FDTD Method Research Articles

Design and analysis of polarization independent MMI based power splitter for PICs

An ultracompact and low loss polarization-independent 1 ​× ​2 power splitter based on multimode interference (MMI) is designed and analyzed using Eigenmode expansion (EME) and variational FDTD method on silicon on insulator. The numerical tool shows that the excess loss of the power splitter is 0.04 ​dB for TE and 0.06 ​dB for TM polarization at wavelength 1550 ​nm while the polarization differential loss (PDL) is ​< ​0.07 ​dB over wavelength 1500 ​nm–1600 ​nm. Moreover, the optimized MMI structure has a fabrication tolerance of width ±150 ​nm and a length of ±800 ​nm. In addition, polarization-independent arbitrary power splitter (APS) is designed using cascaded MMI and tapered waveguide as a phase shifter having excess loss ​< ​0.16 ​dB for TE and <0.21 ​dB for TM mode at wavelength 1550 ​nm. The proposed devices have broad applications in optical interconnect and switches for PICs.

Comparative Analysis of Optical Spectra of Plasmonic Nanoparticles of Different Geometrical Shapes

Abstract–Numerical calculations and a comparative analysis of light extinction spectra of single silver nanoparticles shaped as sphere, rod, dumbbell, disk, and triangular prism are performed using the FDTD method. The strong dependence of the results for intensities and positions of maxima of localized plasmon resonance peaks on the geometrical shape of particles.

The FDTD Simulation of QDLED Performance Dependency on the Location of Colloidal Quantum Dots

All types of Light Emitting Diodes (LEDs) are desirable because of their widespread applications. The Quantum Dot-Based Light Emitting Diodes (QDLEDs) have a lot of unique properties attracting more attention. Predicting performance of QDLEDs can lead to a better and more efficient design of the device. In this paper, we have attempted to investigate the dependency of the device performance on the location of Quantum Dots (QDs) and determine the best location for the QDs in the QDLEDs. We use FDTD method to simulate and analysis the QDLEDs structure. The QDs are located in five different positions in TPBi layer then results are compared with each other. The results show that the closer the QDs to the hole transport layer (HTL), the better the luminescence. This improvement would be explained by two charge transport mechanisms including direct charge injection and exciton energy transfer. The results show that when the QDs are closer to the HTL, the device performance is better due to the greater balance of carriers. In this condition holes can transfer from the HTL to the valence band easier.

Rotation of an ellipsoidal dielectric particle in the focus of a circularly polarized gaussian beam

Forces and torque acting on an ellipsoidal dielectric particle in the focus of a circularly polarized spherical wave are considered. The simulation is carried out on the basis of the diffraction field obtained by the FDTD method. The calculation of the force and the torque was carried out using the Maxwell stress tensor. It is shown that in the focus of a circularly polarized spherical wave, an ellipsoid is affected by a torque with respect to its center that will tend to rotate it around the optical axis. In this case, the ellipsoid is located in the plane transverse to the optical axis. When the ellipsoid is moved from the optical axis, a light force appears, which acts against this displacement, therefore, there is an optical trap on the optical axis.

Ultra-broadband perfect absorber utilizing a multi-size rectangular structure in the UV-MIR range

We propose an ultra-broadband perfect absorber (UBPA) utilizing a multi-size rectangular structure, which consists of multi-layer silicon/iron (Si/Fe) units. A single-layer model is designed based on the theory of dipole equivalent circuit, and a nine-layer model is demonstrated with the FDTD method. Surprisingly, the absorber shows an average absorptivity of over 96% in the range of 300–3000 nm under the normal incident, which covers from the ultraviolet to mid-infrared (UV-MIR) region. A good tolerance of incident angle and polarization state is proved. It is found that the average level of absorption still exceeds 91% at a larger viewing angle of ±70° under the TM polarization. The excellent absorption performance is revealed by the slow-wave effect, localized surface plasmon resonance (LSPR), and propagating surface plasmons (PSPs). In addition, both chromium and iron films are used in the multi-layer structure to avoid the iron oxidation. Thus, the proposed absorber reduces the cost of actual production and can be applied in many areas, such as solar cells and emitters.

Design of tri-band chiral graphene based terahertz patch antenna

In this paper, a novel terahertz patch antenna is designed using a very thin layer of graphene as the radiating patch, to get tri-band operation. An attempt, is made to design both achiral and chiral graphene patch tri-band for 0.46/0.58/0.66-THz. The simulation has been carried out by using a full wave electromagnetic simulator based on FDTD method. We then expect these results to be of interest to scientists in the field of the interaction between the electromagnetic wave and grapheme to design potential application.

Rotation of an elliptical dielectric particle in the focus of a circularly polarized Gaussian beam

A force and a torque exerted on an elliptical dielectric particle in the focus of a spherical circularly polarized laser beam are considered. The numerical simulation is conducted using a diffraction field obtained by an FDTD method, with the force and torque derived using a Maxwell’s stress tensor. It is shown that an optical torque is exerted on the center of an elliptical particle put in the focus of a circularly polarized spherical wave, making it rotate around the optical axis. The rotation occurs when the elliptical microparticle is situated in a transverse plane to the optical axis. When shifting the ellipsoid from the optical axis, an optical trapping force appears that prevents its displacement, meaning that the particle finds itself in an optical trap on the optical axis.

Mathematical Modelling of Electric Field Generated by Vertical Grounding Electrode in Horizontally Stratified Soil Using the FDTD Method

Mathematical Modelling of Electric Field Generated by Vertical Grounding Electrode in Horizontally Stratified Soil Using the FDTD Method

Wideband performance limitations of the C-FDTD in the discretization impoverishment of a curved surface

PurposeThis paper aims to explore the limitations of the conformal finite difference time-domain method (C-FDTD or Dey–Mittra) when modeling perfect electric conducting (PEC) and lossless dielectric curved surfaces in coarse meshes. The C-FDTD is a widely known approach to reduce error of curved surfaces in the FDTD method. However, its performance limitations are not broadly described in the literature, which are explored as a novelty in this paper.Design/methodology/approachThis paper explores the C-FDTD method applied on field scattering simulations of two curved surfaces, a dielectric and a PEC sphere, through the frequency range from 0.8 to 10 GHz. For each sphere, the mesh was progressively impoverished to evaluate the accuracy drop and performance limitations of the C-FDTD with the mesh impoverishment, along with the wideband frequency range described.FindingsThis paper shows and quantifies the C-FDTD method’s accuracy drops as the mesh is impoverished, reducing C-FDTD’s performance. It is also shown how the performance drops differently according to the frequency of interest.Practical implicationsWith this study, coarse meshes, with smaller execution time and reduced memory usage, can be further explored reliably accounting the desired accuracy, enabling a better trade-off between accuracy and computational effort.Originality/valueThis paper quantifies the limitations of the C-FDTD in coarse meshes in a wideband manner, which brings a broader and newer insight upon C-FDTD’s limitations in coarse meshes or relatively small objects in electromagnetic simulation.

Hybrid 3D SERS substrate for Raman spectroscopy

In this paper, we focused on a hybrid, low-cost, sensitive 3D substrate for surface-enhancement Raman scattering (SERS), where silver nanoparticles (SNPs) with a diameter of 40 nm were covered on the gold-coated roughened monocrystalline silicon. The SNPs were fabricated using a hydrothermal method. The SERS enhancement factors of gold-coated roughened silicon, gold-coated roughened silicon with thin layer SNPs or with thick layer SNPs, were studied. The physical mechanism of the hybrid substrate with the high enhancement is revealed with the electromagnetic calculations using the FDTD method.

REFLECTION OF LIGHT FROM THE DIFFRACTION GRATING WITH TRIANGULAR PROFILE

we study the light diffraction at a reflective grating with triangular profile in scalar wave optics approximation. The case of 1D diffusively reflective rough surface can be described in the first approximation as a random set of reflective gratings with triangular profiles, which are characterised by normal (Gaussian) distribution of amplitude and spatial period. We have obtained the condition for amplitude and period of a diffraction grating in the case of absence of secondary reflections, and the dependence of optical path difference on amplitude and spatial period of the triangular profile. We have investigated the influence of triangular profile parameters on the intensity of reflected wave. We have measured the relative intensity (reflection coefficients) of rough surface reference samples in the case of normal incidence. The relative intensity of reflected wave in the case of normal incidence is used in the design of optical contactless methods for the characterisation of rough surfaces in range of 0.05…0.25 mm. We suggested an optical scheme for the surface roughness measurements, and tested it on the reference samples of rough surfaces. We investigated the dependence of reflected wave intensity on the diffraction angle, and simulated it using numerical solutions of Maxwell equation (FDTD methods). Therefore, we demonstrate that measurements of relative intensity of the reflected wave in the normal to sample plane direction in an objective focal plane allow for determination of the roughness of diffusely reflective surfaces

Research on the moving plasma photonic crystals based on the novel symplectic finite-difference time-domain method

For the Symplectic Finite-difference Time-domain (SFDTD) method has higher accuracy and lower numerical dispersion, it is better than the traditional FDTD method. Although the SFDTD method has a lot of advantages, it cannot be used on the moving medium in previous research. Therefore, the discrete scheme of the Maxwell’s equations is rewrote with velocity variable added. With the difference scheme in magnetic field remains unchanged, the difference scheme in electric field changed, the novel SFDTD method is used on the moving Plasma Photonic Crystals (PPCs). Also, with the numerical simulation of the moving PPCs by the SFDTD method, this article proves that the transmission coefficients of the PPCs can be changed with the velocity variable added.

Study on the microstructure and its coloration mechanism of peacock feather by the FDTD method

Animal body colors have attracted researcher’s attention because of their functions of reducing accessibility to predators, helping to capture prey, helping to court and so on. In the paper, peacock feather structure and mechanism of forming colors were relatively systematically studied. The experimental data of the microstructure of green male peacock “eyespot” parts were obtained, and their reflective optical characteristics were tested. The theoretical results simulated using a finite difference time domain method are well consistent with the above experimental results. Therefore, it was confirmed that peacock feather structural colors mainly come from two-dimensional photonic crystal structure. It further proves that the feasibility of the finite difference time domain method. This study is of great significance in printing and dyeing industry, textile industry and other fields in China.

Simulation of current distribution in a wind turbine blade using the FDTD method

Lightning can pose one of the major natural threats to wind turbines. In special, rotor blades are the most sensitive components to lightning due to their material, constructive nature and movement. Modern multimegawatt wind turbine blades use a combination of glass fiber and carbon fiber reinforced plastic components (CFRP). The last one is electrically conductive and needs to be considered as part of the lightning protection system. In this paper, we present the application of the FDTD method to investigate the lightning current distribution in a wind turbine blade equipped with a 25 m CFRP spar. We found, that for low spar-to-down conductor bonding electric contact resistances, peak currents are higher in the spar, but most of the energy is conducted by the down conductor. The high peak currents in the CFRP would produce intense resistive voltage drops at the connections with the risk of sparks if milliohm connection resistances cannot be achieved. The simulations show that voltages between isolated CFRP laminates of the spar should not pose a threat of sparking if the insulation properties of glass fiber can be ensured in the entire spar. Dangerous voltages between the down conductor and the CFRP spar can occur if the bonding connection at the tip is located far from the end of the spar.

Controllable fabrication of lateral periodic nanoporous GaN and its enhanced photocatalytic water splitting performance

Gallium nitride (GaN) is considered as one of the most promising candidates for water splitting due to its wide band gap and good chemical stability. Here, we fabricate different kinds of lateral periodic, well-ordered nanoporous GaN in wafer scale using cyclic anodization. The nanoporous morphologies can be modulated precisely by changing the waveforms of the applied voltage during the anodization process. The photocurrent of the lateral periodic nanoporous GaN increases by ~5.1 times compared with the planar GaN. The enhanced photocatalytic performance is mainly attributed to the three dimensional modulation of the electric fields of incident light as simulated by FDTD method. This approach could pave a way to develop the III-nitride semiconductor with fine nanostructure for photocatalytic applications.

As2Se3-Ge11.5As24Se64.5 based mid-infrared dual nano-slot optical waveguide with huge and wavelength tunable dispersion

An As2Se3-Ge11.5As24Se64.5 based dual nano-slot waveguide with huge chromatic dispersion at mid-infrared is proposed. The large chromatic dispersion at the target wavelength is achieved induced by resonance interaction. The characteristics of dispersion are investigated by employing the FDTD method. The simulation results indicate that by optimizing the geometrical parameters, the maximum dispersion of -3.48×105 ps·nm-1·km-1 over a full width at FWHM of 2 nm at 3000 nm has been attained. A flat and ultra-large dispersion of -3.48×105 ps·nm-1·km-1 from 2980 to 3010 nm is achieved by cascading the dual-slot waveguides. The relative dispersion magnitude fluctuation is less than 1.85%.

On the Evaluation of the Voltage Rise on Transmission Line Tower Struck by Lightning Using Electromagnetic and Circuit-Based Analyses

Voltage and current waveforms of transmission lines struck by lightning are calculated for use in back flashover analysis. Calculation by using equivalent circuits is the general practice, however, there are limited experimental results for reference to evaluate validity of developed equivalent circuits under various line conditions. Calculation results by numerical electromagnetic analysis can be used as references if they are proved reliable. In this paper, the voltage rises at a model of a 154 kV transmission line hit by lightning is calculated by Method of Moments (MoM) and FDTD for comparison. They solve Maxwell's equations by using different algorithms, so, if the calculated results by these methods reasonably agree under various line conditions, the results of these numerical analyses are regarded reliable. The calculated voltage and current waveforms by the two numerical methods agree well under a variety of footing resistance of transmission towers, thus the authors conclude that the calculated results by FDTD or MoM can be employed as references to evaluate validity of circuit models for back flashover analyses. Thus, the results calculated by circuit analysis are compared with those calculated by FDTD. The multistory tower model (Ishii model) better reproduces the voltage waveforms in a wide range of the footing resistance than simple circuit models of a tower, and can be easily tuned for further accuracy.

Experimental Study on Multi-Channel Positioning Technology of High Voltage Switchgear

This paper introduces the basic principle of high voltage switchgear discharge, expounds several common discharge types, and studies the precise localization of partial discharge of high voltage switchgear based on hyperboloid positioning method and space grid search method. The simulation test of the diagnostic process is used to test the feasibility of the above method. On the basis of precise positioning of the power supply, the local discharge power supply is simplified to a Gaussian current source, and the pulse parameters are calculated by the combination of the simulated annealing algorithm and the fdtd method. Evaluation. Simulation results show that the method of using multiple sensor measurements can accurately evaluate the equivalent pulse width τ and equivalent current amplitude i0 of the simulated Gaussian pulse.

Determination of the Eigenfunction’s and Eigenvalue’s of Quantum dots by FDTD

In this Article, we consider quantum dots with different structures and solve the Schrodinger equations for them by finite difference time-domain method and obtain the Eigenfunction’s and the Eigenvalue’s of these points.The FDTD method have an analysis that demonstrates the high accuracy of this method for solving quantum equations.The FDTD method is a suitable method for simulating electromagnetic phenomena, in this Article we present a simple formulation for the Schrodinger equation in FDTD. In fact, we get help from the idea of FDTD and solve quantum equations. The most important structures we have simulated with this method are cubic quantum dot, spherical quantum dot, elliptical quantum dot and partial truncate-shaped quantum dots on the wetting layer. It is very difficult to solve the Schrodinger equation analytically for these structures, but by using the numerical method we obtain the Eigenfunction’s and Eigenvalue’s in a simpler way.

Strong negative longitudinal component of the Poynting vector in a tightly focused cylindrical vector beam

It was shown that tightly focused cylindrical vector beam of m-th order produces reverse energy flow in the focal plane (m=2). If m=3 the reverse energy flow on the axis is equal to zero and near the axis it increases in proportion to a square of the distance to the axis. The azimuthally polarized beam of the m-th order is an example of a polarization vortex. Previously, the reverse energy flow in the focus was obtained only for vortex beams with a topological charge m and circular polarization. Numerically, using the FDTD method and the Richards-Wolf formulae, it was shown that in the focus of the zone plate such laser beams produce regions the Poynting vector opposite to the direction of propagation of the beam.