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

Coupling between the spin and orbital angular momentum of light has led to a variety of exotic spin–orbit photonic effects, establishing a paradigm of nanophotonic meta-devices to control and manipulate light at the nanometer length scale. For the advancement of spin–orbit photonic technologies, quantitative characterization and unambiguous physical interpretation of the various spin–orbit interaction (SOI) effects exhibited in complex nanophotonic systems are of utmost importance. This Perspective addresses some of these outstanding challenges in the domain of spin–orbit photonics, focusing on the simultaneous manifestation of multiple SOI effects in hybridized nanophotonic systems and the role of polarization-based techniques in their characterization and quantification. After introducing the fundamentals and physical origins of SOI effects, we present a polarization Mueller matrix technique as a powerful tool to probe, decouple, and independently quantify these effects in a unified experimental framework, demonstrated with hybridized waveguided plasmonic crystals. We further discuss the potential of structured light and tailored polarization to enable unconventional SOI phenomena in simple nanostructured metamaterials and metasurfaces. These advancements not only enhance our fundamental understanding of SOI phenomena across micro- and nanoscale optical systems but also pave the way for the development of multifunctional and tunable spin–orbit photonic devices.