  Integrated quantum photonics relies critically on the purity, scalability,
integrability, and flexibility of a photon source to support diverse quantum
functionalities on a single chip. Up to date, it remains an open challenge to
realize an efficient monolithic photon-pair source for on-chip application.
Here we report a device on the silicon-on-insulator platform that utilizes
dramatic cavity enhanced four-wave mixing in a high-Q silicon microdisk
resonator. The device is able to produce high-purity photon pairs in a comb
fashion, with an unprecedented spectral brightness of $6.24 \times 10^7 {\rm
pair/s/mW^2/GHz}$ and photon-pair correlation with a coincidence-to-accidental
ratio of $1386 \pm 278$ while pumped with a continuous-wave laser. The superior
performance, together with the structural compactness and CMOS compatibility,
opens up a great avenue towards quantum silicon photonics with unprecedented
capability of multi-channel parallel information processing for both integrated
quantum computing and long-haul quantum communication.
