  Semiconductor lasers with time-delayed optical feedback display a wide range
of dynamical regimes, which have found various practical applications. They
also provide excellent testbeds for data analysis tools for characterizing
complex signals. Recently, several of us have analyzed experimental intensity
time-traces and quantitatively identified the onset of different dynamical
regimes, as the laser's current increases. Specifically, we identified the
onset of low-frequency fluctuations (LFFs), where the laser intensity displays
abrupt dropouts, and the onset of coherence collapse (CC), where the intensity
fluctuations are highly irregular. Here we map these regimes when both, the
laser current and the feedback strength vary. We show that the shape of the
distribution of intensity fluctuations (characterized by the standard
deviation, the skewness, and the kurtosis) allows to distinguish between noise,
LFFs, and CC, and to quantitatively determine (in spite of the gradual nature
of the transitions) the boundaries of the three regimes. Ordinal analysis of
the inter-dropout time intervals consistently identifies the three regimes
occurring in the same parameter regions as the analysis of the intensity
distribution. Simulations of the well-known time-delayed Lang-Kobayashi model
are in good qualitative agreement with the observations.
