Spin-orbit interactions (SOI) of light involve the coupling between the spin (polarization) and orbital angular momentum (OAM) of light. These interactions are fundamental in optics and arise from the intrinsic properties of light, such as its polarization and spatial distribution. SOI effects are observed in various optical phenomena, including the spin-Hall effect, spin-to-orbital angular momentum conversion, and spin-directional coupling in structured fields. These effects are crucial in modern optics, especially at subwavelength scales, and are essential for controlling and manipulating light in nano-optics, photonics, and plasmonics. Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM). SAM is associated with the polarization of light, while OAM is related to the spatial distribution of the light beam. These angular momenta are influenced by geometric phases, which arise from the coupling between the spin and the rotation of the coordinate system. The spin-Hall effect, for example, describes the transverse shift of light beams due to their spin, and is a manifestation of SOI. Similarly, spin-to-orbital angular momentum conversion occurs in nonparaxial fields, where the spin of light influences its orbital angular momentum. SOI effects are also observed in anisotropic and inhomogeneous structures, such as metasurfaces and metamaterials. These structures can be designed to control the spin and orbital properties of light, enabling applications in optical manipulation, imaging, and spintronics. For instance, anisotropic structures can induce geometric phases that lead to spin-dependent shifts and directional coupling of light. In addition, evanescent waves, which decay exponentially in space, exhibit unique spin properties. These waves carry transverse spin angular momentum, which is distinct from the usual longitudinal spin of light. This transverse spin is a fundamental aspect of SOI and plays a crucial role in the coupling between light and surface plasmon-polaritons. Overall, SOI effects are inherent in all optical processes and are essential for understanding and controlling light at subwavelength scales. These effects are crucial for the development of advanced optical technologies, including high-resolution imaging, optical communications, and quantum information processing.Spin-orbit interactions (SOI) of light involve the coupling between the spin (polarization) and orbital angular momentum (OAM) of light. These interactions are fundamental in optics and arise from the intrinsic properties of light, such as its polarization and spatial distribution. SOI effects are observed in various optical phenomena, including the spin-Hall effect, spin-to-orbital angular momentum conversion, and spin-directional coupling in structured fields. These effects are crucial in modern optics, especially at subwavelength scales, and are essential for controlling and manipulating light in nano-optics, photonics, and plasmonics. Light carries both spin angular momentum (SAM) and orbital angular momentum (OAM). SAM is associated with the polarization of light, while OAM is related to the spatial distribution of the light beam. These angular momenta are influenced by geometric phases, which arise from the coupling between the spin and the rotation of the coordinate system. The spin-Hall effect, for example, describes the transverse shift of light beams due to their spin, and is a manifestation of SOI. Similarly, spin-to-orbital angular momentum conversion occurs in nonparaxial fields, where the spin of light influences its orbital angular momentum. SOI effects are also observed in anisotropic and inhomogeneous structures, such as metasurfaces and metamaterials. These structures can be designed to control the spin and orbital properties of light, enabling applications in optical manipulation, imaging, and spintronics. For instance, anisotropic structures can induce geometric phases that lead to spin-dependent shifts and directional coupling of light. In addition, evanescent waves, which decay exponentially in space, exhibit unique spin properties. These waves carry transverse spin angular momentum, which is distinct from the usual longitudinal spin of light. This transverse spin is a fundamental aspect of SOI and plays a crucial role in the coupling between light and surface plasmon-polaritons. Overall, SOI effects are inherent in all optical processes and are essential for understanding and controlling light at subwavelength scales. These effects are crucial for the development of advanced optical technologies, including high-resolution imaging, optical communications, and quantum information processing.