Tunable near-degenerate frequency conversion using doped photonic crystal fibre

Future quantum communication networks will rely on the ability to coherently transfer quantum information between different wavelength bands. Coherent frequency conversion in optical fibre by Bragg-scattering four-wave mixing is a promising route to achieving this, but requires fibres with precise dispersion control and broadband transmission at signal, target and pump wavelengths. Here we introduce a photonic crystal fibre with a germania-doped core, for which the group velocities at 1550nm and 920 nm are approximately matched, with good optical guidance even at long wavelengths. With low chromatic walk-off, large lengths of this fibre can be used to achieve frequency conversion between two wavelengths several nanometers apart in the GaAs quantum dot emission band. We demonstrate this with up to 78% internal conversion efficiency by pumping with two nearby C-band wavelengths. By cascading this interaction, we also show the generation of a frequency comb. We further demonstrate the potential of this fibre for downconversion between the GaAs dot band and telecoms C-band.