  We consider non-linear plane gravitational waves as propagating space-time
defects, and construct the Burgers vector of the waves. In the context of
classical continuum systems, the Burgers vector is a measure of the deformation
of the medium, and at a microscopic (atomic) scale, it is a naturally quantized
object. One purpose of the present article is ultimately to probe an
alternative way on how to quantize plane gravitational waves.
