Temperature-insensitive source of polarization-entangled photon pairs through noncritical phasematching in single-domain KTiPO4

Noncritical phasematched (NCPM) Type-II spontaneous parametric downconversion (SPDC) was used to produce highly nondegenerate polarization-entangled photon pairs in a 50mm single-domain potassium titanyl phosphate (KTP) crystal. The center wavelength of the idler photon and high entanglement quality of the source were observed to have a low temperature dependence. The high temperature stability makes this approach of generating and distributing polarization-entangled photon pairs suitable for field deployment without temperature control. In addition to the wavelengths of the signal and idler photons being in the visible and telecom bands respectively, the photons have narrow linewidths, making the NCPM approach of generating entangled photon pairs suitable for multi-channel entanglement distribution where the signal photon can be transmitted through free space and the idler photon can be transmitted through fiber.