Polarization ray picture of coherence for vectorial electromagnetic waves

We elucidate a ray picture of coherence for vectorial electromagnetic waves by using the Stokes parameters for light rays defined by the optical Wigner function. Paraxial propagation is formulated as a complementary Huygens principle. We show that the degrees of coherence are averages of the phase difference where the weights are the Stokes parameters for light rays. We analyze the van Cittert-Zernike theorem for vectorial waves in terms of ray propagation. We show that simple polarization measurements in a Young interferometer determine the degrees of coherence for vectorial electromagnetic waves