  Future quantum networks will rely on the ability to coherently transfer
optically encoded quantum information between different wavelength bands.
Bragg-scattering four-wave mixing in optical fiber is a promising route to
achieving this, but requires fibers with precise dispersion control and
broadband transmission at signal, target and pump wavelengths. Here we
introduce a photonic crystal fiber with a germanium-doped core featuring group
velocity matching at 1550 nm, the telecoms C-band, and 920 nm, within the
emission range of efficient single photon sources based on InAs quantum dots.
With low chromatic walk-off and good optical guidance even at long wavelengths,
large lengths of this fiber are used to achieve nanometer-scale frequency
shifts between wavelengths around 920 nm with up to 79.4\% internal conversion
efficiency, allowing dissimilar InAs dots to be interfaced. We also show how
cascading this frequency conversion can be used to generate a frequency comb
away from telecoms wavelengths. Finally, we use the fiber to demonstrate
tunable frequency conversion of weak classical signals around 918 nm to the
telecoms C-band.
