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Low loss and ultra-broadband design of an integrated 3 dB power splitter centered at 2 μm

APPLIED OPTICS 2024年第3期63卷 662-667页

作者： Liu, Zhiming Dong, Yue Xu, Yin Zhang, Bo Ni, Yi Jiangnan Univ Sch IoT Engn Dept Elect Engn Wuxi 214122 Peoples R China Soochow Univ Sch Optoelect Sci & Engn Suzhou 215006 Peoples R China Soochow Univ Collaborat Innovat Ctr Suzhou Nano Sci & Technol Suzhou 215006 Peoples R China Soochow Univ Key Lab Adv Opt Mfg Technol Jiangsu Prov Suzhou 215006 Peoples R China Soochow Univ Key Lab Modern Opt Technol Educ Minist China Suzhou 215006 Peoples R China

Because chemical gas is sensitive to absorption in the 2 gm band, and 2 gm matches the absorption band of the remote sensing material, many remote sensors and optical sensors are designed to operate in the 2 gm wavelength region. In this paper, we designed an integrated 3 dB power splitter centered at 2 gm. The study of this device is built on a silicon -on -insulator (SOI) platform. We introduced a subwavelength grating (SWG) to improve the performance of the device. We used the three-dimensional finite -difference time -domain (3D FDTD) method to analyze the effect of the structure on the power splitter. The insertion loss (IL) of the fundamental TE mode is only 0.04 dB at 2 gm and its bandwidth of IL <0.45 dB is 940 nm (1570-2510 nm). It is suitable for multidomain and all -band photonic integrated circuits at 2 gm. (c) 2024 Optica Publishing Group

关键词： Fiber optic communications finite-difference time-domain method Optical directional couplers Remote sensing Semiconductor lasers Waveguide gratings

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Investigations on Optical Absorption and the Pyro-phototronic Effect with Selectively Patterned Black Silicon for Advanced Photodetection

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ACS APPLIED MATERIALS & INTERFACES 2024年第18期16卷 23960-23972页

作者： Nataraj, Charumathi Mohanta, Kallol Badhirappan, Geetha Priyadarshini PSG Inst Adv Studies Dept Phys Nanostruct Surfaces & Thin Films Lab Coimbatore 641004 Tamil Nadu India PSG Inst Adv Studies Dept Phys Hybrid Elect Lab Coimbatore 641004 Tamil Nadu India

A novel property existing in the stain-etching technique that eliminates the need for expensive etchant masks in the texturization process of silicon wafers was identified. Through the combination of grayscale lithography and stain-etching methodologies, selective patterning of silicon with AR-P 3510 T, a positive-photoresist mask, was carried out. The etch area ratio was varied in nine different patterns of various feature sizes ranging from 400 to 1500 mu m. The optical characteristics of the patterned substrates were determined from diffuse reflectance spectroscopy analysis, and the results were supported with finite-difference time-domain simulations. Complimenting the improvement in optical properties, the electrical losses in microwell-patterned photodetector devices have been reduced with an electro-optic optimum value of the surface enhancement factor, gamma. The photodetecting efficiency of a selectively patterned microwell photodetector device exceeded the planar and black silicon photodetector devices with a considerable improvement in the pyro-phototronic effect. This work suggests an alternative for black silicon optoelectronic devices providing a new route to fabricate selectively patterned substrates with an achieved detectivity 16- and 20-fold higher than black and planar silicon photodetector devices, respectively.

关键词： grayscale lithography stain etching blacksilicon finite-difference time-domain method self-poweredphotodetector pyro-phototronic devices

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Eigendecomposition-free inverse design of meta-optics devices

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OPTICS EXPRESS 2024年第8期32卷 13986-13997页

作者： Huang, Yi Zhu, Ziwei Dong, Yunxi Tang, Hong Zheng, Bowen Podolskiy, Viktor A. Zhang, Hualiang Univ Massachusetts Dept Elect & Comp Engn Lowell MA 01854 USA Columbia Univ Dept Comp Sci New York NY 10027 USA Univ Massachusetts Dept Phys & Appl Phys Lowell MA 01854 USA

The inverse design of meta-optics has received much attention in recent years. In this paper, we propose a GPU-friendly inverse design framework based on improved eigendecomposition-free rigorous diffraction interface theory, which offers up to 16.2 x speedup over the traditional inverse design based on rigorous coupled-wave analysis. We further improve the framework's flexibility by introducing a hybrid parameterization combining neural-implicit and traditional shape optimization. We demonstrate the effectiveness of our framework through intricate tasks, including the inverse design of reconfigurable free-form meta -atoms.

关键词： Diffraction theory finite-difference time-domain method Inverse design Machine learning Neural networks Refractive index

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Realization of a low loss thin-film lithium niobate edge coupler based on a staircase structure

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OPTICS EXPRESS 2024年第26期32卷 46712-46725页

作者： Wang, Mengke Yao, Hao Deng, Jiayao Sun, Yuzhe Hu, Zhefeng Chen, Kaixin Univ Elect Sci & Technol China Sch Optoelect Sci & Engn Chengdu 610054 Peoples R China

Thin film lithium niobate (TFLN) has been proven to be a promising platform to realize high-performance integrated photonic devices. However, due to the large mode field mismatch between fibers and TFLN waveguides, low-loss edge couplers are necessary for practical TFLN devices. In this paper, we experimentally demonstrated a low-loss TFLN edge coupler based on our previously proposed staircase structure. The edge coupler has a minimum feature size of 3.0 mu m and exhibits a high tolerance to lithographic overlay misalignment, ensuring its feasibility for fabrication using a contact aligner. Special etching mask patterns and etching processes were developed to efficiently fabricate the desired staircase structure. Test results show that a fiber-to-chip coupling loss of 1.5 dB/facet for TE polarized light is achieved at 1560 nm wavelength, and the polarization-dependent loss (PDL) is lower than 0.5 dB. To the best of our knowledge, it is the first low-loss TFLN edge coupler fabricated with a contact aligner, which paves the way for low-cost fabrication of practical TFLN devices. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Fiber waveguides finite-difference time-domain method Grating coupler Lithium niobate Photonic devices Thin films

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Incoherent phenomena in anisotropic periodic structures: from modeling to experimental demonstration

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OPTICS EXPRESS 2024年第16期32卷 27822-27834页

作者： Postava, K. Ciompa, P. Kohut, T. Drong, M. Jesko, R. Jaffres, H. Fordos, T. Kotacka, L. Drouhin, H-J VSB Tech Univ Ostrava Fac Mat Sci & Technol 17 listopadu2172-15 Ostrava 70800 Czech Republic VSB Tech Univ Ostrava Nanotechnol Ctr CEET 17 listopadu2172-15 Ostrava 70800 Czech Republic Thales & Univ Paris Saclay CNRS Lab Albert Fert 1 Ave A Fresnel F-91767 Palaiseau France Inst Polytech Paris Ecole Polytech CNRS LSICEADRFIRAMIS F-91128 Palaiseau France

The periodic structures are widely studied in numerous optical applications and there is a number of good tools for numerical modeling of such a structures (for example rigorous coupled-wave analysis, finite-difference time-domain, finite element method etc.). However, when it comes to the modeling of incoherent effects in many cases of practical interest, the current methods are not rigorous enough or depend on computationally demanding averaging of coherent response. In this paper, we present a novel approach to modeling of incoherent effects in structures with lateral periodicity based on scattering matrix formalism, as a way to describe optical response of a structure, and on application of incoherent wave summation in the form of infinite geometric series and generalized Mueller matrix calculus. This method can be combined with any of the existing coherent methods of modeling periodic structures and it offers significantly faster computational performance than partially coherent/incoherent methods based on averaging. It is compared with other methods for modeling of incoherent effects and also with experimental spectroscopic data. This method is then used to explain phenomena emerging from the complex interaction between diffraction grating and thick substrate. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Diffraction gratings finite element method finite-difference time-domain method Matrix methods Mueller matrices Vertical cavity surface emitting lasers

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Analysis on scattering and inner near-field characteristics of a uniaxial anisotropic sphere by an off-axis high-order Bessel (vortex) beam

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION 2024年第11期41卷 2054-2064页

作者： Li, Zheng Jun Yang, Kai Qu, Tan Bai, Jing Shang, Qing Chao Xidian Univ Sch Phys Xian 710071 Shaanxi Peoples R China Xidian Univ Collaborat Innovat Ctr Informat Sensing & Understa Xian 710071 Shaanxi Peoples R China Xidian Univ Sch Elect Engn Xian 710071 Shaanxi Peoples R China Xian Univ Posts & Telecommun Sch Elect Engn Xian 710121 Shaanxi Peoples R China

Based on the generalized Lorenz-Mie theory (GLMT) and the Fourier transform method, a theoretical approach is introduced to study the scattering of a uniaxial anisotropic sphere illuminated by an off-axis high-order Bessel (vortex) beam (HOBVB). According to the orthogonality of the associated Legendre function and exponential function, a concise expression of the expansion coefficients of the off-axis HOBVB in terms of the spherical vector wave functions (SVWFs) is derived that can effectively reconstruct the HOBVB with all conical angles. The differences of scattering characteristics of a uniaxial anisotropic sphere illuminated by an on-axis and off-axis HOBVB and a plane wave are exhibited. Influences of the topological charge, conical angle, particle size, and off-axis distance on the angle distributions of the radar cross-section (RCS), scattering and extinction efficiencies, and asymmetric factor are analyzed in detail. The unique internal and near-field distributions of a uniaxial anisotropic spherical particle illuminated by an on-axis and off-axis HOBVB are demonstrated. The results provide insights into the scattering and Bessel beam-matter interactions and may find important applications in optical propagation and optical micromanipulation, microwave engineering, target shielding, and near-field measurement. (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 scattering finite-difference time-domain method Fourier transforms Mie scattering Scattering media Stimulated emission depletion microscopy

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Simulation of a SiN 2 x 2 adiabatic 3-dB coupler for 800-nm to 1000-nm wavelength range

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APPLIED OPTICS 2024年第23期63卷 6240-6243页

作者： Blanco, Miguel Angel Nava Avila, Gerardo Antonio Castaivon Tecnol Monterrey Sch Engn & Sci Ave Eugenio Garza Sada 2501 Monterrey 64849 Mexico

We conducted numerical simulations on a 2 x 2 adiabatic 3-dB coupler tailored for the 800-nm to 1000-nm range, operating on a silicon-nitride (SiN) platform. Through the finite difference time domain method, we achieved a power splitting ratio close to 3 dB with a tight tolerance of +/- 0.27 dB and an insertion loss below 0.19 dB across the wavelength range of 800 nm to 1000 nm. Additionally, we simulated a 2 x 2 switch utilizing two 2 x 2 adiabatic 3-dB couplers, revealing a theoretical extinction loss of approximately - 14 dB, particularly prominent around 900 nm. (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： Biosensors finite-difference time-domain method Numerical simulation Optical directional couplers Photonic devices Silicon photonics

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Pearcey Talbot-like plasmon: a plasmonic bottle array generation scheme

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OPTICS LETTERS 2024年第16期49卷 4673-4676页

作者： Ruan, Zhang Zhang, Junxi Chen, Yanru Feng, Zien Li, Yanghong Wu, Hailong Wen, Shibin Wang, Guanghui Deng, Dongmei South China Normal Univ Sch Informat & Optoelect Sci & Engn Guangdong Prov Key Lab Nanophoton Funct Mat & Devi Guangdong Basic Res Ctr Excellencefor Struct & Fun Guangzhou 510006 Peoples R China

In this Letter, a surface wave, the Pearcey Talbot-like plasmon, which has the properties of self-imaging and multiple autofocusing, is presented as a novel, to the best of our knowledge, plasmonic bottle array generation scheme. With originality, the overall structure and the partial intensity of the plasmonic bottle array can be adjusted through the initial input, and modifying the Pearcey function enables the plasmonic bottle array to exhibit self-bending characteristics, which makes particle capture and manipulation easier and more flexible. A scheme to generate the plasmon is proposed, and we prove it by the finite-difference time-domain numerical simulations. (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： Airy beams finite-difference time-domain method Numerical simulation Optical computing Spatial light modulators Surface waves

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Experimental verification of terahertz surface plasmon resonance using the Dirac electron system Bi2SexTe(3-x)

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OPTICAL MATERIALS EXPRESS 2025年第4期15卷 788-797页

作者： Sugimoto, Hinano Nishimura, Kana Takahashi, Mayuko Okano, Ryo Kitamura, Miho Sugawara, Katsuaki Souma, Seigo Sato, Takafumi Kobayashi, Masaki Tabata, Hitoshi Univ Tokyo Grad Sch Engn Dept Bioengn Tokyo 1138656 Japan Univ Tokyo Grad Sch Engn Dept Elect Engn & Informat Syst Tokyo 1138656 Japan High Energy Accelerator Res Org KEK Inst Mat Struct Sci Tsukuba 3050801 Japan Tohoku Univ Dept Phys Sendai 9808578 Japan Tohoku Univ Adv Inst Mat Res WPI AIMR Sendai 9808577 Japan

Although the surface plasmon resonance excited by a Dirac electron system has gained considerable attention in the terahertz region, studies have been limited to grating-coupling surface plasmon resonance (GC-SPR) in Bi2Se3. In this study, we experimentally demonstrated terahertz prism-coupled surface plasmon resonance (PC-SPR) and GC-SPR in topological insulator systems, viz. Bi2Se3 (GC-SPR), Bi2Se2Te (GC-SPR), and Bi2Se3 (PC-SPR). The physical properties measured using angle-resolved photoemission spectroscopy indicate that the presence of surface state near the Fermi level is insufficient for SPR excitation;linearity of the Dirac cone is essential for SPR excitation in the THz range. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Bismuth finite-difference time-domain method Surface plasmon resonance Terahertz time-domain spectroscopy Thin films Total internal reflection

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Design terahertz polarizers and vector polarized vortex terahertz wave generators based on the effective dielectric constant of metal gratings

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OPTICS EXPRESS 2024年第19期32卷 33357-33368页

作者： Cai, Mengqiang Wu, Zhixu Yan, Weichao Lei, Jiangtao Xia, Yong Tang, Rongxin Nanchang Univ Inst Space Sci & Technol Nanchang 330031 Peoples R China Nanchang Univ Sch Informat Engn Nanchang 330031 Peoples R China

Polarization and phase devices for terahertz waves have important applications in terahertz detection, imaging, communication, etc. Spatially variable metal gratings can be used for broad-spectrum, miniaturized, and low-cost terahertz polarization and phase modulation devices. Based on the effective dielectric constant and the theory of light propagation in multilayer media, we obtain the relationship between the transmittance and extinction ratio and the parameters such as the duty cycle of the metal grating, the frequency of the incident terahertz wave, the angle of incidence, the thickness of the metal grating, the refractive index of the substrate, and the thickness of the substrate. We propose a method of designing a spatially variable metal grating located on a transparent substrate. The designed spatially variable metal grating is also used to modulate the terahertz spatial polarization and phase to generate terahertz optical fields whose polarization and phase change simultaneously in space, such as azimuthally vector vortex terahertz optical fields, radially vector vortex terahertz optical fields, and so on. This will have important applications in terahertz time-domain spectroscopic detection, terahertz terahertz communication, and so on.

关键词： finite element method finite-difference time-domain method Metal gratings Optical fields Phase modulation Terahertz detectors

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