Simulating frequency splittings and loss in Fabry-Pérot cavities

Finite-element simulations of optical cavities are presented, showing frequency splittings in the resonance spectrum. These can be directly compared to and understood by recent theory and experiments presented in van Exter et al. (2022, Phys. Rev. A 106, 013501), Koks et al. (2022, Phys. Rev. A 105, 063502) and Post et al. (2025, Phys. Rev. A 112, 033537). They provide strong evidence for the nonparaxial theory, but point out limitations of predicted mirror-shape corrections. The simulations also provide model-independent predictions of modal losses for optical cavities.