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Separation of the valley exciton-polariton in two-dimensional semiconductors with an anisotropic photonic crystal

Physical Review B 2020年第24期101卷 245418-245418页

作者： Ruoming Peng Changming Wu Huan Li Xiaodong Xu Mo Li Department of Electrical and Computer Engineering University of Washington Seattle Washington 98195 USA Department of Physics University of Washington Seattle Washington 98195 USA Department of Material Science and Engineering University of Washington Seattle Washington 98195 USA

Excitons in two-dimensional (2D) transition metal dichalcogenides (TMDC) are stable at room temperature because of high exciton binding energies. They can be selectively addressed based on the unique optical selection rules from angular momentum conservation for the K/K′ valley state and the helicity of circularly polarized light. When coupled with the optical modes in optical cavities, excitons can form exciton-polaritons, exploiting which in 2D TMDC may lead to optoelectronic devices for room temperature operation. The valley degree of freedom of the excitons, however, is mostly lost when forming exciton-polaritons because the cavity mode usually does not have a well-defined spin angular momentum. Here, we theoretically demonstrate that the valley information of exciton-polaritons can be preserved and resolved in a photonic cavity made of birefringent materials. Because of the optical anisotropy, the guided resonance modes have a net transverse spin angular momentum and selectively couple to exciton-polaritons with the corresponding valley state. In the strong-coupling regime, the exciton-polariton behaves in a way like the Rashba effect in the solid. The dispersion of the K/K′ exciton-polariton splits in momentum space based on its valley state, similar to electron spins in Rashba systems. Realizing valley-dependent exciton-polaritons affords a possibility to explore valley exciton dynamics in a strongly coupled system and will contribute to the study of excitonic, polaritonic devices, Bose-Einstein condensation, and superfluidity in semiconductors.

关键词： Exciton polariton Photonic crystals 2-dimensional systems finite-difference time-domain method finite-element method

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Plasmonic Antennas with Electric, Magnetic, and Electromagnetic Hot Spots Based on Babinet’s Principle

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Physical Review Applied 2020年第5期13卷 054045-054045页

作者： Martin Hrtoň Andrea Konečná Michal Horák Tomáš Šikola Vlastimil Křápek Central European Institute of Technology Brno University of Technology Purkyňova 123 Brno 612 00 Czech Republic Materials Physics Center CSIC-UPV/EHU Paseo Manuel de Lardizabal 5 San Sebastián 20018 Spain Institute of Physical Engineering Brno University of Technology Technická 2 Brno 616 69 Czech Republic

We theoretically study plasmonic antennas featuring areas of extremely concentrated electric or magnetic field, known as hot spots. We combine two types of electric-magnetic complementarity to increase the degree of freedom for the design of the antennas: bowtie and diabolo duality and Babinet’s principle. We evaluate the figures of merit for different plasmon-enhanced optical spectroscopy methods and optical trapping: field enhancement, decay rate enhancement, quality factor of the plasmon resonances, and trapping potential depth. The role of Babinet’s principle in interchanging electric and magnetic field hot spots and its consequences for practical antenna design are discussed. In particular, diabolo antennas exhibit slightly better performance than bowties in terms of larger field enhancement and larger Q factor. For specific resonance frequency, diabolo antennas are considerably smaller than bowties, which makes them favorable for the integration into more complex devices but also makes their fabrication more demanding in terms of spatial resolution. Finally, we propose a Babinet-type dimer antenna featuring electromagnetic hot spot with both the electric and magnetic field components treated on an equal footing.

关键词： Classical optics Integrated optics Interference & diffraction of light Nanoantennas Plasmonics Surface plasmon polariton Surface plasmons finite-difference time-domain method

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WBPAT for FDTD simulation of microwave devices with homogeneous waveport

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IET MICROWAVES ANTENNAS & PROPAGATION 2019年第2期13卷 239-245页

作者： Bo, Xi Chao Zhang, Jian Feng Jiang, Hao Lin Cui, Tie Jun Southeast Univ Sch Informat Sci & Engn Nanjing 210096 Jiangsu Peoples R China

Accurate power-to-amplitude transformation (PAT) has been proposed for the continuous wave (CW, i.e. sinusoidal wave or multi-carrier) to stimulate the quantitative electromagnetic fields under specified average input power with the finite-difference time-domain (FDTD) method for simulation of microwave devices. In this study, the authors propose wideband PAT (WBPAT), by which quantitative amplitude and phase of electromagnetic fields at desired frequencies can be accurately extracted for microwave devices with homogeneous waveport under specified average input power when the excitation waveform of specified waveguide mode is wideband impulse signal. In the proposed WBPAT, the information of incident wave for normalisation is needed, which is investigated and discussed. Furthermore, a post-processing procedure called as the mode-impedance-modified normalisation is proposed to consider the frequency dependence of mode impedance, in which the mode impedance in wideband is obtained by FDTD simulation, per se. The average input power is defined for each frequency within the frequency range. As a result, accurate amplitude and phase, which is equivalent to that by frequency-domain methods or TD methods with the excitation of CW after steady state, can be extracted. Several numerical examples show the validity of the proposed method.

关键词： frequency-domain analysis finite difference time-domain analysis microwave devices waveguides WBPAT FDTD simulation microwave devices homogeneous waveport continuous wave sinusoidal wave quantitative electromagnetic fields finite-difference time-domain method wideband impulse signal mode-impedance-modified normalisation frequency-domain methods waveguide mode wideband power-to-amplitude transformation CW

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Numerical Simulation for MRI RF Coils and Safety

EMAGRES

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EMAGRES 2020年第2期9卷 127-142页

作者： Kabil, Julie M. Gopinath, Anand Columbia Univ Columbia Magnet Resonance Res Ctr New York NY USA Univ Minnesota Elect & Comp Engn Minneapolis MN USA

This article introduces the basic electromagnetic theory, different solvers principles, and also more practical matters such as a practical workflow, the need and means of validating a simulation, and a nonexhaustive ... 详细信息

关键词： finite element method finite-difference time-domain method finite-integration technique RF coils MRI safety RF safety RF heating

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An FDTD TF-SF Boundary on Face-Centered Cubic Grids

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APPLIED COMPUTATIONAL ELECTROMAGNETICS SOCIETY JOURNAL 2020年第4期35卷 367-374页

作者： Shi, Lijuan Yang, Lixia Feng, Wei Jiangsu Univ Dept Phys Zhenjiang 212013 Jiangsu Peoples R China Jiangsu Univ Dept Commun Engn Zhenjiang 212013 Jiangsu Peoples R China

The implementation of total-field/scattered-field (TF-SF) boundary for finite-difference time-domain (FDTD) method was proposed based on face-centered cubic (FCC) grids. On the basis of the arrangement of fields components in the FCC voxel, the update equations for the electric and magnetic field components of the TF-SF boundary are derived. The resonant frequency of a cavity is calculated to illustrate that the FCC grid scheme is more accurate as compared to the equivalent Yee grid method. Then, by simulating the amplitude distribution of the vertical and oblique incident plane waves in the whole calculation region, the effectiveness of the TF-SF boundary is verified numerically.

关键词： Face-centered cubic grids finite-difference time-domain method total-field/scattered-field boundary

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FDTD Simulation: Simultaneous Measurement of the Refractive Index and the Pressure Using Microdisk Resonator with Two Whispering-Gallery Modes

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SENSORS 2020年第14期20卷 3955.-3955页

作者： Zhang, Ping He, Dongyue Zhang, Chen Yan, Zhiruo Tianjin Univ Sch Elect & Informat Engn Minist Educ Tianjin 300072 Peoples R China Tianjin Univ Key Lab Adv Ceram & Machining Technol Minist Educ Tianjin 300072 Peoples R China

In this paper, an approach to measure both the refractive index (RI) and the pressure simultaneously using two Whispering-Gallery Modes (WGMs) in a microdisk resonator is theoretically proposed. Due to the difference in the energy distribution of the first and second order WGMs, the sensitivity of two modes toward the variation of RI and pressure applied to the device show differences. An RI sensitivity of 29.07 nm/RIU and pressure sensitivity of 0.576 pm/kPa for WGM (1,36), and an RI sensitivity of 38.68 nm/RIU and a pressure sensitivity of 0.589 pm/kPa for WGM (2,28) are obtained through the 3D finite-difference time-domain (3D-FDTD) simulation. Dual parametric sensing can be achieved by solving the second-order inverse sensitivity matrix. Therefore, strain-optical coupling behavior is effectively eliminated. The dual sensing scheme we proposed provides a novel approach to overcome the difficulty of multi-sensing applications based on the flexible photonic device.

关键词： microdisk resonator whispering-gallery mode refractive index pressure finite-difference time-domain method

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Transfer of Information using Surface-Plasmon-Polariton Waves 19

Transfer of Information using Surface-Plasmon-Polariton Wave...

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Conference on Optical Interconnects XIX

作者： Agrahari, Rajan Lakhtakia, Akhlesh Jain, Pradip K. Indian Inst Technol BHU Dept Elect Engn Varanasi 221005 Uttar Pradesh India Penn State Univ NanoMM Nanoengn Metamat Grp Dept Engn Sci & Mech University Pk PA 16802 USA Indian Inst Technol BHU Mat Architecture Ctr Varanasi 221005 Uttar Pradesh India Natl Inst Technol Dept Elect & Commun Patna 800005 Bihar India

ISBN: (数字)9781510624917

ISBN: (纸本)9781510624917

The limitations of electronic and optical interconnects inside a semiconductor chip could be overcome by the used of plasmonic-polaritonic interconnects whereby information is carried by surface-plasmon-polariton (SPP) waves guided by planar metal/dielectric interface. Investigating the propagation of a pulse-modulated carrier SPP wave when the metal is either abruptly terminated or bent and the dielectric material is air, we have found that SPP-wave-based interconnects can be effective conduits of information.

关键词： Plasmonic communication surface-plasmon-polariton wave finite-difference time-domain method

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Theoretical Analysis of Photonic Band Gaps and Defect Modes of Novel Photonic Crystal Waveguides Consisting of Si-Ion Implanted SiO₂ Using the finite-difference time-domain method

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5th International Symposium on Silicon Science/1st International Conference on Advanced Micro-Device Engineering

作者： Umenyi, Amarachukwu Valentine Kawashiri, Shin-ya Miura, Kenta Hanaizumi, Osamu Gunma Univ Dept Elect Grad Sch Engn Kiryu Gunma 376 Japan

ISBN: (纸本)9780878492176

In this paper, photonic crystals (PC) based on 2-D periodic arrays of air holes were investigated on Si-ion implanted SiO2 using finite-difference time-domain (FDTD) simulations. The PC design parameters based on the telecommunication wavelength (lambda=1.55 mu m) were obtained by varying the radius to lattice constant ratio (r/a) from 0.2 to 0.45. We analyzed both transverse electric (TE) and transverse magnetic (TM) mode propagation in triangular-lattice PCs. The result obtained shows that a PC bandgap (PBG) exists for TE-mode propagation in the Si-ion implanted SiO2 patterned 2-D triangular lattice of air holes. We have also calculated the dispersion relations for the TE mode of a line defect in the structure and shown a fabricated sample. These analyses are obviously important for fabricating novel PC waveguides, which can easily be integrated into the existing silicon technology for directing light from one part of a chip to the other.

关键词： ion implantation finite-difference time-domain method photonic crystal waveguide silicon photonics photonic bandgap

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A Stochastic FDTD method for Rectangular Objects with Geometric Uncertainties 8

A Stochastic FDTD Method for Rectangular Objects with Geomet...

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8th International Conference on Modern Circuit and System Technologies (MOCAST)

作者： Salis, Christos Kantartzis, Nikolaos Zygiridis, Theodoros Univ Western Macedonia Dept Informat & Telecommun Engn Kozani 50131 Greece Aristotle Univ Thessaloniki Dept Elect & Comp Engn Thessaloniki 54124 Greece

ISBN: (纸本)9781728111841

The uncertainties present in various dielectric materials may have an effect on the properties of the electromagnetic components. Deterministic schemes are unable to capture the statistics of the examined quantities and as a result, reliable outcomes cannot be extracted. In this paper, we present a novel two-dimensional (2D) finite-difference time domain (FDTD) method, that manages to calculate the statistics of the involved fields in a single simulation. The proposed algorithm is a variation of the Stochastic FDTD method and is suitable for assessing random media uncertainties, as well as to estimate the variation in the width and height of a random rectangular dielectric. Numerical results indicate the validity of our scheme compared with the Monte Carlo approach.

关键词： finite-difference time-domain method Monte Carlo Non-uniform grids Stochastic FDTD Uncertainty problems

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Computing complex dispersive refractive indices from thin film optical properties of materials 22

Computing complex dispersive refractive indices from thin fi...

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22nd Annual Conference on Novel Optical Systems, methods, and Applications XXII

作者： Banerjee, S. Takayanagi, I. Mori, K. Nakamura, J. Cole, J. B. Hoshino, T. Itoh, M. Brillnics Japan Inc Tokyo Japan Natl Acad Sci Washington DC USA Univ Tsukuba Inst Appl Phys Tsukuba Ibaraki Japan

ISBN: (数字)9781510629042

ISBN: (纸本)9781510629042

Nanophotonic devices, such as CMOS image sensor (CIS) pixels, are formed by stacking multiple layers of semiconductor materials. The complex refractive indices of these materials vary with the wavelength of light. Currently, industrial development of photonic devices includes a design step where light propagation is simulated using numerical methods, such as finite-difference time-domain (FDTD). Such simulations require that the refractive indices of the constituent materials be known accurately. Most commonly employed methods for computing the real and imaginary parts of the dispersive refractive indices are based either on the evaluation of the Kramers-Kronig (K-K) integral, or on the use of theoretical models of permittivity. These methods rely on the experimentally measured reflectivity or transmissivity spectra of thin films of a material to determine its refractive indices. In the first part of this paper, we describe the computation of the dispersive refractive indices of certain materials using an optimization routine based on a genetic algorithm and the coherent reflectivity and transmissivity spectra of thin-films. This approach finds the global optimum unlike earlier methods based on local optimization techniques. In the second part of the paper, we evaluated the K-K integral and used the Lorentz model of permittivity to compute the real part of the refractive index of Rhodamine B from its imaginary part. The imaginary part was determined from the transmission spectrum of a thin film of Rhodamine B. Recently, we used a similar strategy to compute the dispersive refractive index of an on-chip color filter commonly used for CIS pixel.

关键词： CMOS Image Sensors silicon photonics subwavelength optics design and simulation finite-difference time-domain method refractive indices of materials thin films

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