Truly unentangled photon pairs without spectral filtering.

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 a Schmidt number arbitrarily close to unity. This will permit the generation of heralded single-photon states with unit purity.