  Direct UV-written waveguides are fabricated in silica-on-silicon with
birefringence of $(4.9 \pm 0.2) \times 10^{-4}$, much greater than previously
reported in this platform. We show that these waveguides are suitable for the
generation of heralded single photons at telecommunication wavelengths by
spontaneous four-wave mixing. A pulsed pump field at 1060 nm generates pairs of
photons in highly detuned, spectrally uncorrelated modes near 1550 nm and 800
nm. Waveguide-to-fiber coupling efficiencies of 78-91% are achieved for all
fields. Waveguide birefringence is controlled through dopant concentration of
$\mathrm{GeCl_4}$ and $\mathrm{BCl_3}$ using the flame hydrolysis deposition
process. The technology provides a route towards the scalability of
silica-on-silicon integrated components for photonic quantum experiments.
