Effective matching in a nonlinear directional coupler with waveguide mismatching and nonuniform nonlinearity.

A variable-coupling-coefficient nonlinear directional coupler with mismatching and nonuniformity is studied by means of coupled mode equations with effective mismatching. It is pointed out that the effective mismatching can be cancelled out for any given input power by properly adjusting the magnitudes of the mismatching and nonuniformity. Numerical examples are given to show that complete power transfer between two waveguides can be achieved for a mismatched and nonuniform nonlinear directional coupler and for a Gaussian as well as an exponential variable-coupling-coefficient nonlinear directional coupler.