  A new method for generating entangled photons with controllable frequency
correlation via spontaneous parametric down-conversion (SPDC) is presented. The
method entails initiating counter-propagating SPDC in a single-mode nonlinear
waveguide by pumping with a pulsed beam perpendicular to the waveguide. The
method offers several advantages over other schemes, including the ability to
generate frequency-correlated photon pairs regardless of the dispersion
characteristics of the system. Numerical evidence demonstrates the improvement
provided by this source in the special case of frequency-correlated two-photon
states.
