PPLN-based nonlinear platforms for a narrowband nondegenerate photon-pair source in quantum communication

Study of two periodically poled lithium niobate (PPLN) waveguide platforms, focused on their nonlinear optical response and, in particular, on the spectral emission properties of the crystal cavity generating the down-converted photon pairs, using a continuous-wave (CW) laser in the C band. The cascaded second-harmonic (SHG) and sum-frequency generation (SFG) processes provide a third-harmonic generation (THG), whose output is the pump beam for the spontaneous parametric down-conversion (SPDC) occurring in a doubly resonant optical parametric oscillator (OPO), which, working below threshold, produces narrowband energy-time correlated photon pairs at 780 and 1560 nm, whose linewidth is imposed by the single longitudinal modes of the cavity. The aim is to develop a single photon-pair source for multi-photon interference experiments between independent sources.