Abstract
Optical excitable devices that mimic neuronal behavior can be building-blocks of novel, brain-inspired information processing systems. A relevant issue is to understand how such systems represent, via correlated spikes, the information of a weak external input. Semiconductor lasers with optical feedback operating in the low frequency fluctuations regime have been shown to display optical spikes with intrinsic temporal correlations similar to those of biological neurons. Here we investigate how the spiking laser output represents a weak periodic input that is implemented via direct modulation of the laser pump current. We focus on understanding the influence of the modulation frequency. Experimental sequences of inter-spike-intervals (ISIs) are recorded and analyzed by using the ordinal symbolic methodology that identifies and characterizes serial correlations in datasets. The change in the statistics of the various symbols with the modulation frequency is empirically shown to be related to specific changes in the ISI distribution, which arise due to different phase-locking regimes. A good qualitative agreement is also found between simulations of the Lang and Kobayashi model and observations. This methodology is an efficient way to detect subtle changes in noisy correlated ISI sequences and may be applied to investigate other optical excitable devices.
Highlights
Excitable behavior is observed in many nonlinear, natural systems [1]
Because information processing in the brain is associated with the excitable action potentials that propagate through neuronal axons [2], many efforts are being done to develop excitable devices that could mimic neuronal behavior in bio-inspired information processing networks
We have experimentally investigated the spiking output of a semiconductor laser with optical feedback in the low-frequency fluctuations (LFF) regime, under weak current modulation
Summary
Excitable behavior is observed in many nonlinear, natural systems [1]. Such excitable systems respond to external perturbations in an all-or-none manner. For perturbations below the excitable threshold the response is of small amplitude and linear, unable to drive the system far away from its rest state. For perturbations above the threshold the response is nonlinear and corresponds to a large excursion of the system’s variables in phase space, manifested by a spike. Because information processing in the brain is associated with the excitable action potentials that propagate through neuronal axons [2], many efforts are being done to develop excitable devices that could mimic neuronal behavior in bio-inspired information processing networks. Semiconductor lasers with optical injection [3,4,5], optical feedback [6, 7] or saturated absorber [8,9,10,11] have been investigated with this purpose
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