  Translation Matrix Formalism has been used to find an exact analytic solution
for linear light propagation in a finite one-dimensional (1D) periodic
stratified structure. This modal approach allows to derive a closed formula for
the electric field in every point of the structure, by simply imposing a
convenient form for the boundary conditions. We show how to apply this result
to Second Harmonic Generation (SHG) in the undepleted pump regime.
