It is rediscovered that some early works on conventional waveguides

including several published papers by the author

are applicable to optical fiber and film waveguides. This paper shows that the coupling coefficients for ideal modes

for local modes and for superlocal modes are all related by similar matrices in the sense of Lowey

and as far as discrete modes are concerned

the "equivalence"expressions derived by Marcuse are special cases of our general results. Physical arguments will illustrate the reasonable-ness

under certain restrictions

of extending the applicability of the said relations to cases which also in-elude a continuum of modes.