Fine structure in Fabry-Perot microcavity spectra

Abstract

Optical cavities can support many transverse and longitudinal modes. A paraxial scalar theory predicts that the resonance frequencies of these modes cluster in different orders. A nonparaxial vector theory predicts that the frequency degeneracy within these clusters is lifted, such that each order acquires a spectral fine structure, comparable to the fine structure observed in atomic spectra. In this paper, we calculate this fine structure for microcavities and show how it originates from various nonparaxial effects and is codetermined by mirror aberrations. The presented theory, which applies perturbation theory to Maxwell's equations with boundary conditions, proves to be very powerful. It generalizes the effective one-dimensional description of Fabry-Perot cavities to a three-dimensional multi-Transverse-mode description. It thereby provides physical insights into several mode-shaping effects and a detailed prediction of the fine structure in Fabry-Perot spectra.