- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
Spatially-Controllable Hot Spots for Plasmon-Enhanced Second-Harmonic Generation in AgNP-ZnO Nanocavity Arrays
摘要： Plasmon-enhanced second-harmonic generation (PESHG) based on hybrid metal-dielectric nanostructures have extraordinary importance for developing efficient nanoscale nonlinear sources, which pave the way for new applications in photonic circuitry, quantum optics, and biosensors. However, the relatively high loss of excitation energies and the low spatial overlapping between the locally enhanced electromagnetic field and nonlinear materials still limit the promotion of nonlinear conversion performances in such hybrid systems. Here, we design and fabricate an array of silver nanoparticle-ZnO (AgNP-ZnO) nanocavities to serve as an efficient PESHG platform. The geometry of AgNP-ZnO nanocavity arrays provides a way to flexibly modulate hot spots in three-dimensional space, and to achieve a good mutual overlap of hot spots and ZnO material layers for realizing efficient SH photon generation originating from ZnO nanocavities. Compared to bare ZnO nanocavity arrays, the resulting hybrid AgNP-ZnO design of nanocavities reaches the maximum PESHG enhancement by a factor of approximately 31. Validated by simulations, we can further interpret the relative contribution of fundamental and harmonic modes to Ag-NP dependent PESHG performances, and reveal that the enhancement stems from the co-cooperation effect of plasmon-resonant enhancements both for fundamental and harmonic frequencies. Our findings offer a previously unreported method for designing efficient PESHG systems and pave a way for further understanding of a surface plasmon-coupled second-order emission mechanism for the enhancement of hybrid systems.
关键词： second-harmonic generation,hybrid nanostructure,finite-difference time-domain,plasmonics
更新于2025-09-09 09:28:46
-
Hourglass nonlinear photonic crystal cavity for ultra-fast all-optical switching
摘要： In this paper, a new design of an ultra fast all optical switch based on a new photonic crystal cavity combined with Kerr effect is proposed and its performance is studied. Numerical methods such as plane wave expansion (PWE) and finite difference time domain (FDTD) are used to perform simulations and study the optical properties of the proposed switch. Switching from ON to OFF status occurred when the resonant wavelength is shifted due to Kerr effect. The simulation results show that switch has a high-speed response of ~15ps and since it has an ultra-small size of 273.24 μm2, it has a potential to be used in integrated optical-circuits.
关键词： All-optical switching,Finite-Difference Time-Domain method,Optical Kerr effect,Photonic crystal cavity
更新于2025-09-09 09:28:46
-
Dislocation-induced thermal transport anisotropy in single-crystal group-III nitride films
摘要： Dislocations, one-dimensional lattice imperfections, are common to technologically important materials such as III–V semiconductors, and adversely affect heat dissipation in, for example, nitride-based high-power electronic devices. For decades, conventional nonlinear elasticity models have predicted that this thermal resistance is only appreciable when the heat flux is perpendicular to the dislocations. However, this dislocation-induced anisotropic thermal transport has yet to be seen experimentally. Using time-domain thermoreflectance, we measure strong thermal transport anisotropy governed by highly oriented threading dislocation arrays throughout micrometre-thick, single-crystal indium nitride films. We find that the cross-plane thermal conductivity is almost tenfold higher than the in-plane thermal conductivity at 80?K when the dislocation density is ~3?×?1010?cm?2. This large anisotropy is not predicted by conventional models. With enhanced understanding of dislocation–phonon interactions, our results may allow the tailoring of anisotropic thermal transport with line defects, and could facilitate methods for directed heat dissipation in the thermal management of diverse device applications.
关键词： dislocations,time-domain thermoreflectance,thermal transport,anisotropy,group-III nitride films
更新于2025-09-09 09:28:46
-
Ultra-low Noise Balanced Detectors for Optical Time Domain Measurements
摘要： Two ultra-low noise balanced detectors used for optical time domain measurements are presented in this paper. Both simultaneously achieve high bandwidth and low noise that is extremely difficult to realize in commercial detectors. Two-stage amplification circuits based on transimpedance amplifiers (TIAs) were used for these detectors, with special modifications implemented for different applications. To further suppress noise, a low noise junction field effect transistor (JFET) is connected between the photodiode and TIA to reduce the impact of amplifier leakage current in one of the detectors. Benefiting from this design, a 70 MHz sensitive detector with a gain of 3.2E5 V/W and low noise equivalent power density (NEP) of 2.2 pW/rtHz was implemented. For another balanced detector used in higher bandwidth applications, the differential transimpedance amplifier circuit is used, with the detector achieving a 250 MHz bandwidth with a gain of 5E4 V/W, equivalent to NEP of 6.2 pW/rtHz. Due to the difficulty of achieving high bandwidth with low noise, we perform theoretical analysis and simulations for our designs to ensure that these two design goals are realized simultaneously. The performance of the detectors is consistent with our analysis. In addition, a simplified optical testing system was built to test and calculate the performance of the detectors in their respective applications. The results show that both detectors are well balanced and achieve a common mode rejection ratio (CMRR) greater than 50 dB.
关键词： Balanced detectors,optoelectronic devices,time domain measurements,circuit simulations,noise measurements
更新于2025-09-09 09:28:46
-
A research on fiber-optic vibration pattern recognition based on time-frequency characteristics
摘要： To detect and recognize any type of events over the perimeter security system, this article proposes a fiber-optic vibration pattern recognition method based on the combination of time-domain features and time-frequency domain features. The performance parameters (event recognition, event location, and event classification) are very important and describe the validity of this article. The pattern recognition method is precisely based on the empirical mode decomposition of time-frequency entropy and center-of-gravity frequency. It implements the function of identifying and classifying the event (intrusions or non-intrusion) over the perimeter to secure. To achieve this method, the first-level prejudgment is performed according to the time-domain features of the vibration signal, and the second-level prediction is carried out through time-frequency analysis. The time-frequency distribution of the signal is obtained by empirical mode decomposition and Hilbert transform and then the time-frequency entropy and center-of-gravity frequency are used to form the time-frequency domain features, that is, combined with the time-domain features to form feature vectors. Multiple types of probabilistic neural networks are identified to determine whether there are intrusions and the intrusion types. The experimental results demonstrate that the proposed method is effective and reliable in identifying and classifying the type of event.
关键词： time-frequency domain features,time-frequency analysis,empirical mode decomposition,time-frequency entropy,Event recognition,pattern recognition,center-of-gravity frequency,time-domain features
更新于2025-09-04 15:30:14
-
[IEEE 2018 48th European Microwave Conference (EuMC) - Madrid, Spain (2018.9.23-2018.9.27)] 2018 48th European Microwave Conference (EuMC) - Pulse-Distortion Analysis for Millimeter-Wave Time-Domain Material Identification
摘要： Analyzing the frequency dependent dielectric properties can be used to identify and distinguish materials in biomedical instruments. In the millimeter-wave range, the dielectric properties of biological tissues are mainly determined by their water content. For instance, it has been shown, that cancer cells have a lower water content than healthy skin cells, resulting in a significant dielectric contrast between them. In this work, we analyze the pulse distortion observed in measurements of the millimeter-wave reflection of water and porcine skin. We propose to use the distortion caused by the frequency dependent reflection coefficient at the interface of a material as a feature for identification. Using a simplified model for the reflection coefficient of the material under test, we simulate the distortion caused by the frequency dispersion. In simulation as well as in measurement, we observe different startup transients depending on the dispersion properties of a material under test. The startup behavior can therefore be used as feature, to directly identify dispersive materials in the time domain.
关键词： Dielectric,Time-domain analysis,Electromagnetic,Biomedical,Measurements,Characterization,Measurement,Pulse,Wavelet Generator,Reflection
更新于2025-09-04 15:30:14
-
Theoretical Analysis of Lattice-Mediated Plasmon Resonance Using Finite-Difference Time-Domain Method
摘要： Although much progress has been made on lattice plasmon mode (LPM), there is still a lack of systematic studies on LPM generation; questions remain unanswered on topics such as high-order LPM generation, LPM generation from near-coupling complex elements, and modulation of incidence energy. Here, we systematically evaluated the properties of multiple high-order LPM, energy flow modulation of incident polarization, element, angle of incidence, and hybrid of dual lattice using the finite-difference time-domain method. This study presents a clear illustration of LPM and will help on further development of LPM and plasmonics-based fields.
关键词： Plasmonics,Finite-Difference Time-Domain Method,Lattice Plasmon Mode,Localized Surface Plasmon Resonance
更新于2025-09-04 15:30:14
-
LOW-LOSS COMPLEX PERMITTIVITY AND PERMEABILITY DETERMINATION IN TRANSMISSION/REFLECTION MEASUREMENTS WITH TIME-DOMAIN SMOOTHING
摘要： An approach is proposed for determination of the complex permittivity and permeability of low-loss materials, eliminating half-wavelength resonances occurring in transmission/re?ection (T/R) measurements. To this end, we apply time-domain smoothing for removing resonant artifacts from the wave impedance obtained with the conventional T/R method, assuming that we do not have such artifacts in the refractive index. Accordingly, the permittivity and permeability are found from the smoothed wave impedance and conventional refractive index. Our method is validated by measurements for two di?erent low-loss materials, nylon and lithium ferrite, and those results are discussed. Further, results from the present approach are compared to those from the approximate approach derived in our previous work.
关键词： complex permittivity,transmission/re?ection measurements,permeability,low-loss materials,time-domain smoothing
更新于2025-09-04 15:30:14
-
Three-dimensional anisotropic thermal conductivity tensor of single crystalline β-Ga <sub/>2</sub> O <sub/>3</sub>
摘要： β-Ga2O3 has attracted considerable interest in recent years for high power electronics, where the thermal properties of β-Ga2O3 play a critical role. The thermal conductivity of β-Ga2O3 is expected to be three-dimensionally (3D) anisotropic due to the monoclinic lattice structure. In this work, the 3D anisotropic thermal conductivity tensor of a (010)-oriented β-Ga2O3 single crystal was measured using a recently developed elliptical-beam time-domain thermoreflectance method. Thermal conductivity along any direction in the (010) plane as well as the one perpendicular to the (010) plane can be directly measured, from which the 3D directional distribution of the thermal conductivity can be derived. Our measured results suggest that at room temperature, the highest in-plane thermal conductivity is along a direction between [001] and [102], with a value of 13.3 ± 1.8 W m?1 K?1, and the lowest in-plane thermal conductivity is close to the [100] direction, with a value of 9.5 ± 1.8 W m?1 K?1. The through-plane thermal conductivity, which is along the [010] direction, has the highest value of 22.5 ± 2.5 W m?1 K?1 among all the directions. The temperature-dependent thermal conductivity of β-Ga2O3 was also measured and compared with a theoretical model calculation to understand the temperature dependence and the role of impurity scattering.
关键词： monoclinic lattice,β-Ga2O3,anisotropic,time-domain thermoreflectance,thermal conductivity
更新于2025-09-04 15:30:14
-
The implementation of unconditionally stable higher order PML based on the implicit CNAD-FDTD algorithm
摘要： An unconditionally stable implementation of the higher order complex frequency-shifted perfectly matched layer (CFS-PML) based on the Crank–Nicolson-approximate-decoupling (CNAD) algorithm and the bilinear transform (BT) method is proposed to terminate the finite-difference time-domain (FDTD) lattice. The proposed scheme not only takes advantage of the CNAD algorithm in terms of reducing computational time but also has the advantage of the conventional FDTD algorithm in terms of absorbing performance. Two numerical examples are provided to validate the proposed implementation in the homogenous free space and lossy FDTD domains. The results show that the proposed scheme can overcome the Courant–Friedrich–Levy condition compared with the conventional FDTD method and further enhance the absorbing performance compared with the first order PML implementation.
关键词： finite-di?erence time-domain (FDTD),Bilinear transform (BT),Crank-Nicolson-approximate-decoupling (CNAD),complex frequency-shifted perfectly matched layer (CFS-PML)
更新于2025-09-04 15:30:14