Abstract
Allowing subwavelength-scale-digitization of optical wavefronts to achieve complete control of light at interfaces, metasurfaces are particularly suited for the realization of planar phase-holograms that promise new applications in high-capacity information technologies. Similarly, the use of orbital angular momentum of light as a new degree of freedom for information processing can further improve the bandwidth of optical communications. However, due to the lack of orbital angular momentum selectivity in the design of conventional holograms, their utilization as an information carrier for holography has never been implemented. Here we demonstrate metasurface orbital angular momentum holography by utilizing strong orbital angular momentum selectivity offered by meta-holograms consisting of GaN nanopillars with discrete spatial frequency distributions. The reported orbital angular momentum-multiplexing allows lensless reconstruction of a range of distinctive orbital angular momentum-dependent holographic images. The results pave the way to the realization of ultrahigh-capacity holographic devices harnessing the previously inaccessible orbital angular momentum multiplexing.
Highlights
Allowing subwavelength-scale-digitization of optical wavefronts to achieve complete control of light at interfaces, metasurfaces are suited for the realization of planar phaseholograms that promise new applications in high-capacity information technologies
As such, outgoing spatial frequencies leaving the meta-hologram possess a helical wavefront inherited from the incident Orbital angular momentum (OAM) beam, which implies that the OAMconserving meta-hologram could create OAM-pixelated holographic images
Owing to mathematically orthogonal OAM modes without a topological charge limit, a large number of OAMdependent information channels can be multiplexed by a single meta-hologram with high spatial-resolution, which holds great promise for ultrahigh-capacity holographic devices and systems
Summary
Allowing subwavelength-scale-digitization of optical wavefronts to achieve complete control of light at interfaces, metasurfaces are suited for the realization of planar phaseholograms that promise new applications in high-capacity information technologies. Owing to the subwavelength nature of plasmonic[1] and dielectric[17,18,19,20] meta-atoms, high-resolution metasurfaces have revolutionized the photonic design of metaholograms for holographic displays[21,22,23,24], optical encryption[25,26], and nonlinear holography[27] In this context, meta-holograms responsive to different physical properties of light including polarization[28], helicity[29], wavelength[30], and incidence angle[31] have recently been exploited to address independent information channels for high-capacity holographic multiplexing. We adopted subwavelength Gallium Nitride (GaN) nanopillars on a transparent sapphire substrate to digitize designed meta-holograms at a visible wavelength of 632 nm To this purpose, three types of meta-holograms with discrete spatial frequency distributions are designed, including OAM-conserving (Fig. 1a), -selective (Fig. 1b), and -multiplexing (Fig. 1c) metaholograms, respectively. An OAM-conserving meta-hologram with a discrete spatial frequency distribution is able to produce OAM-pixelated holographic images by preserving the OAM property of incident OAM beams in each pixel of reconstructed holographic images (Fig. 1a)
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