  We report on quantum frequency conversion of near-infrared photons from a
wavelength of 854nm to the telecommunication O-band at 1310nm with 8% overall
conversion efficiency. Entangled photon pairs at 854nm are generated via
type-II spontaneous parametric down conversion. One photon is mixed with a
strong pump field in a nonlinear ridge waveguide for its conversion to 1310nm.
We demonstrate preservation of first and second order coherence of the photons
in the conversion process. Based on this we infer the coherence function of the
two-photon state and compare it with the actual measured one. This measurement
demonstrates preservation of time-energy entanglement of the pair. With 88%
visibility we violate a Bell inequality.
