  We put forth an approach to obtain a quantum master equation for the
propagation of light in nonlinear fiber optics by relying on simple quantum
pictures of the processes (linear and nonlinear) occurring along propagation in
an optical fiber. This equation is shown to be in excellent agreement with the
classical Generalized Nonlinear Schrodinger Equation and predicts the effects
of self-steepening and spontaneous Raman scattering. Last, we apply these
results to the analysis of two cases of relevance in quantum technologies:
single-photon frequency translation and spontaneous four-wave mixing.
