In a reciprocal medium, transmission of electromagnetic (EM) waves is symmetric along opposite directions which restrict design and implementation of various systems in optics and photonics. Asymmetric transmission (AT) is essential for designing isolators and circulators in optics and photonics, and it benefits other applications such as photovoltaic systems, lasers, cloaking, and EM shielding. While bulky nonreciprocal devices based on magnetic field biases have been well known, creating AT in subwavelength structures is more challenging, and structures with a subwavelength thickness that show AT have drawn a lot of attention over the last decade.
View Article and Find Full Text PDFThe refractory metal-oxide semiconductors are an overlooked platform for nanophononics that offer alloys with high melting points and tunable optical constants through stoichiometry changes and ion intercalation. We show that these semiconductors can form metamaterial coatings (metacoatings) made from a set of highly subwavelength, periodic metal-oxide layers (≤20 nm) with a varying and graded refractive index profile that includes a combination of high and low refractive indices and plasmonic layers. These metacoatings exhibit vibrant, structural color arising from the periodic index profile that can be tuned across the visible spectrum, over ultralarge lateral areas through bottom-up thermal annealing techniques.
View Article and Find Full Text PDFA variety of alternative plasmonic and dielectric material platforms-among them nitrides, semiconductors, and conductive oxides-have come to prominence in recent years as means to address the shortcomings of noble metals (including Joule losses, cost, and passive character) in certain nanophotonic and optical-frequency metamaterial applications. Here, it is shown that chalcogenide semiconductor alloys offer a uniquely broad pallet of optical properties, complementary to those of existing material platforms, which can be controlled by stoichiometric design. Using combinatorial high-throughput techniques, the extraordinary epsilon-near-zero, plasmonic, and low/high-index characteristics of Bi:Sb:Te alloys are explored.
View Article and Find Full Text PDFPhotonic materials with tunable and switchable ultraviolet (UV) to high-energy visible (HEV) optical properties may benefit applications such as sensing, high-density optical memory, beam-steering, adaptive optics, and light modulation. Here, for the first time we demonstrate a nonvolatile switchable dielectric metamaterial operating in the UV-HEV spectral range. Nanograting metamaterials in a layered composite of low-loss ZnS/SiO and the chalcogenide phase-change medium germanium-antimony-telluride (GeSbTe or GST) exhibit reflection resonances at UV-HEV wavelengths that are substantially modified by light-induced (amorphous-crystalline) phase transitions in the chalcogenide layer.
View Article and Find Full Text PDFElectrostriction is a property of all naturally occurring dielectrics whereby they are mechanically deformed under the application of an electric field. It is demonstrated here that an artificial metamaterial nanostructure comprising arrays of dielectric nanowires, made of silicon and indium tin oxide, is reversibly structurally deformed under the application of an electric field, and that this reconfiguration is accompanied by substantial changes in optical transmission and reflection, thus providing a strong electro-optic effect. Such metamaterials can be used as the functional elements of electro-optic modulators in the visible to near-infrared part of the spectrum.
View Article and Find Full Text PDFAmorphous bismuth telluride (Bi:Te) provides a composition-dependent, CMOS-compatible alternative material platform for plasmonics in the ultraviolet-visible spectral range. Thin films of the chalcogenide semiconductor are found, using high-throughput physical vapor deposition and characterization techniques, to exhibit a plasmonic response (a negative value of the real part of relative permittivity) over a band of wavelengths extending from ~250 nm to between 530 and 978 nm, depending on alloy composition (Bi:Te at% ratio). The plasmonic response is illustrated via the fabrication of subwavelength period nano-grating metasurfaces, which present strong, period-dependent plasmonic absorption resonances in the visible range, manifested in the perceived color of the nanostructured domains in reflection.
View Article and Find Full Text PDFOrganometallic perovskites, solution-processable materials with outstanding optoelectronic properties and high index of refraction, provide a platform for all-dielectric metamaterials operating at visible frequencies. Perovskite metasurfaces with structural coloring tunable across visible frequencies are realized through subwavelength structuring. Moreover, a threefold increase of the luminescence yield and comparable reduction of luminescence decay time are observed.
View Article and Find Full Text PDFWe present a high-throughput and scalable technique for the production of metal nanowires embedded in glass fibres by taking advantage of thin film properties and patterning techniques commonly used in planar microfabrication. This hybrid process enables the fabrication of single nanowires and nanowire arrays encased in a preform material within a single fibre draw, providing an alternative to costly and time-consuming iterative fibre drawing. This method allows the combination of materials with different thermal properties to create functional optoelectronic nanostructures.
View Article and Find Full Text PDFA switchable perfect absorber with multispectral thermal imaging capability is presented. Aluminum nanoantenna arrays above a germanium antimony telluride (GST) spacer layer and aluminum mirror provide efficient wavelength-tunable absorption in the mid-infrared. Utilizing the amorphous-to-crystalline phase transition in GST, this device offers switchable absorption with strong reflectance contrast at resonance and large phase-change-induced spectral shifts.
View Article and Find Full Text PDFWe demonstrate that optical activity in amorphous isotropic thin films of pure Ge2Sb2Te5 and N-doped Ge2Sb2Te5N phase-change memory materials can be induced using rapid photo crystallisation with circularly polarised laser light. The new anisotropic phase transition has been confirmed by circular dichroism measurements. This opens up the possibility of controlled induction of optical activity at the nanosecond time scale for exploitation in a new generation of high-density optical memory, fast chiroptical switches and chiral metamaterials.
View Article and Find Full Text PDFCarrier-type reversal to enable the formation of semiconductor p-n junctions is a prerequisite for many electronic applications. Chalcogenide glasses are p-type semiconductors and their applications have been limited by the extraordinary difficulty in obtaining n-type conductivity. The ability to form chalcogenide glass p-n junctions could improve the performance of phase-change memory and thermoelectric devices and allow the direct electronic control of nonlinear optical devices.
View Article and Find Full Text PDFNano-scale MoS2 thin films are successfully deposited on a variety of substrates by atmospheric pressure chemical vapor deposition (APCVD) at ambient temperature, followed by a two-step annealing process. These annealed MoS2 thin films are characterized with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), micro-Raman, X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-VIS-NIR spectrometry, photoluminescence (PL) and Hall Effect measurement. Key optical and electronic properties of APCVD grown MoS2 thin films are determined.
View Article and Find Full Text PDFNon-volatile, bidirectional, all-optical switching in a phase-change metamaterial delivers high-contrast transmission and reflection modulation at near- to mid-infrared wavelengths in device structures down to ≈1/27 of a wavelength thick.
View Article and Find Full Text PDFReaction order in Bi-doped oxide glasses depends on the optical basicity of the glass host. Red and NIR photoluminescence (PL) bands result from Bi(2+) and Bin clusters, respectively. Very similar centers are present in Bi- and Pb-doped oxide and chalcogenide glasses.
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