  We report on the observation of a high visibility Hong-Ou-Mandel interference
of two heralded photons emitted from a spontaneous parametric down
conversion~(SPDC) pumped by continuous-wave~(cw) light. A non-degenerate photon
pair at 1541~nm and 1580~nm is generated by cw-pumped SPDC through a
periodically poled lithium niobate waveguide. The heralded single photon at
1541~nm is prepared by the detection of the photon at 1580~nm. We performed the
experiment of the Hong-Ou-Mandel interference between heralded single photons
in separated time bins and observed a high visibility interference. All
detectors we used are superconducting nanowire single-photon detectors and an
overall temporal resolution of the photon detection is estimated as 85 ps,
which is sufficiently shorter than the coherence time of the heralded photons.
