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Multifunctional electrically switchable metalens

APPLIED OPTICS 2024年第31期63卷 8074-8081页

作者： Wang, Yu Cui, Dajian Yang, Gughui Wang, Yue Wang, Chunhui Harbin Inst Technol Natl Key Lab Tunable Laser Technol Harbin 150001 Heilongjiang Peoples R China Harbin Inst Technol Sch Elect & Informat Engn Harbin 150001 Heilongjiang Peoples R China

Here, we propose three all-solid-state, electrically switchable, transmissive, and multifunctional metalens arrays comprising tunable metal-oxide material BaTiO3 (BTO) nanopillars with different structural parameters. To produce the required phase profile for each metalens, the rectangular nanopillars, as the unit cell of the BTO structure, are developed to support arbitrary combinations of two independent phase shifts (0-2 pi) with bias voltage states of 0 V and 60 V, at first. Second, the structure parameters of different functional metalens arrays are generated efficiently and accurately based on the dual-phase modulation characteristics of a single structure. Finally, we use the finite-difference time-domain method to simulate the three kinds of switchable metalenses. The results show that the three metalenses can realize the function of adjustable focus position, switchable beam focusing and beam deflection, and switchable beam focusing and beam splitting. (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： finite-difference time-domain method Indium tin oxide Optical elements Phase modulation Phase shift Transparent conducting oxides

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Ultra-thin crystalline silicon solar cell with a stepped pyramid nanostructure for efficient absorption

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APPLIED OPTICS 2024年第26期63卷 6986-6992页

作者： Zhang, Heng Cao, Yuchun Chen, Ning Liu, Haotuo Feng, Yongtao Wu, Xiaohu Changzhou Univ Sch Energy Changzhou 213164 Jiangsu Peoples R China Shandong First Med Univ & Shandong Acad Med Sci Med Sci & Technol Innovat Ctr Jinan Shandong Peoples R China Harbin Univ Sci & Technol Key Lab Adv Mfg Intelligent Technol Minist Educ Harbin 150080 Peoples R China Shandong Inst Adv Technol Thermal Sci Res Ctr Jinan 250100 Peoples R China

Incorporating micro-nano structures onto the surface of crystalline silicon (c-Si) solar cells to optimize their light absorption capability and improve photoelectric conversion efficiency is a feasible approach. Here, we propose an ultra-thin c-Si solar cell with a stepped pyramid nanostructure for efficient absorption, which consists of the Ag reflective layer, the c-Si absorption layer, and the c-Si stepped pyramid structure. The calculated outcomes demonstrate that the ultra-thin c-Si solar cell's average absorption at the wavelength of 350-1100 nm is 90.9%, while the average absorption for AM1.5G solar radiation is 92.1%. By comparing the absorption of solar cells with a different number of steps, it's proved that the proposed solar cell achieves optimal absorption. Investigation into the electric field distribution reveals that the high absorption of the solar cell is generated through the dipole resonance, local electric field enhancement, and combined effects of multiple light reflections and scattering. The calculation of the electrical output characteristics shows that the proposed solar cell achieves a photoelectric conversion efficiency of 21.2%. This study will provide a meaningful exploration into the design and optimization of solar cells that can use solar energy efficiently. (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： Field enhancement finite-difference time-domain method Silicon solar cells Solar cell efficiency Solar cells Solar energy

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GaSb-based mid-wave computational multispectral infrared detectors based on photonic crystal plates

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OPTICS EXPRESS 2025年第2期33卷 3373-3385页

作者： Zhang, Yang Lu, Lidan Chen, Yang Shi, Leidong Chen, Weiqiang Zhu, Lianqing Beijing Informat Sci & Technol Univ Sch Instrument Sci & Optoelect Engn Beijing 100192 Peoples R China

The mid-wave multispectral detector combines the traditional spectrometer and infrared detector technologies to provide image information and spectral information at the same time, which has an important role in both civil and military fields. To solve the working band limitation and low energy utilization, this paper presents an integrated superlattice mid-wave multispectral hypersurface detector that can be used for computational multispectroscopy for the first time, which consists of photonic crystal (PC) plates of GaSb material, and uses PC microstructures to modulate the incident spectra, which can be used to reconstruct incident signals with computational multispectroscopy methods. In this paper, the finite difference time domain method (FDTD) is used to simulate the structural parameters of different PCs, and finally calculate the correlation coefficients of the transmission spectra of the different structures as well as the energy utilization rate. The simulation results show that the optimized structures have unique response curves and rich spectral features, with the average value of Pearson correlation coefficients (PCCs) < 0.3 and energy utilization >50%. It can be utilized in various fields, including astronomical remote sensing, medical diagnostics, and military reconnaissance.

关键词： finite-difference time-domain method Imaging systems Infrared detectors Modulation techniques Physical vapor deposition Remote sensing

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Improving optical coupling in monolithically integrated lasers on silicon by selective area growth

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OPTICAL MATERIALS EXPRESS 2025年第5期15卷 967-976页

作者： Skipper, Alec m. Feng, Kaiyin Koscica, Rosalyn Leake, Gerald Shang, Chen Harame, David Bowers, John Univ Calif Santa Barbara Inst Energy Efficiency Santa Barbara CA 93106 USA Univ Calif Santa Barbara Dept Elect & Comp Engn Santa Barbara CA 93106 USA Univ Calif Santa Barbara Mat Dept Santa Barbara CA 93106 USA RF SUNY Polytech Inst Albany NY 12203 USA

The direct growth of III-V lasers on silicon has the potential to allow for low-cost production of silicon photonic integrated circuits on a 300 mm wafer-scale. However, coupling loss severely limits the performance in current implementations of direct growth processes due to the growth of undesirable polycrystalline material on silicon dioxide sidewalls. In this work, we report the use of selective area molecular beam epitaxy growth to reduce the formation of this polycrystalline material during the growth process and improve the coupling efficiency. Furthermore, we demonstrate electrically pumped continuous wave lasers directly grown on foundry-fabricated silicon photonic integrated circuit wafers using this technique.

关键词： Crystalline materials finite-difference time-domain method Laser amplifiers Quantum dot lasers Silicon nitride Silicon photonics

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Dominance of plasma-induced modulation in terahertz generation from gas filament

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OPTICS EXPRESS 2024年第3期32卷 4277-4294页

作者： Guo, Huicheng Du, Henglei Zhan, Qiang Zhang, Xiaoxue Wang, Wenkang Liu, Chengpu Chinese Acad Sci State Key Lab High Field Laser Phys Shanghai 201800 Peoples R China Chinese Acad Sci Shanghai Inst Opt & Fine Mech CAS Ctr Excellence Ultraintense Laser Sci Shanghai 201800 Peoples R China Univ Chinese Acad Sci Ctr Mat Sci & Optoelect Engn Beijing 100049 Peoples R China Tongji Univ Inst Precis Opt Engn Sch Phys Sci & Engn China MOE Key Lab Adv Microstruct Mat Shanghai 200092 Peoples R China Guangdong Ocean Univ Phys & Photoelect Sci Dept Zhanjiang 524088 Peoples R China

In this paper, we revisit the fundamental mechanism responsible for terahertz generation from laser-induced plasma filament based on the photocurrent model by employing a blend of analytical calculation and numerical simulation. By using the frequency-decomposed finite-difference time-domain (FD-FDTD) method, the role of two-color field and photocurrent radiation in terahertz generation from plasma filament is visually separated, and the driving effect of photocurrent radiation is confirmed pretty significant within the process. Then, a pair of numerical experiments are taken to further analyze the driving effect of photocurrent radiation, and it is revealed that plasma-induced modulation to photocurrent radiation is actually the underlying physical mechanism of terahertz generation from plasma filament. Furthermore, a three-step diagram is introduced to reillustrate the overall physical process and provides a more comprehensive explanation. In addition, the mechanism of plasma-induced modulation to photocurrent radiation in terahertz generation is substantiated by taking theoretical prediction and numerical simulation of minimal filament length required for achieving stable backward terahertz emission, which directly confirms the validity and significance of plasma-induced modulation to photocurrent radiation in terahertz generation from laser-induced plasma filament.

关键词： Femtosecond lasers finite-difference time-domain method Laser energy Numerical simulation Plasma filaments Ultrafast lasers

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Cylindrical aperture three-dimensional synthetic aperture imaging with pulsed terahertz waves

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OPTICS EXPRESS 2024年第23期32卷 40190-40201页

作者： Du, Yuanhao Feng, Hui Wu, Shuai Univ Sci & Technol China Sch Phys Sci Hefei 230026 Peoples R China

In this paper, we report a three-dimensional synthetic aperture imaging method with pulsed terahertz waves realized by a terahertz time-domain spectrometer. In contrast to synthetic aperture imaging systems operating at microwave or millimeter-wave frequencies where the frequency of the transmitter is scanned in the frequency domain, in our imaging system, all the frequency components are contained in a single terahertz pulse that can be generated and detected by photoconductive antennas. The image algorithm was analyzed theoretically and confirmed numerically using the finite-difference time-domain method. A key with plentiful detailed structures was used as the object to be imaged to demonstrate the three-dimensional imaging capabilities of this method. The resolution of the imaging system is 0.3 mm for the linear dimension and 0.1 mm for the circular dimension, as tested by the experimental setup. Finally, an optically opaque plastic pen with and without the cartridge was imaged, and the shape and location of the cartridge could be observed from the reconstructed three-dimensional terahertz images, demonstrating the non-destructive evaluation capabilities of this imaging method. Benefiting from the improvements in the experimental setup in this study, the imaging speed was significantly improved compared with that of the step-by-step scanning method commonly used in terahertz imaging systems with a single transmitter/receiver pair. This imaging method avoids the image degradation caused by specular reflections in active quasi-optical focal plane imaging and the lack of semiconductor devices working at several THz frequencies for synthetic aperture imaging, and may be used for non-destructive evaluation of objects with complex surfaces and internal structures. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： finite-difference time-domain method High speed imaging Imaging systems Imaging techniques Terahertz imaging Three dimensional imaging

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Inverse design of narrowband thermal emitter with tandem films structures using simulated annealing algorithm

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OPTICS EXPRESS 2024年第26期32卷 47154-47162页

作者： Pan, Haonan Ou, Chunhui Yang, Shuai Wang, Jian Luo, Yi Hunan Univ Coll Comp Sci & Elect Engn Changsha 410082 Peoples R China Tsinghua Univ Dept Elect Engn Beijing 100084 Peoples R China

An inverse design method of narrow-band thermal emitter with a tandem films structures is proposed here, which is accomplished by the simulated annealing algorithm. Using this method, two kinds of structures are designed, which peak absorption rate is 0.8261 at 5.34 mu m with a Q-factor of 175, and 0.8931 at 3.56 mu m with a Q-factor of 132. The electric field distribution within the structure is analyzed using the finite-difference time-domain method (FDTD), and behavior similar to a Tamm plasmon state. The simulation and experiment of the inverse design method shows good agreement. Such inverse design method is very promising in mid-infrared simulator and detection.

关键词： Bragg reflectors finite-difference time-domain method Inverse design Metal gratings Modulation techniques Rigorous coupled wave analysis

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Investigation of optical polarization characteristics of ultraviolet-C AlGaN multiple quantum wells by angle-resolved cathodoluminescence

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OPTICS EXPRESS 2024年第10期32卷 17048-17057页

作者： Gong, Honglin Zhu, Lihong Cai, Yaqi Yang, Renlong Guo, Weijie Chen, Huanting Chen, Zhong Lu, Yijun Xiamen Univ Sch Elect Sci & Engn Dept Elect Sci Natl Innovat Platform Fus Ind & Educ Integrated Ci Xiamen 361005 Peoples R China Minnan Normal Univ Sch Phys & Informat Engn Key Lab Light Field Manipulat & Syst Integrat Appl Zhangzhou 363000 Peoples R China

AlGaN-based ultraviolet -C (UV -C) light -emitting diodes (LEDs) face challenges related to their extremely low external quantum efficiency, which is predominantly attributed to the remarkably inadequate transverse magnetic (TM) light extraction efficiency (LEE). In this study, we employ angle -resolved cathodoluminescence (ARCL) spectroscopy to assess the optical polarization of (0001) -oriented AlGaN multiple quantum well (MQW) structures in UV -C LEDs, in conjunction with a focused ion beam and scanning electron microscopy (FIB/SEM) system to etch samples with various inclination angles ( Theta ) of sidewall. This technique effectively distinguishes the spatial distribution of TM- and transverse electric (TE)-polarized photons contributing to the luminescence of the MQW structure. CL spectroscopy confirms that UV -C LEDs with a Theta of 35 degrees exhibit the highest CL signal compared to samples with other Theta . Furthermore, we establish a model using finite difference time domain (FDTD) simulation to validate the mechanism of the outcomes. The complementary contribution of TM and TE photons at different specific angles are distinguished by ARCL and confirmed by simulation. At angles near the sidewall, the CL is dominated by the TM photons, which mainly contribute to the increased LEE and the decreased degree of polarization (DOP) to make the spatial distribution of CL more uniform. Additionally, this method allows us to analyze the polarization of light without the need for polarizers, enabling the differentiation of TE and TM modes. This distinction provides flexibility for selecting different emission mode based on various application requirements. The presented approach not only opens up new opportunities for enhanced UV -C light extraction but also provides valuable insights for future endeavors in device fabrication and epitaxial film growth. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

关键词： Bragg reflectors finite-difference time-domain method Light extraction Numerical simulation Quantum efficiency Scanning electron microscopy

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Quasi-bound states in the continuum in a metal nanograting metasurface for a high figure-of-merit refractive index sensor

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OPTICS EXPRESS 2024年第1期32卷 762-773页

作者： Tang, Xisaina He, Rong Chen, Cheng Huang, Zian Guo, Junpeng Fudan Univ Dept Opt Sci & Engn Shanghai 200433 Peoples R China Fudan Univ Yiwu Res Inst Yiwu 322000 Zhejiang Peoples R China Univ Alabama Huntsville Dept Elect & Comp Engn Huntsville AL 35899 USA

In this work, we investigate the bound states in the continuum (BICs) in a gold nanograting metal -insulator -metal metasurface structure at oblique angles of incidence. The nanograting metasurface consists of a gold nanograting patterned on a silicon dioxide dielectric film deposited on a thick gold film supported by a substrate. With rigorous full -wave finite difference time domain simulations, two bound states in the continuum are revealed upon transverse magnetic wave angular incidence. One BIC is formed by the interference between the surface plasmon polariton mode of the gold nanograting and the FP cavity mode. Another BIC mode is formed by the interference between the metal -dielectric hybrid structure guided mode resonance mode and the FP cavity mode. While true BIC modes cannot be observed, quasi-BIC modes are investigated at angles of incidence slightly off from the corresponding true BIC angles. It is shown that quasi-BIC modes can suppress radiation loss, resulting in narrow resonance spectral linewidths and high quality -factors. The quasi-BIC mode associated with the surface plasmon polariton mode is investigated for refractive index sensing. As a result, a high sensitivity refractive index sensor with a large figure -of -merit of 364 has been obtained.

关键词： Coupled mode theory Electron beam lithography finite-difference time-domain method Refractive index Thin film deposition Waveguide modes

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RDDA method for characterization of photonic nanojets

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APPLIED OPTICS 2024年第10期63卷 2543-2551页

作者： Ataii, Mohammad Reza Amjad, Jafar Mostafavi Inst Adv Studies Basic Sci IASBS 444 Prof Yousef Sobouti BlvdPOB 45195-1159 Zanjan Iran

This paper presents a reduced discrete dipole approximation (RDDA) method as a flexible and powerful tool for computing the field distribution of photonic nanojets (PNJs) based on superposition of the induced dipole radiation fields with a low number of lattice points at the surface of microparticles. Microparticles with spherical and ellipsoidal shapes have been studied using the RDDA method to produce PNJs. The incident beam polarization and filling factor effects in the PNJs' shape and confinement strength have been characterized by quality factor Q . The best confined PNJs have been found in microellipsoids with a specific range of the shape parameter and filling factor values. (c) 2024 Optica Publishing Group

关键词： Azimuthally polarized beams Cylindrical vector beams finite-difference time-domain method Fresnel diffraction Refractive index Total internal reflection

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