Return-map for low-frequency fluctuations in semiconductor lasers with optical feedback

We show that the phenomenon of low-frequency fluctuations (LFF) , commonly observed in semiconductor lasers with optical feedback, can be explained by a simple return-map, implying a tremendous simplification in the description of the slow time-scale dynamics of the system. Experimentally observed parameter dependencies are simply explained by the calculated return-maps. Our approach partly decouples the slow and the fast time-scale behaviour. The latter is often described in terms of chaotic itinerary, but this does not provide an explanation for the low-frequency fluctuations themselves.