Interspike-interval correlations induced by two-state switching in an excitable system

Abstract

We study correlations of intervals between pulses in an excitable system, using a semiconductor laser with optical feedback as an experimental model system. First we show, by means of a combination of experimental observations and theoretical analysis, that for an intermediate range of the laser's pump current the interspike intervals are positively correlated over a few lags, an effect that can be theoretically explained by an intrinsic two-state switching in the laser dynamics. The same theory can be also applied if the laser is externally driven by a dichotomous switching of the pump current, a scenario that allows for a controlled change of the spike rates of the two states over orders of magnitude. Varying one of the pump levels, we find experimentally that the correlation between adjacent intervals is maximized at a finite pump level corresponding to an optimal ratio of dropout rates in the two states. Our theory confirms these findings and reveals how the regularity of spiking in the two states shapes the correlation maximum.