Investigating spin-orbit interaction of light in micro- and nanophotonic systems using polarization Mueller matrix.

This article focuses on the challenges and methodologies for characterizing and interpreting spin–orbit interaction (SOI) effects of light in complex nanophotonic systems. It reviews the fundamental origins of SOI—arising from the coupling between spin angular momentum (SAM) and orbital angular momentum (OAM) of light—and discusses how these effects manifest in various optical phenomena, including the photonic spin Hall effect and vortex beam generation. A key contribution is the presentation of polarization Mueller matrix (MM) microscopy as a unified experimental framework to probe, decouple, and quantitatively analyze multiple simultaneous SOI effects in hybridized nanostructured metamaterials, such as waveguided plasmonic crystals (WPCs). The article highlights how structured light and tailored polarization states can induce and enhance unconventional SOI phenomena, and demonstrates that hybridized resonances in nanostructures enable tunable and amplified SOI effects, with potential applications in multifunctional spin–orbit photonic nanodevices.