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Anapole mechanism of bound states in the continuum in symmetric dielectric metasurfaces

Physical Review B 2024年第24期109卷 L241405-L241405页

作者： Izzatjon Allayarov Antonio Calà Lesina Andrey B. Evlyukhin Hannover Centre for Optical Technologies Institute of Transport and Automation Technology Cluster of Excellence PhoenixD Institute of Quantum Optics

We present a general multipole mechanism based on the lattice anapole effect leading to the excitation of high-Q resonances in dielectric metasurfaces with the simplest unit cell (i.e., a unit cell with inversion symmetry containing only one nanostructure) and irradiation conditions (i.e., normal incidence). Using multipole techniques, we show analytically and numerically that these resonances are related to the conversion of bound states in the continuum (BICs) to quasi-BICs by simply changing the metasurface period. It is also shown that BICs and quasi-BICs, in turn, are realized through destructive interference (anapole effect) between multipoles of the same parity. The main advantage of such a conversion BIC to quasi-BIC compared to those proposed earlier is that it does not require distortion of symmetric properties of metasurfaces, special conditions of irradiation, or displacement of elements in composite unit cells. The results obtained give an important insight into the physics of high-Q resonances in meta-optics and can simplify and expand the application of metasurfaces for tunable lasing, nonlinear generation, energy trapping manipulation, and enhanced sensing techniques.

关键词： Bound states in the continuum Metasurfaces Nanoantennas Photonics finite-difference time-domain method

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Novel Focusing Performances of High-Numerical-Aperture Micro-Fresnel Zone Plates with Selective Occlusion

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PHOTONICS 2025年第4期12卷

作者： Liu, Qiang Wu, Yunpeng Deng, Yuanhao Wang, Junli Liu, Wenshuai Yao, Xiaomin Shaanxi Univ Technol Sch Mech Engn Hanzhong 723000 Peoples R China Shaanxi Univ Technol Shaanxi Key Lab Ind Automat Hanzhong 723000 Peoples R China

In this study, novel focusing performances of high-numerical-aperture (NA) micro-Fresnel zone plates (FZPs) with selective occlusion are identified and investigated through numerical calculations based on vectorial angular spectrum (VAS) theory, and further rigorously validated using the finite-difference time-domain (FDTD) method. The central occlusion of a standard micro-FZP can significantly extend the depth of focus while keeping the lateral size of the focusing spot essentially unchanged. When a standard micro-FZP only retains two separated transparent rings and all other rings are obstructed, it will result in multi-focus phenomena;at the same time, the number of focal points is equal to the difference in number between the two separated transparent rings. Furthermore, a focusing light needle can be generated by combining the central occlusion and wavelength shift of a standard micro-FZP. This study not only provides new ideas for the design and optimization of micro-FZPs but also provides reference for the expansion of practical applications of FZPs.

关键词： Fresnel zone plate diffraction occlusion vectorial angular spectrum theory finite-difference time-domain method

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Improving the Light Harvest of Plasmonic Based Organic Solar Cells by Utilizing Dielectric Core-Shells

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PLASMONICS 2025年第6期20卷 4007-4019页

作者： Mulat, Simenew A. Hone, Fekadu G. Bekri, Nika Tegegne, Newayemedhin A. Addis Ababa Univ Dept Phys Addis Ababa 1176 Ethiopia Addis Ababa Sci & Technol Univ Dept Math Phys & Stat Addis Ababa 16417 Ethiopia Addis Ababa Sci & Technol Univ Sustainable Energy Ctr Excellence Addis Ababa 16417 Ethiopia Addis Ababa Sci & Technol Univ Nanotechnol Ctr Excellence Addis Ababa 16417 Ethiopia

The plasmonic properties of nanoparticles (NPs) such as silver (Ag) can be improved by utilizing core-shell materials in order to improve photon harvest in organic solar cells (OSCs). In this work, we utilized four dielectric materials, namely TiO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}, SnO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}, ZnO, and SiO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document}, to improve the near-field and far-field enhancement in addition to pushing the LSPR of Ag NPs to the visible region. The plasmon-assisted photon harvesting in P3HT:PCBM-based inverted organic solar cell (OSC) devices was investigated using a 70 nm silver nanosphere (Ag NS) coated with dielectrics. This study employed a 3D finite-difference time-domain (FDTD) method for the analysis. The results show that the PCE of P3HT:PCBM could be enhanced by more than 26% when the NPs were embedded in the active layer due to the synergistic effect of near-field and far-field enhancement, with TiO2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$_2$$\end{document} that has a higher dielectric constant compared to others and bare Ag NPs. Furthermore, it was observed that backscattering as the dominant scatte

关键词： Plasmonic organic solar cells Dielectric coating finite-difference time-domain method Local surface plasmon resonances effect

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Nanosecond laser-induced surface damage growth and its mechanism of single crystal CaF2 (111) at 193 nm

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OPTICS EXPRESS 2025年第7期33卷 15067-15080页

作者： Shan, Chong Kou, Huamin Jiang, Dapeng Liu, Rongrong Zhang, Zhen Lu, Zhuowei Fang, Lizhi Han, Ping Lian, Yafei Peng, Xing Zhao, Yuanan Su, Liangbi Chinese Acad Sci Shanghai Inst Ceram State Key Lab Funct Crystals & Devices Shanghai 201899 Peoples R China Chinese Acad Sci Shanghai Inst Opt & Fine Mech State Key Lab High Field Laser Phys Shanghai 201800 Peoples R China Natl Univ Def Technol Coll Intelligent Sci & Technol Changsha 410073 Hunan Peoples R China

The damage growth of calcium fluoride crystal (CaF2) induced by 193 nm laser irradiation poses a significant risk to the operation of deep-ultraviolet photolithography. It is crucial to explore the damage growth characteristics and mechanism of CaF2 crystal induced by a 193 nm laser for the safe operation of integrated photolithography systems. This paper analyzed the trend of 193 nm laser-induced damage growth of CaF2 crystal surfaces and obtained the damage growth coefficients and thresholds of three CaF2 crystal test samples. By analyzing the chemical composition variation and the electrical field modulation of initial damage, it was concluded that the laser-induced modification around initial damage and the electric field modulation at the center of initial damage would affect the damage growth properties. Meanwhile, the different absorption and growth thresholds of the same initial damage would also result in different damage growth characteristics. This research provides reliable information for improving CaF2 crystal's damage resistance ability and prolonging its lifetime in deep-ultraviolet lithography systems. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： finite-difference time-domain method Laser damage Laser induced damage thresholds Laser operation Ultrafast lasers Ultraviolet lasers

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Achieving bi-anisotropic coupling through uniform temporal modulations without inversion symmetry disruption

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OPTICS LETTERS 2024年第9期49卷 2493-2496页

作者： Wang, Neng Feng, Fanghu Wang, Guo P. I. N. G. Shenzhen Univ Coll Elect & Informat Engn China State Key Lab Radio Frequency Heterogeneous Shenzhen 518060 Peoples R China

Temporal modulations provide a new approach for realizing metamaterials. In this study, through the imposition of uniform temporal modulations, we achieve two types of reciprocal bi-anisotropic metamaterials. Notably, these achievements do not rely on any spatial modulation, preserving inversion symmetry at any instantaneous time. This stands in sharp contrast to the scenario of traditional bianisotropic metamaterials, where the disruption of inversion symmetry by spatial arrangements is necessary. Conditions for realizing nonzero bi-anisotropic coupling are discussed and verified through full -wave simulations. Our work will stimulate research in the field of temporal bi-anisotropic metamaterials, as well as the application of temporal modulations in manipulating photonic spin angular momentum. (c) 2024 Optica Publishing Group

关键词： finite-difference time-domain method Fourier transforms Frequency modulation Metamaterials Modulation Phase modulation

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High-performance etchless lithium niobate layer electro-optic modulator enabled by quasi-BICs

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OPTICS LETTERS 2024年第1期49卷 113-116页

作者： Liu, Guiqiang Zong, Shu Liu, Xiaoshan Chen, Juan Liu, Zhengqi Jiangxi Normal Univ Coll Phys & Commun Elect Nanchang 330022 Jiangxi Peoples R China

A facile strategy is proposed for a high-performance electrooptic modulator with an etchless lithium niobate (LN) layer assisted by the silicon resonator metasurface, which pioneers the way to engineer an ultra -sharp spectral line shape via the excitation of quasi -bound states in the continuum (BICs). Meanwhile, strong out -of -plane electric/magnetic fields within the proximity area to the electro-optic layer lead to ultra -sensitive modulations. As a result, only a slight voltage change of 0.2 V is needed to fully shift the resonances and then realize switching modulation between the "off" and "on" states. The findings pave new, to the best of our knowledge, insights in reconfiguration of spatial optical fields and offer prospects for functional optoelectronic devices. (c) 2023 Optica Publishing Group

关键词： finite element method finite-difference time-domain method Indium tin oxide Lithium niobate Q factor Spatial light modulators

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Boosting strong self-hybrid coupling in simple bulk transition metal dichalcogenides metasurfaces

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OPTICS EXPRESS 2024年第26期32卷 46557-46568页

作者： Wang, Jingyu Wu, Suze Yang, Weimin Shanxi Normal Univ Sch Phys & Informat Engn Taiyuan 030000 Peoples R China Zhangzhou Inst Technol Sch Elect Informat Zhangzhou 363000 Peoples R China

The emergence of exciton-polaritons in transition metal dichalcogenides (TMDs) has sparked keen interest due to their exceptional optical features, enabling investigations into fascinating physical phenomena such as superfluidity and Bose-Einstein condensation. However, the comprehensive examination of strong coupling, featuring substantial Rabi splitting, simultaneously engaging surface plasmon polariton (SPP) modes, anapole resonances, and excitons, remains limited. In this contribution, we computationally unravel the strong coupling of an SPP-anapole-exciton complex, supported by a novel metasurface design featuring a bulk WS2 nanodisk array separated by a SiO2 spacer and overlaid with an Al film. This innovative setup fosters profound interactions among SPP modes, anapole states, and excitons within the bulk WS2 nanodisks, resulting in an impressive Rabi splitting of 407 meV. Our proposed hybrid metasurfaces present a promising avenue for achieving strong coupling among diverse optical responses in light-matter interactions, thereby catalyzing the development of advanced polaritonic devices with novel functionalities.

关键词： Bose Einstein condensates finite-difference time-domain method Light matter interactions Metasurfaces Refractive index Resonant modes

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Low-loss grating coupler with a subwavelength structure on a thin-film lithium niobate substrate

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OPTICS LETTERS 2024年第2期49卷 222-225页

作者： Huang, Jing Chen, Nuo Chen, Kaizhong Chu, Tao Zhejiang Univ Coll Informat Sci & Elect Engn Hangzhou 310027 Peoples R China

We demonstrated a low-loss O-band grating coupler on an x-cut thin-film lithium niobate substrate by implementing subwavelength and apodized structures. The subwavelength gratings were used to mitigate the refractive index discontinuity between the input taper and grating region, which was the first application of such a structure for grating coupler optimization on a thin-film lithium niobate substrate. The coupling efficiency was measured to be -1.99 dB/coupler at a wavelength of 1312.8 nm, which was the lowest loss among the reported lithium niobate grating couplers that do not use metal mirrors. The proposed design does not require metal mirrors or any additional material layers and can be easily fabricated with a single-step lithography and etching (c) 2024

关键词： finite-difference time-domain method Grating coupler Lithium niobate Refractive index Scanning electron microscopy Subwavelength structures

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Observation of spectral splitting of whispering-gallery modes in asymmetrical photonic molecules

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OPTICS LETTERS 2024年第16期49卷 4581-4584页

作者： Wang, Jianwei Sun, Jiapeng Zhang, Yu Liu, Zhihai Li, Hanyang Harbin Engn Univ Coll Phys & Optoelect Engn Harbin 150001 Peoples R China

This Letter investigates mode splitting via whispering gallery modes (WGMs) in asymmetrical photonic molecules (PMs) composed of size-mismatched dual microspheres fabricated from fused silica. The characteristics of asymmetrical PMs were analyzed both numerically and experimentally, focusing specifically on the separation and intensity differences of splitting peaks. The splitting spectra exhibited a redshift, and the separation of two splitting peaks reached a maximum in symmetrical PMs, with a minimal difference in intensity also observed. It was noted that the splitting peaks shifted in opposite directions for the same PMs when coupling points with the tapered fibers were varied. This phenomenon can be applied to select similarly sized microparticles and to recognize PMs in optical devices. 2024 Optica Publishing Group

关键词： Coupled mode theory finite-difference time-domain method Optical devices Single mode fibers Tapered fibers Whispering gallery modes

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Bragg-like microcavity formed by collision of single-cycle self-induced transparency light pulses in a resonant medium

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OPTICS LETTERS 2024年第10期49卷 2549-2552页

作者： Arkhipov, Rostislav Pakhomov, Anton Diachkova, Olga Arkhipov, Mikhail Rosanov, Nikolay St Petersburg State Univ St Petersburg 199034 Russia Ioffe Inst St Petersburg 194021 Russia

The coherent interaction of extremely short light pulses with a resonant medium can result in the formation of population difference gratings. Such gratings have been created by pulses that are pi/2 or smaller. This paper demonstrates that a microcavity with Bragg -like mirrors can be formed by colliding two single -cycle attosecond self-induced transparency pulses in the center of a two -level medium. The parameters of this structure can be quickly adjusted by increasing the number of collisions, which showcases the ability to control the dynamic properties of the medium on a sub -cycle time scale by using attosecond pulses. (c) 2024 Optica Publishing Group

关键词： Attosecond pulses Bragg reflectors Fiber Bragg gratings finite-difference time-domain method Optical filters Transparency

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