Effects of conjugate fields on the nonlinear propagation of light

We have studied the influence of the nonlinear interaction between the electromagnetic field and its conjugate ('negative frequency field') through the inclusion of new terms in the nonlinear polarisation. We have found that this new terms modify the usual nonlinear Self-phase modulation as well as giving rise to completely new phase-matched radiations emitted by light propagating in microresonators and fiber loops.