ABSTRACT
A good example closely connected to nonlinear optics literature is the case of quasi-monochromatic weakly nonlinear wave phenomena which is well described by the nonlinear Schrodinger equation and close “cousins.” Similarly, when the dynamics is still weakly nonlinear, but instead energy flows between two or more modes coupled by some resonant mechanism, then one obtains a coupled system of equations. The simplest example of this is the presence of birefringence in an optical fiber, where the single guided mode can have two states of polarization. The chapter shows how universal the coupled mode equations are. With the fast and furious progress in optical technology, devices such as fiber Bragg gratings, dual or multi-core photonic crystal fibers and binary arrays are now a reality to test and implement applications, or for the study of fundamental physics using table top experiments.
