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Optical dark solitons in purely cubic-quintic nonlinear lattices

OPTICS EXPRESS 2025年第4期33卷 7205-7217页

作者： Zhu, Xing Fan, Yan Belic, Milivoj R. Mihalache, Dumitru Xiang, Dan Zeng, Liangwei Guangzhou Maritime Univ Sch Arts & Sci Guangzhou 510725 Peoples R China Hamad Bin Khalifa Univ Coll Sci & Engn Doha 23874 Qatar Horia Hulubei Natl Inst Phys & Nucl Engn Bucharest 077125 Romania Guangzhou Maritime Univ Sch Comp Sci Guangzhou 510725 Peoples R China Shenzhen Univ Coll Phys & Optoelect Engn Shenzhen 518060 Peoples R China

In this work, we establish the existence of different dark soliton families in the nonlinear Schr & ouml;dinger equation with purely cubic-quintic nonlinear lattices, including individual dark solitons and soliton clusters with varying numbers of valleys. We explore two types of cubic-quintic lattices, the competing lattices (with the nonlinear terms of opposite signs) and the defocusing lattices (with the nonlinear terms of the same signs). The spacing between the valleys of dark soliton clusters is chosen as an integer multiple of the lattice's period. We find that the stability domains of dark solitons in the defocusing lattices are larger than those in the competing lattices. The stability domains of dark soliton families are obtained by linear stability analysis and confirmed by direct numerical simulations. Both stable and unstable propagations of such families are displayed, highlighting the distinct dynamics introduced by these nonlinear interactions and their impact on the formation and stability of dark solitons. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Bose Einstein condensates Bright solitons Dark solitons finite-difference time-domain method Numerical simulation Wave types

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Individual axis control for industrial robots by posture-variant dynamic compensation and feedback control using the FDTD method

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ADVANCED ROBOTICS 2024年第1期38卷 29-47页

作者： Padron, Juan Tatsuda, Kenta Ohishi, Kiyoshi Yokokura, Yuki Miyazaki, Toshimasa Nagaoka Univ Technol Dept Elect Elect & Informat Engn Nagaoka Niigata Japan

Industrial robots experience posture-dependent inertial variation and interference forces between joints, which in turn generates undesired vibrations due to the inherent elasticity of the reduction gears, making it difficult to control each axis independently. Conventionally, dynamic compensation is used to compensate the robot dynamics and decouple each axis, while state feedback control based on a two-inertia model is used for dealing with the vibrations caused by the elasticity of the reduction gears. However, the control design for this approach usually assumes a fixed moment of inertia, so its performance is compromised when large and fast changes in the robot posture occurs. In this paper, a posture-variant approach that takes into account the posture-dependent inertial variation in real time is proposed to achieve exact dynamic compensation and independent control of each axis regardless of the robot posture. The state equations of the posture-variant two-inertia system model for each robot axis are discretized using the finite-difference time-domain (FDTD) method and adapted on both the dynamic compensation and feedback control parts, allowing to easily redesign the whole control system considering the inertial variation at each control cycle. The effectiveness of the method is confirmed by experimental verification on a 6-axis industrial robot.

关键词： Industrial robot dynamic torque compensation finite-difference time-domain method

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Phase distribution and circular dichroism switchable terahertz chiral metasurface

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OPTICS EXPRESS 2024年第7期32卷 12104-12117页

作者： Xie, Dongliang Chen, Luzhen Luo, Tao Kang, Wenhui Qu, Yi Wang, Tianwu Hainan Normal Univ Haikou 571158 Peoples R China Beijing Univ Posts & Telecommun Beijing 100876 Peoples R China Hainan Normal Univ Coll Phys & Elect Engn Academician Team Innovat Ctr Hainan Prov Key Lab Laser Technol & Optoelect Funct Mat Hainan Haikou 571158 Peoples R China Chinese Acad Sci Guangdong Prov Key Lab Terahertz Quantum Electroma GBA Branch Aerosp Informat Res Inst Guangzhou 510700 Peoples R China

Chiral metasurfaces have many applications in the terahertz (THz) band, but they still lack modulation flexibility and functionality expansion. This paper presents a terahertz chiral metasurface with switchable phase distribution and switchable circular dichroism (CD). The metasurface unit consists of a metallic inner ring embedded in vanadium oxide and a vanadium oxide outer ring, state switching by thermal control of vanadium oxide and a change in the frequency of the incident wave. Based on the switchable phase distribution, we designed a focusing vortex beam generator with adjustable focal lengths through simulation. Based on the switching CD capability, we simulate its mode switching in near -field imaging using numerical simulation, and innovatively propose an optical encryption method. Utilizing the chiral property, we also designed dual -channel switchable holographic imaging in the same frequency band, which combined with the state change of VO2 can realize a total of 4 holograms switching. Our proposed metasurface is expected to provide new ideas for the study of optical encryption and wavefront modulation of dynamics. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： finite-difference time-domain method Fourier transforms Image encryption Multiplex holography Numerical simulation Optical encryption

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Formation and practical implementation of a helical radiation wavefront in the mid-infrared range

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JOURNAL OF OPTICAL TECHNOLOGY 2024年第3期91卷 152-158页

作者： Budarin, Anton S. Skvortsov, Leonid A. Kuznetsov, Evgeniy Silantyev, Ilya, V Miakonkikh, Andrew, V Pavlov, Aleksandr Yu. Galiev, Rinat R. Davlyatshina, Asiya R. Avramchuk, Alexander, V Khabibullin, Rustam A. M F Stelmakh Polyus Res Inst Moscow 117342 Russia Natl Res Univ Moscow Inst Phys & Technol Dolgoprudnyi 141701 Moscow Russia Russian Acad Sci K A Valiev Inst Phys & Technol Moscow 117218 Russia Russian Acad Sci V G Mokerov Inst Ultra High Frequency Semicond Ele Moscow 117105 Russia

Subject of study. The interaction of mid-infrared (IR) light with a metasurface based on silicon scattering elements on a sapphire substrate and its subsequent propagation in the far field were studied. Aim of study. . The aim was the development of the metasurface design, its manufacture, and the formation of a vortex beam with a helicoidal wavefront in the medium-wave IR range, measuring the intensity profile of the converted radiation. method. The finite difference time domain algorithm was used to calculate the characteristics of radiation scattering on the metasurface element. An algorithm of dynamic mode decomposition was applied to analyze the spatial spectrum of radiation obtained as a result of the passage of a plane wave through a plate with the selected design. For the manufacture of the metasurface, the following methods were used: plasma chemical vapor deposition, electron beam lithography, thermal evaporation, atomic layer deposition, reactive ion etching in inductively coupled plasma, and anisotropic cryogenic etching. Main results. A metasurface design was developed for the formation of a laser beam with a helicoidal wavefront in the medium-wave IR range. The parameters of the silicon scattering elements on a sapphire substrate were determined using numerical modeling. The efficiency and characteristics of the spatial spectrum of the constructed metasurface were investigated. It was established that the energy fraction of the secondary harmonics decreased with the distance along the beam propagation. As a result of this work, a vortex beam with an annular intensity distribution in the cross-section was experimentally obtained in the mid-IR range of the spectrum. Practical significance. The metasurface created in the course of this work, including the process of its design and manufacturing technology, may be of potential interest for use in free space optical communications based on mid-infrared quantum cascade lasers with multiplexing orthogonal spa

关键词： Atomic layer deposition Chemical vapor deposition Electron beam lithography finite-difference time-domain method Free space optics Laser beams

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Light scattering patterns of pendant drops. II. Simulation method and mechanism analysis

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OPTICS EXPRESS 2025年第6期33卷 14483-14500页

作者： Duan, Qingwei Li, Qinyao Han, Xiang'e Ren, Kuan fang Xidian Univ Sch Phys Xian 710071 Peoples R China

The study of light scattering by particles promotes our understanding of natural phenomena and drives advancements in optical technologies. However, the existing methods and models face challenges in addressing the light scattering by nonspherical particles of size much larger than light wavelength, such as pendant drops found in nature (e.g., on leaves) or laboratories (e.g., in capillary tubes). The experimental results presented in the companion paper revealed that pendant drops exhibit unique and complex light scattering patterns distinct from those of spherical drops. Understanding how pendant drops scatter light remains an unresolved scientific challenge. In this paper, the simulation for the light scattering patterns of real pendant drops is achieved by extending the vectorial complex ray model we developed earlier for three-dimensional scattering. The simulated results are carefully examined and agree well with the experimental findings. In addition, the mechanisms underlying these complex light scattering patterns are also investigated, offering novel insights into how scattering pattern evolves with drop-shape deformation. Beyond the theoretical importance, this work permits interrelation of the light scattering patterns with the drop's shape, size, and refractive index/temperature, thus holding practical potential, particularly in developing relevant optical measurement techniques. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： finite-difference time-domain method Light transmission Measurement and metrology Phase shift Refractive index Total internal reflection

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Compact and low-loss on-chip silicon crossing based on subwavelength grating slot waveguides

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OPTICS EXPRESS 2025年第3期33卷 4902-4914页

作者： Zhu, Jiabao Yu, Qianli Jin, Yuelong Huang, Chongjia Guo, Zhenzhao Hao, Peng Xiao, Jinbiao Wu, Shengbao Hebei Univ Coll Phys Sci & Technol Photon Informat Innovat Ctr Hebei Prov Ctr Opt Sensing Innovat Baoding 071002 Peoples R China Fuzhou Univ Sch Phys & Informat Engn Inst Micro Nano Devices & Solar Cells Fuzhou 350108 Peoples R China Southeast Univ Sch Elect Sci & Engn Natl Res Ctr Opt Sensing Commun Integrated Network Nanjing 210096 Peoples R China

We propose and experimentally demonstrate a compact crossing based on a sub- wavelength grating slot waveguide (SWG-SW), leveraging the anisotropic properties of two orthogonal SWG-SWs to suppress diffraction effects in the crossing region for the input TE polarization mode. The design utilizes the unique mode characteristics of the SWG-SW, enabling low-loss mode transitions through the crossing with a simple and compact hollow structure design at its center. By integrating the above crossing with a well-designed slot-to-SWG-SW mode converter, a crossing for the widely used slot waveguides is achieved, with a footprint of similar to 18x18 mu m2. Simulation results show that the device achieves an insertion loss (IL) of <0.35 dB and a crosstalk (CT) of <-40 dB over a bandwidth range of 1500-1600 nm. Experimental results confirm that within the wavelength range of 1500-1580 nm, the IL is approximately 0.4 dB, and CT values are below-28 dB. To further improve the device performance, additional side grating arrays are incorporated into the design. The optimized structure with side gratings achieves IL of <0.13 dB and CT values around-35 dB. Experimental measurements of the device with side gratings demonstrate a stable IL of approximately 0.1 dB and CT values consistently below-35 dB, marking a significant improvement over the original design. To the best of our knowledge, this is the first experimentally verified crossing for slot waveguides. Further analysis indicates that the device exhibits an exceptionally broad bandwidth of approximately 576 nm (1257 nm to 1833nm) with IL < 1 dB and CT < -30 dB. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Effective refractive index finite-difference time-domain method Mode division multiplexing Slot waveguides Subwavelength gratings Waveguide gratings

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Edge mode resonance in the dark state by a finite beam

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OPTICS LETTERS 2025年第1期50卷 81-84页

作者： Ko, Y. H. Magnusson, R. Kongju Natl Univ Div Elect Elect & Control Engn Cheonan 31080 South Korea Univ Texas Arlington Dept Elect Engn Arlington TX 76019 USA

We treat edge-mode resonance that may exist at boundaries of transversely finite beams illuminating a photonic lattice. The lattice is in the dark state signifying a perfect bound state in the continuum (BIC). The dark state is non-radiative in symmetric systems because lateral waves cannot couple to the lattice due to destructive interference between counter-propagating waves. However, if the incident beam is spatially finite, the balance is broken at beam boundaries, and edge modes are induced supporting local electromagnetic fields. Numerical studies illustrate key properties including coupled-wave near fields, spectral signatures at resonance, and local field profiles for representative beam geometries. The work contributes fundamentally to the understanding of resonant metasurfaces that are of high scientific interest worldwide. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： Destructive interference Diffraction gratings finite-difference time-domain method Gaussian beams Metasurfaces Waveguide modes

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Design of ultrahigh-Q silicon microring resonators based on free-form curves

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OPTICS EXPRESS 2024年第6期32卷 9553-9561页

作者： Han, Zhe Qi, Yan Wang, Yu Wang, Yanwei Fan, Yuanyuan Yan, Boxia Zhou, Mi Wang, Qian Inst Microelect Chinese Acad Sci Beijing 100029 Peoples R China Univ Chinese Acad Sci Sch Integrated Circuits Beijing 101408 Peoples R China

A design method for ultrahigh -Q microring resonators (MRRs) based on Bezier free -form curves was proposed and demonstrated. An MRR consisting of a specially designed 180 degrees waveguide bend, a directional coupler, and two low -loss multi -mode strip waveguides was designed. The free -form curves were used to increase the degree of freedom in the design, shaping the waveguide bend with a gradient width and curvature. This design effectively reduced the propagation loss caused by the roughness of waveguide sidewalls and the mode mismatch loss caused by the excitation of high order modes. The small effective radius of only 20 mu m enabled the MRR to have a large free spectral range (FSR) and a compact and flexible structure. The MRR was manufactured using a standard process provided by foundry and measured to have an ultrahigh loaded Q factor of 1.86 x 106 and a FSR of about 1 nm.

关键词： finite-difference time-domain method Optical resonators Q factor Ring resonators Waveguide design Waveguide modes

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Design of a switchable triple-waveguide-based TE-converted polarization beam splitter based on lithium niobate

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APPLIED OPTICS 2024年第29期63卷 7741-7746页

作者： Xia, Jun Fei, Yedeng Ni, Yi Jiangnan Univ Sch IoT Engn Dept Elect Engn Wuxi 214122 Peoples R China

The lithium-niobate-on-insulator (LNOI) platform has been the new force to drive the developments of integrated photonics, where efficient polarization management and mode conversion are the fundamental issues to be solved. In this work, we proposed a switchable TE-converted polarization beam splitter (PBS) based on optical phase change material (PCM) and a triple-waveguide in simulation. To optimize and analyze the proposed design, the 3D finite difference time domain (3D-FDTD) method is applied in this work. The simulated results indicate that when PCM is in the amorphous state, the device can effectively separate the TM and TE modes, achieving a low insertion loss (<0.5 dB) for both modes at 1550 nm. While the PCM is in the crystalline state, the proposed device can realize the efficient conversion from the input TE0 0 mode to output TE1 1 mode, which obtains a mode conversion efficiency of 99.5%, crosstalk of - 26 dB, and insertion loss of 0.5 dB at 1550 nm. We hope such a device can make compact integration and capacity improvement for the integrated photonics in LNOI. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： Beam splitters finite-difference time-domain method Integrated photonics Lithium niobate Mode conversion Mode division multiplexing

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Plasmonic lithography fast imaging model based on least square fitting for periodic patterns

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APPLIED OPTICS 2024年第32期63卷 8454-8464页

作者： Ding, Huwen Dong, Lisong Li, Ziqi He, Jianfang Ma, Le Rui, Dinghai Wei, Yayi Chinese Acad Sci Inst Microelect EDA Ctr Beijing 100029 Peoples R China Univ Chinese Acad Sci Sch Integrated Circuits Beijing 101408 Peoples R China Guangdong Greater Bay Area Appl Res Inst Integrate Guangzhou 510700 Peoples R China

As a new and alternative lithography technology, plasmonic lithography can break through the diffraction limit of traditional lithography by exciting the surface plasmon polaritons to make the evanescent wave at the mask participate in imaging. Plasmonic lithography is capable of fabricating deep subwavelength structures for nanophotonics, metasurfaces, and various other applications, and it is expected to be applied to integrated circuit manufacturing. The photoresist aerial image distribution of different mask patterns can be calculated by establishing an imaging model, which is the basis for understanding and further optimizing imaging. Based on the idea of machine learning and least square fitting, a fast imaging model for plasmonic lithography is established, including a one-dimensional line/space periodic pattern and a two-dimensional square hole pattern, which can be used as a supplement to the previous model developed by Ding et al. [Opt. Express 31, 192 (2023)]. Compared with the rigorous numerical method, the fast imaging model can greatly improve the calculation speed with high accuracy. Under the same hardware conditions, the calculation speed of the 1D fast imaging model is improved by two orders of magnitude, and the 2D fast imaging model is improved by about 25 times, which creates conditions for the development of computational lithography technology. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： Deep learning Diffraction limit finite element method finite-difference time-domain method Rigorous coupled wave analysis Subwavelength structures

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