105 research outputs found
Freestanding dielectric nanohole array metasurface for mid-infrared wavelength applications
We designed and simulated freestanding dielectric optical metasurfaces based
on arrays of etched nanoholes in a silicon membrane. We showed phase
control and high forward transmission at mid-infrared wavelengths by tuning the
dimensions of the holes. We also identified the mechanisms responsible for high
forward scattering efficiency and showed that these conditions are connected
with the well-known Kerker conditions already proposed for isolated scatterers.
A beam deflector was designed and optimized through sequential particle swarm
and gradient descent optimization to maximize transmission efficiency and
reduce unwanted grating orders. Such freestanding silicon nanohole array
metasurfaces are promising for the realization of silicon based mid-infrared
optical elements
Vanadium dioxide as a natural disordered metamaterial: perfect thermal emission and large broadband negative differential thermal emittance
We experimentally demonstrate that a thin (~150 nm) film of vanadium dioxide
(VO2) deposited on sapphire has an anomalous thermal emittance profile when
heated, which arises due to the optical interaction between the film and the
substrate when the VO2 is at an intermediate state of its insulator-metal
transition (IMT). Within the IMT region, the VO2 film comprises nanoscale
islands of metal- and dielectric-phase, and can thus be viewed as a natural,
disordered metamaterial. This structure displays "perfect" blackbody-like
thermal emissivity over a narrow wavelength range (~40 cm-1), surpassing the
emissivity of our black soot reference. We observed large broadband negative
differential thermal emittance over a >10 {\deg}C range: upon heating, the
VO2/sapphire structure emitted less thermal radiation and appeared colder on an
infrared camera. We anticipate that emissivity engineering with thin film
geometries comprising VO2 will find applications in infrared camouflage,
thermal regulation, infrared tagging and labeling.Comment: 3 figure
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Holographic Detection of the Orbital Angular Momentum of Light With Plasmonic Photodiodes
Metallic components such as plasmonic gratings and plasmonic lenses are routinely used to convert free-space beams into propagating surface plasmon polaritons and vice versa. This generation of couplers handles relatively simple light beams, such as plane waves or Gaussian beams. Here we present a powerful generalization of this strategy to more complex wavefronts, such as vortex beams that carry orbital angular momentum, also known as topological charge. This approach is based on the principle of holography: the coupler is designed as the interference pattern of the incident vortex beam and focused surface plasmon polaritons. We have integrated these holographic plasmonic interfaces into commercial silicon photodiodes, and demonstrated that such devices can selectively detect the orbital angular momentum of light. This holographic approach is very general and can be used to selectively couple free-space beams into any type of surface wave, such as focused surface plasmon polaritons and plasmonic Airy beams.Physic
Quantum-Coherence-Enhanced Surface Plasmon Amplification by Stimulated Emission of Radiation
We investigate surface plasmon amplification in a silver nanoparticle coupled
to an externally driven three-level gain medium, and show that quantum
coherence significantly enhances the generation of surface plasmons. Surface
plasmon amplification by stimulated emission of radiation is achieved in the
absence of population inversion on the spasing transition, which reduces the
pump requirements. The coherent drive allows us to control the dynamics, and
holds promise for quantum control of nanoplasmonic devices.Comment: 5 pages, 4 figure
Global optimization of metasurface designs using statistical learning methods
International audienceOptimization of the performance of flat optical components, also dubbed metasurfaces, is a crucial step towards their implementation in realistic optical systems. Yet, most of the design techniques, which rely on large parameter search to calculate the optical scattering response of elementary building blocks, do not account for near-field interactions that strongly influence the device performance.In this work, we exploit two advanced optimization techniques based on statistical learning and evolutionary strategies together with a fullwave high order Discontinuous Galerkin Time-Domain (DGTD) solver to optimize phase gradient metasurfaces. We first review the main features of these optimization techniques and then show that they can outperform most of the available designs proposed in the literature. Statistical learning is particularly interesting for optimizing complex problems containing several global minima/maxima. We then demonstrate optimal designs for GaN semiconductor phase gradient metasurfaces operating at visible wavelengths. Our numerical results reveal that rectangular and cylindrical nanopillar arrays can achieve more than respectively 88% and 85% of diffraction efficiency for TM polarization and both TM and TE polarization respectively, using only 150 fullwave simulations. To the best of our knowledge, this is the highest blazed diffraction efficiency reported so far at visible wavelength using such metasurface architectures
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