  A nonlinear planar waveguide pumped by a beam orthogonal to its surface may
serve as a versatile source of photon pairs. Changing pump-pulse duration,
pump-beam transverse width, and angular decomposition of pump-beam frequencies
characteristics of a photon pair including spectral widths of signal and idler
fields, their time durations as well as degree of entanglement of two fields
can be changed significantly. Using the measured spectral widths of the
down-converted fields and width of a coincidence-count dip in a Hong-Ou-Mandel
interferometer entropy of entanglement can be determined.
