High-index dielectric and semiconductor nanoparticles supporting strong electric and magnetic resonances have drawn significant attention in recent years. However, until now, there have been no ...experimental reports of lasing action from such nanostructures. Here, we demonstrate directional lasing, with a low threshold and high quality factor, in active dielectric nanoantenna arrays achieved through a leaky resonance excited in coupled gallium arsenide (GaAs) nanopillars. The leaky resonance is formed by partially breaking a bound state in the continuum generated by the collective, vertical electric dipole resonances excited in the nanopillars for subdiffractive arrays. We control the directionality of the emitted light while maintaining a high quality factor (Q = 2,750). The lasing directivity and wavelength can be tuned via the nanoantenna array geometry and by modifying the gain spectrum of GaAs with temperature. The obtained results provide guidelines for achieving surface-emitting laser devices based on active dielectric nanoantennas that are compact and highly transparent.
Present research shows the results of concrete mechanical and durability characteristic containing Copper Slag (CS) substituted with Fine Aggregates (FA) of the Beas river in which FA substitution ...levels with CS were maintained at 0%, 20%, 40%, & 60%. With the upcoming results of compressive strength test & split tensile strength tests, mechanical properties were investigated, while on the grounds of the Initial Surface Absorption of water for a cube and water absorption values, durability properties were tested. The Best results for mechanical and durability properties of the concrete were observed for 40% substitution of fine aggregates from the Beas river with Copper Slag (CS).
Policy directives in several nations are focusing on the development of smart cities, linking innovations in the data sciences with the goal of advancing human well-being and sustainability on a ...highly urbanized planet. To achieve this goal, smart initiatives must move beyond city-level data to a higher-order understanding of cities as transboundary, multisectoral, multiscalar, social-ecological-infrastructural systems with diverse actors, priorities, and solutions. We identify five key dimensions of cities and present eight principles to focus attention on the systems-level decisions that society faces to transition toward a smart, sustainable, and healthy urban future.
Graphene has recently emerged as a viable platform for integrated optoelectronic
and hybrid photonic devices because of its unique properties. The optical
properties of graphene can be dynamically ...controlled by electrical voltage and
have been used to modulate the plasmons in noble metal nanostructures. Graphene
has also been shown to support highly confined intrinsic plasmons, with
properties that can be tuned in the wavelength range of 2 μm to 100 μm. Here we
review the recent development in graphene-plasmonic devices and identify some of
the key challenges for practical applications of such hybrid devices.
Summary
Community‐wide greenhouse gas (GHG) emissions accounting is confounded by the relatively small spatial size of cities compared to nations—due to which, energy use in essential infrastructures ...serving cities, such as commuter and airline transport, energy supply, water supply, wastewater infrastructures, and others, often occurs outside the boundaries of the cities using them. The trans‐boundary infrastructure supply chain footprint (TBIF) GHG emissions accounting method, tested in eight U.S. cities, incorporates supply chain aspects of these trans‐boundary infrastructures serving cities, and is akin to an expanded geographic GHG emissions inventory. This article shows the results from applying the TBIF method in the rapidly developing city of Delhi, India.
The objectives of this research are to (1) describe the data availability for implementing the TBIF method within a rapidly industrializing country, using the case of Delhi, India; (2) identify methodological differences in implementation of the TBIF method between Indian versus U.S. cities; and (3) compare broad energy use metrics between Delhi and U.S. cities, demonstrated by Denver, Colorado, USA, whose energy use characteristics and TBIF GHG emissions have previously been shown to be similar to U.S. per capita averages.
This article concludes that most data required to implement the TBIF method in Delhi are readily available, and the methodology could be translated from U.S. to Indian cities. Delhi's 2009 community‐wide GHG emissions totaled 40.3 million metric tonnes of carbon dioxide equivalents (t CO
2
‐eq), which are normalized to yield 2.3 t CO
2
‐eq per capita; nationally, India reports its average per capita GHG emissions at 1.5 t CO
2
‐eq. In‐boundary GHG emissions contributed to 68% of Delhi's total, where end use (including electricity) energy in residential buildings, commercial and industrial usage, and fuel used in surface transportation contributed 24%, 19%, and 21%, respectively. The remaining 4% of the in‐boundary GHG emissions were from waste disposal, water and wastewater treatment, and cattle. Trans‐boundary infrastructures were estimated to equal 32% of Delhi's TBIF GHG emissions, with 5% attributed to fuel processing, 3% to air travel, 10% to cement, and 14% to food production outside the city.
Abstract
All-dielectric nanophotonics is a rapidly developing and practical alternative to plasmonics for nanoscale optics. The electric and magnetic Mie resonances in high-index low-loss dielectric ...nanoresonators can be engineered to exhibit unique scattering responses. Recently, nanophotonic structures satisfying parity-time (PT) symmetry have been shown to exhibit novel scattering responses beyond what can be achieved from the conventional nanoresonators. The complex interference of the magnetic and electric Mie resonances and lattice modes excited in PT-symmetric nanoantenna arrays give rise to a scattering anomaly called lasing spectral singularity (SS), where the scattering coefficients tend to infinity. In our previous work (Tapar, Kishen and Emani 2020
Opt. Lett.
45
5185), we demonstrated the existence of lasing SSs in vertically stacked two-dimensional (2D) GaInP PT-symmetric metasurface. In this paper, we analyse the direction-sensitive scattering response of the PT-symmetric GaInP metasurface by decomposing the total scattered field into the electric and magnetic multipoles. The far-field scattering response at the singularity is highly asymmetric for incidence from either the gain or loss side and can be tuned by changing the geometry. By analysing the phase of even- and odd-parity higher-order multipoles, we explain the observed scattering response over a broad parameter space in terms of the generalized Kerker effect. The interference between the direction-dependent excitation of different order multipoles and the overall 2D-lattice resonance opens a route towards designing a special class of tunable sources exhibiting direction-sensitive emission properties.
Electrical excitation of light using inelastic electron tunneling is a promising approach for the realization of ultra-compact on-chip optical sources with high modulation bandwidth. However, the ...practical implementation of these nanoscale light sources presents a challenge due to the low electron-to-photon transduction efficiencies. Here, we investigate designs for the enhancement of light generation and out-coupling in a periodic Ag-SiO2-Ag tunnel junction due to inelastic electron tunneling. The structure presents a unique advantage of a simple fabrication procedure as compared to the other reported structures. We achieve a resonant enhancement in the local density of optical states up to three orders of magnitude over vacuum for the periodic metal-insulator-metal tunnel junction. By efficiently coupling the gap plasmon mode and the lattice resonance, an enhanced radiative efficiency of ∼0.53 was observed, 30% higher as compared to the uncoupled structure.
Active optical metasurfaces have attracted significant research attention in recent times. The conventional thermal and free-carrier induced index-tuning mechanisms have been widely explored to ...realize dynamic modulation of the optical properties. However, their modulation efficiency is limited by the intrinsic response of functional materials. The recent advances in the concept of PT (parity-time) symmetry and spatiotemporal modulation of permittivity have opened new avenues to realize dynamic tunability. In this work, we propose an all-dielectric PT-symmetric metasurface to tune the intensity and angular response of light through dynamic gain–loss modulation. Our approach shows tunable asymmetric transmission in a vertically stacked Ga0.5In0.5P phased-array metasurface. The overall metasurface is optimized for operation at a wavelength of 655 nm (typical PL emission peak of Ga0.5In0.5P). The transmission is predominantly in the zeroth diffraction order (η0 ∼ 0.80, η1 ∼ 0.18) for loss side normal incidence, and an amplified transmission is observed in the first diffraction order (η0 ∼ 0.04, η1 ∼ 0.79) for gain side incidence. In addition to the asymmetric transmission for normal incidence, the proposed metasurface also exhibits asymmetric amplification in transmission for oblique incidence. An optimal arrangement of gain–loss resonators combined with tunable pumping (either optical or electrical) can pave the way toward on-chip reconfigurable nanophotonic devices.
Electrically driven nanoantennas for on-chip generation and manipulation of light have attracted significant attention in recent times. Metal-insulator-metal (MIM) tunnel junctions have been ...extensively used to electrically excite surface plasmons and photons
via
inelastic electron tunneling. However, the dynamic switching of light from MIM junctions into spatially separate channels has not been shown. Here, we numerically demonstrate switchable, highly directional light emission from electrically driven nano-strip Ag-SiO
2
-Ag tunnel junctions. The top electrode of our Ag-SiO
2
-Ag stack is divided into 16 nano-strips, with two of the tunnel junctions at the centre (
S
L
and
S
R
) acting as sources. Using full-wave electromagnetic simulations, we show that when
S
L
is excited, the emission is highly directional with an angle of emission of 30° and an angular spread of ∼11°. When the excitation is switched to
S
R
, the emission is redirected to an angle of 30° with an identical angular spread. A directivity of 29.4 is achieved in the forward direction, with a forward-to-backward ratio of 12. We also demonstrate wavelength-selective directional switching by changing the width, and thereby the resonance wavelength, of the sources. The emission can be tuned by varying the periodicity of the structure, paving the way for electrically driven, reconfigurable light sources.
We numerically show switchable, wavelength-selective directional emission from Ag-SiO
2
-Ag tunnel junctions. The emission can be switched by selective excitation of the top electrode, paving the way for electrically-driven tunable light sources.
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