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Low-loss and low-cross talk polarization-insensitive multimode silicon waveguide crossing

OPTICS LETTERS 2024年第17期49卷 4930-4933页

作者： Chen, Yun Wang, Pengjun Fu, Qiang Sun, Yuhan Zou, Yi Dai, Shixun Chen, Weiwei Chen, Haoqi Li, Jun Dai, Tingge Yang, Jianyi Ningbo Univ Fac Elect Engn & Comp Sci Ningbo 315211 Peoples R China Wenzhou Univ Coll Elect & Elect Engn Wenzhou 325035 Peoples R China Ningbo Univ Coll Sci & Technol Ningbo 315300 Peoples R China ShanghaiTech Univ Sch Informat Sci & Technol Shanghai 201210 Peoples R China Ningbo Univ Res Inst Adv Technol Lab Infrared Mat & Devices Ningbo 315211 Peoples R China Zhejiang Univ Dept Informat Sci & Elect Engn Hangzhou 310027 Peoples R China

A polarization-insensitive multimode silicon waveguide crossing is investigated and experimentally characterized in this Letter. By employing the particle swarm optimization (PSO) algorithm and finite difference time domain (FDTD) method, the lengths and widths of the waveguides in the proposed device are optimized for attaining wide bandwidth, small insertion loss (IL), low cross talk (CT), and compact size. Measurement results reveal that the footprint of the presented device is 11.92 mu m x 11.92 mu m. From 1520 to 1600 nm, the measured insertion loss and cross talk are smaller than 0.67 dB and -28.6 dB in the case of the TE0 mode, lower than 0.65 dB and -28.7 dB in the case of the TE1 mode, less than 0.48 dB and -36.3 dB in the case of the TM0 mode, and lower than 0.62 dB and -28 dB in the case of the TM1 similar technologies, are reserved.

关键词： Chemical vapor deposition Crosstalk Electron beam lithography finite-difference time-domain method Polarization division multiplexing Silicon

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Active dual quasi-BICs in a dielectric metasurface with VO2 for slow light and optical modulation

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OPTICS LETTERS 2024年第18期49卷 5147-5150页

作者： Zhong, Ying Guo, Tian Wang, Qianqian Du, Wei Tang, Chaojun Yan, Zhendong Nanjing Forestry Univ Coll Sci Nanjing 210037 Peoples R China Yangzhou Univ Coll Phys Sci & Technol Yangzhou 225002 Peoples R China Zhejiang Univ Technol Dept Appl Phys Hangzhou 310023 Peoples R China

We investigate the temperature tunable dual quasi-bound states in the continuum (qBICs) in a silicon/vanadium dioxide (Si/VO2) hybrid metasurface with Q-factor being as large as 9.3 x 10(6) and 2.8 x 10(7) by breaking the in-plane C-2 symmetry. The far-field scattering of multipoles and near-field distributions confirm that the toroidal dipole and magnetic quadrupole dominate the dual qBICs resonance. The high performance of slow light with ultralarge group index exceeding 5.6 x 10(5) and the inverse quadratic law between the group index and asymmetric parameter are achieved. By temperature tuning of the VO2 thin film at the sub-10 K scale, a modulation depth of 90% and the ON/OFF ratio exceeding 12.8 dB are obtained. The proposed temperature tunable dual qBICs have potential applications in the fields of tunable slow light, temperature switches, and sensors. (C) 2024 Optica Publishing Group. All rights, including for text and datamining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： Fano resonance finite-difference time-domain method Laser induced damage thresholds Near infrared Slow light Thin films

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Enhanced light extraction efficiency for the inclined-sidewall-shaped AlGaN-based DUV LED by using an omni-directional reflector with a thin hybrid dielectric layer

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OPTICS LETTERS 2024年第15期49卷 4405-4408页

作者： Liu, Zhaoqiang Dong, Yifei Wang, Linhao Jia, Tong Chu, Chunshuang Tian, Kangkai Zhang, Yonghui Zhang, Zi-Hui Sun, Xiaowei Hebei Univ Technol Sch Elect & Informat Engn State Key Lab Reliabil & Intelligence Elect Equip Key Lab Elect Mat & Devices Tianjin 5340 Xiping Rd Tianjin 300401 Peoples R China Guangdong Univ Technol Sch Integrated Circuits 100 Waihuan West Rd Guangzhou 510006 Guangdong Peoples R China Southern Univ Sci & Technol Inst Nanosci & Applicat Shenzhen 518055 Peoples R China Southern Univ Sci & Technol Dept Elect & Elect Engn Shenzhen 518055 Peoples R China

In this Letter, an omni-directional reflector (ODR) with a thin hybrid dielectric layer (hybrid-ODR) is proposed to enhance the light extraction efficiency (LEE) for inclined-sidewall-shaped AlGaN-based deep ultraviolet light-emitting diode (DUV LED) by inserting a thin diamond with high refraction index into a conventional Al/Al2O3- 2 O 3- based ODR. The three-dimensional finite-difference time- domain (3D FDTD) simulation results show that the LEE of TM-polarized light for the DUV LED with hybrid-ODR is enhanced by 18.5% compared with Al/Al2O3-based 2 O 3-based ODR. It is because the diamond can transform the evanescent wave in Al2O3 2 O 3 into the propagating light wave in diamond, thereby preventing effective excitation of the surface plasmon polariton (SPP) on the surface of the metal Al. Moreover, the Brewster's angle effect causes the TM-polarized light in diamond to propagate effectively into AlGaN. Furthermore, decreasing the total thickness of the dielectric layer also improves the scattering effect of the inclined sidewall. However, the utilization of hybrid-ODR results in a slight reduction in the LEE for transverse electric (TE) polarized light because the light is confined to the diamond layer and eventually absorbed by the metal Al. (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： Diamond Evanescent waves finite-difference time-domain method Light extraction Refractive index Ultraviolet light emitting diodes

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Tunable giant Goos-Hänchen shift in Au-ReS2-graphene heterostructure

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OPTICS LETTERS 2024年第12期49卷 3484-3487页

作者： Yan, Yunpeng Zha, Mingjie Liu, Junxi Tu, Jiaxing Liu, Zhibo Nankai Univ Minist Educ TEDA Inst Appl Phys Key Lab Weak Light Nonlinear Photon Tianjin 300457 Peoples R China Nankai Univ Sch Phys Tianjin 300457 Peoples R China Shanxi Univ Collaborat Innovat Ctr Extreme Opt Taiyuan 030006 Shanxi Peoples R China

Enhancing and flexibly controlling the Goos-H & auml;nchen (GH) shift directly is a significant challenge. Here, we report a tunable giant GH shift in a Au-ReS2-graphene heterostructure. The GH shift of this heterostructure demonstrates strong anisotropy and a unique "sign inversion" feature as the graphene reaches a specific thickness. Flexible control and enhancement of the GH shift to the centimeter scale can be achieved by simply rotating the crystallization direction of the heterostructure. Utilizing this feature, we designed an anisotropic refractive index sensor with a high sensitivity of 1.31 x 108 mu m/RIU. This marks an order of magnitude improvement over previous research and introduces a rotation-dependent sensitivity adjustment feature. The tunable giant GH shift provides a promising approach for future designs of optical sensing and modulation devices. nologies, are reserved.

关键词： finite-difference time-domain method Modulation Optical sensing Phase shift Reflection coefficient Refractive index

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Transient cavity-cavity strong coupling at terahertz frequency on LiNbO3 chips

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OPTICS EXPRESS 2024年第7期32卷 12763-12773页

作者： Ma, Ruobin Lu, Yao Qi, Jiwei Xiong, Hao Xu, Xitan Huang, Yibo Wu, Qiang Xu, Jingjun Nankai Univ TEDA Appl Phys Inst Minist Educ Key Lab Weak Light Nonlinear Photon Tianjin 300457 Peoples R China Nankai Univ Sch Phys Tianjin 300457 Peoples R China Nankai Univ Shenzhen Res Inst Shenzhen 518083 Guangdong Peoples R China

Terahertz (THz) microcavities have garnered considerable attention for their ability to localize and confine THz waves, allowing for strong coupling to remarkably enhance the light -matter interaction. These properties hold great promise for advancing THz science and technology, particularly for high-speed integrated THz chips where transient interaction between THz waves and matter is critical. However, experimental study of these transient time -domain processes requires high temporal and spatial resolution since these processes, such as THz strong coupling, occur in several picoseconds and microns. Thus, most literature studies rarely cover temporal and spatial processes at the same time. In this work, we thoroughly investigate the transient cavity -cavity strong -coupling phenomena at THz frequency and find a Rabi-like oscillation in the microcavities, manifested by direct observation of a periodic energy exchange process via a phase -contrast time -resolved imaging system. Our explanation, based on the JaynesCummings model, provides theoretical insight into this transient strong -coupling process. This work provides an opportunity to deeply understand the transient strong -coupling process between THz microcavities, which sheds light on the potential of THz microcavities for high-speed THz sensor and THz chip design. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： finite-difference time-domain method Imaging systems Lithium niobate waveguides Nonlinear frequency conversion Spatial resolution Stimulated Raman scattering

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

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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 372-372页

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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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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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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