  We develop and apply an effective analytic theory of a non-collinear,
broadband type-I parametric down-conversion to study a coupling efficiency of
the generated photon pairs into single mode optical fibers. We derive
conditions necessary for highly efficient coupling for single and double type-I
crystal producing polarization entangled states of light. We compare the
obtained approximate analytic expressions with the exact numerical solutions
and discuss the results for a case of BBO crystals.
