Silicon Photonic Wires for Broadband Polarization Entanglement at Telecommunication Wavelengths

We present designs for silicon-on-insulator nanowaveguide sources capable of generating polarizationentangled photon pairs with high concurrence (approximately 0.98) across the S, C, and L bands (approximately 1475-1625 nm) in the telecommunications spectrum via degenerate-pump spontaneous four-wave mixing. Silica-clad waveguides with Si film thickness 280 nm, width in the range 700-800 nm, and length up to 1 cm are shown to be optimum, generating near-perfect entangled pairs over a bandwidth >100 nm around 1550 nm. Further, the use of relatively narrow pump bandwidths (<10 GHz) can still yield a concurrence > 0.95 in waveguides up to 7 mm long despite the presence of large polarization-mode dispersion in these high-index-contrast structures. Such broadband integrated sources can be employed in multichannel wavelength-division multiplexed entanglement-based quantum key distribution protocols over standard optical-fiber networks.