A thin-film periodically poled lithium niobate waveguide was designed and fabricated which generates entangled photon pairs at telecommunications wavelengths with high coincidences-to-accidentals counts ratio $\mathrm{CAR}>67000$, two-photon interference visibility $V>99\%$, and heralded single-photon autocorrelation $g_H^{(2)}(0)<0.025$. Nondestructive in situ diagnostics were used to determine the poling quality in 3D. Megahertz rates of photon pairs were generated by less than a milliwatt of pump power, simplifying the pump requirements and dissipation compared to traditional spontaneous parametric down-conversion lithium niobate devices.

• Received 29 January 2020
• Accepted 7 April 2020

DOI:https://doi.org/10.1103/PhysRevLett.124.163603

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Published by the American Physical Society