  The generation of mid-infrared pulses in monolithic and electrically pumped
devices is of great interest for mobile spectroscopic instruments. The gain
dynamics of interband cascade lasers (ICL) are promising for mode-locked
operation at low threshold currents. Here, we present conclusive evidence for
the generation of picosecond pulses in ICLs via active mode-locking. At small
modulation power, the ICL operates in a linearly chirped frequency comb regime
characterized by strong frequency modulation. Upon increasing the modulation
amplitude, the chirp decreases until broad pulses are formed. Careful tuning of
the modulation frequency minimizes the remaining chirp and leads to the
generation of 3.2 ps pulses.
