We introduce a simple and flexible concept for a heralded—spectrally pure—single-photon source. The scheme uses a probabilistic photon-pair source pumped with a continuous-wave laser, whereby a rapid gating InGaAs/InP single-photon avalanche diode provides a synchronous clock for the system. The low timing jitter of the detector temporally resolves, and hence spectrally filters, the heralded photons. We demonstrate the concept by combining this with a narrow-band integrated silicon nitride photon-pair source. This simple architecture is capable of heralding photons with high spectral purity in the telecom band but could be adapted to other wavelengths and bandwidth regimes.
Pereira et al. (Mon,) studied this question.