  Entangled photon pairs generated within integrated devices must often be
spatially separated for their subsequent manipulation in quantum circuits.
Separation that is both deterministic and universal can in principle be
achieved through anti-coalescent two-photon quantum interference. However, such
interference-facilitated pair separation (IFPS) has not been extensively
studied in the integrated setting, where the strong polarization and wavelength
dependencies of integrated couplers -- as opposed to bulk-optics beamsplitters
-- can have important implications for performance beyond the identical-photon
regime. This paper provides a detailed review of IFPS and examines how these
dependencies impact separation fidelity and interference visibility. Focus is
given to IFPS mediated by an integrated directional coupler. The analysis
applies equally to both on-chip and in-fiber implementations, and can be
expanded to other coupler architectures such as multimode interferometers. When
coupler dispersion is present, the separation performance can depend on photon
bandwidth, spectral entanglement, and the linearity of the dispersion. Under
appropriate conditions, reduction in the separation fidelity due to loss of
non-classical interference can be perfectly compensated for by classical
wavelength demultiplexing effects. This work informs the design as well as the
performance assessment of circuits for achieving universal photon pair
separation for states with tunable arbitrary properties.
