  We demonstrate that an integrated silicon microring resonator is capable of
efficiently producing photon pairs that are completely unentangled; such pairs
are a key component of heralded single photon sources. A dual-channel
interferometric coupling scheme can be used to independently tune the quality
factors associated with the pump and signal and idler modes, yielding a
biphoton wavefunction with Schmidt number arbitrarily close to unity. This will
permit the generation of heralded single photon states with unit purity.
