Observation of microcavity fine structure

Abstract

We experimentally show that resonance spectra of optical microcavities have a fine structure that resembles the one observed in atoms. We can identify the polarization-resolved modes in the spectrum and distinguish between two intrinsic effects that cause fine structure: (1) an optical spin-orbit coupling and (2) nonparaxial propagation and reflection. The measured effects are intrinsic to cavities and are therefore present in any cavity, in contrast to accidental effects like astigmatism. The analogy of fine structure with atomic physics is surprisingly fruitful and gives accurate theoretical predictions which agree which experiments. This analogy can even predict further splittings like a hyperfine splitting, which in our microcavities is explained by a Bragg effect.