Spin-orbit Interaction Of Light And Its Evolution Characteristics In Subwavelength Structures

Spin-orbit interactions of light exist in all basic optical processes and play an important role in modern optics.It has attracted intensive research interest.Studying the spinorbit interactions of light in subwavelength structures can help us understand the mechanism of the interaction between light and matter and have a broad application prospect in many fields,including precision metrology,beam manipulation,polarization switchers,polarization sorters,quantum information and quantum computing.Therefore,it is of great theoretical significance and application value to explore the spin-orbit interactions of light in subwavelength structures.In this thesis,we study the spin-orbit interactions of light based on nanoparticles,subwavelength antenna,waveguides,and composite structures with antenna and waveguide.We investigate the interaction between the spin and extrinsic orbital angular momenta of light,and the interaction between the spin and intrinsic orbital angular momenta of light in theory.The main researches are as follows:We explore the interaction between spin and extrinsic orbital angular momenta in nanopaticle and subwavelength antennna structure and realize spin Hall effect in scattering far-field.Basing on the dipole model,we derive the analytical expression of the beam barycenter of the scattering far-field for an ellipsoidal Rayleigh particle.By analyzing the relationship between the beam barycenter and the spin state of the incident light,we obtain the conditions that realize the spin Hall effect of light.We illustrate the rationality of the analytical expression by comparing it with the simulation results.We calculate the optical force and torque exerted on the particle by considering the interaction between light and ellipsoidal Rayleigh particle.The results show that the transverse optical force is a manifestation of the spin Hall effect.In order to realize the enhanced spin Hall effect of light,we use an bianisotropic antenna to investigate.It is found that the size of antenna and electromagnetic coupling are the main factors affecting the spin Hall effect of light.We realize the transverse scattering by the reasonable design of antenna structure.We also explore the effect of the angle of incident light,the size and number of antennas on the spin Hall effect of light.We calculate the optical force and torque related to the spin Hall effect of light.We study the interaction between spin and extrinsic orbital angular momenta in composite structures with antenna and waveguide,and realize the unidirectional coupling ofwaveguide mode.Firstly,we derive the relationship between the spin state of incident light and the propagation direction of waveguide mode,and theoretically analyze the conditions for unidirectional coupling.On this basis,we design two kinds of nanoscale antenna arrays to excite TE0-like mode and TE1-like mode,and realize the spin Hall effect of light.The obtained unidirectional propagations possess ultra-high contrast ratio and mode purity.Besides,we use the waveguide mode transmitted in opposite direction to decouple the circularly polarized light with opposite spin state through the nanoantenna array,which realizes the reverse spin Hall effect of light.In the end,we propose a method to realize the TE0-like mode with high mode purity excited by the motion of electron beam,and give the relationship between the direction of motion of electron beam and the propagation direction of waveguide mode.We use the antenna array for decoupling the TE0-like mode in the waveguide to light in the vacuum,and the decoupled light is circularly polarized.The whole process contains the reverse spin Hall effect and realizes the circularly polarization of Cherenkov radiation.We investigate the interaction,transformation and evolution of spin and extrinsic orbital angular momenta in subwavelength waveguides,and obtain the relationship of optical angular momentum and torque.When a circularly polarized light is normally incident on the end of the hollow metal waveguide,the partial spin angular momentum of light is converted to the intrinsic orbital angular momentum.We derive the analytical expressions of the angular momentum of light in hollow metal waveguides theoretically.We analyze and verify the influence of waveguide shape on evolution characteristics of angular momenta.Considering the interaction between light and metal waveguide,we derive the relationship between the torque acting on the metal waveguide and the angular momentum of light,and obtain the evolution characteristic of the torque.Besides,we study the interaction and evolution characteristics of the spin and orbital angular momenta of light in the silicon waveguide theoretically,and analyze the relationship between angular momentum of light and torque in the silicon waveguide.The research reveals the intrinsic orbital angular momentum of light is essential to the angular momentum conservation of the system.Futhermore,we control the ratio between the orbital angular momentum and the total angular momentum by changing the wavelength of incident light and the size of waveguide.We design a three-segment waveguide structure to realize the polarization conversion of light and explore the torque exerted on the waveguide.It provides theoretical guidance for the application of spin-orbit interaction of light in photonic technology.