  We study the geometrical properties of null congruences generated by an
aligned null direction of the Weyl tensor (WAND) in spacetimes of the Weyl and
Ricci type N (possibly with a non-vanishing cosmological constant) in an
arbitrary dimension. We prove that a type N Ricci tensor and a type III or N
Weyl tensor have to be aligned. In such spacetimes, the multiple WAND has to be
geodetic. For spacetimes with type N aligned Weyl and Ricci tensors, the
canonical form of the optical matrix in the twisting and non-twisting case is
derived and the dependence of the Weyl and the Ricci tensors and Ricci rotation
coefficients on the affine parameter of the geodetic null congruence generated
by the WAND is obtained.
