  We analyze how imperfections in single-photon detectors impact the
characterization of photon-pair sources. We perform exact calculations to
reveal the effects of multi-pair emissions and of noisy, non-unit efficiency,
non photon-number resolving detections on the Cauchy-Schwarz parameter, on the
second order auto-correlation and cross-correlation functions, and on the
visibilities of both Hong-Ou-Mandel and Bell-like interferences. We consider
sources producing either two-mode squeezed states or states with a Poissonian
photon distribution. The proposed formulas are useful in practice to determine
the impacts of multi-pair emissions and dark counts in standard tests used in
quantum optics.
