High-performance quantum entanglement generation via cascaded second-order nonlinear processes

In this paper, we demonstrate the generation of high-performance entangled photon-pairs in different degrees freedom from a single piece fiber pigtailed periodically poled LiNbO$_3$ (PPLN) waveguide. We utilize cascaded second-order nonlinear optical processes, i.e. second-harmonic (SHG) and spontaneous parametric down conversion (SPDC), to generate photon-pairs. Previously, performance photon pairs is contaminated by Raman noise photons pigtails. Here integrating PPLN waveguide with rejecting filters, obtain coincidence-to-accidental ratio (CAR) higher than 52,600 photon-pair detection rate 52.3 kHz 3.5 kHz, respectively. Energy-time, frequency-bin time-bin entanglement prepared coherently superposing correlated two-photon states these freedom, The energy-time achieve maximum value CHSH-Bell inequality S=2.708$\pm$0.024 interference visibility 95.74$\pm$0.86%. fidelity 97.56$\pm$1.79% spatial quantum beating 96.85$\pm$2.46%. S=2.595$\pm$0.037 tomographic 89.07$\pm$4.35%. Our results provide potential candidate for light source photonics.