Photon pair generation in lithium niobate waveguide periodically poled by femtosecond laser

Reliable generation of single photons is of key importance for fundamental physical experiments and quantum protocols.The periodically poled lithium niobate[LN]waveguide has shown promise for an integrated quantum source due to its large spectral tunability and high efficiency,benefiting from the quasi-phase-matching.Here we demonstrate photon-pair sources based on an LN waveguide periodically poled by a tightly focused femtosecond laser beam.The pair coincidence rate reaches～8000 counts per second for average pump power of 3.2 mW[peak power is 2.9 kW].Our results prove the possibility of application of the nonlinear photonics structure fabricated by femtosecond laser to the integrated quantum source.This method can be extended to three-dimensional domain structures,which provide a potential platform for steer-ing the spatial degree of freedom of the entangled two-photon states.