  We investigate a method to produce photon pairs by four-wave mixing in
photonic crystal fibers (PCFs). By controlling the wavelength of the pump
light, which determines the phase matching condition for four-wave mixing, we
can obtain a broader spectrum of photon pairs than undesired Raman-scattered
photons. We observe two-photon interference of photon pairs from a PCF with the
help of an unbalanced Mach-Zehnder interferometer. Two-photon interference
fringes with 83% visibility, which exceeds the classical limit of 50%, are
obtained.
