states can generate structured spatial light fields via the comprehensive manipulations of the helical phase, polarization, and propagation of the light. Intuitively, the equal-weighted superposition of OAM states with TCs of opposite signs may generate spatial modes of petal-like intensity with nonzero or zero global OAMs, and superpositions of higher-order OAMs may produce wheel-like modes with azimuthal variations of intensity in high dimensions. A variety of methods or devices have been developed to enable the superposition of OAMs. These include liquid crystal q-plates, [1][2][3] spatial light modulators, [4,5] crystal prism pairs, [6] microscopic ring resonators, [7,8] and other optical elements. [9][10][11] Moreover, the progress in OAM superposition has brought about many important applications in classical physics and quantum sciences. Classical applications include particle trapping, [12] optical communications, [13,14] and relativistic laser-matter interactions. [15,16] In the quantum field, important advancements have been made in quantum communications, [17][18][19] quantum information processing, [20,21] and quantum calculations. [22,23] The potential to miniaturize superposed spatial modes of OAM to nanoscale is promising for the implementation of integrated on-chip devices. Metasurfaces consisting of monolayers of subwavelength metallic/dielectric structures have become an efficient way to manipulate light at the subwavelength scale. In recent several years, the study of metasurfaces has attracted great interest in areas as phase-controlled, [24] broadband vectorial holograms, [25] broadband achromatic metalenses, [26] and the coherent control of plasmonic spin-Hall effects. [27] The development of metasurfaces for the manipulation of OAM states has also been studied extensively. [28][29][30][31][32][33][34][35] In the past year, significant progress has been made in achieving arbitrarily controlled OAM superposition states via metasurface engineering. Devlin et al. have proposed the metasurface J-plate to realize the superposition of independent OAM states and to convert SAMs into total angular momentum states. [36] Using a reflective plasmonic metasurface, Yue et al. demonstrated various OAM superpositions in multiple channels by changing the polarization of the illumination. [37,38] By designing a nonlinear plasmonic metasurface for the simultaneous control of the OAM and SAM, Li et al. achieved the OAM superposition of the modes of the second Superposition of orbital angular momentum (OAM) states and the structured intensity are providing new approaches for manipulating optical information and light-matter interactions. While superposition of OAMs in free space has been well studied, further extensions to surface plasmon polariton (SPP) confined in near-field would be crucial for miniaturing and integrating platforms. Here, the plasmonic metasurfaces consisting of rotated nanoslits arranged in a segmented spiral are proposed to realize the superposition of two SPP OAM states. The nanoslit rota...
Nanoscale lattices of arbitrary orders are generated by truncated spiral metasurfaces combining geometric and dynamic phases.
Vector vortices with spatially varying polarization are interesting phenomena and have motivated many recent studies. A vector vortex in the wavefield of a surface plasmon polariton (SPP) may be extended to the sub-wavelength scale, which would be more significant. However, the formation of vector vortices requires the polarization state to possess components parallel to the surface of metal films. In this study, we generated radially polarized vector plasmonic vortices using the metasurface spiral of orthogonal nanoslit pairs. We theoretically derived the x and y component expressions in the central point area of the spiral and obtained a doughnut-shaped intensity distribution with radial polarization. The Jones matrix of the metasurface spiral was generated to describe the polarization characteristics. The results were validated by performing finite-difference time-domain simulations. In addition, we used a Mach-Zehnder interferometer system to extract the intensity and phase distributions of different components of the SPP field. The experimental doughnut-shaped radially polarized vector vortex was consistent with the theoretical and simulated results.
Vector beams contain complex polarization structures and they are inherently non-separable in the polarization and spatial degrees of freedom. The spatially variant polarizations of vector beams have enabled many important applications in a variety of fields ranging from classical to quantum physics. In this study, we designed and realized a setup based on Mach-Zehnder interferometer for achieving the vector beams at arbitrary points of higher-order Poincaré sphere, through manipulating two eigenstates in the Mach-Zehnder interferometer system with the combined spiral phase plate. We demonstrated the generation of different kinds of higher-order Poincaré beams, including the beams at points on a latitude or longitude of higher-order Poincaré sphere, Bell states for |l| = 1 and |l| = 2, radially polarized beams of very high order with l = 16, etc. Vector beams of high quality and good accuracy are experimentally achieved, and the flexibility, feasibility and high efficiency of the setup are demonstrated by the practical performance.
A kind of plasmonic nanostructure is proposed that can generate the arbitrary superposition of orbital angular momentum (OAM) states in surface plasmons (SPs), which is achieved by combining the segmented spirals with nanoslit pairs. The structures can independently modulate both the phase and amplitude of SP waves, and thus enable the superposition of two OAM states with arbitrary topological charges (TCs) as well as free control of their relative amplitudes. Superposed states distributed over the entire Bloch sphere and hybrid superposed states with different TCs were constructed and experimentally demonstrated. This work will offer more opportunities for multifunctional plasmonic devices.
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