Spatiotemporal coupled-mode theory in dispersive media under a dynamic   modulation
  A simple and general formalism for mode coupling by a spatial, temporal or spatiotemporal perturbation in dispersive materials is developed. This formalism can be used for studying various linear and non-linear optical interactions involving a dynamic modulation of the interaction parameters such as non-reciprocal phenomena, time reversal of signals and spatiotemporal quasi phase matching 
Brenda Dana, Lilya Lobachinsky and Alon Bahabad
physics.optics