Impact of propagation losses on photon-pair generation in silicon

We present a semi-classical numerical model to estimate the impact of linear scattering loss and nonlinear absorption losses on the biphoton flux and their quantum correlations generated via spontaneous four-wave mixing in silicon nanowaveguides. The counter-intuitive observed enhancement of pair correlations with increasing loss is attributed to the dominant effect of reduced accidental counts from multiphoton generation, with a corresponding trade-off for the source brightness. Silicon nanowaveguides are shown to be capable of generating highly correlated paired photons with coincidental-to-accidental ratio (CAR) as high as ∽3400 and spectral brightness 2.8×105 pairs/s/GHz/mW, even in the presence of linear propagation loss of 1 dB/cm and nonlinear losses (two-photon absorption (TPA) and free-carrier absorption (FCA)), over a length of 1-cm with an input pump power of 1 mW. Loss and the corresponding Langevin noise are modeled using distributed beam splitters along the waveguide length to encapsulate the phenomenological coupling to the background reservoir (vacuum fluctuations). The proposed numerical model is more general compared to previous analytical models, particularly for including dispersion and wavelength-dependent losses, and more accurate for noise estimation in the high-photon-flux regime such as optical parametric amplifiers and squeezed state generation.