  We present a spectrally decorrelated photon pair source bridging the visible
and telecom wavelength regions. Tailored design and fabrication of a solid-core
photonic crystal fiber (PCF) lead to the emission of signal and idler photons
into only a single spectral and spatial mode. Thus no narrowband filtering is
necessary and the heralded generation of pure photon number states in ultrafast
wave packets at telecom wavelengths becomes possible.
