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Performance analysis of all-optical NAND, NOR, and XNOR logic gates using photonic crystal waveguide for optical computing applications

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OPTICAL ENGINEERING 2020年第5期59卷

作者： Rao, Dalai G. Sankar Swarnakar, Sandip Kumar, Santosh Godavari Inst Engn & Technol Dept Elect & Commun Engn Rajahmundry Andhra Pradesh India DIT Univ Dept Elect Elect & Commun Engn Dehra Dun Uttarakhand India Liaocheng Univ Sch Phys Sci & Informat Technol Shandong Key Lab Opt Commun Sci & Technol Liaocheng Shandong Peoples R China

All-optical photonic integrated devices have gained great attention in the field of optical computing and large-scale integration. All-optical logic gates are useful for optical signal processing and optical communication network. The flexible devices presented here satisfy the functionality of NAND (NOT-AND), NOR (NOT-OR), and XNOR (exclusive NOR) logic gates using only one structure with proper changes in the phase of an applied light signal. The design of all-optical logic gates is implemented with photonic crystal waveguides using square lattice silicon rods. The performance of the structure is simulated, verified, and analyzed by the finite-difference time-domain method, with the principle of interference effect at a wavelength of 1550 nm. The contrast ratio (CR) of NAND, NOR, and XNOR logic gates is 17.59, 14.3, and 10.52 dB, respectively, with an optimized size of 7.2 mu m x 5.4 mu m. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)

关键词： photonic crystal waveguide finite-difference time-domain method all-optical logic gates beam-interference principle

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Numerical simulation of vibration damping by granular materials

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APPLIED ACOUSTICS 2020年第0期162卷 107189-000页

作者： Takeshima, M. Asakura, T. Tokyo Univ Sci 2641 Yamazaki Noda Chiba 2780022 Japan

The present paper proposes a novel simulation method combining the finite-difference time-domain (FDTD) method and the discrete-element method (DEM) in order to investigate the damping effect of bending vibration of a plate caused by granular materials. The DEM is used to obtain the motion of the granular material, whereas the FDTD is used for vibration analysis of the plate-like structure. Firstly, the numerical scheme of each method and the coupling scheme of these methods are described in detail. Then, the validity of the proposed method was confirmed by comparing the calculation and measurement results. Finally, based on the numerical and measurement results, we confirmed that the damping of the plate caused by additionally arranged granular materials varies greatly depending on the excitation force acting on the plate. (C) 2019 Elsevier Ltd. All rights reserved.

关键词： finite-difference time-domain method Discrete-element method Vibration damping

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Toward a High-Resolution Reconstruction of 3D Nerve Fiber Architectures and Crossings in the Brain Using Light Scattering Measurements and finite-difference time-domain Simulations

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Physical Review X 2020年第2期10卷 021002-021002页

作者： Miriam Menzel Markus Axer Hans De Raedt Irene Costantini Ludovico Silvestri Francesco S. Pavone Katrin Amunts Kristel Michielsen Institute of Neuroscience and Medicine (INM-1) Forschungszentrum Jülich 52425 Jülich Germany Zernike Institute for Advanced Materials University of Groningen 9747AG Groningen Netherlands National Institute of Optics—Italian National Research Council (INO-CNR) 50125 Firenze Italy European Laboratory for Non-Linear Spectroscopy University of Florence 50019 Sesto Fiorentino Italy Cécile and Oskar Vogt Institute for Brain Research University Hospital Düsseldorf University of Düsseldorf 40204 Düsseldorf Germany Jülich Supercomputing Centre Forschungszentrum Jülich 52425 Jülich Germany

Unraveling the structure and function of the brain requires a detailed knowledge about the neuronal connections, i.e., the spatial architecture of the nerve fibers. One of the most powerful histological methods to reconstruct the three-dimensional nerve fiber pathways is 3D-polarized light imaging (3D-PLI). The technique measures the birefringence of histological brain sections and derives the spatial fiber orientations of whole human brain sections with micrometer resolution. However, the technique yields only a single fiber orientation for each measured tissue voxel even if it is composed of fibers with different orientations, so that in-plane crossing fibers are misinterpreted as out-of-plane fibers. When generating a detailed model of the three-dimensional nerve fiber architecture in the brain, a correct detection and interpretation of nerve fiber crossings is crucial. Here, we show how light scattering in transmission microscopy measurements can be leveraged to identify nerve fiber crossings in 3D-PLI data and demonstrate that measurements of the scattering pattern can resolve the substructure of brain tissue like the crossing angles of the nerve fibers. For this purpose, we develop a simulation framework that permits the study of transmission microscopy measurements—in particular, light scattering—on large-scale complex fiber structures like brain tissue, using finite-difference time-domain (FDTD) simulations and high-performance computing. The simulations are used not only to model and explain experimental observations, but also to develop new analysis methods and measurement techniques. We demonstrate in various experimental studies on brain sections from different species (rodent, monkey, and human) and in FDTD simulations that the polarization-independent transmitted light intensity (transmittance) decreases significantly (by more than 50%) with an increasing out-of-plane angle of the nerve fibers and that it is mostly independent of the in-plane crossing

关键词： Birefringence Neuroscience Polarization of light Axons Brain Polarization finite-difference time-domain method Light scattering Polarized optical microscopy

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Numerical study on slow-light effects in an ultra-compact grating-based Fabry-Perot cavity

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OPTICAL AND QUANTUM ELECTRONICS 2020年第4期52卷 210-210页

作者： Ma, Chengju Zhang, Yuebin Xu, Yiping Liu, Yinggang Li, Dongming Wen, Jin Xian Shiyou Univ Sch Sci Xian 710065 Peoples R China Yangtze Univ Sch Phys & Optoelect Engn Jingzhou 434023 Hubei Peoples R China

In this paper, we propose a slow-light element based on a grating-based Fabry-Perot cavity (GBFPC). Using three-dimensional finite-difference time-domain simulation, the slow-light properties that depend on its structural parameters are systematically investigated. A slow-light effect with the maximum group index about 14.6 and the slow-light bandwidth about 874 GHz at near 1550 nm wavelength is achieved. Moreover, we find that changing of the GBFPC's structural parameters, such as bus waveguide width W, grating period p, and period number N, has greater impact on its slow-light properties than its other parameters. This study helps lay a solid foundation for designing excellent slow-light elements based on a Fabry-Perot cavity.

关键词： Slow light Grating-based Fabry-Perot cavity finite-difference time-domain method

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Plasmonic Biosensing with Aluminum Thin Films under the Kretschmann Configuration

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ANALYTICAL CHEMISTRY 2020年第13期92卷 8654-8659页

作者： Lambert, Alexander S. Valiulis, Santino N. Malinick, Alexander S. Tanabe, Ichiro Cheng, Quan Univ Calif Riverside Dept Chem Riverside CA 92521 USA Osaka Univ Grad Sch Engn Sci Osaka 5608531 Japan

Aluminum has recently attracted considerable interest as a plasmonic material due to its unique optical properties, but most work has been limited to nanostructures. We report here SPR biosensing with aluminum thin-films using the standard Kretschmann configuration that has previously been dominated by gold films. Electron-beam physical vapor deposition (EBPVD)-prepared Al films oxidize in air to form a nanofilm of Al2O3 yielding robust stability for sensing applications in buffered solutions. FDTD simulations revealed a sharp plasmonic dip in the visible range that enables measurement of both angular shift and reflection intensity change at a fixed angle. Bulk and surface tests indicated that Al films exhibited superb sensitivity performance in both categories. Compared to Au, the Al/Al2O3 layer showed a marked effect of suppressing nonspecific binding from proteins in human serum. Further characterization indicated that Al film demonstrated a higher sensitivity and a wider working range than Au films when used for SPR imaging analysis. Combined with its economic and manufacturing benefits, the Al thin-film has the potential to become a highly advantageous plasmonic substrate to meet a wide range of biosensing needs in SPR configurations.

关键词： Sensitivity Biosensor finite-difference time-domain method Plasmon

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Field enhancement assisted graphene-based microring modulator for high modulation depth

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IET OPTOELECTRONICS 2020年第6期14卷 391-398页

作者： Joshi, Swati Kaushik, Brajesh Kumar Indian Inst Technol Roorkee Dept Elect & Commun Engn Microelect & VLSI Grp Roorkee 247667 Uttarakhand India

This study aims at optimising the graphene coverage in a microresonator for the design of an efficient modulator by using a combination of graphene induced losses and phase shift. The graphene integration in the ring can provide tunability by means of altering the loss and coupling coefficient by changing the graphene coverage or its chemical potential. The fundamental parameters of graphene integrated all-pass ring resonator are extracted based on the transmission characteristics using finite-difference time-domain method. As compared to conventional graphene-oxide-semiconductor straight waveguide, graphene integrated on an all-pass ring resonator shows enhanced optical absorption and phase shift due to field enhancement factor. A modulator based on graphene tunable loss and phase shift is investigated taking into account the field enhancement factor. For 1.55 mu m radiation and ring radius of 3.75 mu m with 22% graphene coverage, a maximum modulation depth of 12.6 dB is demonstrated based on electrostatic control of graphene chemical potential. The proposed modulator can feature operational speed in the range of 10 GHz that is useful in a variety of electro-optic applications.

关键词： micro-optics optical modulation integrated optics graphene optical resonators optical tuning finite difference time-domain analysis micromechanical resonators optical losses light absorption light transmission micro-optomechanical devices optical design techniques field enhancement factor graphene tunable loss phase shift graphene coverage graphene chemical potential modulation depth efficient modulator graphene induced losses coupling coefficient finite-difference time-domain method optical absorption field enhancement assisted graphene-based microring modulator fundamental parameters graphene integrated all-pass ring resonator transmission characteristics ring radius electrostatic control microresonator radius 3 75 mum wavelength 1 55 mum C

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Numerical simulation of terahertz radiation in photoconductive antenna

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MICROWAVE AND OPTICAL TECHNOLOGY LETTERS 2020年第8期62卷 2708-2714页

作者： Xiong, Zhong-gang Deng, Hu Chen, Jun-xue Chen, Lin-yu Liu, Quan-chen Guo, Jin Shang, Li-ping Southwest Univ Sci & Technol Sch Informat Engn Mianyang Sichuan Peoples R China

The terahertz radiation in photoconductive antenna involves the multiple physical processes. It is a challenge to simulate the terahertz radiation in photoconductive antenna. A numerical simulation tool for the photoconductive antenna is very necessary to effectively design and optimize the terahertz radiation source. In this paper, by introducing the auxiliary equations describing the dynamic behaviors of carriers in the semiconductor into the Maxwell's equations, we use the three-dimensional finite-difference time-domain method to solve these equations and obtain the time-domain solutions in the nearfield of antenna. A near-to-far-field transformation in the layered medium is adopted in order to obtain the wave pattern of terahertz radiation in the far field. Assisted by the developed simulation tool, the terahertz time-domain waveforms and other terahertz radiation characteristics for the photoconductive antenna can be presented. By comparing with the experimental results reported in the references, the validity and reliability of these physical models and the developed simulation tool are demonstrated. More importantly, the results given in this paper will be of great significance to design and optimize the radiation performance of photoconductive antenna with different structures.

关键词： finite-difference time-domain method low-temperature grown GaAs photoconductive antennas terahertz radiation

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An FDTD Investigation of Orthogonality and the Backscattering of HF Waves in the Presence of Ionospheric Irregularities

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JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS 2020年第10期125卷 e2020JA028201-e2020JA028201页

作者： Smith, D. R. Tan, T. Dao, E. Huang, C. Simpson, J. J. Univ Utah ECE Dept Salt Lake City UT 84112 USA Duke Univ ECE Dept Durham NC USA US Air Force Geospace Environm Impacts & Applicat Branch Res Lab Kirtland AFB NM USA

One of the most successful instruments used to investigate the Earth's ionosphere is coherent scatter radars such as the Super Dual Auroral Radar Network (SuperDARN). Their method of mapping plasma convection at high latitudes is contingent on irregularities that momentarily exist in the ionosphere and are elongated along the direction of the geomagnetic field. Under these conditions, SuperDARN transmits high-frequency (HF) waves that are then backscattered from these plasma irregularities. In order for maximum backscatter to occur, the wave vector of the incident wave must be orthogonal to the magnetic field lines. This is called the "orthogonality condition." Over the years, ray tracing results have generated many assumptions, where and how orthogonality occurs. However, since ray tracing only tracks the primary direction of energy flow and typically does not account for diffraction, it provides an incomplete understanding of the interaction of HF waves with small ionospheric irregularities. This work investigates the orthogonality assumptions by modeling at high-resolution HF electromagnetic wave interactions with small-scale irregularities in the ionosphere. Specifically, the finite-difference time-domain (FDTD) method is employed to determine where orthogonality occurs in the ionosphere and the number of times the condition is satisfied during the simulation. The results provide insights into the orthogonality condition as a function of source frequency and elevation angle for both unperturbed and perturbed ionospheres. From these results, small-scale irregularities are observed to sometimes contribute significantly to the production of backscatter. A discussion is provided to highlight where three existing orthogonality condition assumptions are incorrect or misleading.

关键词： finite-difference time-domain method plasma irregularities polar cap patch SuperDARN orthogonality condition backscatter

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Numerical analysis of effective refractive index bio-sensor based on graphene-embedded slot-based dual-micro-ring resonator

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INTERNATIONAL JOURNAL OF MODERN PHYSICS B 2020年第17期34卷

作者： Zhao, C. Y. Chen, P. Y. Li, P. Y. Zhang, C. M. Hangzhou Dianzi Univ Coll Sci Hangzhou Zhejiang Peoples R China Shanxi Univ Inst Optoelect State Key Lab Quantum Opt & Quantum Opt Devices Taiyuan Peoples R China Nokia Solut & Networks Hangzhou 310053 Peoples R China

We propose a novel bio-sensor structure composed of slot dual-micro-ring resonators and mono-layer graphene. Based on the electromagnetically induced transparency (EIT)-like phenomenon and the light-absorption characteristics of graphene, we present a theoretical analysis of transmission by using the coupled mode theory and Kubo formula. The results demonstrate the EIT-like spectrum with asymmetric line profile. The modefield distributions of transmission spectrum are obtained from 3D simulations based on finite-difference time-domain (FDTD) method. Our bio-sensor exhibits theoretical sensitivity of 330 nm/RIU, a minimum detection limit of 3.6 x 10(-4) RIU, the maximum extinction ratio of 4.4 dB, the quality factor of 1.288 x 10(3) and a compact structure of 15 mu m x 10 mu m. Finally, the bio-sensor's performance is simulated for glucose solution. Our proposed design provides a promising candidate for on-chip integration with other silicon photonic element.

关键词： finite-difference time-domain method bio-sensor graphene micro-ring resonator

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Optimised low dispersive ID-WLP-FDTD method based on scaling factor

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ELECTRONICS LETTERS 2020年第17期56卷 887-888页

作者： Ding, Jinchao Univ Elect Sci & Technol China Sch Elect Sci & Engn Chengdu 611731 Peoples R China

An optimised low numerical dispersion unconditionally stable finite-difference time-domain (FDTD) method based on the isotropic dispersion (ID) scheme and weighted Laguerre polynomials (WLP) is presented. The proposed method adopts a scaling factor for permittivity and permeability in the ID-WLP-FDTD method, which can generate almost the exact phase velocity for a single frequency. In contrast with the traditional WLP-FDTD method and ID-WLP-FDTD method, the numerical dispersion of the new method is significantly reduced, and the proposed method can guarantee high accuracy and high efficiency simultaneously.

关键词： finite difference time-domain analysis polynomials ID-WLP-FDTD method optimised low numerical dispersion finite-difference time-domain method isotropic dispersion scheme traditional WLP-FDTD method weighted Laguerre polynomials

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