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Register a new userHybrid waves localized at hyperbolic metasurfaces
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We reveal the existence of a new type of surface electromagnetic waves supported by hyperbolic metasurfaces, described by a conductivity tensor with an indefinite signature. We demonstrate that the spectrum of the hyperbolic metasurface waves consists of two branches corresponding to hybrid TE-TM waves with the polarization that varies from linear to elliptic or circular depending on the wave frequency and propagation direction. We analyze the effect of losses of the surface waves and derive the corresponding analytical asymptotic expressions.
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Efficient hybrid plasmonic-photonic metasurfaces that simultaneously take advantage of the potential of both pure metallic and all-dielectric nanoantennas are identified as an emerging technology in flat optics. Nevertheless, post-fabrication tunable hybrid metasurfaces are still elusive. Here, we present a reconfigurable hybrid metasurface platform by incorporating the phase-change material Ge$_{2}$Sb$_{2}$Te$_{5}$ (GST) into metal-dielectric meta-atoms for active and non-volatile tuning of properties of light. We systematically design a reduced-dimension meta-atom, which selectively controls the fundamental hybrid plasmonic-photonic resonances of the metasurface via the dynamic change of optical constants of GST without compromising the scattering efficiency. As a proof-of-concept, we experimentally demonstrate miniaturized tunable metasurfaces that control the amplitude and phase of incident light necessary for high-contrast optical switching and anomalous to specular beam deflection, respectively. Finally, we leverage a deep learning-based approach to present an intuitive low-dimensional visualization of the enhanced range of response reconfiguration enabled by the addition of GST. Our findings further substantiate dynamically tunable hybrid metasurfaces as promising candidates for the development of small-footprint energy harvesting, imaging, and optical signal processing devices.
Dyakonov surface wave existing at the interface with anisotropy offers a promising way of guiding light in two-dimension with almost no loss. However, predicted decades ago, the experimental demonstration of the Dyakonov surface wave seems always challenging for the weak anisotropic indices from the natural materials. Here we experimentally demonstrated a Dyakonov surface wave mode propagating in a hyperbolic metasurface at the visible frequency. Dyakonov surface waves at the two surfaces of the metasurface can be supported simultaneously by the hyperbolic anisotropy and form a Dyakonov typed mode with low loss and a large allowed angle band. A detailed theoretical analysis and numerical simulations prove that the electric field of such a surface wave mode shows transverse spin, whose direction is determined by the orientations of the hyperbolic anisotropy and surface normal, based on which we experimentally observed the photonic spin Hall effect of the surface wave mode in our metasurface.
Metasurfaces offer the potential to control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. Existing metasurfaces frequently utilize metallic polaritonic elements with high absorption losses, and/or fixed geometrical designs that serve a single function. Here we overcome these limitations by demonstrating a reconfigurable hyperbolic metasurface comprising of a heterostructure of isotopically enriched hexagonal boron nitride (hBN) in direct contact with the phase-change material (PCM) vanadium dioxide (VO2). Spatially localized metallic and dielectric domains in VO2 change the wavelength of the hyperbolic phonon polaritons (HPhPs) supported in hBN by a factor 1.6 at 1450cm-1. This induces in-plane launching, refraction and reflection of HPhPs in the hBN, proving reconfigurable control of in-plane HPhP propagation at the nanoscale15. These results exemplify a generalizable framework based on combining hyperbolic media and PCMs in order to design optical functionalities such as resonant cavities, beam steering, waveguiding and focusing with nanometric control.
Motivated by the recent growing demand in dynamically-controlled flat optics, we take advantage of a hybrid phase-change plasmonic metasurface (MS) to effectively tailor the amplitude, phase, and polarization responses of the incident beam within a unique structure. Such a periodic architecture exhibits two fundamental modes; pronounced counter-propagating short-range surface plasmon polariton (SR-SPP) coupled to the Ge2Sb2Te5 (GST) alloy as the feed gap, and the propagative surface plasmon polariton (PR-SPP) resonant modes tunneling to the GST nanostripes. By leveraging the multistate phase transition of alloy from amorphous to the crystalline, which induces significant complex permittivity change, the interplay between such enhanced modes can be drastically modified. Accordingly, in the intermediate phases, the proposed system experiences a coupled condition of operational over-coupling and under-coupling regimes leading to an inherently broadband response. We wisely addressing each gate-tunable meta-atom to achieve robust control over the reflection characteristics, wide phase agility up to 315? or considerable reflectance modulation up to 60%, which facilitate a myriad of on-demand optical functionalities in the telecommunication band. Based on the revealed underlying physics and electro-thermal effects in the GST alloy, a simple systematic approach for realization of an electro-optically tunable multifunctional metadevice governing anomalous reflection angle control (e.g., phased array antenna), near-perfect absorption (e.g., modulator), and polarization conversion (e.g., wave plate) is presented. As a promising alternative to their passive counterparts, such high-speed, non-volatile MSs offer an smart paradigm for reversible, energy-efficient, and programmable optoelectronic devices such as holograms, switches, and polarimeters.
In passive linear systems, complete combining of powers carried by waves from several input channels into a single output channel is forbidden by the energy conservation law. Here, we demonstrate that complete combination of both coherent and incoherent plane waves can be achieved using metasurfaces with properties varying in space and time. The proposed structure reflects waves of the same frequency but incident at different angles towards a single direction. The frequencies of the output waves are shifted by the metasurface, ensuring perfect incoherent power combining. The proposed concept of power combining is general and can be applied for electromagnetic waves from the microwave to optical domains, as well as for waves of other physical nature.
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