Departement d’Optique P. M. Dueux, Institut FEMTO{ST, Unite Mixte de Recherche du CNRS 6174,Universite de Franche-Comte, route de Gray 16, Besan˘con F-25030, France(Dated: March 5, 2014)Radio-frequency phase modulation of frequency entangled photons leads to a two-photon inter-ference pattern in the frequency domain. In recent experiments, the pattern was measured withnarrow-band frequency lters which select photons belonging to a given frequency bin. Here weshow how photons can be grouped into even and odd frequencies by using periodic frequency lterscalled interleavers. In our theoretical analysis we show how this reduces the high-dimensional pho-ton state to an e ective two-dimensional state. This is of interest for applications such as quantumcryptography or low-dimensional tests of quantum nonlocality. We then report an experimentalrealization of this proposal. The observed two-photon interference pattern and violation of theCHSH inequality { the simplest binary-outcome Bell inequality { are in good agreement with thetheoretical predictions.