  Entangled photon-pairs are a critical resource in quantum communication
protocols ranging from quantum key distribution to teleportation. The current
workhorse technique for producing photon-pairs is via spontaneous parametric
down conversion (SPDC) in bulk nonlinear crystals. The increased prominence of
quantum networks has led to growing interest in deployable high performance
entangled photon-pair sources. This manuscript provides a review of the
state-of-the-art for bulk-optics-based SPDC sources with continuous wave pump,
and discusses some of the main considerations when building for deployment.
