A Scalar Wigner Theory for Polarized Light in Nonlinear Kerr Media
  A scalar Wigner distribution function for describing polarized light is proposed in analogy with the treatment of spin variables in quantum kinetic theory. The formalism is applied to the propagation of circularly polarized light in nonlinear Kerr media and an extended phase space evolution equation is derived along with invariant quantities. We further consider modulation instability as well as the extension to partially coherent fields. 
T. Hansson, E. Wallin, G. Brodin, M. Marklund
physics.optics quant-ph