. Our method can be adapted in principle to other nonlinear delay systems which exhibit intrinsic noise to test for traces of determinism.
Our work is of general relevance for research in nonlinear dynamics, as many of our results and methods can be adapted for other delay systems and provide general insights into the characteristics of delay-coupled systems.