Coupling among parallel waveguides

A new coupled-mode formalism1,2 is employed to analyze wave propagation and power transfer among N-parallel waveguides. The waveguides need not be identical. In the derivation, which will not be presented, we retain a residue field that is the difference between the exact array mode and superposition of the individual waveguide modes. By requiring that the residue field be orthogonal to each individual waveguide mode, we obtain a formulation in the same form as the usual theory but with more accurate propagation constants and coupling coefficients. A comparison of array modes and their propagation constants as computed by the new theory with the exact solutions shows that the new results are considerably more accurate than those obtained from the prior theory.