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An optical 2-to-4 decoder based on photonic crystal X-shaped resonators covered by graphene shells

OPTICAL AND QUANTUM ELECTRONICS 2023年第5期55卷 452-452页

作者： Raad, Ali Nayyeri Saghaei, Hamed Mehrabani, Yavar Safaei Islamic Azad Univ Dept Comp Engn North Tehran Branch Tehran Iran Islamic Azad Univ Dept Elect Engn Shahrekord Branch Shahrekord Iran Islamic Azad Univ Energy Res Ctr Shahrekord Branch Shahrekord Iran

This paper presents a novel design of a high-speed optical 2-to-4 decoder based on the photonic crystal (PhC) composed of silicon rods. The proposed structure consists of three inputs (one for enable and two for decoder inputs), three PhC X-shaped resonators, several waveguides, and four outputs. Each resonator includes silica rods covered by graphene shells. The plane-wave expansion (PWE) method is used to calculate the band structure of the fundamental PhC. The finite-difference time-domain (FDTD) method is applied to compute optical light's transmission efficiency and electric field distribution inside the designed decoder. We demonstrate that the proposed decoder can operate in the third communication window, ranging from 1530 to 1565 nm. The numerical results reveal that the normalized transmission values less than 30% and greater than 50% are supposed to be logics 0 and 1, respectively. The decoder's maximum delay and total footprint are 2.5 ps and 690 mu m(2), respectively. Thus, due to the decoder's relatively simple and low-cost fabrication and its applications in photonics-based systems, the proposed device can be used in optical communications and networking.

关键词： Photonic crystal Optical decoder Graphene Resonator Plane-wave expansion method finite-difference time-domain method

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Low-Cost Plasmonic Platform for Photon-Emission Engineering of Two-Dimensional Semiconductors

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Physical Review Applied 2023年第4期19卷 044012-044012页

作者： Anuj Kumar Singh Kishor K. Mandal Yashika Gupta Abhay Anand V.S. Lekshmi Eswaramoorthy Brijesh Kumar Abhinav Kala Saurabh Dixit Venu Gopal Achanta Anshuman Kumar Department of Physics Laboratory of Optics of Quantum Materials IIT Bombay Mumbai 400076 India Department of Condensed Matter Physics and Material Science Tata Institute of Fundamental Research Homi Bhabha Road Mumbai 400005 India

Although the field of two-dimensional (2D) materials has democratized materials science by making high-quality samples accessible cheaply, due to the atomically thin nature of these systems, an integration with nanostructures is almost always required to obtain a significant optical response. Traditionally, these nanostructures are fabricated via electron beam lithography or focused ion beam milling, which are expensive, and large-area fabrication can be further time-consuming. In order to overcome this problem, we report the integration of 2D semiconductors on a cost-effective and large-area fabricated nanocone platform. We show that the plasmon modes of our nanocone structures lead to photoluminescence enhancement of monolayer WSe2 by about eight to ten times compared with the nonplasmonic case, consistent with finite-difference time-domain simulations. Excitation power-dependent measurements reveal that our nanocone platform enables a versatile route to engineering the relative exciton trion contributions to the emission.

关键词： Nanophotonics Transition metal dichalcogenides Crystal growth Etching Film deposition finite-difference time-domain method Photoluminescence Raman spectroscopy

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Enhancing two-photon spontaneous emission in rare earths using graphene and graphene nanoribbons

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Physical Review B 2023年第19期107卷 195420-195420页

作者： Colin Whisler Gregory Holdman D. D. Yavuz Victor W. Brar University of Wisconsin-Madison

The enhancement of two-photon spontaneous emission (2PSE) from trivalent and divalent rare earth ions in proximity to graphene and graphene nanoribbons is calculated for achievable experimental conditions using a combination of finite difference time domain simulations and direct computation of transition rates between energy levels in rare earths. For Er3+, we find that the 2PSE rate is initially 8 orders lower than the single-photon spontaneous emission rate but that, with enhancement, 2PSE can reach 2.5% of the overall decay. When graphene nanoribbons are used, we also show that the emission of free-space photon pairs from Er3+ at 3–3.2 μm via 2PSE can be increased by ∼400. Our calculations show significantly less relative graphene-enhanced 2PSE than previous works, and we attribute this variation to differences in emitter size and assumed graphene mobility. We also show that the internal energy structure of the ion can have an impact on the degree of 2PSE enhancement achievable and find that divalent rare earths are more favorable.

关键词： Electronic structure of atoms & molecules Spontaneous emission Surface plasmons Graphene Nanoribbon finite-difference time-domain method

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Plasmon Hybridization-Induced Ultra-broadband High Absorption from 0.4 to 1.8 Microns in Titanium Nitride Metastructures

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PLASMONICS 2021年第3期16卷 799-809页

作者： Wu, Shiwen Luo, Tengfei Xiong, Guoping Univ Texas Dallas Dept Mech Engn Richardson TX 75080 USA Univ Nevada Dept Mech Engn Reno NV 89557 USA Univ Notre Dame Dept Aerosp & Mech Engn Notre Dame IN 46556 USA

Titanium nitride (TiN) metadevices as perfect absorbers are studied using finite-difference time-domain (FDTD) simulations. In this paper, we demonstrate a metastructure including a top silica (SiO2) layer, two layers of TiN nano-ribbon arrays, a SiO2 dielectric layer, and a TiN film to realize efficient solar energy harvesting. We theoretically optimize the geometrical parameters of each active layer to achieve high absorption rates with an average value of up to 95% within an ultra-wide band from 0.4 to 1.8 microns, covering over 93% of total energy in the solar spectrum. Our detailed analysis of the electric field enhancement indicates that such ultra-broadband high absorption in the visible/near-infrared ranges can be attributed to surface plasmon resonances, Fabry-Perot resonances, and strong plasmon hybridization between adjacent TiN nano-ribbons. Together with refractory properties of TiN and SiO2, the designed metadevice may exhibit great potential in efficient solar energy harvesting applications, particularly in harsh environments.

关键词： Metastructures finite-difference time-domain method Plasmonic hybridization Nano-ribbon arrays Ultra-broadband absorption

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Publication guidelines for papers involving computational lithography

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Journal of Micro/Nanopatterning, Materials and Metrology 2021年第4期20卷

作者： Levinson, Harry J. HJL Lithography (United States)

Editor-in-Chief Harry Levinson introduces a new set of guidelines for papers related to computational lithography.

关键词： Computational lithography Computer simulations finite-difference time-domain method Lithography Photomasks Network architectures Neural networks New and emerging technologies Physics Semiconducting wafers

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Diffraction Phenomena in time-Varying Metal-Based Metasurfaces

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Physical Review Applied 2023年第4期19卷 044014-044014页

作者： Antonio Alex-Amor Salvador Moreno-Rodríguez Pablo Padilla Juan F. Valenzuela-Valdés Carlos Molero Department of Information Technology Universidad San Pablo—CEU CEU Universities Campus Montepríncipe Boadilla del Monte (Madrid) 28668 Spain Department of Signal Theory Telematics and Communications Universidad de Granada Granada 18071 Spain

This paper presents an analytical framework for the analysis of time-varying metal-based metamaterials. Specifically, we particularize the study to time-modulated metal-air interfaces embedded between two different semi-infinite media that are illuminated by monochromatic plane waves of frequency ω0. The formulation is based on a Floquet-Bloch modal expansion, which takes into account the time periodicity of the structure (Ts=2π/ωs) and integral-equation techniques. It allows us to extract the reflection and transmission coefficients as well as to derive nontrivial features about the dynamic response and dispersion curves of time-modulated metal-based screens. In addition, the proposed formulation has an associated analytical equivalent circuit that gives a physical insight into the diffraction phenomenon. Similarities and differences between space- and time-modulated metamaterials are discussed via the proposed circuit model. Finally, some analytical results are presented to validate the present framework. Good agreement is observed with numerical computations provided by a self-implemented finite-difference time-domain (FDTD) method. Interestingly, the present results suggest that time-modulated metal-based screens can be used as pulsed sources (when ωs≪ω0), beam formers (ωs∼ω0) to redirect energy in specific regions of space, and analog samplers (ωs≫ω0).

关键词： Metamaterials Metasurfaces Bloch-Floquet theorem Electromagnetic wave theory finite-difference time-domain method

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Higher-harmonic generation in boron-doped silicon from band carriers and bound-dopant photoionization

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Physical Review Research 2023年第4期5卷 043141-043141页

作者： Fanqi Meng Frederik Walla Sergey Kovalev Jan-Christoph Deinert Igor Ilyakov Min Chen Alexey Ponomaryov Sergey G. Pavlov Heinz-Wilhelm Hübers Nikolay V. Abrosimov Christoph Jungemann Hartmut G. Roskos Mark D. Thomson Physikalisches Institut J. W. Goethe-Universität Max-von-Laue-Strasse 1 60438 Frankfurt am Main Germany Helmholtz-Zentrum Dresden-Rossendorf Bautzner Landstrasse 400 01328 Dresden Germany Institute of Optical Sensor Systems German Aerospace Center (DLR) 12489 Berlin Germany Institut für Physik Humboldt-Universität zu Berlin 12489 Berlin Germany Leibniz-Institut für Kristallzüchtung (IKZ) 12489 Berlin Germany Institut für Theoretische Elektrotechnik RWTH Aachen 52062 Aachen Germany

We investigate ultrafast harmonic generation (HG) in Si:B, driven by intense pump pulses with fields reaching ∼100kVcm−1 and a carrier frequency of 300 GHz, at 4 K and 300 K, both experimentally and theoretically. We report several findings concerning the nonlinear charge carrier dynamics in intense sub-THz fields: (i) Harmonics of order up to n=9 are observed at room temperature, while at low temperature we can resolve harmonics reaching at least n=11. The susceptibility per charge carrier at moderate field strength is as high as for charge carriers in graphene, considered to be one of the materials with the strongest sub-THz nonlinear response. (ii) For T=300 K, where the charge carriers bound to acceptors are fully thermally ionized into the valence subbands, the susceptibility values decrease with increasing field strength. Simulations incorporating multi-valence-band Monte Carlo and finite-difference-time-domain (FDTD) propagation show that here, the HG process becomes increasingly dominated by energy-dependent scattering rates over the contribution from band nonparabolicity, due to the onset of optical-phonon emission, which ultimately leads to the saturation at high fields. (iii) At T=4K, where the majority of charges are bound to acceptors, we observe a drastic rise of the HG yields for internal pump fields of ∼30kVcm−1, as one reaches the threshold for tunnel ionization. We disentangle the HG nonlinear response into contributions associated with the initial photoionization and subsequent motion in the bands, and show that intracycle scattering seriously degrades any contribution to HG emission from coherent recollision of the holes with their parent ions.

关键词： Carrier dynamics High-order harmonic generation Multiphoton or tunneling ionization & excitation Strong electromagnetic field effects Ultrafast phenomena finite-difference time-domain method Monte Carlo methods Terahertz spectroscopy

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Research on the electromagnetic scattering from foam sea based on small slope approximation

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JOURNAL OF ENGINEERING-JOE 2021年第4期2021卷 226-233页

作者： Li, Xin-Hong Yichun Univ Coll Math & Comp Sci Yichun Peoples R China

In order to improve the research of electromagnetic scattering characteristics and mechanism of the foam in the marine environment, considering the complexity and sensitivity of the electromagnetic scattering characteristics of the sea surface, the electromagnetic scattering characteristics of the foam sea surface are studied by the improved small slope approximation (SSA) method. The double Debye dielectric constant model is adopted to calculate the dielectric constant of seawater and foam. Based on the Elfouhaily sea spectrum model, the expression of scattering coefficient of the foam sea surface under SSA is derived, and then the theoretical calculation results of the SSA method are compared with the finite-difference time-domain method and the measured values in the literature, which verifies the effectiveness of the proposed algorithm. The model of the relationship between the thickness of the foam layer and the wind speed is established, and the composite backscattering characteristics of the ocean below the wind speed of 20 m/s are simulated. It is found that as the wind speed increases, the foam layer becomes thicker and the scattering intensity increases. The foam layer will weaken the ocean specular reflection and increase the diffuse reflection, which is more obvious when viewed at grazing and large incidence angle, and when the incident angle is greater than 83 degrees, the inflexion point caused by the foam will be clearly observed in the backscattering curve. The results of this study can provide a reference for civil and military activities and optimise the detection capability in the marine environment.

关键词： Dielectric permittivity permittivity Instrumentation and techniques for geophysical, hydrospheric and lower atmosphere research scattering coefficient Other numerical methods ocean waves Numerical approximation and analysis slope approximation scattering intensity increases radiowave propagation velocity 20.0 m/s SSA method wind speed Radiowave propagation Surface waves, tides, and sea level foam layer finite difference time-domain analysis Winds and their effects in the lower atmosphere backscatter Elfouhaily sea spectrum model electromagnetic wave scattering marine environment wind rough surfaces composite backscattering characteristics Electromagnetic wave propagation foam sea surface finite-difference time-domain method seawater electromagnetic scattering characteristics

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Inverse design of arbitrary optical helicity patterns

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Physical Review Research 2023年第3期5卷 033076-033076页

作者： Romuald Kilianski Robert Bennett School of Physics & Astronomy University of Glasgow Glasgow G12 8QQ United Kingdom

Superposing multiple plane waves can generate helicity lattices in which the optical helicity varies regularly in space. Here we propose an inverse design method for constructing arbitrary helicity structures based on placing a digital object consisting of dielectric inclusions in three-dimensional space. We apply the method to design structures that reproduce two-dimensional lattices embedded within a three-dimensional region using only a single plane wave as an input. In order to demonstrate the power and flexibility of our method, we go beyond the paradigm of a regular lattice and propose structures which can create arbitrary images consisting of regions of varying helicity, again using only a single plane wave as an input.

关键词： Optical lattices & traps Optimization problems finite-difference time-domain method

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Mode Interference Effect in Optical Emission of Quantum Dots in Photonic Crystal Cavities

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Physical Review X 2022年第2期12卷 021042-021042页

作者： A. Lyasota C. Jarlov M. Nyman A. Miranda M. Calic B. Dwir A. Rudra A. Shevchenko E. Kapon Laboratory of Physics of Nanostructures Institute of Physics Ecole Polytechnique Federale de Lausanne (EPFL) CH-1015 Lausanne Switzerland Centre of Excellence for Quantum Computation and Communication Technology School of Physics University of New South Wales Sydney New South Wales 2052 Australia Department of Applied Physics Aalto University P.O. Box 13500 FI-00076 Aalto Finland

Radiation properties of a pointlike source of light, such as a molecule or a semiconductor quantum dot, can be tailored by modifying its photonic environment. This phenomenon lies at the core of cavity quantum electrodynamics (CQED). Quantum dots in photonic crystal microcavities have served as a model system for exploring the CQED effects and for the realization of efficient single-photon quantum emitters. Recently, it has been suggested that quantum interference of the exciton recombination paths through the cavity and free-space modes can significantly modify the radiation. In this work, we report an unambiguous experimental observation of this fundamental effect in the emission spectra of site-controlled quantum dots positioned at prescribed locations within a photonic crystal cavity. The observed asymmetry in the polarization-resolved emission spectra strongly depends on the quantum dot position, which is confirmed by both analytical and numerical calculations. We perform quantum interferometry in the near-field zone of the radiation, retrieving the overlap and the position-dependent relative phase between the interfering free-space and cavity-mode-mediated radiative decays. The observed phenomenon is of importance for realization of photonic-crystal light emitters with near unity quantum efficiency. Our results suggest that the full description of light-matter interaction in the framework of CQED requires a modification of the conventional quantum master equation by also considering the radiation mode interference.

关键词： Cavity quantum electrodynamics Light-matter interaction Nanophotonics Open quantum systems Photonic crystals Photonics Quantum description of light-matter interaction Quantum interference effects Single photon sources Quantum cavities Quantum dots finite-difference time-domain method finite-element method Interferometry Optical spectroscopy Photoluminescence Quantum master equation time-resolved photoluminescence

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