Observation of microcavity fine structure

TL;DR

This paper reports the observation of fine structure in optical microcavity resonance spectra, revealing polarization splitting caused by intrinsic spin-orbit coupling and non-paraxial effects, especially significant in small-radius cavities.

Contribution

It provides experimental evidence of polarization-resolved mode splitting in microcavities due to intrinsic effects, aligning with theoretical predictions.

Findings

Resonance spectra exhibit polarization-dependent splitting.

Fine structure scales inversely with mirror radius of curvature.

Intrinsic effects dominate in small-radius microcavities.

Abstract

We observe fine structure in the resonance spectra of optical microcavities. We identify the polarization-resolved modes in the spectrum and find that resonance frequencies split in accordance with the theoretical prediction. The observed fine structure is dominantly caused by an optical spin-orbit coupling and non-paraxial propagation and reflection. Both effects are intrinsic, i.e. present in an ideal rotation-symmetric system, and scale inversely proportional to the mirror radius of curvature. For cavities with a small radius of curvature, the influence of fine structure on the resonance spectrum is important and unavoidable and should thus be taken into account.