A coupled-mode formulation based on the second-order coupled-mode equations

We present a trial solution for second-order coupled-mode equations and derive power-conservation law from the coupled-mode equations. We investigate the validity of using the second-order equations and the slowly varying envelope approximation, and the numerical results show that the usual assumption, which is that the total field may be expressed as a linear combination of individual guided modes, must be modified when the structure is strongly coupled. (C) 1997 John Wiley & Sons, Inc.