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Register a new userAll-Dielectric Silicon/Phase-Change Optical Metasurfaces with Independent and Reconfigurable Control of Resonant Modes
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All-dielectric metasurfaces consisting of arrays of nanostructured high-refractive-index materials, typically Si, are re-writing what is achievable in terms of the manipulation of light. Such devices support very strong magnetic, as well as electric, resonances, and are free of ohmic losses that severely limit the performance of their plasmonic counterparts. However, the functionality of dielectric-based metasurfaces is fixed-by-design, i.e. the optical response is fixed by the size, arrangement and index of the nanoresonators. A far wider range of applications could be addressed if active/reconfigurable control were possible. We demonstrate this here, via a new hybrid metasurface concept in which active control is achieved by embedding deeply sub-wavelength inclusions of a tuneable chalcogenide phase-change material within the body of high-index Si nanocylinders. Moreover, by strategic placement of the phase-change layer, and switching of its phase-state, we show selective and active control of metasuface resonances. This yields novel functionality, which we showcase via a dual- to mono-band meta-switch operating simultaneously in the O and C telecommunication bands.
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Metasurfaces are optically thin metamaterials that promise complete control of the wavefront of light but are primarily used to control only the phase of light. Here, we present an approach, simple in concept and in practice, that uses meta-atoms with a varying degree of form birefringence and rotation angles to create high-efficiency dielectric metasurfaces that control both the optical amplitude and phase at one or two frequencies. This opens up applications in computer-generated holography, allowing faithful reproduction of both the phase and amplitude of a target holographic scene without the iterative algorithms required in phase-only holography. We demonstrate all-dielectric metasurface holograms with independent and complete control of the amplitude and phase at up to two optical frequencies simultaneously to generate two- and three-dimensional holographic objects. We show that phase-amplitude metasurfaces enable a few features not attainable in phase-only holography; these include creating artifact-free two-dimensional holographic images, encoding phase and amplitude profiles separately at the object plane, encoding intensity profiles at the metasurface and object planes separately, and controlling the surface textures of three-dimensional holographic objects.
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.
Nonlinear metasurfaces have become prominent tools for controlling and engineering light at the nanoscale. Usually, the polarization of the total generated third harmonic is studied. However, diffraction orders may present different polarizations. Here, we design an high quality factor silicon metasurface for third harmonic generation and perform back focal plane imaging of the diffraction orders, which present a rich variety of polarization states. Our results demonstrate the possibility of tailoring the polarization of the generated nonlinear diffraction orders paving the way to a higher degree of wavefront control.
The improvement of light-emitting diodes (LEDs) is one of the major goals of optoelectronics and photonics research. While emission rate enhancement is certainly one of the targets, in this regard, for LED integration to complex photonic devices, one would require to have, additionally, precise control of the wavefront of the emitted light. Metasurfaces are spatial arrangements of engineered scatters that may enable this light manipulation capability with unprecedented resolution. Most of these devices, however, are only able to function properly under irradiation of light with a large spatial coherence, typically normally incident lasers. LEDs, on the other hand, have angularly broad, Lambertian-like emission patterns characterized by a low spatial coherence, which makes the integration of metasurface devices on LED architectures extremely challenging. A novel concept for metasurface integration on LED is proposed, using a cavity to increase the LED spatial coherence through an angular collimation. Due to the resonant character of the cavity, extending the spatial coherence of the emitted light does not come at the price of any reduction in the total emitted power. The experimental demonstration of the proposed concept is implemented on a GaP LED architecture including a hybrid metallic-Bragg cavity. By integrating a silicon metasurface on top we demonstrate two different functionalities of these compact devices: directional LED emission at a desired angle and LED emission of a vortex beam with an orbital angular momentum. The presented concept is general, being applicable to other incoherent light sources and enabling metasurfaces designed for plane waves to work with incoherent light emitters.
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