  Generation of photon pairs from randomly poled nonlinear crystals is
investigated using analytically soluble model and numerical calculations.
Randomly poled crystals are discovered as sources of entangled ultra broad-band
signal and idler fields. Their photon-pair generation rates scale linearly with
the number of domains. Entanglement times as short as several fs can be
reached. Comparison with chirped periodically-poled structures is given and
reveals close similarity.
