Nonreciprocal cross-polarization coupling in whispering-gallery microresonators

Abstract

Coupling of light from a microresonator TE mode to a coresonant TM mode will have a different strength than that of coupling from the TM mode to the TE mode. This coupling nonreciprocity, deriving from the optical spin-orbit interaction, is modeled numerically and confirmed experimentally by observing coupled-mode induced transparency and Autler-Townes splitting. By measuring the throughput spectrum in both polarizations when the input directly excites modes of only one polarization, the coupling strengths in both directions can be determined simultaneously by fitting to the numerical model. Some examples and implications are discussed here.