On the Expansion of Axial Field Components in Terms of Normal Modes in Perturbed Waveguides (Letters)

Arguments are proposed according to which, in the Maxwell equations giving the axial field components, the expansion of the transverse field components in terms of unperturbed normal modes could be differentiated term by term. This would be allowed when the perturbed transverse field respects the possible nullity conditions imposed by the boundaries of the unperturbed waveguide and when it has no singularity.