  Frequency-entangled photons can be readily produced using parametric
down-conversion. We have recently shown how such entanglement could be
manipulated and measured using electro-optic phase modulators and narrow-band
frequency filters, thereby leading to two-photon interference patterns in the
frequency domain. Here we introduce new theoretical and experimental
developments showing that this method is potentially a competitive platform for
the realization of quantum communication protocols in standard
telecommunication fibres. We derive a simple theoretical expression for the
coincidence probabilities and use it to optimize a Bell inequality.
Furthermore, we establish an equivalence between the entangled- photon scheme
and a classical interference scheme. Our measurements of two-photon
interference in the frequency domain yield raw visibilities in excess of 99%.
We use our high quality setup to experimentally validate the theoretical
predictions, and in particular we report a violation of the CH74 inequality by
more than 18 standard deviations.
