  Temporal coherence of individual signal or idler beam, determined by the
spectral correlation property of photon pairs, is important for realizing
quantum interference among independent sources. To understand the effect of
chirp on the temporal coherence property, two series of experiments are
investigated by introducing different amount of chirp into either the pulsed
pump or individual signal (idler) beam. In the first one, based on spontaneous
four wave mixing in a piece of optical fiber, the intensity correlation
function of the filtered individual signal beam, which characterizes the degree
of temporal coherence, is measured as a function of the chirp of pump. The
results demonstrate that the chirp of pump pulses decreases the degree of
temporal coherence. In the second one, a Hong-Ou-Mandel type two-photon
interference experiment with the signal beams generated in two different fibers
is carried out. The results illustrate that the chirp of individual beam does
not change the temporal coherence degree, but affect the temporal mode
matching. To achieve high visibility, apart from improving the coherence degree
by minimizing the chirp of pump, mode matching should be optimized by managing
the chirps of individual beams.
