Plasmonic Metasurface For The Generation Of Vector Beams And The Manipulation Of Plasmonic Orbital Angular Momentum

The polarization and phase are the basic characteristics of an electromagnetic field,and their manipulation enables many interesting optical phonomenon and plays an important role in other areas.Traditional approaches to controlling the light polarization states and phase employ the birefringence and total internal reflection in crystals and polymers,or change the geometrical shape and variation of the spatial profile of the refractive index.However,these components using conventional methods are bulky and very often operate only within a narrow wavelength range,resulting in difficulties in optical system miniaturization and integration,insufficient for emerging technologies with increasingly demanding requirements.Relative to conventional optical elements,metasurfaces have shown novel optical phenomena and promising functionalities with more compact platforms and more straightforward fabrication processes.Metasurfaces are two-dimensional(2D)or planar versions of metamaterials with subwavelength thickness.It has been widely studied in the past decade due to their unique interaction with electromagnetic waves.Their exceptional ability to manipulate waves is due to their strong interaction with electric and/or magnetic fields,which is typically provided by resonant effects controlled by the geometry of the unit cells.These capabilities lead to a wide range of applications such as abnormal refraction,superlenses,spin-orbital convertion,vortex generator,and hologram.Vectorial optical field with spatially variant polarization distribution has arracted accelarate consideration for their interesting applications as tight focusing,partical manipulation,optical micromanipulation,superresolution imaging and laser accelerating.Driven by such interesting applications,many methods have been proposed and attempt to generate vector beams.The generation of high-order Poincare sphere,hybide-order Poincare spher and generalized Poincare spher accelarate the progess of vector fied in some extent.This dissertation mainlycombining the results in the areas of metasurface and vector light field,and with the spin-to-orbit conversion of the nano-structures in the plasmonic metasurface,this project focuses on the generation of different high-order vector light fields and the superposition of the orbital angular momentum in the surface plasmon polaritons.The research contents of the main chapters are listed as follows:1.We investigated a method of generating a radially polarized vector vortex in the SPP field produced by a metasurface spiral of orthogonal nanoslit pairs.We introduced a theory that models the field generated by a single orthogonal nanoslit pair.Combining the nanoslit pairs with spiral geometry to construct a metasurface spiral and using the Huygens–Fresnel principle,we derived expressions for the x-and y-components in the central point area of the metasurface spiral and obtained a doughnut-shaped intensity distribution.Simultaneously,the polarization ellipses in(Ex,Ey)coordinates were drawn and qualitatively demonstrated the formation of a radially polarized SPP vector vortex.Our analytical method provides physical insight into the characteristics of plasmonic component fields.To understand the polarization properties,the Jones matrix of the metasurface spiral was derived.The theoretical and simulation data were agreed closely with each other.In addition,we constructed a Mach–Zehnder interferometer system to measure the SPP wavefields.Overall,the extracted data maps for the distributions of the amplitude and phase as well as the radial polarization state were reasonably consistent with the theoretical and simulation results.We expect this work to facilitate the design of plasmonic polarization devices and manipulation of on-chip SPP fields.2.We propose plasmonic metasurface consisting of orthogonal nanoslit pair to manipulate polarization and for the first time to generate RPVB with linearly polarized illumination.We demonstrate that when orthogonal nanoslit pairs are arranged in column,the polarization of generated plasmonic wavelets varies linearly with orientations of the nanoslit pairs but is perpendicular to the column with regardless of incident linearly polarized light.Basing on this characteristic,we design metasurface of the nanoslit pairs with gradually varied orientation arranged in the Archimedes spiral.The Pancharatnam-Berry(PB)phase induced by the rotation of nanoslit pairs is exactly compensated by phase of the increased spiral radius,and RPVBs are achieved under illuminations of different linearly polarized lights.The detailed theoretical analyses,the finite difference time domain(FDTD)simulations and experimental performance demonstrate the generation of the RPVB.3.In this letter,we propose a plasmonic metasurface consisting of spatially variant subwavelength nanoslits with different width arranging on the segmented Archimedes spiral to produce any HOP sphere beams which are conventionally generated in complicated optical systems with many ordinary optical devices.In the metasurface engineering,we incorporate the segmented spiral configuration with rotated rectangular nanoslit unit cell.On one hand,the nanoslit divides the incident circular polarized light into two parts.One is direct transmission maintaining polarization state,and the other part is circularly polarized with opposite handedness.The second part also experiences a geometrical phase ?g(?)= 2??(?),where ? is azimuthal angle,?=±1 denotes the polarization helicity of the incident light,and ?(?)=q?+?0 is the nanoslit orientation,q is the rotation order of nanoslit and ?0 is the initial angle.Varying the width of nanoslits,the transmission and conversion efficiency of CP light are modulated.On the other hand,the spiral with geometric order m modulates the propagation phase by varying the optical path of m? within azimuthal angle of 2?,and the propagation phase with order lo acts on both directly transmitted and polarization converted parts.Then the directly transmitted wave becomes vortex beam of m order with circular polarization of unchanged handedness,and conversion part becomes a vortex beam of m-2q? order with circular polarization of opposite handedness.When orbital charge m is the same as rotation order q,addition of these two parts forms the superposition of two cross-circularly polarization vortex beams with adjusted coefficients.Subsequently the vortex beams on HOP sphere can be easily obtained.We introduce the theory for the phase and polarization control and confirm it experimentally HOP sphere beams including CV vortex beams of azimuthal order |l|=1,2,4,6 and |l|=10.The method provides a simple,feasible,and flexible way to simultaneous control of phase and polarization and generation of HOP sphere beams,it also hold promi se for the novel functionalities to nano-photonic devices e.g.,encoding and retrieving photonics states in the spin-orbital space and render this technology very attractive for diverse applications in both classic physics and quantum science.4.We designed novel metasurfaces to realize the arbitrary superposition of SPP OAM states by combining the spin-dependent geometric and position-dependent dynamic phases.As shown,the metasurface controls the geometric and dynamic phases by way of slits of rotation order q arranged on a segmented spiral of order m.This configuration generates two corresponding OAM states |l1 = ?(2q-1)+ m> and |l2 = ? + m>.By leveraging the parameters of the metasurface m,q,the initial slit orientation ?0,and the incident circular polarization of the spin ?,superposition of arbitrary SPP OAM states can be achieved in a straightforward and flexible manner.The petal-like structured SPP intensity patterns of the superposition were experimentally observed in the near-field of the metasurface,and more detailed properties and evolutions of the superposition state were analyzed via FDTD simulations.The superposition of arbitrary two SPP OAM states in the near-field has fundamental advantages over the usual method of generating a single OAM state,and should prove useful in a variety of applications,including conventional and quantum communications,quantum information,and on-chip integration engineering.