  Optical fibers have been considered an optimal platform for third-order
parametric down-conversion since they can potentially overcome the weak
third-order nonlinearity by their long interaction length. Here we present, in
the first part, a theoretical derivation for the conversion rate both in the
case of spontaneous generation and in the presence of a seed beam. Then we
review three types of optical fibers and we examine their properties in terms
of conversion efficiency and practical feasibility.
