  We demonstrate lasing in GaAs photonic crystal waveguides with InAs quantum
dots as gain medium. Structural disorder is present due to fabrication
imperfection and causes multiple scat- tering of light and localization of
light. Lasing modes with varying spatial extend are observed at random
locations along the guide. Lasing frequencies are determined by the local
structure and occur within a narrow frequency band which coincides with the
slow light regime of the waveguide mode. The three-dimensional numerical
simulation reveals that the main loss channel for lasing modes located away
from the waveguide end is out-of-plane scattering by structural disorder.
