This theoretical and numerical study generalizes the Petermann factor, a measure of mode nonorthogonality, to systems operating at exceptional points (EPs) in non-Hermitian physics. To demonstrate and verify the developed theory, the authors perform full-wave finite element simulations of a realistic photonic system consisting of two microrings coupled to a waveguide with embedded mirrors. The software JCMsuite was used for these numerical simulations to compute the complex eigenfrequencies and mode patterns, and to extract the spectral response strength at the EP.
J. Kullig, et al. Generalized Petermann factor of non-Hermitian systems at exceptional points. arXiv:2506.15807v2 (2025).