Abstract
Summary form only given. Zero-lag synchronization in semiconductor lasers (SLs) with mutual coupling interaction has been investigated lately in two, three or even networks of coupled elements. Nevertheless, this type of synchronization may suffer from de-synchronization events within an overall highly correlated synchronized behavior. The intermittent de-synchronization events are noise and/or parameter mismatch induced and have been observed both as fast and frequent events in the coherence-collapse regime and as slower and less-frequent events in the low-frequency fluctuation (LFF) regime, in the case of bi-directionally coupled SLs [1,2].In our investigation we adopt a star SL network with strong bidirectional coupling between the N peripheral nodes and the central hub node (fig. 1). Coupling, biasing conditions and mismatch among the SLs parameters (eg. frequency detuning up to several GHz) have been shown to determine the network's overall operation [3,4]. In almost all cases for which a well-synchronized network is set under highly correlated chaotic signals, shortduration de-synchronization events among clusters of nodes - or even all nodes - are evident (fig. 2).The role of the central hub node in the generated dynamics at the peripheral nodes and the comparative signal properties has been evaluated to be crucial in this topology. In contrary to [5], where sub-threshold SL biasing (IH<;Ithr) operation has been considered, the hub SL's current is set above threshold (IH>Ithr). Zero-lag crosscorrelation values among the SLs are steadily high and further improve by increasing IH. Nevertheless, when analyzing the performance on the least correlated pair of the SL network, a remarkable behavior is recorded; for gradually increasing IH above threshold, this pair exhibits locally a degraded performance (up to 2.3Ithr). This reduced cross-correlation which is reimbursed with further increase in the biasing current. Overall, large IH values result in de-synchronization effects' deterioration, up to elimination. In parallel, this improvement is accompanied by an interchange in the leader-laggard dynamics between the hub laser and the cluster of star lasers. Fig. 3a shows the number of SLs with dynamics that lead the hub laser's dynamics with a time delay IJ+=IJ (equal to the time distance between hub and star SLs), while fig. 3b shows the opposite behavior, with the number of SLs that lag behind the hub laser's dynamics (IJ-=-IJ). The hub turns from lagging to leading the dynamics of the network for current values larger than 2.8Ithr, mastering the emission of each single star SL through a common powerful drive signal and eliminating de-synchronization events.
Published Version
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