The authors present a contour-integration-based framework for computing poles and zeros of electromagnetic response functions in non-Hermitian photonic systems. They demonstrate the approach on a dielectric metasurface, determining complex-valued reflection zeros and poles, their sensitivities to geometric parameters, and performing residue-based modal expansions. The numerical simulations were performed using the finite-element Maxwell solver JCMsuite to solve scattering problems at complex frequencies along integration contours.
F. Binkowski et al. Poles and zeros in non-Hermitian systems: Application to photonics. Phys. Rev. B 109, 045414 (2024).