Coordinate transformation method as applied to asymmetric gratings with vertical facets

The differential formalism introduced by J. Chandezon during the seventies has been successfully applied to the study of waveguides and to diffraction problems. Until now it was believed that the method could be applied only if the interfaces between media were described by graphs of functions. We show that an eigenoperator formulation of the method allows one to solve a larger set of profiles. This theoretical result is applied to gratings having a vertical facet.