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Spin‐controlled vortex generation and spin‐Hall effect, two distinct effects discovered in optics, have been extensively studied recently. However, while physical origins of two effects are both due to spin‐orbit interactions, their inherent connections remain obscure which also hinders further explorations on the manipulations of them. Here, in studying the scattering of a spin‐polarized light beam at sharp interfaces, an intriguing phase transition between vortex generation and spin‐Hall shift trigged by varying the incidence angle is revealed. After reflection/refraction, the beam contains two components: normal and abnormal modes acquiring spin‐redirection‐Berry phases and Pancharatnam–Berry phases, respectively. Inside the abnormal beam, two classes of wave components gain Pancharatnam–Berry phases with distinct topological natures, generating intrinsic and extrinsic orbital angular momenta (OAM), respectively. Enlarging incidence angle changes the relative portions of these two contributions, making the abnormal beam undergo a phase transition from vortex generation to spin‐Hall shift. Such intriguing effect is experimentally observed at a purposely designed metamaterial slab, exhibiting efficiency enhanced by several‐thousand times compared to that at a conventional slab. These findings unify two previously discovered effects in a single framework, reinterpret previous results with clearer pictures, and shed light on understanding other physical effects involving the competition between intrinsic and extrinsic OAM. [ABSTRACT FROM AUTHOR]

The fruitful progress toward light manipulation in reflective (R) or transmissive (T) geometry (half‐space) has facilitated strong aspiration towards full‐space wave control. Although R–T synergistic strategy promises large‐capacity and integrated functionality, it imposes difficulty and challenges for direction of arrival (DoA) in full space via an ultrathin flat device. As of today, very limited demonstrations are reported for single‐wavelength and linear‐polarization operation in full space, significantly limiting the exploitable degrees of freedom (DoFs) for real‐world applications. Herein, a triple‐layer wavelength‐direction multitasking scheme for wide‐angle and large‐capacity DoA is reported, which is pivotal for blind‐free radar detection. By engineering two anisotropic sub‐meta‐atoms with high quality factor and simultaneous in‐plane and out‐of‐plane symmetry breaking, four R and two T spin‐conversion channels are achieved in wide‐angle operation with high efficiency and insulation. Above features and released DoFs would be extraordinarily beneficial for large‐capability and angle‐engineered advanced applications. Two proof‐of‐concept metadevices, i.e., a large‐scanning kaleidoscopic‐beam generator and a wide‐angle reverser for multi‐target tracking, are devised to verify the significance. Numerical and experimental results show predesigned functions at six channels with measured efficiency over 75%. The findings in achieving multi‐DoF multitasking can stimulate great interest in radar applications with versatile forming beams and multi‐channel integration. [ABSTRACT FROM AUTHOR]

Abstract: The emerging invisibility schemes mainly adopt transformation optics, scattering cancellation, light diffusion, and metasurface‐based phase restoration techniques. However, those aforementioned invisibility achievements natively depend on the predefined curvature, polarization, frequency, and/or angle of the incident wave. Here, an invisibility strategy of using an ultrathin parabolic‐phase metasurface and its applications to achieve diffusive invisibility for dual‐polarization channels and multifrequency channels is reported. Such strategy can intrinsically split the wavenumber of the scattering wave and therein is termed as wavenumber‐splitting metasurface. For verification, two proof‐of‐concept examples are experimentally characterized. The first prototype manifests dual‐polarized near‐isotropic diffusive scattering immune from wide‐angle incidences. The second demonstration exhibits bifunctionality of combined diffusive invisibility and vortex scattering in dual‐polarization channels. In both cases, theoretical, numerical and experimental results agree well, illustrating a well‐separated triple‐band versatile scattering behavior. This approach addresses the fundamental issue of real invisibility under bistatic detection without complex optimization, thanks to the physical essence of numerous splitting wave vectors. Such strategy opens an upstream way to realize invisibility as well as holding the potentials for downstream applications such as stealth and camouflaging devices. [ABSTRACT FROM AUTHOR]

Achieving flexible and highly directive emissions toward pre-designed directions has intrigued long-held interest in both science and engineering community, but most available efforts suffer the issues of bulky size, limited functionalities, and low efficiency. Here, we propose a general strategy to efficiently and flexibly control the emission beams with dual functionalities realized independently by orthogonal excitations. To overcome the polarization cross-talking, a novel planar multi-mode anisotropic meta-atom is designed by incorporating the screening effect of a surrounding wire loop. As the result, we can design the polarization-dependent phase profile under certain polarization, without worrying about their influences on the other polarization. As an illustration, two proof-of-concept metasurfaces are actualized at microwave frequencies, of which one combines the functionalities of focused-beam and large-angle multibeam emissions while another hybrids the functionalities of beam-steering and small-angle multibeam emissions. Theoretical, full-wave simulation, and experimental results are in excellent agreement with each other, which collectively demonstrate the desired performances of our bifunctional devices. Our proposed strategy paves the way to realize high-performance multifunctional optical devices with high integration and complex wavefront manipulations. [ABSTRACT FROM AUTHOR]

Compact and miniaturized devices with flexible functionalities are always highly demanded in optical integrated systems. Plasmonic nanosieve has been successfully harnessed as an ultrathin flat platform for complex manipulation of light, including holography, vortex generation, and nonlinear processes. Compared with most of the reported single-functional devices, multifunctional nanosieves might find more complex and novel applications across nanophotonics, optics, and nanotechnology. Here, a promising roadmap for nanosieve-based helical devices is experimentally demonstrated, which achieves full manipulations of optical vortices, including its generation, hybridization, spatial multiplexing, focusing and nondiffraction propagation, etc., by controlling the geometric phase of spin light via over 121 thousands of spatially rotated nanosieves. Thanks to such spin-conversion nanosieve helical elements, it is no longer necessary to employ the conventional two-beam interferometric measurement to characterize optical vortices, while the interference can be realized natively without changing any parts of the current setup. The proposed strategy makes the far-field manipulations of optical orbital angular momentum within an ultrathin interface viable and bridges singular optics and integrated optics. In addition, it enables more unique extensibility and flexibility in versatile optical elements than traditional phase-accumulated helical optical devices. [ABSTRACT FROM AUTHOR]

Simultaneously independent control of phase, amplitude, and polarization is pivotal yet challenging for manipulating electromagnetic waves by transmissive metasurfaces. Huygens' metasurface affords a high‐efficiency recipe primarily by engineering phase‐only meta‐atoms, restricting itself from realizing unprecedentedly complex functions of the transmission beam. Here, a 3D chirality‐assisted metasurface concept relying on integrated magnetoelectric meta‐atoms is proposed. It empowers the completely decoupled and arbitrary control of phase and amplitude at large incident angles and arbitrary polarizations. This strategy thus facilitates very sophisticated beam manipulations at close‐to‐unity cross‐polarized efficiency via trilayer integrated resonators with mutual twist. The prescribed phase coverage can be determined by geometrical footprints of the unit cell, while the global azimuthal twist unlocks the capability of tuning amplitudes without affecting the phase. The concept and significance of it are validated to implement several proof‐of‐prototype demanding functionalities by thin metasurfaces of λo/12, which generate self‐accelerating diffraction‐free Airy beams, lateral and axial dual focusing, and even specific multiplexed beam shaping, respectively. This finding opens up an alternative way in very fine control of light with minimalist complexity and advanced performance. It can stimulate novel and high‐performance versatile photonic metadevices, thanks to the fully independent control of phase, amplitude, and polarization. The decoupling of amplitude, phase and polarization is analogous to the mechanical counterpart of three‐gear systems. The traditional dilemma is that tuning of either part will automatically affect the rest. This locks up metasurface functions and thereby limits its potentials. Now the authors' concept unlocks those "gears" such that each could be independently tuned, providing unprecedented access to the flatland of high‐efficiency metasurfaces. [ABSTRACT FROM AUTHOR]