  The second part of the article is devoted to field transfers by diffraction
that are represented by fractional Fourier transformations whose orders are
complex numbers. The corresponding effects on the Wigner distributions
associated with optical fields are still represented by $4\times4$ matrices
operating on the scaled phase-space, but unlike matrices involved in the first
part, those matrices decompose into two matrices that essentially represent
2--dimensional hyperbolic rotations, not elliptical rotations. The result is
applied to the theory of unstable resonators.
