Revealing the spin optics in conic-shaped metasurfaces

Abstract

Ellipse and hyperbola are two well-known curves in mathematics with numerous applications in various fields, but their properties and inherent differences in spin optics are less understood. Here, we investigate the peculiar optical spin properties of the two curves and establish a connection between their foci and the spin states of incident light. We show that the optical spin Hall effect is the intrinsic optical spin property of ellipse, where photons with different spin states can be exactly separated to each of its two foci. While a hyperbola exhibits optical spin-selective effect, where only photons with one particular spin state can be accumulated at its foci. These properties are then experimentally demonstrated in near field by arranging nanoslits in conic shape. Based on the spin properties of the curves, we design spin-based plasmonic devices with various functionalities. Our results reveal the intrinsic optical spin properties behind conic curves and provide a route for designing spin-based plasmonic device.

Spin‐Controlled Integrated Near‐ and Far‐Field Optical Launcher

“…Upon the illumination of a beam at normal incidence, the nanoslit simultaneously generates SPPs in the near field that propagates along the metallic surface, and scatters the incident light into the far field. Under the circular polarization (CP) incidence, the nanoslit generates locally a geometric phase of σθ for the surface waves 5,20 , while a geometric phase 2σθ in its cross polarization for the transmitted wave 22,32 , where σ=±1 corresponds to the spin state of right-(RCP) and left-circular polarization (LCP) for the incident light and θ is the orientation angle of the nanoslit relative to the x axis. By utilizing different geometric phases of the nanoslit in the near and far fields, we are able to integrate both the near-and far-field functionalities into a single structure.…”

“…To achieve high-intensity focusing, we modify the metasurface design into a circular configuration, such that both the near field and the scattered far field can be focused into a 2D spot. In the near field, the SPPs generated by each slit propagating toward opposite directions exhibits a π-phase difference, which should be taken into account in the design of the metasurface 20 . The detail of the design is provided in Supplementary Note 2.…”

“…The ultra-thin metasurface provides a novel route for design of compact optical components. These characteristics make the metasurface a promising candidate for a variety of applications, including the optical spin Hall effect [19][20][21] , anomalous refraction 18,[22][23][24] , metalens [12][13][14][15] , optical vortex generation [25][26][27] and optical holography [28][29][30][31] .…”

Space‐Frequency‐Domain Gradient Metamaterials

“…The space‐variant phase distribution of metamaterial exerts strong effects on the wavefront shape, in which arrays of elements with designed phase gradients in space achieve many unnatural phenomena such as anomalous refraction, super resolution imaging, and invisibility cloaking . In recent years, metamaterials have also been shown useful in many other scenarios, such as optical launcher and metalenses with multiple functionalities, beam scanning for detection of targets, transmission of multiple vortex modes to enhance the communication capacity, generation of multiple beams in space for computational imaging, and control of EM waves in a digital manner from the information science perspective . The phase distributions of metamaterials play the key role in realizing the above unnatural physical phenomena and interesting functionalities, whereas the existing theories and methods are usually focused on the performance of metamaterials with phase gradients in space, so that the frequency‐domain properties are rarely explored.…”

Polarization Controlled Dual Functional Reflective Planar Metalens in Near Infrared Regime

“…Lots of models like the nanoslit [17], nanohole [18,19], and graphene ribbons [20][21][22][23][24] have been introduced in metalens design, where 2π phase shift resulting from the designed antennas is needed in controlling the wavefront. Although a polarization-independent metalens [12,25] and polarization-conversion metalens [26] have been reported in former works, and the designed metalenses are always adjusted to manipulate different kinds of incident waves with various structures [27][28][29][30], the metalens, with its function controlled by incident polarization state [31,32], has not been fully investigated.…”