  We present experimental and simulated results to quantify the impact of
nonlinear noise in integrated photonic devices relying on spontaneous four-wave
mixing. Our results highlight the need for design rule adaptations to mitigate
the otherwise intrinsic reduction in quantum state purity. The best strategy in
devices with multiple parallel photon sources is to strictly limit photon
generation outside of the sources. Otherwise, our results suggest that purity
can decrease below 40%.
