Nonclassical two-photon interference between independent telecommunication light pulses converted by difference-frequency generation

We experimentally demonstrated the Hong-Ou-Mandel (HOM) interference between two photons after visibleto-telecommunication wavelength conversion. In the experiment, we prepared a heralded single photon by using spontaneous parametric down conversion (SPDC) and the other photon from a weak laser source at 780 nm. We converted the wavelength of both photons to the telecommunication wavelength of 1522 nm by using difference-frequency generation in a periodically poled lithium niobate, and then observed the HOM interference between the photons. The observed visibility is 0.76 +/- 0.12 which clearly shows the nonclassical interference of the two photons. The high-visibility interference