Matrix coupled mode theory model of strongly-coupled multiwaveguide optical nonlinear directional couplers

This paper discusses an improved coupled mode theory model for the nonlinea r directional coupler in the strong-coupling range. A new single-line matri x equation is derived for the multiwaveguide case. For the two-guide case, a new critical power formula and two exact identities are derived. Interrel ation between the overlap integral and nonlinear cross-coefficients is demo nstrated. It is shown that inconsistent inclusion of these terms in previou s approaches leads to inaccuracies. Results obtained by consistent inclusio n of these terms and our critical power formula show a great improvement in accuracy over previous analyses in strong-coupling.