  Generation of photon pairs from compact, manufacturable and inexpensive
silicon (Si) photonic devices at room temperature may help develop practical
applications of quantum photonics. An important characteristic of photon-pair
generation is the two-photon joint spectral intensity (JSI), which describes
the frequency correlations of the photon pair. In particular, heralded
single-photon generation requires uncorrelated photons, rather than the highly
anti-correlated photons conventionally obtained under continuous-wave (CW)
pumping. Recent attempts to achieve such a factorizable JSI have used short
optical pulses from mode-locked lasers, which are much more expensive and
bigger table-top or rack-sized instruments compared to the Si microchip pair
generator, dominate the cost and inhibit the miniaturization of the source.
Here, we generate photon pairs from a Si microring resonator by using an
electronic step-recovery diode to drive an electro-optic modulator which carves
the pump light from a CW optical diode into pulses of the appropriate width,
thus potentially eliminating the need for optical mode-locked lasers.
