  We calculate that an appropriate modification of the field associated with
only one of the photons of a photon pair can suppress generation of the pair
entirely. From this general result, we develop a method for suppressing the
generation of undesired photon pairs utilizing photonic stop bands. For a
third-order nonlinear optical source of frequency-degenerate photons we
calculate the modified frequency spectrum (joint spectral intensity) and show a
significant increase in a standard metric, the coincidence to accidental ratio.
These results open a new avenue for photon-pair frequency correlation
engineering.
