  Implementations of many quantum communication protocols require sources of
photon pairs. However, optimization of the properties of these photons for
specific applications is an open problem. We theoretically demonstrate the
possibility of extending the maximal distance of secure quantum communication
when a photon pair source and standard fibers are used in a scenario where
Alice and Bob do not share a global time reference. It is done by manipulating
the spectral correlation within a photon pair and by optimizing chromatic
dispersion in transmission links. Contrary to typical expectations, we show
that in some situations the secure communication distance can be increased by
introducing some extra dispersion.
