Spin-Orbit Interactions Of Light In Anisotropic Metamaterials

Light has both spin angular momentum and orbital angular momentum analogous to electrons,which can be determined by the polarization and spatial degrees of freedom of light.These two types of angular momentum can undergo coupled interactions,called spin-orbit interaction of light.Such interactions exist in all fundamental optical processes,but their effects can be neglected at the macroscopic scale.In subwavelength scales,spin-orbit interactions strongly affect fundamental optical processes(including propagation,reflection,focusing,scattering,diffraction,and imaging)and are critical physical effects in nano-photonics and plasmonics.Metamaterials have been widely used in many scientific fields because of their artificially designed idiosyncratic permittivity and permeability,which provide extremely rich possibilities for manipulating electromagnetic waves.With the improvement of micro/nano fabrication technology and related theories,anisotropic superstructures,as an important branch of superstructures,have attracted much attention for their ability to modulate the electromagnetic response in different directions independently.More importantly,anisotropic electromagnetic structures can significantly enhance the spin-orbit interaction of light and efficiently manipulate the spin and orbital angular momentum of light,thus exhibiting the potential for applications in enhanced photonic spin Hall effect,field manipulation,and high-efficient optical differential operation.In this dissertation,we study the spin-orbit interaction of light in anisotropic metamaterials and achieves the following results.1.The photonic spin Hall effect is an optical effect that depends on the material properties.The spin Hall shift in conventional materials is only on the nanometer scale,belonging to a weak effect.The enhancement of the photonic spin Hall effect is essential for precision measurements and optical device development.In this dissertation,we investigate the spin-orbit interaction of light in hyperbolic metamaterials in conjunction with a modified beam transport theory,and we find that the incident beam near the photonic Dirac point exhibits an enhanced photonic spin Hall effect.The mechanism of this enhancement is revealed using geometric phase theory.2.In studying the reflection behavior of the arbitrary angular spectrum in the beam at hyperbolic metamaterials,we find that the reflected polarization state undergoes a spin-flip and acquires a vortex phase when the beam is incident near the photonic Dirac point.Combining the Stokes parameters,the polarization state change and the geometric phase change of this process are described by the higher-order Poincare sphere.It is revealing that the spin-orbit interaction is enhanced due to the optical simplification point,which converts the spin angular momentum into orbital angular momentum,thus generating a vortex beam corresponding to the topological charge.In addition,the angular spectrum distribution of vertical incidence characterizes the topological charge distribution near the paired Dirac points,which verifies the topological invariance of the whole system.These results enrich the means of characterizing the topological states and provide new ideas for the reverse design of metamaterials to manipulate the evolution of the optical field polarization.3.Optical differential operation is the core principle of edge detection,which has the advantages of broadband,lossless and low power consumption compared with traditional methods.However,the current research mainly focuses on first-order differentiation.Few higher-order optical differentiators have been studied.The weak spin-orbit interaction due to the inherent electromagnetic structure in conventional materials restricts the effectiveness of edge detection and hinders further applications.This paper proposes a scheme to enhance the effect of differential operations using an anisotropic dielectric thin plate from geometric phase theory and beam transmission theory.The spinreconfigured Pancharatnam-Berry phase,induced by the topological phase transition of polarization structure,causes the spin-flip component to capture the vortex phase corresponding to the second-order differentiation.By introducing an anisotropic dielectric constant response in epsilon-near-zero metamaterials,the spin-orbit angular momentum conversion is significantly increased,and the efficiency of the optical differential operation is remarkably enhanced.The research results are expected to have valuable applications prospects in all-optical image processing,microscopic biological imaging,and quantum imaging.