  Using numerical simulations, we study propagation of linearly-chirped optical
pulses in a homogeneously broadened two-level medium. We pay attention to the
three main topics -- validity of the rotating-wave approximation (RWA), pulse
compression, and collisions of counter-propagating pulses. The cases of long
and single-cycle pulses are considered and compared with each other. We show
that the RWA does not give a correct description of chirped pulse interaction
with the medium. The compression of the chirp-free single-cycle pulse is
stronger than of the chirped one, while the opposite is true for long pulses.
We demonstrate that the influence of chirp on the collisions of the long pulses
allows to control the state of the transmitted radiation: the transmission of
the chirp-free pulse can be dramatically changed under collision with the
chirped counter-propagating one, in sharp contrast to the case when both pulses
are chirped. On the other hand, the collisions of the chirped single-cycle
pulses can be used for precise control of medium excitation in a narrow spatial
region.
