  In this Letter, we report a first experimental realization of bright
ultra-broadband (180 THz) fiber-based biphoton source with widely spectrally
separated signal and idler photons. Such a two-photon source is realized due to
the joint use of broadband phase-matching of interacting light waves and high
optical nonlinearity of a silica-core photonic crystal fiber. The high
performance of the developed fiber source identifies it as an important and
useful tool for a wide range of optical quantum applications.
