Mode retrieval from intensity profile measurements using irradiant waveguide-modes

The fields radiated from the waveguide were used to analyze propagating mode content in an oversized circular corrugated waveguide. The radiated fields were calculated by the Kirchhoff integral in the paraxial approximation. The irradiant waveguide modes of the radiated field are orthogonal within the paraxial approximation. The complex fractions in the irradiant mode expansion were deduced from an iteration process in which the reconstructed amplitude profile from the complex fractions coincided with the measured amplitude profile.