Abstract

Mutually coupled semiconductor lasers exhibit low frequency intensity dropouts which are strongly correlated in time but with a constant time lag between the two signals [1]. The experimental setup consists of two device-identical semiconductor lasers (optical spectra agree within 0.1 nm, slope efficiency within 2%, and threshold current within 5%). Light from either laser is injected into the other laser with a uniform time delay τ. The dynamics of the mutually coupled system resembles that of low frequency fluctuations found in semiconductor lasers subject to delayed external feedback. Simulation of the mutually coupled system using two coupled single mode rate equations reproduce the results. The low frequency fluctuations and strong time correlation was attributed to the phenomenon of optical synchronization, however the appearance of the lag was unexplained.

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