Rigorous Scattering Matrix Analysis of a Fabry–Perot Open Resonator

A completely novel electromagnetic model of a Fabry–Perot open resonator is proposed and validated in this article. The idea that led to the invention of this model is to split the analysis of the resonator into a few nonresonant sections, thus, substantially alleviating computational effort involved in the analysis of such a large high- $Q$ structure. Each section of the resonator, including mirrors, is represented as a multimode scattering matrix and the whole resonator is considered as a cascade of two-port networks. Mode analysis applied in the proposed model allows representing fields propagating along the resonator in the form of an orthogonal set of cylindrical waveguide modes. Due to versatility and large computational efficiency, the method can be used to account for electromagnetic phenomena that cannot be solved with commonly used models of the Fabry–Perot open resonator based on a scalar paraxial approximation. The obtained solution is validated against experimental data. It is also shown that the spurious mode coupling occurring in the measurement of electrically thick dielectric sheet materials can be explained using the proposed scattering matrix method.