On the different formulations of the coupled-mode theory for parallel dielectric waveguides

Three different formulations of the coupled-mode theory for parallel dielectric waveguides are derived by substituting proper polarization vectors into a very general, unconjugated form of the reciprocity theorem. It is shown that the origins of errors of the three formulations can be clearly perceived through the derivation process. Power transfer characteristics predicted by the three coupled-mode theories are compared with the exact numerical results to show the relative accuracy of these theories.<
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