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Distinct linear polarization of core-shell particles at near-backscattering directions

OPTICS EXPRESS 2023年第26期31卷 44648-44671页

作者： Li, Meng Bi, Lei Lin, Wushao Zhejiang Univ Sch Earth Sci Key Lab Geosci Big Data & Deep Resources Zhejiang Hangzhou 310027 Peoples R China

The degree of linear polarization (-P-12/P-11) of scattered light by particles with a core-shell structure may display a distinct negative minimum at near-backscattering directions. However, the specific range of microphysical parameters within which this phenomenon occurs and the underlying physical mechanism are still unclear. Therefore, this study systematically investigated the impacts of particle size, shell-core ratio and refractive index on the negative minimum of -P-12/P-11 at near-backscattering angles for both coated spheres and coated super-spheroids. The findings reveal that the pronounced negative minimum at near-backscattering angles mostly appeared when the size parameter defined in terms of the mean radius was smaller than approximately 14.5 (e.g., the mean radius is smaller than approximately 2 mu m at 0.865 mu m wavelength) and the shell-core ratio was in a range of 1.4-1.9. The presence of weakly- and moderately-absorptive shells would lead to pronounced negative polarization at near backscattering directions. However, as the core absorption increased, the amplitude of negative minimum decreased and then stabilized. As for coated super-spheroids, the non-sphericity of the shell tended to suppress the negative polarization at near-backscattering directions. As a result, the pronounced negative minimum (<-0.4) mostly appeared when the aspect ratio and roundness of the shell were close to unity (the overall shape of the particle was nearly-spherical). However, the negative minimum of -P-12/P-11 showed little dependence on the shape of the core. Furthermore, the Debye series approach was employed to investigate the underlying mechanism of the negative minimum of -P-12/P-11 for coated spheres. The results demonstrated that the interference among the partial waves underwent one internal reflection on the shell-medium interface and, without internal reflection on the core-shell interface, led to the pronounced negative polarization at near-backscattering

关键词： Computational electromagnetics finite-difference time-domain method Negative index materials Optical properties Refractive index Remote sensing

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Study on Chinese Speech Intelligibility Under Different Low-Frequency Characteristics of Reverberation time Using a Hybrid method

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ARCHIVES OF ACOUSTICS 2023年第2期48卷 151-157页

作者： Huang, Wuqiong Peng, Jianxin Xie, Tinghui South China Univ Technol Sch Phys & Optoelect Guangzhou Peoples R China South China Univ Technol State Key Lab Subtrop Bldg Sci Guangzhou Peoples R China Shijiazhuang Tiedao Univ Sch Architecture & Art Shijiazhuang Peoples R China

Reverberation time (RT) is an important indicator of room acoustics, however, most studies focus on the mid-high frequency RT, and less on the low-frequency RT. In this paper, a hybrid approach based on geometric and wave methods was proposed to build a more accurate and wide frequency-band room acoustic impulse response. This hybrid method utilized the finite-difference time-domain (FDTD) method modeling at low fre-quencies and the Odeon simulation at mid-high frequencies, which was investigated in a university classroom. The influence of the low-frequency RT on speech intelligibility was explored. For the low-frequency part, dif-ferent impedance boundary conditions were employed and the effectiveness of the hybrid method has also been verified. From the results of objective acoustical parameters and subjective listening experiments, the smaller the low-frequency RT was, the higher the Chinese speech intelligibility score was. The syllables, consonants, vowels, and the syllable order also had significant effects on the intelligibility score.

关键词： low frequency speech intelligibility classroom finite-difference time-domain method

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Modelling structural colour from helicoidal multi-layer thin films with natural disorder

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OPTICS EXPRESS 2023年第22期31卷 36531-36546页

作者： Davis, T. J. Ospina-Rozo, L. Stuart-Fox, D. Roberts, A. Univ Melbourne ARC Ctr Excellence Transformat Opt Syst Sch Phys Melbourne Vic 3010 Australia Univ Melbourne Sch Biosci Melbourne Vic 3010 Australia

A coupled mode theory based on Takagi-Taupin equations describing electromagnetic scattering from distorted periodic arrays is applied to the problem of light scattering from beetles. We extend the method to include perturbations in the permittivity tensor to helicoidal arrays seen in many species of scarab beetle and optically anisotropic layered materials more generally. This extension permits analysis of typical dislocations arising from the biological assembly process and the presence of other structures in the elytra. We show that by extracting structural information from transmission electron microscopy data, including characteristic disorder parameters, good agreement with spectral specular and non-specular reflectance measurements is obtained. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Coupled mode theory Electromagnetic scattering Fiber Bragg gratings finite-difference time-domain method Light diffraction Thin films

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Toroidal dipole resonances enable giant vortical dichroism in folded metamaterials

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OPTICS LETTERS 2025年第9期50卷 3102-3105页

作者： Peng, Kangzhun Luo, Shiqi Li, Zhi-yuan Liang, Wenyao South China Univ Technol Sch Phys & Optoelect Guangzhou 510640 Peoples R China

Chiral optical effects have significant applications in material science and nanophotonics, particularly in chiral material detection and optical sensing. The toroidal dipole resonance, as a unique electromagnetic multipolar mode, has attracted considerable attention for its distinctive response characteristics in optical research. In this work, we propose a folded metamaterial and investigate the interaction between photonic orbital angular momentum and the toroidal dipole resonances in the designed chiral metamaterials. By varying the folded angle of the metamaterial, we analyze the variations in vortical dichroism response and find that the folded angle significantly affects the intensity and contrast of the vortical dichroism effect. By using electromagnetic multi-pole resonances theory, we verify that the vortical dichroism enhancement is mainly driven by toroidal dipole resonance intensity and confirm chiral toroidal dipole resonances in the orbital angular momentum dimension. This study provides what we believe to be a new pathway for flexible orbital angular momentum manipulation and the development of chiral toroidal dipole optical devices, especially in optical communications and optical holography applications. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： Dichroism finite-difference time-domain method Optical detection Optical materials Optical sensing Optical vortex beams

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A Novel 3-D DGTD-FDTD Hybrid method with One Overlapping Virtual Layer

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APPLIED COMPUTATIONAL ELECTROMAGNETICS SOCIETY JOURNAL 2023年第8期38卷 558-565页

作者： Wu, Qingkai Wang, Kunyi Lin, Zhongchao Zhang, Yu Zhao, Xunwang Xidian Univ Sch Elect Engn Xian 710071 Peoples R China

Compared with the traditional finite difference time -domain (FDTD) method, the discontinuous Galerkin time -domain (DGTD) method may face the issue of intense computation. In this paper, a novel 3-D DGTD-FDTD hybrid method is proposed to dramatically reduce the unknowns of the DGTD method. Instead of the common mass -lumped elements, this virtual layer of the Yee grid is implemented on the intersecting boundary, which simplifies the mesh generation and reduces the number of unknowns. To validate the proposed method, two examples of sphere scattering and horn antenna are considered. The simulation results demonstrate the effectiveness of the proposed method.

关键词： Discontinuous Galerkin time-domain method finite-difference time-domain method hybrid method transient analysis

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High performance on-chip polarization beam splitter at visible wavelengths based on a silicon nitride small-sized ridge waveguide

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OPTICS EXPRESS 2023年第23期31卷 38419-38429页

作者： Zheng, Xinzhi Zhao, Chenxi Ma, Yujie Qiao, Shijun Chen, Shuai Zhang, Zhaojie Yu, Mingyang Xiang, Bingxi Lv, Jinman Lu, Fei Zhou, Cangtao Ruan, Shuangchen Shenzhen Technol Univ Coll Engn Phys Ctr Adv Mat Diagnost Technol Shenzhen Key Lab Ultraintense Laser & Adv Mat Tech Shenzhen 518118 Peoples R China Shenzhen Univ Shenzhen 518118 Peoples R China H Chip Technol Grp Corp Tianjin 300450 Peoples R China Shenzhen Technol Univ Coll New Mat & New Energies Shenzhen 518118 Peoples R China Shandong Univ Sch Informat Sci & Engn Jinan 250100 Shandong Peoples R China

Due to sensitive scaling of the wavelength and the visible-light absorption properties with the device dimension, traditional passive silicon photonic devices with asymmetric waveguide structures cannot achieve polarization control at the visible wavelengths. In this work, a simple and small polarization beam splitter (PBS) for a broad visible-light band, using a tailored silicon nitride (Si3N4) ridge waveguide, is presented, which is based on the distinct optical distribution of two fundamental orthogonal polarized modes in the ridge waveguide. The bending loss for different bending radii and the optical coupling properties of the fundamental modes for different Si3N4 ridge waveguide configurations are analyzed. A PBS composed of a bending ridge waveguide structure and a triple-waveguide directional coupler was fabricated on the Si3N4 thin film. The TM excitation of the device based on a bending ridge waveguide structure shows a polarization extinction ratio (PER) of >= 20 dB with 33 nm bandwidth (624-657 nm) and insertion loss (IL) < 1 dB at the through port. The TE excitation of the device, based on a triple-waveguide directional coupler with coupling efficiency distinction between the TE0 and TM0 modes, shows a PER of > 18 dB with 50 nm bandwidth (580-630 nm) and insertion loss (IL) < 1 dB at the cross port. The on-chip Si3N4 PBS device is found to possess the highest known PER at a visible broadband range and small (43 mu m) footprint. It should be useful for novel photonic circuit designs and further exploration of Si(3)N(4)PBSs. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Beam splitters finite-difference time-domain method Optical properties Quantum light sources Silicon nitride Thin films

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Simulation of spatiotemporal light dynamics based on the time-dependent Schrödinger equation

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OPTICS EXPRESS 2023年第24期31卷 39941-39952页

作者： Richter, Maria Morales, Felipe Patchkovskii, Serguei Husakou, Anton Max Born Inst Nonlinear Opt & Short Pulse Spect Max Born Str 2a D-12489 Berlin Germany

We establish a first-principle model for the simulation of spatiotemporal light pulse dynamics based on the combination of the time-dependent Schrodinger equation and the unidirectional propagation equation. The proposed numerical scheme enables computationally efficient simulation while being stable and accurate. We use the new model to examine self-focusing of a short pulse in atomic hydrogen and show that an accurate description of the excited-levels dynamics can only be achieved by a propagation model with an ab-initio description of the light-matter interaction, which accounts for the laser-dressed multilevel structure of the system, including bound and free states, and its sub-cycle response.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Femtosecond pulses finite-difference time-domain method High harmonic generation Kerr effect Light matter interactions Light propagation

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Enhancing light extraction efficiency of 242 nm DUV micro-LEDs via hybrid nanorod arrays

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OPTICS LETTERS 2025年第9期50卷 2828-2831页

作者： Zhu, Licai Lu, Shunpeng Jiang, Ke Ben, Jianwei Zhang, Shanli Hao, Jialong Peng, Jiale Zhang, Ruojia Li, Dabing Sun, Xiaojuan Chinese Acad Sci Changchun Inst Opt Fine Mech & Phys State Key Lab Luminescence Sci & Technol Changchun 130033 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

Deep-ultraviolet (DUV) micro-LEDs are pivotal for applications such as maskless lithography and germicidal disinfection. However, improving light extraction efficiency (LEE) remains a significant challenge. This study presents a novel, to the best of our knowledge, strategy to enhance LEE by employing gold thin-film annealing and dry-etching techniques to fabricate disordered p-GaN/p-AlGaN hybrid nanorod arrays. The enhancement mechanism involves directly reflecting the transverse electric (TE) mode within the escape cone at the p-AlGaN/Al mirror interface, thereby minimizing absorption by p-GaN. Simultaneously, TE and transverse magnetic (TM) modes outside the escape cone are scattered by the nanorods and redirected into the escape cone, promoting forward emission. 3D finite-difference time domain simulations predict a 79% increase in LEE for TM and a 187% improvement for TE. Experimentally, we observe a 140% enhancement in peak light output power (LOP), a 148% boost in external quantum efficiency (EQE), and a 146% increase in wall-plug efficiency (WPE) at 1 mA compared to planar designs. This innovative approach markedly advances the performance of DUV micro-LEDs, fostering new possibilities in high-efficiency DUV technologies. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： finite-difference time-domain method Light extraction Quantum efficiency Scanning electron microscopy Thin films Total internal reflection

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finite-difference time-domain simulation of floor-impact sound excited by one-dimensional contact model and its application to auralization of floor-impact sound

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ACOUSTICAL SCIENCE AND TECHNOLOGY 2021年第1期42卷 22-35页

作者： Asakura, Takumi Tokyo Univ Sci 2641 Yamazaki Noda Chiba 2780022 Japan

To develop a numerical method of determining the time and frequency characteristics of the external forces excited by various impact sources, the collision between the free-fall mass and the elastic platelike structure are modeled by the one-degree-of-freedom contact model structured on the discrete wave-based numerical analysis of bending vibration with the finite-difference time-domain (FDTD) method. Moreover, the calculated impact sounds were auralized and applied to the evaluation experiment of the subjective impression of loudness and annoyance. As the basic study, the excitation characteristics of generally used devices that is, the impact ball, bang machine, and tapping machine and human trotting are simulated and used for a numerical simulation targeting the prediction of the impact sound pressure levels inside a wall-type concrete structure. After that, the proposed method was applied to a subjective evaluation experiment of the loudness and annoyance influenced by a floor-impact sound on various types of floor slab. The results have shown that the loudness and annoyance induced by the floor-impact sound indicated a high correlation with the maximum A-weighted sound pressure level.

关键词： finite-difference time-domain method Impact vibration Voigt model Floor-impact sound

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Three-dimensional finite-difference time-domain simulation of moving sound source and receiver with directivity

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JAPANESE JOURNAL OF APPLIED PHYSICS 2023年第SJ期62卷 SJ1015-SJ1015页

作者： Tsuchiya, Takao Teshima, Yu Hiryu, Shizuko Doshisha Univ Dept Informat Syst Design Kyoto 6100321 Japan Doshisha Univ Dept Biomed Sci & Informat Kyoto 6100321 Japan

In this paper, the implementation of a moving sound source and receiver with directivity in the three-dimensional finite-difference time-domain method is described. Fundamental solutions of moving monopole, dipole, and cardioid sources are theoretically derived. Some numerical experiments were performed on the three-dimensional sound field for a moving source and receiver. The numerical experiments showed that the effect of moving velocity on amplitude differs for the monopole and dipole or cardioid sources. Furthermore, it was found that the directivity characteristics of dipole and cardioid sources vary depending on the beam and moving directions. The present method can be accurately applied to the moving sound source and receiver with directivity.

关键词： finite-difference time-domain method three-dimensional analysis moving source moving receiver directivity

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