  We report the observation of correlated photon pairs generated by spontaneous
parametric down-conversion in a quasi-phase matched KTiOPO4 nonlinear
waveguide. The highest ratio of coincidence to single photon count rates
observed in the 830 nm wavelength region exceeds 18%. This makes nonlinear
waveguides a promising source of correlated photons for metrology and quantum
information processing applications. We also discuss possibilities of
controlling the spatial characteristics of the down-converted photons produced
in multimode waveguide structures.
