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

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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Band-pass and Band-stop Plasmonic Filters Based on Wilkinson Power Divider Structure

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PLASMONICS 2024年第2期19卷 733-742页

作者： Korani, Nastaran Abbasi, Abdollah Danaie, Mohammad Semnan Univ Fac Elect & Comp Engn Semnan Iran

In this paper, plasmonic band-pass and band-stop filters employing ring resonators within the framework of the Wilkinson power divider structure are presented. It is shown that the resonance wavelengths can be effectively manipulated by adjusting the inner and outer radii of the ring resonators. Furthermore, by precisely controlling the gap size between the ring resonators and the waveguides, we have successfully designed efficient band-pass and band-stop filters. This study encompasses a thorough investigation into the propagating modes of surface plasmon polaritons (SPPs) within these filters. The transmission characteristics of the proposed filters are meticulously examined and analyzed using the finite-difference time-domain (FDTD) method. The proposed plasmonic filters exhibit a compact size, thus holding promising potential for integrated optics applications. Moreover, they possess the inherent capability to eliminate higher-order modes, enhancing their utility in practical implementations which require a single mode response. The proposed design has the possibility of manipulating the filtering wavelength by adjusting the stubs and ring parameters. This capability opens up exciting avenues for tuning the filter's response and tailoring it to the desired application requirements.

关键词： Surface plasmon polaritons bandpass filter-bandstop filter finite-difference time-domain method

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Reducing shape errors in the discrete dipole effective media

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OPTICS EXPRESS 2023年第26期31卷 43401-43415页

作者： Zhu, Yingying Liu, Chao Yurkin, Maxim a. Nanjing Univ Informat Sci & Technol Collaborat Innovat Ctr Forecast & Evaluat Meteorol Nanjing 210044 Peoples R China Nanjing Univ Informat Sci & Technol Sch Atmospher Phys Aerosol Cloud Precipitat Key Lab China Meteorol Adm Nanjing 210044 Peoples R China Ozyegin Univ Ctr Energy Environm & Econ TR-34794 Istanbul Turkiye Novosibirsk State Univ Novosibirsk 630090 Russia

The discrete dipole approximation (DDA) simulates optical properties of particles with any given shape based on the volume discretization. These calculations cost a large amount of time and memory to achieve high accuracy, especially for particles with large sizes and complex geometric structures, such as mixed black-carbon aerosol particles. We systematically study the smoothing of the DDA discretization using the effective medium approximation (EMA) for boundary dipoles. This approach is tested for optical simulations of spheres and coated black-carbon (BC) aggregates, using the Lorenz-Mie and multiple-sphere T-Matrix as references. For spheres, EMA significantly improves the DDA accuracy of integral scattering quantities (up to 60 times), when the dipole size is only several times smaller than the sphere diameter. In these cases, the application of the EMA is often comparable to halving the dipole size in the original DDA, thus reducing the simulation time by about an order of magnitude for the same accuracy. For a coated BC model based on transmission electron microscope observations, the EMA (specifically, the Maxwell Garnett variant) significantly improves the accuracy when the dipole size is larger than 1/4 of the monomer diameter. For instance, the relative error of extinction efficiency is reduced from 4.7% to 0.3% when the dipole size equals that of the spherical monomer. Moreover, the EMA-DDA achieves the accuracy of 1% for extinction, absorption, and scattering efficiencies using three times larger dipoles than that with the original DDA, corresponding to about 30 times faster simulations.

关键词： Effective medium theory Effective refractive index finite-difference time-domain method Optical properties Optical testing Refractive index

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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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High-sensitivity miniaturized spectrometers using photonic crystal slab filters

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OPTICS LETTERS 2024年第19期49卷 5483-5486页

作者： Wu, Jingjun Tang, Feng Wei, Cong Chen, Fujia Chen, Peng Liu, Shuangli Li, Ang Pan, Shilong Ye, Xin Ma, Jun Wang, Pan Chen, Hongsheng Yang, Yihao Zhu, Rihong Zheng, Wanguo Yang, Zongyin Nanjing Univ Sci & Technol Sch Elect & Opt Engn Nanjing 210094 Peoples R China Mianyang Scitech City Inst Photon Technol Mianyang 621025 Peoples R China Zhejiang Univ Coll Informat Sci & Elect Engn Hangzhou 310027 Peoples R China Zhejiang Univ State Key Lab Modern Opt Instrumentat Hangzhou 310027 Peoples R China Southwest Univ Sci & Technol Sch Informat Engn Mianyang 621010 Peoples R China Nanjing Univ Aeronaut & Astronaut Key Lab Radar Imaging & Microwave Photon Minist Educ Nanjing 210016 Peoples R China

Miniaturized spectrometers have emerged as pivotal tools in numerous scientific and industrial applications, offering advantages such as portability, cost-effectiveness, and the capability for onsite analysis. Despite these significant benefits, miniaturized spectrometers face critical challenges, particularly in sensitivity. Reduced dimensions often lead to compromises in optical path length and component quality, which can diminish detection limits and limit their applications in areas such as low-light-level measurements. Here we developed a compact spectrometer that integrates an array of photonic crystal slab filters with band-stop spectral transmission characteristics into an image sensor. Compared to traditional gratings or bandpass filter strategies, where each detector can only read light of a single wavelength component, our band-stop strategy allows each detector to read the light of all wavelengths except the band-stop wavelength. This maximizes energy extraction from incident signals, significantly improving the sensitivity of the spectrometer. Spectral reconstruction is achieved mathematically using pre-calibrated band-stop responses combined with a single coded image. Our spectrometer delivers a spectral resolution of 1.9 nm and demonstrates sensitivity more than ten times greater than that of conventional grating spectrometers during fluorescence spectroscopy of Ascaris lumbricoides. The design is fully compatible with complementary metal-oxide-semiconductor (CMOS) technology, allowing for mass production at low costs and thus promising broad deployment in sensitive applications

关键词： Bandpass filters finite-difference time-domain method Fluorescence spectroscopy Image sensors Photonic crystals Waveguide modes

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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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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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Compact and efficient photonic lanterns through multi-stage tapering

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OPTICS LETTERS 2024年第17期49卷 4779-4782页

作者： Hou, Lijie Yang, Linbo Yang, Zhiqun Liu, Yaping Huang, Zhanhua Zhang, Lin Tianjin Univ Sch Precis Instruments & Optoelect Engn State Key Lab Precis Measuring Technol & Instrume Key Lab Optoelect Informat TechnolMinist EducTi Tianjin 300072 Peoples R China North Univ China Coll Semicond & Phys Taiyuan 030051 Shanxi Peoples R China Peng Cheng Lab Shenzhen 518038 Peoples R China

Photonic lanterns (PLs) have been recently used in modedivision multiplexed systems with a low insertion loss, a low mode-dependent loss (MDL), and a wide bandwidth. However, the cross talk (XT) performance of the PLs requires further enhancement within a short taper length. In this Letter, a multi-stage cascaded scheme for short PLs is proposed to further improve the performance on losses and XT. The XT of the optimized 6-mode 3-stage PL is below -23.4 dB, while the total length is only 6 cm. To the best of our knowledge, this is the first quantitative optimization of a 3-stage tapered PL, resulting in a compact structure and excellent performance. Furthermore, we experimentally validate the feasibility of the 3-stage tapering process. (c) 2024 Optica Publishing Group

关键词： Beam propagation methods Carbon dioxide lasers Effective refractive index finite element method finite-difference time-domain method Mode division multiplexing

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Parameter Sensitivity Analysis of 3D-Printed W-Band Reflective Fresnel Lens Antenna based on Acrylonitrile Butadiene Styrene Plastic

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APPLIED COMPUTATIONAL ELECTROMAGNETICS SOCIETY JOURNAL 2023年第3期39卷 231-236页

作者： Futatsumori, Shunichi Natl Inst Maritime Port & Aviat Technol Elect Nav Res Inst Surveillance & Commun Dept Chofu Tokyo 1820012 Japan

To improve the design of the 3D-printed W-band reflective Fresnel lens antenna based on acrylonitrile butadiene styrene (ABS) plastic, we have examined the parameter sensitivity related to the dielectric material constant. Although we have developed a high- gain millimeter-wave reflective Fresnel lens antenna, the material constant of the ABS filament used in 3D printing needs further investigation to optimize antenna performance. First, a 150-mm-diameter W-band reflector Fresnel antenna is designed and analyzed using finite- difference time-domain (FDTD) analysis. The analyzed and measured maximum antenna gains are 33.3 and 32.4 dBi, respectively. Subsequent sensitivity analysis focused on the impact of the loss tangent, relative dielectric constant, and folding length of the lens, based on both FDTD analysis and measurements.

关键词： 3D printer acrylonitrile butadiene styrene plastic finite-difference time-domain method reflective Fresnel lens antenna relative dielectric constant

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Advanced optical nanolithography by enhanced transmission through bull's eye nanostructured meta-mask

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NANOPHOTONICS 2023年第11期12卷 2041-2050页

作者： Kim, Taeyeon Ahn, Heesang Kim, Soojung Song, Hyerin Choi, Jong-ryul Kim, Kyujung Daegu Gyeongbuk Med Innovat Fdn K MEDI Hub Med Device Dev Ctr Daegu 41061 South Korea Pusan Natl Univ Dept Cogno Mechatron Engn Busan 46241 South Korea Pusan Natl Univ Dept Opt & Mechatron Engn Busan 46241 South Korea Pusan Natl Univ Bio IT Fus Technol Res Inst Busan 46241 South Korea

Plasmonic optical nanolithography using extraordinary optical transmission through a metallic nanohole mask has been actively applied to the high-resolution fabrication of nanostructures over a large area. Although there have been studies on improving the nanostructure fabrication performance in optical nanolithography, such as on adjustable external gap spacing, additional performance enhancement is required for practical applications and commercialization of large-area and high-resolution nanostructure array fabrication techniques. In this study, we design and apply a plasmonic bull's eye nanostructured meta-mask to enhance the performance of optical nanolithography. Through simulation results and experimental verification, it is confirmed that advanced optical nanolithography using the bull's eye nanostructured meta-mask has several merits compared to conventional Talbot lithography using nanoholes: (1) Optical nanolithography using the bull's eye nanostructured meta-mask effectively fabricates nanopillar arrays even at a shorter exposure time than conventional optical lithography using nanoholes. (2) It is possible to create a large-area nanopillar array with various nanopillar diameters by exposure time control in optical nanolithography using the bull's eye meta-mask. (3) Using water or objective immersion oil to increase the refractive index of the contact medium, light can be focused on smaller sizes, and large-area nanopillar arrays with smaller nanopillar diameters are established. With the upgradation of hardware for large-area fabrication, application of immersion media supplying techniques, and additional studies to establish complex nanostructures, optical nanolithography using the bull's eye nanostructured meta-mask is an efficient modality to produce various nanostructure-based devices.

关键词： bull's eye extraordinary optical transmission finite-difference time-domain method nanolithography optical lithography plasmonic meta-mask

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