Quantum properties of counter-propagating two-photon states generated in a planar waveguide

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.