Manipulation Characteristics Of Photonic Spin Hall Effect By Graphene Composite Structures

As a finite-width linear polarization beam reflects or refracts at an interface,its left and right circularly polarized components will undergo different geometric phase and shift transversely.Such a phenomenon is referred to as the photonic spin Hall effect(PSHE).As one of the basic phenomena of photon spin-orbit interaction,PSHE provides a new paradigm for a tunable spin photonic device and shows tremendous potential in precision metrology,quantum information,and micro-nano optics.Adjusting the incident light filed or optical parameters of the interface,the RytoVladimirskii-Berry geometric phase in the momentum space or the PancharatnamBerry geometric phase in the real space is modulated,which in turn manipulates the spin split of PSHE.In this dissertation,graphene,whose optical parameters can be tuned dynamically,is introduced in the reflected interface,and then the manipulation characteristics of the graphene-based interfaces and the graphene-based metasurfaces on PSHE are studied.The calculation model of PSHE as linear polarization light incidence is established and the weak measurement setup is introduced.Also,the impact of pitch angle on results of weak measurement is analyzed.The variation of the RytoVladimirskii-Berry geometric phase is revealed based on the three-dimensional reflection model of the Gaussian beam,and the expressions of the spin shift are derived.The left and right circularly polarized components will shift transversely perpendicular to the refractive index gradient with equal magnitude and different directions.In addition,the spin-independent Imbert-Fedorov angular shift will be introduced as incident polarization is not horizontal or vertical.The spin shift is measured by setting the pre-selection and post-selection to be nearly perpendicular in weak measurement experiment where the spin shift is coupled to the Gaussian beam.After that,the impact of pitch angle on PSHE and weak measurement are discussed base on the relationship between pitch angle and incident polarization state.It is proved that the variation of pitch angle will influence the amplification factor of the spin shift.Furthermore,the amplification factor is very sensitive to pitch angle when the sum of deviation angle and post-selection angle is zero.The manipulation characteristics of the graphene-based interfaces on spin shift of PSHE is studied.The theoretical model of PSHE at a complex index interface is established.It is found that the spin-dependent phase shift and transverse shift in the momentum space are generated because of the graphene complex index,which corresponds to the spin line shift and the spin angular shift in the real space.The manipulation characteristics of the spin line shift and spin angular shift varies with Fermi energy.The spin angular shift is decided by the imaginary part of the Fresnel coefficient.The value and direction of the spin angular shift of PSHE can also be tuned by the Fermi energy of graphene.By contrast,the Fermi energy has an obvious spin line shift only when the incident angle is around the Brewster angle and the incident polarization is horizontal.The spin line shift and spin angular shift are measured by weak measurement with the real and imaginary weak value,respectively.The manipulation characteristics of graphene-based metasurface on wave vector spin splitting of PSHE is studied.The metasurface element is proposed with a circular cross-polarized reflection coefficient of 0.885,and the reflected circular crosspolarized component has spin-dependent Pancharatnam-Berry geometric phase delay as the element orientation being changed.After that,phase gradient metasurface is structured by arrangingthose elements with the same rotation angle interval,and the two circular polarized components undergo continuous spin-dependent phase gradient ranging from 0 to 2?.The wave vector of reflected light occurs spin-splitting with inverse reflected angle for linear polarization light normal incidence,and such a phenomenon is also called PSHE.To achieve the purpose of manipulating wave vector spin splitting,the period length is adjusted to alter the spin-dependent geometric phase gradient,and it is found that the reflected angle is inversely proportional to the period length.Besides,the circular cross-polarized reflection coefficient is tuned by Fermi energy of graphene,and in turn to manipulate the electric field intensity of the spin-splitting light.Moreover,the phase gradient metasurface can be efficiently operated over wide band with a high circular crosspolarized reflection coefficient by setting appropriate Fermi energy.Finally,abnormal PSHE is achieved by off-center flat lens metasurface.As a result,the left circular polarized component is focused along one side and the right circular polarized component is scattered along another side.