  Four-wave mixing in the form of Bragg scattering (BS) has been predicted to
enable quantum noise less frequency conversion by analytic quantum approaches.
Using a semi-classical description of quantum noise that accounts for loss and
stimulated and spontaneous Raman scattering, which are not currently described
in existing quantum approaches, we quantify the impacts of these effects on the
conversion efficiency and on the quantum noise properties of BS in terms of an
induced noise figure (NF). We give an approximate closed-form expression for
the BS conversion efficiency that includes loss and stimulated Raman
scattering, and we derive explicit expressions for the Raman-induced NF from
the semi-classical approach used here.
