ON THE DIFFERENT FORMULATIONS OF THE COUPLED-MODE THEORY FOR PARALLELDIELECTRIC WAVE-GUIDES

Three different formulations of the coupled-mode theory for parallel d ielectric waveguides are derived by substituting proper polarization v ectors into a very general, unconjugated, form of the reciprocity theo rem. It is shown that the origins of errors of the three formulations can be clearly perceived through the derivation process. Power transfe r characteristics predicted by the three coupled-mode theories are com pared with the exact numerical results to show the relative accuracy o f these theories.